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PubMed1992

Some qualitative and quantitative aspects of the fast-rotating clinostat as a research tool.

In 1958 the geneticist H.J. Muller proposed an extension of the principle of the (slow) plant clinostat which --to a certain extent--abolishes g effects on plant growth (geotropism). Muller predicted that a feeling of weightlessness would be experienced by a human being attached to a clinostat platform, the rotation speed of which is enhanced compared to that of the plant clinostat. This method (called fast-rotating or fast clinostat) was developed by the author in the mid 1960s to investigate the effects of weightlessness on small living objects. This chapter describes the method qualitatively on the basis of a macroscopic functional model and of empirical results obtained using a fast-rotating clinostat microscope. Some practical hints in using the slow and fast clinostat principles are given.

Animals↗
PubMed1992

The simulation of microgravity conditions on the ground.

This chapter defines weightlessness as the condition where the acceleration of an object is independent of its mass. Applying this definition to the clinostat, it argues that the clinostat is very limited as a simulator of microgravity because it (a) generates centrifugal forces, (b) generates particle oscillations with mass-dependent amplitudes of speed and phase shifts relative to the clinorotation, (c) is unable to remove globally the scalar effects of gravity such as hydrostatic pressure, which are independent of the direction of gravity in the first place, and, (d) generates more convective mixing of the gaseous or liquid environment of the test object, rather than eliminating it, as would true weightlessness. It is proposed that attempts to simulate microgravity must accept the simulation of one aspect of microgravity at a time, and urges that the suppression of convective currents be a major feature of experimental methods that simulate microgravity.

Biophysical Phenomena↗
PubMed1994

Changes of insulin in plasma and receptor for insulin in various tissues after the exposure of rats to space flights and hypokinesia.

The explanation of the mechanism of the response to gravity changes is of great importance for the determination of the capacity of human subjects to adapt to the load of gravitational stress. Therefore several studies were performed to investigate the activity of endocrine system, since the hormones are involved in the regulation of physiological functions and metabolic processes. However the studies of endocrine system activity during altered gravity conditions, especially during the weightlessness are influenced by the several interventions in biomedical observations due to operational program of astronauts, wide variability in individual response and tolerance, use of extensive countermeasures, differences in the type of space missions and in the studies after landing also a hypergravity effect at landing and variability in postflight readaptation process. The significant changes of plasma insulin and glucose levels were observed in astronauts during space flights and in the first days of recovery period. In the first inflight period plasma insulin levels were increased, unchanged or decreased however after 4-5 weeks of exposure to weightlessness a decrease of insulin plasma levels were noted. After space flights an increase of plasma insulin levels were demonstrated in experimental animals and in human subjects. Since plasma insulin level is considered as most important factor involved in the regulation for insulin receptors in target tissues, an investigation of insulin receptors in various tissues was performed in rats exposed to space flight or to hypokinesia (model used for simulation of some effects of microgravity).

Adipose Tissue↗
PubMed1999

Relatively shorter but intensive isotonic exercise in legs prevented the decrease in maximal aerobic power after 20 days of head down tilt bed rest in man.

As a countermeasures for the decrease in maximal oxygen uptake (VO2max) during prolong simulated weightlessness, it has been suggested that intensive isotonic legs exercise was useful. The reason is possibly that a dynamic and intensive resistance exercise training makes to maintain not only the volume of exercising muscles but also cardiac output. For the reason, it has been studied the effects of 3 different exercise training on VO2max during simulated weightlessness.

Bed Rest↗
PubMed1999

Hindlimb-suspension and spaceflight both alter cGMP levels in rat choroid plexus.

Effects of actual and simulated weightlessness on choroidal guanylate cyclase activity were evaluated by assaying the production of cyclic guanosine monophosphate (cGMP), a second messenger involved in mechanisms regulating the secretion of cerebrospinal fluid (CSF) in choroid plexus. Cyclic cGMP was measured, using radio-immunoassay, in choroidal extracts of hindlimb-suspended rats (HLS rats), adapted to an anti-orthostatic restraint for 30 min., or for 3, 9 or 14 days and after a 17-day spaceflight (Life and Microgravity SpaceLab experiment; LMS). Basal cGMP levels were slightly but significantly decreased in the first 30 min. of the HLS experiment, whereas they were significantly increased in rats adapted to longer anti-orthostatic restraints. LMS flight rats demonstrated a similar increase in the choroidal cGMP baseline. After natriuretic peptide stimulation, i.e. using ANP (atrial natriuretic peptide) or BNP (brain natriuretic peptide), choroidal cGMP contents were typically increased (by 1.5-2 times; p<0.05) in control rats (LMS and HLS experiments), but not significantly elevated in suspended rats, except for those adapted to HLS for 14 days. In these animals the ANP-dependent cGMP production was significantly increased (by about 3 times; p<0.005). The ANP- or BNP-dependent responses were similarly abolished in LMS flight rats, which were dissected 4-6 hours after return to Earth's gravity. The role of corticosteroids was also investigated during the LMS experiment. Results on choroidal functions revealed a lack of significant change of cGMP levels between adrenalectomized and sham-operated rats. For the first time, it is reported that both basal and ANP- stimulated cGMP levels are dramatically changed over the first 14 days of suspension, i.e. with experiments known to simulate some effects of weightlessness. Basal choroidal cGMP levels are also increased after 17 days in space, suggesting that space adaptation also impacts choroidal guanylate cyclase activities. However, the absence of ANP-dependent cGMP increase, observed in LMS flight animals, suggests that HLS could not simulate all the spaceflight effects. Thus, these preliminary results seem to show that a natriuretic peptides-independent s stem is involved in choroidal adaptation to spaceflight.

Adaptation, Physiological↗
PubMed1999

[Counteracting effect of Chinese herbs-compounds on "blood stasis" induced by bed rest].

Objective. To observe the improved effect of syndromes of blood stasis by taking Chinese medicine during bed-rest simulated weightlessness. Method. Ten subjects were randomly divided into two groups: Chinese medicine group and control group. Both of them were exposed to HDBR -6 degrees for a week. The Chinese medicine group took Chinese medicine during the bed rest, and the control group took sugar water. Result. Syndromes of blood stasis of Chinese medicine group had a significant relief. And some physiological parameters, such as blood pressure, pulse graph, and amount of urine, maintained the level of pre-bed rest. While the control group was more severe than the Chinese medicine group in syndromes of blood stasis. Conclusion. Chinese medicine can be a measure in preventing the effect of weightlessness.

Adolescent↗
PubMed2001

[Effects of vitamin K on bone metabolism in tail-suspended rats].

Objective. To study the effects of vitamin K on bone metabolize in simulated weightlessness rats. Method. Male SD rats were divided into three groups (n = 9): the free active control (FAC), the tail-suspended control (SC), and the tail-suspended group treated with vitamin K (SVK) (50 mg/kg weight/d). The experiment lasted for 3 weeks. Bone biomechanical properties, bone mineral contents (BMC) and bone biochemical markers of bone metabolism were determined. Result. Compared with SC, total and bound bone gla protein (BGP) of serum, BMC of the femur and tibia, femoral mechanical properties, ALP activity of tibia all increased significantly; while NO content of femoral trunk decreased significantly. Conclusion. Vitamin K improved the bone metabolism and bone structure, decreased bone loss, increased bone biomechanical properties, decreased catagmatic fatalness. It proved that vitamin K prevented bone loss of simulated weightlessness rats.

Alkaline Phosphatase↗
PubMed2000

[Effects of different training methods on cardiovascular autonomic regulation during bedrest].

Objective. To investigate the effects of different training methods on cardiovascular autonomic regulation under bedrest. Method. 15 healthy male volunteers aged 19-22 participated tests in head-down tilt (HDT) -6 degrees bedrest in order to observe the changes of cardiovascular system under simulated weightlessness. They were divided into control (5 men), hypoxia training (5 men) and Fangsong training (5 men) groups. 24 h dynamic ECG were recorded on the 2nd day of pre-bedrest, on the 3rd, 14th and 18th day of bedrest and on the 7th day of the post- bedrest. All spectra were estimated from entire 24 h HRV, before, during and after Fangsong and hypoxia training by autoregressive (AR) modeling method. Normalized low-frequency (LF%) was a quantitative marker of cardiac sympathetic activity, normalized high-frequency (HF%) reflected the changes in cardiac vagal activity, and LF/HF was considered to be related to sympathovagal balance or sympathetic activity. Result. In control group, LF% and HF% were all significantly reduced (P<0.05), LF/HL showed no significant changed during bedrest. In Fangsong group, HF% increased markedly (P< 0.05), while in hypoxia group, LF% increased markedly (P< 0.05). Conclusion. Fangsong training counteracted markedly the reduction in vagal activity, while hypoxia training counteracted markedly the decrease in sympathetic activity. It was possible that HRV indices could be used to evaluate the efficiency of countermeasures counteracting the adverse effects of weightlessness.

Adaptation, Physiological↗
PubMed1965

On the biological role of gravity.

The paper is dedicated to the memory of Galileo Galilei whose work is a great contribution to the development of a new branch of science--gravitation biology. Penetration of man into outer space necessitates a study of the role of gravity in the onto- and phylogenetic development of living organisms. This allows one to get insight into the biological action of weightlessness under the conditions of long-term space flight. The paper summarizes some results of the investigation of weightlessness effects in experiments on animals and during flights of Soviet and American astronauts. The rearing of animals in a special centrifuge under the conditions of prolonged action of accelerations simulating an increased gravity affects noticeably the formation of vegetative (height, weight, metabolism) and animal (vestibulo-tonic reflexes) functions as well as reactivity of the organism. Experiments employing the rearing of animals in a centrifuge represent one of the most promising methods of studying the urgent problem--biological action of increased and decreased gravitation conditions.

Acceleration↗
PubMed2002

Percutaneous aspiration of fluid for management of peritonitis in space.

BACKGROUND: As a medical emergency that can affect even well-screened, healthy individuals, peritonitis developing during a long-duration space exploration mission may dictate deviation from traditional clinical practice due to the absence of otherwise indicated surgical capabilities. Medical management can treat many intra-abdominal processes, but treatment failures are inevitable. In these circumstances, percutaneous aspiration under sonographic guidance could provide a "rescue" strategy. HYPOTHESIS: Sonographically guided percutaneous aspiration of intra-peritoneal fluid can be performed in microgravity. METHODS: Investigations were conducted in the microgravity environment of NASA's KC-135 research aircraft (0 G). The subjects were anesthetized female Yorkshire pigs weighing 50 kg. The procedures were rehearsed in a terrestrial animal lab (1 G). Colored saline (500 mL) was introduced through an intra-peritoneal catheter during flight. A high-definition ultrasound system (HDI-5000, ATL, Bothell, WA) was used to guide a 16-gauge needle into the peritoneal cavity to aspirate fluid. RESULTS: Intra-peritoneal fluid collections were easily identified, distinct from surrounding viscera, and on occasion became more obvious during weightless conditions. Subjectively, with adequate restraint of the subject and operators, the procedure was no more demanding than during the 1-G rehearsals. CONCLUSIONS: Sonographically guided percutaneous aspiration of intra-peritoneal fluid collections is feasible in weightlessness. Treatment of intra-abdominal inflammatory conditions in spaceflight might rely on pharmacological options, backed by sonographically guided percutaneous aspiration for the "rescue" of treatment failures. While this risk mitigation strategy cannot guarantee success, it may be the most practical option given severe resource limitations.

Animals↗
PubMed2002

[Effects of head down tilt on intra-ocular pressure, near vision, and visual field and the protection effect of Chinese herbs].

Objective. To observe the influences of 21 d head down tilt (HDT) bed rest on the intra-ocular pressure, visual field and near vision in human and to study the countermeasure of Chinese herb against weightlessness. Method. Ten subjects were randomly divided into control group and Chinese herb group. -6 degrees HDT was used to simulate weightlessness. Intra-ocular pressure, near vision and vision field were measured before, during and after bed rest in both groups. Result. Intra-ocular pressure and near vision showed a wave-like decrease change during bed rest, and there exists a certain coherence between them. Visual field showed no obvious changes. Taking Chinese herb was able to antagonize the decreasing of intra-ocular pressure and near vision during various phases of bed rest. Conclusion. 1) Bed rest could lead to the decreasing of intra-ocular pressure and near vision; 2) Taking Chinese herb was able to antagonize the negative influences of bed rest on visual function.

Adult↗
PubMed2003

[The water-salt balance and renal function in space flights and in model experiments].

Study of a condition of mineral and water-electrolyte metabolism, function of kidneys, and their hormonal regulation during model experiments (hypokinesia, bed rest, immersion etc.), and also in space flights and in readaptation period, has shown a major role of water-electrolyte homeostasis during general adaptation of humans and animals to new conditions of life and to conditions of weightlessness in particular. The change in regulation of volumes of fluid milieu in an initial period of weightlessness was shown to be the consequence of redistribution of blood and hemodynamics of the shifts resulting in change of production of volume-regulation hormones, formation of negative water balance, and redistribution of fluid in the organism among various fluid compartments. At later stages of flight or long-term hypokinesia, a change of water-electrolyte homeostasis occurs with a decrease in the kidneys excretion of sodium, and diuresis, but with an increased excretion of calcium and production of ADH and RAAS hormones. Following returning to earth gravitation, the majority of astronauts have adaptive reactions, compensating for the loss extracellular fluid and mineral substances and formation of "earth" water-electrolyte homeostasis. For estimation of water-electrolyte homeostasis and the functions of kidneys in astronauts, various functional loading tests have been developed. The developed system of preventive maintenance is successfully used for abolition of adverse changes at various stages of space flight and in readaptation period.

Astronauts↗
PubMed2005

Jumping in simulated and true microgravity: response to maximal efforts with three landing types.

BACKGROUND: Exercise is a promising countermeasure to the physiological deconditioning experienced in microgravity, but has not proven effective in eliminating the ongoing loss of bone mineral, most likely due to the lack of high-impact forces and loading rates during in-flight activity. We wanted to determine lower-extremity response to high-impact jumping exercises in true and simulated microgravity and establish if 1-G force magnitudes can be achieved in a weightless environment. METHODS: Jumping experiments were performed in a ground-based zero-gravity simulator (ZGS) in 1 G, and during parabolic flight with a gravity-replacement system. There were 12 subjects who participated in the study, with 4 subjects common to both conditions. Force, loading rates, jump height, and kinematics were analyzed during jumps with three distinct landings: two-footed toe-heel, one-footed toe-heel, and flat-footed. Gravity replacement loads of 45%, 60%, 75%, and 100% bodyweight were used in the ZGS; because of time constraints, these loads were limited to 60% and 75% bodyweight in parabolic flight. RESULTS: Average peak ground-reaction forces during landing ranged between 1902+/-607 and 2631+/-663 N in the ZGS and between 1683+/-807 and 2683+/-1174 N in the KC-135. No significant differences were found between the simulated and true microgravity conditions, but neither condition achieved the magnitudes found in 1 G. CONCLUSION: Data support the hypothesis that jumping exercises can impart high-impact forces during weightlessness and that the custom-designed ZGS will replicate what is experienced in true microgravity.

Adult↗
PubMed2005

[Effects of 100 Hz vibration on ultrastructure of soleus muscle in tail-suspended rats].

OBJECTIVE: To study the effects of 100 Hz vibration on ultrastructure of intrafusal and extrafusal fibers in soleus muscle of tail-suspended rats. METHOD: Weightlessness was simulated by tail suspension of female rats. The ultrastructure of intrafusal and extrafusal fibers of soleus muscle were examined after exposure to 100 Hz vibration. RESULT: The ultrastructure of intrafusal and extrafusal fibers of soleus muscles showed obvious retrograde changes after 7 d tail suspension, whereas these changes were not obvious after 7 d tail suspension plus 100 Hz vibration. CONCLUSION: High frequency vibration can counteract the effect of simulated weightlessness on ultrastructure of intrafusal and extrafusal fibers in soleus muscles of rats.

Animals↗
PubMed2001

Effects of spaceflight and cage design on abdominal muscles of male rodents.

We examined the effects of a 16-day spaceflight mission on the size of muscle fibers in the rectus abdominis, external oblique and transversus abdominis muscles of adult male Fisher rats. The rats were individually housed in orbit, in contrast to the one previous spaceflight investigation of the same muscles, where the rats were group-housed pregnant females. The cross-sectional area of the muscle fibers was used as a measure of muscle atrophy or hypertrophy. The transversus, which is presumed to be the primary expiratory muscle and consequently works against internal hydrostatic pressures that are not likely to change much between 1 G and weightlessness, did not change in size. However, both the rectus abdominis (a spinal flexor) and the external oblique (a rotator of the torso), which resist gravity in the 1 G environment, showed significant signs of atrophy after extended exposure to microgravity. The atrophy of the external oblique was diametrically opposite to hypertrophy of the same muscle observed in group-housed rodents previously exposed to spaceflight. Although the two missions differed in several factors, such as the gender of the rats and mission duration, we believe that housing of the animals was the key factor that accounted for the different responses of the external oblique. Previous research has shown that group-housed rats in spaceflight exhibited seven times more rotations of their torsos than matched ground controls. Thus unloading of the musculoskeletal system may not be achieved in weightlessness when animals have the freedom to interact with each other.

Abdominal Muscles↗
PubMed1991

Pars distalis vasculature: Discovery Shuttle STS-29 rats compared to ground-based antiorthostatic rats.

The anterior pituitary glands of male, adult Long Evans rats carried 5 days in the Space Shuttle Discovery (STS-29) have been compared with two groups of ground-based controls. All of the animals were part of a study (SE82-08) into the effects of gravity versus a microgravity environment on fracture healing. All had sustained a right, mid-shaft fibular osteotomy. The duration of the study was 10 days, and animals in all groups were weight bearing for the 5 days prior to shuttle lift off. The three experimental groups consisted of four rats each: flight (F) and two ground-based control groups, weight bearing (WB) and suspended (S). The suspension group was in a Holton/Sweeney head-down suspension apparatus (antiorthostatic) for the final 5 days of the study. The anterior pituitary glands of F and WB rats were essentially identical. The vasculature and parenchymal cells appeared unaffected in both instances. However, the anterior pituitary glands of S rats were dramatically altered. The vasculature was widely expanded with proteinaceous deposition covering the lumenal endothelial surfaces, and entrapping numerous platelets and aggregates of red blood cells. Parenchymal cells were highly vacuolated, occasionally with membranous vacuoles, but most often revealing large, clear cytoplasmic zones unlined by any membranes. Whereas profiles of exocytosis were numerous in F rats, and present in WB rats, they were essentially absent in S rats. These results indicate that weightlessness over a 5-day flight period does not influence the structural integrity of the anterior pituitary gland and may in fact promote secretory granule release. However, the head-down tilt model, frequently used to study fracture repair under conditions that mimic weightlessness, has a profound impact on the vasculature of the anterior pituitary gland which then affects the structural and functional characteristics of the parenchymal cells.

Animals↗
PubMed1993

Effect of injury on mast cells of rat gastrocnemius muscle with respect to gravitational exposure.

The proteolytic enzyme, chymase, was used to identify mast cells in rat gastrocnemius muscles which were crush-injured or incised in order to determine if mast cells exhibited proliferation and degranulation. Some of the crush-injured rats were subjected to 0 g for 14 days after injury on the Cosmos 2044 satellite to study the effects of weightlessness on the mast cell response. A variety of ground-based injured models were used, including a group of hindlimb-unloaded animals acting as controls and testing the suitability of the hindlimb-unloaded animal as a model for muscle healing during weightlessness. In most cases, the numbers of mast cells and their apparent size increased after injury. When mast cell degranulation was evident, the granules containing chymase often were free in the loose connective tissue and along the edge of myofibers. The mast cell response was most exaggerated in animals subjected to 0 g and least visible in the hindlimb-unloaded ones. Thus, gravitational stress may influence mast cell physiology and the hindlimb-unloaded animal may not be a good model for investigating muscle healing.

Animals↗
PubMed1993

Egocentric references and human spatial orientation in microgravity. II. Body-centred coordinates in the task of drawing ellipses with prescribed orientation.

This article describes the results of the "ellipses" experiment conducted during the second French-Soviet spaceflight (project Aragatz). The realization of oriented motor tasks, on the basis of internal body representation and without visual feedback, was chosen as a paradigm for studying the determinants of spatial orientation under weightlessness. The process of drawing ellipses in the air, using arm movements with axes parallel or perpendicular to the longitudinal body axis, was studied under normal gravity and in weightlessness, and recorded using a video computer motion-analyzing system (Kinesigraph). On Earth, the experiments were performed in standing and lying positions, and in flight, in the erect position with the feet fixed to the floor. In general, performance of the task in microgravity was not disturbed. Under conditions of spaceflight, the longitudinal ellipse was inclined forward in accordance with the inclination of the whole body relative to the fixed feet. On Earth, the angle between the long axes of longitudinal and transverse ellipses deviated from 90 degrees by 20-30 degrees. The same deviation persisted under microgravity conditions. The distinctive features of ellipses traced by individual subjects were also preserved. It is concluded that an egocentric reference system ensures normal performance of sensorimotor tasks in the absence of a gravitational reference.

Adaptation, Psychological↗