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PubMed2001

Revised hypothesis and future perspectives.

Results from space have been unexpected and not predictable from the results of ground-based simulations. Therefore, the concept of how weightlessness and gravity modulates the regulation of body fluids must be revised and a new simulation model developed. The main questions to ask in the future are the following: Does weightlessness induce a diuresis and natriuresis during the initial hours of space flight leading to an extracellular and intravascular fluid volume deficit? Can sodium in excess be stored in a hitherto unknown way, particularly during space flight? Why are fluid and sodium retaining systems activated by spaceflight? Why are the renal responses to saline and water stimuli in space attenuated compared with those of ground simulations? How can the effects of weightlessness on fluid and electrolyte regulation be correctly simulated on the ground? The information obtained from space may be of relevance to fluid and electrolyte balance in edematous patients.

Blood Volume↗

PubMed1993

[Human gas and energy exchange in space flight and simulation research].

Human gas-energy exchange under extreme conditions is considered in the above work. Major attention is given to energy exchange and external respiration of humans in space flight, as well as in the models of space vehicles and during simulation of physiological effects of weightlessness.

Energy Metabolism↗

PubMed2001

Effects of depressed myocardial contractility induced by microgravity on cardiovascular response to orthostatic stress: a computer simulation.

The aim of present study is to investigate the role played by the depression of myocardial contractility in the mechanism of cardiovascular deconditioning and orthostatic intolerance (OI) induced by space weightlessness. Based on our previous model, which was used to simulate cardiovascular response to lower body negative pressure (LBNP), we incorporated the factor of changes of myocardial contractility into the model by multiplying a coefficient to the time-varying elastance that represents the changes of cardiac contractility. By decreasing the coefficient progressively, we simulated the changes of heart rate (HR), blood pressure (BP), and cardiac output (CO) during LBNP after 0-30% of myocardial contractility depression combined with 12% decrease of the total blood volume. Simulation results indicate that depressed myocardial contractility induces more augment of HR, and more decrement of BP and CO during LBNP and suggest that the depression of myocardial contractility degenerate cardiovascular response to orthostatic stress.

Blood Pressure↗

PubMed1976

Physiological effects induced by antiorthostatic hypokinesia.

The main purpose of the present investigation was to reproduce some physiological reactions in the sensory system which are similar to those observed during the first day of the adaptation to weightlessness. This was achieved by a 5-day bed rest experiment during which the test subjects were kept in the antiorthostatic position at angles of 0 degrees, -4 degrees, -8 degrees, -12 degrees. Our investigations allowed simulation of the acute stage of adaptation to weightlessness and assessment of gravity-induced blood redistribution in the development of the above physiological reactions.

Adaptation, Physiological↗

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↗

PubMed1998

[Methodologic aspects of body water kinetic dynamic studies].

In studying the level of hydration and liquid phases (LPs) in a space mission there use the stable and/or radioactive isotopes. The investigations are unique, the methods are adequate but not adapted in full measure to the challenges of the problem under study. The methodical approaches to the study of the dynamics of water metabolism are not available. Repeated introduction of the markers for these purposes is not acceptable. Another problem associates with taking the markers orally. In this case, a concentration of the markers will depend on the absorption and excretion processes. Prior to, during and in the readaptation period these functions will be different, making a correlation of the accumulated data difficult. There advances a possible version of solving these problems, namely, to use for the dynamic studies the residual contents of the markers in the LPs after single injection. However, this approach calls for investigating the kinetics of markers in weightlessness or during its ground-based simulation. The kinetics of tritium water has been studied in 6 volunteers under conditions of the 5-day bedrest and in 9 healthy men during free motor activity. There determined the characteristics of marker kinetics in a healthy man during his routine living activities. Under bedrest conditions there have been noted slowing-down of the rate and a decrease in the degree of marker accumulation in the body after its single injection, the shift of a period of relative stabilization of marker content in LP to the more late dates of experiment, slowing-down of the marker excretion rate from the body.

Adaptation, Physiological↗

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↗

PubMed1982

[Past and present medical and biological studies in Italy on microgravity].

Since 1957, Italian workers have been carrying out experiments on the physiological and pathological effects of the weightlessness encountered during space travel. Most of this work has been done at the Air Force Aviation Medicine Study and Research Centre, Rome, while other research has been conducted at the Department of Human Physiology, University of Milan. Various original devices (axis subgravitis tower, triaxial clinostats, etc.) have been devised and constructed to simulate partial and total weightlessness. They have been employed well ahead of actual space flights in investigations of the effects of weightlessness on vestibular function, sensory and muscle coordination, the position of the diaphragm and its adjacent viscera, locomotion, plant growth, rapid adaptation phenomena, etc. One experiment conducted during orbital flight was called Orbiting Frog Otolith. This investigated vestibular function under statis and dynamic conditions in the absence of weight. An Italian three-dimensional ballistocardiography experimental project will be conducted during the first Spacelab flight.

Electrocardiography↗

PubMed2002

[Microgravity and weightlessness: experimental model accelerates nutritional pathology].

Short space flights affect nutritional intakes, body composition and functional parameters. Prolonged space flights (SF) over weeks or months further worsen these alterations and result in acute or chronic physical deterioration at earth return. Current planning of SF to Mars, with microgravity conditions for more than 2 years, stresses the need for developing and optimising a nutritional program and physical countermeasures to prevent body mass atrophy and functional body alterations. This review presents the models of microgravity simulation on earth and the main effects of weightlessness on body composition, protein metabolism, hormonal profile and muscle function. It summarizes contradictory findings related to the oxidative stress related to SF. It discusses potential countermeasures (nutrition, physical activity) to the negative effects of microgravity on human body. Future research possibilities in ground and space medicine are evoked.

Aerospace Medicine↗

PubMed1971

The ecology of micro-organisms in a closed environment.

Experimental data are presented which have a bearing on the susceptibility of astronauts to infectious diseases. These experiments include the observation of growth by two bacteria in Biosatellite 2, in which higher mean densities were attained than in earth-based controls. In addition, weightlessness combined with the special environment of a space vessel may affect the physiology of the astronauts. Earth-based studies in closed chambers were carried out under a variety of conditions with regard to pressure and oxygen content. One notable result was the transfer of micro-organisms from subject to subject. Comparative experiments were carried out in Antarctica and it was shown that the tests in closed chambers differed markedly from the Antarctica experience. The objectives and procedures of microbiological tests of the Gemini and Apollo programs are outlined.

Aerospace Medicine↗

PubMed1997

Similar mutant frequencies observed between pairs of monozygotic twins.

The relative contribution of both genetic and environmental factors to spontaneous mutation frequency in humans is unknown. We have investigated the contribution of genetic factors to this phenomenon by determining the in vivo mutant frequency at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in circulating T-lymphocytes obtained from pairs of monozygotic twins. hprt mutant frequencies were determined three times over fourteen days in six sets of monozygotic male twins (mean age 30) taking part in a Russian Space Program inclined bed rest experiment. Blood samples were obtained prior to, during, and immediately following the experiment. Mononuclear cells were separated, frozen, and flown to Canada for analysis using the hprt T-lymphocyte clonal assay. There is no evidence within this data set to demonstrate that the period of inclined bed rest to simulate the effects of weightlessness had any effect on the observed mutant frequency. However, the average mutant frequency for the six sets of Russian twins was found to be three times higher than that of Western counterparts. More surprisingly, the spontaneous mutant frequency of monozygotic twins was found to be much more similar within pairs than between pairs of twins. These data suggest that the contribution of genetics in the determination of mutation frequency is substantial. However, whether high concordance within twin pairs reflects shared environmental experience as well as common genetic factors is not entirely clear. More data will be required to distinguish genetic from environmental factors and to determine the degree to which mutant frequency is genetically determined.

Adult↗

PubMed1994

Cardiovascular responses to repetitive exposure to hyper- and hypogravity states produced by parabolic flight.

Physiologic changes to repetitive hyper- and hypogravity stresses occurring during eight to ten parabolas on NASA's KC-135 aircraft were studied. Hemodynamic responses in 11 subjects in 4 different postures (supine, standing, sitting, and semisupine Space Shuttle launch position) were determined using noninvasive impedance cardiography. Five seconds of heart rate, cardiac index, thoracic fluid index, stroke index, ejection velocity index, and ventricular ejection time data were averaged during four different gravity (g) states: 1.3g (before parabola onset); 1.9g (parabola entry); 0g (parabola peak); and 1.7g (parabola exit) for each subject. The standing position was associated with the largest changes in the cardiovascular response to hypo- and hypergravity. The thoracic fluid index did not indicate a headward redistribution during transition from a simulated launch position to weightlessness. Analysis of the eight to ten parabolas revealed that, in general, values obtained at 1.8g differed from 1.6g, 0g differed from 1.6 and 1.3g, and 1.6g differed from 1.3g. The factors of gravity, thoracic fluid index, and cardiac index exhibited significant differences that were most likely to occur between parabola 1 versus parabolas 6, 7, and 8, and parabola 2 versus parabolas 4 through 8. Only the parameter of thoracic fluid index exhibited significance for parabolas 3 versus parabolas 6 and 7.

Adult↗

PubMed1993

Influence of suspension on the expression of protective immunological memory to murine Listeria monocytogenes infection.

Female BDF1 mice were immunized with virulent Listeria monocytogenes, which resulted in the generation of a long-lived state of protective immunological memory for this facultative intracellular bacterial pathogen. The influence of antiorthostatic suspension, a ground-based model employed to simulate certain aspects of weightlessness that occur during spaceflight, on the capacity of these mice to express memory immunity was evaluated. Memory-immune mice were suspended by the tail in the orthostatic or antiorthostatic position and were reinfected with a lethal dose of virulent L. monocytogenes. It was found that suspension did not influence the kinetics of bacterial growth in vivo when the rechallenge infection was started concurrently with the suspension. However, mice that were reinfected on day 2 or 4 of the suspension exhibited an enhanced capacity to eliminate the infection. Attenuation of this enhancing effect was observed when mice were infected on day 7 of the suspension. These results indicate that the stress of antiorthostatic suspension can influence the capacity of the murine host to express protective immunological memory to pathogenic bacteria.

Animals↗

PubMed1994

Influence of antiorthostatic suspension on resistance to murine Listeria monocytogenes infection.

The present study was designed to evaluate the influence of antiorthostatic suspension, a ground-based modeling system employed to simulate certain aspects of weightlessness that occur during space flight, on the capacity of mice to resist infection with the facultative intracellular bacterial pathogen Listeria monocytogenes. Female BDF1 mice were suspended by the tail in the orthostatic or antiorthostatic position and were infected with a sublethal dose of virulent L. monocytogenes at various times during the suspension. It was found that suspension did not influence the kinetics of bacterial growth in vivo if the infection was started concurrently with the suspension. However, mice that were antiorthostatically suspended 2, 4, or 7 days before the onset of infection exhibited an enhanced capacity to eliminate the challenge infection. Suspending mice on day 2 of the infection did not alter the kinetics of bacterial growth. Finally, the enhancement of resistance to the primary Listeria infection was accompanied by failure of the mice to generate long-term protective immunological memory to the challenge organism. Collectively, these results indicate that the stress of antiorthostatic suspension can influence the capacity of mice to resist bacterial infection.

Animals↗

PubMed1987

Changes in nuclear magnetic resonance (T2) relaxation of limb tissue with bed rest.

Bed rest is used to simulate the effects of weightlessness on human physiology. A spin-echo procedure was used to image the lower leg of 15 normal male volunteers before and after 5 weeks of horizontal bedrest. In addition to noninvasively measuring muscle size changes, accurate T2 images were produced to investigate possible relaxation time changes immediately (2-4 h) and 1-2 days after bed rest. Subcutaneous fat showed no change in T2, bone marrow showed a decrease, and muscle showed no change immediately after bed rest but increased 1-2 days following reambulation.

Adipose Tissue↗

PubMed1997

Cultivation of fall armyworm ovary cells in simulated microgravity.

A methodology is presented to culture Fall Armyworm Ovary cells in simulated micrograviy using a novel bioreactor developed by NASA, the High-Aspect Ratio Vessel. In this vessel, the growth and metabolic profile for these insect cells were profoundly different than those obtained in shaker-flask culture. Specifically, stationary phase in the NASA vessel was extended from 24 h to at least 7 d while cell concentration and viability remained in excess of 1 x 10(7) viable cells/ml and 90%, respectively. Measurements of glucose utilization, lactate production, ammonia production, and pH change indicate that simulated microgravity had a twofold effect on cell metabolism. Fewer nutrients were consumed and fewer wastes were produced in stationary phase by as much as a factor of 4 over that achieved in shaker culture. Those nutrients that were consumed in the NASA vessel were directed along different metabolic pathways as evidenced by an extreme shift in glucose utilization from consumption to production in lag phase and a decrease in yield coefficients by one half in stationary phase. These changes reflect a reduction in hydrodynamic forces from over 1 dyne/cm2 in shaker culture to under 0.5 dyne/cm2 in the NASA vessel. These results suggest that cultivation of insect cells in simulated microgravity may reduce production costs of cell-derived biologicals by extending production time and reducing medium requirements.

Ammonia↗

PubMedDate not supplied

Life support system using water electrolysis.

The purpose of the integrated physiologico-hygienic and biotechnological laboratory experiment was to evaluate the effect of life support subsytems placed inside a sealed cabin on the cabin environment and, consequently, on the human performance and activity, and also to assess the operability of subsystems by the crewmen and disclose any resulting difficulties.

Air Conditioning↗

PubMed1992

Countermeasures against space flight related bone loss.

This paper reviews human data concerning bone loss and attempted countermeasures during spaceflight and bed rest, a commonly employed technique to simulate the effects of weightlessness on the musculoskeletal system.

Bed Rest↗