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At least 523 records · Page 29Linked to original sources
PubMed1998

Effects of a 60-day confinement on the blood pressure, hormonal responses and body fluids of a mixed crew.

During the EXEMSI experiment, an international crew of 4 subjects (1 woman and 3 men) was confined for 60 days in a normobaric diving chamber (with 1060 mbar atmospheric pressure) to simulate life in a space station and to assess the effects of confinement on psychological and physiological factors. Blood pressure and blood volume regulating hormones (atrial natriuretic peptide, renin, aldosterone) and urine data (24-h urine outputs, ionogram) were measured before (BDC: baseline data collection), during (D: day) and after (R: recovery) confinement. We also measured energy expenditure and total body water, 14 days before, and after 27 days of confinement, by the double-labeled water method. We found a marked increase in 24-h urine output during most of the confinement in the men and the woman. Body weight (-1.8 +/- 0.9 kg) and energy expenditure (-1064 +/- 143 kcal/d, p<0.01) decreased in the 3 men. The total body water (TBW) decreased by 1.5 +/- 1.2 l in the men. Stress was not indicated by plasma and urine catecholamines but plasma growth hormone was elevated on D2 (p<0.01 vs. BDC) in the men. This study shows that confinement conditions can modify body fluid (increases in 24-h urine outputs and TBW changes) and energetic metabolisms.

Adaptation, Physiological↗
PubMed1998

Effects of clinorotation on the polysaccharide content of resynthesized walls of protoplasts.

Changes in cellulose and callose content during cell wall regeneration in Brassica oleracea protoplasts have been examined by cytofluorimetry following their exposure to the conditions of the horizontal clinostat (2 r.p.m.) for 10 days. In comparison with controls, cellulose content decreased 4-fold and 28% of the protoplasts failed to resynthesize a wall in the clinorotated sample. The callose content was almost doubled in clinostated cells. Callose synthesis fluctuated in both control and clinorotated protoplasts. The results support the idea that inhibition of cellulose synthesis in protoplasts grown on the clinostat is caused by a change of plasmalemma fluidity and functioning, and also by a disturbance to the state of cytoplasmic calcium under conditions of simulated microgravity.

Brassica↗
PubMed1996

Central venous pressure in humans during microgravity.

Based on the results of head-down simulation studies and the results of parabolic flights, the hypothesis was tested that central venous pressure (CVP) in humans increases during microgravity (weightlessness) compared with during the ground-based supine position. CVP was recorded with an intravascular pressure transducer in seven healthy humans during short (20-s) periods of microgravity created by parabolic-flight maneuvers and in one astronaut before, during, and up to 3 h after launch of the Spacelab D-2 mission (Space Transport System-55). When the subjects were supine during the parabolic maneuver, CVP decreased during microgravity from 6.5 +/- 1.3 to 5.0 +/- 1.4 mmHg (P < 0.05). during the Spacelab D-2 mission, CVP was 6.2 mmHg during the initial minutes of microgravity, which was very similar to the value of 6.5 mmHg in the supine position 3.5 h before launch of the space shuttle. During the subsequent 3 h of weightlessness, CVP during rest varied between 2.0 and 6.2 mmHg. We conclude that CVP during short (20-s) and longer (3-h) periods of microgravity is close to or below that of the supine position on the ground.

Adult↗
PubMed1994

Gravitational response of the slime mold Physarum.

The acellular slime mold Physarum polycephalum is used as a model system to investigate the graviresponse of single cells which possess no receptors specialized for the perception of gravity. To obtain insights into the gravity-signal transduction mechanism the light response of the cell is used: Macroplasmodia of the slime mold show clear geo- and phototaxes. Gravity increases and white light decreases transiently the contraction frequency of plasmodial strands whereby both responses follow the same time pattern. Since mitochondria play a major role in changing the contraction rhythm in response to light and gravity stimuli, the simultaneous and subsequent inductions of the opposing light and gravity responses and their mutual influences on one another were investigated. The experiments were performed in weightlessness (0 g)--simulated on the fast-rotating clinostat as well as in actual weightlessness during the IML-1 Space Shuttle mission. The results indicate that mitochondria (chondriome) are part of the acceleration-stimulus reaction chain in Physarum. Two models for a direct gravireceptor mechanism are discussed.

Animals↗
PubMedDate not supplied

Evaluation of theories of complex movement planning in different levels of gravity.

Due to high redundancy of degrees of freedom in the human body, we can perform any movement, from the simplest to the most complex, in many different ways. Several studies are still trying to identify the motor strategies that master this redundancy and generate the movements whose characteristics are highly stereotyped. The aim of this work is to build a simulator that is able to evaluate different motor planning hypotheses. The most interesting applications of this tool occur in studies of the motor strategy in microgravity conditions. The comparison between simulated movements and kinematics data recorded both on Earth, and during a 5-month mission on board the Mir station shows that for a complex whole-body movement (such as trunk bending) a single planning criterion cannot explain all movement aspects. However, the simulator allows an understanding of the motor planning adaptation of astronauts. In space, the lack of equilibrium constraint (which on Earth brings about the center of mass control) leads to a new motor strategy that minimizes dynamic interactions with the floor.

Adaptation, Physiological↗
PubMed2005

Skinfold thickness versus isotope dilution for body fat assessment during simulated microgravity: results from three bed-rest campaigns in men and women with and without countermeasures.

Because body composition is altered during head-down bed rest (HDBR), body mass can not be used as an index of energy balance. Consequently diet allowances should not be based on body mass evolution but on fat mass changes. Though criticized, skinfold thickness (ST) is the costless, easiest and fastest method to use for such an objective. The aim of this study was to compare the percentage of body fat (%BF) estimated by ST with the isotope dilution of H2 18O. We compiled data from three HDBR campaigns, one on women (n=8) in November 1998 and two on the same men (n=8) in December 1997 (without countermeasure) and January 1998 (with thigh-cuffs countermeasure), according to a crossover design. Body composition was assessed before and after 6 days of HDBR. %BF was derived from the biceps, triceps, sub-scapular and sup-iliac ST according to Durnin and Wormersly (1974). Fat-free mass was measured on the same day by H2 18O dilution and fat mass was calculated by the difference with body mass and expressed as a percentage. Based on precision tests, the minimum measurable change by ST was 1.1%BF for single measurement point. Both intercepts (F (4,30)=0.89, P=0.45) and slopes (F (4,30)=0.74; P=0.57) of the ST versus dilution relationships were not affected by the periods (December vs January), experimental conditions (control vs HDBR vs HDBR + thigh cuffs) or sex allowing the derivation of a common relationship %BF(st)=0.94 x %BF(dil) (F (1,47)=97.9, P<0.0001; non-significant intercept excluded) with a bias between methods of -1.7+/-2.0 %BF (95% CI: -5.8, 2.4 %BF). ST can be used to measure %BF during HDBR provided great care is placed on training and changes are higher than 1.1 %BF. If the method can be applied for in-flight energy balance monitoring given the high observed energy deficit, a tight monitoring of the individual nutritional status as needed during simulation appears, however, dubious based on this solely method.

Adiposity↗
PubMed2001

A virtual environment for simulated rat dissection.

Animal dissection for the scientific examination of organ subsystems is a delicate procedure. Performing this procedure under the complex environment of microgravity presents additional challenges because of the limited training opportunities available that can recreate the altered gravity environment. Traditional crew training often occurs several months in advance of experimentation, provides limited realism, and involves complicated logistics. We have developed an interactive virtual environment that can simulate several common tasks performed during animal dissection. In this paper, we describe the imaging modality used to reconstruct the rat in virtual space, provide an overview of the simulation environment and briefly discuss some of the techniques used to manipulate the virtual rat.

Animals↗
PubMed2001

Orientation of root hair growth is influenced by simulated microgravity.

We have tried to investigate the mechanisms supporting the plagiotropic growth (growth in parallel to the Earth) of root hairs in simulated microgravity. Our strategy to understand the regulation of such type of growth depends upon the study of cytoskeleton topography and calcium ions distribution in root hairs both in control and simulated microgravity.

Actins↗
PubMed2005

Morpho-functional alterations in testicular and nervous cells submitted to modelled microgravity.

Humans, as well as other life forms, have developed on earth under the terrestrial gravitational field. Questions concerning the effect of the gravity vector changes on the animal physiology have begun to emerge only in the last decades. Physiological alterations were observed during space flights, but space-born investigations at cellular levels are still very limited. Earth-bound simulations of low gravity obtained with the 3-dimensional Random Positioning Machine are extensively utilized to explore the effects of microgravity on cell function. After only a few minutes, weightlessness affected the cytoskeleton of lymphocytes, astrocytes, neurons and testicular cells, disorganizing microtubules, intermediate filaments and microfilaments. Cell division was impaired, mitochondria were disrupted and apoptotic phenomena occurred. Expression of proteins involved in transmembrane ion and water transport were also affected. In the Leydig cells the key enzymes (3beta- and 17beta-hydroxysteroid dehydrogenases) leading to testosterone synthesis were depressed. However, after 20 h of clinorotation the cells were able to synthesize heat shock proteins that initiated protection and recovery. The cytoskeleton was again well organized, normal mitosis occurred and the percentage of apoptotic cells returned to the range of 5%, similar to the control cultures. Ion and water transmembrane proteins and steroid dehydrogenases returned to normal levels. Long-term experiments showed that low gravity induced only transient alterations in the cultured cells, which were able to adapt to the gravity vector changes and to regain normal activity. These data may explain the physiological adaptation occurring in astronauts during and after space flights.

Animals↗
PubMed1995

Morphogenesis and cell wall changes in maize shoots under simulated microgravity conditions.

Various plant organs show a spontaneous curvature on a three-dimensional clinostat. Changes in the cell wall metabolism underlying the curvature were examined in maize shoots. In coleoptile nodes, no differences were detected in either the level or the composition of cell wall polysaccharides between the convex and the concave halves. However, the convex side showed a higher activity of (1 --> 3),(l --> 4)-beta-glucan breakdown, which appears to be associated with the curvature. In the elongating region of coleoptiles, the accumulation of wall polysaccharides occurred in the convex side. There was no significant difference in the glucanase activity between both sides. Thus, the spontaneous curvature in different regions of maize shoots may be brought about through different mechanisms under simulated microgravity conditions.

Cell Wall↗
PubMed2003

Inertial shear forces and the use of centrifuges in gravity research. What is the proper control?

Centrifuges are used for 1 x g controls in space flight microgravity experiments and in ground based research. Using centrifugation as a tool to generate an Earth like acceleration introduces unwanted inertial shear forces to the sample. Depending on the centrifuge and the geometry of the experiment hardware used these shear forces contribute significantly to the total force acting on the cells or tissues. The inertial shear force artifact should be dealt with for future experiment hardware development for Shuttle and the International Space Station (ISS) as well as for the interpretation of previous space-flight and on-ground research data.

Acceleration↗
PubMed1983

Influence of zero gravity simulation on time course of mitosis in microplasmodia of Physarum polycephalum.

Detrimental effects of weigntlessness are no longer expected to hinder successful mitosis. Experiments in space and on the fast clinostat give no hints of this. Nevertheless we are thinking of a g sensitivity during the process of chromosome condensation and distribution. The time course of nuclear division in microplasmodia of the slime mold Physarum polycephalum was investigated under 0 g simulation on the fast rotating clinostat in comparison to 1 g controls. The result of this experiment is: A significant shortening of mitosis under 0 g simulation compared to 1 g controls.

Animals↗