STEM Today by Abhishek Sinha

STEM TODAY January 2018, No. 28

CONTENTS Cardiovascular issues during reÂentry into Earth's atmosphere

The most profound Cardiovascular deconditioning occur during and after gravitational transitions. There is a possibility that crew will experience impaired control of the spacecraft during landing along with impaired ability to immediately egress following a landing on a planetary surface (Earth or other) after long-duration space flight.

Editorial Editor: Mr. Abhishek Kumar Sinha Editor / Technical Advisor: Mr. Martin Cabaniss

STEM Today, January 2018, No.28

Disclaimer ( Non-Commercial Research and Educational Use ) STEM Today is dedicated to STEM Education and Human Spaceflight. This newsletter is designed for Teachers and Students with interests in Human Spaceflight and learning about NASAâ&#x20AC;&#x2122;s Human Research Roadmap. The opinion expressed in this newsletter is the opinion based on fact or knowledge gathered from various research articles. The results or information included in this newsletter are from various research articles and appropriate credits are added. The citation of articles is included in Reference Section. The newsletter is not sold for a profit or included in another media or publication that is sold for a profit. Cover Page Astronaut Bruce McCandless on First-ever Untethered Spacewalk Astronaut Bruce McCandless, II, mission specialist, uses his hands to control his movement in space while using the nitrogen propelled manned maneuvering unit (MMU). He is participating in a extravehicular activity (EVA), a few meters away from the cabin of the shuttle Challenger. McCandless is centered in a background of clouds and earth in this view of his EVA. He is floating without tethers attaching him to the shuttle. Image Credit: NASA

Back Cover NASA Celebrates 50 Years of Spacewalking In this Feb. 7, 1984 photograph taken by his fellow crewmembers aboard the Earth-orbiting Space Shuttle Challenger on the STS-41B mission, NASA astronaut Bruce McCandless II approaches his maximum distance from the vehicle. McCandless became the first astronaut to maneuver about in space untethered, during this first "field" tryout of a nitrogen-propelled, hand-controlled backpack device called the Manned Maneuvering Unit (MMU). Image Credit: NASA

STEM Today , January 2018

Editorial Dear Reader

STEM Today, January 2018, No.28

All young people should be prepared to think deeply and to think well so that they have the chance to become the innovators, educators, researchers, and leaders who can solve the most pressing challenges facing our world, both today and tomorrow. But, right now, not enough of our youth have access to quality STEM learning opportunities and too few students see these disciplines as springboards for their careers. According to Marillyn Hewson, "Our children - the elementary, middle and high school students of today - make up a generation that will change our universe forever. This is the generation that will walk on Mars, explore deep space and unlock mysteries that we can’t yet imagine". "They won’t get there alone. It is our job to prepare, inspire and equip them to build the future." STEM Today will inspire and educate people about Spaceflight and effects of Spaceflight on Astronauts. Editor Mr. Abhishek Kumar Sinha

Editorial Dear Reader The Science, Technology, Engineering and Math (STEM) program is designed to inspire the next generation of innovators, explorers, inventors and pioneers to pursue STEM careers. According to former President Barack Obama, " Science is more than a school subject, or the periodic table, or the properties of waves. It is an approach to the world, a critical way to understand and explore and engage with the world, and then have the capacity to change that world..." STEM Today addresses the inadequate number of teachers skilled to educate in Human Spaceflight. It will prepare , inspire and educate teachers about Spaceflight. STEM Today will focus on NASA’S Human Research Roadmap. It will research on long duration spaceflight and put together latest research in Human Spaceflight in its monthly newsletter. Editor / Technical Advisor Mr. Martin Cabaniss

STEM Today, January 2018, No.28

Human Health Countermeasures (HHC) Cardiovascular issues during re-entry into Earth's atmosphere

Main Medical results of extended flights on space station MIR in 1986-1990

During 1986-1990, seven prime crews (PC) carried out missions on the Mir space station and an 8th prime crew has started its space work which will be finished in 1991. A total of 18 cosmonauts (including the 8th prime crew) have participated in extended missions on the Mir space station, one cosmonaut being launched twice. The most regular inflight changes have occurred in the latter part of electrocardiographic tracings (12 standard leads). These demonstrate a decrease of T-wave amplitude in most leads in all cosmonauts. Analysis of hemodynamic parameters has shown a tendency for an increase in mean heart rates (HR) and a lack of change in stroke volume (SV), cardiac output (CO) and actual specific peripheral resistance (SPRa). Ultrasonic examinations of the physician cosmonaut made during months 7-8 inflight did not reveal changes in left ventricular volumes, SV or ejection fraction (EF).

STEM Today, January 2018, No.28

Arterial pressure (AP) measurements showed that diastolic pressure (DBP) had a tendency to decrease(P < 0.18) and pulse pressure (PP) to increase (P < 0.07). Abdominal ultrasonic examinations carried out by V. S. Bednenko et al. both inflight (7 cosmonauts examinedâ&#x20AC;&#x201C;4 at the end of 5-6 months, 3 at the end of 8-9 months) and postflight (16 cosmonauts) demonstrated: a moderate increase in the size of the liver, spleen, kidneys, pancreas, blood filling of the lungs, cross-sectional area of the large ventral vessels, and a clearer vascular pattern of liver; decreased acoustic density of the pancreas; signs of lateral renal pelvic enlargement with a decrease in renal parenchyma (decreased parenchymal-pelvic system area ratios). These changes are considered to be echographic signs of venous engorgement. An increased gall bladder area and dilatation of the common bile duct also point to the development of bile congestion in the biliary tree. In contrast to the preflight period graded physical exercise tests on a bicycle ergometer during flight (at a work load of 125 W and 175 W for 5 and 3min, respectively with a l min interval) resulted in insignificant rises of HR, a decrease of SV and CO (by 14.5 and 15.1%) decline in D BP by 6.8% and a PP increase of 13.5% (P < 0.01). These reactions point to the nature of adaptive inflight processes uncovered by exposure to graded exercise when findings are compared to the preflight period.

Important Result

Postflight hemodynamic studies during graded step-wise exercise conducted by A. F. Zhernakov et al. demonstrated a more distinct increase in absolute values of HR, systolic AP and diastolic AP (in most cases); and smaller increment of SV and shortening of the left ventricular ejection period vs its corrected value for changes in HR. No HR and ECG changes of an ischemic type were found. Severity of hemodynamic changes did not depend on flight duration. When compared to pretest hemodynamic parameters, lower body negative pressure (LBNP) tests (at -25, -35, and -45mmHg for 1, 3, and 5 min respectively) applied in flight led to decreases of SV (5.2%) and CO (8%) as well as an increase in SPRa (15.7%). Blood pressure did not change significantly. Inflight relative and absolute increases in SPRa were considered to be reactions to prevent pronounced changes in SV, CO and BP. It should be noted that cardiovascular responses to postflight postural tests had no correlation with flight duration.

Results of ultrasonographic studies of the heart and arterial and venous peripheral vessels in different parts of human body

Hemodynamics of cosmonauts was studied by A. R. Kotovskaya and G. A. Fomina in relative rest and in a functional test with the lower bodyâ&#x20AC;&#x2122;s negative pressure before, during, and after space flights aboard orbital

Page 4

stations Salyut 7 and Mir. 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). The method of studies was approved by the Biological Ethics Committee of the Institute for Biomedical Problems, Russian Academy of Sciences. All cosmonauts participating in the studies were familiarized with the method and signed informed consent forms. RESULTS Studies of Hemodynamics at Rest Changes in the conventional parameters of general hemodynamics-heart rate (HR) and blood pressure (BP)during space flight was mostly insignificant. 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.

STEM Today, January 2018, No.28

According to EchoCG data, the left ventricular end-diastolic volume (EDV) decreased compared to the preflight value. During the first month of flight, this decrease was small (3-6%) but tended to increase to 8-10% by months 5-6 of flight. The high degree of correlation (r = 0.95) between the dynamics of this parameter and the total body fluid volume led authors to assume that the decreased blood filling of heart chambers was due to hypovolemia, which was detected throughout the exposure in microgravity(Table 1).

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 standpoint, 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. Similar data demonstrating a decrease in SV and LVEF in American astronauts at the end of long-term (up to 144 days) space flights were obtained by Martin et al. However, from the standpoint of these authors, these data testified to a decrease in the contractile ability of the myocardium during long-term flights, despite the fact that both parameters rapidly recovered within the first days after return to the Earth. Authors assumed that the tendency of SV to decrease with a slight decrease in EF should be regarded as a manifestation of the hypokinetic syndrome under hypovolemic conditions. The physical ability to perform a large amount of physical activity and numerous operations associated with intensive physical activity (e.g., several spacewalks during one flight) can be regarded as evidence that, during long-term flights, the pumping function of the heart remains at a good level. 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. Under the Earthâ&#x20AC;&#x2122;s gravity, the high tone of the arterial vessels of the lower body and the low resistance in cerebral, pulmonary, and renal vessels ensure normal blood supply of vitally important organs.

Page 5

In microgravity, blood is redistributed from the region with high vascular resistance to low-resistance zones, which initiates all subsequent changes in the cardiovascular system, including the changes in the vascular tone. Among the regions of the cardiovascular system located above the heart, the cervicocephalic hemodynamics (blood circulation in the head and neck region) is of the most interest. The resistance and the blood flow of common carotid arteries, and the blood filling and blood flow parameters of the jugular veins were researched. The intracephalic blood flow was estimated by the results of study of the medial cephalic artery (a component of the arterial circle of Willis).

STEM Today, January 2018, No.28

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 significantly 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. Authors assumed that this tendency should be regarded as a sign of venous stasis developing in the cervicocephalic region. It should be noted that the changes in the arterial cerebral blood flow during space flight were several times less pronounced 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 long-term 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

Page 6

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. The role of extramural pressure created by the muscles and perivascular tissues surrounding the veins in the increase in the venous capacity was also mentioned by other authors.

STEM Today, January 2018, No.28

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 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).

Page 7

STEM Today, January 2018, No.28

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 long-term 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 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: (1) If the cerebral blood flow deficiency in the pre-flight 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%); (2) If the cerebral blood flow deficiency in the pre-flight 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

Page 8

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 legsâ&#x20AC;&#x2122; veins, a deterioration of the regulation of blood flow, a decrease in hydration and volemia, and the initial individual pre-flight orthostatic tolerance of subjects.

STEM Today, January 2018, No.28

Earth Reentry Stage It was shown earlier that long-term exposure in microgravity causes hemodynamic changes leading to deconditioning of the cardiovascular system and a decrease in the functional reserves of the body. This is of principal importance during the reentry of cosmonauts to the Earth. The final stage of flight, the reentry to the Earth, is one of the most difficult stages of flight, emotionally saturated and accompanied by stress. 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 heartâ&#x20AC;&#x2122;s rhythm (Fig. 3), 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).

Page 9

Hemodynamic State after the End of Space Flight The results of studies performed in the post-flight 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 long-term 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.

STEM Today, January 2018, No.28

Autonomic regulation of circulation and cardiac contractility in the space flight of physician cosmonaut V.V. Polyakov.

Autonomic regulation of circulation and cardiac contractility in V.V. Polyakov during his 438-day space flight (> 14 months) were evaluated in three experiments entitled Pulstrans, Night, and Hotter by R.M. Baevsky, M. Moser, G.A. Nikulina, V.V. Polyakov, Funtova. and A.G. Chernikova. The findings were published in paper titled "Autonomic regulation of circulation and cardiac contractility during a 14-month space flight" in 1998.

Page 10

STEM Today, January 2018, No.28

Heart-rate variability and cardiac contractility in the Pulstrans Experiment Figures 3 and 4 show temporal variations of the basic cardiologic parameters measured in the Pulstrans experiment in the course of the 14-month space flight. As can be seen in Fig. 3A, systolic and diastolic pressures

Page 11

during the flight were lower by 10-15 mm Hg than before it. The decreases were most marked on days 147-189 and 257 of the flight. The heart rate rose somewhat at first but reached the preflight level on days 200 and 340 of flight. The heart rate was at its maximum on day 250 of flight when it exceeded the preflight level by 10 beats/min. The SCG amplitude had increased by day 55 of flight, was markedly increased on day 250-257 (Table l), and was highest near the end of the flight, on days 340 and 410.

Important Result

STEM Today, January 2018, No.28

The drastic increase of the SCG amplitude in the first few days after landing when it exceeded about 10-fold the preflight level. The BCG amplitude showed less marked increases and had three maxima - on days 189 ,257 and 410 of flight. Of much interest seems to be the considerable (nearly 1.5-fold) increase in the SCG/BCG ratio at the end of flight , although a much larger (nearly 20-fold) increase in this ratio was noted in the first few days after landing.

Heart-rate variability values (Table 1 and Fig. 3B, 3C) demonstrated phasic changes. The SD showed a tendency toward a reduction during the first 6 months, a marked increase in the next two months of flight (days 220-257) and a reduction near the end of straying for 14-months in weightlessness. Worthy of note are also big changes in the ratio of spectral components (PNS and SNS) of the heart rate variability during months 7 and 8 of the flight. The power of respiratory waves fell sharply (indicating reduced activity of the parasympathetic component of regulation), whereas the power of LF waves with periods of 20-50 seconds showed a similarly large increase (indicating heightened activity of the sympathetic component). The power of MF spectral component showed a decrease during first 5 months of flight with minima at day 147, but it increase till preflight level at days 250-257 and than fall sharply, especialy in postflight period. The relative power of MF had other dynamics (Fig.3B). It minima is observed at days 250-257. Diurnal variations in heart-rate variability values The data on alterations in mean 24-h values of heart rate variability parameters are indicative of at least two important features of circulation regulation during the 14-month flight (fig.4): 1. The heart rate significantly decreased in the course of the flight, whereas the SD (standard deviation) increased; 2. The absolute power of the heart-rateâ&#x20AC;&#x2122;s variability high frequency (HF) component decreased, whereas that of its MF component increased.

Mean 24-h values of the heart rate and SD were closest to their background (terrestrial) values on day 165 of flight, but spectral components differed considerably from their background values during that period. Of interest is separate consideration of mean diurnal and nocturnal data. Of particular interest in this respect is the graphic representation of "morning-evening-night" relationships in the form of a so-called phase plane (Fig.5). Here, heart rate values are plotted on one axis while values of the absolute power of MF component are plotted on the other. It can be seen that the "regulation area" (i.e. the area of the triangles formed by the "morning-evening" and "evening-night" vectors) during the preflight period is approximately the same as on day 165 of flight. The "regulation area" is greatly reduced and is characterized by a considerable elongation of the "evening-night" vector early during the flight (day 12) and at its end (day 391). Moreover, the direction of the "morning-evening" vector changed by the end of flight. These data show that the circadian organization of the regulation of circulation changes in the course of a prolonged flight, which may be due to the inclusion of the hypothalamic-pituitary level in regulation processes. Ultradian rhythms during the 14-month flight The relevant data obtained during Polyakovâ&#x20AC;&#x2122;s 14month flight are presented in Fig. 6. It is the dynamics of factor K. Fig. 6 compares the mean values of factor K obtained in the Night experiments of V.V. Polyakov and of the four cosmonauts who were on a 6-month flight. It can be seem that factor K increased during the first 3 months

Page 12

STEM Today, January 2018, No.28

of flight in all five cosmonauts, and that its values in the 6th-7th months of flight were close in all of them to those recorded preflight. A second increase in this factor was observed for V.V. Polyakov in the 8th-10th months of flight.

Page 13

Page 14

STEM Today, January 2018, No.28

Particular attention was paid to analyzing waves in the hour range. The presence of distinct 90-minute cycles and their clearly defined structures reflect sleep of good quality. The 90-minute periodicities were evaluated by

Page 15

STEM Today, January 2018, No.28

cross-spectral analysis. The baseline data used were the means of heart rate, respiratory rate, motor activity, BCG amplitude, and heart rate/respiratory rate ratio. The periodicities of each parameter pair that correlated better than others are shown in Table 2. The basic crosspectral period increased in the 2nd-3th months of flight and then returned to a normal value of 102 minutes in the 5th-6th months before showing a second increase to 227-240 minutes in the 9th-10th months.

Important Result

In the first 6 months of the 14 month flight, the dynamics of cardiovascular parameters in V.V.Polyakov was virtually the same as in the other cosmonauts. Thereafter, however, the following differences were noted for Polyakov: • A tendency of the heart rate to decrease, particularly in night time, to values below those recorded early during the flight; • Alterations in the amplitude and duration of super slow oscillations of physiologic parameters in the 7th8th months, with a fall in the total power of the oscillations and a rise of their relative power in the interval of 3.5-35 minutes; • The tendency of SCG and BCG amplitudes to substantially increase, particularly in the 8th-9th and 14th months of flight; • Considerable rise in daily average values of the absolute power of the heart rate’s variability MF component accompanied by a fall in its HF component.

The three important aspects after the first 6 months of Polyakov’s sojourn in space:

Page 16

• Activation of a new, additional adaptive mechanism in the 8th-9th months of flight, as is evidenced by alterations in the periodicity and power of superslow wave oscillations (ultradian rhythms) reflecting the activity of the subcortical cardiovascular centers and of the higher levels of autonomic regulation; • Growth of cardiac contractility (both the SCG and BCG) accompanied by a decrease in heart rate during the last few months of flight; and • A considerable increase in the daily average values of absolute power of heart rate’s variability MF component, which reflects the activity of the vasomotor center.

STEM Today, January 2018, No.28

The above-mentioned increases, toward the end of the flight, of vasomotor wave amplitudes in the MF range well agree with the growth of cardiac contractility (SCG and BCG amplitude). If an increase in vascular tone in the upper part of the body does not result in elevated arterial pressure but occurs when the arterial pressure is somewhat lowered, this may be interpreted as a consequence of augmented filling with blood of the vascular bed because of an increase either in the stroke volume or in the volume blood flow rate. Since the circulating blood volume is known to be reduced and the stroke volume not to increase during a prolonged space slight, the only way in which the volume blood flow rate can be increased may be a rise in the rate of blood ejection into large vessels, which will require additional energy expenditure. That such a compensatory mechanism operates is suggested by the increased amplitudes of seismo and ballistocardiograms in the second half of the 14-month flight. On the other hand, authors can see the activation of the vasomotor center which is responsible for maintaining adequate vascular tone. This appears to be a second mechanism by which arterial pressure is sustained. This mechanism is associated with elevated activity of subcortical sympathetic centers which appear to be in turn activated by higher levels of regulation. V.V. Polyakov returned to Earth aboard Soyuz TM-20 on March 22, 1995. Upon landing, V.V. Polyakov opted not to be carried the few feet between the Soyuz capsule and a nearby lawn chair, instead walking the short distance. V.V. Polyakov wore two anti-g suits (KARKAS-3 and CENTAUR). +Gz loads in the course of descent from orbit instigated a syndrome characteristic of return to Earth from prolonged microgravity, i.e. a sensation of fierce pressure on the body, difficult breathing and speech, sine tachycardia, tachypnea, singular arrhythmias, petechial hemorrhage in the back integument, and vestibular/autonomous reactions. However, no evidence of any unusual physiological reactions that had never been seen in the other cosmonauts donned in the anti-g suits on earlier and less extended (from 65- to 366-day) missions were found. Extra systoles were registered on the phase of return to Earth after the 438-day but not previous 241-day mission of the space physician; they were probably associated with aging as he made his maiden flight at 47, and the second, at 53. The results speak in favor of the countermeasures against the adverse effects of microgravity applied during the mission, and the anti-g suits worn on the stage of return to Earth. Tolerance of +Gz-loads during descent was analyzed based on the data about 4 female cosmonauts in 5 space flights. The space flights were conventionally divided into short- (8-16 days) and long-term (169 days). In two space flights (16 and 169-d long), tubeless anti-g suit Centaur was warn during descent. In these space flights, g-tolerance of females was quite satisfactory advocating for the possibility for women to fly to space without any constraints. When the anti-g suit was not used, female physiological systems were stressed heavier than male. The spacesuit smoothed away this difference.

Page 17

References Arbeille Ph, Fomina G, Pottier J, Porcher M, Coulon J, Kotovskaya A, Poliakov V. Heart, and peripheral arteries and veins during the 14 month MIR space flight. J Gravit Physiol. 1996 Sep;3(2):93-4. PubMed PMID: 11540298.

Arbeille Ph, Fomina G, Pottier J, Porcher M, Coulon J, Kotovskaya A, Poliakov V. Hemodynamic response to LBNP during the 14 month MIR spaceflight (94-95). J Gravit Physiol. 1996 Sep;3(2):95-6. PubMed PMID: 11540299.

Fomina GA, Kotovskaia AR. [Shifts in human venous hemodynamics in long-term space flight]. Aviakosm Ekolog Med. 2005 Jul-Aug;39(4):25-30. Russian. PubMed PMID: 16353623.

Grigoriev AI, Bugrov SA, Bogomolov VV, Egorov AD, Polyakov VV, Tarasov IK, Shulzhenko EB. Main medical results of extended flights on space station Mir in 1986-1990. Acta Astronaut. 1993 Aug;29(8):581-5. Review. PubMed PMID: 11541636.

STEM Today, January 2018, No.28

Baevsky RM, Moser M, Nikulina GA, Polyakov VV, Funtova II, Chernikova AG. Autonomic regulation of circulation and cardiac contractility during a 14-month space flight. Acta Astronaut. 1998 Jan-Apr;42(18):159-73. PubMed PMID: 11541600.

Kotovskaia AR, Vil’-Vil’iams IF, Elizarov SI, Yliatovskii NV, Gavrilova LN, Liamin VR. [Tolerance of +Gz loads by space physician Poliakov VV during the active phases of his 438-days space mission]. Aviakosm Ekolog Med. 1997;31(1):29-34. Russian. PubMed PMID: 9156676.

Koloteva MI, Kotovskaia AR, Vil’-Vil’iams IF, Luk’ianiuk VIu, Gavrilova LN. [G-tolerance of female cosmonauts during descent in space flights of 8 up to 169 days in duration]. Aviakosm Ekolog Med. 2001;35(6):24-30. Russian. PubMed PMID: 11915747.

Kotovskaia AR, Koloteva MI, Luk’ianiuk VIu, Zhernavkov AF, Kondratiuk LL. [Individual prediction by the analysis of preflight ECG data of cardiac function disorders in cosmonauts during standard deorbit after longterm space flights and in the period of postflight observation]. Aviakosm Ekolog Med. 2008 Jul-Aug;42(4):1420. Russian. PubMed PMID: 19140467.

Kotovskaia AR, Vil’-Vil’iams I, Gavrilova LN, Elizarov SIu, Uliatovskii NV. [Tolerance of +Gx by MIR 22 – 27 main crew in space flights]. Aviakosm Ekolog Med. 2001;35(2):45-50. Russian. PubMed PMID: 11496421.

Kotovskaia AR, Vil’-Vil’iams IF, Luk’ianiuk VIu, Kataev IuV. [+Gx-tolerance by the Cosmonauts of ISS crews 1, 6-9 and visiting crews 1-7 aboard Soyuz vehicles]. Aviakosm Ekolog Med. 2005 Sep-Oct;39(5):3-9. Russian. PubMed PMID: 16447946.

Kotovskaia AR, Vil’-Vil’iams IF, Gavrilova LN, Luk’ianiuk VIu, Iarov AS, Kriutchenko SG, Mishakova TV, Kleev VV. [Human tolerance of +Gx loads in anti-G suits during deorbiting of the "Soiuz" space vehicles]. Aviakosm Ekolog Med. 1998;32(6):30-6. Russian. PubMed PMID: 9934440.

Kotovskaia AR, Vil’-Vil’iams IF, Fomina GA. [Correlation of the cosmonauts’ physiological reactions to +Gx loads during deorbit with the hemodynamic shifts in the period of short-term microgravity]. Aviakosm Ekolog Med. 2005 Mar-Apr;39(2):9-15. Russian. PubMed PMID: 16078416.

Fomina GA, Kotovskaia AR, Zhernavkov AF, Pochuev VI. [Possibility to predict cosmonauts’ orthostatic tolerance following short-and long-term space flights]. Aviakosm Ekolog Med. 2007 Jul-Aug;41(4):20-4. Russian. PubMed PMID: 18035709.