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At least 469 records · Page 26Linked to original sources
PubMed1998

Time-course of human muscle fibre size reduction during head-down tilt bedrest.

The first studies of space flown rats revealed that in m.soleus (SOL) slow-twitch fibers (ST) were reduced in size more pronouncedly than fast-twitch fibers (FT). The same differences in the fiber atrophy levels were found in rats after hind-limb suspension. At the same time, the studies on humans exposed to real and simulated weightlessness demonstrated that at least in m.vastus lateral (VL) the ST and FT fibers' levels of atrophy were almost similar. The discrepancies in the results of human and rat studies are believed to be explained by: i/species-specificity in muscle plasticity pattern; ii/differences in characteristics of muscles usually being under rat and human studies (SOL vs VL); iii/observation of different stages of the atrophy development in different species; The study was aimed to test these hypotheses.

Adenosine Triphosphatases↗
PubMed2001

[Isokinetic concentric dynamometry of knee flexors and extensors in young male].

Objective. To investigate the effects of different moving speeds on isokinetic dynamometry of knee flexors and extensors, and to provide normative data for comparative purposes in strength evaluations. Method. Thirty healthy male were tested at 60, 180, and 240 deg/sec angular velocities using a REV9000 testing and rehabilitation system. Result. Both PT (peak torque) and PT/BW (peak torque/body weights) showed significant differences (P< 0.01, P< 0.05) between flexors and extensors, and declined significantly with increased speed (P< 0.001). Peak torque differences between dominant and nondominant knee (Di%) was 10%. TPT (time to peak torque) tended to decrease as moving speeds increased (P< 0.001). APT (angle of peak torque) were 50%-70% for quadriceps, and 32%-45% for hamstrings; H/Q (hamstrings peak torque/quadriceps peak torque) was 50%-60%; WF (work fatigue) was 65%. Conclusion. The results provided a reference for strength evaluations in space medicine and space physiology, especially under simulated weightlessness and microgravity.

Aerospace Medicine↗
PubMed2003

[Effects of microgravity on human cognitive function in space flight].

In researches of space flight, studies on the effects of microgravity on cognitive function were relatively few. This paper reviews recent progress on this topic. It was shown that under the condition of microgravity, spatial orientation, motion perception and early process of object recognition were impaired to a certain degree. Capability of muscle movement and coordination was lowered, while higher cognitive functions, such as logic reasoning task, the speed and accuracy of short-term memory retrieval were less affected by microgravity. But long-term memory tasks and performance in which attention processes were needed (e.g., tracking task, selective response task), were impaired during space flight or under simulated weightlessness condition.

Cognition↗
PubMed1992

Increased orthostatic blood pressure variability after prolonged head-down tilt.

The effect of simulated weightlessness on orthostatic blood pressure regulation was evaluated with passive 70 degrees head-up tilt (HUT) after 10 days 6 degrees head-down tilt (HDT). Six healthy male volunteers were studied. Continuous recording of finger blood pressure (BP) was obtained non-invasively with a FinapresTM device. Instantaneous heart rate (HR) was derived from the electrocardiogram. To quantify orthostatic BP variability, a fast fourier transform (FFT) of the beat-by-beat BP- and RR-interval values was performed. Control HR before HUT after the 10-day HDT period was increased, probably due to an arousal state of the test subjects. The change in BP induced by HUT was not influenced by 10 days' HDT, in contrast to the HR rise which increased from 24 +/- 2 beats/min to 41 +/- 7 beats/min (P less than 0.05). After HDT the total variance in orthostatic BP almost doubled. FFT indicated that this increase in variance can be ascribed to BP oscillations with a frequency of around 0.1 Hz. In three subjects transient HR decelerations during HUT after HDT were observed. Analysis of the relationship between BP and HR in the transients showed that each HR decrease was preceded by a BP increase above normal. These HR decelerations seemed, therefore, to be an effect of the vagal part of the arterial baroreflex and did not necessary signal an impending vasovagal syncope. The present study indicates that although 10 days' HDT do not influence absolute BP responses to 70 degrees HUT BP was maintained by an increased sympathetic activity, reflected by an increased HR response and an augmented variance in BP around 0.1 Hz.

Adult↗
PubMedDate not supplied

[Indices of human blood acid-base equilibrium and enzymatic activity in short-term antiorthostatic hypokinesia].

Before and after a 5 day head-down tilt of 4.5 degrees blood samples were withdrawn from different areas of the cardiovascular system of healthy male volunteers. Blood was sampled by means of selective catheterization. Parameters of acid-base equilibrium and activities of aminotransferases and alkaline phosphatase were measured. After immobilization the most significant changes were observed in the blood outflowing from the brain in which significant metabolic acidosis and increased activity of aspartate aminotransferase occurred. A slight increase in the activity of aspartate aminotransferase was also observed in the blood outflowing from the liver and kidneys. It is concluded that brain is the organ which is subjected to short-term simulated weightlessness in the highest degree.

Acid-Base Equilibrium↗
PubMed1989

Microgravity-induced changes in human bone strength.

A decrease of spongy tissue strength of iliac bone has been identified in healthy men under conditions of simulated weightlessness (bed rest). Countermeasures have significantly prevented this decrease. Additional investigations have indicated probability of degenerative-destructive bone change development under conditions of usual human activity as a consequence of bone strength decrease.

Animals↗
PubMed1985

[Oral glucose tolerance tests in man during a 150-day space flight (Salyut 7-Soyuz T9)].

This study was conducted on the pilot specialist of the Salyut 7-Soyuz T9 complex during a 150 days space flight. Glucose tolerance tests were made 3 days before flight, on days 60 and 88 during flight and on days 25 and 55 after flight. The study confirms the decrease of fasting plasma glucose observed during the 3 Skylab missions and demonstrates blunted glucose tolerance curves. The changes were not found during ground based studies using bed rest to simulate weightlessness state. The origin of this abnormality is discussed.

Adult↗
PubMed1987

Vital capacity and airflow measured from partial flow-volume curves during 5 degrees head-down tilt.

Ten healthy young males were subjected to 7 min of 5 degrees head-down tilt, during which their forced vital capacity, peak flow rate (from complete flow-volume curves), and MEF 40% and 25% (airflows when 40% and 25% of the vital capacity remains in the lungs) from the partial curves were measured. The values of these variables and the heart rate and blood pressure were not significantly different from the values obtained in the supine position. In view of these findings it is concluded that the increase in the intra-thoracic blood volume, known to occur with 5 degrees head-down tilt used as a model for simulating weightlessness, does not embarrass respiratory mechanics.

Adult↗
PubMedDate not supplied

[Human cardiac activity during the 1st hours and days of exposure to antiorthostatic hypokinesia (according to the results of echocardiography)].

Six healthy volunteers (aged 19-24) were exposed to head-down tilt (at-10 degrees) for 7 days. The study revealed phasic changes of intracardiac circulation and the pump function which were not accompanied by contractility disorders. On the whole, the changes represented a manifestation of cardiovascular adaptation to hemodynamic shifts that are typical of this type of simulated weightlessness. The echocardiographic parameters varied similarly during the head-down tilt test and the joint Soviet-French experiment onboard Salyut-7.

Adaptation, Physiological↗
PubMedDate not supplied

[Effect of short-term antiorthostatic hypokinesia on the pressure in various parts of the healthy human cardiovascular system].

Before and after 5-day head-down tilting (-4.5 degrees) blood pressure was measured in different cardiovascular compartments by the technique of selective catheterization: the upper bulb of the internal jugular vein, superior and inferior venae cavae, hepatic, renal and iliac veins, right atrium and right ventricle, coronary sinus, pulmonary and radial arteries. After exposure the pressure in extrathoracic vessels increased by 1.4 mm Hg on the average: in the internal jugular vein it rose by 1.7 mm Hg whereas in the iliac vein by 1.0 mm Hg. The blood pressure in the intrathoracic vessels of the systemic circulation increased, as a rule, by no more than 0.5--0.8 mm Hg. This elevation was characteristic of diastolic regions of the pressure curve (x- and y-collapse). The pressure in pulmonary vessels--pulmonary artery and left atrium--showed a trend for a decrease of 1.3 mm Hg. The factors that may be responsible for the dissimilar changes of pressure in different cardiovascular compartments under the influence of short-term simulated weightlessness are discussed.

Adult↗
PubMed1984

Water immersion and the kidney: implications for volume regulation.

Studies from this laboratory have demonstrated that head-out immersion in isothermic water causes a cephalad redistribution of blood volume. The resultant central hypervolemia induces a marked natriuresis and diuresis and suppression of plasma renin activity, plasma aldosterone, and plasma arginine vasopressin. All of these changes are thought to be attributable to stimulation of cardiopulmonary receptors. Immersion also produces an augmentation of prostaglandin E (PGE) excretion, which reflects increased renal PGE synthesis. The ability of immersion in induce a prompt and profound central hypervolemia, without concomitant alterations in plasma composition, indicates that immersion might be a preferred investigative tool for assessing the effects of volume expansion on renal function and hormonal responsiveness in both normal individuals and patients with edematous disorders. In addition, this model constitutes an appropriate tool for simulating weightlessness.

Blood Volume↗
PubMedDate not supplied

[Evaluation of the changes in the bone structures of the human axial skeleton in prolonged space flight].

Changes in the mineral content of the left heel bone of the Salyut-6 crewmembers who made 75--184-day flights were measured by direct photon absorptiometry. The postflight results were compared with the predicted rate of bone atrophy. This parameter was derived from the data concerning variations in the mineral content of spongy bones of men and animals exposed to actual and simulated weightlessness for various time intervals. The efficiency of countermeasures against the adverse effect of weightlessness on bones was assessed. It is concluded that crewmembers with a high content of minerals in spongy structures of the axial skeleton and a low basal metabolism should be selected for prolonged space missions.

Atrophy↗
PubMedDate not supplied

[Human reaction of external respiration and gas exchange in the acute period of adaptation to water immersion].

Responses of respiration and gas exchange of 6 test subjects to 3-day dry immersion were investigated. It was found that an exposure to immersion was accompanied by decreases in respiratory volume, vital lung capacity, maximum pulmonary ventilation, and breathing time retention during inhalation and expiration. These changes were paralleled by an increase in the portion of the functional dead space and a decrease in the portion of the efficient alveolar volume. The permeability of respiratory tracts remained unchanged. These changes seem to be of the type of total respiratory insufficiency induced by circulatory disorders. This may be one of the factors responsible for a decline in human tolerance to exercises and acceleration applied after an exposure to simulated weightlessness.

Adaptation, Physiological↗
PubMedDate not supplied

[Tailward acceleration tolerance of middle-aged persons before and after a 7-day immersion].

Before and after 7-day immersion 6 healthy male test subjects, aged 41 to 49, were exposed to +3 GZ for 60 sec in a centrifuge with an arm of 7.25 m. The runs were repeated 12 times. The test subjects well tolerated the exposure before and after immersion. However, after immersion the physiological systems functioned in a more stressful manner than prior to immersion. This can be attributed to the deconditioning caused by simulated weightlessness. The comparison of the experimental findings with the literature data gives evidence that the pattern and level of physiological changes induced by an exposure to +3 GZ for 60 sec in the test subjects, aged 41 to 49, do not differ significantly from those in younger (aged 23 to 36) people.

Acceleration↗
PubMedDate not supplied

[Characteristics of human urinary excretion of vitamins C, B1 and B6 during 182-day head-down tilt hypokinesia].

Renal excretion of ascorbic acid, thiamin and 4-pyridoxic acid was studied in 18 test subjects exposed for 182 days to head-down tilt. Two groups of subjects (6 subjects each) performed exercises of different work load and the third - control - group was exposed to hypokinesia as such. It was shown that exercises produced a beneficial effect on vitamin metabolism. It is recommended to develop preliminary adaptation to the work load planned as a countermeasure in real or simulated weightlessness.

Adult↗
PubMedDate not supplied

[The morphometric indices of the peripheral blood lymphocytes under conditions of 120-day head-down tilt hypokinesia].

Study of changes coursing in the body under conditions of a space flight are particularly important now, when the duration of missions has increased and the effects of all flight factors on the operator activity of crew members should be taken into consideration. Dynamic study of these processes is possible only in weightlessness simulation experiments on the Earth. Morphometric parameters of peripheral blood lymphocytes under conditions of 120-day antiorthostatic hypokinesia were studied. The detected adaptation changes in lymphocytes indicate that these cells can sufficiently rapidly react to the said exposure. Apparently, it is the adaptation changes we observe both in antiorthostatic hypokinesia and after long space flights.

Adaptation, Physiological↗