ISOPTWPO Today

D ECEMBER 2015, N O 23

ISOPTWPO Today

Cover Image Astronaut Douglas H. Wheelock

ISOPTWPO Today, December 2015, No.23

Image Credit: JSC2007-E-08803 (5 Dec. 2006) — Astronaut Douglas H. Wheelock, mission specialist

Biography Page NASA Unveils Celestial Fireworks as Official Hubble 25th Anniversary Image The sparkling centerpiece of Hubble’s anniversary fireworks is a giant cluster of about 3,000 stars called Westerlund 2, named for Swedish astronomer Bengt Westerlund who discovered the grouping in the 1960s. The cluster resides in a raucous stellar breeding ground known as Gum 29, located 20,000 light-years away from Earth in the constellation Carina.

Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team Preflight Interview: Douglas Wheelock Image Credit: NASA

Back Cover Cassini Closes in on Enceladus, One Last Time A thrilling chapter in the exploration of the solar system will soon conclude, as NASA’s Saturn-orbiting Cassini spacecraft makes its final close flyby of the ocean-bearing moon Enceladus. Cassini is scheduled to fly past Enceladus at a distance of 3,106 miles (4,999 kilometers) on Saturday, Dec. 19, at 9:49 a.m. PST (12:49 p.m.

EST). Although the spacecraft will continue to observe Enceladus during the remainder of its mission (through September 2017), it will be from much greater distances – at closest, more than four times farther away than the Dec. 19 encounter. The upcoming flyby will focus on measuring how much heat is coming through the ice from the moon’s interior – an important consideration for understanding what is driving the plume of gas and icy particles that sprays continuously from an ocean below the surface. "Understanding how much warmth Enceladus has in its heart provides insight into its remarkable geologic activity, and that makes this last close flyby a fantastic scientific opportunity," said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. By design, the encounter will not be Cassini’s closest. The flyby was designed to allow Cassini’s Composite Infrared Spectrometer (CIRS) instrument to observe heat flow across Enceladus’ south polar terrain.

Image Credit: NASA/JPL-Caltech

2015, International Space Agency (ISA) ISOPTWPO TODAY First release, November 2013 Notice: This is "Final Edition" of ISOPTWPO Today.

Editorial Dear Reader It is my pleasure to introduce the ISOPTWPO. ISOPTWPO(International Space Flight & Operations - Personnel Recruitment, Training, Welfare, Protocol Programs Office) is part of ISA, which support research on Human Space Flight and its complications.

The International Space Agency (ISA) was founded by Mr. Rick Dobson, Jr., a U.S. Navy Veteran, and established as a non-profit corporation for the purpose of advancing Man’s visionary quest to journey to other planets and the stars.

ISOPTWPO will research on NASA’S Human Research Roadmap. It will also research on long duration spaceflight and publish special issues on one year mission at ISS and twin study.

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Mr. Martin Cabaniss

Director Mr. Martin Cabaniss ISOPTWPO – International Space Agency(ISA) http: // www. international-space-agency. us/ Email:martin.cabaniss@international-space-agency.us

Editorial Dear Reader Hello, my name is Abhishek Kumar Sinha, and I am Assistant Director of the ISOPTWPO and editor of ISOPTWPO TODAY. Coinciding with the start of a new stage in International Space Agency’s history, ISOPTWPO TODAY returns with even greater momentum.

In articles covering ISOPTWPO research activities/findings , we have special features on NASA’S Human Research Roadmap, and the Special Edition on " Risk of Performance Decrements and Adverse Health Outcomes Resulting from Sleep Loss, Circadian Desynchronization, and Work Overload ".

I hope you will enjoy the ISOPTWPO TODAY. Mr. Abhishek Kumar Sinha

Assistant Director Mr. Abhishek Kumar Sinha ISOPTWPO – International Space Agency(ISA) http: // www. international-space-agency. us/ Email:abhishek.kumar.sinha@international-space-agency.us

IN THIS EDITION

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Risk of Performance Decrements and Adverse Health Outcomes Resulting from Sleep Loss, Circadian Desynchronization, and Work Overload Astronauts experience sleep loss, circadian desynchronization, and work overload, there is a possibility that performance decrements and adverse health outcomes will occur. Sleep loss, circadian desynchronization, and work overload occur to some extent for ground and flight crews, prior to and during spaceflight missions. Ground evidence indicates that such risk factors may lead to performance decrements and adverse health outcomes, which could potentially compromise mission objectives. Efforts are needed to identify the environmental and mission conditions that interfere with sleep and circadian alignment, as well as the individual vulnerabilities and resiliencies to sleep loss and circadian desynchronization.

Special Edition on Sleep Loss

Risk of Performance Decrements and Adverse Health Outcomes Resulting from Sleep Loss, Circadian Desynchronization, and Work Overload Sleep is a vital physiological requisite for humans, needed for survival like air, water and food. Sleep loss, disruption of circadian rhythms, and work overload are critical fatigue-causing factors that can compromise safety and lead to increased errors and degraded performance and productivity. Workers in safety-sensitive occupations, including truck drivers, shiftworkers, medical residents, and airline pilots are at increased risk for accidents due to lost sleep, circadian desynchrony, and work overload. The combination of sleep loss, circadian desynchrony and work overload associated with shiftwork has also been linked to both short and long-term health consequences including metabolic syndrome, diabetes, and cancer. These short and long-term consequences necessitate the careful management of each component of the risk during NASA missions.

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Studies of shift workers in a variety of industries have shown that compromising any one of these factors is sufficient to lead to performance decrements . Work overload leads to extended duration work shifts, which in turn cause acute and chronic sleep loss and circadian misalignment. In combination, the fatigue resulting from these factors has been shown to have compounded consequences including increased lapses in attention and neurobehavioral impairment.

There are four sleep-related determinants of alertness and performance including: 1. Nightly sleep duration (chronic sleep loss): The average adult obtains approximately 8.5 hours of sleep per night when provided with extended sleep opportunity under optimal conditions . However, there is a wide range in individual sleep need, ranging from 6.1 to 10.3 hours when individuals are offered a controlled 16 hour daily sleep opportunity . These findings support the notion that some people are natural short sleepers, while others are natural long sleepers. There is a strong genetic basis underlying the regulation of normal sleep, along with influences of age and gender . A recent report from a panel of experts assembled by the American Academy of Sleep Medicine recommends that adults 18-60 years get 7 or more hours of sleep on a regular basis "to promote optimal health". Similarly, the National Sleep Foundation advises 7-9 hours as the daily sleep need for most adults .

Despite these recommendations, work and life demands, poor sleep hygiene and sleep disorders result in most adults obtaining less sleep than they require, with nearly 30% of the US population reportedly obtaining six or fewer hours of sleep per night . Analysis of time use data reveals that work and sleep time are inversely related and that evening television viewing is strongly correlated with the timing of sleep onset , suggesting that the majority of sleep loss is self-selected, not reflective of an individual’s actual sleep need.

When a person is not able to consistently achieve their required number of hours of sleep at night, a chronic sleep debt begins to accumulate. With each day of inappropriately short sleep, cognitive performance worsens . Laboratory studies illustrate that when healthy research subjects are restricted to four, six, or eight hours of time in bed per night, their performance steadily degrades, while their subjective feeling of sleepiness increases only modestly and then reaches a plateau . These findings suggest that most people are unable to accurately gauge how much sleep loss affects their performance.

2. Number of hours awake (acute sleep loss): Acute sleep deprivation arises from spending too many continuous hours awake. This phenomenon occurs when a person stays awake beyond the maximum threshold of the homeostatic sleep drive. For example, under controlled laboratory conditions, the average number of continuous hours that a person can stay awake with sustained vigilance is approximately 16 hours, however, when a person who needs sleep after 16 hours stays awake beyond the 16 hour threshold, acute sleep deprivation occurs . The functional consequence of this phenomenon has been demonstrated in laboratory studies where performance quickly degrades with increasing number of hours awake . Other research has demonstrated that sustained wakefulness of only 19 hours can lead to performance decrements equivalent to those of someone with a blood alcohol concentration of 0.05% and when wakefulness is extended to 24 hours, performance on a simple reaction time task further declines to that of a person whose blood alcohol concentration is 0.10%.

3. Sleep inertia (impaired performance upon waking): Sleep inertia is an impairment in alertness and performance that dissipates asymptotically from waking until approximately two to four hours after waking . The brain does not fully wake immediately upon the transition to wakefulness and as a result performance impairments occur until the effects of sleep inertia have dissipated.

The negative effects of sleep inertia are enhanced based on prior sleep history, the sleep stage from which one is awoken and circadian phase.

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Special Edition on Sleep Loss

4. Circadian phase (time of day): Alertness and performance fluctuate with a circadian rhythm, such that during the time when the circadian drive to sleep is strongest, performance is worst . Circadian misalignment is the term used to describe the phenomenon where a person attempts to initiate sleep and engage in wakefulness during times when there is circadian opposition to such activities. Jet-lag is a common situation in which this is experienced. The functional consequence of engaging in activities during adverse circadian phases is significantly impaired cognitive performance.

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Sleep/Fatigue Risk (#13) MLD Version 1

Sleep quality : including the ability to fall asleep and remain asleep – and sleep duration are dependent upon circadian phase, length of prior wake duration, and time within the sleep episode . Quantification of this dependency has demonstrated that proper alignment of scheduled sleep episodes to the circadian pacemaker is important for sleep consolidation and sleep structure . High sleep efficiency is best maintained for eight hours when sleep is initiated approximately six hours before the endogenous circadian minimum of core body temperature . Sleep onsets before or after this time result in significantly lower sleep efficiencies, either due to increased wake during the sleep episode or shorter sleep episode durations. This phase relationship between the rest-activity cycle and the endogenous circadian timing system implies that even small circadian phase delays of the sleep propensity rhythm with respect to the rest-activity schedule can result in sleep onset insomnia or substantial wake after sleep onset.

Work Overload:It poses an additional risk in operational settings and can be considered as a product of time on task, task complexity, and task intensity. Not easily measured, most studies that evaluate work overload primarily consider time on task or task duration measures . Recent duty hour limit regulations in commercial trucking (FMCSA, 2011) and aviation (FAA, 2012) have attempted to address work overload by limiting hours of driving to 11 within a 14-hour duty period or by setting a maximum flight duty period based on the number

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Special Edition on Sleep Loss of flight segments flown by a pilot (e.g., 4 segments limits to a 13-hour duty). For spaceflight operations, NASA utilizes "fitness for duty standards" that nominally limits crewmembers to 6.5 hours per day and recommends that crewmembers adhere to a 48-hour work week. Setting limits can be especially important during periods of critical operations.

The NASA definition of a critical overload workload for a spaceflight crew is 10-hour work days that are undertaken for more than 3 days per week, or more than 60 hours per week (NASA STD-3001, Volume 1). Work underload can also pose issues as low levels of task related arousal, monotony, and time-on-task can unmask underlying physiological symptoms of sleep loss and circadian desynchronization.

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MEASUREMENT OF SLEEP, CIRCADIAN PHASE AND WORKLOAD Polysomnography (PSG) and Electroencephalogram (EEG): The gold standard for assessing sleep stage, duration, timing and quality is through PSG and EEG. The EEG is collected through electrodes placed at designated locations on the scalp and face as indicated by the International 10-20 system. The EEG records brain activity during sleep, which can be analyzed to determine sleep stage, and the precise timing of sleep onset and offset, along with the frequency, number and duration of waking during a sleep episode. The EEG may also be analyzed to evaluate the power density of brain waves in order to provide information about sleep homeostasis.

PSG includes the addition of sensors to measure respiration, body position and heart rate.

Actigraphy: An actigraph is a small wrist-worn device that contains an accelerometer to measure sleep through inactivity relative to activity. Some actigraphs contain additional features, such as light-sensing diodes for the collection of ambient light information or event markers for recording pre-specified study events. Actigraphy data provides a high degree of accuracy with respect to sleep duration compared to EEG, but actigraphy does not provide information about sleep stage or power.

Subjective Rating Scales: The Karolinska Sleepiness Score, Stanford Sleepiness Scale and Samn Perelli Scale are each single item ratings of self-assessed sleepiness. Such scales are widely used in field studies due to their ease of implementation and convenience. Self-ratings are the least reliable method for measuring alertness.

Although these subjective scales are not necessarily representative of the magnitude of impairment experienced during sleep deprivation, such selfassessments do track circadian and homeostatic indicators of fatigue.

Melatonin: Under normal light dark conditions, melatonin (N-acetyl-5-methoxytryptamine) is produced during darkness by the pineal gland upon receiving input from the SCN. In darkness or dim lighting, circadian-related performance impairment and alertness inversely correlate with the rise and fall of melatonin, such that as melatonin rises, alertness and performance fall. This makes melatonin production a biomarker for circadian-related performance impairment and reductions in alertness.

Melatonin may be measured in plasma or saliva and its metabolite, 6-sulfatoxymelatonin (aMT6s) may be measured in urine. In order to be useful as a biomarker, melatonin must be measured with some regularity over the course of 24 hours.

Cortisol: Cortisol follows a circadian rhythm with a morning peak and can be measured to evaluate circadian phase. Cortisol is also a stress hormone that is produced during episodes of stress or anxiety and in response to sleep loss, making it difficult to use for circadian phase assessments in field studies.

Temperature: Core body temperature fluctuates with a circadian rhythm that parallels the rise and fall of alertness and performance. Collection of core body temperature may be achieved via a rectal thermistor or through ingestible temperature sensors. Oral and tympanic temperature also follow a circadian rhythm and have been used to evaluate circadian phase in field studies. Temperature measurements are subject to masking of the underlying rhythm by external factors and are considered somewhat less reliable markers of the circadian system than melatonin.

Neurobehavioral Assessment: Human performance impairment may be estimated using regularly timed standardized test batteries. Although a variety of test batteries have been used to assess the impact of sleep loss and circadian phase, the most common test used for this purpose is the psychomotor vigilance task (PVT). Reaction time, along with errors of omission (lapses) and errors of commission (false starts) as measured by the PVT are highly sensitive to circadian phase and acute sleep loss.

Sleep Diaries: Sleep diaries are subjective logs regarding sleep timing, duration and quality that participants record daily. Although sleep diaries correlate with EEG and actigraphy, numerous studies have shown that participants typically overestimate sleep in sleep diaries. Sleep diaries are often used to enhance the reliability of

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actigraphy.

Spaceflight Evidence Occurrence of Sleep Loss During Spaceflight Throughout the history of spaceflight numerous studies have been conducted to describe the nature of sleep in space and to quantify the frequency and magnitude of sleep loss. These studies have employed a variety of measures to evaluate sleep including polysomnography, actigraphy, subjective scales and questionnaires/interviews .

Results from seven Category II and Category III studies (n = 177) are summarized in Table 1. These studies show that astronauts sleep an average of about six hours while in space, irrespective of the spaceflight mission examined or methodology used to quantify sleep. This amount of sleep is less than the amount recommended by the National Sleep Foundation and American Academy of Sleep Medicine to maintain satisfactory alertness, performance and health. It is also nearly two hours less than the eight hours recommended for astronauts per (NASA STD-3001, Volume 1). Collectively, these studies suggest that astronauts experience chronic sleep loss during spaceflight.

Although there is a general consensus between studies that sleep duration in space is approximately six hours, it is unclear whether this is due to a majority of astronauts requiring less sleep than the general population, or whether factors related to spaceflight, such as work overload, the habitability of the sleep environment, and/or microgravity, lead to reduced sleep duration. Each study that has been completed provides unique information on why sleep duration in space may be shorter than recommended.

It is possible that the astronaut population is over-represented by individuals who require less sleep than the general population, however, all studies completed to date have shown that astronauts sleep less during spaceflight relative to on Earth. A post-flight debriefing survey that was conducted in 1988 (Category III) found that 58 crewmembers from nine space shuttle missions (ranging in duration from 4 to 9 days) reported sleeping on average 6 hours per day while in space compared to 7.9 hours terrestrially . Sleep was most reduced during the

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Special Edition on Sleep Loss

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first and last days of a mission (total 5.6 and 5.7 hours, respectively). Many crew members reported fewer than five hours sleep on some nights, and some crewmembers slept two hours or less . The variability in the duration of sleep episodes suggests that some proportion of sleep loss arises from external factors rather than differences in intrinsic sleep need.

Recent evidence validates the findings of the survey study conducted by Santy and supports the notion that sleep loss during spaceflight is present even on recent spaceflight missions. Barger and colleagues completed the largest study of sleep in space using actigraphy and sleep logs over ten years of spaceflight on Shuttle and ISS (Category II). They found that Shuttle astronauts averaged about 20 minutes less in space relative to a two-week preflight period and about 47 minutes less relative to the week after landing (Barger et al. 2014).

This finding does not appear to be strictly related to work overload on short-duration Shuttle missions.

During long-duration missions on ISS, Barger and colleagues reported that astronauts averaged about 19 minutes less sleep during spaceflight relative to a two-week pre-mission period and about 52 minutes less relative to the first week after landing (Barger et al. 2014). These findings are very similar to a report by Dinges and colleagues, who completed a study using subjective sleep logs (Category III) among 18 ISS astronauts (4F) and reported an average sleep duration of about 20 minutes less during spaceflight relative to preflight (Dinges et al.

2013). In both of these studies the pre-flight data collection occurred during the training flow for the mission, which could have caused sleep loss during the pre-flight interval.

Similar findings were also reported during earlier missions. Kelly studied four (1F) Shuttle astronauts during a 10-day mission using logbook reports and found that in-flight sleep was reduced by 15% compared to pre-flight (Category III, (Kelly et al. 2005). Gundel reported that the in-flight polysomnographic sleep duration for four astronauts aboard Mir averaged about 16 minutes less than baseline (Category II (Gundel et al. 1997)). A study of three astronauts on three separate Skylab missions (Category II), with varied mission lengths, revealed that in-flight polysomnographic sleep averaged about an hour less than pre-flight although this may have been due to reduced time in bed during that mission (Frost et al. 1976).

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Despite the observation that astronaut sleep duration on the ground is longer relative to during spaceflight, it should be noted that the majority of studies have reported that astronauts sleep less than seven hours on the ground. It is possible that this reflects a shorter sleep need relative to the general population, but it may reflect reduced opportunity for sleep due to work overload and for ISS astronauts, overseas training, during preflight preparations. Dijk and colleagues evaluated five astronauts (Category II) during STS-90 and STS-95 using PSG and actigraphy and found that in-flight sleep duration averaged about 13 minutes less than preflight (Dijk et al.

2001).

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Notably, they found that astronauts slept longer when they were assigned to wear electrodes for the collection of sleep data. This finding suggests that the astronauts studied during these missions were capable of sleeping longer during spaceflight, but did not do so when their sleep was not being actively evaluated through PSG. This finding suggests that it is possible for astronauts to sleep longer than six hours during spaceflight and that other mission-related factors account for some of the observed sleep reduction in space.

In order to identify factors related to sleep loss during spaceflight, Whitmire and colleagues gathered subjective reports of sleep experiences during Shuttle operations from 74 astronauts using a survey and interview (Category III). Approximately half (54%) agreed that it was easy to fall asleep in space and about half (47%) reported that it was easy to stay asleep in space (Whitmire 2013). Various factors were reported as interfering with the ability to fall asleep including "thinking/active mind," mission-related work issues, physical discomfort, lighting and unfamiliarity with the shuttle environment and microgravity. A lack of time to ’wind down’ was also cited as an issue for some, while 20% reported no issues with falling asleep. Shuttle noise, such as from alarms, was most reported as disturbing sleep while noises from the galley water pump or the A/G communication bleed did not disrupt sleep. A number of respondents mentioned using earplugs although some felt they were uncomfortable.

Sleep Environment Within the Shuttle vehicle, most crewmembers slept in the middeck, but some have reported sleeping on the flight deck, which offered a level of privacy and allowed for less crowding in the middeck. In the flight deck however light poured in through the windows, minimizing the use of this area for sleep. Once in a designated area, crewmembers positioned themselves using sleeping bags, which they could tether to stable items such as a wall, ceiling or floor, keeping them from floating into objects or other crew and disrupting their sleep period (Figure 1).

Harnesses and tether points throughout the Shuttle allowed each crewmember to select their own sleeping area and customize it to their liking. Astronauts could have a just few tether points on their sleeping bag tied down or multiple, depending on the preference they had for feeling more secure. Crewmembers could strap the harnesses as taut or as loose as they preferred. The more firm the harness, the more pressure the astronaut could feel, which simulated laying down on an actual bed or mattress on Earth. Other crewmembers have reported they preferred to ’free float’ (Fuller, n.d.).

Sleeping on the Shuttle involved adjusting to not only the environmental aspects, but also missionrelated factors such as the schedule and the workload.

Shuttle missions were often regarded as high-tempo "sprints" as crewmembers worked diligently to complete tasks within their approximately 2-week visits into space. While flight rules generally protected 8 hours of sleep time, astronauts had to accommodate incidents of night time operations, slam shifting and "schedule creep" that would occur when workloads spilled into times that were ’off the clock’.

The sleep experience of each crewmember depended not only on the environmental and the mission-related factors, but also on the individual’s vulnerabilities, resiliencies, and their personal adaptation to spaceflight.

As noted by Baker, Barratt and Wear (2008), crewmembers are largely functional upon arrival into micrograv-

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Special Edition on Sleep Loss ity, but several stages of adaptation occur over periods of days to weeks as their physiological systems adapt to weightlessness, individually and in combination with other systems. Notable responses include fluid shifts, of which symptoms have been reported lasting a few hours (e.g. nasal discomfort) to potentially more longer term outcomes (e.g. slightly elevated intracranial pressure), as well as space motion sickness, which has affected crewmembers for a period of over several days into their missions. In addition, anecdotally, individual crewmembers have reported a feeling of "space fog," where their thinking is fuzzy and not as clear headed as usual. Individual adaptation to the physiological demands of microgravity, therefore, served as a potential contributor to crewmembers’ ability or inability to sleep on orbit, but characterizing its influence is beyond the scope of this investigation.

Factors relating to three outcomes-"falling asleep in space," "staying asleep in space," and "sleep over the course of the space mission"-were evaluated. Bivariate correlations between potential predictors and the outcomes were assessed. Multiple regression analyses for "falling asleep in space" and "staying asleep in space" were also conducted. Factors that arose in the interviews but were not found to be statistically significant from the surveys are also discussed where applicable.

The results of the data analysis are reported below, in the following format: • Falling Asleep

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– An overview of "falling asleep in space," and "falling asleep in space" versus "falling asleep on Earth."

– An overview of the survey results, including the factors that are significantly associated with ease of falling asleep in space (as reported by astronauts).

– An overview of the interview results, including factors that astronauts discussed as hindrances to falling asleep in space.

– A section for each significant factor, including additional results from related survey items and/or relevant reports from astronauts acquired during the interview.

– Multiple regression analysis to test which of the significant factors, when taken together, predicted ease of falling asleep in space.

• Staying Asleep – An overview of "staying asleep in space," and "staying asleep in space" versus "staying asleep on Earth."

– An overview of the survey results, including the factors that are significantly associated with the ability to stay asleep in space (as reported by astronauts).

– An overview of the interview results, including factors that astronauts discussed as creating awakenings during sleep in space.

– A section for each significant factor, including additional results from related survey items and/or relevant reports from astronauts acquired during the interview.

– Multiple regression analysis to test which of the significant factors, when taken together, predicted ability to stay asleep in space.

• Sleep Over the Course of the Mission – An overview of sleep over the course of the mission.

– An overview of the survey results, including the factors that are significantly associated with changes in sleep over the course of the mission (as reported by astronauts).

– A section for each significant factor, including additional results from related survey items and/or relevant reports from astronauts acquired during the interview.

Outcome 1: Falling Asleep in Space Participants were asked to indicate their level of agreement with the item "Other things being equal, it was easy for me to fall asleep in space" (i.e., during their Shuttle mission) on a fivepoint Likert scale. The rankings were "strongly disagree," "disagree," "neither agree nor disagree," "agree," and "strongly agree." For the analysis below, responses indicating "strongly disagree" and "disagree" were combined into one "disagree" category, and responses indicating "strongly agree" and "agree" were combined into one "agree" category.

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Many crewmembers reported it is not easy to fall asleep during Shuttle missions Although just over half (54%) of the participants agreed that it is easy to fall asleep in space, 36% disagreed that it is easy to fall asleep in space (Figure 2). However, as will be shown later, some crewmembers used medications to help them fall asleep. The responses to this item therefore may reflect the perspectives of crewmembers that used medications to facilitate sleep onset.

Falling asleep in space and falling asleep on Earth By comparison, 79% of participants agreed that it is easy to fall asleep on Earth, whereas 14% disagreed (Figure 2). Ease of falling asleep on Earth did not predict ease of falling asleep in space (r = .02, not significant). Therefore, the fact that astronauts fall asleep easily on Earth does not mean that they will do so in the spaceflight environment. However, astronauts who find it difficult to fall asleep on Earth are less likely to fall asleep easily in space (r = .27, p = .03). Most crewmembers reported experiencing more difficulty with falling asleep in space than with falling asleep on Earth. When it comes to how easily an astronaut falls asleep, a "good" sleeper on Earth is not necessarily a "good" sleeper in space. However, a "bad" sleeper on Earth is likely to be a "bad" sleeper in space.

Factors Related to Falling Asleep in Space: Overview of Survey Results Different aspects of the spaceflight scenario may contribute to difficulty with sleep onset for different individu-

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Special Edition on Sleep Loss als. The survey and interview included items related to various potential stressors: mission characteristics, such as schedules and work-related concerns; environmental factors, such as noise and light; crew factors, such as commander policies; and individual factors, such as "seeing" light flashes and the use of stimulants. The items were categorized into four primary topics, each composed of several factors (Figure 3).

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Factors Related to Falling Asleep in Space: Overview of Interview Results During the interviews, participants were asked to discuss what kept them from falling asleep. Their responses were later coded and categorized.

The primary responses that emerged from the interviews (Figure 4) were consistent with most of the responses from the survey. Other potential contributors to sleep difficulties, such as the unfamiliarity of the environment and physical discomfort, were also brought up by astronauts during the interviews.

As a result, the relationship between the factors and the outcome "falling asleep in space" was evaluated; results are reported in Figure 5. Where significant correlations existed, additional analysis of related survey items and/or qualitative analysis of related interview data were conducted. Interview discussions related to "unfamiliarity with environment" and "physical discomfort" were prevalent despite the lack of significant relationship found in the survey data. Therefore, additional information generated from the interviews is also provided for these topics.

When crewmembers were asked to discuss factors that may have kept them from falling asleep during the

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Special Edition on Sleep Loss mission, 21% of their responses indicated that difficulty falling asleep was a nonissue, whereas 79% of their responses were about hindrances to sleep onset. "Thinking /active mind" was reported as a primary hindrance to sleep onset; 21% of the responses revealed that "thinking" about upcoming tasks, concerns or anxiousness about the mission, or other concerns, hindered sleep; a few responses (4 out of 26) related to "excitement."

Workload, timeline, and schedule issues were identified as hindrances to sleep in 11% of the responses. For some individuals, the scheduled workload infringed on "pre-sleep" time and did not allow for "wind-down." One participant stated, "On Earth, I get physically tired and that helps me sleep; I don’t get that in orbit. There, you have to get your mind ready to sleep, and I didn’t feel I was able to unwind, and I wasn’t physically tired. I had to take Ambien."

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Other hindrances to sleep that were identified included physical discomfort, lighting, and unfamiliarity with the environment and microgravity. In addition to discussing hindrances, 18% of the responses mentioned that sleep medication aided with sleep onset. In 20% of the responses, participants stated that difficulty falling asleep was not an issue.

Survey Results: "Thinking" and Falling Asleep Five items assessed whether certain concerns kept participants from being able to sleep during their mission. Post hoc factor analysis defined the construct of "thinking" by these items, which included anxiety about the mission, upcoming tasks, safety, and individual and crew performance. The frequency analysis in Figure 6 demonstrates, however, that when crewmembers reported thinking as a hindrance to falling asleep, these concerns were typically mission- and task-related concerns. Thinking related to safety or crewmates’ performance was minimally identified as an issue. A significant negative correlation was found between thinking/anxiousness and falling asleep; the more astronauts thought about the mission, the less easily they fell asleep (r = -.54, p = .001).

Interview Results: "Thinking" and Falling Asleep The interview questions did not include items specific to thinking or ruminations. Interview questions about workload, schedules, and hindrances to falling asleep, however, yielded statements related to thinking, anxiousness, and concerns: "[Unknowns did affect sleep]. It’s not something that really kept me awake at night, but I think it was just something, just another thing that was on my mind. It was the first couple of days and I think it was just sort of the anxiety of, ’I’m in space and I don’t want to screw up,’ and, ’what am I going to do tomorrow?’ Just sort of the

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Special Edition on Sleep Loss general, ’I’m really here. It’s really the mission and my actions really matter now, and I don’t want to screw up.’ It was that sort of just brain wander kind of thought that kept me from sleeping those first couple of nights, I think."

"My brain wandering [inhibited sleep]. Once you’re there for a couple of days, and you do your normal routine, and you realize ,’I’m trained for all this stuff and none of it is really stuff I’ve never seen before,’ other than habitability kind of things. That’s the stuff you haven’t seen before, but once you do a day or two of pre- and post-sleeps, and you figure out your routine, it’s then that it’s okay."

"The night before the event and that’s why I’m up late, studying. I’m kind of running through that in my mind, and so if I’m going to have trouble getting to sleep it’ll be on those kinds of nights. Similarly on orbit, particularly on orbit before... EVA days and the rendezvous and handoff, they were real big-hitter days for me, and those were also on the early part of the mission."

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"I’m sure my stress level increased as the mission went along just because you’re getting more and more fatigued, so I think I’m more easily stressed. That may have contributed to a greater difficulty sleeping more hours during the night later in the mission." "I think for the folks who didn’t get a lot of sleep, it was probably the anxiety over the workload more than the complexity of the task that was driving it. All the sleep loss on ours was stress related. " "It’s more my thoughts or my level of alertness or excitement which got me awake." "The timeline keeps you from falling asleep because you’ve got too much to do, and you’re worried about the next morning and what you have to do and there was a couple of days where we had time off where they schedule in for a half day and you can relax a little bit, but I don’t remember relaxing a whole lot at any time in the, on any of my missions. You can’t relax and you’re rushing to go to bed and you know that you’re an hour into your pre-sleep and you’ve got to get up in like 6 hours and you’re going to get 4, 4-and-a-half hours of sleep.."

Conclusion: Thinking and Falling Asleep Astronauts who report thinking about the mission and upcoming tasks generally report more difficulty falling asleep in space. Thus, future flyers should, before spaceflight, consider methods that could help manage their thoughts and concerns. Strategies from cognitive behavioral therapy, such as taking a few moments to jot down thoughts and concerns before attempting to go to sleep, may be useful to flyers. Preflight training should be provided that incorporates such strategies, which are implementable in the spaceflight environment.

Survey Results: "Scheduled Workload" and Falling Asleep Post hoc factor analysis defined "scheduled workload" as mission workload, time for winding down, time for setting up for sleep, and unexpected problems. A significant correlation was found between scheduled workload and difficulty falling asleep; the more demanding astronauts perceived the schedule, the less likely they were to fall asleep easily (r = .38, p = .002, Figure 3). Additional items on the survey assessed workload issues, timelines, and wind-down.

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Special Edition on Sleep Loss Schedule-related issues led to not being ready for sleep at lights-out "frequently" or "always" for some crewmembers. Whereas 59% of respondents indicated that lack of time to wind down "rarely" or "never" made them "not ready for sleep," 20% indicated that lack of time to wind down "frequently" or "always" made them "not ready for sleep" (Figure 7). Lack of time to set up for sleep was identified as a sleep hindrance "frequently/always" by 13% of the respondents, while 12% of respondents indicated that working late resulted in a sleep hindrance "frequently/always."

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Wind-down time is an important factor for many crewmembers Close to half of the crewmembers disagreed that "it was not important to wind down in order to go to sleep in space"; that "the mission schedule did not affect my ability to wind down for sleep"; and that "the mission schedule provided adequate time for me to wind down for sleep" (Figure 8).

A variety of options can facilitate wind-down Participants were asked to indicate on the survey what they did for wind-down time in space, and what they do for wind-down time on Earth (Figure 9). In space, "nothing" was identified as the most common way they spend winddown time (50%), followed by spending time with crewmates (41%), listening to music (31%), other (17%), reading (9%), internet and email (8%), looking out the window (7%) and watching movies (3%).

Most respondents who indicated "nothing" in space related the inactivity to the fact that there simply was not enough time for wind down, rather than their choosing to do "nothing" for wind-down time.

Crewmembers indicated that on Earth, watching television (59%) serves as their primary way to wind down, followed by reading (53%), spending time with spouse/family (48%), nothing (17%), listening to music (16%), and other (11%). Notably, spending time with other crewmembers represented a sizeable percentage of winddown time in both scenarios.

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Special Edition on Sleep Loss

Interview Results: Scheduled Workload Consistent with the survey results, when asked during the interview to discuss how the scheduled workload affected sleep, 35% of the crewmember responses indicated that the workload did not affect their sleep; however, 32% stated that the workload affected their sleep by either reducing sleep time or hindering their ability to fall asleep or stay asleep (Figure 10). A fifth of the responses described workload effects on presleep. As described by one crewmember, "Pre-Sleep wasn’t really for winding down-was more for doing things you had to do before sleep." For others, however, the pre-sleep period included an opportunity to wind down. As seen in the survey analysis, winddown time was considered an important precursor to falling asleep. Interestingly, 13% of the responses indicated that the scheduled workload facilitated sleep.

One astronaut stated that the workload "helped me sleep better because I was so tired."

Interview Comments by the Participants: Scheduled Workload "It really didn’t [affect sleep]. We all got to bed on time, and if somebody was running behind, somebody else helped them; but I think for the most part we pretty much stayed on time with stuff."

"As far as that goes, the schedule was the schedule. We had plenty of time in the morning to do our breakfast and hygiene. We had plenty of time at night to write an email or look out the window, so I think there was a very good balance between work and sleep and some personal admin time."

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Special Edition on Sleep Loss "We ended up with some days that were really short on sleep, 6 hours maybe at most is what we had scheduled, and even then, maybe a couple of us woke up just a couple of us woke up early or something like that. I think we had a lot of work, the inspection stuff that we did both flight day two and then the two days of final inspection before we came home were really long days. EVA days were really long days."

"A couple of times we had to get up early we did some sleep shifting, too, to get things latched up for undock or something, I think. So for the most part it actually officially ate into our sleep on probably three or four of the 11 days or the 11 nights, and then we, with our own discretion, went ahead and shaved off another hour of pre-sleep and maybe a half an hour of real sleep on a couple of extra days beyond that, too."

"We’re busy when we’re up there, but I felt that there was enough time scheduled for pre- and post-sleep to kind of take care of business and ’wind down.’ The other thing was that our crew was also - everybody kind of pitched in if we had to [work] pre-sleep time, you have four people there doing it instead of the people who are just timelined to kind of get things done so people could start unwinding. So getting.. we kind of put a team effort to get in all the little stuff you got to do, so that you can focus on getting your bed set up and those kinds of things, so I think that was helpful."

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"It is very fast paced. The biggest thing about being up there is you don’t get a sense for where you are in the day. You really just can’t sit there and say whether it’s morning, afternoon, or evening. I just have to keep on looking at the schedule on my watch and see where the heck I am. Still I can’t tell you it’s evening, I could tell you it’s 3 hours before I’m going to bed, but it doesn’t register to me like that’s nighttime or that it would be 7:00 at night versus 9:00 at night. It’s just to me, like, time to do something.

Everything that works for me is how long before I have an event coming up. So that makes it kind of weird and it probably plays into your over all psyche and then the big thing is since the chronic fatigue, since it’s cumulative, you don’t know where you are in that if you had like a scale of how fatigued am I, you don’t really know."

"I would be busy from the time I got up in the morning to the time I went to sleep that I had no problems falling asleep and I’d pretty much sleep through unless somebody got up and kicked you or started the WHC, which wasn’t very often."

Conclusion: Scheduled Workload and Falling Asleep Since schedule-related issues led to not being ready for sleep at lights out "frequently" or "always" for some crewmembers, and wind-down time is an important factor for many crewmembers to faciliate sleep onset, flight planners should consider scheduling a specific allotment of time for wind-down. Time alloted for winding-down would help manage thoughts and concerns before spaceflight. Commanders should make every effort to understand crewmembers who require time to unwind before sleep and should encourage those crewmembers to take time to unwind.

Survey and Interview Results: Noise and Light, and Falling Asleep Noise The survey analysis indicated that noises such as the galley water pump (r = .02, ns), alarms (r =-.09, ns), and Air/Ground (A/G) communication bleed (r = -.18, ns) did not keep astronauts from falling asleep easily. This finding might be attributable to earplug use on orbit. The survey did not include an item to determine who wore earplugs during their space mission, or which types of earplugs they may have worn. The interview questions did include the item, "How much did noise exposure affect your sleep in space and how did you manage it?"

Thirty four of the responses mentioned wearing earplugs in flight, but this does not necessarily indicate that the other respondents did not wear earplugs in flight. Unfortunately, there is no way to quantify who did and who did not wear earplugs during their mission. Noise was not discussed as a hindrance to falling asleep when participants were asked, "What kept you from falling asleep in space?" Lights, however, were brought up as a hindrance to sleep in 4% of the responses.

Lights During the interviews, crewmembers were asked, "How much did light exposure affect your sleeping in space, and how did you manage it?" While 27% responded that light was not an issue in flight, 38% discussed wearing eye masks and 6% mentioned that light intrusion was sometimes an issue in space. Those who indicated that light was not an issue in flight may have also indicated that they used countermeasures such eye masks and window blinds. Respondents who specifically discussed light as an issue on orbit also mentioned that they did not like wearing the eye masks.

Consistent with this finding, survey analysis found that lights, in the form of inadequate window shades (r = -.39, p = .002) did keep astronauts from falling asleep easily. Light was an issue for some individuals. The flight deck was recognized as having "light leakage" through the blinds. A variety of eyeshades should be provided so

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Special Edition on Sleep Loss that crewmembers who find the current ones uncomfortable can have a means through which to minimize light exposure during sleep episodes.

Interview Comments by the Participants: Lights "I have the blackout blinds and curtains, so it’s pretty dark in my room. So I don’t like any extra light....[Light] comes in through little cracks, but also [with the] ...recent soft shades to cover the flight deck windows, the each one of those stitches [across the middle] is a little hole for light leakage. So on the day side of a pass, no matter how well you try to block the light, it’s still pretty damn bright....I don’t like the eye thing, bugs me in space."

"I think we were very meticulous about [covering the window in the Middeck] and then we had the inner deck access covered. The Middeck is pretty dark and then a lot of times you can sleep with those little masks blindfold things."

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"Eyeshades are really good; I never wear those on Earth. They were a huge advantage. In the flight deck, with the window shades carefully placed up... there’s still light in there; the sun is just so bright, those window shades don’t make it dark. On orbit, we kept middeck dark by closing the shutter between the middeck and the flight deck.

We also wore eyeshades, and kept the lighting low. People who used the WCS didn’t turn the lights on. Lighting can be a problem but we managed it on the Shuttle flight."

Conclusion: Noise, Light, and Falling Asleep Since light hinders sleep onset for some individuals, and noise was not reported as a hindrance to sleep onset (however, this may be because of earplug use), a variety of earplugs and eyeshades should be made available to crewmembers so that they can select the ones that are most comfortable for their mission.

Survey Results: Crew-Related Factors and Falling Asleep The survey included items to assess the perceived effect of commander’s sleep policy. Post hoc factor analysis defined "commander policies" by items related to whether the commander had assigned sleep locations and set restrictions regarding lights out, after-hours activities, and noise. Analysis showed that whether the commander established a sleep policy did not affect how easily astronauts fell asleep (r = .10, ns). Looking at just the lights-out aspect of the commander’s sleep policy, a strict lights-out policy did not make it easier for astronauts to fall asleep (r = .004, ns).

The survey included items to assess the degree of pre-mission sleep preparation undertaken by the crew. Post hoc factor analysis defined "sleep preparation" by items related to whether the crew had discussed factors related to sleep such as lights out, Waste Collection System (WCS) usage, early awakenings, and use of sleep medicines. Correlation analysis showed that discussing sleep issues before the mission did not affect how easily astronauts fell asleep (r = .14, ns).

The survey included items to assess the degree of crewmember noise and activity experienced during sleep episodes. Post hoc factor analysis defined "crewmember noise and activity" by items related to the assessment of crewmembers engaging in noisy activities or otherwise disruptive activities such as use of WCS and snoring.

Correlation analysis showed that crewmembers who snored (r = .03, ns), turned on the lights (r = -.12, ns), were noisy (r = -.04, ns), jostled others (r = -.03, ns), or used the WCS (r = -.17, ns) did not keep their fellow crewmembers from falling asleep.

Conclusion: Crew-Related Factors and Falling Asleep These results and the lack of discussion of these issues during the interview suggest commander policy and discussing sleep before launch did not help or hinder sleep onset. Fellow crewmembers also did not hinder sleep onset.

Survey Results: Sleep Medication and Falling Asleep in Space Sleep medication use was a primary topic in the survey. Participants were asked to report why they used sleep medication during spaceflight missions; each respondent could indicate more than one reason. Whereas 22% of responses indicated that participants did not take medications during their mission, 71% of the responses indicated that participants used sleep medications to fall asleep during their spaceflight mission. It is important to note that some participants were first time flyers, while others were veteran flyers; the data presented below do not differentiate between these two categories.

Interestingly, ease of falling asleep in space was negatively associated with taking sleep medications (r = .51, p < .001). These results may be due to our measurement of perceived ease of falling asleep rather than actual time it took to fall asleep. Additionally, sleep medication use may have been reported by those who do not

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fall asleep easily in space: those who struggled with falling asleep therefore tended to use sleep medications, while, on the other hand, astronauts who did not report difficulty falling asleep, typically did not take sleep medications.

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Special Edition on Sleep Loss Ease of Falling Asleep in Space and Use of Sleep Medicine on Earth Use of sleep medicine on Earth (r = .51, p <.001) and to a greater extent use of sleep medicine on Earth when traveling or schedule-shifting (r = .69, p <.001) predicted use of sleep medicine in space. Astronauts who are willing to use sleep medicine on Earth are more likely to use sleep medicine in space.

Figure 12 graphically illustrates that use of sleep medicine is much less common on Earth than it is in space (Figure 11) and that astronauts also find it much easier to fall asleep on Earth than in space. However, comparing Figure 12 to Figure 11 shows that when astronauts experience difficulty falling asleep in space, they are more likely to use sleep medicine.

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Ease of Falling Asleep in Space and Type of Sleep Medication Participants were asked to indicate which type of medications they took during their missions. Of the 64 participants, a total of 102 responses were given (Figure 13). The most commonly used medication was Ambien (65%), followed by Sonata (28%) and then Ambien CR.

Please note participants were asked to consider their medication use on all of their missions. Interview data reveal that some participants may have not taken any medications (hence, "none") on one mission, but taken medications during a later mission.

Repeat flyersâ&#x20AC;&#x2122; experience with sleep and medications on orbit may differ from those with a single flight experience. Additionally, participants were asked to indicate all that apply; thus, a medication that may have been tried once received a "check," just as did a medication that was taken multiple times throughout a mission.

Interview Results: Sleep Medications During the interviews, participants were asked to discuss reasons why they chose a particular medicine, advantages and disadvantages of that medication compared to other medications, and recommendations to others for

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Special Edition on Sleep Loss using medication during spaceflight. The types of responses given to these questions varied.

Comments about side effects or strengths of a medication, for instance, were often mentioned in answering the first question about why particular medications were taken; as a result, the subsequent question about advantages and disadvantages may not have been posed again. Responses to these four items, therefore, were coded and categorized as a whole.

Table 1 presents a summary of the number of participants who indicated that they have used at least one of the listed medications in space. Within the number of participants who used each medication, a subset of them brought up disadvantages of those medications.

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Questions about specific side effects of the medications were not asked; rather, the questions were open-ended.

The responses generated, therefore, may present the most salient aspects of that medication for those individuals.

Likewise, advantages of the medications were mentioned during the interview (Table 2). Specific questions about advantages of the medications were not asked; rather, the questions were open-ended. The responses generated, therefore, may present the most salient aspects of each medication for the individuals who used it.

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Special Edition on Sleep Loss

A summary of advantages and disadvantages of the five sleep medications in bar graph form (Figure 14) indicates that 19% to 33% of crewmembers who took Phenergan, Sonata, or Ambien found it effective. In the aggregate, disadvantages "outweighed" advantages for Phenergan and Ambien but not Sonata. Difference between Earth and Space was considered a negative effect for a handful of users who had reported taken Ambien.

Conclusion: Sleep Medication Use Astronauts, even those who tend to fall asleep easily on Earth, in general report more difficulty falling asleep in space. Use of sleep medications was much less common on Earth than in space, and astronauts report using sleep medications when they have difficulties falling asleep in space. Future flyers should be willing to try sleep medications in space, even if they have never tried them on Earth or rarely take them on Earth.

Interview data suggests, however, that participants should ground-test medications before flight if possible.

Individuals reported different experiences with sleep medications. Ground testing should be implemented in a manner analogous to a spaceflight scenario. One crewmember reported ground-testing medication to evaluate its effectiveness for a daytime nap rather than overnight sleep, but the crewmember found that this ground testing prior to a nap inadequately represented how he used sleep medication later on orbit (before retiring for the night).

Survey Results: Use of Stimulants and Falling Asleep Survey analysis showed that astronauts who reported having used stimulants (caffeine pills and Provigil) in space did not find it as easy to fall asleep as those who were stimulant-free (r = -.28,p = .03).

The survey did not include a question specifically regarding the amount of caffeine that crewmembers drank on orbit. However, keeping caffeine use in space equivalent to usage on Earth did not affect whether it was easy to fall asleep in space (r = -.07, ns), and a possibility of withdrawal effects due to heavy consumption of caffeine on the ground (more than 2 cups of coffee or 5 sodas a day) also did not predict ease of falling asleep in space (r = -.06, ns).

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Interview Results: Stimulants and Falling Asleep On the survey (n = 65), 10 participants indicated that they had taken Provigil during their mission; two participants in the pilot study interviews (n = 10) also indicated that they had taken Provigil, for a total of 12 participants out of 75 (16%). Eleven participants specified that they brought Provigil on their mission but did not use it.

During the interviews, participants were asked to discuss the use of Provigil during their mission. Twenty participants provided feedback related to Provigil, about their ground experience or flight experience, or simply general comments about its effects. Feedback was generally mixed, with 50% of comments favorable toward the use of Provigil, 25% not favorable, 15% neutral, and 10% reflecting concerns about other crewmembers using Provigil (Figure 15).

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Interview Comments by the Participants: Alertness Medications "I had [Provigil] with me, I didn’t use it. I have used it since on particular, a couple of critical days where I’ve been up all night, and still have more to do the next day and I wanted to make sure I’m still alert. And it actually works really well. If somebody really needed it, you know, I might recommend Provigil, but I don’t know. Do we know that much about it? Do we know if there are any effects?"

"At least here on Earth, it’s very effective. And it’s not like doing a No-Doze, it’s very effective without ... it’s like the lights go on and you’re, ’Oh I’m awake now.’ Then you can go to sleep. It’s very nice."

"My main problem on my first flight was that the more I worried about getting enough sleep, the less I slept...

[During this recent flight] I took an alertness medication before EVA. I didn’t see any adverse effects at all from it [and knowing it was available] probably gave me the ability to get an extra hour of sleep each night because I wasn’t worried about stuff anymore."

"When I drug tested Provigil the first time, I actually went to sleep with the stuff. I thought it might be a sleep med. I didn’t really know what it was.... I just didn’t use it [during the mission]."

"I think it’s fair when I say I observe that [people use the stimulants] and I was a little bit worried about it.

The use of stimulants is done quite a bit. I do not understand why though."

"I used it before my second and third EVA. The reason why I did that was because on my first EVA, I was incredibly fatigued, so much so that I wasn’t even sure I could do it. And I said I didn’t want to go through that again, so I took half of one before my second and third EVA and that was with good results. I don’t really like to use more than what is absolutely necessary. So it was a necessary trade off. I don’t like using it, but I thought it was more dangerous not to use it. So that was my threshold when it became more dangerous not to use it, I would use it. Not that I think it’s that dangerous, it’s just ... I would rather not if I have to."

"Yeah, I would recommend it, especially if you’re not getting a lot of sleep and you know you’re sleep shifted and you are coming out of another sleep shift and you know, you got to perform and you got to be able to focus in and you’re a little bit groggy. It helped me focus in." "I think it’s different for everybody. Everybody’s body reacts differently. I just wanted to have it available if I thought I might need an alertness medication and that’s the way I would do it.

Just be prepared but don’t count on it."

Conclusion: Stimulant Use and Falling Asleep On the basis of the varying reports on Provigil and its effectiveness, ground testing of Provigil is recommended.

Additionally, further information and protocols for evaluating alertness medications are recommended.

Survey Results: Fatigue and Falling Asleep Survey analysis revealed that astronauts who said that when they were fatigued, it was harder for them to fall asleep, also reported that they did not fall asleep easily during their mission (r =-.30, p = .02). Astronauts who stated that they do fall asleep more easily when fatigued did not report falling asleep more easily during their mission (r = .12, ns).

Interview Results: Fatigue and Falling Asleep

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Special Edition on Sleep Loss When asked during the interview to discuss the effects of fatigue during their mission, 38 (57%) of the crewmember responses indicated that they did not perceive any impact from fatigue, whereas 29 (43%) indicated that they were cognizant of fatigue during their mission. Of those 29, seven (21%) stated they it was effortful to work through the fatigue and felt slowed down, six (21%) stated they felt cumulative effects of fatigue toward the end of their mission, five (17%) attributed mistakes or lapses in attention and short-term memory to fatigue, and two individuals (7%) stated that their crew and ground interactions were noticeably different when they felt fatigued.

Interview Comments by the Participants: Fatigue and Falling Asleep "Fatigue had the effect that I’d ask somebody to watch me, especially towards the end of mission you get pretty tired.

And it’s just "Hey, let’s just watch things today. Everybody is getting a little bit tired. It’s been a long mission." It affected me in that you had to pull the team in more. To my knowledge at least, I didn’t make any mistakes based on being tired. That just may be a factor that I had made sure people were watching me."

"I never really felt super tired. I just kind of felt pretty good the whole time." "[Fatigue] was accumulating through the whole mission so it was harder and harder to keep pushing on. I wanted to pull back and do less. No motivation."

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"It was just that one day that it was getting close to bedtime and I actually started finding myself, while standing around the table talking to crewmembers, just caught myself dosing off, standing up. It was kind of cool. I don’t know if I really felt "fatigued-fatigued," it was just the good kind of fatigue where you put in a hard day’s work."

"I mean, you’re tired; you’re maybe a little bit of a headache because of the CO2 . You know the gears and wheels aren’t moving up there as well. You’re slower and you have to think more, and you just feel a little bit listless, and you know, like you need some sleep. But you can’t sleep because you don’t - it’s not sleep time, you don’t have the time. The CO2 issues are a huge deal for some people and I’m one of them, and they make it worse because you’re continually there. You’re going on with a bad-splitting headache the whole time, too. So it’s tough to feel that you can’t tell if you’re just fatigued, if it’s CO2 or if it’s both. But you know, after a while, the lack of ... 4-and-a-half, 4 hours of sleep a night in a high-CO2 and things like that, it starts getting to people. You can tell with some people when they’re really tired or fatigued because they get irritable. You can tell behavioral changes in them..."

"I think the crew really performed well until the end of the mission. I don’t think it affected anybody else’s ability to do anything. We managed to get everything done. We work together, we work as a team. We work - never go solo on critical activities. We watch out for each other. We built that into the whole plan."

"I didn’t see any degradation in performance from people due to fatigue. I know we had long days, but everybody seemed to be fine. I didn’t see anybody have to say, "Oh man, I’m really getting tired and I need a break." I didn’t notice that."

"I have to be frank: We were tired, all of us were tired, and I was worried about us on our first mission. I never made a mistake that had an impact, which I felt pretty lucky about. I did notice between us that we were making mistakes, perhaps never hit the switch, but we were making mistakes between us before we hit the switch. And as you got fatigued that happened more. But because of the way we do it, we never made a mistake that impacted anything. Most of the mistakes were prior to "hitting a switch".

"When you’re fatigued, you double that up. Kind of slow down because it’s more important not to make a mistake then how fast it took you to set things up. So you kind of slow down and do it very consciously... On my first mission, I did notice, and again, I think because I am aware of fatigue because of all that previous experience and how you have to manage it, I did notice that between us we were making mistakes, perhaps never hit the switch, but we were making mistakes between us before we hit the switch. And as you got fatigued, that happened more.

But because of the way we do it, we never made a mistake that had an impact on anything. Most of the mistakes were prior to hitting a switch. So I was pleased with that, but frustrated with how stupid we were going out to the pad tired. In such a wonderful experience and you’re fatigued from ignition time at lift off. I realized next time we’re going to do this better."

Conclusion: Fatigue and Falling Asleep The interview responses highlighted certain aspects of fatigue that are important to consider. Some crewmember responses suggest that some respondents sought evidence of fatigue based on their general level of "tiredness" throughout the mission. Hence, if they did not feel "tired," these crewmembers may have dismissed fatiguerelated performance effects as possible outcomes. Ground research has shown that although some individuals under conditions of chronic partial sleep deprivation indicate low levels of subjective sleepiness, their performance continues to degrade, as measured by cognitive tools such as the Psychomotor Vigilance Task.

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Other crewmembers, however, present a considerable awareness of potential fatigue effects. As noted by several crewmembers, tasks had to be performed more carefully because of fatigue. One respondent noted, "I was able to maintain the same level of performance, but that came at a much higher concentration level."

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Survey and Interview Results: Physical Discomfort and Falling Asleep Survey analysis revealed that physical factors such as use of restraints (r = -.18, ns), headache (r = -.10, ns), back pain (r = -.02, ns), needing to use the WCS (r = -.08, ns), or being too hot (r = -.04, ns) or too cold (r = -.12, ns) did not affect how easy it was to fall asleep. During the interviews, however, when participants were asked to discuss what kept them from falling asleep during their mission, 9% of the responses given related to physical comfort. For this reason, some of the interview items related to physical comfort are evaluated below.

• Head Restraint Sixty-eight percent of participants indicated they used a head restraint, whereas 32% did not. Of the participants who indicated they used a head restraint, about 31% stated that restraining their head was an important aspect of ensuring optimal sleep. Various methods were discussed for restraining the head, including the Velcro strap, the sleeping bag, and articles of clothing, such as a pair of pants. Some crewmembers indicated various reasons for their use of a restraint, such as to alleviate "a bloated head" and ambient light exposure, as well as to create a sense of pressure against a pillow. Some participants started their missions using the restraints, citing the initial importance of the restraints, but then adapted to the feel of their head "floating" in microgravity and ceased using the restraint. The head was the most frequently cited part of the body mentioned as needing to be restrained to aid sleep onset.

• Arm Restraint In discussing arm restraints, participants responded by indicating whether their arms were usually kept inside their sleeping bag (43, or 57%), usually kept outside of their sleeping (11, or 14%), or varied (22, or 29%). Of the respondents, 23 (30%) revealed that their preference was based on temperature.

• Leg Restraint In discussing leg restraints, participants provided varying responses that included restraining legs during earlier missions or at the beginning of each mission, as well as indicating they did use a restraint-the sleeping bag-or that they let their legs float freely in the sleeping bag. Thus, responses were not amenable to frequency counts. Of the 74 respondents, however, 33 (45%) discussed restraining knees into the fetal position, and half of the respondents who indicated they pulled their knees into the fetal position, mentioned that this was done to alleviate back pain.

• Torso Restraint Most participants did not seem to use torso restraints: 23they used torso restraints, and 77% did not.

• Headache No interview questions were specific to headaches; however, during the discussions related to caffeine and airflow, headaches were mentioned by crewmembers. Participants indicated that they continued to drink caffeine on orbit so as to not incur a caffeine headache. With respect to airflow, 60 (85%) of the crewmembers indicated that airflow did not prevent them from getting a good night’s sleep while 11 (15%) stated that they, at times, did not get enough air. Carbon dioxide (CO2 ) "pockets" were discussed as a potential hindrance to sleep. CO2 seems to be a concern for crewmembers and, in some instances, crewmembers pointed out that they were unsure whether adverse effects (such as headaches) were related to fatigue or high CO2 levels.

• Cold Sleeping near a vent (such as in the air lock) reportedly aided potential issues with CO2 pockets; however, these locations are often cold, and thus present another aspect of discomfort for crewmembers to consider. Several crewmembers mentioned "being cold" as a hindrance to falling asleep in space.

• Back pain No interview questions were specific to back pain, but during discussion of some of the questions, back pain was mentioned by participants. In response to the item regarding "leg restraints," a number of individuals (17 respondents) reported restraining the knees for the purpose of alleviating back pain.

• Conclusion: Physical Discomfort and Falling Asleep Interview responses revealed that back pain and headaches (often attributed to CO2 ), as well as being cold and head "sensations" (attributed to microgravity) caused some discomfort for some individuals. Further investigations into alleviating back pain in the microgravity environment and characterizing CO2 levels in flight are recommended.

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Special Edition on Sleep Loss Conclusion: Falling Asleep in Space The findings and recommendations detailed below are based on the accumulated evidence shared by Shuttle flyers. We have summarized what these astronauts said about falling asleep in space:

• Being able to fall asleep easily on Earth does not ensure that you will find it just as easy to fall asleep in space. However, if you have difficulty falling asleep on Earth, you are likely to have difficulty falling asleep in space.

• Thinking about the mission and upcoming tasks makes it harder to fall asleep.

• A heavy mission schedule makes it harder to fall asleep.

• Light makes falling asleep more difficult.

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• Sleep medicines make it easier to fall asleep in space. Many astronauts who do not use sleep medicines on Earth use them in space.

• Fatigue may make it harder to fall asleep.

A crewmember who cannot fall asleep may wish to follow these recommendations based on the results of the study: • Use a sleeping mask.

• Write out thoughts, concerns, and plans for the next day’s activities before going to sleep.

• Allow a few minutes (at least) for a brief wind-down time.

• Minimize the use of stimulants. Astronauts who used stimulants in space found it harder to fall asleep.

• Take a sleeping pill.

Outcome 2: Staying Asleep in Space Participants were asked to indicate their level of agreement with the item "In space, I am rarely disturbed during my sleep and can sleep through anything" on a five-point Likert scale. The rankings were "Strongly Disagree," "Disagree," neither "Neither Agree nor Disagree," "Agree," and "Strongly Agree." For the analysis below, the responses "Strongly Disagree" and "Disagree" were combined into one "Disagree" category, and the responses "Strongly Agree" and "Agree" were combined into one "Agree" category. Many crewmembers report it is not easy to stay asleep during Shuttle missions. Forty-seven percent of the participants agreed that their sleep was rarely disturbed in space, and 42% disagreed (Figure 16).

Staying Asleep in Space and Staying Asleep on Earth By comparison, 42% of participants reported that their sleep is rarely disturbed on Earth, whereas 36% disagreed that their sleep is rarely disturbed on Earth.

Whether sleep was disturbed on Earth did not predict whether sleep was disturbed in space (r = .06, ns). Thus, participants who report that they sleep without being disturbed on Earth should not assume that they will sleep as soundly in space, and those who report sleep disturbances on Earth should anticipate awakenings from sleep in space.

Factors Related to Staying Asleep in Space Different aspects of the spaceflight scenario may contribute to difficulty with staying asleep for some individuals. The survey and interview included items related to various potential stressors: mission characteristics, such as schedules and work-related concerns; environmental factors, such as noise and light; crew factors, such as

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commander policies; and individual factors, such as use of stimulants. The items were categorized into these four primary topics, each composed of two or three factors (Figure 17).

Factors Related to Staying Asleep in Space: Overview of Interview Results During the interviews, participants were asked to discuss what kept them from staying asleep. Responses were later coded and categorized by the team. The primary categories to emerge from the interview responses were consistent with the categories and constructs included in the survey that showed a significant correlation with staying asleep (Figure 18).

As a result, the relationship between each of the survey constructs and the outcome of "staying asleep in space" was evaluated; results are reported in Figure 19. Where significant correlations exist, additional analysis of re-

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Special Edition on Sleep Loss lated survey items and/or qualitative analysis of related interview data were conducted.

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Several participants further discussed "unexplained wake-ups" and "medication wearing off" during the interviews. Therefore, additional information generated from the interviews is also provided for these two topics.

When asked to discuss factors that may have awakened them from sleep during the mission, 20% of crewmember responses indicated that difficulty falling asleep was a non-issue, whereas 80% of crewmember responses discussed hindrances to sleep onset. Issues related to "physical discomfort" were reported as a primary hindrance to sleep onset; 19% of the responses discussed issues related to back pain, waking up to use the WCS, headaches, and temperature issues.

Noises related to the Shuttle (such as alarms) were identified as causing awakenings in 16% of the responses.

Fourteen percent of responses indicated uncertainty about what factors were causing awakenings. Crewmember disturbances, such as noise or jostling, were identified in 13% of the responses. Thinking was identified in 8% of the responses, sleep medications wearing off in 5% of the responses, and other issues in 5% of responses.

Comments from interviews: "I can’t put my finger on anything that would have woken me up, but I tended to wake up after 3 or 4 hours of sleep, regardless of how I got to sleep or how long it took me to get to sleep. I would wake up and - without a noticeable stimulus to wake up, just woke up.

I’ve always thought it was just sort of a normal part of my sleep pattern. I get in one of those phases that you’re close to being awake and I wake up...or coming out of that four hour Ambien cycle where it was wearing off."

"Big noises, jets firing, unplanned stuff when they don’t tell you it’s coming when you’re in your sleep. Lights, and a couple of times people got up and running into stuff." "Nothing I could put my finger on. Occasionally a master alarm or something but that’s pretty rare."

"The only things that woke me up, I think, were just this crackling of the speaker, that even with earplugs in, it would just wake me up. Other than that, it was just things that delayed me getting to sleep but then once I got to sleep the only things that I remember waking up were noises, like this crackling or somebody going to the bathroom, which I really don’t remember happening even the first night. So I think our crew was pretty good about that."

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Special Edition on Sleep Loss "Nothing that I remember."

"I would wake up but I couldn’t think of anything in particular. I think once I woke up and ... thinking about the mission. I’m sure part of that was thinking about what I’m going to do the next day, but I can’t think of anything in particular that woke me up."

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Survey Results: "Thinking" and Staying Asleep Five items assessed whether thinking kept participants from being able to sleep during their mission. Post hoc factor analysis defined the construct of "thinking" by items asking participants to rate their level of anxiety about the mission, upcoming tasks, safety, and individual and crew performance. The frequency analysis on page 12, as well as Figure 6, demonstrates that when crewmembers reported thinking as a hindrance to falling asleep, these concerns were typically related to the mission and upcoming tasks. A significant negative correlation was found between "thinking" and staying asleep; the more astronauts reported thinking about the mission, the less they stayed asleep (r = -.37, p = .003).

Interview Results: "Thinking" and Staying Asleep The interview questions did not include items specific to thinking or ruminations. Interview questions about factors that created awakenings, however, yielded statements from participants about thinking, anxiousness, and concerns.

Participant responses included these : "Sometimes if I have a lot on my mind. Like if I’m not able to do everything that I was supposed to do that day, not so much that I’m worried about it, but I’m trying to figure out how I can fit it in the for the next day, or if there was some problem unresolved or some issue that we are working that is not well resolved or well understood, I’ll probably be thinking about that as I sleep. It may result in unrestful sleep."

"You could be having a big day the next day, but if there’s some concern that it’s not going to work out well, it’s not going to have a good outcome, that’s when you’re going to lay awake tossing and turning."

"Part of it too is I think there’s a fear on Shuttle missions. I want to make sure I get back to sleep because I need it. You’re like, "Hey, I want to try and stay rested." It’s a long mission. It’s almost like, well, I can take this thing or I can chance it that I won’t fall asleep. If you are having trouble getting to sleep, you start thinking about it. Oh shoot, now you’re toast. It’s like when you have some big event and you’re worried about it which is keeping you from sleeping. Then you go, "Oh my god, I’ve been laying here 30 minutes and I’m still awake." It just snowballs at that point because the mind just starts racing."

"I could never get comfortable enough to sleep well, and it was mostly worry. And this happens sometimes [on Earth], if I need to get up early for something and am worried about being awake and ready the next day."

Survey Results: "Scheduled Workload" and Staying Asleep Post hoc factor analysis defined "scheduled workload" as mission workload, time for winding down, time for setting up for sleep, and unexpected problems. A significant correlation was found between scheduled workload and difficulty staying asleep; the more demanding astronauts perceived the schedule to be, the less likely they were to stay asleep (r = .32, p =.01).

Although this correlation was significant, the interview question "Please discuss the things that woke you up in space" did not yield responses related to schedules or timelines. Participants did bring up "thinking," which was often associated with workload issues. As previously mentioned, "thinking" and "scheduled workload" are two interrelated constructs with shared variance. Partial correlation analysis controlling for "thinking" found a non-significant relationship between "scheduled workload" and "staying asleep in space" (r = .19, ns). A significant relationship was found, however, between "thinking" and "staying asleep in space" when controlling for "scheduled workload" (r = -.28, p = .000). Therefore, the correlation seen between "scheduled workload" and "staying asleep in space" is likely a result of thinking about upcoming tasks and the mission.

Survey and Interview Results: Shuttle Noise and Staying Asleep Of the noises that arose from the Shuttle, only alarms woke astronauts from their sleep (r = - .36, p = .003).

Noises such as the galley water pump (r = -.17, ns) and A/G communication bleed (r = -.15, ns) did not wake astronauts once they were asleep. Understandably, alarms are cause for awakening, but according to the results of crewmember interviews in this investigation, earplugs and other mitigation strategies kept noises such as the galley water pump and A/G communication bleed from disturbing their sleep.

Sixteen percent of responses provided during the interview indicated that some participants attributed sleep

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Special Edition on Sleep Loss disturbances to noises from the Shuttle. Sources of the reported noises included : • Alarm • Fan noise • Shuttle printer turning on for uplinks • The crackling of the speaker

Participants also said that unanticipated noises were the ones that awakened them: "I think the key is whether or not the noises are expected, and expected noises don’t generally bother me. Unexpected noises are more interesting, so they tend to wake you up. On Earth, we manage that by trying to keep a quiet house, and on orbit we manage it by all getting to sleep at the same time so there really was no noise to worry about other than fans. That’s just a constant noise and it doesn’t worry anybody."

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"I generally kind of sleep pretty solid. I’m not saying it doesn’t bug me at all, but generally it’s got to be a loud noise or a very sudden noise to get me up. I think the nice thing about that airflow through that air duct, and then there’s the general airflow, is it did have sort of a low hum background noise because of the airflow going through this duct that was right by my head. I think that was enough of a little white noise level that any clunking that was happening in other nearby areas was masked."

"Something unexpected or pretty loud, like somebody making noises while sleeping, that will wake me up, too, just because of the loudness and proximity."

When asked to discuss "How much did noise exposure affect your sleep in space and how did you manage it?" 34 of the participants mentioned wearing earplugs whereas 14 specified that they did not. Several participants mentioned the earplugs were uncomfortable, while others emphasized how well they worked. Earplugs referred to as "Foamies" seemed to be a favorite of crewmembers. Participants stating earplugs were "uncomfortable" did not clarify whether these earplugs were Foamies as well.

Lights in the form of inadequate window shades (r = -.16, ns) and light flashes (r = -.24, ns) did not typically disturb astronauts once they were asleep. Two participants who slept on the flight deck (where external light is prevalent) mentioned that light occasionally woke them up.

Survey Results: Crew-Related Factors and Staying Asleep The survey included items to assess the effect of the commander’s sleep policy. Post hoc factor analysis defined "commander policies" by items related to whether the commander had assigned sleep locations and set restrictions regarding lights out, after-hours activities, and noise. Analysis showed that the commander’s establishment of a sleep policy did not affect whether participants stayed asleep (r = -.04, ns).

The survey included items to assess the degree of pre-mission sleep preparation undertaken by the crew. Post hoc factor analysis defined "sleep preparation" by items related to whether the crew had discussed factors related to sleep such as lights out, WCS usage, early awakenings, and use of sleep medicines. Correlation analysis showed that discussing sleep issues before the mission did not affect whether participants reported staying asleep (r = -.13, ns).

The survey included items to assess the degree of crewmember noise and activity experienced during sleep episodes. Post hoc factor analysis defined "crewmember noise and activity" by items related to the assessment of crewmembers engaging in noisy activities or otherwise disruptive activities such as use of WCS and snoring.

Correlation analysis showed that when crewmembers were noisy (r = -.26, p = .04) they woke their fellow crewmembers. However, specific crewmember noise and activity such as crewmembers who snored (r = -.11, ns), turned on the lights (r = -.24, ns), jostled others (r = -.18, ns), or used the WCS (r = -.19, ns) did not disturb the sleep of their fellow crewmembers.

Based on the survey results, commander policy and discussing sleep before launch did not help or hinder sleep. General noise generated by fellow crewmembers was identified as a cause of awakenings, although specific crewmember noises and activities were not identified as causes. The interview data yielded additional information related to crewmember disturbances. When asked to identify "what woke you up in space," nine participants identified noise from the WCS, and four indicated jostling.

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When asked to discuss how crowdedness affected their mission, many participants responded that crowdedness wasn’t an issue. "Spreading out" to other locations (on the flight deck and on the ISS) helped minimize the number of crewmembers in the middeck.

These are some of the participant comments about crowding: "I think the first couple of days in space when you’re in this ’honeymoon’, crowding doesn’t affect you at all because you’re just adapting to a new environment. Then we go to the station. Then guys spread out all over the station, and so on the flight deck, we only had two people. So it never really changed. On the middeck when all the other five guys were on the middeck the first couple of nights, it didn’t seem too crowded. The perception was there was plenty of room. Then when we lived on the station for 12 days and then we came back in the Shuttle, I think that there was a huge perception that it was crowded and constrained. And everybody just wanted to get away from each other kind of thing."

"So my perception was [crowding] would have been troubling. It would have been troubling if I would have been on the middeck."

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"Once you’re asleep, you don’t know you’re crowded. It is crowded, that’s why I slept on station. But you just deal with it."

"Well once you’re asleep, you don’t know your crowded, so you just go to sleep, ...but when you get up in the morning and you try to go to bed, you’re rushing around and you’re moving around in the Shuttle, that’s one of the reasons I went to sleep in station, because there’s in more space in station and it’s wider. I mean, you just deal with it and you go to sleep and you get up."

"Crowdedness was not an issue because we made sure we were restrained, everybody did a good job restraining themselves and nobody moved around once it was bedtime. It was the rule. You stay in bed."

"Bumped into a crewmember one night and that woke me up. I moved my bag a little bit the next night to eliminate that possibility."

Several discussion points were related to the degree of planning and communication involved with determining sleep locations to minimize awakenings. The salience of sleep locations can be seen in the crewmembers’ responses to the two questions about the positive and negative issues of their flight: "The other part is to keep your own stuff out of the way, and as it gets toward bedtime, get all your stuff put away and all your areas and stuff cleaned up so that everyone can put their sleeping bag out. We call it self- Keep your stuff put away. All of it, especially at the end of the day."

"If they are people who maybe don’t need as much sleep or wake up early, they might like to go to the flight deck, but it does kind of constrain the middeck area to have a lot of people there which could be a CO2 issue or just maybe trying to find a comfortable space for everybody to sleep. If every crewmember likes to be on the floor sort in that bed like orientation, it might be hard to find seven locations like that on the middeck. Make sure that the plan accommodates the orientation that people would like to sleep and/ or if they want to be up to look out the window."

"One of the things is if crewmembers like me who do get up in the middle of the night or don’t need that much sleep, if they wanted to call home. You know because different times, it might be an ideal time to have satellite hookup so you could talk to your family. If you could provide a place that’s quiet enough for people to do that and not wake up the rest of the crew. That’s a benefit. The people that can’t sleep, it gives them something to do to connect with their family. If they’re tense, they can get over it." "There were a couple of times where some people got up and you know, they’re new or they’re first time fliers and they’re banging around and all that flying by."

"Nobody slept on the flight deck for us and that was sort of the designated place. ’Hey, if you can’t sleep, go up there. Don’t sit in your sleeping bag and be miserable. Just go up there and look at the Earth and enjoy the time while you’re in space and maybe you’ll get tired while you’re there and go back to bed.’ I liked that a lot. I never did that, but I thought it was a great idea, and it was a peace of mind kind of thing to know that there is a place where you can go and just kind of ’chill out’ and not affect, nobody can hear you and you’re not going to wake others up if you go. You can flip on the lights up there and just exist and look at the Earth. When we were docked, I liked how we were all given the freedom to go sleep in other modules."

"Well, after docking to the space station and spreading out a lot more, that keeping the PP O2, well it keeps the

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Special Edition on Sleep Loss PP CO2 carbon dioxide a little bit lower, which I think helps people sleep, too." "Picking a sleep location and being conscious of WCS use and trying to minimize use."

Conclusion: Crew-Related Factors and Staying Asleep Sleep location was related to sleep disturbances. Private sleeping quarters could have minimized the issues with crowdedness; crewmembers, however, managed for the duration of their mission to make the best of their situation. Recommendations from crewmembers indicate that there were advantages to spreading out for sleep between the middeck and flight deck (less CO2 buildup, roomier) and advantages to all sleeping on the middeck (allowing those who were awake to visit the flight deck). Planning ahead and communication were discussed as key aspects of ensuring optimal sleep location under the circumstances.

Survey Results: Sleep Medication and Staying Asleep in Space Sleep medication use was a primary topic in the survey. Participants were asked to report why they used sleep medication during missions; each respondent could indicate more than one reason. Whereas 22% of the responses indicated that participants did not take medications during their mission, 23% of the responses indicated that other participants did use sleep medications in flight to stay asleep, and 23% of the responses indicated that participants used sleep medications in flight to go back to sleep (71% of responses were for falling asleep; participants could mark more than one answer).

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Sleep medication use was negatively associated with the item "My sleep was rarely disturbed in space" (r = -.44, p < .001). Participants who reported that they slept undisturbed in space did not typically use sleep medicine. Astronauts whose sleep was easily disturbed in space, however, did tend to use sleep medicine.

Staying Asleep Staying asleep during the night on Earth and use of sleep medicine on Earth are not related (r =.04, ns). Many astronauts sleep without waking during the night on Earth whereas many others frequently wake during the night (Figure 21). Regardless of how well they sleep, astronauts do not habitually use sleep medicine on Earth.

However, comparing Figure 21 with Figure 20 (use of sleep medicine in space) shows that when astronauts have difficulty staying asleep in space, they are more likely to use sleep medicine.

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Survey and Interview Results: Stimulants and Staying Asleep Astronauts who used stimulants in space were not more likely to report increased awakenings during the night than were their stimulant-free crewmembers (r = -.08, ns). Interview data did not indicate that crewmembers attributed awakenings to their use of stimulants.

Survey Results: Physical Discomfort and Staying Asleep The survey included items regarding backaches, headaches, needing to use the WCS, and temperature. Survey analysis revealed that astronauts identified back pain (r = -.33, p = .01) and needing to use the WCS (r = -.25, p = .05) as sleep disturbances. Other physical factors such as headache (r = -.23, ns), being too hot (r = -.03, ns), or being too cold (r = -.10, ns) did not lead to awakenings.

Interview Results: Physical Discomfort No interview questions were focused on specific comfort issues such as headaches or back pain; most questions related to physical comfort involved the use of harnesses and restraints. When participants were asked to discuss factors that may have awakened them from sleep during the mission, 19% of responses indicated that physical discomfort was a source of awakenings for crewmembers.

Some specific statements provided by participants: "Usually, it was some form of temperature discomfort I think. You know, when it was time to stick my arms out the holes or it was time to bring my arms back in the holes. Maybe it’s some lower back pain, or maybe a dry mouth, or a temperature discomfort would wake me up....I never remember having a problem falling back asleep." "Peeing. I’d say over the 13-day mission it probably happened five times, five or six times."

"Early on, it was a little back pain, so Id tend to reposition. After that I didn’t have that. After the first couple of nights, I didn’t have any. Like I mentioned before, somebody going to the restroom, or I think we had an alarm or two go off throughout mission, so that would wake us up briefly. I mean that’s probably normal, pretty standard, you’re going to get an alarm here and there. That’s about it. So nothing, just a couple of things here and there."

"I think I was uncomfortable. I guess I could never get comfortable enough to sleep well." "The first night, I woke up

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Special Edition on Sleep Loss because I kind of felt like I was falling and I think that was a function of me not having the sleeping bag pretty taut.

One night, I can’t remember if it was the night before we came home or whatever, and I actually ran out of Ambien, I just didn’t sleep that night at all. I was pretty much conscious the entire night. I’m sure I probably got a little bit of sleep here and there, but for the most part I really did not have a restful night of sleep."

"I can remember waking me up were being cold on several occasions, and then on the night I slept in the Middeck, it was being bumped by a crewmember who was getting up to go to the bathroom."

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Conclusion: Physical Discomfort and Staying Asleep Survey and interview responses indicated that physical discomfort was significantly associated with increased awakenings. Judging by the experiences of these crewmembers, future flyers should consider limiting liquids before bedtime and ensuring they have enough clothing to cover up if they feel cold. Several crewmembers mentioned that they restrained their legs into the fetal position as a means to alleviate backaches and pain.

When asked about their use of leg restraints, 45% of participants discussed restraining their knees into the fetal position, and for over 50% of these responses, lifting the knees was discussed specifically as a way to alleviate back pain. The torso harness could be used to facilitate this sleeping position.

Multiple Regression Analysis and Staying Asleep in Space Only those predictors with a significant relationship to Staying Asleep in Space were entered in the regression equation. Multiple regression analysis was used to test which significant factors predicted participants’ experience of staying asleep in space. The results of the regression indicated that one predictor explained 57% of the variance (R2 = .57, p < .01). It was found that that thinking about the mission significantly predicted difficulty staying asleep in space ( β = -.64, p <.05). Scheduled workload, Shuttle noise, crewmember noise and activity, sleep medication use, and physical discomfort did not predict difficulty falling asleep - although back pain approached significance (β=-.89, p < .059).

Interview Results: Unexplained Wake-Up When participants were asked to discuss factors that may have awakened them from sleep during the mission, 14% of responses indicated that they were not sure what led to the awakenings.

These are some of the specific statements provided by participants: "There were 2 nights up there that I just woke up early about an hour-and-a-half one night and maybe an hour or 45 minutes the other and couldn’t go back to sleep. I just got up early. Everybody has that– I don’t want to make it sound like it’s every single night that I just go to bed for 8 hours and never, ever wake up. I’m just giving you the normal routine, but even on the Earth there’ll be the occasional you wake up and it’s 3:30 or 4:00 in the morning and you can’t go back to sleep. It’s very, very rare that I have that."

"Occasionally I’d wake up in the middle of the night for unknown reasons and then just move around a little bit. Stretch around a little bit and go back to sleep."

"Nothing specific, other than waking up early-not sure why, because I was still tired." "I can’t put my finger on anything that would have woken me up, but I tended to wake up after 3 or 4 hours of sleep, regardless of how I got to sleep or how long it took me to get to sleep. I would wake up and - without a noticeable stimulus to wake up, just woke up."

"I think I’d just wake up, and that’s interesting because it wouldn’t be needing to go pee, so I don’t know what woke me up. I just woke up."

Interview Results: Medication Wearing Off When participants were asked to discuss factors that may have awakened them from sleep during the mission, 5% of responses attributed awakenings to medication wearing off.

These are some of the specific statements provided by participants: "Nothing [woke me up]. Except Ambien wearing off after 4 hours. It’s to the minute. It’s like an alarm. It’s a sleep machine and an alarm clock all in one. So an alarm clock in 4 hours for me. Rarely did I get more than 4 hours of sleep, though, so it really was not an issue often. With 6 hours, you might see you only have 2 more hours, you don’t take another one. There was probably a couple of times, got 8 hours so I’d take another one if there was first 3 or 4 more hours to go."

"I think maybe the Ambien wearing off. I think that was kind of a trigger-it seemed to wear off at around 4 hours and then I was ready for the next dosage of something. The finite duration of the Ambien. Honestly, I would wake

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Special Edition on Sleep Loss up in the middle of the night for absolutely no reason. It was just bang, and I’d say, it’s 4 hours after I took the Ambien isn’t it?" I’d check my watch, Yep, 4 hours after I took the Ambien. That happened every night. I don’t know [why that is]." "Either Ambien wearing off or just part of my normal sleep pattern."

Conclusion: Staying Asleep in Space The findings and recommendations detailed below are based on the accumulated evidence shared by the Shuttle flyers who participated in this study. We have summarized in this section what these astronauts said about staying asleep in space.

Staying asleep in space is harder for those who: • Perceive a more demanding mission schedule and workload • Have a tendency to think about work • Have noisy crewmates • Experience back pain during the night, and/or

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• Need to use the WCS

Occurrence of Sleep Inertia During Spaceflight There have been no studies that have systematically documented the impact of sleep inertia on performance during spaceflight. Despite this, astronaut journal reports suggest that sleep inertia and an inability to quickly transition from sleep to wake does occur. For example, one astronaut reported "The morning started disastrously.

I slept through two alarms, one set for 0600 and another a half-hour later to remind me to take some CEO pictures. My body apparently went on strike for better working conditions."

This lack of information on the impact of sleep inertia represents a gap in understanding, particularly since astronauts could be required to respond to an emergency at any time of day or night. Sebok notes that "understanding and managing sleep inertia is highly relevant to spaceflight operations as there is no way to know when a failure could occur and there is about a 30% chance that it could be during the astronauts’ sleep period and their ability to react could be impaired when quick actions are needed".

Occurrence of Circadian Desynchronization During Spaceflight Circadian desynchronization can arise from two situations. First, the imposed sleep-work schedule can lead to a scheduled wakefulness occurring during the circadian nadir and scheduled sleep occurring during the wake-promoting portion of the circadian rhythm. Second, under a stable sleep-wake schedule, the endogenous circadian rhythm can drift to an earlier or later phase due to insufficient or inappropriately timed light exposure.

Both of these causes of circadian desynchronization have been observed during spaceflight.

Sleep-work schedules were responsible for considerable sleep disruption and circadian misalignment during the Gemini missions due to the need for one member of a two-crew operation to be awake at all times. On Gemini IV, the astronauts slept in four-hour shifts, with one crewmember sleeping while the other was awake . This led to substantial fatigue, likely related to circadian desynchronization and resulting sleep loss. A similar problem was apparent on Gemini V, but given the severity of the astronaut’s sleep disruption due to the poor sleeping environment, the astronauts worked with mission control to change their schedule and allow them to sleep at the same time .

This resulted in each astronaut experiencing a longer, more consolidated sleep. Although some subsequent NASA missions varied between a split-sleep watch schedule and having all astronauts sleep at the same time, the majority of recent missions on ISS, shuttle and Mir involved having all crewmembers sleep at the same time, although not always on a 24-hour schedule.

Few investigators have examined biomarkers of circadian rhythms during spaceflight, but each study that has been reported has revealed evidence of circadian misalignment. In a case study of an astronaut studied for eight days aboard the Space Station Mir (Category III), Gundel and colleagues reported a circadian phase shift of 2-3 hours in the body temperature rhythm and in subjective mood ratings relative to baseline, despite a 24-hour imposed sleep-wake schedule. In a subsequent Category III study of four astronauts aboard Mir, studied for 103, 30, 23 and 7 nights, Gundel and colleagues reported that three of four astronauts had an average phase

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Special Edition on Sleep Loss delay of two hours in the circadian rhythm of core body temperature compared to baseline . In this study, participantâ&#x20AC;&#x2122;s phase assessments were conducted throughout each individualâ&#x20AC;&#x2122;s mission. The participant that did not appear to have a phase delay relative to baseline had an approximately eight-hour range in baseline circadian phase over four days of data collection, suggesting that that participant may have experienced some schedule or workload-induced circadian misalignment prior to spaceflight. This circadian misalignment was associated with a reduction in sleep efficiency, despite the fact that the astronauts had a longer sleep opportunity during spaceflight.

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In a similar study of long-duration spaceflight in a single astronaut aboard Mir for 100 days (Category III), Monk and colleagues reported that the participantâ&#x20AC;&#x2122;s oral temperature rhythm appeared to remain entrained to the imposed 24-hour schedule during the first two-thirds of the mission, but a drift in his circadian rhythm timing was apparent during the last third of spaceflight . Sleep duration was also reduced during the last third of the mission and performance on cognitive tests revealed an increase in speed, but a decrease in accuracy.

These findings suggest that circadian misalignment may be responsible for some proportion of sleep loss and performance impairment during spaceflight.

Non-24 hour operations during spaceflight have also been associated with circadian misalignment among astronauts. Monk and colleagues examined the circadian rhythms of four astronauts during a Shuttle mission (Category III), where the scheduled timing of sleep was advanced (shifter earlier), by 25 minutes a day for a two-week mission. Using body temperature, cortisol and dim light melatonin onset (DLMO) measures, they found that the astronauts were able to shift their circadian rhythms, but there were individual differences in the phase angle of entrainment (i.e. the timing of the circadian nadir relative to sleep), where some participants had relatively advanced circadian phases and others had relatively delayed circadian phases. In a similar study of five astronauts aboard two Space Shuttle missions (Category III), Dijk and colleagues reported that the circadian rhythm of cortisol did not shift in conjunction with an imposed 20 minute daily advance shift in scheduled sleep timing, leading to progressive circadian desynchrony with each day in flight.

In a recent Category III evaluation of circadian rhythms during spaceflight, Flynn-Evans and colleagues applied a mathematical model to estimate the timing of the circadian nadir among 21 astronauts aboard the International Space Station; crewmembers were studied an average of 155 days each, 3,248 days total. In this study it was reported that the estimated circadian phase occurred outside the sleep episode 19% of the time during spaceflight. This resulted in the loss of one-hour of total sleep on misaligned compared to aligned sleep episodes, along with a higher prevalence of sleep medication use during misaligned sleep episodes.

There are several possible reasons for the occurrence of circadian misalignment during spaceflight. Stable circadian entrainment to an imposed schedule requires the presence of light of sufficient intensity, wavelength and duration, timed to facilitate entrainment and a schedule that is within the limits of entrainment for an individual. In low-Earth orbit, the period of the solar light-dark cycle is 90 minutes, which is far too short for circadian entrainment in humans. In the absence of supplemental exposure to light of sufficient intensity during wake episodes and darkness during sleep episodes, the 90-minute light dark cycle would be expected to elicit circadian misalignment. Exposure to light has been reported during scheduled sleep episodes due to lack of free time during scheduled wake episodes for looking out windows . Conversely, there may be situations where lighting conditions during wake episodes are insufficient to maintain entrainment.

Some modules on ISS and on Space Shuttle do not have windows and are illuminated by artificial lighting that may be insufficient to maintain stable circadian entrainment. Each of these issues would be a concern during deep space missions, where episodes of constant light or constant darkness may be experienced and where internal light intensity may be restricted due to energy consumption. It is also important to note that circadian entrainment to light occurs through ocular light exposure. There have been several documented cases of intra-ocular pressure leading to concerns about visual impairment during spaceflight . Given that eye diseases associated with progressive deterioration of vision have been associated with circadian rhythm disorders and non-24-hour sleep wake disorder , it is important to evaluate whether the circadian misalignment observed during spaceflight relates to ambient lighting conditions or changes within the eye that prevent appropriate circadian entrainment.

In addition to the importance of light in maintaining circadian entrainment, astronauts are often required to maintain wakefulness at adverse circadian phases due to mission demands. Launch windows are limited to narrow bands of time each day to ensure that the vehicles achieve a suitable orbit for a given mission. If that launch window occurs during the biological night, the astronauts need to awaken several hours prior to the appointed launch time. In the weeks prior to flight, astronauts typically adopt an advancing or delaying sleep schedule in order to be awake at launch time . Additionally, in order to prepare for events, US astronauts have

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Special Edition on Sleep Loss been historically scheduled to sleep at times on a non-24 hour schedule that would be expected to impose circadian misalignment.

For example, Nicholson evaluated Apollo sleep schedules and found that they were insufficient to allow for circadian entrainment. Shuttle astronauts were frequently required to shift sleep timing each day in order to allow for wakefulness at an appropriate window for landing. Astronauts on long-duration missions have typically adopted a 24-hour schedule, but would be required to "slam-shift," whereby they suddenly are required to sleep at a time many hours before or after their nominal bedtime in order to have scheduled wakefulness coincide with mission events. These abrupt shifts in the imposed sleep-wake schedule can also induce circadian misalignment.

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Apollo Mission Sleep Notes Apollo 7 Apollo 7 has been described as Apollo’s ’shakedown cruise’ in Earth orbit, the first flight of the Command and Service Modules (CSM) with a crew onboard. Because NASA had only 13 1/2 months to complete the task of completing a successful landing mission "before this decade is out", the flight plan was full. If at all possible, NASA wanted to be able to next fly the CSM on a far more ambitious mission. Because this was the first crew to fly a CSM, at least one of them would be awake at all times; the need to fit two sleep periods into each 24 hours made the flight plan even tighter. And, finally, all three crewmembers developed head colds early in the flight, which didn’t help their productivity and probably contributed to the bad relations that developed during the flight between Apollo 7 Commander Schirra and Houston.

The crew removed their suits not long after reaching Earth orbit and these were stowed under one of the couches. Sleeping bags were secured under the other two couches with straps and the sleeping crewmembers slept in the bags, floating in zero-gravity. The crew did not have to cover the spacecraft windows during sleep but, rather, covered their heads with sleeping bag fabric and were not bothered by the sunlight. Biomedical data, including heart rate, were available from only one crewman at any one time. A switch on the instrument console could be set at one of three positions. The crew made regular reports on water consumption and any medication taken. Reports on the amount and quality of sleep were made occasionally. Crew status reports became more formalized, starting with Apollo 9 and becoming part of the daily routine with Apollo 11.

(Adapted from the Apollo 7 Mission Report) Like prior (Mercury/Gemini) crews, all three crewmembers experienced a sensation of fullness of the head shortly after achieving orbit. After the flight, the Commander stated that he became aware of head cold symptoms within an hour of launch, but did not report his cold to Houston until about 15 hours. Twenty-four hours later, the other two crewmembers reported having head colds.

"The crew reported poor sleep for about the first three day of the flight and experienced both restful and poor sleep after that period." Late in the mission, at 214 hr 40 min. Apollo 7 Commander Schirra recommended that Apollo 8 Commander Frank Borman immediately begin a review of his mission’s timeline from liftoff onward "for sleep (and) work cycles, and for food periods."

Apollo7 Sleep Notes

Apollo 8 From the Apollo 8 Mission Report: Real-time changes to the flight plan were required because of crew fatigue, particularly during the last few (lunar) orbits before the transearth injection maneuver." As can be seen in Sleep Notes derived , at 31:40:49 Apollo 8 Commander Frank Broman told Houston "We would like to see, in looking over the flight plan - perhaps we ought to put the rest periods a little bit shorter and more frequent. It seems it might work out better. We got all out of kilter on it yesterday. We are sort of trying to get back in a normal cycle." As can be seen in the following comparison of the planned and actual sleep periods, by and large the crew did switch to a pattern of shorter, more frequent sleep periods.

During the 20 hours spent in lunar orbit, the crew had planned only short naps and, except for timing variations, this is what they got. In addition to engine burns, tests of navigation/guidance/landmark tracking procedures that would be used by later crews, preparations for the engine burn that would take them back to Earth, and general spacecraft operations, the crew spent a lot of time taking photographs and providing television broadcasts for a global television audience. On this landmark voyage, with support from Houston, the crew was ready to find a way to get sufficient rest within the context of mission requirements. CDR Frank Borman took a 100-mg sleeping tablet before the first rest period.

Apollo8 Sleep Notes

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Apollo 9 Extract from the Apollo 9 Mission Report: " Work/rest cycles.- This mission was the first in which all three crewmen slept simultaneously. A definite improvement over the previous two flights was observed in the estimated quantity and quality of sleep. The lack of postflight fatigue was correspondingly evident during the physical examination on recovery day. It should be further recognized, however, that crew work load during the last 5 days of flight was significantly lighter than on previous missions. The flight plan activities for the first half of the mission resulted in excessively long work periods for the crew, and the time allocated for eating and sleeping was inadequate. Crew performance, nonetheless, was outstanding. Departures from the crew’s normal circadian periodicity also contributed to some loss of sleep during this time. The crew experienced a shift in their sleep periods, which varied from 3 to 6 hours from their assumed Cape Kennedy sleep time."

A table from the Mission report summarizes crew sleep reports. Apparently, the LMP was able to sleep despite his difficulty adapting to weightlessness. He took a Seconal for the Flight Day 4 sleep, one for Day 5, one for Day 6, one for Day 10; he had generally good sleep.

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Apollo9 Sleep Notes

Apollo 10 From the Apollo 10 Mission Report: "The three crewmen were scheduled to sleep simultaneously, and in general, they slept very well during the nine periods. Estimates of the quality and quantity of sleep were based entirely on subjective reporting by the crew. In postflight debriefings, the Commander commented that the sleep stations and sleeping bags were satisfactory."

During the last day of the translunar coast, Houston scheduled a 14-hour rest period for the crew in preparation for lunar orbit insertion and, then, after another, relatively-short rest period, the LM flight.

Apollo 10 Sleep Notes

Apollo 11 From the Apollo 11 Mission Report, Pilots’ Report (Section 4.12.6): "The rest period was almost a complete loss. The helmet and gloves were worn to relieve any subconcious anxiety about a loss of cabin pressure and presented no problem. But noise, lighting, and a lower-than-desired temperature were annoying. It was uncomfortably cool in the suits, even with water-flow disconnected. Oxygen flow was finally cut off, and the helmets were removed, but the noise from the glycol pumps was then loud enough to interrupt sleep. The window shades did not completely block out light, and the cabin was illuminated by a combination of light through the shades, warning lights, and display lighting. The Commander was resting on the ascent engine cover and was bothered by the light entering through the telescope (Alignment Optical Telescope, AOT). The Lunar Module Pilot estimated he slept fitfully for perhaps 2 hours and the Commander did not sleep at all, even though body positioning was not a problem. Because of the reduced gravity, the positions on the floor and on the engine cover were both quite comfortable."

There was never much spare room in the LM cabin and, after the EVA, two rock boxes added to the clutter.

After taking photographs out the windows to further document their EVA, Armstrong and Aldrin had a meal and then jettisoned the PLSSs and other gear, primarily in the interest of reducing the LM weight for the return to orbit, but also to give them more elbow room. Lunar gravity is weak enough that there is no discomfort in standing for hours at a stretch but, for their rest period, Aldrin tried to make himself comfortable on the floor across the front of the cabin and Armstrong got up on the engine cover farther aft. Later crews had hammocks, which made sleeping much more comfortable; and the last three crews were able to remove their suits for the rest periods, which allowed them to sleep well.

LMP Buzz Aldrin took aspirin on occasion to help him sleep. No other sleeping tablets were taken.

Apollo 11 Sleep Notes

Apollo 12 From the Apollo 12 Mission Report : "Sleep periods during translunar coast began approximately 7 to 9 hours after the crew’s normal bedtime of 11 p.m. The crew reported that they had no particular trouble in adapting to

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Special Edition on Sleep Loss the shifted sleep periods. However, the first flight day was extremely long, and the crew was thoroughly fatigued by the time the first sleep period began 17 hours after lift-off. The crewmen slept well in the command module during the translunar and transearth coast phases, and the Lunar Module Pilot took at least two unscheduled naps during transearth coast. However, they reported their sleep periods were longer than necessary, since they would invariably awaken about 1 hour ahead of time and would usually remain in their sleep stations until time for radio contact. The lunar module crew slept only about 3 hours on the lunar surface prior to the second extravehicular activity period. In the next sleep period, following rendezvous and docking, all three crewmen in the command module slept only 3 or 4 hours, which was less than desirable. Biomedical monitoring during sleep periods was very limited. The crew complained that it was inconvenient to hook up to the biomedical harness while in the sleeping bags ; hence, very little data were received."

The short sleep the LM crew had between their two EVAs was due to signifcant pain Apollo 12 Commander Pete Conrad had in his shoulders because the suit was too short. After about 3 hours of fitful sleep, Conrad woke LMP Alan Bean so that Al could undo the laces on Pete’s lower legs, let it out to relieve Conrad’s pain, and re-lace them. A full discussion can be found in the Apollo 12 Lunar Surface Journal after 122:37:27.

The short sleep after rendezvous and docking was due to the need to control the large quantity of lunar dust the LM crew brought up on their suits and gear that was to be transferred to the Command Module for the trip back to Earth. They also had to prepare for and perform the Transearth injection burn. They made up for the two short sleeps with a 12-hour marathon once they were on the way home.

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Apollo 12 Sleep Notes

Apollo 13 The landing planned for this mission had to be abandoned because of an explosion in an oxygen tank in the Service Module that made the crew totally dependant on the limited resouces of the LM prior to re-entry into Earth’s atmosphere.

From the Apollo 13 Mission Report, "The crew reported sleeping well the first 2 days of the mission. They all slept about 5-1/2 hours during the first sleep period. During the second period, the Commander, Command Module Pilot, and Lunar Module Pilot slept 5, 6, and 9 hours, respectively. The third sleep period was scheduled for 61 hours, but the orygen tank incident at 56 hours precluded sleep by any of the crew until approximately 80 hours. After the incident, the command module was used as sleeping quarters until the cabin temperature became too cold. The crew then attempted to sleep in the lunar module or the docking tunnel, but the temperature in these areas also dropped too low for prolonged, sound sleep. In addition, coolant pump noise from the lunar module and frequent communications with the ground further hindered sleep. The total sleep obtained by each crewman during the remainder of the mission after the incident (about 87 hours from the incident to splashdown) is estimated to have been 11, 12, and 19 hours for the Commander, Command Module Pilot, and Lunar Module Pilot, respectively."

Apollo 14 From the Apollo 14 Mission Report: "The shift of the crew’s normal terrestrial sleep cycle during the first four days of flight was the largest experienced so far in the Apollo series. The displacement ranged from 7 hours on the first mission day to 11-1/2 hours on the fourth. The crew reported some difficulty sleeping in the zero-g environment, particularly during the first two sleep periods. They attributed the problem principally to a lack of kinesthetic sensations and to muscle soreness in the legs and lower back. Throughout the mission, sleep was intermittent; i.e., never more than 2 to 3 hours of deep and continuous sleep. The lunar module crewmen received little, if any, sleep between their two extravehicular activity periods. The lack of an adequate place to rest the head, discomfort of the pressure suit, and the 7-degree starboard list of the lunar module caused by the lunar terrain were believed responsible for this insomnia. The crewmen looked out the window several times during the sleep period for reassurance that the lunar module was not starting to tip over. Following transearth injection, the crew slept better than they had previously. The lunar module crewmen required one additional sleep period to make up the sleep deficit that was incurred while on the lunar surface. The crewmen reported during postflight discussions that they were definitely operating on their physiological reserves because of inadequate sleep. This lack of sleep caused them some concern; however, all tasks were performed satisfactorily."

The suit contributed to the lack of sleep in the Apollo 14 LM because the neckring made it difficult to position the head comfortably. The last three crews removed their suits for each rest period, which eliminated this problem.

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Special Edition on Sleep Loss It is interesting to note that the Apollo 15 LM sat on the lunar surface with a larger tilt but that the crew did not report any feeling that the LM was about to tip over. The Apollo 14 tilt was 7 degrees to the right (LMP’s side of the cabin down), the Apollo 15 LM was tilted back 6.9 degrees and left 8.6 degrees, with a total tilt of 11.0 degrees.

In a 9-day mission, CDR Al Shepard only got about 41 hours of sleep, LMP Ed Mitchell got about 46, and CMP Stu Roosa got 44 hours. In contrast, during the ten days of Apollo 12, each crew member got about 70 hours of sleep. Although none of the first three crews who landed on the Moon got much sleep while they were on the surface, the Apollo 14 crew was the only crew - since the adoption of all-crew rest periods for Apollo 9 to get inadequate sleep in the Command Module.

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Apollo 14 Sleep Notes

Apollo 15 From the Apollo 15 Mission Report: "Very little shift of the crew’s normal terrestrial sleep cycle occurred during the translunar and transearth coast phases of this mission. As a result, all crewmen received an adequate amount of sleep during these periods. Displacement of the terrestrial sleep cycle during the three lunar surface sleep periods ranged from 2 hours for the first sleep period to 7 hours for the third sleep period. This shift in the sleep cycle, in addition to the difference between the command module and lunar module sleep facilities, no doubt contributed to the lunar module crewmen receiving less sleep on the lunar surface than was scheduled in the flight plan. However, the most significant factors causing loss of crew sleep were operational problems. These included hardware malfunctions as well as insufficient time in the flight plan to accomplish assigned tasks.

During the first sleep period, the crewmen went to sleep one hour later than planned and had to arise one hour early to fix a cabin oxygen leak. The crewmen again were an hour late in getting to sleep for the second lunar surface sleep period. The final sleep period was changed so that the beginning of the period was 2 1/2 hours later than originally planned. The period, which had been planned to last 7 hours, was terminated after 6 1/2 hours to begin preparations for the final extravehicular activity. Lengthening the work days and reducing the planned sleep periods on the lunar surface coupled with a significant alteration of the lunar module crewmen’s circadian rhythm produced a sufficient fatigue level to cause them to operate on their physiological reserves until they returned to the command module." As indicated in the table (below) of Sleep Comments from the ALSJ, the crew decided early in the planning processes that they were going to build the mission on a 24-hour Houston day. Despite the Mission comments quoted above, Dave and Jim believed that they’d gotten adequate sleep. Certainly, they got more quality sleep on the lunar surface than any prior crew.

From the Pilot’s Report in the Apollo 15 Mission Report: "The crew was able to sleep fairly well. Noise was minimized by configuring the environmental control system in accordance with the checklist and by using earplugs.

The temperature was ideal for sleeping in the constant-wear garment and sleeping bag, or in the constant-wear garment and coveralls. A wider hammock would improve the conditions for sleeping. A slight light leak through the stitching on the window shades interfered with getting to sleep."

Apollo 15 Sleep Notes

Apollo 16 From the Apollo 16 Mission Report : "In contrast to the Commander’s Apollo 10 experience, he slept well during all the scheduled sleep periods. Typically, the Commander’s sleep was uninterrupted for 4 to 5 hours after which he would awaken, get a drink of water, and return to sleep for the rest of the night. The Lunar Module Pilot slept well during all sleep periods except the first. However, the Command Module Pilot reported that he slept uninterrupted only two nights of the mission and, characteristically, would awaken about once every hour. He also stated that he never felt physically tired nor had a desire for sleep. On this mission, displacement of the terrestrial sleep cycle ranged from 30 minutes to 5 hours during translunar coast, and from 3 1/2 hours to 7 hours during the three lunar-surface sleep periods. This shift in the sleep cycle on the lunar surface contributed to some loss of sleep; however, this was the first mission in which the lunar module crewmen obtained an adequate amount of good sleep while on the lunar surface. This assessment of the amount of sleep is based on a correlation of heart rate during the mission sleep periods with preflight sleep electroencephalograms and heart rates. The estimates of sleep duration made by ground personnel were in general agreement with the crew’s subjective evaluations."

From the Pilot’s Report : "The crew slept exceptionally well although the cabin temperature varied. The ear plugs were not used; it was felt that they were unnecessary. For the first sleep period on the lunar surface, the

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Special Edition on Sleep Loss Commander donned only his sleeping bag, whereas the Lunar Module Pilot wore his liquid cooled garment while in his sleeping bag. For the second and third sleep periods, both crewmen wore their liquid cooled garments while in the sleeping bags. The intravehicular garments were never used. There was some light leakage into the cockpit ; however, it did not prevent the crew from sleeping. The Lunar Module Pilot aided his first sleep period by taking Seconal; however, he was awakened three times - the first two times by master alarms caused by the reaction control system ’A’ problem, and the third time by an apparent loss of communications lock during a handover which produced noise in his earphones. The first sleep period lasted about 8 hours. In general, the cabin configuration is acceptable to get a good night’s sleep."

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Apollo 16 Sleep Notes

Apollo 17 From the Apollo 17 Mission Report Biomedical Evaluation: "As on previous missions, displacement of the terrestrial sleep cycle contributed to some loss of sleep. In addition, changes to the flight plan occasionally impacted previously planned crew sleep periods. In general, however, an adequate amount of good sleep was obtained by all crewmembers. The estimates of sleep duration made by ground personnel were in general agreement with the crew’s subjective evaluations. All three crewmen averaged approximately six hours of sleep per day throughout the mission. Only during the first sleep period was the amount of sleep obtained (approximately three hours) inadequate from a medical point of view. The crew reported that the Seconal effectively induced sound and undisturbed sleep for a period of four to five hours. Sleep restraints were used for every sleep period by all three crewmen. The Commander also emphasized the importance of programming an eight-hour sleep period each day."

From the the Mission Report’s Pilots’ Report: "The planning to include a short sleep period in the first day allowed the crew to return to a normal work-rest cycle ... (On the lunar surface) the liquid cooling garments were doffed at the end of each extravehicular activity and the constant wear garment was donned for sleep. The crew believed that their sleep was much more comfortable in the constant wear garment partly because it was cleaner than the liquid cooling garment. Also, the constant wear garment removed the general level of pressure that a tight-fitting liquid cooling garment exerts on the body."

Apollo 17 Sleep Notes

Occurrence of Work Overload During Spaceflight Category III evidence reveals work overload during some spaceflight missions, including those of the Skylab and Apollo Programs. The workload during the second Skylab mission steadily increased over eight weeks, while crewmembers of the third Skylab mission reported that they quickly ran into difficulty due to work overload.

The fast-paced schedule and workload of the mission caused the crewmembers to consistently feel behind on tasks, which was associated with an overall reduction in morale. At the start of the 45th day of their 59-day mission, the crewmembers of Skylab 3 refused to perform scheduled tasks. Mission Control personnel later acknowledged that the schedule had been such that it had not given the crewmembers adequate time in which to adjust to their environment. Category III evidence from the Apollo Program also reveals that some of the Apollo crews reported intense sleepiness and mental fatigue while they were performing lunar EVAs . Shuttle missions to ISS involved faced-paced work schedules as crews perform complex, critical tasks. Of the 22 EVAs that were conducted during 2007, nine of these dangerous, and critical, endeavors lasted seven or more hours.

Astronauts surveyed about workload reported mission factors that challenged sleep including night operations, slam shifting and "schedule creep" that led to workload tasks being shifted into times that were intended to be "off the clock". The more demanding the scheduled workload was perceived to be, the less easily they reported being able to fall asleep and stay asleep. Some reported not being ready for sleep at scheduled bedtime due to work scheduling and lack of time to "wind down". For those astronauts interviewed, about the same number didn’t feel that scheduled workload impacted sleep as did feel that sleep quality and quantity were reduced.

During the Skylab Missions, Frost and colleagues studied three astronauts at multiple time points over 28, 59, and 84-day missions, where astronauts maintained a 24-hour schedule (Category III,). They found changes in sleep quality, as defined by sleep architecture, relative to baseline, including increased Stage 3 (slow wave sleep), variable Stage 4 (slow wave sleep) and increased rapid eye movement (REM) sleep. They also found that the number of awakenings remained stable or decreased during spaceflight relative to baseline, however, this may relate to the reduced sleep opportunity that they observed during spaceflight.

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Special Edition on Sleep Loss Of note, they reported individual variation in response to the spaceflight environment over time. They reported that the participant who completed the 28-day mission experienced a significant decrease in total sleep time over the course of the mission, but that this was as a result of selfselected shorter sleep episodes. In contrast, the participant who completed the 84-day mission reportedly experienced sleep difficulty during the first half of the flight, with longer sleep latency and short sleep duration, but better sleep outcomes during the second half of the mission.

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Four studies of objective sleep quality were conducted on Mir, where operations were maintained on a 24hour schedule. These evaluations revealed that astronauts experienced reduced REM latency and increased slow wave sleep (SWS) during the second sleep cycle. One astronaut had significant problems with a long latency and poor sleep efficiency leading the authors to describe those problems as "space insomnia" . Similarly, Stickgold conducted a polysomnography study of five NASA-Mir astronauts who provided an average of 24 inflight nights of sleep recording . In this study, in-flight REM sleep time was reduced by more than 50% compared to pre-flight and in-flight total sleep time was reduced by 27% compared to pre-flight even though in-flight time in bed was longer. As a result, sleep efficiency was significantly reduced in-flight to an average of 63%, which is consistent with clinically-defined poor sleep quality.

In an EEG study of eight astronauts aboard Mir, slow wave sleep was reportedly reduced compared to preflight (Category III). In contrast to the report by Frost, late in the mission study participants experienced more awake time, movement arousals and more transitions to stage 1 sleep compared to preflight. In a fourth study conducted aboard Mir, Stoilova and colleagues evaluated astronauts completing flights ranging from 9 to 241 days aboard Mir. They found that sleep latency shortened relative to baseline and that the time from sleep onset to slow wave sleep onset lengthened from the beginning to the end of the missions.

Objective sleep quality was studied on two Shuttle flights (Category II). Monk studied four astronauts at two time points during a 17-day mission using PSG and found no differences between sleep early flight and late flight though all astronauts had decreased time in bed (TIB) and slow wave sleep in-flight . Among five participants studied during two short-duration Shuttle flights, Dijk and colleagues found that the final third of sleep episodes showed changes in sleep with more wake time and reduced slow wave sleep. A form of ’REM rebound’ occurred with a "prominent" increase during post-flight sleep. It is important to note that the imposed schedule during these studies involved daily shifts in sleep timing, in contrast to the Skylab and Mir studies, which maintained 24-hour operations.

Subjective sleep quality ratings collected regarding sleep in space have been mixed. In studies where sleep quality ratings were collected in conjunction with other sleep measures, sleep quality has been consistently rated as poorer than ground-based sleep quality. Dijk reported that Shuttle astronauts rated sleep quality and being physically rested as significantly worse for inflight sleep relative to ground-based sleep. Similarly, Barger and colleagues found that sleep quality was rated significantly worse during spaceflight as collected in daily sleep logs. In contrast, in a sleep log study conducted by Dinges and colleagues, sleep quality ratings were generally rated as ’good’. Similarly, in a post-flight interview and survey by Whitmire, about half of the respondents (52%) agreed that sleep quality improved during spaceflight, while only 6% disagreed that their sleep quality improved; given the retrospective nature of this assessment however, these findings may be limited.

A unique analysis of ISS astronaut journals revealed evidence of decreased sleep quality through passive, personal reporting; Category III). In this analysis, Stuster found that astronauts reported being tired more often during the first quarter of ISS missions relative to later in the missions. Interestingly, astronauts reported more naps during the third and fourth quarters supporting the notion that adaptive strategies may be learned and employed. This finding suggests that sleep quality may improve with time in space or it may indicate that astronauts habituate to their subjective perception of poor sleep quality.

Journal entries by astronauts reveal the impact of reduced sleep quality on performance outcomes: • "Very tired. Woke up at 2 am and couldn’t get back to sleep. Finally fell asleep and overslept" • "The time shift is starting to make the end of the day tough. We are pretty tired right now having shifted about 6 hours over the weekend" • "I need to get more sleep tonight than the past few. I can feel the fatigue accumulating and it will be important to be rested for the undocking in a few days."

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Occurrence of reduced alertness and performance arising from sleep loss, circadian desynchronization, and work overload during spaceflight Ground-based evidence strongly indicates that sleep loss, circadian desynchronization, and work overload lead to performance decrements. There have been few studies of cognitive performance during spaceflight and even fewer that included sleep, circadian rhythms, and workload measures. In addition, the studies completed to date have evaluated few study participants over varying times of day on varying mission durations. Finally, it is difficult to compare the results of different studies due to the lack of standard measures of cognitive function.

Table 2 summarizes the results from studies of performance during spaceflight.

Benke evaluated the response time and accuracy of one cosmonaut before, during and after a 6-day mission on Mir and found no significant decrements in performance (Category III). A separate case study conducted

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by Manzey and colleagues suggests that fatigue-related performance decrements may occur for certain types of tasks Category III). In this study, a single astronaut completed mood, fatigue, and workload rating scales, along with a grammatical reasoning task, memory search task, unstable tracking task, and a dual task that consisted of unstable tracking with concurrent memory search, before, during, and after an eight-day mission on Mir. In this study, there was no difference in speed and accuracy of short-term memory retrieval and no impairment in logical reasoning relative to ground-based measures. The participant did experience a reduction in fine manual control movements during the unstable tracking task and greater interference effects during the dualtask and memory search. These performance impairments correlated with the astronaut’s subjective ratings of fatigue. In another study conducted on Mir, four astronauts studied during a 17-day mission rated their alertness degraded from measurements early in-flight to later in the mission , although no performance testing was conducted on that mission.

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Newman and Lathan conducted a Category II experiment on cosmonauts during spaceflight and did not find impairments in a memory-search performance task, although tracking disruptions were apparent. In contrast, a performance monitoring study by Schiflett et al. included daily assessments of the different mental functions of three astronauts during a 13-day shuttle mission. Tracking performance, timesharing efficiency, and memorysearch performance were all found to be impaired in space. The researchers hypothesized that the impairment in memory-search performance in two of the three astronauts was not related to microgravity but, rather, was a side effect of decreased alertness and fatigue.

In the most comprehensive study of sleep, circadian rhythms and performance conducted, Dijk and colleagues studied five astronauts during two Shuttle flights and found a non-significant trend toward worse performance in-flight relative to before or after flight . A detailed analysis of the time course of changes involving neurobehavioral measures, which was based on two measures that were derived from the psychomotor vigilance task (PVT) and the probed recall memory test, suggested that most of the study participants exhibited a decline in performance during the last week before launch, a further decline in-flight, and a slow recovery post-flight.

Recently, Whitmire conducted a survey and interview study and found that for those astronauts who reported worsening quality of sleep over the course of their shuttle mission, there was a positive correlation with reports of increased fatigue as the mission progressed. Despite this correlation, over half of the astronauts (57%) that participated in an interview did not perceive any impact from fatigue during their mission. A few acknowledged mistakes in attention and short-term memory as being due to fatigue and a minority of individuals felt that interactions between crew and ground personnel were noticeably different when fatigued .

The comments that astronauts made regarding fatigue reveal individual differences in perception and response to fatigue-related performance decrements: • "I was able to maintain the same level of performance, but that came at a much higher concentration level."

• "Fatigue had the effect that I’d ask somebody to watch me."

• "When you’re fatigued...it’s more important to not make a mistake...kind of slow down and do it very consciously."

Sex differences in response to conditions of sleep loss, circadian desynchronization, and work overload during spaceflight Sex differences have not been systematically studied during spaceflight. A recent review investigating published and unpublished research related to sex and gender differences in behavioral adaptation to human spaceflight revealed very few investigations of sex differences during spaceflight. This examination included a total of 201 (30 females and 171 males) astronauts and cosmonauts from 1988-2013. Representation from the US astronauts corps included 26 females and 103 males. The lack of studies on sex differences during spaceflight likely relates to the small number of female astronauts available for study.

Preliminary data communicated from D. F. Dinges to Goel for inclusion in the review stated that several measures including PVT, self-reported sleep duration, sleep quality, workload, stress, and tiredness that were collected in-flight and postflight on 18 astronauts (4F) showed no sex-based differences on any of the measures.

Given the lack of information on sex differences related to sleep during spaceflight, it is important that data

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Countermeasures Pharmacological Countermeasures Sleep medication use by astronauts is the most prevalent fatigue countermeasure used during spaceflight. Shuttle astronauts who participated in a post-flight debriefing reported more sleep medication use on dual-shift than on single-shift missions (50% vs 19%; (Category III). Barger et al. found that about three-quarters of both Shuttle and ISS astronauts reported using sleep medications during their missions, including on 52% of nights aboard the Shuttle ( Category II), although sleep medication use was associated with a faster sleep latency, it was not associated with a longer sleep duration. Consistent with the findings of Barger et al., the majority of shuttle astronauts responding to a survey (71%) indicated that sleep medications were used to help with falling asleep. For those that reported using medications, zolpidem (65%), zaleplon (28%), and continuous release zolpidem (22%) were most reported (Category III). About a quarter of the respondents indicated that they used sleep medications to get back to sleep after a mid-sleep waking, with those whose sleep was more easily disturbed more likely to do so.

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There is little data on the use of wake promoting medications during spaceflight. In a post-flight interview, Whitmire and colleagues found that 75% of the astronauts interviewed reported use of alertness medications during their mission. Those astronauts that reported use of stimulants in the form of caffeine pills or modafanil also reported being less able to fall asleep.

A Category I trial was conducted during STS-90 and STS-95 in order to evaluate the efficacy of melatonin as a countermeasure compared to placebo. In this study of five astronauts, melatonin improved sleep latency compared to placebo, but there were no differences in other sleep parameters.

A recent analysis of medication records from 24 ISS astronauts from 20 missions lasting 30 days or more reveals that the most common medications used during spaceflight were for sleep, pain, congestion, or allergy.

Medication use was generally consistent with that prescribed to the adult population, with the exception of sleep medications, which were about ten times more prevalent in spaceflight. Many medication uses were linked to schedule changes (Category III).

Light Brainard and colleagues conducted a series of studies to evaluate the LED-based Solid State Light Assemblies (SSLAs) for deployment during spaceflight. They found that the lighting generated from the SSLAs is sufficient to allow for adequate visual performance, color discrimination, and melatonin suppression. The SSLAs are scheduled for launch in 2016 and will replace ISS fluorescent lights. These lights have been designed with 3 settings: 1) white light for high visual acuity; 2) blue-enriched white light for high circadian/alertness; 3) blueminimized white light for low circadian/alertness (pre-sleep), leading to a Dynamic Lighting Schedule (DLS).

Despite the extensive ground-based work to develop and optimize the SSLAs for spaceflight, it will be important to evaluate the effectiveness of the light as a countermeasure on ISS in order to design lighting schemes for deep space missions. Accordingly, a flight study is scheduled to begin on the ISS once the lights are deployed in 2016.

Schedule Currently flight surgeons work with other operational personnel to modify flight schedules to allow for adequate sleep and time off on a case-by-case basis. A scheduling dashboard is under development to track behavioral health and mission stressors and to enable early stage detection and mitigation. Performance models based on sleepwake history can inform scheduling decisions related to both critical tasks and countermeasure implementation. Given the prevalence of schedule-induced circadian desynchrony experienced during spaceflight, objective evaluation of scheduling countermeasures deployed during spaceflight is advised.

Effects of long-term microgravity exposure in space on circadian rhythms of heart rate variability A disordered body clock is linked with aging and a shortened lifespan as well as with diseases, such as sleep disorders, carcinogenesis, obesity and diabetes. Although these biological rhythms are reportedly affected by the external world, the life environment in space has only microgravity, which is vastly different from that on Earth.

It also has no 24-h light-dark cycle. Previous analyses of short-term space stays showed that a disordered circadian rhythm is associated with sleep disturbance and alterations in life rhythms. Furthermore, many scientists expect that exposure to space environments that include microgravity might cause damage to important organs including the cardiovascular system.

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Special Edition on Sleep Loss This study examined 24-h electrocardiographic records of astronauts on an extended mission in space, examining what effects the long-term stay had on their heart rate and autonomic nervous functions.

The study subjects were 10 healthy astronauts (eight men, two women) who participated in ISS Expeditions 19-25 from 2009 to 2010. Three of the 10 subjects were excluded from these analyses because some of their data were missing. The mean (±SD) age of the seven subjects was 52.0 ± 4.2 (47-59) years. Their mean stay in space was 172.6 ± 14.6 days (163-199 days). On the average, astronauts had already experienced space flight 2.29 ± 0.49 times. The subjects were healthy adults who had passed NASA class III physical examinations. This study obtained all the subjects’ consent and gained approval from the ethical committee jointly established by the Johnson Space Center and JAXA.

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RESULTS Evaluation of autonomic activities and their transition during a long stay in space Figure 1(a-d) shows results of one subject (ID01) who developed strong bradycardia at DF1. LF components decreased significantly during both sleep and waking spans compared with those before the flight (p<0.0001).

The HF component, representing the quality of rest, decreased significantly (Figure 1b). The VLF and ULF components increased significantly compared to pre-flight (p<0.0001). VLF became large during sleep (Figure 1b) and increased prominently for several hours immediately after wake-up (p=0.0001) (Figure 1b).

Spectral analysis conducted after 6 months in space (DF3) shows that the LF component representing baroreceptor response was still lower than that recorded before the flight (p<0.0001) (Figure 1c). No significant difference was found as compared to DF1. The baroreceptor response started to decrease at DF1 and continued with no change during flight. By contrast, the HF component greatly improved compared with pre-flight and DF1 (p<0.0001). In particular, the HF component during sleep increased markedly. Even in cases when it decreased at DF1, it improved during flight (Figure 1c). VLF markedly increased as compared to pre-flight and continued unchanged (p<0.0001)(Figure 1c).

Although no significant difference was found between the VLF components during sleep from that at DF1, it continued to increase significantly compared with that before flight. Immediately after wake-up, the ULF component increased further than during DF1 (p=0.0017) (Figure 1c). Although after return the LF component became slightly lower than that before flight (p=0.049), it increased significantly compared with that during flight (p<0.0001) (Figure 1d), suggesting that it may have recovered after return. The HF component, representing the quality of rest, was mildly decreased compared with that before flight (p=0.046), but it was much lower than that recorded during flight (p<0.0001) (Figure 3d).

VLF recovered to the same level as that before flight. The prominent increase of the VLF component during sleep, observed during flight, became less pronounced (Figure 1d). Although the ULF component still showed peaks several hours after wake-up as during the flight, this prominence decreased significantly after return (p<0.0001) (Figure 1d).

Figure 1(e-h) presents results of another subject (ID04), who developed mild bradycardia at DF1. A significant decrease of the LF component was also found, similar to the case depicted in Figure 1(a-d) (ID01) (p<0.0001), but no significant change of the HF component was found. Unlike Figure 1(a-d), both ULF and VLF components became significantly lower as compared to pre-flight. In particular, ULF decreased greatly (p<0.0001).

In late flight (DF3), although the ULF component remained significantly lower than that before flight, the LF, HF and VLF components improved. In particular, the HF component was significantly increased compared with that before flight. Figure 1(i-l) shows results of yet another subject (ID05), who developed mild tachycardia at DF1.

The spectral analysis in early flight (DF1) revealed a decrease in the LF component (p<0.0001). It was uniformly low during both sleep and waking (all night and all day); the HL component was also low all night and all day. Moreover, it increased markedly during the night. The VLF and ULF components decreased as compared to pre-flight (p<0.0001). The ULF component was especially low at all times, showing no increase after waking, as had been seen before flight.

During DF3, after 6 months in space, the heart rate improved to the level before flight. The circadian rhythm became more distinct compared with that during DF1. The LF and HF components did not recover and were lower than during DF1 (p<0.0001). While showing tendencies to improve compared with DF1, the VLF and ULF components were still lower than before flight (Figure 1l)

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Special Edition on Sleep Loss Change in indexes of heart rate variability of all astronauts Time-domain analyses of heart rate variability showed that r-MSSD and CVRR, representing parasympathetic activities, decreased in ID01 and improved in ID02 and ID03. In ID04 to ID06, parasympathetic activities decreased at DF1. Regarding the ratio of LF to HF, representing the balance between sympathetic activities and parasympathetic functions, sympathetic activities were dominant in ID01, ID03, ID05 and ID07, as were parasympathetic activities in ID02 and ID04.

Furthermore, ID06 had no change. HF components are transmitted exclusively by parasympathetic nerves and used as index representing parasympathetic functions. In ID02 and ID03, they were increased at DF1, but decreased in ID01. In subjects showing mild bradycardia, they did not change at DF1 in ID04 and decreased to the level of 60% of that before flight in ID05 (Table 1).

In both individuals exhibiting tachycardia (ID05 and ID06), at DF1, the HF components decreased by 30% as compared to pre-flight. On the other hand, during DF3, all individuals except for ID04 showed recovery of the HF component from the decrease at DF1. In addition, HF components in ID01, ID02 and ID03 increased by 20% or more as compared to pre-flight. Results after their return revealed no pattern because HF components varied among astronauts.

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Authors observed the effect on, and the change in, SDNN,SDANN and TI, presumed to represent life prognosis. Actually, SDNN at DF1 increased in five individuals: ID01, ID02, ID03, ID05 and ID07). However, SDNN was nearly unchanged in ID07 and decreased in ID04. During DF3, SDNN decreased below the level of those before flight in ID03 and ID06 but increased above that level in the other astronauts.

Results show that SDNN (5 min) was 145.8 on average, changing from the lowest value of 72.3 to the highest value of 220.3. The SDANN (5 min) during flight was observed to increase by 20% or more in ID01, ID02 and ID03.

Furthermore, they decreased in ID06 but increased mildly in ID07. In ID01, ID02 and ID03 it showed an increase by 20% or more; SDANN after return also increased significantly in ID03 but decreased significantly in ID01 and ID02. In ID04 and ID05, with significant decrease of SDANN at DF3, SDANN improved after their return.

In ID06, they improved in the late flight period but decreased again after return. In one individual (ID07), they were maintained with no change, but increased after return.

SDANN (5 min) was 127.3 on average: the lowest value was 63.4; the highest value was 218.1. At DF1, TI decreased in ID01 and ID04; increased in ID02, ID03, ID05 and ID07; and did not change in ID06. At DF3, it decreased to near 70% of that before flight in two individuals (ID01 and ID03) but did not decrease in one individual with high bradycardia (ID02).

It decreased to 68% in one individual (ID06) and changed only slightly compared with that before flight in another (ID07). Although the response of TI at DF1 varied, TI never decreased below 19, which is the level reported to be associated with a bad prognosis. The mean value was 34.8, with lowest and highest values of 21.3 and 58.0, respectively.

Illustrative example of change in circadian rhythm of NN intervals Figure 2 shows biological rhythms of RR intervals. It shows results of one subject (ID01) before flight (Figure 2a,b), one month after lift-off (DF1) (Figure 2c,d), after 6 months in space (DF3) (Figure 2e,f), and after return (Figure 2g,h).

Spectral analysis and the least-squares fit of a multiple-cosine model based on major components detected

by MEM were obtained for the NN interval data edited by mathematically removing noise from the RR interval series using the Mem/Calc software.

As Figure 2(a) shows, before flight, the NN intervals average about 700ms in the waking state, were gradually prolonged to 800-900ms during sleep, and shortened again to 700ms after waking up. Periods extracted from the MEM analysis include two large components with periods of 22.71 h and 11.80 h, accounting for 31.6 and 34.9% of the variance, respectively (66.5% total), Figure 2(b) (left).

These two components are expected to represent the circadian rhythm. In addition, 7.31-h and 5.30-h components were also detected and used to approximate the circadian waveform accounting for 80.5% of the total variance (Figure 2b, right). At DF1 (Figure 2c), the NN intervals vary around 700ms during the waking state, which is not very different from that pre-flight. They lengthened to 900-1100ms during sleep, which is longer

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Furthermore, NN intervals transiently dropped in association with exercise from 18:30 to 19:00. MEM analysis detected components with periods of 26.79 h (51.9%) and 12.93 h (23.3%), corresponding to the circadian and circasemidian components (Figure 2d). These two large components are expected to represent the circadian rhythm characterizing the NN intervals.

The record obtained after about 6 months in space (Figure 2e) shows that NN intervals before sleep averaged about 700 ms, increased to 850-1000ms during sleep (development of bradycardia), and decreased to 500-600ms (development of tachycardia) at the time of awakening. The MEM analysis detects two major components with periods of 24.00 h and 11.68 h accounting for 35.6 and 30.2% of total power, respectively, with barely any other periodic component (Figure 2f, left). The clear peaks at periods close to 24 h and 12 h suggest that the circadian clock mechanism had recovered from the disturbance immediately after flight, and had even improved compared with that before flight.

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The reconstructed signal (Figure 2f, right) shows a clear circadian variation. Analyses of NN intervals after return (Figure 2g) show that they were 800-950ms during sleep, less prolonged during sleep than in space, and recovered to the level before flight. In this case, the sleeping span was greatly shortened to about 3.5 h.

The MEM analysis detected components with periods of 18.17 h and 9.34 h, accounting for 16.4 and 39.8% of total power, respectively, with barely any other periodic components (Figure 2h, left). The short 9.34-h component was the most prominent. Overall, the spectral power was markedly decreased. Whether the lack of a clear circadian rhythm is related to the short sleeping span remains to be determined.

Circadian periodicity of all seven astronauts before, during and after flight Figure 3 shows each astronaut’s circadian period estimate of the NN interval data. On the average, the mean period varied within the circadian range of 24 ± 4 h before, during and after flight (Pre: 22.36 ± 2.50; DF1: 25.46 ± 4.37; DF2: 23.17 ± 5.97; DF3: 22.46 ± 1.75; Post: 26.16 ± 7.18; p=0.0002). The inter-individual variation was significantly less during DF3.

This observational study, conducted during a long-term space stay of at least 6 months, showed that although the circadian period became less marked after one month in space (26.8 ±7.8 versus 23.0 ± 1.7 h), it improved, clustering more tightly around 24 h by the end of the stay. As reported earlier, exposure to a new environment, such as space can greatly affect human physiology. In this study, after one month at the ISS, heart rate and autonomic activities, especially parasympathetic functions, changed greatly, as did NN intervals and the circadian period of autonomic nerves. The process by which the seven astronauts reacquired their circadian rhythms differed from one individual to another: three developed high bradycardia, two developed mild bradycardia, and two developed tachycardia in space as compared to pre-flight conditions. The difference in individual response patterns suggests that the capability of adapting to the space environment.varies among individuals. Previous reports describe that a short-term stay in space is associated with a decrease in the baroreflex reflex arc, including baroreceptor and transient malnutrition. Responding to a decreased circulating blood volume, arteries tense and constrict to maintain blood volume. Sympathetic activities increase transiently, reducing parasympathetic activities. In this study, however, only four of seven individuals manifested increased sympathetic activities. In two other astronauts, parasympathetic activity increased. In other words, the response of the autonomic nervous system did not reflect the same tendency in all astronauts, but it did show that the method of response varied among individuals. In these two cases, it is considered that parasympathetic activities increased. In turn, sympathetic activities decreased so that HR decreased at DF1. However, in one of them (ID01) and in another case (ID04), it was the result of an abnormal accommodation of the low LF power. In the other case (ID05), both the parasympathetic and sympathetic activities were reduced. Mild bradycardia should hence be manifested as the sympathetic system changed more. In two cases (ID06, ID07), it is considered that parasympathetic activities were reduced to cause tension of the sympathetic nerve system and tachycardia, in keeping with previous reports. In this study, the ULF and VLF components highly increased in three individuals (ID01-03) during DF1.

Astronauts come under strong stress immediately after launch into space. Therefore, the ACTH-cortisol system is activated at the level of nerves. Consequently, cortisol is increased. The highly activated ULF and VLF components in heart rate variability shown in this study suggest such responses in immune and endocrine systems.

At last, there was a possibility that sampling rate of this study (128 Hz) affected the different result of HRV of each astronaut. Moving to space, human beings become affected by the microgravity environment. According to previous reports, exposure to microgravity can lead to confused information input to the inner ear vestibule and muscle spindle or tendon, causing a central shift of fluids and thereby reducing heart and vascular regulatory functions.

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According to a study of circadian rhythm in intraoral temperature and agility of one cosmonaut who stayed

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Three factors may have helped the astronauts to reacquire a 24-h synchronized circadian rhythm. First, regular light-dark and sleep-wake cycles are set when astronauts start living at the ISS, where lights are turned on at 7:30 GMT and turned off at 19:30 GMT. The illuminance during that time is 200-500 lux, which is effective for biological rhythms to adjust. It can be inferred that these conditions may be effective to recover biological rhythms. Second, since the feeding schedule can be expected to synchronize biological rhythms independently of the lighting schedule, establishing regular eating habits in space is important. Third, the increase of HF power during sleep may have played a role, as well-activated parasympathetic function during sleep improves sleep quality and increases the secretion volume of melatonin, which is likely to contribute to the improvement of circadian rhythms.

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Ad Astra ! To The Stars! In Peace For All Mankind !

Mr. Rick R. Dobson, Jr. (Veteran U.S Navy)

International Space Agency(ISA) ( Non 足 Profit Organization ) P.O. Box 541053 Omaha, Nebraska 68154 United States