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At least 883 records · Page 49Linked to original sources
PubMed1996

[Experimental morphological studies of stress-inducing effects of weightlessness in rats flown aboard Spacelab-2].

Adrenals and thymus of rats flown for 14 days on board the US space life sciences laboratory, Spacelab-2 (SLS-2), were analyzed histologically and histomorphometrically. Adrenals of the rats sacrificed on flight day 13 did not exhibit any morphological signs of elevated functional activity. Within 5 hours following the mission, the functioning of adrenals was growing, while thymus displayed sites of thymocyte histolysis and suppression of cell mitotic activity. Taken together, these observations infer the development of stress. Based on the morphological criteria, a conclusion has been drawn that the exposure on board SLS-2 did not exert any expressed stress-inducing effect on the rats and it was the transfer from microgravity to the normal gravity that produced acute gravitational stress of moderate severity.

Adrenal Glands↗
PubMed1996

[Adaptive potentials of mammals under conditions of weightlessness].

Review and analysis of experiments with Wistar rats in microgravity allows to deduce that compensatory-adaptive potentials of mammals in space flight lasting up to 1/50th of their life span suffice for rapid elimination of space-induced metabolic and structural alterations on return to Earth, maintenance of adequate reactions to acute and chronic stresses in the post-flight period, demonstration of a stereotype of pre-flight elaborated conditional reflexes and pregnancy dominant, normal reproductive function and life span. Consideration is given to individual differences in body responses to the micro-g environment. A conclusion is made to the effect that the role of individual stamina and reactivity will be gaining in importance with increasing duration of space flights.

Adaptation, Physiological↗
PubMedDate not supplied

[Changes in central and peripheral hemodynamics during prolonged anti-orthostatic hypokinesia as a model of weightlessness].

Central and peripheral circulation was studied rheographically in 6 test subjects during a 30-day bed rest experiment and in 9 test subjects during a 49-day bed rest. The bed rested subjects were kept in a head-down position at an angle of --4 degrees. At an early stage of the experiments the cardiac output and stroke volume increased, the total peripheral resistance decreased, the tone of major regional vessels decreased and that of small vessels increased. During the 3rd-7th weeks the changes were just the opposite: cardiac output and stroke volume decreased, the total peripheral resistance increased the tone of major regional vessels increased and that of small vessels decreased. At the end of the bed rest experiment the cardiac output and stroke volume increased and the tone of regional vessels changed accordingly. Circulation parameters returned to the pretest level, at least, 3-4 weeks after the end of the best rest experiments.

Adult↗
PubMed2000

Magnetic compensation of gravity forces in (p-) hydrogen near its critical point: application to weightless conditions

We report a study concerning the compensation of gravity forces in two-phase (p-) hydrogen. The sample is placed near one end of the vertical z axis of a superconducting coil, where there is a near-uniform magnetic field gradient. A variable effective gravity level g can thus be applied to the two-phase fluid system. The vanishing behavior of the capillary length l(C) at the critical point is compensated by a decrease in g and l(C) is kept much smaller than the cell dimension. For g ranging from 1 to 0.25 times Earth's gravity (modulus g(0)) we compare the actual shape of the meniscus to the expected shape in a homogeneous gravity field. We determine l(C) in a wide range of reduced temperature tau=(T(C)-T)/T(C)=[10(-4)-0.02] from a fit of the meniscus shape. The data are in agreement with previous measurements further from T(C) performed in n-H2 under Earth's gravity. The effective gravity is homogeneous within 10(-2)g(0) for a 3 mm diameter and 2 mm thickness sample and is in good agreement with the computed one, validating the use of the apparatus as a variable gravity facility. In the vicinity of the levitation point (where magnetic forces exactly compensate Earth's gravity), the computed axial component of the acceleration is found to be quadratic in z, whereas its radial component is proportional to the distance to the axis, which explains the gas-liquid patterns observed near the critical point.

Journal Article↗
PubMed2004

Importance of direction of vibration on the onset of Soret-driven convection under gravity or weightlessness.

This paper considers the influence of the direction of vibration on the stability threshold of two-dimensional Soret-driven convection. The configuration is an infinite layer filled with a binary mixture, which can be heated from below or from above. The limiting case of high-frequency and small-amplitude vibration is considered for which the time-averaged formulation has been adopted. The linear stability analysis of the quasi-mechanical equilibrium shows that the problem depends on five non-dimensional parameters. These include the thermal Rayleigh number (Ra(T)), the vibrational parameter (R), the Prandtl number (Pr), the Lewis number (Le), the separation ratio (S) and the orientation of vibration with respect to the horizontal heated plate (alpha). For different sets of parameters, the bifurcation diagrams are plotted Ra(c) = f(S) and k(c) = g(S), which are the critical thermal Rayleigh and the critical wave numbers, respectively. Our results indicate that, relative to the classical case of static gravity, vibration may affect all regions in Ra(c)-S stability diagram. In the case of mono-cellular convection, by using a regular perturbation method, a closed-form relation for the critical Rayleigh number is found. Several physical situations in the presence or in the absence of gravity (micro-gravity) are discussed.

Journal Article↗
PubMed2002

Fluid volume changes and LBNP response after simulated weightlessness with varied oral sodium supply.

There is evidence on body fluid volume effects of head-down tilt bed rest and altered oral sodium supply, but the combined impact of both has not been investigated in detail. We therefore studied circulatory adaptation to 8 days -6 degrees head down bed rest (HDBR) with different levels (-140 to -430 mM/d) of oral sodium load (SL). We expected decreased extracellular volume and increased aldosterone and PRA levels with low sodium load, and hypothesized that these effects get exaggerated with additional HDBR, also influencing lower body suction (LBNP) responses. Variations in sodium status seem to influence plasma but not interstitial volume, confirming recent results of another group who used different experimental conditions.

Journal Article↗
PubMed2002

On the analysis of hand synergies during grasping in weightlessness.

The aim of this paper was to analyse how the strategies implemented by the Central Nervous System to control the hand during grasping are modified under microgravity conditions. Two right-handed subjects carried out simple grasping tasks during parabolic flights. The trajectories of the fingers of the hand were recorded using a sensorised glove and processed in order to extract a variable (here indicated as K) which can indicated the degree of synergies existing among the fingers. The results showed that K was quite small during the trial at 1g while becoming significantly greater than 1 during the first parabolas. Then, the value k decreased to the values at 1 g after some parabolas. These results suggested a possible adaptation process of the manipulation abilities during the permanence at 0g conditions. Future extensive trials will be performed in order to confirm these preliminary results.

Journal Article↗
PubMedDate not supplied

[Status of cardiodynamics in long-term weightlessness].

This paper presents data on the phasic structure of the cardiac cycle of the left ventricle of cosmonauts who flew for 96 to 237 days on Salyut-6-Soyuz and Salyut-7-Soyuz. Cardiodynamic changes at rest that developed largely during the first month of flight involved a mild preload syndrome. During flight months 2 to 8 the cardiac function became relatively stabilized. Provocative tests, i. e. LBNP and exercise tests, presented inflight modified the relationship between cardiac cycle phases when compared to the Earth observations. The modifications are suggestive of predominant adrenergic effects on the heart. Analysis of the phasic structure of the cardiac cycle has revealed no cardiovascular deconditioning. All the variations can be regarded as adaptive reactions to microgravity.

Adaptation, Physiological↗