Search PubMed⌕ Search

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.

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

At least 127 records · Page 7Linked to original sources
PubMedDate not supplied

[Effect of weightlessness on the functions of perception and the reproduction of gravitational vertical in response to optokinetic stimulation].

In weightlessness spatial orientation largely depends on coordinated interaction of sensory systems involved in static orientation. The purpose of the present study was to quantify perception of spatial coordinates in response to optokinetic stimulation. Effects of weightlessness were simulated by dry water immersion hypokinesia. A custom-made optokinetic stimulator equipped with a device to measure perception of the gravitational vertical in response to optokinetic stimulation was used. A special platform with rubber bungee cords was employed to determine the role of the proprioceptive afferent input. It was demonstrated that during immersion day 1 the angle of erroneous perception of the vertical line consistently increased. By immersion day 3 the angle diminished suggesting adaptive developments. Additional proprioceptive inflow during immersion reduced significantly the error of perception. These findings indicate that the proprioceptive afferent input plays an important role in the mechanisms of spatial orientation at an early stage of exposure to weightlessness.

Adult↗
PubMedDate not supplied

[Chief methods of modeling the biological effects of weightlessness].

The paper describes basic principles related to weightlessness simulation. In ground-based experiments zero-g is simulated with respect to the conceptual mechanisms of weightlessness effects on the body. The main components of the effects are considered to be elimination of deformations and fluid redistribution. The paper surveys and summarizes different methods of weightlessness simulation. It discusses advantages and disadvantages of water immersion, prolonged bed rest, hypokinesia, suspension in special devices with many degrees of freedom, walking on a treadmill at different angles, etc. The paper describes simulation of accentuated individual effects of zero-g during an exposure to longitudinal acceleration. It presents experimental physiological methods of simulation and symptoms of zero-g effects under normal laboratory conditions. The paper emphasizes inadequate use of some simulation techniques.

Bed Rest↗
PubMed1988

Leg vascular responsiveness during acute orthostasis following simulated weightlessness.

Ten men (35-49 years old) underwent lower body negative pressure (LBNP) exposures before and after 10 d of continuous 6 degrees head-down bedrest in order to predict the effect of weightlessness on the responsiveness of leg vasculature to an orthostatic stress. Heart rate (HR), mean arterial blood pressure (MAP), and impedance rheographic indices of arterial pulse volume (APV) of the legs were measured during rest and at 1 min of -30 mm Hg LBNP. Bedrest-induced deconditioning was manifested by decreases (p less than 0.05) in plasma volume (17%), peak oxygen uptake (16%), and LBNP tolerance (17%). Resting HR was unchanged after bedrest, but HR was higher (p less than 0.05) at 1 min of -30 mm Hg LBNP after, compared with before, bedrest. Responses of MAP to -30 mm Hg LBNP were not altered by bedrest. Resting APV was decreased (p less than 0.05) by simulated weightlessness. However, APV was reduced (p less than 0.05) from rest to 1 min -30 mm Hg LBNP by the same relative magnitude before and after bedrest (-21.4 +/- 3.4% and -20.5 +/- 2.7%, respectively). We conclude that peripheral arterial vasoconstriction, as indicated by reductions in APV during LBNP, was not affected by bedrest. These results suggest that there was no apparent alteration in responsiveness of the leg vasculature following simulated weightlessness. Therefore, it appears unlikely that control mechanisms of peripheral resistance contribute significantly to reduced orthostatic tolerance following spaceflight.

Adaptation, Physiological↗
PubMed1987

Potential benefits of maximal exercise just prior to return from weightlessness.

The purpose of this study was to determine whether performance of a single maximal bout of exercise during weightlessness within hours of return to earth would enhance recovery of aerobic fitness and physical work capacities under a 1G environment. Ten healthy men (36-51 yr) underwent maximal supine exercise followed by upright maximal exercise before and after a 10-d bedrest period in the 6 degrees headdown position. A graded maximal supine cycle ergometer test was performed before and at the end of bedrest to simulate exercise during weightlessness. Following 3 h of resumption of the upright posture from the supine exercise test, a second maximal exercise test was performed on a treadmill to measure work capacity under conditions of 1G. Compared to before bedrest, peak VO2 decreased (p less than 0.05) by 8.7% and peak HR increased (p less than 0.05) by 5.6% in the supine cycle test at the end of bedrest. However, there were no significant changes in peak VO2 and peak HR in the upright treadmill test following bedrest. These data, based on a simulation, suggest that one bout of maximal leg exercise prior to return from 10 d of weightlessness may be adequate to restore preflight aerobic fitness and physical work capacity.

Adult↗
PubMedDate not supplied

[Skeletal musculature of rats during modeling of the physiological effects of weightlessness (morphological study)].

In the experiment rats were suspended in the head-down position (at -15 to -20 degrees) for 21 days. To study the effect of this exposure on skeletal muscles of their fore- and hindlimbs, morphological and histochemical methods were used. Changes in the hindlimbs were similar to those seen in real weightlessness of similar duration. The two antigravitational muscles - soleus and gastrocnemius muscles - showed greatest changes, i.e. atrophic and metabolic shifts. The biceps brachii muscle that changes insignificantly in the weightless state developed a destructive process (with degradation of myofibers) that was later replaced with a reparative process. The changes in this muscle are assumed to be associated with hemodynamic disorders. It is recognized that the method of rat suspension is adequate for a ground-based study of morphological effects of weightlessness on hindlimbs and is unacceptable for that of forelimbs where the exposure induces microcirculation disorders.

Animals↗
PubMedDate not supplied

[Use of freeze-dried products in weightlessness].

The paper describes the manufacture of food products that can be eaten in weightlessness with the aid of regular table-ware. The consistence of products was altered as a result of an addition of water or modified starch. The resultant products were tested during short-term weightlessness aboard the aircraft-laboratory TU-104A. It was demonstrated that in weightlessness products having sufficient viscosity can be eaten with the help of regular table-ware. An addition of thickening agents, e. g. modified starch, helped to obtain products with necessary properties.

Cooking and Eating Utensils↗
PubMed1981

[Features of the lifting reflex in the white rat following prolonged space flight (effect of weightlessness and artificial gravity)].

The latent time of the lifting reflex (LTLR) was studied in weightless and centrifuged SPF-Wistar rats before and after 19-day space flights onboard Cosmos-936 and 1129. The LTLR was determined when the lifting reflex was induced in a special trainer on the basis of the mechanical component of muscle reaction (MCMR) and electromyography of the oculomotor and gastrocnemius muscles. The LTLR persisted in all the animals postflight. The LTLR of weightless rats as determined by the MCMR increased significantly, and as determined by electromyography, remained unchanged. Centrifuged rats did not show significant changes in the LPLR. It is believed that the initial stages of the lifting reaction - vestibular receptors and conductive pathways - remained unaltered in weightlessness. Changes in the LPLR observed after prolonged space flights are consequent on muscle function, representing the final stage of the lifting reflex.

Animals↗
PubMed1978

[Comparative study of the lymphoid organs of rats aboard a space flight under weightless and artificial gravity conditions].

A comparative histological investigation of the thymus, spleen and inguinal lymph nodes has been performed in the rats flown for 18.5 days on board the biosatellite "Cosmos-936" under the conditions of weightlessness and artificial gravitation (acceleration 1 g) imitating terrestrial magnetism. It has been stated that in the animals that were under the conditions of weightless ness during the flight and were sacrificed 4.5--13 h after they have landed the Earth, accidental involution of lymphoid organs is noted with morphological signs in them of an acute stress in the form of massive degeneration of the thymus lymphocytes and neutrophilic infiltration of the spleen. In rats that during the flight were subjected to the effect of artificial gravitation there was noted neither involution of the lymphoid organs nor morphological signs of acute stress in them. One of the main cause of acute stress in the rats subjected to weightlessness during the space flight is supposed to be transition to the terrestrial gravitation.

Animals↗
PubMed1980

[Effect of weightlessness and artificial gravitation on morphological manifestations of the adrenal cortex reaction in rats after space flight on board the biosatellite "Cosmos-936"].

Comparing the changes revealed in the adrenals of rats subjected to weightlessness and artificial gravitation, it has been stated that rotation of the animals in the centrifuge, while flying (with an acceleration of lg), prevents development of morphological stress reaction as a response to landing. After the effect of weightlessness, return to normal gravitation is accompanied with definite signs of an acute stress-reaction in the rat adrenal cortex. Differences in the adrenal reaction of the animals of the groups compared speak in favour of the fact that application of artificial gravitation in an orbital space flight contributes to level the changes resulting from weightlessness and, hence, increase the organism's stability to stress effects, while returning to the Earth.

Adrenal Cortex↗
PubMed1980

Effect of weightlessness and centrifugation on red cell survival in rats subjected to space flight.

Rats were flown aboard the Soviet biosatellite Cosmos 936 for 18.5 d during August, 1977. Five rats were subjected to near-weightless space flight, as with Cosmos 782, and five rats were subjected to a 1-G force via an on-board centrifuge. These rats and three control groups were injected with 2-14C glycine 19 d preflight. The flight rats were recovered from orbit after 18.5 d of space flight. Erythrocyte hemolysis and lifespan were evaluated in the five groups of rats by quantitation of radioactive carbon monoxide exhaled in the breath which arises from the breakdown of the previously labeled hemoglobin. The results support our previous findings wherein hemolysis was found to increase as a result of weightless space flight. A comparison to the centrifuged animals indicates that artificial gravity attenuates the effect of weightlessness on hemolysis and appears to normalize the hemolytic rate in the early postflight period.

Animals↗
PubMed1993

Multisensory, cognitive, and motor influences on human spatial orientation in weightlessness.

Exposure to weightlessness affects the control and appreciation of body position and orientation. In free fall the perception of one's own orientation and that of the surroundings is dependent on the presence or absence of contact cues, whether part of the body is visible in relation to the architecturally defined verticals of the space craft, cognitive factors, and exposure history. Sensations of falling are not elicited in free fall when the eyes are closed or the visual field is stabilized. This indicates that visual and cognitive factors as well as vestibular ones must be implicated in the genesis of such sensations under normal circumstances. Position sense of the limbs is also degraded in free fall. This may be due to alterations in skeletal muscle spindle gain owing to a decreased otolith-spinal activation. We provide evidence that during initial exposure to weightlessness there is a decrease in muscle stiffness which affects movement accuracy. The altered loading of the skeletal muscles due to the head and body being weightless are shown to be significant etiological factors in space motion sickness.

Cognition↗
PubMed1977

Discussion of the combined effect of weightlessness and ionizing radiation on the mammalian body: morphological data.

The combined effect of weightlessness and ionizing radiation, from the Cs137 source at 800 rads for 24 h, on the animal body was studied. The morphological examination of organs and tissues of rats flown aboard the biosatellite Cosmos-690, kept in the ground-based simulation experiment, and kept in the vivarium, indicated prevalence of radiation-induced changes in both experimental groups of rats. An exposure of animals to space flight factors did not produce a substantial aggravation of radiation-induced effects. This is indicated by the lack of significant differences in the weight of testes, thymus, and spleen of flight and simulation rats. However, this exposure affected adversely the development of reparative processes in the hemopoietic tissue of bone marrow. Inflight irradiation aggravated weightlessness-induced changes. A combined effect of weightlessness and irradiation did not result in the summation of the effects exerted on skeletal muscles by either factor alone.

Animals↗
PubMed1996

[Orientation illusions in weightlessness].

Results of the ANKETA and OPROSNIK experiments performed by 102 cosmonauts in and post flight were analysed. It is shown that perceptive disturbances (orientation illusions) developed in the period of early adaptation to weightlessness were not an inherent feature of individual persons but regular responses of the body sensory systems. The character, intensity, duration, and the dynamics of illusion responses in space mission are described. Forms of the vestibular disorders, types of adaptation of the sensory systems and classification of spontaneous illusion responses in the weightless environment are presented. Hypothesis for possible mechanisms of the illusion responses in weightlessness is suggested.

Adaptation, Psychological↗
PubMed1996

[Effect of weightlessness on the mother-fetus system (results of embryological experiment NIH-R1 abroad the "Space Shuttle"].

Female rats were exposed to weightlessness in the mid-deck of US "Space Shuttle" in the period between days 9 to 20 of pregnancy and examined on Earth post flight. No significant structural anomalies threatening the life and normal development were found in newborn rats carried by mothers under the conditions of weightless exposures. Water, Na, K, Ca, Fe and Cu contents in fetal and placental tissues of the flight animals were not changed. Differences between the flight and ground-based synchronous controls, or the rates of formation of the fetal skeleton were not revealed. Comparison of these data with results of the experiment aboard biosatellite "Cosmos 1514" in which female rats stayed in weightlessness from day 13 to 18 of pregnancy indicates that the two-fold increase of space flight duration did not add changes in the state of fetuses.

Animals↗
PubMed1976

Effect of penetrating radiation on skeletal muscles of rats in weightlessness.

The isoenzyme composition of lactate dehydrogenase of soleus and plantaris muscles of rats flown for 20.5 d aboard the biosatellite Cosmos-690 and irradiated with a dose of 800 rad was investigated. The muscles exposed to weightlessness per se and weightlessness combined with radiation showed similar changes in their carbohydrate metabolism. On return to 1 G, readaptation of irradiated rats developed less rapidly than of animals exposed to weightlessness alone.

Animals↗
PubMed2002

Lipid peroxidation in rat brain is increased by simulated weightlessness and decreased by a soy-protein diet.

This study tested whether or not simulated weightlessness by tail-suspension increases the levels of lipid peroxidation products in rat brain. The brain tissues of rats on a soybean diet were also assayed for lipid peroxidation products to evaluate the possible role of soy-protein as a dietary anti-oxidant. Male Sprague-Dawley rats were used. Group 1 rats were fed standard Purina rat chow ad libidum and served as controls. Group 2 rats were fed a soybean diet containing 37% soy-protein and were not tail-suspended. Group 3 rats were fed standard Purina rat chow ad libidum and were tail-suspended to induce simulated weightlessness. After 2 wk, all of the rats were killed. Each whole brain was segmented into frontal cortex, cerebellum, and brain stem. After a specific weight of each segment was excised, the residual tissues were combined and used as a whole brain sample. The samples were analyzed for lipid peroxidation products by a chromogenic assay that reacts with malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE). The mean concentrations of lipid peroxidation products (MDA plus 4-HNE) in whole brain, frontal cortex, cerebellum, and brain stem of the control rats ranged from 16 to 18 micromol/g; the corresponding means ranged from 10 to 13 micromol/g in rats fed the soybean diet, and from 22 to 26 micromol/g in the tail-suspended rats. Thus, the mean levels of lipid peroxidation products in brain tissues were decreased in the rats fed the soy diet and were increased in the rats that were tail-suspended to simulate weightlessness, when compared to those of rats fed a regular diet.

Aldehydes↗
PubMed2002

Effect of simulated weightlessness on pressure-volume relationships of femoral veins in vivo of New-Zealand rabbits.

OBJECTIVES: To observe the change of pressure-volume relationships of femoral veins of rabbits after simulated weightlessness. METHODS: Head-down tilt(HDT) -20 degrees rabbit model was used to simulate weightlessness .24 healthy male New-Zealand Rabbits were randomly divided into 21d HDT group, 10d HDT group and control group, with 8 in each. The pressure-volume relationships of rabbits femoral veins were measured. RESULT: The femoral vein P-V relationship curves of HDT groups were shifted to larger volume change ratio than that of control group. The P-V relationship curve of the 21d HDT group was shifted more obviously than that of HDT-10d. B1 and B2 in quadratic equations of 21d HDT group were significantly higher than these value of 10d HDT group and control group during expansion (inflow) and collapse (outflow) (P<0.01). CONCLUSIONS: The femoral venous compliance increased after weightlessness simulation and the femoral venous compliance of 21d-HDT increased more obviously than that of 10d-HDT.

Comparative Study↗
PubMed1999

Brain norepinephrine changes with simulated weightlessness and relation to exercise training.

Maintenance of nervous system function during periods of a deconditioning syndrome is important to prevent diminished psychological/behavioral, and physiological function observed during periods of bed rest, physical inactivity, and weightlessness. A main neurotransmitter is norepinephrine (NE), and its regulation yields insight into nervous system function. This research tested the hypotheses that, 1) deconditioning syndrome induced by simulated weightlessness of 9 days via the head-down tilt (HDT) model results in a blunted noradrenergic turnover rate in selected brain tissue and, 2) that exercise training acts as a countermeasure for these changes in noradrenergic activity. Male Sprague-Dawley rats (3 months, n = 60) were divided into either a HDT (HDT, n = 20), cage control (CAGE-CN, n = 20) or an exercise trained HDT (HDT-EX, n = 20) group. Each group was further subdivided into a saline (n = 10) or alpha-methyl-tyrosine (AM, n = 10) (200 mg/kg) injected subgroup. Animals in the HDT groups were tail suspended in a 30 degrees head-down tilt position for 9 days. Norepinephrine turnover was determined 3 h following administration of saline or alpha-methyl-para-tyrosine. The NE turnover rate (ng gm(-1) x h(-1)) for the CN, HDT, and HDT-EX groups, respectively, were as follows: locus coeruleus, 63 +/- 33, *134 +/- 65, 85 +/- 61; hypothalamus, 195 +/- 50, *47 +/- 47; *93 +/- 34; cerebellum, 10 +/- 18, *65 +/- 15, *53 +/- 19; cerebral cortex, 6 +/- 20, *28 +/- 15, *68 +/- 22. (*Denotes significant difference from the control group at the p < or = 0.05 level of significance; +denotes significant difference from the HDT group at the p < or = 0.05 level of significance.) These findings suggest that: 1) norepinephrine turnover rate adapts in a tissue-specific manner following a 9-day tail suspension, 2) increased norepinephrine turnover rates and norepinephrine tissue content in the HDT group are consistent with neural adaptation to a chronic stress response.

Analysis of Variance↗