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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Flow Redistribution Between Legs and Brain During STS 93 Re-Entry and Landing

The objective was to quantify bit by bit the arterial hemodynamic response to the successive acceleration induced fluid shifts during re-entry and landing. Method: The astronaut instrumented himself with a flat Doppler probe fixed on the skin, a blood pressure arm cuff, and 3 ECG electrodes. The ICMS (integrated cardiovascular monitoring system, 15x15x25 cu cm, battery powered) designed to monitor Blood pressure, ECG, cerebral and femoral flows was fixed below the astronaut sit in the middeck. Recordings started 5 minutes before de-orbiting (TIG) and stopped 5 min after wheels stop. Results. During re-entry blood pressure increased by 20% at TIG, and then by 25 to 30% during the highest Gz accelerations (approx 1 S g ) . The cerebral flow remained decreased by 10 to 15% below inflight value all during the Entry and landing phases. Conversely the femoral flow increased at TIG and entry ( + l0 to 20%), recovered at 0.lg, and then decreased in proportion with the Gz acceleration (-10% to -40% from 0.5g to 1.5g). The reduction in Femoral flow was associated with an opposite variation in lower limb vascular resistance. Consequently the cerebral flow/femoral flow ratio decreased at TIG and entry (-20%), and then increased according to the Gz acceleration level ( + l0 to +40% from 0.5 to 1.5g). Conclusion: During orthostatic tests (Stand LBNP tests) the cerebral to femoral flow ratio allowed to quantify the efficiency of the flow redistribution between these 2 areas and predicted orthostatic intolerance. In the present case the astronaut was found orthostatically tolerant at postflight tilt tests, but we suggest that during re-entry this parameter could predict the occurrence of syncope in severely disadapted astronauts.

Arbeille, P.↗
NASA NTRS1977

Heat Acclimation and Water-Immersion Deconditioning: Fluid Electrolyte Shifts with Tilting

One of the major problems encountered by astronauts exposed to space flight is a reduction of orthostatic tolerance on return to earth. Many studies have been performed in an attempt to define the physiologic mechanism of orthostatic intolerance and to develop some remedial treatment. Exercise training does not appear to enhance orthostatic tolerance . In contrast, heat acclimation (i.e., exercise training in the heat) has been reported to enhance orthostatic tolerance. Since plasma volume increases with both exercise training and heat acclimation, it is not clear what role fluid and electrolytes play in determining tolerance to hydrostatic pressure. The purpose of this study was to compare the effects of exercise training in a cool environment and heat acclimation on resting plasma volume (PV) and the ensuing fluid and electrolyte shifts which occur during head-up tilting before and after water immersion deconditioning.

Conertino, V. A.↗
NASA NTRS2002

Human muscle sympathetic nerve activity and plasma noradrenaline kinetics in space

Astronauts returning from space have reduced red blood cell masses, hypovolaemia and orthostatic intolerance, marked by greater cardio-acceleration during standing than before spaceflight, and in some, orthostatic hypotension and presyncope. Adaptation of the sympathetic nervous system occurring during spaceflight may be responsible for these postflight alterations. We tested the hypotheses that exposure to microgravity reduces sympathetic neural outflow and impairs sympathetic neural responses to orthostatic stress. We measured heart rate, photoplethysmographic finger arterial pressure, peroneal nerve muscle sympathetic activity and plasma noradrenaline spillover and clearance, in male astronauts before, during (flight day 12 or 13) and after the 16 day Neurolab space shuttle mission. Measurements were made during supine rest and orthostatic stress, as simulated on Earth and in space by 7 min periods of 15 and 30 mmHg lower body suction. Mean (+/- S.E.M.) heart rates before lower body suction were similar pre-flight and in flight. Heart rate responses to -30 mmHg were greater in flight (from 56 +/- 4 to 72 +/- 4 beats min(-1)) than pre-flight (from 56 +/- 4 at rest to 62 +/- 4 beats min(-1), P < 0.05). Noradrenaline spillover and clearance were increased from pre-flight levels during baseline periods and during lower body suction, both in flight (n = 3) and on post-flight days 1 or 2 (n = 5, P < 0.05). In-flight baseline sympathetic nerve activity was increased above pre-flight levels (by 10-33 %) in the same three subjects in whom noradrenaline spillover and clearance were increased. The sympathetic response to 30 mmHg lower body suction was at pre-flight levels or higher in each subject (35 pre-flight vs. 40 bursts min(-1) in flight). No astronaut experienced presyncope during lower body suction in space (or during upright tilt following the Neurolab mission). We conclude that in space, baseline sympathetic neural outflow is increased moderately and sympathetic responses to lower body suction are exaggerated. Therefore, notwithstanding hypovolaemia, astronauts respond normally to simulated orthostatic stress and are able to maintain their arterial pressures at normal levels.

STS-90 Shuttle Project↗
NASA NTRS1987

Considerations in prescribing preflight aerobic exercise for astronauts

The physiological effects of prolonged exposure to weightlessness are discussed together with the effects of aerobic exercise on human characteristics affected by weightlessness. It is noted that, although early data on orthostatic intolerance after spaceflight led to a belief that a high level of aerobic fitness for astronauts was detrimental to orthostatic tolerance on return to earth, most of the data available today do not suport this contention. Aerobic fitness was found to be beneficial to cardiovascular function and to mental performance; therefore, it may be important in performing extravehicular activities during flight.

Frey, Mary Anne Bassett↗
NASA NTRS1997

The German/Russian MIR 1997 Mission: An Overview

Session TP4 includes short reports concerning: (1) Life Science Experiments During the German-Russian Mir '97 Mission; (2) Orthostatic Intolerance Following Microgravity: A Role for Autonomic Dysfunction; (3) Heart Rate Variability and Skin Blood Flow in Man During Orthostatic Stress in Weightlessness; (4) Effects of Microgravity and Lower Body Negative Pressure on Circulatory Drives from Excercising Calf Muscles; (5) The Mir Station in Its Second Decade: Crew Science Operation During Mir '97; (6) Metabolic WARD (Water, Sodium, Calcium, and Bone Metabolism) and Endocrinological Experiments During the Mir '97 Mission; (7) Long-term Monitoring of the Spine-geometry During the Mir '97 Mission: Introduction of a New Method; and (8) Effects of 20 days of Microgravity (German/Russian Mir '97 Mission) on the Mechanical and Electromyographic Characteristics of Explosive Efforts of the Lower Limbs and of Cycloergometric Exercises of Mild to Sprint-Like Intensity.

Source record↗
NASA NTRS2011

Effects of 30-, 60-, and 90-Day Bed Rest on Postural Control in Men and Women

INTRODUCTION Head-down-tilt bed rest (HDT) has been used as a safe gr ound-based analog to mimic and develop countermeasures for the physiological effects of spaceflight, including decrements in postural stability. The purpose of this investigation was to characterize the effects of 30-, 60-, and 90-day bed rest on postural control in men and women. METHODS Twenty-nine subjects (18M,11F) underwent 13 days of ambula tory acclimatization and were placed in 6? HDT for 30 (n=12), 60 (n=8), or 90 (n=9) days, followed by 14 days of ambulatory recovery. Computerized dynamic posturography (CDP) was used to assess changes in sensory and motor components of postural control, and recovery after HDT. Sensory Organization Tests (SOTs) objectively evaluate one?s ability to effectively use or suppress visual, vestibular, and proprioceptive information for postural control. Stability during the SOTs was assessed using peak-to-peak sway and convergence toward stability limits to derive an equilibrium score. Motor Control Tests (MCTs) evaluate one?s ability to recover from unexpected support surface perturbations, with performance determined by center-of-pressure path length. Whole-body kinematic data were collected to determine body-sway strategy used to maintain stability during each condition. Baselines were determined pre-HDT. Recovery was tracked post-HDT on days 0, 1, 2, and 4. RESULTS Immediately after HDT, subjects showed decreased performance on most SOTs, primarily on sway-referenced support conditions, typically returning to baseline levels within 4 days. MCT performance was not significantly affected. There were no significant gender or duration differences in performance. Kinematic data revealed a tendency to use ankle strategy to maintain an upright stance during most SOT conditions. Interestingly, six subjects (2M,4F) experienced orthostatic intolerance and were unable to complete day 0 testing. CONCLUSION HDT mimics some un loading mechanisms of spaceflight and elicits orthostatic issues present post-spaceflight (contributing to instability); however, it does not sufficiently address the vestibular dysfunction which occurs post-spaceflight.

Esteves, Julie↗
NASA NTRS1989

A model for plasma volume changes during short duration spaceflight

It is well established that plasma volume decreases during spaceflight and simulated weightlessness (bedrest). The decrement in plasma volume is thought to contribute to the orthostatic intolerance that has been observed in some crew members following spaceflight. To date, no studies have evaluated the effectiveness of fluid countermeasures of varying osmolality in the restoration of plasma volume and orthostatic tolerance in a controlled study. The overall objectives of this project were to: (1) provide a model that would rapidly and safely produce a fluid loss comparable to that which occurs during short duration spaceflight; and (2) design a study that would determine the optimal drink solution to restore orthostatic tolerance and describe the mechanism(s) whereby orthostatic tolerance is restored. In summary, Lasix can be used as a way of simulating the plasma volume changes that occur during short duration spaceflight. The total loss of plasma is comparable to spaceflight. Lasix is fast acting, and has relatively few side effects. The present design for evaluating the optimal fluid countermeasures will have important implications in restoring orthostatic tolerance and function in the latter stages of spaceflight when it is essential for safe operation of the spacecraft.

Davis, John E.↗
NASA NTRS2004

Mechanisms of postspaceflight orthostatic hypotension: low alpha1-adrenergic receptor responses before flight and central autonomic dysregulation postflight

Although all astronauts experience symptoms of orthostatic intolerance after short-duration spaceflight, only approximately 20% actually experience presyncope during upright posture on landing day. The presyncopal group is characterized by low vascular resistance before and after flight and low norepinephrine release during orthostatic stress on landing day. Our purpose was to determine the mechanisms of the differences between presyncopal and nonpresyncopal groups. We studied 23 astronauts 10 days before launch, on landing day, and 3 days after landing. We measured pressor responses to phenylephrine injections; norepinephrine release with tyramine injections; plasma volumes; resting plasma levels of chromogranin A (a marker of sympathetic nerve terminal release), endothelin, dihydroxyphenylglycol (DHPG, an intracellular metabolite of norepinephrine); and lymphocyte beta(2)-adrenergic receptors. We then measured hemodynamic and neurohumoral responses to upright tilt. Astronauts were separated into two groups according to their ability to complete 10 min of upright tilt on landing day. Compared with astronauts who were not presyncopal on landing day, presyncopal astronauts had 1). significantly smaller pressor responses to phenylephrine both before and after flight; 2). significantly smaller baseline norepinephrine, but significantly greater DHPG levels, on landing day; 3). significantly greater norepinephrine release with tyramine on landing day; and 4). significantly smaller norepinephrine release, but significantly greater epinephrine and arginine vasopressin release, with upright tilt on landing day. These data suggest that the etiology of orthostatic hypotension and presyncope after spaceflight includes low alpha(1)-adrenergic receptor responsiveness before flight and a remodeling of the central nervous system during spaceflight such that sympathetic responses to baroreceptor input become impaired.

Clinical Trial↗
NASA NTRS1997

Efficacy of compression of different capacitance beds in the amelioration of orthostatic hypotension

Orthostatic hypotension (OH) is the most disabling and serious manifestation of adrenergic failure, occurring in the autonomic neuropathies, pure autonomic failure (PAF) and multiple system atrophy (MSA). No specific treatment is currently available for most etiologies of OH. A reduction in venous capacity, secondary to some physical counter maneuvers (e.g., squatting or leg crossing), or the use of compressive garments, can ameliorate OH. However, there is little information on the differential efficacy, or the mechanisms of improvement, engendered by compression of specific capacitance beds. We therefore evaluated the efficacy of compression of specific compartments (calves, thighs, low abdomen, calves and thighs, and all compartments combined), using a modified antigravity suit, on the end-points of orthostatic blood pressure, and symptoms of orthostatic intolerance. Fourteen patients (PAF, n = 9; MSA, n = 3; diabetic autonomic neuropathy, n = 2; five males and nine females) with clinical OH were studied. The mean age was 62 years (range 31-78). The mean +/- SEM orthostatic systolic blood pressure when all compartments were compressed was 115.9 +/- 7.4 mmHg, significantly improved (p < 0.001) over the head-up tilt value without compression of 89.6 +/- 7.0 mmHg. The abdomen was the only single compartment whose compression significantly reduced OH (p < 0.005). There was a significant increase of peripheral resistance index (PRI) with compression of abdomen (p < 0.001) or all compartments (p < 0.001); end-diastolic index and cardiac index did not change. We conclude that denervation increases vascular capacity, and that venous compression improves OH by reducing this capacity and increasing PRI. Compression of all compartments is the most efficacious, followed by abdominal compression, whereas leg compression alone was less effective, presumably reflecting the large capacity of the abdomen relative to the legs.

Non-NASA Center↗
NASA NTRS2003

Summary of Research Adaptions of Visceral and Cerebral Resistance Arteries to Simulated Microgravity

The proposed studies were designed address the effects of simulated microgravity on vascular smooth muscle and endothelial cell function in resistance arteries isolated from visceral tissues (spleen, mesentery and kidneys) and cerebrum. Alterations in vascular function induced by microgravity are particularly relevant to the problems of orthostatic intolerance and reduced exercise capacity experienced by astronauts upon re-entry into the earth's gravitational field. Decrements in contractile function or enhanced vasodilatory responsiveness of peripheral resistance arteries could lead to decreased peripheral resistance and orthostatic hypotension. Alternatively, augmentation of contractile function in cerebral resistance arteries could lead to increased cerebral vascular resistance and diminished perfusion of the brain. The Specific Aims and hypotheses were proposed in this grant. Following each of the Specific Aims, progress toward addressing that specific aim is presented. With the exception of Specific Aim VI (see aim for details), all aims have been experimentally addressed as proposed. The final six months of the granting period will be used for manuscript preparation; manuscripts in preparation will contain results from Specific Aims I-IV. Results from Specific Aims V and VI have been published.

Delp, Michael↗
NASA NTRS2001

Effect of Exercise Training and +Gz Acceleration Training on Men

Countermeasures for reduction in work capacity (maximal oxygen uptake and strength) during spaceflight and enhanced orthostatic intolerance during re-entry, landing and egress from the return vehicle are continuing problems. The purpose for this study was to test the hypothesis that passive-acceleration training; supine, interval, exercise plus acceleration training and exercise combined with acceleration training would improve orthostatic tolerance in ambulatory men; and that addition of the aerobic exercise conditioning would not alter this improved tolerance from that of passive-acceleration training. Seven men (24-38 yr) underwent "Passive" training on the Ames human-powered centrifuge (HPC) for 30 min, "Exercise" training on the cycle ergometer with constant +Gz acceleration; and "Combined" exercise training at 40% to 90% of the HPC +Gz(max) exercise level. Maximal supine exercise loads increased significant (P<0.05) by 8.3% (Passive), 12.6% (Exercise), and by 15.4% (Combined) after training, but their post-training maximal oxygen uptakes and maximal heart rates were unchanged. Maximal time to fatigue (endurance) was unchanged with Passive was increased (P<0.05) with Exercise and Combined training. Thus, the exercise in the Exercise and Combined training Phases resulted in greater maximal loads and endurance without effect on maximal oxygen uptake or heart rate. There was a 4% to 6% increase (P<0.05) in all four quadriceps muscle volumes (right and left) after post-Combined training. Resting pre-tilt heart rate was elevated by 12.9% (P<0.05) only after Passive training suggesting that the exercise training attenuated the HR response. Plasma volume (% Delta) was uniformly decreased by 8% to 14% (P<0.05) at tilt-tolerance pre- vs. post-training indicating essentially no effect of training on the level of hypovolemia. Post-training tilt-tolerance time and heart rate were increased (P<0.05) only with Passive training by 37.8% and by 29.1%, respectively. Thus, addition of exercise training appeared to attenuate the increased Passive tilt-tolerance.

Greenleaf, John E.↗
NASA NTRS1991

Effect of prolonged LBNP and saline ingestion on plasma volume and orthostatic responses during bed rest

Orthostatic intolerance remains a significant problem following space flight despite frequent use of the saline fluid-loading countermeasure and volitional use of an anti-gravity suite during reentry and landing. The purpose of this project is to examine the plasma volume (PV), endocrine, and orthostatic responses of bedrested subjects following 2-hr and 4-hr treatments of lower body negative pressure (LBNP) and saline ingestion. Ten healthy men were randomly assigned into 2 groups. Group A underwent a 4-hr LBNP/saline treatment on best rest day 5 and the 2-hr treatment on day 11. Group B underwent the 2-hr treatment on day 6 and the 4-hr treatment on day 10. Blood volume was determined before and after bed rest using radiolabelling. Changes in PV between measurements were calculated from changes in hematocrit and estimated red cell volume. Urinary excretion of anti-diuretic hormone (ADH) and aldosterone (ALD) were measured each day during the study. Orthostatic responses were measured using a ramp LBNP protocol before bed rest, before each treatment, and 24 hours after each treatment. Both 2-hr and 4-hr treatments resulted in a restoration of PV to pre-bed rest levels which persisted at least 24 hours. This increase in PV was associated with significant increases in urinary excretion of ADH and ALD. Twenty-four hours after the 4-hr treatment, the heart rate and pulse pressure response to LBNP were significantly lower and stroke volumes during LBNP were increased. Twenty-four hours after the 2-hr treatment, there was no evidence of improvement in orthostatic responses. These results suggest that a countermeasure which simply restores PV during space flight may not be sufficient for restoring orthostatic responses.

Fortney, Suzanne M.↗
NASA NTRS2002

Exercise Versus +Gz Acceleration Training

Decreased working capacity and "orthostatic" intolerance are two major problems for astronauts during and after landing from spaceflight in a return vehicle. The purpose was to test the hypotheses that (1) supine-passive-acceleration training, supine-interval-exercise plus acceleration training, and supine exercise plus acceleration training will improve orthostatic tolerance (OT) in ambulatory men; and that (2) addition of aerobic exercise conditioning will not influence this enhanced OT from that of passive-acceleration training. Seven untrained men (24-38 yr) underwent 3 training regimens (30 min/d x 5d/wk x 3wk on the human-powered centrifuge - HPC): (a) Passive acceleration (alternating +1.0 Gz to 50% Gzmax); (b) Exercise acceleration (alternating 40% - 90% V02max leg cycle exercise plus 50% of HPCmax acceleration); and (c) Combined intermittent exercise-acceleration at 40% to 90% HPCmax. Maximal supine exercise workloads increased (P < 0.05) by 8.3% with Passive, by 12.6% with Exercise, and by 15.4% with Combined; but maximal V02 and HR were unchanged in all groups. Maximal endurance (time to cessation) was unchanged with Passive, but increased (P < 0.05) with Exercise and Combined. Resting pre-tilt HR was elevated by 12.9% (P < 0.05) only after Passive training, suggesting that exercise training attenuated this HR response. All resting pre-tilt blood pressures (SBP, DBP, MAP) were not different pre- vs. post-training. Post-training tilt-tolerance time and HR were increased (P < 0.05) only with Passive training by 37.8% and by 29.1%, respectively. Thus, addition of exercise training attenuated the increased Passive tilt tolerance. Resting (pre-tilt) and post-tilt cardiac R-R interval, stroke volume, end-diastolic volume, and cardiac output were all uniformly reduced (P < 0.05) while peripheral resistance was uniformly increased (P < 0.05) pre-and post-training for the three regimens indicating no effect of any training regimen on those cardiovascular variables. Plasma volume (% delta) was uniformly decreased by 8% to 14% (P < 0.05) at tilt-tolerance pre- vs. post-training for all regimens indicating no effect of these training regimens on the level of vascular fluid shifts.

Greenleaf, John E.↗
NASA NTRS2001

Familial orthostatic tachycardia due to norepinephrine transporter deficiency

Orthostatic intolerance (OI) or postural tachycardia syndrome (POTS) is a syndrome primarily affecting young females, and is characterized by lightheadedness, palpitations, fatigue, altered mentation, and syncope primarily occurring with upright posture and being relieved by lying down. There is typically tachycardia and raised plasma norepinephrine levels on upright posture, but little or no orthostatic hypotension. The pathophysiology of OI is believed to be very heterogeneous. Most studies of the syndrome have focused on abnormalities in norepinephrine release. Here the hypothesis that abnormal norepinephrine transporter (NET) function might contribute to the pathophysiology in some patients with OI was tested. In a proband with significant orthostatic symptoms and tachycardia, disproportionately elevated plasma norepinephrine with standing, impaired systemic, and local clearance of infused tritiated norepinephrine, impaired tyramine responsiveness, and a dissociation between stimulated plasma norepinephrine and DHPG elevation were found. Studies of NET gene structure in the proband revealed a coding mutation that converts a highly conserved transmembrane domain Ala residue to Pro. Analysis of the protein produced by the mutant cDNA in transfected cells demonstrated greater than 98% reduction in activity relative to normal. NE, DHPG/NE, and heart rate correlated with the mutant allele in this family. CONCLUSION: These results represent the first identification of a specific genetic defect in OI and the first disease linked to a coding alteration in a Na+/Cl(-)-dependent neurotransmitter transporter. Identification of this mechanism may facilitate our understanding of genetic causes of OI and lead to the development of more effective therapeutic modalities.

Review, Tutorial↗
NASA NTRS1993

Evaluation of bioimpedance for the measurement of physiologic variables as related to hemodynamic studies in space flight

Orthostatic intolerance, following space flight, has received substantial attention because of the possibility that it compromises astronaut safety and reduces the ability of astronauts to function at peak performance levels upon return to a one-g environment. Many pre- and post-flight studies are performed to evaluate changes in hemodynamic responses to orthostatic challenges after shuttle missions. The purpose of this present project is to validate bioimpedance as a means to acquire stroke volume and other hemodynamic information in these studies. In this study, ten male and ten female subjects were subjected to simultaneous measurements of thoracic bioimpedance and Doppler ultrasonic velocimetry under supine, 10 degree head down and 30 degree head up conditions. Paired measurements were made during six periods of five seconds breath holding, over a two minute period, for each of the three positions. Stroke volume was calculated by three bioimpedance techniques and ultrasonic Doppler.

Taylor, Bruce C.↗
NASA NTRS1973

Lower body negative pressure, experiment M092

Evaluation of orthostatic intolerance has been achieved by the use of lower body negative pressure (LBNP). The LBNP technique, though independent of gravity, simulates its effect by exposing the legs and the lower abdomen to reduced ambient pressures. This LBNP experiment, conducted during the 56-day simulation of the Skylab environment, was designed to supply baseline information on cardiovascular responses to periodic orthostatic stress. Impaired orthostatic tolerance, manifested by the increased heart rate, diminished systolic and pulse pressure, and increased tendency to syncope in the upright position, or during LBNP, was not observed in this experiment.

Johnson, R. L.↗
NASA NTRS2013

Individual Differences in the Temporal Profile of Cardiovascular Responses to Head Down Tilt and Orthostatic Stress with and Without Fluid Loading

Susceptibility of healthy astronauts to orthostatic hypotension and presyncope is exacerbated upon return from spaceflight. Hypo-volemia is suspected to play an important role in cardiovascular deconditioning following exposure to spaceflight, which may lead to increased peripheral resistance, attenuated arterial baroreflex, and changes in cardiac function. The effect of altered gravity during space flight and planetary transition on human cardiovascular function is of critical importance to maintenance of astronaut health and safety. A promising countermeasure for post-flight orthostatic intolerance is fluid loading used to restore loss fluid volume by giving crew salt tablets and water prior to re-entry. Eight men and eight women will be tested during two, 6-hour exposures to 6o HDT: 1) fluid loading, 2) no fluid loading. Before and immediately after each HDT, subjects will perform a stand test to assess their orthostatic tolerance. Physiological measures (e.g., ECG, blood pressure, peripheral blood volume) will be continuously monitored while echocardiography measures are recorded at 30-minute intervals during HDT and stand tests. Preliminary results (N=4) clearly show individual differences in responses to this countermeasure and the time course of physiological changes induced by HDT.

Cowings, Patricia↗
NASA NTRS1999

Functional Performance Evaluation

The Extended Duration Orbiter Medical Project (EDOMP) was established to address specific issues associated with optimizing the ability of crews to complete mission tasks deemed essential to entry, landing, and egress for spaceflights lasting up to 16 days. The main objectives of this functional performance evaluation were to investigate the physiological effects of long-duration spaceflight on skeletal muscle strength and endurance, as well as aerobic capacity and orthostatic function. Long-duration exposure to a microgravity environment may produce physiological alterations that affect crew ability to complete critical tasks such as extravehicular activity (EVA), intravehicular activity (IVA), and nominal or emergency egress. Ultimately, this information will be used to develop and verify countermeasures. The answers to three specific functional performance questions were sought: (1) What are the performance decrements resulting from missions of varying durations? (2) What are the physical requirements for successful entry, landing, and emergency egress from the Shuttle? and (3) What combination of preflight fitness training and in-flight countermeasures will minimize in-flight muscle performance decrements? To answer these questions, the Exercise Countermeasures Project looked at physiological changes associated with muscle degradation as well as orthostatic intolerance. A means of ensuring motor coordination was necessary to maintain proficiency in piloting skills, EVA, and IVA tasks. In addition, it was necessary to maintain musculoskeletal strength and function to meet the rigors associated with moderate altitude bailout and with nominal or emergency egress from the landed Orbiter. Eight investigations, referred to as Detailed Supplementary Objectives (DSOs) 475, 476, 477, 606, 608, 617, 618, and 624, were conducted to study muscle degradation and the effects of exercise on exercise capacity and orthostatic function (Table 3-1). This chapter is divided into three parts. Part 1 describes specific findings from studies of muscle strength, endurance, fiber size, and volume. Part 2 describes results from studies of how in-flight exercise affects postflight exercise capacity and orthostatic function. Part 3 focuses on the development of new noninvasive methods for assessing body composition in astronauts and how those methods can be used to correlate measures of exercise performance and changes in body composition.

Greenisen, Michael C.↗