ISOPTWPO TODAY

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ISOPTWPO Today

Cassie - The Cosmic Hedgehog CASSiE (Cosmic Ambassador for Space Science and Engineering) is a knitted hedgehog developed by Vix Southgate as a STEM (Science, Technology, Engineering and Mathematics) initiative to inspire the next generation of Space explorers and engineers.

With the help and advice of STEM Ambassador Commander Camilla Corona, and Vic Minett on BBC Radio, CASSiE was born at the beginning of October 2012.

The Cosmic Hedgehog is an educational initiative for use in Primary schools. Her aim is to inspire and engage with young children using Space Exploration to interest the children in Science, Technology, Engineering and Mathematics (STEM) subjects.

CASSiE needs support and other people to utilise her as part of existing projects that incorporate Space Science and Engineering in Schools.

CASSiE and members of her family are available to take trips to the edge of space on educational balloon experiments in return for promotion and publicity opportunities.

If you would like CASSiE to visit your school, society, or company please contact VixenUK or email spacemascotuk@gmail.com directly. — Image Credit: Cassie - The Cosmic Hedgehog (with permission)

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Risk of Cardiac Rhythm Problems during Space Flight Heart rhythm disturbances have been seen among astronauts. Most of these have been related to cardiovascular disease, but it is not clear whether this was due to pre-existing conditions or effects of space flight. It is hoped that advanced screening for coronary disease has greatly mitigated this risk. Other heart rhythm problems, such as atrial fibrillation, can develop over time, necessitating periodic screening of crewmembers’ heart rhythms. Beyond these terrestrial heart risks, some concern exists that prolonged exposure to microgravity may lead to heart rhythm disturbances. Although this has not been observed to date, further surveillance is warranted.

Indeed, there are known and well - defined changes in the cardiovascular system with space flight: a) plasma volume is reduced; b) left ventricular mass in decreased; c) the autonomic nervous system adapts to the microgravity environment.

Combined, these physiologic adaptations suggest that changes in cardiac structure and neurohumoral environment during space flight could alter electrical conduction, although the evidence supporting this contention consists mostly of minor changes in QT interval in a small number of astronauts after long-duration space flight.

During Skylab, all 9 American crewmembers exhibited some form of rhythm disturbance. Most of these rhythm disturbances consisted of single PVCs and were clinically insignificant. However, one crewmember experienced a 5 beat run of ventricular tachycardia during a lower - body negative pressure protocol, and another had periods of "wandering supraventricular pacemaker" during rest and following exercise.

More recently, it has been shown that the corrected QT interval (QTc), a marker of ventricular repolarization, was prolonged slightly in a small number of astronauts after long - duration space flight. In - flight Holter monitoring was not performed during these space flights. Thus, it is not known whether this prolongation was associated with any known arrhythmias. In-flight Holter monitoring was undertaken in the early Space Shuttle era.

Virtually no changes in arrhythmias were documented in flights of 4 to 16 days during either intravehicular or extravehicular operations compared to preflight measurements.

Indeed, in these studies, the frequency of arrhythmias may actually have been reduced in flight, though the day - to - day variability of these arrhythmias, which is known to be quite wide, was not quantified. However, aboard the Mir space station, PVCs were detected that were not present before flight and a 14 - beat run of ventricular tachycardia was documented.

More recently, several conditions that may predispose crewmembers to arrhythmias have been identified. D’Aunno et al. found that after long-duration missions QTc intervals are slightly prolonged in crewmembers who did not have prolonged QTc intervals after their short-duration Space Shuttle flights, and several investigators have found decreases in left ventricular mass following space flight.

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ISOPTWPO TODAY One crewmember during Apollo 15 experienced a 22-beat nodal bigeminal rhythm, which was followed by premature atrial beats.This crewmember reported extreme fatigue during the incident, but only when questioned about it by crew surgeons; thus, it was not severe enough to impact the mission. Twenty-one months later the crew member suffered from coronary artery disease and a cardiac infarction without suggestive ECG changes.

Apollo 15 ECG tracings obtained during periods of cardiac arrhythmia. (a) shows the normal heart beat converting to a nodal bigemini rhythm; (b) shows the bigemini rhythm converting to premature auricular contractions.

Cardiovascular measurements obtained from Apollo crewmembers during their evaluations, heart rate was the most easily measured and yielded the most accurate and predictable values.

Table contains heart - rate data on individual crewmembers during three conditions of orthostatic stress evaluations: (1) resting supine control, (2) the highest level of LBNP [-SO mm Hg (-67 x 102 N/m2 )], and (3) passive standing.

Resting supine heart rate is elevated significantly in 13 of 24 crewmen (54 percent) at the first postflight evaluation; the group response is elevated at the two-percent level of confidence.

A trend toward preflight values is subsequently evident. By the third postflight evaluation, only three of fifteen individuals (20 percent) show significant elevations in resting supine heart rate, and the group mean value is not statistically different from the preflight group mean heart rate (n = 15, paired).

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ISOPTWPO TODAY Following the same comparisons, the application of -50 mm Hg (-67 x 102 N/m2 ) LBNP produced significantly elevated heart rates in 14 of 17 Apollo crewmen (82 percent) at the first postflight evaluation, with a group elevation significant at the O.1-percent level.

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-40 mm Hg (-53 x 102 N/m2 ) LBNP and was not tested at -50 mm Hg (-67 x 102 N/m2 ) LBNP on recovery day. Five other crewmembers (the Apollo 8 CMP, the Apollo 8 LMP, the Apollo 9 LMP, the Apollo 16 CMP, and the Apollo 16 LMP) developed presyncopal symptoms at some point before protocol completion during their immediate postflight Human Spaceflight Edition c International Space Agency(ISA)

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ISOPTWPO TODAY 50 mm Hg (-67 x 102 N/m2 ) stress; the Apollo 15 Commander experienced similar symptoms during his second postflight evaluation. Although more crewmembers, immediately postflight, demonstrated a larger heart rate increment over preflight values during LBNP stress than during the resting control period, statistically significant group differences disappeared by the third postflight evaluation. Passive vertical standing results indicated a similar increase in heart rate immediately postflight, with eight of nine crewmembers (89 percent) having heart rates above their 95 percent preflight envelope, and the group mean value being elevated at the 0.1 percent level.

In the Skylab missions, several instances of ventricular PVCs, supraventricular PVCs, and nodal arrhythmia were recorded. The arrhythmias occurred during effort tests, extravehicular activities (EVAs), lower body negative pressure sessions, and throughout the entire mission. These included two consecutive PVCs in one astronaut during exercise and an episode of atrioventricular dissociation preceded by sinus bradycardia in two astronauts.

Skylab Crew Health Crew Surgeons’ Reports During the flight phase of the Skylab missions, the Crew Surgeons relied to a great extent on the daily private medical conference with the crews over an air-to-ground loop from the NASA Mission Control Center to monitor crew health. For continuous clinical evaluation of the crew, the Crew Surgeon had access to medical parameters derived from the experiment data and was also dependent on the following monitored areas for clinically related information: • Radiological health • Skylab environmental data, incuding toxicological evaluation • Medical data obtained from the Operational Bioinstrumentation System during the scheduled extravehicular activities Postflight, the Crew Surgeon coordinated all the medical activities relating directly to the crew. He was the medical team leader on the recovery ship and had prime responsibility for the continuous clinical care of the crew especially during the medical experiments, and later at Johnson Space Center.

Skylab 2 Medical examinations performed on the three crewmen at specified intervals beginning 40 days preflight did not reveal any major change in any crewmember’s health status. They remained in good health throughout the preflight phase, except for the Pilot who developed a 24-hour illness resembling a viral gastroenteritis about 1 month before flight, just coincident with the initiation of the Flight Crew Health Stabilization Program.

In-flight, on mission day 1, the Commander developed a left serous otitis media, which required the extended use of an oral decongestant as well as a topical nasal decongestant. On mission days 3 through 7, the Commander also used a topical steroid cream to relieve the symptoms of a probable mild contact dermatitis of his right arm. Complying with a preflight decision, the Scientist Pilot took one scopolamine/dextroamphetamine sulfate capsule just after insertion, and the medication was not repeated. Prior to extravehicular activity, the Scientist Pilot and the Pilot utilized a topical nasal decongestant prophylactically; the Pilot also took a systemic decongestant.

No significant arrhythmias developed in-flight. Early terminations of the Lower Body Negative Pressure experiment by the Scientist Pilot and Pilot were sporadic, and in this mission the maximum level of exposure to lower body negative pressure was reduced following early termination of the Lower Body Negative Pressure test. The Commander and Pilot took hypnotic medication of choice on the night of mission day 27 to help accommodate a change to their work/rest schedule for entry and splashdown. Entry itself on the 29th day was nominal. Postsplash (on the water) the heart rates were: Commander, 84;Scientist Pilot, 84; and Pilot, 76 beats per minute.

Aboard the ship on recovery day vertigo, postural instability (especially with eyes closed), reflex hyperactivity, and paresthesias of the lower extremities were prominent findings. The Scientist Pilot developed seasickness while still in the Command Module and the most prominent symptoms cleared in 4 to 6 hours. Scaling of the skin of the hands was noted on the Commander and the Scientist Pilot. The Pilot experienced a vagal response (decreasing heart rate, pale and sweaty appearance) in the recovery period of the Metabolic Activity experiment , which lasted just a few minutes. Muscle and joint soreness, generally confined to the lower back and lower extremities, were first noted on the first day post recovery. During the ongoing postflight period of surveillance, no significant medical problems

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ISOPTWPO TODAY developed as an apparent result of the long duration in weightless space flight. No drugs were taken except for vitamins.

Skylab 3 Preflight, no infectious diseases or other medical problems were experienced by the crew during the 30-day preflight period, the last 21 days of which included the Flight Crew Health Stabilization Program.

Launch and orbital insertion were nominal. Shortly after orbital insertion, the Pilot began to experience nausea; this was aggravated by head movement. One hour after insertion, the Pilot took an antimotion sickness capsule, scopolamine/ dextroamphetamine sulfate, with good relief. The crew entered the Orbital Workshop 9 hours and 45 minutes after lift-off. Following strenuous work to activate the Orbital Workshop, the Pilot vomited once.

During the second mission day, the Commander and Scientist Pilot also experienced some motion sickness during continued Orbital Workshop activation; they took scopolamine/dextroamphetamine sulfate, as required, for alleviation of symptoms. This indisposition caused a loss of work time during the first 3 days of flight. Two additional days elapsed before all symptoms had dissipated. Since medical experiments were not run until mission day 5, subjective voice reports by the crew were the only means of health assessment during this time. On mission day 5, after the first medical experiments were conducted, objective clinical data were available to aid in evaluating the crew’s health. In general, the crewmembers remained in excellent health except for a few minor clinical problems and rare sporadic early terminations of the Lower Body Negative Pressure experiment by the Commander and the Scientist Pilot.

The Pilot reported a painless sty on the left upper eyelid on mission day 29, which responded to an ophthalmic antibiotic ointment and cleared by mission day 32. On mission day 33, the Commander reported the beginning of a boil under his right arm. Instructions from the ground to the Commander were to avoid using stick-type deodorant, and the wearing of garments which fitted tightly under the arms. No medications were recommended and the condition cleared in about 48 hours. A recurrence of the boil in approximately the same area on mission day 50 again lasted only 48 hours, and did not require any medication.

The crew maintained high levels of daily exercise during the mission. Extravehicular activities were successfully completed on mission days 10, 28, and 57 without medical problems.

The crew slept 6 hours on the night prior to entry and were awake approximately 15 hours prior to splashdown on mission day 60. The Scientist Pilot took an antimotion sickness capsule approximately 40 minutes prior to the entry burn, while the Commander and Pilot took their antimotion sickness medication approximately 5 to 10 minutes after the burn. Prior to the burn, all three crewmen inflated their orthostatic counter measure garments. The entry was nominal. At about 20 to 30 minutes after splashdown while still in the Command Module, the Scientist Pilot checked the pulse rate of each crewman and obtained the following values: Commander, 88; Scientist Pilot, 70; and Pilot 62 beats per minute. Pulse checks by the Crew Surgeon immediately after the Command Module was aboard the recovery ship were similar. Blood pressures were within acceptable ranges for these crewmen. All three crewmen egressed the Command Module on their own power.

Postflight the cardiovascular deconditioning observed was carefully documented, but no clinically serious events occurred. As in Skylab 2, vertigo, postural instability, hyperreflexia, dry skin, and slight fissuring of the hands were noted. On recovery, a previous back strain suffered by the Commander recurred from a situation combining "lifting" and loss of balance. On recovery day the Commander developed presyncope during the stand test. The Pilot had a vagal response, also associated with presyncope, during the recovery phase of the Metabolic Activity experiment M171 . The overall rate of recovery postflight was more rapid than that observed in the first manned Skylab mission.

Skylab 4 In Skylab 4, the Flight Crew Health Stabilization Program lasted 27 days due to a 6 - day slip in the launch for evaluating and correcting potential launch vehicle problems. The crew underwent preflight evaluations, which were augmented by several new experiments, such as echocardiography and pulmonary function evaluation. Several items noted in the medical history and clinical examinations and requiring attention for the upcoming flight were: a history of low back pain (lumbo-sacral strain) experienced by the Commander in the preflight period, and the concern as to whether there would be recurrence of this pain on his return to Earth; some recurring variable left ear drum injection and lability of blood pressure noted during the preflight period in the Scientist Pilot; and the history of recurrent

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ISOPTWPO TODAY nasal congestion and a tendency toward lability of blood pressure in the Pilot. Cardiovascular review of these men showed no evidence of nor tendencies toward arrhythmias. These findings were well documented in order to permit evaluation of any in-flight changes. The crew remained in good health throughout the preflight period.

This crew also had no formal scheduled in - flight medical examinations. Data from experiments and "as necessary" medical evaluations continued to provide the necessary information for monitoring of health status. A heart rate and blood pressure stress evaluation for clinical reasons would be obtained on any individual at least every 4 days, if for some reason the experiments Lower Body Negative Pressure experiment M092, Vectorcardiogram experiment M093 , and Metabolic Activity experiment M171 could not be run. This longest mission happily was characterized by the absence of any major illness or injury. However, it is important to point out that in this mission there were numerous symptomatic events that required variable amounts of medication .

For all Skylab 4 crewmen, the initial medication was the prescribed antimotion sickness drugs; the Scientist Pilot did not experience motion sickness and the Commander had minimal malaise for 3 days. The Pilot had significant nausea with vomiting for 1 day and then malaise for 2 more days. The second major recurrent use of medication was lip balm and skin cream to prevent drying of the lips and skin, respectively. The sleep medications were utilized intermittently throughout the mission by all the crewmen. Decongestants (topical and systemic) were used during the mission. These were used both prophylactically during the extravehicular activities and for specific symptomatic relief of the feeling of fullness in the head, nose, and ears.

The Scientist Pilot utilized aspirin twice for transient headaches on mission days 17 and 67. On mission days 75 through 79, he utilized wet packs to help resolve a minimal papular rash on the left neck and ear area. The Pilot had a rash in the upper mid-back area, which was treated as a fungal infection, and which did resolve after about a week and a half.

The observed in-flight problems were not related to preflight problems except remotely; one could state that the Pilot’s prior history might have indicated the greater susceptibility to upper respiratory congestion.

In following the crew, the Daily Health Status Summary sheet was a comprehensive guide. It was updated for this particular mission and was kept by the person in aeromedical monitoring position working in direct support of the Mission Operation Control Room Surgeon. Data for this summary were prepared from the Evening Status Report which gave sleep, medication, exercise, and experiments M071 (Mineral Balance, ch. 18), M073 (Bioassay of Body Fluids, ch. 23), and M172 (Body Mass Measurement, ch. 19) data, from the dump tapes, and from the private medical conference. The latter permitted subjective and objective crew observations about their responses to the stressor tests [Lower Body Negative Pressure and Metabolic Activity ] as well as the general status of living in zero-g.

Vectorcardiographic data became especially valuable as the Pilot began demonstrating vectorcardiographic parameters differing significantly from preflight. None of these deviations from preflight "norms" were considered clinically abnormal. In summary, there were neither clinically significant cardiac arrhythmias nor vectorcardiographic changes in-flight.

Instrumental in maintaining crew health was maintenance of a proper environment. It should be stressed, there were no significant problems in maintaining the limits of environmental conditions of total pressurre, oxygen, and carbon dioxide. Other parameters, such as temperature and relative humidity, were more variable. These parameters were influenced by the orbital inclination and Sun angle of the Skylab complex and the performance of the supplementary thermal protection devices; additionally, potential off-gassing from the heated spacecraft was satisfactorily circumvented.

Personal cleanliness was fairly well maintained by use of the shower or by sponge baths but proved to be time consuming.

The increased quantity and quality of exercise available to the crew were important in maintaining the crew health of Skylab 4. For each successive mission the exercise time had been increased from one-half hour, to 1 hour, to 1 and one-half hours per day, respectively. In Skylab 4 the bicycle ergometer, the Mark I (an isokinetic force generating pulley), the Mark II (springs), and Mark III (the standard Apollo exercise device), the treadmill, and isometric exercises were available to counteract the effect of the zero-g environment; the crew had the highest overall average of quantifiable work output from their exercise.

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The maintenance of nutrition was satisfactory; the Skylab 4 crew ate at essentially preflight caloric levels and were quite satisfied with the taste of the food. The high density food bars, utilized to extend provisions when the Skylab 4 mission was extended to 84 days, were tolerated well by the crew although they left a subjective sense of hunger. As in Skylab 3, vitamin supplementation was maintained. The weight losses for the Skylab 4 crewmen were less than those for the crewmen of the other two missions.

The work/rest cycle was a key problem in this last mission. During the early phase of this mission the crew was scheduled at a pace comparable to the pace attained by Skylab 3 crewmen in the latter part of their mission. New experiments, stowage confusion, onboard equipment malfunctions, and the sheer length of the mission were all contributing factors to produce psychological stresses which were slowly resolved over the first half of the mission. As the end of the mission approached, two late single-block shifts of sleep time were made, as the preferred mode, to adjust the crew to the circadian shift required. Crew comments postflight indicated this was a suitable and effective approach to the time shift required. Earlier piecemeal shifting in Skylab 2 and Skylab 3 was not subjectively as effective.

In preparation for entry, scopolamine/dextro-amphetamine sulfate was prescribed for all three crewmen at approximately 2 hours prior to intended splashdown. The crew inflated their counter measure garments prior to burn and reinflated them to compensate for the increasing internal pressure as the Command Module was pressurized during descent.

As in Skylab 3, the splashdown was initially in stable-2 (heat shield up), and changed to stable-1 (heat shield down) within a nominal time frame.Initial "on water" pulse rates were: Commander, 70; Scientist Pilot, 80; and Pilot, 80 beats per minute. Blood pressure and pulse readings taken inside the spacecraft were acceptable and the crew egressed and walked essentially unassisted.

The triad of vertigo, postural instability and reflex hyperactivity was again noted postflight. This time it was the Commander who experienced a vagal response with presyncope at the end of forced expiration in pulmonary function testing. Petechiae were noted in the lower legs of all three crewmembers late on recovery day, and during the day afterwards. Muscle and joint soreness during exercise developed postflight, but only to a minimal degree. The postflight period was free of any illnesses or injuries. Postflight physiological readaptation, as measured by the experiments revealed the crew to be in as good or better status than the crews of the two earlier missions.

In addition, an isolated incident of a non-sustained 14-beat ventricular tachycardia (Figure 2), with a maximum heart rate of 215 beats per minute, was recorded using in-flight Holter monitoring abroad the Mir.Although not part of a systematic scientific study,this case provides additional evidence of arrhythmias during long-duration space flight.

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ISOPTWPO TODAY It is unknown whether long-duration exposure to microgravity itself may precipitate cardiac arrhythmias. Based on observations and clinical judgment, medical operations personnel have suggested that some of these incidents may have been related to pre-existing, undiagnosed coronary artery disease. Additional pre-selection crew screening tests, including calcium scoring, have been added to reduce such occurrences in the future.

Reference: 1.Evidence Based Review: Risk of Cardiac Rhythm Problems during Space Flight,NASA 2.NASA SP-368 BIOMEDICAL RESULTS OF APOLLO

Characteristics of Adaptation and Maladaptation of Human Cardiovascular System under Space Flight Conditions Hemodynamics of cosmonauts was studied in relative rest and in a functional test with the lower body’s negative pressure before, during, and after space flights aboard orbital stations Salyut 7 and Mir using instruments produced in France.

Over 200 complex studies of hemodynamics of 26 cosmonauts were performed during space flights of different duration (from 8 to 438 days) in the period from 1982 to 1999 using modern methods (ultrasound echocardiography, 2D echography of visceral vessels, Doppler flowmetry, and occlusion aeroplethysmography).

During space flights, the orthostatic stability was monitored in the lower body negative pressure (LBNP) test, which to a certain extent mimics the orthostatic blood movement.The test consisted of three stages and included exposures at 25 mm Hg for 5 min, 35 mm Hg for 1 min, and 45 mm Hg for 5 min. The blood flows in the aorta, medial cerebral artery, and femoral artery were monitored ultrasono graphically. The determined parameters included the stroke volume, the volume blood flow, the MCA and FA resistance index, MCA and FA blood flow ratio, and the cerebral blood flow deficiency index, which reflects the total reduction in the blood flow through MCA for 5 min of exposure to negative pressure (45 mm Hg) compared to the blood flow through MCA recorded for 5 min at rest before the test. The capacity and compliance of leg veins was estimated by occlusion aeroplethysmography of the legs. Changes in the calf volume after application of occlusion pressure (10, 20, 30, 40, 50, and 60 mm Hg) were recorded using an air measurement cuff.

Studies of Hemodynamics at Rest According to EchoCG data, exposure to microgravity in the first three months caused individual oppositely directed changes in the stroke volume (SV) and cardiac output (CO). Further exposure in microgravity (months 4 - 6) was accompanied by a statistically significant decrease in SV and CO (p < 0.05) in all cosmonauts.

According to EchoCG data, the left ventricular end diastolic volume (EDV) decreased compared to the preflight value. Ë?6 During the first month of flight, this decrease was small (3 - 6%) but tended to increase to 8 - 10% by months 5U of flight. The high degree of correlation (r = 0.95) between the dynamics of this parameter and the total body fluid volume led us to assume that the decreased blood filling of heart chambers was due to hypovolemia, which was detected throughout the exposure in microgravity.

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ISOPTWPO TODAY In turn, the decrease in EDV was the most probable cause of a certain decrease in the SV. The left ventricular ejection fraction (LVEF; LVEF = SV/EDV) in all cases remained within the range of standard values: changes from 69 Âą 2% before flight to 64 Âą 2% during exposure to microgravity for six month and longer, from our stand point, cannot be regarded as significant. As early as on day 1 - 3 after the return to Earth, the LVEF value practically coincided with the preflight values. Ultrasonographic studies of the cardiovascular system in flights of different duration, which have been carried out for almost 20 years, have not revealed any case of reduced pumping function of the heart.

The results of ultrasonographic studies of the large arterial and venous vessels showed that microgravity significantly affects peripheral hemodynamics (both arterial and venous). Microgravity induced changes were especially pronounced in regions located below and above the heart level.

A characteristic phenomenon important for cerebral blood flow, observed in microgravity, was a significant (by 25 - 35% compared to the preflight data) dilatation of jugular veins, which was accompanied by a slowed blood flow through them (Fig. 1). This phenomenon was observed in all cosmonauts starting from the first days of flight. As the duration of exposure in microgravity increased, the cross section of jugular veins tended to further increase(on average, by 38.9 Âą 9.0% compared to the preflight data).

This was accompanied by indirect signs of a labored blood return through the jugular veins: the cosmonauts mentioned that it was difficult for them to pronounce long sentences, because the sensation of blood flow to the head was drastically enhanced in this case and signifi cantly decreased after a deep expiration.

A significant increase in the cross section of jugular veins during conversation, comparable to that observed in the Valsalva test, was detected. These data demonstrate the effect of intrathoracic pressure on the blood flow to the right heart: during conversation (i.e., during exhalation with resistance), the pressure in the thorax increases, which hampers venous return. During deep inhalation, conversely, the pressure in the thorax and in the right atrium decreases; as a result, the blood flow to the right heart (the so called suction effect) is enhanced.

At the beginning of flight (during the first week), blood redistribution was accompanied by a slight (p >0.05) increase in the resistance to the blood flow in the common carotid, internal carotid, and medial cerebral arteries. Two to three weeks later, these parameters returned to the norm. As the duration of exposure to microgravity increased, the resistance index of the medial cerebral artery tended to gradually increase in all cosmonauts; in month 5 - 6 of flight, it increased by 5 - 6% compared to the preflight value. The volume cerebral blood flow remained at the preflight level until the third month of space flight. Starting from month 5 - 6 of the space flight, a slight (by 4 - 6%) decrease in the volume blood flow through the medial cerebral artery was detected in the majority of the examined cosmonauts.

It should be noted that the changes in the arterial cerebral blood flow during space flight were several times less proHuman Spaceflight Edition c International Space Agency(ISA)

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ISOPTWPO TODAY nounced than the changes in the venous blood return through the jugular veins. Despite the signs of venous stasis, the arterial cerebral blood flow at rest during exposure in microgravity changed insignificantly.

A characteristic phenomenon observed during space flights was a significant and progressive decrease in the resistance of the renal arteries throughout the exposure in microgravity (by -5.3 Âą 2.0% at the beginning of flight and -15.4 Âą 3.1% at the end of half year flights, p < 0.01).

The correlation between the changes in the blood flow and resistance index of renal arteries and volemia was first established in experiments performed with animals and then verified in clinical studies. The comparison of the results of hemodynamic studies with the results obtained by Noskov et al., who studied the dynamics of fluids during longterm flights , showed that changes in the resistance index of renal arteries and in the total body fluid amount are strongly correlated (Table 1). The resistance of other large branches of the abdominal aorta (mesenteric artery, celiac trunk, and splenic artery) also decreased during exposure in microgravity. A simultaneous dilatation of the splenic, portal, and hepatic veins was observed .

The results of measurement of the blood flow through the abdominal veins showed that venous return is slowed down not only in the cervicocephalic region but also in the abdominal region.

The exposure in microgravity was accompanied by a decrease in the resistance to blood flow through the femoral arteries and a considerable dilatation of the great venous vessels of the legs. This phenomenon largely accounted for the development of orthostatic intolerance. The major role of venous vessels of the legs in the etiology of orthostatic intolerance was mentioned by many researchers. L.L. Shik, a well known Russian physiologist, believed that the increased compliance of the leg veins is the key factor underlying the development of orthostatic disorders and that the absence of a hydrostatic gradient causes a decrease in the intravascular venous pressure and a decrease in the turgor of tissues surrounding the leg veins.

An increase in the cross section area of the femoral veins by 20 - 50% was recorded during ultrasonographic scanning starting from week 3 of flight. In the majority of cosmonauts examines, it steadily increased during six month exposure in microgravity. This finding allowed us to assume that the decrease in the hydration of soft tissues and in the tone of the skeletal muscles of the legs, which developed during flights in space, significantly reduced the extramural pressure on the walls of veins, thereby increasing the so called vein free compliance zone (Table 2).

It was also important to determine how the capacity of venous vasculature of the legs changes in microgravity against the background of hypovolemia and blood redistribution to the upper body. Such studies were performed using occlusion aeroplethysmography, which allows the exact parameters of venous filling and return, including the so called "leg venous network capacity," to be determined. This parameter makes it possible to estimate, which blood volume can be redistributed to leg veins in the orthostatic test, or the under exposure of the lower body to negative pressure (to 50 mm Hg.) (the LBNP test).

It was discovered that, during space flights, the leg venous network capacity significantly increased as early as in the first week of flight. During the first month of exposure in microgravity, these changes increased, reached a maximum in the second or third months of flight, and remained stably increased throughout the period of exposure in Human Spaceflight Edition c International Space Agency(ISA)

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ISOPTWPO TODAY microgravity (Table 2).

In some cosmonauts, the capacity of the legsâ&#x20AC;&#x2122; venous network continued to increase until the end of flight. In microgravity, 100% of the studies using occlusion plethysmography showed that an increase in the calf volume (i.e., blood stagnation) was observed at a lower occlusion pressure than on the Earth (10 mm Hg), which has never been detected in the Earthâ&#x20AC;&#x2122;s gravity both before and after flight. This fact indirectly confirms the assumption that exposure in microgravity causes (1) a decrease in the intravascular pressure in the distal leg veins and (2) an increase in the vein free compliance zone of the legs.

The fact that this effect was recorded beginning from the very early studies in flight (on day 5) and completely disappeared on the first day after the end of the flight,allowed us to postulate that it is based mostly on a rapid hemodynamic process, namely, blood redistribution.

Thus, hemodynamic changes (slowed venous return, decreased resistance of the lower body vasculature, and increased leg venous network capacity) were detected in cosmonauts at rest. Each of these changes might facilitate the development of orthostatic intolerance.

Study, Estimation, and Prediction of Orthostatic Tolerance during Space Flights (According to LBNP Tests) The functional test with lower body negative pressure (LBNP) makes it possible to control changes in the orthostatic tolerance during flight. Studies performed under Earth conditions showed that, under LBNP exposure, similarly to the orthostatic effect, part of the blood is displaced to the leg vessels and is temporarily withdrawn from circulation, thereby reducing the circulating blood volume. The term "orthostatic tolerance" means that the human body successfully copes with such a decrease in the circulating blood and that it can maintain blood pressure and ensure a normal blood supply of the vitally important organs (first of all, the brain).

To perform ultrasonographic studies of the hemodynamic response to LBNP exposure, special sensors and systems for their fixation were designed, which made it possible to maintain constant position of sensors on the body and continuously record Doppler signals from the blood flow through the cerebral and femoral arteries throughout the test.

Studies in terrestrial experiments with antiorthostatic hypokinesia, which partially mimics the microgravity effects, allowed us to establish that the physiological response to LBNP is manifested in an increase in the resistance of the femoral arteries, which limits the blood flow in the leg vessels and hampers the cerebral blood supply . At the same time, changes in the vascular tone in other regions ensure the CO redistribution so that the relative proportion of cerebral blood flow in CO increases. In other words, the changes in peripheral hemodynamics are aimed at maintaining the cerebral blood supply. The ultrasonographic study of the hemodynamic response to LBNP made it possible to determine the parameters that allow orthostatic tolerance to be estimated and predicted the resistance index of femoral arteries, blood flow redistribution (the proportion of blood flow through the cerebral and femoral arteries), and the cerebral blood flow deficiency index. The latter makes it possible to assess the decrease in the volume blood flow through the middle cerebral artery for 5 min of LBNP or the orthostatic effect compared to the same parameter measured for 5 min at rest before the test.

Note that the changes in HR and BP determined in LBNP tests during space flights were often close to the preflight data; i.e., no decrease in the orthostatic tolerance was observed. At the same time, the dynamics of the above listed ultrasonic parameters indicated that the hemodynamic response deviated from the normal profile.

At the initial period of longterm space flights (up to approximately day 50), the HR and BP dynamics in the LBNP test almost did not differ from the preflight profile. However, the vasoconstrictor response of the femoral arteries under exposure to negative pressure decreased.

The cerebral blood changes insignificantly; i.e., at this stage of space flights, the ability for the redistribution of blood flow, with preferential blood supply to the brain was retained. As the duration of exposure in microgravity increased, the ability of the femoral arteries to respond to LBNP with increased resistance continued to worsen, which resulted in a gradual increase in the deficiency of the cerebral blood flow in the test (Fig. 2); i.e., the decrease in the LBNP tolerance was becoming more pronounced. Importantly, no tendency in the changes in the hemodynamic response to LBNP during space flights to stabilize has been revealed: the orthostatic tolerance decreased more or less rapidly throughout the exposure in microgravity. Multiyear data show that, after space flights of equal duration, the decrease in the orthostatic tolerance may significantly vary in different individuals, because the degree of orthostatic

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ISOPTWPO TODAY tolerance significantly differs in different subjects.

During long term flights, the most noticeable changes were detected in the cerebral blood flow deficiency index in different cosmonauts subjected to LBNP tests. In some cosmonauts, this parameter fluctuated insignificantly from test to test; in others, changes markedly increased with an increase in the flight’s duration.

The comparison of the results of studies performed during flights with the preflight data revealed the following consistent patterns:

• If the cerebral blood flow deficiency in the preflight LBNP tests was insignificant (on average, 3.85 ± 0.88%), its increase during flight was also insignificant (from 4.6 ± 2.88 to 7.54 ± 1.95%; on average, 8%).

• If the cerebral blood flow deficiency in the preflight LBNP tests varied from 8 to 15% (on average, 12.09 ± 2.97%), this parameter measured in flight gradually increased from test to test and accounted for 21.78 ± 5.8% at the end of six month flights.

Thus, the better the orthostatic tolerance was before flight, the smaller the effect that was exerted on it by the exposure in microgravity.

The results of these studies showed that the decrease in the orthostatic tolerance of cosmonauts observed during exposure in microgravity is determined by a decrease in the vasoconstrictor capacity of the main arteries and an increase in the compliance and capacity of the legs’ veins, a deterioration of the regulation of blood flow, a decrease in hydration and volemia, and the initial individual preflight orthostatic tolerance of subjects Earth Reentry Stage The G load causes significant changes in the cardiovascular system. Exposure to the G load during descent reveals the reserves and weak points of the body, first of all, in the cardiovascular system . G load causes marked disturbances in the heart’s rhythm , deterioration of vision (and even occurrence of blackouts), and other undesirable phenomena.

After the landing of the spacecraft, all cosmonauts show signs of orthostatic instability of different degree (asthenia, paleness in the face, giddiness, hyperhydrosis, and a precollaptoid state at attempts to independently leave the spacecraft and to take vertical position).

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ISOPTWPO TODAY Hemodynamic State after the End of Space Flight The results of studies performed in the postflight period using active and passive orthostatic tests demonstrated a decrease in orthostatic tolerance in all cosmonauts. The expression of orthostatic intolerance was more pronounced after longterm flights (Table 3).

These data completely agree with the results of ultrasonographic studies of the hemodynamic response to LBNP during space flights. It was established that the degree of the decrease in the orthostatic tolerance and in the tolerance to LBNP during flights was correlated with their initial preflight level.

Reference: 1."A. R. Kotovskaya and G. A. Fomina",Characteristics of Adaptation and Maladaptation of Human Cardiovascular System under Space Flight Conditions

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ISOPTWPO The ISOPTWPO is International Space Flight & Operations - Personnel Recruitment, Training, Welfare, Protocol Programs Office (International Space Academy). It is a division of the ISA organization.

Mr. Martin Cabaniss is director and Mr. Abhishek Kumar Sinha is Assistant Director of ISOPTWPO. Ad Astra ! To The Stars! In Peace For All Mankind !

Mr. Rick R. Dobson, Jr.(Veteran U.S Navy) â&#x20AC;&#x201D; International Space Agency (ISA)

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