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Preparing for life in space.
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Space flight effects on the skeletal muscles of rats.
Morphological and histochemical examinations of the skeletal muscles of rats flown for 22 d aboard the Cosmos-605 biosatellite have demonstrated atrophic and dystrophic developments in the soleus muscle accompanied by metabolic changes in the muscle tissue. The changes were reversible but did not disappear entirely 27 d postflight. Early atrophic developments were seen in the m. gastrocnemius, m. quadriceps, and m. ext. digitorum longus on the second postflight day. The comparative study of the muscles of flight and simulation rats has shown that pathology developed in the muscles as a result of diminished motor activity of animals being aggravated by weightlessness.
Results of medical investigations carried out on board the Salyut orbital stations.
The purpose of the medical investigations carried out in flights of the Soviet orbital station Salyut were: to further studies and clarification of the phenomenology and mechanisms of changes in the main functions of the human body during prolonged weightlessness; to accumulate additional data on human responses at an early stage of adaptation to weightlessness; to assess the effectiveness of countermeasures against adverse effects of weightlessness during and after flight. The orbital station was equipped with a set of countermeasuring devices: a trainer for physical exercises (a treadmill), gravity simulation suit for long wear, bicycle ergometer, anti-G suit to be worn immediately post-flight, drugs, etc. The system of medical control included daily recordings of electrocardiography and respiration and regular physical examinations using provocative tests (physical exercises of a known force, lower-body negative pressure). Specific biomedical investigations were performed before, during and after flight. As in previous flights, the atmosphere in the habitable modules was similar to that on the earth. Food supply met the requirements for basic nutrients and satisfied individual preferences of the crew members. In addition to the time required to fulfil the flight programme, the work-rest schedule allowed the cosmonauts 8 hours sleep, four meals, 2.5 hours physical training and personal time. The biomedical investigations carried out during and after flight furnished information towards a better understanding of human responses to the effects of space flight factors and the mechanisms underlying their development.
Significance of vestibular organs in problems of weightlessness.
Two important questions concerning the organs of equilibrium are posed by orbital and space flights. The first is whether exposure to weightlessness may evoke symptoms of vestibular origin, and the second is how to prevent symptoms of vestibular origin should it be decided to abolish weightlessness by causing the spacecraft to spin. It is important to determine whether vestibular symptoms are to be ascribed to the otolith apparatus or to the semicircular canals, or to both. During exposure to weightlessness the usual gravitational stimulus to the otolith apparatus is lost, and this reduction in afferent input might be expected to disturb the integrative patterns in the central nervous system. All such disturbances are special instances of a common cause for the appearance of functional syndromes such as seasickness. If orbiting vehicles are caused to rotate in order to abolish weightlessness, the angular velocity will be determined by the effective radius of rotation and the rate of spin, i.e., how nearly it is desired to simulate 1 g. At very short radii the complicating effects of exposure of the body to variations in centripetal force must be considered. With longer radii the principal stress will arise as a result of constant rotation, which, in combination with head movements, generates Coriolis forces. These forces cause bizarre patterns of stimulation of the semicircular canals which in turn may result in illusions and "canal sickness". This type of motion sickness has its origin in the semicircular canals and deserves the term "canal sickness". The angular velocities which represent a negligible stress or a tolerable stress are defined. A brief description is given of illusory phenomena and other manifestations together with the time-course of the adaptive process.
Comparison of cardiovascular function during the early hours of bed rest and space flight.
This paper reviews the cardiovascular responses of six healthy male subjects to 6 hours in a 5 degrees head-down bed rest model of weightlessness, and compares these responses to those obtained when subjects were positioned in head-up tilts of 10 degrees, 20 degrees, and 42 degrees, simulating 1/6, 1/3, and 2/3 G, respectively. Thoracic fluid index, cardiac output, stroke volume, and peak flow were measured using impedance cardiography. Cardiac dimensions and volumes were determined from two-dimensional guided M-mode echocardiograms in the left lateral decubitus position at 0, 2, 4, and 6 hours. Cardiovascular response to a stand test were compared before and after bed rest. The impedance values were related to tilt angle for the first 2 hours of tilt; however, after 3 hours, at all four angles, values began to converge, indicating that cardiovascular homeostatic mechanisms seek a common adapted state, regardless of effective gravity level (tilt angle) up to 2/3 G. Echocardiography revealed that left ventricular end-diastolic and end-systolic volume, stroke volume, ejection fraction, heart rate, and cardiac output had returned to control values by hour 6 for all tilt angles. The lack of a significant immediate change in left ventricular end-diastolic volume, despite decrements in stroke volume (P < .05) and heart rate (not significant), indicates that multiple factors may play a role in the adaptation to simulated hypogravity. The echocardiography data indicated that no angle of tilt, whether head-down or head-up for 4 to 6 hours, mimicked exactly the changes in cardiovascular function recorded after 4 to 6 hours of space flight. Changes in left ventricular end-diastolic volume during space flight and tilt may be similar, but follow a different time course. Nevertheless, head-down tilt at 5 degrees for 6 hours mimics some (stroke volume, systolic and diastolic blood pressure, mean arterial blood pressure, and total resistance), but not all, of the changes occurring in an equivalent time of space flight. The magnitude of the change in the mean heart rate response to standing was greater after six hours of tilt at -5 degrees or 10 degrees. Thus, results from the stand test after 6 hours of bed rest at -5 degrees and 10 degrees, but not at 20 degrees or 42 degrees, are similar to those obtained after space flight.
Effect of hypokinesia and hypodynamia on protein, RNA, and DNA in rat hindlimb muscles.
Weightlessness is associated with a differential atrophic effect on skeletal muscle that has been attributed to both hypokinesia and hypodynamia. A suspension technique was developed to simulate this atrophic effect by inducing hypokinesia/hypodynamia (H/H) in the rat hindlimb. The purpose of the present studies was to assess the effects of H/H on protein, RNA, and DNA contents in hindlimb skeletal muscles. Suspended animals exhibited a differential reduction in absolute muscle protein content with some alterations in protein concentration. Absolute DNA levels did not change in atrophic muscles. There were pronounced effects of suspension on DNA concentration and on protein/DNA, which suggests that muscle atrophy was accompanied by a reduction in muscle cell size. Hindlimb H/H was associated with a decreased absolute content of RNA in atrophic muscles as well as reductions in RNA/DNA. RNA concentration was reduced 16-21% in atrophic muscles. These findings document a pronounced and differential effect of suspension on hindlimb muscle protein and suggest the potential for effects on the capacity for protein synthesis in muscles from suspended animals.
The Life Sciences Programme of the European Space Agency, and opportunities for radiation biology experiments.
With the advent of Europe's commitment to contribute the European Space Agency (ESA) to the NASA Space Transportation System (STS) by means of the Spacelab programme, a new area for research opportunities on Life Sciences has been created for the European scientific community. Although considered as a young and new discipline, the goals of Life Sciences research in space had soon been defined by the ESA advising Life Sciences Working Group in the beginning of 1977. The programme proposals of the various subdisciplines concentrated on the advantageous use of the microgravity environment, to study in more depth the gravity relevance of biological systems. It included, however, also the use of other factors during space flight which cannot be reproduced or adequately simulated on the ground: cosmic radiation in its total spectrum, particularly HZE particles, solar and UV radiation, vacuum, and the combination of radiation and weightlessness, etc. On this basis, call for proposals in the various subdisciplines resulted in experiments also in the field of radiation biology which were flown on the Spacelab 1 mission and which were selected for later missions. In particular, ESA is providing the science community with mission opportunities on Spacelab, either European or International, with platforms to be launched by STS, and with so called multi-user facilities (e.g. Biorack). Typically, the experiments will be the responsibility of the scientists, the integration and mission phase the responsibility of ESA. Both mission definition and experiment selection rests with the ultimate decision of the responsible ESA Programme Board. A further description of missions envisioned, the Spacelab facility, platforms, multi-user facilities and areas of research applicable to radiobiology will be given. ESA's continuing interaction with the scientific community through the Life Sciences Working Group, and the advice on future programmes will be stressed as a vital factor contributing to a European Life Sciences Programme in Space.
Cycling in space to simulate gravity.
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Modeling of phosphate ion transfer to the surface of osteoblasts under normal gravity and simulated microgravity conditions.
We have modeled the transport and accumulation of phosphate ions at the remodeling site of a trabecular bone consisting of osteoclasts and osteoblasts situated adjacent to each other in straining flows. Two such flows are considered; one corresponds to shear levels representative of trabecular bone conditions at normal gravity, the other corresponds to shear level that is representative of microgravity conditions. The latter is evaluated indirectly using a simulated microgravity environment prevailing in a rotating wall vessel bioreactor (RWV) designed by NASA. By solving the hydrodynamic equations governing the particle motion in a RWV using a direct numerical simulation (DNS) technique, the shear stress values on the surface of the microcarriers are found. In our present species transfer model, osteoclasts release phosphate ions (Pi) among other ions at bone resorption sites. Some of the ions so released are absorbed by the osteoblast, some accumulate at the osteoblast surface, and the remainder are advected away. The consumption of Pi by osteoblasts is assumed to follow Michaelis-Menten (MM) kinetics aided by a NaPi cotransporter system. MM kinetics views the NaPi cotransporter as a system for transporting extracellular Pi into the osteoblast. Our results show, for the conditions investigated here, the net accumulation of phosphate ions at the osteoblast surface under simulated microgravity conditions is higher by as much as a factor of three. Such increased accumulation may lead to enhanced apoptosis and may help explain the increased bone loss observed under microgravity conditions.
Shape relaxation of liquid drops in a microgravity environment.
We investigated shape relaxation of liquid drops in a microgravity environment that was created by letting the drops fall freely. The drops were initially levitated in air by an acoustic/electrostatic hybrid levitator. The levitated drops were deformed due to the force balance among the levitating force, surface tension, and gravity. During the free fall, the deformed drops underwent shape relaxation driven by the surface tension to restore a spherical shape. The progress of the shape relaxation was characterized by measuring the aspect ratio as a function of time, and was compared to a simple linear relaxation model (in which only the fundamental mode was considered) for perfectly conductive drops. The results show that the model quite adequately describes the shape relaxation of uncharged/charged drops released from an acoustically levitated state. However, the model is less successful in describing the relaxation of drops that were levitated electrostatically before the free fall. This may be due to finite electrical conductivities of liquids, which somehow affects the initial stage of the shape relaxation process.
Cardiovascular responses to isometric exercise during simulated zero gravity.
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Use of bed rest and head-down tilt to simulate spaceflight-induce immune system changes.
Bed rest, both with and without head-down tilt, has been extensively used as an earth-bound analog to study physiologic effects mimicking those occurring in weightlessness during spaceflight. We have been able to show in six subjects that 4 weeks of head-down tilt bed rest induces a significant decrease in interleukin-2 secretion by PHA-stimulated T lymphocytes. Another study, lasting 113 days, with two subjects showed a decreased interleukin-2 receptor expression in PHA-stimulated peripheral blood mononuclear cells but a decreased interleukin-2 production in one subject only. Under the same conditions, interleukin-1 production was largely increased in both subjects. Several other immune parameters were also analyzed. Increased interleukin-1 production could contribute to bone mineral loss encountered during bed rest and decreased interleukin-2 secretion could play a role in the appearance of infectious diseases often observed during bed red.
Low-G simulation in mammalian research.
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+Gx-tolerance following one-year real and simulated microgravity.
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[Effectiveness and mechanisms of the protective action of sidnocarb in experimental weightlessness and cooling].
Twenty-one subjects took part in experiments with acute cooling (maximally allowable time for swimming in ice-cold water and two-day exposure to winter field conditions) or two-day exposure to microgravity (simulated by water immersion). They were divided into a placebo group (5, 5 and 6 man-exposures) and a sydnocarb group (6, 6 and 4 man-exposures) and examined by biochemical, radioimmune and radioligand methods. It was found that physiological responses to cold and microgravity effects as well as sydnocarb were similar. During cold exposures the thermal steady-state was achieved by taking maximum daily doses of the drug. In thermoneutral water immersion body temperature fall was controlled by therapeutic doses of the drug. Body temperature decline beginning with immersion day 2 can be related to the endogenous decline of heat production due to a new functioning level which is well known in gravitational physiology, i. e. this is the effect of microgravity per se. With respect to old and new information about the pharmacological properties of sydnocarb, mechanisms of its high thermoregulatory effects on CNS structures responsible for heat production and heat loss are discussed.
Calcium phosphate crystallization under terrestrial and microgravity conditions.
Calcium phosphate crystalline powders grown under terrestrial and space (EURECA 1992-1993 flight) conditions in the Solution Growth Facility are analyzed and compared by optical and electron microscopy (scanning and transmission), electron and X-ray microdiffraction and microanalyses. On earth, only small, micrometer size scale, spherolites of hydroxyapatite (HAP) grow. In space, the HAP spherolites reach hundreds of micrometer. Also, octacalcium phosphate (OCP) spherolites up to 3 mm have been obtained. Computer modelling of diffusion in a real chamber has been performed. It suggests high spatial supersaturation gradients at zero gravity which may provide much higher local supersaturations on earth, where convection takes place. The analyses suggest that the dramatic difference between the terrestrial and space samples should come from much lower supersaturation in space.
Modelling and simulation to support the design of a Dutch Protein Crystallization Facility.
This paper reports on the progress made in the development of the Netherlands Protein Crystallization Facility. The facility allows two crystallization techniques: Vapour diffusion and micro-dialysis. The design and development is accompanied by a project in which it tried to model and simulate the events which occur during the vapour diffusion process within the crystallization cell.