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PubMedDate not supplied

[State of skeletal muscle fibers in rats during physical exercise after anti-orthostatic tail suspension in modeling the weightlessness].

The state of myofibers of types I, IIA and IIB of biceps femoris m. of Wistar rats exposed to tail suspension for 14 or 21 days was investigated after they experienced a 15-minute locomotor load: running on a treadmill or hindlimb stretching. In all types of myofibers both exposures prevented the development of most structural and metabolic changes that occurred in response to suspension simulating the physiological effects of weightlessness. The distribution and level of variations of muscle parameters depended on the kind of exposure and type of myofibers.

Animals↗
PubMed1992

The influence of different space-related physiological variations on exercise capacity determined by oxygen uptake kinetics.

Oxygen uptake kinetics, following defined variations of work load changes allow to estimate the contribution of aerob and anaerob energy supply which is the base for determining work capacity. Under the aspect of long duration missions with application of adequate dosed countermeasures, a reliable estimate of the astronaut's work capacity is important to adjust the necessary inflight training. Since the kinetics of oxygen uptake originate in the working muscle group itself, while measurements are performed at the mouth, various influences within the oxygen transport system might disturb the determinations. There are not only detraining effects but also well-known other influences, such as blood- and fluid shifts induced by weightlessness. They might have an impact on the circulatory system. Some of these factors have been simulated by immersion, blood donation, and changing of the body position.

Bed Rest↗
PubMed2006

[The influence of space flights on water-electrolytes turnover and its regulation].

A study of water-electrolyte exchange, the condition of water milieu of the organism, and the volume- and electrolyte homeostasis regulation in space flights, and also in postflight period has shown the important role of the water-salt homeostasis in adaptation of the human and animal organism to weightlessness. Obviously, downturn of food consumption, renal excretion and the intestine output seem to be caused by suppression of activity of mechanisms of ion deposition. The most intensive changes of the liquid milieu volumes occur in the first days of weightlessness or in its ground simulation. And, with prolonged duration, the changes of extracellular liquid volume and the volume of plasma do not extend. After termination of long space flights, activation of renin-aldosterone systems occurs as well as a decrease in efficiency of antidiuretic hormone, misbalance of pressor/unpressor prostanoids. In the period of re-adaptation after space flights, development of desensitization of kidneys to endogenous ADH occurs. This is the basis for researches directed to improvement of the existing scheme of correction of the hydrogenous status of the astronaut organism in the closing stage of flight.

Animals↗
PubMed1984

Thymic involution in the suspended rat model for weightlessness: decreased glucocorticoid receptor concentration.

Hindlimb muscle atrophy, thymic involution and adrenal hypertrophy in rats during spaceflight can be simulated using suspension models. Skeletal muscle and thymus are sensitive to glucocorticoids (GC) and previous studies have demonstrated that muscle atrophy in suspended rats is associated with increased GC receptor concentration. The objectives were to confirm thymic involution during suspension, and determine if involution correlated with increased GC receptor concentration. Seven days of antiorthostatic (AO) suspension of rats produced a significant (P<0.001) reduction in thymic wet weight not associated with an alteration of % water content. GC receptor concentration (pmol/mg protein) decreased 20% (P<0.025) in thymus glands from 7 day AO suspended rats. Suspension, therefore, is associated with involution of the thymus but this is not dependent upon AO positioning. Thymus GC receptor concentrations were depressed in 7 day suspended rats, in contrast with previous observations on skeletal muscle, suggesting that different mechanisms may underlie these responses.

Animals↗
PubMed2000

[A simulated study of effects of simulated hypovolemia on cardiovascular response to orthostatic stress].

Objective. To study the effects of hypovolemia on cardiovascular response to orthostatic stress, and to investigate the role of hypovolemia in the mechanism of cardiovascular deconditioning and orthostatic intolerance induced by space weightlessness. Method. The effects of loss of blood volume had been incorporated in the sub-model of blood redistribution in the model developed for simulating the cardiovascular response to lower body negative pressure (LBNP). With the help of the model, we simulated the changes of heart rate (HR) and blood pressure (BP) during LBNP after 0-25% loss of blood volume. Result. When the amount of decrease of blood volume was less than 5% of the total blood volume, HR and BP could be maintained in normal range during LBNP through baroreflex regulation. When the amount of the decrease of blood volume was more than 15% of the total blood volume, HR and BP could be kept in normal range when the subject was supine and at rest. But BP fell sharply and the cardiovascular system almost collapsed during orthostatic exposure. Conclusion. Decrease of blood volume causes significant degradations of cardiovascular response to orthostatic stress.

Aerospace Medicine↗
PubMed1995

Forehead skin microcirculation during tilt table testing and lower body negative pressure.

Noninvasive skin microcirculation measurements based on a new Near Infrared sensor technique (NIR/Fa. Silicon Sensor GmbH; Berlin) were embeded in a tilt table experiment for simulation of acute effects of weightlessness (HDT -6 degrees) and active standing with the Russian Tschibis-LBNP device. The phenomenon of orthostatic intolerance depends on complex interactions among functional characteristics of central and peripheral cardiovascular control. The purpose of this study was to assess the blood volume and flow motion changes as well as pulsatile spectral pattern during orthostatic and antiorthostatic stress.

Adult↗
PubMed1973

Human sensorimotor coordination following space flights.

Studies have been carried out 18-30 days before the flight and on the second day after landing. The recovery kinetics of cosmonauts who completed the 18-day space flight was followed for 30 days after their return. Muscle tone, indices of muscle strength and parameters of the functions of the extremities were examined, and the ability to maintain vertical posture was studied (stabilography). Flights of short duration did not cause any serious disturbances in the neuromuscular system. Together with this fact, the analysis of the results revealed a certain regularity in the physiological effects as reflected by a decrease in the strength of the torso extensors and the muscle tone of the lower extremities, The tone and strength of the arms altered insignificantly, and the alterations were not an indication of muscular atrophy. Stabilographic studies showed a decrement in the stability of the vertical posture of the cosmonauts. The above alterations were particularly pronounced in the crew members of Soyuz 9. As distinct from the previous flights of the Soyuz spaceships the crew members of Soyuz 9 showed normality in the regulation of vertical posture only on the tenth day after the flight. One of the reasons for the above alterations in postural regulation may be the decrease in muscle tone noted repeatedly after both of the previous space flights and in experiments with simulation of separate effects of weightlessness. Another reason for the deterioration in postural regulation is probably the changes in interaction between the neutral analysers. A possible reason for the apparent defects in stability may be the disturbance of the interaction between various muscle groups, i.e. the disturbance in synergism which is required for the maintenance of vertical posture. Similar alterations were observed in people who had been subjected to bed rest for a long time. Readaptation to the ground environment appeared to proceed in stages. The comparative evaluation of post-flight findings showed that prolonged periods of flights up to 18 days resulted in more pronounced alterations in human sensomotor coordination.

Adaptation, Physiological↗
PubMed1987

Cardiovascular dynamics during the initial period of head-down tilt.

The cardiovascular response to 1 h of 6 degrees head-down tilt was studied in 12 male subjects, ages 30-39 years, to simulate the early effects of weightlessness. Fluid shifts, hemodynamic variables, and indices of myocardial contractility were evaluated by utilizing electrocardiography, systolic time intervals, impedance cardiography, sphygmomanometry, and measurement of calf circumference. Most cardiovascular variables remained stable throughout the initial 30 min of the protocol, even though translocation of fluid from the legs to the thorax commenced immediately with the onset of head-down tilt. In contrast, minutes 30-60 were characterized by reduced stroke volume, cardiac output, mean stroke ejection rate, and Heather Index concomitant with an elevation in mean arterial pressure. Intrathoracic fluid volume continued to increase while leg volume continued to decrease. This latter physiological response suggests intrathoracic sequestration of fluid volume; blood was apparently redistributed to the pulmonary circulation rather than being retained in the great veins.

Adult↗
PubMed2001

Applied horizontal force increases impact loading in reduced-gravity running.

The chronic exposure of astronauts to microgravity results in structural degradation of their lower limb bones. Currently, no effective exercise countermeasure exists. On Earth, the impact loading that occurs with regular locomotion is associated with the maintenance of bone's structural integrity, but impact loads are rarely experienced in space. Accurately mimicking Earth-like impact loads in a reduced-gravity environment should help to reduce the degradation of bone caused by weightlessness. We previously showed that running with externally applied horizontal forces (AHF) in the anterior direction qualitatively simulates the high-impact loading associated with downhill running on Earth. We hypothesized that running with AHF at simulated reduced gravity would produce impact loads equal to or greater than values experienced during normal running at Earth gravity. With an AHF of 20% of gravity-specific body weight at all gravity levels, impact force peaks increased 74%, average impact loading rates increased 46%, and maximum impact loading rates increased 89% compared to running without any AHF. In contrast, AHF did not substantially affect active force peaks. Duty factor and stride frequency decreased modestly with AHF at all gravity levels. We found that running with an AHF in simulated reduced gravity produced impact loads equal to or greater than those experienced at Earth gravity. An appropriate AHF could easily augment existing partial gravity treadmill running exercise countermeasures used during spaceflight and help prevent musculoskeletal degradation.

Adult↗
PubMed1999

Nemaline rod and degeneration of Z band of muscle cell in weightlessness at spaceflight.

There are some studies demonstrating the skeletal muscle degeneration associated with the degeneration of Z band and appearance of nemaline rods in experimental animals of the simulation model for spaceflight but not in human heart tissues. In the present study, therefore, we investigated the pathological changes or degeneration in left auricular heart muscles obtained during operations of mitral valves replacement using both electron and light microscopies. The degeneration of Z band even in the myofibrils of comparatively little damaged cell was found. Furthermore, nemaline rods were detected in most of the heart muscle cells. These results suggest that the existence of nemaline rods is involved in the cell injury in the heart muscle of patients with heart disease without nemaline myopathy. Further study is necessary to know whether the similar pathological findings are observed not only in the skeletal muscle but also in the cardiac muscle in experimental animals of the simulation model for spaceflight or in a prolonged spaceflight.

Animals↗
PubMed1986

Confirmation of gravisensitivity in the slime mold Physarum polycephalum under near weightlessness.

We have investigated Physarum polycephalum, a unicellular organism with no special gravity receptors, on its ability to react to gravity. The first experiments were 0 g-simulation experiments on the fast-rotating clinostat conducted with plasmodial strands of this acellular slime mold. In these earth-bound experiments the observed parameters were periodicity of the contractions and dilatations of the strand's ectoplasm as well as the periodicity and velocity of the striking cytoplasmic (endoplasmic) shuttle streaming. During 0 g-simulation these parameters showed significant changes indicating the existence of a gravisensitivity of the slime mold. The Space-Shuttle experiment (ESA-Biorack in D 1-Mission) should demonstrate the validity of the 0 g-simulation on the fast-rotating clinostat. The experiment was designed in a way enabling the registration of the same parameters as on the clinostat (using the light microscope in combination with a photo diode and a cinecamera). Only one of the two planned measurement sessions was fully successful and provided us with data confirming the results gained on the fast-rotating clinostat: The slime mold showed under real near weightlessness in the D 1-Space Shuttle Mission a transient frequency increase in tis contraction rhythmicity and a (steady) increase in the streaming velocity of its endoplasm.

Animals↗
PubMed1991

Structural and metabolic properties of rat muscle exposed to weightlessness aboard Cosmos 1887.

Male Wistar rats were subjected to 12.5 days of weightlessness aboard Cosmos 1887. Histomorphometric and biochemical analyses were investigated in soleus (SOL), plantaris (PL) and extensor digitorum longus (EDL) muscles of flight rats (group F) and compared with data from two groups of terrestrial controls: one group living free in a vivarium (group V) and another subjected to a flight simulation except for the state of weightlessness (group S). Relative to groups V and S, no alteration in the percentage distribution of fibres had occurred in SOL, PL or EDL, after the flight. In SOL muscles from group F animals, cross-sectional areas of all fibre types were reduced to a greater extent (-40%) than capillary to fibre ratio (-24%) leading to a higher capillary density (+33%) than in V and S groups. In PL, type I, IIA and IIB fibre cross-sectional areas were less decreased (-25%). In EDL, only fast-twitch fibre cross-sectional areas showed an average decrease of 30%. Capillary per fibre ratio was reduced by 15% and 28% respectively in PT and EDL muscles from group F rats compared to control groups V and S. Citrate synthase and 3-hydroxyacyl-coenzyme A dehydrogenase activities remained unchanged in SOL, PL and EDL following spaceflight. These findings indicate greater atrophy and functional alterations (capillarity) compared to those observed after 7 days of microgravity on Cosmos 1667.

Anaerobiosis↗
PubMed1985

The use of suspension models and comparison with true weightlessness: "a resumé".

The topics for this workshop were selected to illustrate the manner in which particular physiological and biochemical phenomena can be assessed using specific animal model systems. Our speakers presented data which offer comparisons of experiments in earthside laboratories with experiments using subjects which have experienced weightlessness in response to orbital flight. In addition, there have been speculative assertions that the earthside experiments mimic or simulate responses which one may expect to see with exposure to micro or zero gravity conditions. The topics focused on at least three areas that appear to be amenable to earthside investigations; in addition, they serve as primary areas for flight experimentation. As the result of animal and human exposures to microgravity experienced during orbital space flight, there is ample evidence of pathophysiological functional and structural alterations in muscle, bone, cardiovascular and related body fluid shift responses. This Animal Model Workshop represents the first of a series of sessions planned for further meetings of the IUPS Commission on Gravitational Physiology.

Animals↗
PubMedDate not supplied

[Potential for modelling the hemodynamic effects of weightlessness by exposure to increased pressure].

Venous and arterial circulation was investigated by simulating cephalad blood shifts generated by an exposure of test subjects (n = 15) to lower body positive pressure (+25 mm Hg) and head-down tilts (at -8 degrees and -15 degrees). At LBPP and tilt -15 degrees arterial pressure increased by 5-15%. During tilt -8 degrees jugular vein blood filling increased by 8-94% in the course of the first 3 hrs and then decreased reaching the baseline (horizontal position) level. During LBPP the parameter changed in a similar manner (increased by 2-50%). During tilt -15 degrees the parameter grew by 10-110% and remained elevated. The exposures gave rise to bradycardia which was more pronounced during -8 degrees and LBPP. The data obtained give evidence that circulation changes during LBPP and head-down tilts are identical. This suggests that LBPP can be used to simulate the effect of cephalad blood shifts, one of the most important effects of weightlessness on the human body.

Adult↗
PubMed2005

A cognitive architecture that combines internal simulation with a global workspace.

This paper proposes a brain-inspired cognitive architecture that incorporates approximations to the concepts of consciousness, imagination, and emotion. To emulate the empirically established cognitive efficacy of conscious as opposed to non-conscious information processing in the mammalian brain, the architecture adopts a model of information flow from global workspace theory. Cognitive functions such as anticipation and planning are realised through internal simulation of interaction with the environment. Action selection, in both actual and internally simulated interaction with the environment, is mediated by affect. An implementation of the architecture is described which is based on weightless neurons and is used to control a simulated robot.

Brain↗
PubMed1998

Effects of microgravity on bone and calcium homeostasis.

Mechanical function is known to be of crucial importance for the maintenance of bone tissue. Gravity on one hand and muscular effort on the other hand are required for normal skeletal structure. It has been shown by numerous experimental studies that loss of total-body calcium, and marked skeletal changes occur in people who have flown in space. However, most of the pertinent investigations have been conducted on animal models, including rats and non-human primates, and a reasonably clear picture of bone response to spaceflight has emerged during the past few years. Osteopenia induced by microgravity was found to be associated with reduction in both cortical and trabecular bone formation, alteration in mineralization patterns and disorganization of collagen, and non-collagenous protein metabolism. Recently, cell-culture techniques have offered a direct approach of altered gravity effects at the osteoblastic-cell level. But the fundamental mechanisms by which bone and calcium are lost during spaceflight are not yet fully known. Infrequency and high financial cost of flights have created the necessity to develop on-Earth models designed to mimic weightlessness effects. Antiorthostatic suspension devices are now commonly used to obtain hindlimb unloading in rats, with skeletal effects similar to those observed after spaceflight. Therefore, actual and "simulated" spaceflights, with investigations conducted at whole body and cellular levels, are needed to elucidate pathogeny of bone loss in space, to develop effective countermeasures, and to study recovery processes of bone changes after return to Earth.

Aerospace Medicine↗
PubMed2002

Clinorotation-induced weightlessness influences the cytoskeleton of glial cells in culture.

During and after spaceflight astronauts experience neurophysiological alterations. To investigate if the impairment observed might be traced back to cytomorphology, we undertook a ground based research using a random positioning machine (clinostat) as a simulation method for microgravity. The outcome of the study was represented by cytoskeletal changes occurring in cultured glial cells (C(6) line) after 15 min, 30 min, 1 h, 20 h and 32 h under simulated microgravity. Glia is fundamental for brain function and it is essential for the normal health of the entire nervous system. Our data showed that after 30 min under simulated microgravity the cytoskeleton was damaged: microfilaments (F-actin) and intermediate filaments (Vimentin, Glial Fibrillary Acidic Proteins GFAP) were highly disorganised, microtubules (alpha-tubulin) lost their radial array, the overall cellular shape was deteriorated, and the nuclei showed altered chromatin condensations and DNA fragmentation. This feature got less dramatic after 20 h of simulated microgravity when glial cells appeared to reorganise their cytoskeleton and mitotic figures were present. The research was carried out by immunohistochemistry using antibodies to alpha-tubulin, vimentin and GFAP, and cytochemical labelling of F-actin (Phalloidin-TRIC). The nuclei were stained with propidium iodide or 4,6-diamidino-2-phenylindole dihydrochloride (DAPI). The cells were observed at the conventional and/or the confocal laser scanning microscope. Samples were also observed at the scanning electron microscope (SEM). Our data showed that in weightlessness alterations occur already visible at the scale of the single cell; if this may lead to the neurophysiological problems observed in flight is yet to be established.

Actins↗
PubMed2003

Inverse dynamic investigation of voluntary trunk movements in weightlessness: a new microgravity-specific strategy.

Present investigation faces the question of quantitative assessment of exchanged forces and torques at the restraints during whole body posture exercises in long-term microgravity. Inverse dynamic modelling and total angular momentum at the ankle joint were used in order to reconstruct movement dynamics at the restraining point, represented by the ankle joint. The hypothesis is that the minimisation of the torques at the interface point assumes a key role in movement planning in 0 g. This hypothesis would respond to an optimisation of muscles activity, a minimisation of energy expenditure and therefore an accurate control of body movement. Results show that the 0 g movement strategy adopted ensures that the integral of the net ankle moment between the beginning and the end of the movement is zero. This expected mechanical constraint is not satisfied when 0 g movement dynamics is simulated using terrestrial kinematics. This accounts for a significant imposed change of movement strategy. Particularly, the efficient compensation of the inertial effects of the segments in terms of total angular momentum at the ankle joint was evidenced. These results explain the exaggerated axial synergies, observed on kinematics and which moved centre of mass (CM) backward from its already backward initial positioning, as a tool for enhancing the compensation and achieving the desired minimisation of the torques exchanges at the restraints.

Abdomen↗