SEARCH · Search PubMed

Results for “WEIGHTLESSNESS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60Linked to original sources

PubMed1997

Vestibular function and sensory interaction in altered gravity.

The effects of weightlessness on vestibular function have been studied since the beginning of manned spaceflight. The results of these studies have been highly variable and to some extent even contradictory, which makes it difficult to draw unambiguous conclusions. This variability is probably due to at least three factors: (1) individual differences in the adaptive process, (2) non-standardized experimental methods and conditions, (3) a lack of integrated experiments. For this reason, we have used a single integrated approach with a specially developed battery of tests. The results thus obtained for 21 cosmonauts on short- and long-term flights are reviewed here, and discussed in the light of the results obtained by others. Changes in the operation of the vestibular system and in all functions based on vestibular afferent input are commonly observed in spaceflight. These changes are characteristic for the process of adaptation and re-adaptation to altered gravity. They occur in a high proportion of persons exposed to such conditions, although there are individual differences with regard to severity, nature, time and duration of occurrence, and the dynamics of the process. Analysis of the observations in a large number of cosmonauts has permitted to distinguish three types of adaptation of the system to altered gravity. The first type of adaptation is characterized by a strong response to any stimulus during the initial adaptation period. The second type of adaptation is characterized by responses that are drastically decreased or even absent. The third type of adaptation is distinguished by the selective response of the sensory system to certain types of stimulation only. After long-term missions the process of re-adaptation usually takes a more severe course than the earlier process of adaptation to microgravity. Both adaptation and re-adaptation follow an undulating course, in which adaptation and re-adaptation are alternating. This is most conspicuous during long-term flights, and it suggests that in the initial stage of adaptation to weightlessness the vestibular input plays a dominant role, while at the end of the adaptation process the visual input prevails.

Eye Movements↗

PubMed2002

Changes in kinetics of cerebral auto-regulation with head-down bed rest.

Thoraco-cephalic fluid shift induced by weightlessness may influence cerebral autoregulation. Our objective was to assess effects of simulated weightlessness by a 7-day head-down bed rest (HDBR) on the kinetics of cerebral blood flow (CBF) autoregulation in eight healthy women (27.9 +/- 0.9 years). This was studied by transcranial Doppler (TCD) of the middle cerebral artery (MCA) during the sudden decrease in blood pressure (BP) induced by quickly deflating thigh cuff aftera 4-min arterial occlusion before (D - 3), during (D2, D5) and after the HDBR (D + 1). BP (Finapres) and MCA maximal blood flow velocity were continuously recorded. Cerebrovascular resistance (CR) was expressed as the ratio of mean BP to mean MCA velocity. The CR slope was defined as changes in CR per second during the BP decrease. The magnitude of the relative decrease in mean BP and MCA velocity as well as the CR slope did not differ significantly before, during and after the HDBR, showing no major impairment of cerebral autoregulation during short-term HDBR. The time to maximum decrease in CR (T1 in s), corresponding to the maximum vasodilation was reduced on D2 (7-2 +/- 0.6) versus D - 3 (9.9 +/- 1-3), D5 (9-6 +/- 0.8) and R + 1 (11.7 +/- 11) probably as a result of the fluid shift. We also looked if the responses during the thigh cuff release differed in women according to their tolerance to the 10 min stand test performed after the HDBR: T1 was larger in the five women who presented orthostatic intolerance suggesting that some differences in cerebral autoregulatory responses may be related to orthostatic intolerance.

Adult↗

PubMed2001

Renal and sympathoadrenal responses in space.

According to a classic hypothesis, weightlessness should promote the renal excretion rate of sodium and water and lead to a fluid- and electrolyte-depleted state. This hypothesis is based on experiments in which weightlessness has been simulated in humans by head-down bed rest and water immersion. However, after 5 to 6 days of space mission, the diuretic and natriuretic responses to an intravenous isotonic saline load were attenuated and plasma norepinephrine and renin concentrations increased compared with those of the acute supine position before flight. Renal fluid excretion after an oral water load was also attenuated in space. Similar decreases were not observed during head-down bed rest. Sympathetic activity is of major importance in regulating blood volume and renal function. Studies in space have indicated that, compared with that while in a supine position on Earth, sympathoadrenal activity is increased during space flights as measured using plasma concentration and urinary excretion of norepinephrine and epinephrine. The space-induced activation of antinatriuretic mechanisms and sympathoadrenal activity could have been caused by early in-flight reduction in total and central blood volume. The decreased plasma volume may be explained by such factors as redistribution of plasma from the lower to the upper body (thin legs and puffy face), reduced food intake, and decreased muscle activity. The decrease in plasma volume and the subsequent increase in sympathetic activity is due, at least in part, to the abrupt cessation of activity in large muscle groups during microgravity, which normally counteracts the effects of gravity in the upright posture. This would lead to accumulation of albumin and fluid in the interstitial space.

Adrenal Glands↗

PubMed1992

Histochemical and contractile responses of rat medial gastrocnemius to 2 weeks of complete disuse.

We studied the histochemical and in situ contractile changes in a rat ankle extensor, medial gastrocnemius, in which activation of muscle fibres by motoneurones was blocked for 14 days, using the sodium channel blocker tetrodotoxin applied to the sciatic nerve. Muscles were atrophied and showed slower twitch responses, greater fusion at subtetanic frequencies of stimulation, and higher twitch/tetanic ratios. Tetanic force/mm2 of fibre area and fatiguability were unchanged. Type II fibres were more atrophied and showed greater decreases in mitochondrial succinate dehydrogenase activity than type I fibres. The contractile changes resulting from complete disuse do not occur in models in which weight-bearing alone has been removed (space flight, hindlimb suspension), suggesting that the residual motoneurone activity reported in models of weightlessness is sufficient to prevent these responses. Similarly, the finding of a greater type II fibre susceptibility to complete disuse, which differs from the pattern seen in models of weightlessness, suggest that this residual motoneurone activity in the latter influences atrophic responses in a manner that is variable among motor unit types, to produce the reported preferential type I atrophy characteristic of removal of weight-bearing.

Animals↗

PubMed1978

Evaporative water loss in man in a gravity-free environment.

Daily evaporative water losses (EWL) during the three Skylab missions were measured indirectly using mass and water-balance techniques. The mean daily values of EWL for the nine crew members who averaged 1 h of daily exercise were: preflight 1,750 +/- 37 (SE) ml or 970 +/- 20 ml/m2 and inflight 1,560 +/- 26 ml or 860 +/- 14 ml/m2. Although it was expected the EWL would increase in the hypobaric environment of Skylab (one-third atmosphere). an average decrease from preflight sealevel conditions of 11% was measured. The results suggest that weightlessness decreased sweat losses during exercise and possibly reduced insensible skin losses as well. The weightlessness environment apparently promotes the formation of an observed sweat film on the skin surface during exercise by reducing convective flow and sweat drippage, resulting in high levels of skin wettedness that favor sweat suppression.

Body Water↗

PubMed1984

Physiological responses to prolonged bed rest and fluid immersion in humans.

Rest in bed and immersion in water have been used for centuries by physicians and healers in treating injury and disease. The qualitative similarity of acute and chronic responses to bed rest, immersion, and weightlessness has sparked renewed interest in and a resultant greater understanding of the mechanisms of disuse deconditioning. Some combination of changes in hydrostatic pressure, reduced total metabolism (exercise), compression force on weight-bearing bones, as well as psychological factors associated with prolonged confinement in a new environment probably comprise the major input stimuli for the adaptive responses. Virtually every physiological system is affected. Early responses involve the fluid, electrolyte, and blood pressure control systems with significant muscular atrophy and decreases in bone density occurring over weeks and months. Much effort has been expended to describe the various responses to bed rest and immersion with understandably less effort devoted to research during weightlessness. Future research should be directed mainly toward an understanding of the mechanisms of these adaptive responses. Additional work is especially needed to elucidate the effects of deconditioning on drug metabolism, functioning of the immune system, carbohydrate metabolism, protein and peptide metabolism in muscle, and calcium metabolism as it affects integrity of bone.

Adaptation, Physiological↗

PubMed1990

Skeletal muscle adaptation in rats flown on Cosmos 1667.

Seven male Wistar rats were subjected to 7 days of weightlessness on the Soviet biosatellite Cosmos 1667. Muscle histomorphometry and biochemical analyses were performed on the soleus (SOL) and extensor digitorum longus (EDL) of flight rats (group F) and compared with data from three groups of terrestrial controls: one subjected to conditions similar to group F in space except for the state of weightlessness (group S) and the others living free in a vivarium (V1, V2). Relative to group V2 (its age and weight-matched control group), group F showed a greater decrease of muscle mass in SOL (23%) than in EDL (11%). In SOL a decrease in the percentage of type I fibers was counterbalanced by a simultaneous increase in type IIa fibers. The cross-sectional area of type I fiber was reduced by 24%. No statistically significant difference in capillarization and enzymatic activities was observed between the groups. In EDL a reduction in type I fiber distribution and 3-hydroxyacyl-CoA-dehydrogenase activity (27%) occurred after the flight. The small histochemical and biochemical changes reported suggest the interest in studying muscular adaptation during a flight of longer duration.

Adaptation, Physiological↗

PubMed1990

Skeletal muscle response to spaceflight, whole body suspension, and recovery in rats.

Comparisons of soleus and extensor digitorum longus (EDL) muscles from male Sprague-Dawley rats (350-400 g) after 7 days of weightlessness, 7 and 14 days of whole body suspension (WBS), and 7 days of recovery from WBS and from vivarium controls were made. Muscle mass loss of approximately 30% was observed in soleus after 7 and 14 days of WBS. Measurement of slow- and fast-twitch fibers showed significant alterations. Reductions in cross-sectional areas and increases in fiber densities in soleus after spaceflight and WBS were related to previous findings of muscle atrophy during unloading. Capillary density also showed a marked increase with unloading. Seven days of weightlessness were sufficient to effect a 20 and 15% loss in absolute muscle mass in soleus and EDL, respectively. However, the antigravity soleus was more responsive in terms of cross-sectional area reductions. After 7 days of recovery from WBS, with normal ambulatory loading, the parameters studied showed a reversal to control levels. Muscle plasticity, in terms of fiber and capillary responses, indicated differences in responses in the two types of muscles and further amplified that antigravity posture muscles are highly susceptible to unloading. Studies of recovery from spaceflight for both muscle metabolism and microvascular modifications are further justified.

Animals↗

PubMed1991

Lung and chest wall mechanics in microgravity.

We studied the effect of 15-20 s of weightlessness on lung, chest wall, and abdominal mechanics in five normal subjects inside an aircraft flying repeated parabolic trajectories. We measured flow at the mouth, thoracoabdominal and compartmental volume changes, and gastric pressure (Pga). In two subjects, esophageal pressures were measured as well, allowing for estimates of transdiaphragmatic pressure (Pdi). In all subjects functional residual capacity at 0 Gz decreased by 244 +/- 31 ml as a result of the inward displacement of the abdomen. End-expiratory Pga decreased from 6.8 +/- 0.8 cmH2O at 1 Gz to 2.5 +/- 0.3 cmH2O at Gz (P less than 0.005). Abdominal contribution to tidal volume increased from 0.33 +/- 0.05 to 0.51 +/- 0.04 at 0 Gz (P less than 0.001) but delta Pga showed no consistent change. Hence abdominal compliance increased from 43 +/- 9 to 70 +/- 10 ml/cmH2O (P less than 0.05). There was no consistent effect of Gz on tidal swings of Pdi, on pulmonary resistance and dynamic compliance, or on any of the timing parameters determining the temporal pattern of breathing. The results indicate that at 0 G respiratory mechanics are intermediate between those in the upright and supine postures at 1 G. In addition, analysis of end-expiratory pressures suggests that during weightlessness intra-abdominal pressure is zero, the diaphragm is passively tensed, and a residual small pleural pressure gradient may be present.

Abdomen↗

PubMed1992

Effects of spaceflight on hypothalamic peptide systems controlling pituitary growth hormone dynamics.

Immunohistochemical and in situ hybridization localization of peptides derived from, and mRNAs encoding, prepro-somatostatin (ppSS) and prepro-growth hormone-releasing factor (ppGRF) was carried out on hypothalami from rats flown on biosatellites COSMOS 1887 and 2044 to investigate possible effects of reduced gravity on central hypophysiotropic systems controlling growth hormone (GH) secretion. Results from the COSMOS 1887 mission indicated that both SS and GRF immunostaining in the median eminence were diminished in flight animals relative to controls; no differences between groups in staining for other peptidergic neurosecretory systems were apparent. Animals flown on COSMOS 2044 displayed a more pronounced depletion of GRF than SS immunoreactivity from neurosecretory terminals in the median eminence. In addition, flight animals displayed significant 46-50% reductions in the number and signal intensity of presumed hypophysiotropic cells in the arcuate nucleus expressing ppGRF mRNA; positively hybridized cells in the region surrounding the ventromedial nucleus were less markedly affected. Both indexes of ppSS mRNA levels in the anterior periventricular nucleus were similar in flight and control rats. An additional group of animals that experienced hindlimb suspension, a manipulation that mimics the effects of weightlessness on several parameters, did not differ from controls in any of the above measures. These data suggest that exposure to microgravity results in a preferential reduction in GRF peptide and mRNA levels in hypophysiotropic neurons, which may contribute to impaired GH secretion described previously in animals subjected to spaceflight. Effects of weightlessness are not mimicked by hindlimb suspension in this system.

Animals↗

PubMed1993

Spaceflight on STS-48 and earth-based unweighting produce similar effects on skeletal muscle of young rats.

Our knowledge of the effects of unweighting on skeletal muscle of juvenile rapidly growing rats has been obtained entirely by using hindlimb-suspension models. No spaceflight data on juvenile animals are available to validate these models of simulated weightlessness. Therefore, eight 26-day-old female Sprague-Dawley albino rats were exposed to 5.4 days of weightlessness aboard the space shuttle Discovery (mission STS-48, September 1991). An asynchronous ground control experiment mimicked the flight cage condition, ambient shuttle temperatures, and mission duration for a second group of rats. A third group of animals underwent hindlimb suspension for 5.4 days at ambient temperatures. Although all groups consumed food at a similar rate, flight animals gained a greater percentage of body mass per day (P < 0.05). Mass and protein data showed weight-bearing hindlimb muscles were most affected, with atrophy of the soleus and reduced growth of the plantaris and gastrocnemius in both the flight and suspended animals. In contrast, the non-weight-bearing extensor digitorum longus and tibialis anterior muscles grew normally. Earlier suspension studies showed that the soleus develops an increased sensitivity to insulin during unweighting atrophy, particularly for the uptake of 2-[1,2-3H]deoxyglucose. Therefore, this characteristic was studied in isolated muscles within 2 h after cessation of spaceflight or suspension. Insulin increased uptake 2.5- and 2.7-fold in soleus of flight and suspended animals, respectively, whereas it increased only 1.6-fold in control animals. In contrast, the effect of insulin was similar among the three groups for the extensor digitorum longus, which provides a control for potential systemic differences in the animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Life sciences space missions. Overview.

It has been known for many years that weightlessness induces changes in numerous physiological systems: the cardiovascular system declines in both aerobic capacity and orthostatic tolerance; there is a reduction in fluid and electrolyte balance, hematocrit, and certain immune parameters; bone and muscle mass and strength are reduced; various neurological responses include space motion sickness and posture and gate alterations. These responses are caused by the hypokinesia of weightlessness, the cephalic fluid shift, the unloading of the vestibular system, stress, and the altered temporal environment.

Animals↗

PubMed1986

The temporal response of bone to unloading.

A model of weightlessness in which the hindlimbs of rats are elevated by their tails at a 40 degrees angle to unload the hindlimbs while maintaining normal weight bearing on the forelimbs has been used to simulate certain conditions of space flight. When we used this model in growing rats, we found that growth in bone weight ceased by 1 week in the hindlimbs and lumbar vertebrae, whereas growth in bone weight in the forelimbs and cervical vertebrae remained unaffected. Within 2 weeks, however, the accretion of bone weight in the hindlimbs and lumbar vertebrae returned to normal despite continued skeletal unloading. Since bone weight in the growing rat is primarily determined by bone formation (bone resorption is modest), we investigated the effects of selective skeletal unloading on bone formation during 2 weeks of hindlimb elevation using radioisotope incorporation (with 45Ca and [3H]proline) and histomorphometry (with tetracycline labeling). The studies using radioisotope incorporation showed that bone formation was inhibited by the fifth day of skeletal unloading. By the 10th to 12th day, bone formation had returned toward normal. In comparison with cortical bone, cancellous bone (lumbar vertebrae and proximal tibiae) incorporated more 45Ca and [3H]proline (indicating greater metabolic activity) and had a greater absolute response to skeletal unloading. The results of these studies were confirmed by histomorphometric measurements of bone formation using triple tetracycline labeling. We conclude that this model of simulated weightlessness results in an initial inhibition of bone formation in the unloaded bones. This temporary cessation of bone formation is followed by a cessation in the accretion of bone weight, which then resumes at a normal rate by 14 days despite continued skeletal unloading. We believe that this cycle of inhibition and resumption of bone formation has profound implications for understanding bone dynamics during space flight, immobilization, or bed rest and offers an opportunity to study the hormonal and mechanical factors that regulate bone formation.

Animals↗

PubMed2005

Regulation of body fluid and salt homeostasis--from observations in space to new concepts on Earth.

The present manuscript summarizes recent discoveries that were made by studying salt and fluid homeostasis in weightlessness. These data indicate that 1. atrial natriuretic peptide appears not to play an important role in natriuresis in physiology, 2. the distribution of body fluids appears to be tightly coupled with hunger and thirst regulation, 3. intrathoracic pressure may be an important co-regulator of body fluid homeostasis, 4. a so far unknown low-affinity, high capacity osmotically inactive sodium storage mechanism appears to be present in humans that is acting through sodium/hydrogen exchange on glycosaminoglycans and might explain the pathophysiology, e.g., of salt sensitive hypertension. The surprising and unexpected data underline that weightlessness is an excellent tool to investigate the physiology of our human body: If we knew it, we should be able to predict changes that occur when gravity is absent. But, as data from space demonstrate, we do not.

Body Fluids↗

PubMed1975

The effect of gravity on galvanic nystagmus in rabbits.

The effect of gravity on a galvanic nystagmus provoked in rabbits was investigated. Weightlessness increased the amplitude but decreased the frequency as well as the speed of the nystagmus. During continuous galvanic stimulation the provoked nystagmus disappeared spontaneously after a period of 60-120 seconds. Weightlessness was able to arouse this nystagmus again. An explanation of this phenomenon might be that galvanic nystagmus undergoes a modifying effect from the vestibular maculae and their state of stimulation.

Acceleration↗

PubMedDate not supplied

[Some problems of space medicine].

The paper discusses the problems to be resolved by space medicine and the main stages in the development of this branch of science, beginning with the vertical launches of rockets and ending with the flights of orbital stations. On the basis of ground-based simulation experiments and real space flights it presents a classification of the major symptomocomplexes that may occur inflight. The paper describes the main stages of adaptation to weightlessness and physiological changes in the weightless state. The paper also outlines further pathways in the development of space medicine.

Adaptation, Physiological↗

PubMed1999

Distribution of 3H-nicotine in rat tissues under the influence of simulated microgravity.

Rat tail suspension offers a useful model to reproduce physiologic responses to weightlessness. The present study was conducted in the head-down-tilt (HDT) rat model to assess changes in metabolism of body tissues employing 3H-nicotine. Twelve male rats were used in the study. Half of the rats were tail suspended at 30 degrees for two weeks on a 12/12 light/dark cycle. During this period, body weight, food and fluid intakes were measured. At term, animals were anesthetized and injected i.v. with a solution containing 4 microcuries of nicotine. After 90 min the animals were sacrificed, exsanguinated and tissues (brain, blood, trachea, salivary gland, lung, heart, esophagus, spleen, kidneys and testes) were harvested. The distribution of 3H-nicotine per gram of each tissue was determined and calculated as percent of total injected radioactivity. Final body weights of suspended animals were significantly (P < 0.05) lower than those of controls (309 +/- 21 vs 350 +/- 11 g). 3H-Nicotine was retained in greatest amounts by the kidneys, followed in order by salivary glands, spleen, and gastrointestinal tissues. Compared to non-suspended control, the tissue retention of nicotine in suspended animals was decreased in the following tissues: esophagus (25%), aorta (25%), fundus (25%), trachea (22%), adrenals (18%), spleen (17%), and pancreas (12%). The decreased retention of nicotine in tissues from suspended animals may be indicative of the fluid shifts and changes in blood flow to those tissue beds. The lack of differences in nicotine retention in liver and kidney between control and suspended groups may implicate a normal metabolic function of these organs even under simulated weightlessness.

Animals↗

PubMedDate not supplied

[Genesis of vestibulo-autonomic disorders in space flight].

Some considerations on the mechanisms of vestibulo-vegetative disturbance in space flight are given on the basis of clinical observations, experience of otoneurological clinic, simulation experiments and examinations of cosmonauts. The starting point in these disturbances was a significant fact of blood redistribution in weightlessness and subsequent changes in hemodynamics, metabolism, etc. The body reactions to weightlessness seem to prepare pronounced vestibulo-vegetative reflexes to threshold and subthreshold vestibular stimuli induced by head and body movements in flight. Some aspects of the vestibular selection and training of cosmonauts are discussed from this point of view.

Autonomic Nervous System↗