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PubMed2005

Neurovestibular and sensorimotor studies in space and Earth benefits.

This review summarizes what has been learned from studies of human neurovestibular system in weightless conditions, including balance and locomotion, gaze control, vestibular-autonomic function and spatial orientation, and gives some examples of the potential Earth benefits of this research. Results show that when astronauts and cosmonauts return from space flight both the peripheral and central neural processes are physiologically and functionally altered. There are clear distinctions between the virtually immediate adaptive compensations to weightlessness and those that require longer periods of time to adapt. However, little is known to date about the adaptation of sensory-motor functions to long-duration space missions in weightlessness and to the transitions between various reduced gravitational levels, such as on the Moon and Mars. Results from neurovestibular research in space have substantially enhanced our understanding of the mechanisms and characteristics of postural, gaze, and spatial orientation deficits, analogous to clinical cases of labyrinthine-defective function. Also, space neurosciences research has participated in the development and application of significant new technologies, such as video recording and processing of three-dimensional eye movements and posture, hardware for the unencumbered measurement of head and body movement, and procedures for investigating otolith function on Earth. In particular, devices such as centrifugation or off-vertical axis rotation could enhance clinical neurological testing because it provides linear acceleration which specifically stimulates the otolith organs in a frequency range close to natural head and body movement.

Earth, Planet↗
PubMed2005

Cardiovascular and fluid volume control in humans in space.

The human cardiovascular system and regulation of fluid volume are heavily influenced by gravity. When decreasing the effects of gravity in humans such as by anti-orthostatic posture changes or immersion into water, venous return is increased by some 25%. This leads to central blood volume expansion, which is accompanied by an increase in renal excretion rates of water and sodium. The mechanisms for the changes in renal excretory rates include a complex interaction of cardiovascular reflexes, neuroendocrine variables, and physical factors. Weightlessness is unique to obtain more information on this complex interaction, because it is the only way to completely abolish the effects of gravity over longer periods. Results from space have been unexpected, because astronauts exhibit a fluid and sodium retaining state with activation of the sympathetic nervous system, which subjects during simulations by head-down bed rest do not. Therefore, the concept as to how weightlessness affects the cardiovascular system and modulates regulation of body fluids should be revised and new simulation models developed. Knowledge as to how gravity and weightlessness modulate integrated fluid volume control is of importance for understanding pathophysiology of heart failure, where gravity plays a strong role in fluid and sodium retention.

Blood Volume↗
PubMed2004

Bone formation induced by a novel form of mechanical loading on joint tissue.

Because of insufficient mechanical loading, exposure to weightlessness in space flight reduces bone mass. In order to maintain bone mass in a weightless condition, we investigated a novel form of mechanical loading--joint loading. Since some part of gravity-induced loading to our skeletal system is absorbed by viscoelastic deformation of joint tissues, we hypothesized that deformation of joint tissues would generate fluid flow in bone and stimulate bone formation in diaphyseal cortical bone. In order to test the hypothesis, we applied directly oscillatory loading to an elbow joint of mice and conducted bone histomorphometry on the diaphysis of ulnae. Using murine femurs ex vivo, streaming potentials were measured to evaluate a fluid flow induced by joint loading. Bone histomorphometry revealed that compared to no loading control, elbow loading increased mineralizing surface, mineral apposition rate, and bone formation rate 3.2-fold, 3.0-fold, and 7.9-fold, respectively. We demonstrated that joint loading generated a streaming potential in a medullar cavity of femurs. The results support a novel mechanism, in which joint loading stimulates effectively bone formation possibly by generating fluid flow, and suggest that a supportive attachment to joints, driven passively or actively, would be useful to maintain bone mass of astronauts during an exposure to weightlessness.

Animals↗
PubMed1983

Biochemical changes in rat liver after 18.5 days of spaceflight.

The effect of "weightlessness" on liver metabolism was examined using tissue from rats flown in earth orbit for 18.5 days aboard the Soviet Cosmos 936 biosatellite. Changes in the activities of certain carbohydrate and lipid enzymes were noted. Of the 28 hepatic enzyme activities assayed, two, palmitoyl-CoA desaturase and lactate dehydrogenase, increased, whereas five, glycogen phosphorylase, 6-phosphogluconate dehydrogenase, both acyltransferases which act on alpha-glycerolphosphate and diglycerides, and aconitate hydratase decreased. The remaining enzyme activities measured were unchanged. In addition, increased levels of liver glycogen and palmitoleate were noted which probably resulted from the lowered glycogen phosphorylase and increased palmitoyl-CoA desaturase activities, respectively, in those animals that experienced weightlessness. These changes caused by weightlessness were transient since all of the aforementioned alterations returned to normal values when measured in the livers of other rats which had flown in the biosatellite 25 days after recovery.

Aconitate Hydratase↗
PubMed1999

Different responses of cerebral vessels to -30 degrees head-down tilt in humans.

This study explored changes of the cerebral circulation and evaluated the responses to weightlessness in 12 volunteers (18-22 yr of age). The velocities, diameters and blood flow volume of the common carotid artery (CCA), internal carotid artery (ICA), vertebral artery (VA) and internal jugular vein (IJV) were measured with color Doppler echogram before and during simulated weightlessness. -30 degrees head-down tilt (HDT) for 45 min was used as a weightlessness simulation model. When the subjects' positions were changed from the supine to -30 degrees HDT, blood flow velocities along the CCA, ICA and IJV decreased significantly (p< 0.05), and their diameters were increased. The subjects were divided into two groups according to measured changes in flow volume of the ICA and IJV: group I with a net in-flow of cerebral blood flow (CBF) and group II with a net out-flow of CBF during HDT. Symptoms were recorded in the two groups during HDT (nasal congestion, sensation of head fullness, headache, and others) and graded on a four-point scale, from absent to serious. Results showed that group I had a higher symptoms score while group II had a lower symptoms score. Although this difference did not reach statistical significance, it suggests that cerebral blood flow changes may be partly responsible for the symptoms observed in subjects during HDT.

Adolescent↗
PubMed1975

Preliminary results of examinations of rats after a 22-day flight aboard the Cosmos-605 biosatellite.

The results of biomedical investigations carried out in flights of the Salyut and Skylab orbital stations give evidence that during prolonged weightlessness cosmonauts and astronauts remain in a good physical and mental condition. They fill specialists with optimism in regards to a further increase of the duration of manned space flights. In order to make reliable plans for such missions, it is necessary to accumulate detailed knowledge about the mechanism of the effect of weightlessness on different functions of the human body. In addition to manned experiments, of great interest are animal experiments. They may yield data that cannot be obtained in human studies, which is obviously very important from the point of view of space medicine. This was the purpose of the experiment carried out in November 1973 on the biosatellite Cosmos-605; 45 rats aboard the biosatellite flew for 22 d. Preliminary results of examinations of rats after a 22-d space flight in the Cosmos-605 satellite demonstrated not only physiological and biochemical but also morphological changes in the animal body due to prolonged weightlessness. These changes were reversible.

Aerospace Medicine↗
PubMed1997

Noninvasive methods in space cardiology.

The development and application of noninvasive methods in space cardiology is discussed. These methods are used in astronautics both to gain new insights into the impact of weightlessness conditions on the human organism and to help solve problems involved in the medical monitoring of space crew members. The cardiovascular system is a major target for the action of microgravity. Noninvasive methods used to examine the cardiovascular system during space flights over the past 30 years are listed. Special attention is given to methods for studying heart rate variability and contactless recording of physiologic functions during night sleep. Analysis of heart rate variability highlights an important principle of space cardiology-gaining the maximum amount of information while recording as little data as possible. With this method, the degree of strain experienced by the systems of autonomic regulation and the adaptational capabilities of the body can be assessed at various stages of a space flight. Discriminant analysis of heart rate variability data enables the psycho-emotional component of stress to be separated from the component associated with the impact of weightlessness. A major advance in space medicine has been the development of techniques for contactless recording of pulse rates, breathing frequency, myocardial contractility, and motor activity during sleep using a sensor installed on the cosmonaut's sleeping bag. The data obtained can be used to study ultradian rhythms, which reflect the activity of higher autonomic centers. An important role of these centers in mobilizing functional reserves of the body to ensure its relatively stable adaptation to weightless conditions is shown.

Aerospace Medicine↗
PubMed1986

Gravisensitivity of the acellular slime mold Physarum polycephalum demonstrated on the fast-rotating clinostat.

The acellular slime mold Physarum polycephalum was used to investigate a postulated general gravisensitivity of cells. Physarum was subjected i) to a rotation on the fast-rotating clinostat, which enables the simulation of weightlessness (0 g), and ii) to single horizontal turns of 180 degrees. On the fast-rotating clinostat the response consists of a frequency increase in radial contractile activity, an oscillation of the mean values (frequency regulation phenomena) and an increase in standard deviation. A combination of 0 g and respiration impediment inhibits the response to 0 g, i. e., the frequency increase in radial contractile activity during weightlessness simulation. Turning the specimens horizontally about 180 degrees in a normally positioned light microscope also leads to a frequency increase in radial contractile activity, but the temporal pattern of the frequency increase differs in comparison to the experiments performed on the clinostat during weightlessness simulation. These results demonstrate the occurrence of gravisensitivity in Physarum polvcephalum. Regulation phenomena and the possible role of mitochondria in graviperception are discussed.

Animals↗
PubMed1999

[Effects of space flight on medicinal plant Agastache rugosa (Fisch. et Mey.) O. Ktze].

OBJECTIVE: To substantiate the effect of space conditions on medicinal plants. METHODS: The seeds of Agastache rugosa were set up in retrievable satellites. After returning to earth, the changes of isozymes of peroxidases, esterase and soluble proteins were studied. RESULTS: The peroxidase activity and protein content of the weightless group were a little lower than those of the earth controlled group, while these two items of the hit group were higher than those of the earth controlled group. The electrophoresis patterns of isoperoxidases and isoeasterase of these three groups, as well as the protein patterns of the weightless group and the earth controlled group were found alike. But the protein patterns of the hit group were different from those of the other two groups. CONCLUSION: The effect of weightlessness is smaller than that of the high energy heavy ions on Agastache rugosa. Different plants have different susceptibility to space conditions.

China↗
PubMed2002

The exercise and environmental physiology of extravehicular activity.

Extravehicular activity (EVA), i.e., exercise performed under unique environmental conditions, is indispensable for supporting daily living in weightlessness and for further space exploration. From 1965-1996 an average of 20 h x yr(-1) were spent performing EVA. International Space Station (ISS) assembly will require 135 h x yr(-1) of EVA, and 138 h x yr(-1) is planned for post-construction maintenance. The extravehicular mobility unit (EMU), used to protect astronauts during EVA, has a decreased pressure of 4.3 psi that could increase astronauts' risk of decompression sickness (DCS). Exercise in and repeated exposure to this hypobaria may increase the incidence of DCS, although weightlessness may attenuate this risk. Exercise thermoregulation within the EMU is poorly understood; the liquid cooling garment (LCG), worn next to the skin and designed to handle thermal stress, is manually controlled. Astronauts may become dehydrated (by up to 2.6% of body weight) during a 5-h EVA, further exacerbating the thermoregulatory challenge. The EVA is performed mainly with upper body muscles; but astronauts usually exercise at only 26-32% of their upper body maximal oxygen uptake (VO2max). For a given ground-based work task in air (as opposed to water), the submaximal VO2 is greater while VO2max and metabolic efficiency are lower during ground-based arm exercise as compared with leg exercise, and cardiovascular responses to exercise and training are also different for arms and legs. Preflight testing and training, whether conducted in air or water, must account for these differences if ground-based data are extrapolated for flight requirements. Astronauts experience deconditioning during microgravity resulting in a 10-20% loss in arm strength, a 20-30% loss in thigh strength, and decreased lower-body aerobic exercise capacity. Data from ground-based simulations of weightlessness such as bed rest induce a 6-8% decrease in upper-body strength, a 10-16% loss in thigh extensor strength, and a 15-20% decrease in lower-body aerobic exercise capacity. Changes in EVA support systems and training based on a greater understanding of the physiological aspects of exercise in the EVA environment will help to insure the health, safety, and efficiency of working astronauts.

Arm↗
PubMed1964

Effects of gravity on the functions of the central nervous system.

The sensitivity of the mammalian central nervous system to gravitational influences involves both direct and indirect factors. Gradual loss of cerebral circulation with increasing acceleration beyond 5 G has been shown to evoke changes in patterns of brain electrical activity, with epileptiform discharges triggered primarily in the hippocampal system of the temporal lobe, and spreading into other brain systems. The relationship of these structures to judgment and discriminative functions is discussed. Complete loss of cerebral circulation is associated with electrical silence in the brain. The possible effects of weightlessness on intracranial fluid distribution are reviewed. Tests of vibrational stimuli in the monkey have disclosed "driving" of electrical brain rhythms at the shaking frequency, particularly in the range from 11 to 15 cycles per second. These effects are unrelated to photic stimulation, and are abolished by anesthesia or death. Tests of discriminative capability at frequencies producing maximum driving have shown increased response latencies and increased errors. The neurophysiological basis for adaptive phenomena in recurrent vestibular stimulation has been found to reside partly in the vestibular nuclei of the medulla, and not to require integrity of connections with higher vestibular centers. The potentiation of responsiveness to vestibular stimulation in the weightless state has been shown to have a basis in the exaggerated responsiveness of medullary vestibular centers following loss of proprioceptive influxes from the spinal cord. The possible contribution of weightlessness to anomalous psychophysiological functions is reviewed. This area presents a major challenge in experimental design, and may require evaluation of such phenomena as distortion of the body image, modified sleep patterns and changes in optimal sleep-work cycles.

Acceleration↗
PubMed1973

Some psychological and engineering aspects of the extravehicular activity of astronauts.

One of the main in-flight problems being fulfilled by astronauts is the preparation for and realization of egress into open space for the purpose of different kinds of extravehicular activity, such as, the performance of scientific experiments, repairing and dismantling operations etc. The astronaut's activity outside the space vehicle is the most difficult item of the space flight programme, which is complicated by a number of space factors affecting a man, viz. dynamic weightlessness, work in a space suit under conditions of excessive pressure, difficulties of space orientation etc. The peculiarities mentioned require special training of the cosmonaut. The physical training involves a series of exercises forming the body-control habits necessary for work in a state of weightlessness. In a new kind of training use is made of equipment simulating the state of weightlessness. From analysis of the available data and the results of my own investigations during ground training and the Soyuz 4 and 5 flights one can establish the following peculiarities of the astronaut's extravehicular activity: (1) Operator response lag in the planned algorithm; (ii) systematic appearance of some stereotype errors in the mounting and dismantling of the outer equipment and in scientific-technical experiments; (iii) a high degree of emotional strain and 30-35% decrease in in-flight working capacity of the astronaut compared with the ground training data; (iv) a positive influence of space adaptation on the cosmonaut and the efficiency of his work in open space; (v) the necessity for further engineering and psychological analysis of the astronaut's activity under conditions of the long space flight of the multi-purpose orbital station. One of the main reasons for the above peculiarities is the violation of the control-coordination functions of the astronaut in the course of the dynamical operations. The paper analyses the extravehicular activity of the astronaut and presents some recommendations for its more efficient realization. Proposals are given concerning the complex engineering, psychological and technical investigations to be made during in-flight egress.

Aerospace Medicine↗
PubMed1999

[Effects of 7 d head-down tilt (-20 degrees) immobilization on pharmacokinetics of gentamicin in rabbits].

OBJECTIVE: To observe pharmacokinetic changes under simulated weightlessness in relevant to body flood flow changes. METHOD: Gentamicin was selected as probe drug in the present study, and rabbits exposed to Head-Down Tilt (HDT, -20 degrees) immobilization were selected as simulated weightlessness animal model. Seven rabbits were treated inf. with 3 mg/kg of gentamicin sulfate pre-HDT and 7 d after HDT. Gentamicin blood samples within 4 h after administration were analyzed by TDxFLx. RESULT: The distribution of gentamicin postponed significantly: a significant decrease in alpha from (0.1838 +/- 0.1076) min-1 before HDT to (0.0591 +/- 0.0334) min-1 after HDT; a significant increase in t1/2 alpha from (5.30 +/- 3.55) min to (15.04 +/- 7.49) min; a significant decrease in k12 from (0.1025 +/- 0.0721) min-1 to (0.0181 +/- 0.0161) min-1, a increase trend in V(C) and V(D). After HDT, CL(S) of gentamicin increased from (2.2 +/- 0.5) ml min-1 kg-1 to (2.7 +/- 0.3) ml min-1 kg-1. CONCLUSION: Simulated weightlessness might induce pharmacokinetic changes.

Adaptation, Physiological↗
PubMed1965

Results of biological experiments carried out under conditions of "Vostok" flights with the participation of cosmonauts A.G. Nikolajev, P.R. Popovich and V.F. Bykovsky.

The data are presented on a study of the effect of space flight factors, particularly of weightlessness and radiation, on the fertilization, growth and development of Drosophila melanogaster and on the mechanism of heredity in Tradescantia paludosa. Copulation, oviposition and development of Drosophila are shown to be possible under 4-day weightless conditions. A distortion in the sex ratio has been registered in the cultures of flies grown in flight. Three types of changes in Tradescantia microspores brought about by flight factors have been revealed, i.e. chromosome rearrangements, distortions in the mitotic mechanism and stimulation of growth processes in the cell. It is suggested that rearrangements of chromosomes are caused by the action of vibrations and accelerations while distortions in the mechanism of mitosis are mainly related to the weightlessness effect.

Animals↗
PubMed2003

[Effects of spirulina on serum lipids, erythrocyte membrane fluidity and vascular endothelial cells in tail-suspended rats].

OBJECTIVE: To study the changes of erythrocyte membrane fluidity, serum lipid and vascular endothelial cell caused by simulated weightlessness in rats and the beneficial effect of spirulina. METHOD: Thirty male SD rats were divided into 3 groups: free control group (group A) and two simulated weightlessness groups (groups B, C). Rats in group A and B were fed with normal forage, and the rats in group C were fed with normal forage supplemented with 5% (W/W) spirulina. Water was taken ad libitum. RESULT: Levels of serum CHO, HDL, TG, HDL-C/CHO and erythrocyte membrane fluidity decreased significantly, and number of vascular endothelial cells in plasma increased markedly in group B as compared with those in group A; The ratio of LDL-C/HDL-C, and atherosclerosis index (AI) decreased, number of vascular endothelial cells significantly lowered; level of CHO, HDL-C and value of the IDmax of plasma as well as erythrocyte membrane fluidity remarkedly increased in group C compared with those in group B. CONCLUSION: Spirulina can improve the physiological conditions of erythrocyte membrane fluidity, serum lipid and vascular endothelial cell caused by simulated weightlessness in rats.

Animals↗
PubMed2004

Effects of tail suspension on electrophysiological characteristics of muscle spindles in isolated rat soleus muscle.

OBJECTIVE: To study changes in electrophysiological characteristics of muscle spindles induced by simulated weightlessness in isolated rats soleus. METHOD: Weightlessness was simulated by tail-suspension in female rats. Using electro-physiological technique, the spontaneous discharge of muscle spindle and its response to ramp-and-hold stretch were observed in isolated soleus of 7 d, 14 d tail-suspended and control rats. RESULT: Soleus muscle spindles of rat manifest a sharp decrease in spontaneous discharge frequency and the response to ramp-and-hold stretch after 7 d tail-suspension. More significant changes were observed in rats after 14 d tail-suspension. CONCLUSION: Simulated weightlessness could induce time-related changes in electrophysiological characteristics of soleus muscle spindles in rat.

Animals↗
PubMed2004

[Effects of high frequency vibration on expression of myosin heavy chain (MHC) in intrafusal and extrafusal fibers in soleus muscles of tail-suspended rats].

OBJECTIVE: To study the effects of high frequency vibration on expression of myosin heavy chain (MHC) in intrafusal and extrafusal fibers in soleus muscles of tail-suspended rats. METHOD: Weightlessness was simulated by tail suspension of female rats. Using immunohistochemistry technique, changes of expression of MHC in intrafusal and extrafusal fibers of soleus muscles were detected. RESULT: Expression of fast MHC in intrafusal and extrafusal fibers of soleus muscles increased during 7 d of simulated weightlessness, whereas during 7 d of tail suspension plus high frequency vibration, these changes were not detected. CONCLUSION: High frequency vibration can counteract the changes in expression of MHC in intrafusal and extrafusal fibers of rats soleus under muscles of rats in simulated weightlessness situation.

Animals↗
PubMed2006

[Effects of inosine injection in expression of myosin heavy chain in intrafusal and extrafusal myofibers in soleus muscle of tail-suspended rats].

AIM: To study the effects of inosine on myosin heavy chain (MHC) activity in rats soleus muscle after tail-suspension. METHODS: Weightlessness was simulated by tail-suspension of rats. Using immunohistochemistry technique, changes of expression of MHC in intrafusal and extrafusal fibers in soleus muscle were detected. RESULTS: Expression of fast MHC in intrafusal and extrafusal fibers in soleus muscle increased after 14 d of simulated weightlessness, whereas in tail-suspended rats given inosine, the expression of fast MHC was not detected. CONCLUSION: Inosine could counteract the changes in expression of MHC in intrafusal and extrafusal fibers of rats soleus under simulated weightless situation.

Animals↗