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PubMed1989

Space Sled--a device for the investigation of the physiological effects of weightlessness.

Space Sled is a device for providing controlled linear acceleration stimuli in the microgravity environment of orbital flight. The scientific objectives of the experiments which used Space Sled on the D-1 Spacelab mission were to study aspects of otolith organ (that is, that part of the inner ear which transduces linear accelerations) function and adaptation in weightlessness. Space Sled comprises electrical and mechanical sub-systems. The latter is made up of a carriage running on twin rails that are fixed to the floor of Spacelab. The assembly is 6 m long with a working section of 3.5 m. The seat accommodating the test subject can be mounted on the carriage in any of three orthogonal positions. The carriage is coupled by a flexible steel cable to a servo-controlled electric motor which is capable of producing a peak acceleration of 2 m/s2 and peak velocity of 2.4 m/s. In the event of failure of comprehensive safety circuits in the electrical sub-system, a mechanical snubber, of crushable honeycomb construction, limits the deceleration to 20 m/s2. Mechanical structures providing carriage guidance, Sled/Spacelab interfaces, carriage latching, motor mounting and cable tensioning are detailed in the paper.

Acceleration↗
PubMed2006

Osteocyte apoptosis is induced by weightlessness in mice and precedes osteoclast recruitment and bone loss.

UNLABELLED: Mechanical stimulation of cultured osteocytic cells attenuates their apoptosis. We report here that, conversely, reduced mechanical forces in the murine model of unloading by tail suspension increases the prevalence of osteocyte apoptosis, followed by bone resorption and loss of mineral and strength. INTRODUCTION: Mechanical loading is critical for the maintenance of bone mass; weightlessness, as with reduced physical activity in old age, bed rest, or space flight, invariably leads to bone loss. However, the cellular and molecular mechanisms responsible for these phenomena are poorly understood. Based on our earlier findings that physiologic levels of mechanical strain prevent apoptosis of osteocytic cells in vitro, we examined here whether, conversely, reduced mechanical forces increase the prevalence of osteocyte apoptosis in vivo and whether this event is linked to bone loss. MATERIALS AND METHODS: Swiss Webster mice or OG2-11beta-hydroxysteroid dehydrogenase type 2 (OG2-11beta-HSD2) transgenic mice and wildtype littermates were tail-suspended or kept under ambulatory conditions. Static and dynamic histomorphometry and osteocyte and osteoblast apoptosis by in situ end-labeling (ISEL) were assessed in lumbar vertebra; spinal BMD was measured by DXA; and bone strength was measured by vertebral compression. RESULTS: We show that within 3 days of tail suspension, mice exhibited an increased incidence of osteocyte apoptosis in both trabecular and cortical bone. This change was followed 2 weeks later by increased osteoclast number and cortical porosity, reduced trabecular and cortical width, and decreased spinal BMD and vertebral strength. Importantly, whereas in ambulatory animals, apoptotic osteocytes were randomly distributed, in unloaded mice, apoptotic osteocytes were preferentially sequestered in endosteal cortical bone--the site that was subsequently resorbed. The effect of unloading on osteocyte apoptosis and bone resorption was reproduced in transgenic mice in which osteocytes are refractory to glucocorticoid action, indicating that stress-induced hypercortisolemia cannot account for these effects. CONCLUSIONS: We conclude that diminished mechanical forces eliminate signals that maintain osteocyte viability, thereby leading to apoptosis. Dying osteocytes in turn become the beacons for osteoclast recruitment to the vicinity and the resulting increase in bone resorption and bone loss.

Animals↗
PubMed1995

Cerebellar afferents to neuroendocrine cells: implications for adaptive responses to simulated weightlessness.

The hypothalamo-neurohypophyseal system as well as the autonomic nervous system is involved in homeostatic responses associated with changes in head position and orthostatic reflex. The responses induced by body tilt on earth are thought to be attributed to changes in inputs from baroreceptors, vestibular organs and proprioreceptors that are normally required for postural control. The information from these organs is sent to the hypothalamus which thereby influences both neuroendocrine and autonomic systems as well as various kinds of emotional behavior. Our findings showing the fastigial input to the hypothalamus suggested that the FN plays a significant role in these homeostatic responses through its connections with the brain stem and the hypothalamus. Figure 4 shows the input-output organization among the hypothalamus, cerebellum and brain stem, described in detail in sections III to V. This hypothesis may help to account for the autonomic and endocrine disorders often observed in weightlessness.

Adaptation, Physiological↗
PubMed2005

Cardiovascular consequences of weightlessness promote advances in clinical and trauma care.

Cardiovascular adaptations driven by exposure to weightlessness cause some astronauts to experience orthostatic intolerance upon return to Earth. Maladaptations of spaceflight that lead to hemodynamic instability are temporary, and therefore astronauts provide for researchers a powerful model to study cardiovascular dysfunction in terrestrial patients. Orthostatic intolerance in astronauts is linked to changes in the autonomic control of cardiovascular function, and so patients that suffer neurocardiogenic syncope may benefit from a greater understanding of the effects of spaceflight on the autonomic nervous system. In addition, appropriate autonomic compensation is fundamental to the maintenance of stable arterial pressures and brain blood flow in patients suffering traumatic bleeding injuries. The application of lower body negative pressure (LBNP), an experimental procedure used widely in aerospace physiology, induces autonomic and hemodynamic responses that are similar to actual hemorrhage and therefore may emerge as a useful experimental tool to simulate hemorrhage in humans. Observations that standing astronauts and severely injured patients are challenged to maintain venous return has contributed to the development of an inspiratory impedance threshold device that serves as a controlled "Mueller maneuver" and has the potential to reduce orthostatic intolerance in returning astronauts and slow the progression to hemorrhagic shock in bleeding patients. In this review, we focus on describing new concepts that have arisen from studies of astronauts, patients, and victims of trauma, and highlight the necessity of developing the capability of monitoring medical information continuously and remotely. Remote medical monitoring will be essential for long-duration space missions and has the potential to save lives on the battlefield and in the civilian sector.

Adaptation, Physiological↗
PubMedDate not supplied

Flight behaviour of pigeons during weightlessness.

Pigeons were subjected to weightlessness caused during parabolic flight in an airplane. Experiments were performed with these birds in their normal state, as well as in conditions with hooded eyes, with the legs bound, and a combination of both handicaps. In all these situations, the flight behaviour of the birds was observed. The results are discussed and comparisons are made with the behaviour of man and fish under similar conditions.

Animals↗
PubMedDate not supplied

The structural and functional organization of the vestibular apparatus of rats exposed to weightlessness for 20 days on board the Sputnik "Kosmos-782".

This investigation of the vestibular apparatus of rats exposed for 20 days to weightlessness on board an earth satellite and to acceleration during take-off and landing has revealed a set of changes in the structural and functional organization, such as adjoinment of the otolith to the utricle receptor surface and peripheral localization of the nucleoli inside the receptor cells' nuclei. Destruction of some receptor cells, apparently due to increased swelling of the vestibular apparatus tissue and alteration of the shape and structure of the otoconia were observed. In the horizontal crista, detachment of the cupula took place.

Acceleration↗
PubMed1989

The flow rate of blood in an environment of weightlessness.

To discuss the decrease in the flow rate of blood experienced by astronauts, a theory of blood flow is presented taking account of the effect of gravity. The theory of two-dimensional Poiseuille flow is adopted. It is assumed that the flow is horizontal and that the width of the upper marginal layer filled with plasma thickens as gravity increases. The parameter xi which mainly indicates the effect of thickening of the upper marginal layer is introduced. The extent of decrease in the flow rate of blood in the environment of weightlessness compared to that in the gravitational field is calculated for various values of xi. The decrease is more remarkable in the flow rate of the cell fraction than that of whole blood for the same value of xi.

Blood Flow Velocity↗
PubMed1990

Spatial reference in weightlessness: perceptual factors and mental representations.

The role of gravity in spatial coordinate assignment and the mental representation of space were studied in three experiments, varying different perceptual cues systematically: the retinal, the visual background, the vestibular, and proprioceptive information. Verbal descriptions of visually presented arrays were required under different head positions (straight/tilt) and under different gravitational conditions (gravity present/gravity absent). The results of two experiments conducted with 2 subjects who participated in a space flight revealed that subjects are able to adequately assign positions in space in the absence of gravitational information, and that they do this by using their head-retinal coordinates as primary references. This indicates that they cognitively adapted to the perceptually new situation. The findings from a third experiment conducted with a larger group of subjects under a condition in which the gravitational information was present but irrelevant to the task being solved (subjects were in a horizontal supine position) show that subjects, in general, are flexible in using cues other than gravitational ones as references when the latter cannot serve as a referential system. These findings, together with the observation that consistent spatial assignment is possible even immediately after first exposure to the perceptually totally novel situation of weightlessness, seem to suggest that the mental representation of space, onto which given perceptual information is mapped, is independent of a particular percept.

Adult↗
PubMedDate not supplied

[Physiologo-hygienic basis for the construction of individual equipment for preventing the adverse effects of weightlessness].

In order to prevent the unfavourable effect of weightlessness, it is recommended to use individual suits for long wear. These include a preventive pressure suit which provides an axial pressure on the skeleton and moments of forces during movement, and a preventive vacuum suit which provides lower body decompression. The suits ensures the conditions for the function of the musculoskeletal apparatus and the cardiovascular system which are close to those on the Earth.

Atmospheric Pressure↗
PubMed1975

Flight behaviour of pigeons in the weightless phase of parabolic flight.

Pigeons were subjected to changes in G-loading during parabolic flight with special attention to their flight behaviour in the weightless periods. Experiments were performed 1) with the eyes covered, 2) with the legs tied to the body, 3) with eyes covered and legs tied, and 4) with none of these handicaps. In all these situations the flight behaviour of the birds was observed. Special attention was paid to the tumble-phenomenon, which appeared birds with covered eyes. The results are discussed and comparisons are made with the behaviour of man and fish under similar conditions.

Animals↗
PubMed1993

Behaviour of newly hatched and adult Japanese quail and the feasibility of adaptation to weightlessness.

The aim of cosmic biology is to create conditions necessary for the long-term stay of man on cosmic orbital complexes and planetary stations. Such conditions should be provided by the autonomous closed ecosystem--a simplified model of the terrestrial biocenosis. As an experimental model of the higher heterotrophic link of this ecosystem the Japanese quail was chosen. This paper presents recent knowledge on the behaviour of newly hatched and adult quails under conditions of weightlessness. Videorecords made as part of the experiments aboard the MIR orbital station do not meet the criteria of systematic behavioural observation required for qualitative and quantitative behavioural analysis on earth. Nevertheless, the data is highly interesting and original, and was therefore analysed and summarized.

Adaptation, Physiological↗
PubMed1984

Role of cardiac volume receptors in the control of ADH release during acute simulated weightlessness in man.

Hemodynamic responses and antidiuretic hormone (ADH) were measured during body position changes designed to induce central blood volume shifts in ten cardiac and one heart-lung transplant recipients to assess the contribution of cardiac volume receptors in the control of ADH release during the initial acute phase of exposure to weightlessness. Each subject underwent 15 min of a sitting-control period (C) followed by 30 min of -6 degrees headdown tilt (T) and 30 min of resumed sitting (S). Venous blood samples and cardiac dimensions were taken at 0 and 15 min of C; 5, 15, and 30 min of T; and, 5, 15, and 30 min of S. Blood samples were analyzed for hematocrit, plasma osmolality, plasma renin activity (PRA), and ADH. Heart rate (HR) and blood pressure (BP) were recorded every two min. Plasma osmolality was not altered by posture changes. Mean left ventricular end-diastolic volume increased (P < .05) from 90 ml in C to 106 ml in T and returned to 87 ml in S. Plasma ADH was reduced by 20% (P < .05) with T and returned to control levels with S. These responses were similar in six normal cardiac-innervated control subjects. These data may suggest that cardiac volume receptors are not the primary mechanism for the control of ADH release during acute central volume shifts in man.

Adult↗
PubMed1997

Integrated regulation in response to simulated weightlessness.

To investigate physiological effects of tail suspension, Ca2+ concentration, immune factors, erythrocyte rheological properties, and growth hormone were determined in rats suspended for 15 and 30 d. The results showed that inhibitory changes of both local factors (proteins secreted by bone cell, Ca(2+)-ATPase in sarcoplasmic reticium) and integrated regulative factors (immune factor, growth hormone) were observed simultaneously with the decrease of bone mineral content, calcium transportation in skeletal muscles as well as erythrocyte deformability. It suggests that both local and integrated regulative processes are functioning in response to the effects of weightlessness.

Animals↗
PubMed1996

[Effects of simulated weightlessness on ultrastructures and oxygen supply and consumption of myocardium in rats].

Weightlessness causes atrophy of myocardium in rats, however, properties of ultra-structural changes and oxygen supply and consumption in myocardium are still unclear. Changes in ultrastructures of left ventricular myocardium in rats tail-suspended for 8W were observed. Qualitative analysis showed that the lysosomes, lipofuscins and degenerate mitochondria increased in myocytes of left ventricle in tail-suspended rats (SUS). The sarcoplasmic reticula were reduced in quantity and shrunken in appearance. The number of extended endothelial projections into the lumen of capillaries increased. Quantitative analysis showed that volume densities of mitochondria and sarcoplasmic reticulum in SUS were reduced by 14.5% and 22.2%, respectively. The number density of mitochondria also had a 12.5% decrease in SUS. The morphometric data-estimated oxygen demand of the myocardium in SUS showed a 16.7% decrease. These results suggested that the feature of the changes be chronic degeneration without the evidence of acute hypoxia in myocardium. The decrease of oxygen consumption of myocardium in SUS didn't cause a reflex reduction in the oxygen supply.

Animals↗
PubMed1996

Endocrine, renal, and circulatory influences on fluid and electrolyte homeostasis during weightlessness: a joint Russian-U.S. project.

Microgravity is known to have a substantial effect on fluid homeostasis. The research described here was planned as part of the first joint Russian-U.S. science program carried out during a Shuttle flight. The aim of the program was to study the nature of the changes in fluid homeostasis induced by microgravity, as well as to determine the possible mechanisms underlying the regulation of fluid balance under conditions of spaceflight. To determine the effects of spaceflight on the homeostasis of fluid and electrolytes, measurements were taken of total body water, extracellular fluid plasma volumes, levels of regulatory hormones, and nutrient consumption before, during, and after a nine-day flight. Changes in renal function were studied before and after the flight. In these 2 subjects, weightlessness was not associated with a decreased extracellular fluid volume. However, there were the characteristic decreases in plasma atrial natriuretic peptide concentrations, and increases in plasma and urinary cortisol. Results indicated decreased urine volume, even through the first 48 hours of flight. Fluid volumes and glomerular filtration rate were increased after landing, probably related to the saline-loading countermeasure used by Shuttle crewmembers. The information obtained as a result of this research will facilitate the development of future research programs, as well as preventive measures for future long-duration spaceflights.

Body Water↗
PubMed1996

[Can a tail-suspension model be applied to simulate the reproduction system under weightlessness?].

A tail-suspension model to simulate weightlessness is widely used for studies on physiological changes not only of the musculoskeletal system but also of the cardiovascular system. In the present study, we applied this model to investigate whether or not it is possible for male spermatogenesis to occur, and for female rats to maintain pregnancy in this model. Two male rats were suspended with the right inguinal canal ligated loosely for 14 days, and female rats were suspended after copulation (the day when spermatozoa were identified on a smear from the female rat, was referred to as Day 0 for her in this paper). The duration of suspension was chosen dependent upon events to be confirmed during the course of pregnancy. To demonstrate the effects of suspension on implantation, the first and second groups consisted respectively of non-suspended rats penetrated at the base of the tail in the same way as suspended rats, and rats suspended during the former half of pregnancy (Days 0-12, and 0-14). The third group consisted of rats suspended during the latter half (Days 10-20, 10-21, 10-26, and 10-28), and in the final group a rat suspended throughout pregnancy (Days 0-22) was placed. Histological analysis of the male rat testes showed that the testes on the ligated side were scarcely impaired, while the others became degenerated presenting similar appearances of cryptorchidism. The levels of serum testosterone were lower than the control values. As for the female rats, one animal in the final group was successful in parturition, and implantation appeared to be delayed in the second group. A tail-suspended rat, if it is acclimatized to its environment, could succeed in parturition. By employing this model, we can certainly elucidate some new aspects of mammalian reproduction in space.

Animals↗
PubMed1997

Effects of simulated weightlessness on erythrocyte deformability in rats.

In order to investigate the mechanism of space anemia, the erythrocyte deformability membrane fluidity and cell shape in 7, 15, 30 day tail-suspended rats were observed. The results were: (1) erythrocyte deformability (DImax and IDI) in suspended rats was significantly lower than that in the control on the 7th day (P<0.05), and had a further decrease on the 15th day (P<0.01), but a recovery was found on the 30th day (P<0.05). (2) membrane fluidity in suspended rats was markedly lower than that in the control group on the 15th and 30th day, degrees of fluorescence polarization was increased (P<0.01), but there was no change on the 7th day. (3) percentage of erythrocytes with abnormal shape in suspended rats was higher than that in the control group during the whole experimental period. The results indicate that the changes of rheological and morphological properties of red cell were induced by simulated weightlessness (SWL), which may be an important cause of space anemia.

Anemia↗
PubMed1997

[Human dynamic equations and analysis of opening the hatch door under weightlessness].

The general human dynamic equations under weightlessness were derived using Kane-Huston's Method. According to manned spaceflight circumstances, specific equations for models of floating in space and having a single point support were derived from the above general equations. The action that the astronaut opens the hatch door was analyzed, the "float" evolution was calculated, and the evolutionary curves were drawn.

Anthropometry↗