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PubMedDate not supplied

The effect of the configuration and the interior design of a virtual weightless space station on human spatial orientation.

In a virtual weightless environment, subjects' orientation skills were studied to examine what kind of cognitive errors people make when they moved through the interior space of virtual space stations and what kind of visual information effectively decreases those errors. Subjects wearing a head-mounted display moved from one end to the other end in space station-like routes constructed of rectangular and cubical modules, and did Pointing and Modeling tasks. In Experiment 1, configurations of the routes were changed with such variables as the number of bends, the number of embedding planes, and the number of planes with respect to the body posture. The results indicated that spatial orientation ability was relevant to the variables and that orientational errors were explained by two causes. One of these was that the place, the direction, and the sequence of turns were incorrect. The other was that subjects did not recognize the rotation of the frame of reference, especially when they turned in pitch direction rather than in yaw. In Experiment 2, the effect of the interior design was examined by testing three design settings. Wall colors that showed the allocentric frame of reference and the different interior design of vertical and horizontal modules were effective; however, there was a limit to the effectiveness in complicated configurations.

Adult↗
PubMed1998

Postnatal development under conditions of simulated weightlessness and space flight.

The adaptability of the developing nervous system to environmental influences and the mechanisms underlying this plasticity has recently become a subject of interest in space neuroscience. Ground studies on neonatal rats using the tail suspension model of weightlessness have shown that the force of gravity clearly influences the events underlying the postnatal development of motor function. These effects depend on the age of the animal, duration of the perturbation and the motor function studied. A nine-day flight study has shown that a dam and neonates can develop under conditions of space flight. The motor function of the flight animals after landing was consistent with that seen in the tail suspension studies, being marked by limb joint extension. However, there were expected differences due to: (1) the unloading of the vestibular system in flight, which did not occur in the ground-based experiments; (2) differences between flight and suspension durations; and (3) the inability to evaluate motor function during the flight. The next step is to conduct experiments in space with the flexibility and rigor that is now limited to ground studies: an opportunity offered by the International Space Station.

Animals↗
PubMed1999

Biomedical study on combined effects of simulated weightlessness and emergent depressurization of spacecraft.

Cabin emergent depressurization (CED) may occur in spacecraft during manned space flight. The purpose of this paper was to study the combined effects of simulated weightlessness (SW) and CED factors on humans and animals. It was found that the amplitude of T wave of human electrocardiograms (ECG) significantly decreased in bed rest and hypoxia compared with the control condition (P<0.05), and that suspension with pure O2 induced severer edema in the lungs of rats than that in only a pure O2 environment. SW and pure O2 caused middle ear congestion and decreased the barofunction during pressure changes. These results indicate that human response to CED factors become more serious under SW because of the blood redistribution.

Aerospace Medicine↗
PubMed2002

Absence of center of mass control for leg abduction in long-term weightlessness in humans.

The present investigation describes for the first time leg lateral abduction performance during long-term microgravity exposure. Two astronauts took part in the experiments, starting 2 weeks into the mission and lasting for 5 months. Results on joint angles kinematics confirm previous investigations on parabolic flights, showing good task fulfillment for both subjects. Special interest was focused on whole body center of mass (CM) positioning. As in short-term microgravity, no initial CM lateral shift toward the 'supporting' leg was observed. In contrast with short-term microgravity and ground-based experiments, no stabilization of the CM medio-lateral position was found but a significant shift of CM toward the moving leg was observed. This suggests that the adaptation to sustained weightlessness might have led to a microgravity-specific motor strategy for leg abduction, which was not focused on CM strategy.

Adult↗
PubMed1997

Structural and functional adaptations of skeletal muscle to weightlessness.

This brief review examines the effects of weightlessness on the structure and function of human and rat skeletal muscle. Data collected from spaceflights or Earth-based models suggest that a rapid atrophy (5-8 days) occurs in lower limb muscles associated with impairments in muscle strength, physical work capacity and locomotor coordination. The reduction in muscle cross-sectional area cannot entirely explain the loss of strength in postural muscles suggesting a reduced neural drive. Muscle atrophy is accompanied by a general shift in the contractile and enzymatic profiles of a slow-twitch oxidative muscle toward that of a fast twitch glycolytic muscle. In humans, limited structural and functional data collected in astronauts after short periods of microgravity are qualitatively similar to those observed in rats after real or simulated microgravity suggesting that animal models are relevant to muscle research in space. A preventive prescription i.e. exercise or pharmacological treatment, cannot be proposed until future research has better defined the basic mechanisms of muscle plasticity during long duration spaceflights.

Adaptation, Physiological↗
PubMed1992

Spatial orientation in weightless environments.

Illusions of body inversion and of vehicle inversion can be evoked by exposure to weightlessness in the microgravity conditions of orbital and parabolic flight. Such illusions can involve all possible combinations of self-inversion and vehicle inversion. In the absence of any patterns of external stimulation, individuals may lose all sense of body orientation to their surroundings while retaining a sense of their overall body configuration and cognitive awareness of their actual position. Touch and pressure cues provide a perceptual 'down' in the absence of visual input. When vision is allowed, apparent orientation is influenced by a variety of factors including the direction of gaze, the architectural layout of the vehicle, and sight of the body. The relative importance of the various factors affecting orientation changes with repeated exposure. The virtual absence of sensations of falling during exposure to free-fall emphasizes the role of cognitive factors in experienced orientation.

Adolescent↗
PubMed2005

The influence of weightlessness on pharmacokinetics.

The primary hostile factor during a spaceflight is the lack of gravity, which can induce space motion sickness and act on bones, muscles and the cardiovascular system. These physiological effects may modify the pharmacokinetics of the drugs administered during the flight producing reduced pharmacological activity or appearance of adverse effects. Given the small number of spaceflights and the difficulties of conducting experiments during missions, pharmacokinetic data obtained in flight are insufficient to determine if drug monitoring is necessary for the drugs present in the onboard medical kit. Therefore, validated earthbound models like tail-suspension performed with animals and long-term bedrest performed with human volunteers are used to simulate weightlessness and to study the pharmacokinetic variations of either absorption, distribution, or elimination of drugs. As a result of these studies, it is possible to make some dosing recommendations but more information is necessary to predict with precision all of the pharmacokinetic variations occurring in spaceflight. To collect more pharmacokinetic information, head-down bedrest studies are still the best solution and as saliva is an appropriate substitution for plasma for some drugs, salivary sampling can be planned during flights.

Animals↗
PubMedDate not supplied

Graviresponses of gliding and swimming Loxodes using step transition to weightlessness.

Cells of Loxodes striatus were adjusted to defined culturing, experimental solution O2-supply, temperature, and state of equilibration to be subjected to step type transition of acceleration from normal gravity, (1 g) to the weightless condition (microgravity) during free fall in a 500 m drop shaft. Cellular locomotion inside a vertical experimental chamber was recorded preceding transition and during 10 s of microgravity. Cell tracks from video records were used to separate cells gliding along a solid surface from free swimmers, and to determine gravitaxis and gravikenesis of gliding and swimming cells. With O2 concentrations > or = 40% air saturation gliders and swimmers showed a positive gravitaxis. In microgravity gravitaxis of gliders relaxed within 5 s whereas gravitaxis relaxation of swimmers was not completed even after 10 s. Rates of horizontal gliders (319 micrometers/s) exceeded those, of horizontal swimmers (275 micrometers/s). Relaxation of gravikinesis was incomplete after 10 s of microgravity. Analysis of the locomotion rates during the g-step transition revealed that gliders sediment more slowly, than swimmers (14 versus 45 micrometers/s). The gravikinesis of gliders cancelled sedimentation effects during upward and downward locomotion tending to maintain cells at a predetermined level inside sediments of a freshwater habitat. At > or = 40% air saturation, gravikinesis of swimmers augmented the speed of the majority of cells during gravitaxis, which favours fast vertical migrations of Loxodes.

Animals↗
PubMed1984

Spatial orientation in weightlessness and readaptation to earth's gravity.

Unusual vestibular responses to head movements in weightlessness may produce spatial orientation illusions and symptoms of space motion sickness. An integrated set of experiments was performed during Spacelab 1, as well as before and after the flight, to evaluate responses mediated by the otolith organs and semicircular canals. A variety of measurements were used, including eye movements, postural control, perception of orientation, and susceptibility to space sickness.

Acceleration↗
PubMed1984

Mass discrimination during prolonged weightlessness.

Thresholds for mass discrimination under zero gravity in flight were found to be higher by a factor of about 1.8 than those for weight discrimination before flight. This suggests that humans are not as sensitive to inertial mass as they are to weight, and that adaptation can only partially compensate for loss of gravity. Weight discrimination thresholds were raised for 2 or 3 days after flight, suggesting an aftereffect of adaptation to weightlessness.

Adaptation, Physiological↗
PubMed1983

Effects of weightlessness on body composition in the rat.

Five male rats were exposed to 18.5 days of weightlessness in the Soviet mission COSMOS 1129 (flight group) and killed after reentry. They were immediately dissected into three major body subdivisions: musculoskeletal system, skin, and pooled viscera analyzed for fat, water, solids, and six elements. These results, expressed as percentages of the fat-free body or its components, were compared with two groups of terrestrial controls: one subjected to a flight simulation in a spacecraft mock-up and the other under standard vivarium conditions. Relative to the control groups the flight group showed 1) a reduced fraction of total body water, 2) a net shift of body water from skin to viscera, 3) a marked diminution in fraction of extracellular water in the fat-free body, 4) a marked reduction in fraction of bone mineral, 5) no change in the quantity of stored fat or adrenal masses, and 6) a net increase in total muscle mass as indicated by total body creatine, protein, and body cell mass.

Adipose Tissue↗
PubMed1988

Trabecular bone remodeling after seven days of weightlessness exposure (BIOCOSMOS 1667).

Seven male rats were exposed to 7 days of weightlessness in the Soviet mission COSMOS 1667 and compared with seven control rats by bone histomorphometric methods. In proximal tibial metaphysis, the trabecular bone volume was markedly reduced in flight animals. Trabeculae were decreased in number and thickness; this probably leads to alteration of bone mechanical properties. Formation activity (reflected by measurements of osteoid seams) was decreased at trabecular and endosteal levels. Resorption activity (estimated by count of osteoclast number and active resorption surfaces using a histoenzymologic method) remained unchanged. The imbalance between these cellular activities appears to be responsible for the loss of trabecular bone mass. In proximal femoral metaphysis, measurements were performed in an area located under the muscular insertions. The trabecular bone volume, despite a slight decrease in flight rats, was not significantly different from that of control rats. Furthermore, osteoclastic and osteoid parameters were unchanged. Differential responses between these two long bones need additional investigations. In thoracic and lumbar vertebrae no detectable change in bone mass and bone resorption parameters was found.

Animals↗
PubMed1978

Distribution of pulmonary ventilation and perfusion during short periods of weightlessness.

Information on the distributions of pulmonary ventilation and perfusion was obtained from four subjects on board a Learjet during 112 weightless periods lasting up to 27 s each. Zero gravity (G) was obtained during all or part of each test by varying the aircraft flight profile. Single-breath N2 washouts were performed with the test inspiration containing an initial bolus of argon at residual volume (RV). When the test inspiration was at 0 G, and the washout at 0 G or greater, the terminal rises and the cardiogenic oscillations in both N2 and argon were small and often absent. If instead the test inspiration was at 1 G with the washout at 0 G, the terminal rises were again small or absent but the cardiogenic oscillations remained. The terminal rise and the cardiogenic oscillations for N2, but not argon, were also nearly eliminated by performing just the preliminary exhalation to RV at 0 G with the test inspiration and washout following at 1 G. Aleveolar plateaus for N2 sloped upward at 0 G apparently due to nontopographical inequalities of ventilation. In further tests during air breathing, recordings were made of expired partial pressure of oxygen PO2) and carbon dioxide (POO2) following a brief hyperventilation and a 15-s breath hold. These recordings revealed marked cardiogenic oscillations in PO2 and PCO2 at 1 G that were enhanced at 2 G but almost eliminated at 0 G. The results suggest that virtually all the topographical inequality of ventilation, blood flow, and lung volume seen under 1-G conditions are abolished during short periods of 0 G.

Adult↗
PubMed1986

Mechanism for negative water balance during weightlessness: an hypothesis.

The mechanism for the apparent decrease in body fluid volume in astronauts during spaceflight remains obscure. The widespread postulate that the hypohydration is the result of the Henry-Gauer reflex, a diuresis caused by inhibition of vasopressin secretion resulting from increased left and perhaps right atrial (central) venous pressure, has not been established with direct measurements on astronauts. An hypothesis is proposed to account for fluid-electrolyte shifts during weightlessness. A moderate but transient increase in central venous pressure occurs when orbit is entered that is insufficient to activate the Henry-Gauer reflex but sufficient to stimulate the release of atrial natriuretic peptides. Increased sodium excretion would facilitate some increased urinary water loss. The resulting relatively dilute plasma and interstitial fluids would cause fluid to shift into the cellular space, resulting in edema in the head and trunk and inhibition of thirst and drinking. Thus the negative water balance in astronauts would be caused by a gradual natriuresis and diuresis coupled with reduced fluid intake.

Biomechanical Phenomena↗
PubMed1995

Central and peripheral sympathetic activities in rats during recovery from simulated weightlessness.

Rats were tail suspended, keeping their forelimbs weight bearing for 14 days, and then allowed to recover for a short (6-h) or a long (24-h) period to assess the behavior of the sympathetic nervous system after weightless simulation. Sympathetic activity was determined by measuring norepinephrine (NE) turnover in the brain stem cell groups involved in central blood pressure control and in organs playing a key role in the cardiovascular regulation (heart and kidneys). The NE turnover was greatly reduced in the rostral (-56%; P < 0.001) and caudal (-73%; P < 0.001) A2 nucleus of suspended rats but was unchanged in the A1, A5, and A6 cell groups compared with attached rats. The NE turnover in the cardiac atria (-34%; P < 0.001) and ventricles (-35%; P < 0.001) and kidneys (-31%; P < 0.001) was decreased after suspension. The central and peripheral sympathetic activities returned to normal within 24 h of release from suspension, but there was hyperactivity after 6 h of recovery. This raises the problem of interpreting the results obtained in animals killed a few hours after return from spaceflight.

Animals↗
PubMed2003

Effect of gender on bone turnover in adult rats during simulated weightlessness.

Prologned spaceflight results in bone loss in astronauts, but there is considerable individual variation. The goal of this rat study was to determine whether gender influences bone loss during simulated weightlessness. Six-month-old Fisher 344 rats were hindlimb unweighted for 2 wk, after which the proximal tibiae were evaluated by histomorphometry. There were gender differences in tibia length, bone area, cancellous bone architecture, and bone formation. Compared with female rats, male rats had an 11.6% longer tibiae, a 27.8% greater cortical bone area, and a 37.6% greater trabecular separation. Conversely, female rats had greater cortical (316%) and cancellous (145%) bone formation rates, 28.6% more cancellous bone, and 30% greater trabecular number. Hindlimb unweighting resulted in large reductions in periosteal bone formation and mineral apposition rate in both genders. Unweighting also caused cancellous bone loss in both genders; trabecular number was decreased, and trabecular separation was increased. There was, however, no change in trabecular thickness in either gender. These architectural changes in cancellous bone were associated with decreases in bone formation and steady-state mRNA levels for bone matrix proteins and cancellous bone resorption. In conclusion, there are major gender-related differences in bone mass and turnover; however, the bone loss in hindlimb unweighted adult male and female rats appears to be due to similar mechanisms.

Animals↗
PubMed2003

Influence of simulated weightlessness on the oral pharmacokinetics of acetaminophen as a gastric emptying probe in man: a plasma and a saliva study.

This study evaluated the effect of simulated weightlessness on gastric emptying, using acetaminophen as a probe and -6 degrees head-down bed rest to simulate zero gravity. Eighteen volunteers were given 1 g of acetaminophen orally before the bed rest and at days 1, 18, and 80. Cmax, tmax, AUC0- infinity, AUC0-t, and t1/2 were calculated for plasma and saliva. The plasma Cmax showed a significant increase (10.43 microg/mL [day 1] to 14.74 microg/mL [day 80]), while tmax significantly decreased (1.41 h [day 1] to 0.91 h [day 80]). Similar results were obtained with saliva, and there were significant increases in the AUCs. The good correlation between the plasma and saliva data suggests that saliva sampling can be valid for acetaminophen pharmacokinetics. The changes in Cmax and tmax indicated more rapid drug absorption, which could have been as a result of faster gastric emptying or an increased blood flow to the intestine.

Acetaminophen↗
PubMed1984

Effects of simulated weightlessness on bone mineral metabolism.

Space flight and bedrest result in a negative calcium balance and osteopenia. The mechanisms underlying these events are not well understood. In particular, it is not clear whether systemic or local factors are preeminent in mediating the effects of gravity on bone mineral content. Using a rat model that unweights only the hindlimbs, we determined whether the osteopenia induced in these rats was generalized or restricted to the unweighted limbs, and whether changes in intestinal calcium transport contributed to the alterations in bone calcium content. In this model, the hindquarters were elevated using the tail at an approximately 40 degrees angle for up to 15 days. The tibia and lumbar vertebra from experimental rats contained substantially less calcium than the same bones from pair-fed controls; at 15 days, the tibia was 86.2 +/- 2.5% of the control value (mean +/- SE), and the vertebra was 75.5 +/- 3.5% of control value (mean +/- SE). However, these differences were found only for the unweighted bones; the mandible and humerus showed no differences between experimental and pair-fed control rats. When calcium uptake by bone was evaluated after 45Ca administration, we observed an initial decrease in uptake at 5 days only in the tibia [percentage of control value, 60.5 +/- 5.5, (mean +/- SE)] and vertebra (percentage of control value, 74.3 +/- 3.7) when experimental animals were compared to pair-fed controls; there was no decrease in the humerus and mandible. However, after 10 days of unweighting , calcium uptake in the tibia and vertebra of experimental animals returned to control levels and by 15 days exceeded control levels (the tibia was 125.8 +/- 5.8% of the control value and the vertebra was 136.2 +/- 9.6% of the control value) despite the progressive decrease in total bone calcium compared to that in pair-fed controls. At no time could we demonstrate a difference in duodenal calcium transport between experimental and control animals. These data suggest that in this model, which simulates certain aspects of weightlessness, changes in local factors within the unweighted bones may have a greater impact on bone mass and turnover than changes in systemic factors that regulate overall bone mineral homeostasis.

Animals↗