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PubMed2001

Morpho-functional adaptations in the bone tissue under the space flight conditions.

Microgravity in space flight--situation of a maximum deficit of supporting loading on the skeleton and good model for finding-out of osteopenia and osteoporosis development laws, which are wide-spreading now and are "civilization diseases". Most typical for bones in conditions of a microgravitation by changes are: a decrease of intensity growth and osteoplastic processes, osteopenia and osteoporosis, decreasing of a mechanical strength and the risk of breaches arising (Oganov V.S., Schneider V. (1996)). Cytological mechanisms of gravity-dependent reactions in a bone tissue remain in many respects not-clear. By the purpose of our work was the analysis of some ultrastructural changes in bone tissue cells of the monkeys (Macaca mulatta), staying during two weeks onboard the biosatellite BION -11.

Adaptation, Physiological↗
PubMed1971

Normalization of the immune status of the human body during prolonged space flight.

During long duration space flights a number of unfavourable situations arise due to changes in endogenous microflora and immunologic reactivity of men. It appears very important to develop procedures that can be used to normalize human resistance to infection. Methods of affecting protein synthesis in immune responsive cells are being investigated. It was found that ribonucleic acids stimulated antibody formation. Application of immunological, immunochemical, and isotopic methods confirmed that one of the main factors were ribonucleotides. Their effect is mainly to accelerate the proliferation of immunocompetent cells. Our experiments have shown that a single parenteral injection of a stimulant of such type is sufficient to sustain capacity for accelerated antibody formation for a long time. A search for non-specific stimulants is needed since they can be effectively used in cases of acute and subacute inhibition of immunity. Their use in combination with specific or non-specific activators may be required in chronic inhibition of immune reactions occurring, for instance, in qualitative and quantitative reduction of normal microflora. Our investigations have demonstrated that germ-free animals and animals with reduced microflora exhibit diminished regional lymphatic nodes, underdeveloped lymphoid tissue of Peyer's plaques and other changes. The paper discusses several methods of maintaining antigen balance.

Aerospace Medicine↗
PubMed2001

Fluid volume control during short-term space flight and implications for human performance.

Space flight exerts substantial effects on fluid volume control in humans. Cardiac distension occurs during the first 1-2 days of space flight relative to supine and especially upright 1g conditions. Plasma volume contraction occurs quickly in microgravity, probably as a result of transcapillary fluid filtration into upper-body interstitial spaces. No natriuresis or diuresis has been observed in microgravity, such that diuresis cannot explain microgravity-induced hypovolemia. Reduction of fluid intake occurs irrespective of space motion sickness and leads to hypovolemia. The fourfold elevation of urinary antidiuretic hormone (ADH) levels on flight day 1 probably results from acceleration exposures and other stresses of launch. Nevertheless, it is fascinating that elevated ADH levels and reduced fluid intake occur simultaneously early in flight. Extracellular fluid volume decreases by 10-15% in microgravity, and intracellular fluid volume appears to increase. Total red blood cell mass decreases by approximately 10% within 1 week in space. Inflight Na(+) and volume excretory responses to saline infusion are approximately half those seen in pre-flight supine conditions. Fluid volume acclimation to microgravity sets the central circulation to homeostatic conditions similar to those found in an upright sitting posture on Earth. Fluid loss in space contributes to reduced exercise performance upon return to 1g, although not necessarily in flight. In-flight exercise training may help prevent microgravity-induced losses of fluid and, therefore, preserve the capacity for upright exercise post-flight. Protection of orthostatic tolerance during space flight probably requires stimulation of orthostatic blood pressure control systems in addition to fluid maintenance or replacement.

Astronauts↗
PubMed2005

Effects of radiation and latent virus on immune responses in a space flight model.

BACKGROUND: The immunosuppressive effects of space flight radiation and reactivation of latent virus infections in human beings are largely unknown. OBJECTIVE: To develop a murine model that can predict the adverse effects of space flight radiation and reactivation of latent virus infection for human beings. METHODS: In experiment I, some BALB/c mice received whole-body gamma-irradiation (3 Gy) on day 0 and murine polyoma virus (PyV) on day 1. In experiment II, mice received irradiation (3 Gy) or none on days 0 and/or 49, and PyV or none on day 1: A1, 3 Gy/PyV/3 Gy; A2, 3 Gy/ PyV/0 Gy; B1, 0 Gy/PyV/3 Gy; B2, 0 Gy/ PyV/0 Gy; C, 3 Gy/0 PyV/0 Gy; and D, 0 Gy/0 PyV/0 Gy. RESULTS: In experiment I, PyV was detected by PCR more frequently in several host organs tested and for a longer period of time in irradiated than in control animals. In experiment II, PyV replication in the spleen was detected in A1>B1 mice on days 10 and 20; both groups cleared PyV by day 49. After irradiation on day 49, reactivated PyV was detected in more B1 than A1 mice. A1 mice had lower spleen weights and cell counts than other groups at all time points. From 0 to 49 days, irradiation suppressed spleen cell proliferation to concanavalin A in all irradiated groups except in B1 when the virus was cleared at day 20. PyV enhanced IFN-gamma production in all groups: B1>A1>C, D (0-49 days; all differences, P < .05). CONCLUSION: This small animal model of space flight suggests that the combined effects of radiation and virus replication will significantly affect T-lymphocyte-mediated immunity that may lead to chronic viral infection and malignancy.

Animals↗
PubMed2001

Space flight: a challenge for normal bone homeostasis.

Space flight results in loss of bone mass, especially in weight-bearing bones, a condition that is suggested to be similar to disuse osteoporosis. As models to elucidate the underlying mechanism, bed rest studies were performed and bone metabolism in the rat both during space flight and during hindlimb unloading was investigated. The general picture is that bone formation is decreased partly as a result of reduced osteoblast function, whereas bone resorption is unaltered or increased. This deficit in bone mass can be replaced, but the time span for restoration exceeds the period of unloading. Changes in blood flow, systemic hormones, and locally produced factors are contributing in a yet undefined way to the response of osteoblastic cells to loading. The pathway by which loading and/or gravity are transduced into biochemical signals is still unknown. In vitro studies with osteoblastic cells show that their differentiation and cell morphology are altered during space flight. Elucidation of the involved signaling pathways has only recently been started. It is hoped that as the mechanisms by which bone responds to mechanical (un)loading are further understood, this insight will influence the treatment of other etiologies of osteoporosis.

Animals↗
PubMed2001

Effects of exposure to space flight on endocrine regulations in experimental animals.

This minireview summarizes the results of the observations on changes in endocrine functions of rats exposed to space flights for various periods. The results found after space flights are compared with those obtained from rats in acute or repeated restrain stress. A slight increase of plasma catecholamine levels was observed in rats after space flight of longer duration (>14 days), but no changes in catecholamine content in the activity of catecholamine synthesizing enzymes were noted in adrenal medulla and in hypothalamus. The norepinephrine content was, however, decreased in several nuclei selected from hypothalamus of flight rats. Plasma corticosterone levels were increased after space flight and morphological examination of pituitary showed elevated activity of corticotrophs. However, the plasma levels of ACTH were not increased in rats 6 hours after space flight. These changes in plasma hormone levels affected the activity of enzymes involved in metabolism of amino acids in liver and lipolysis in adipose tissue. The plasma levels of testosterone and triiodothyronine were diminished after space flight suggesting the suppression of the thyroid and gonadal activity. Increase of plasma insulin and glucose levels were found in rats after space flight, but the glucagon values were not changed. Comparing these results from flight rats with the animals exposed to acute or repeated stress indicate that long stay in microgravity do not represent very intensive stressogenic stimulus for adrenocortical and sympatho-adrenomedullar systems, and hormone alterations observed after space flight may be due to acute gravitational stress resulting from a return to Earth gravity. Therefore further studies including the inflight animal experiments on a board of International Space Station are necessary for elucidation of the effects of microgravity on endocrine functions.

Animals↗
PubMed1997

Altered astronaut lower limb and mass center kinematics in downward jumping following space flight.

Astronauts exposed to the microgravity conditions encountered during space flight exhibit postural and gait instabilities upon return to earth that could impair critical postflight performance. The aim of the present study was to determine the effects of microgravity exposure on astronauts' performance of two-footed jump landings. Nine astronauts from several Space Shuttle missions were tested both preflight and postflight with a series of voluntary, two-footed downward hops from a 30-cm-high step. A video-based, three-dimensional motion-analysis system permitted calculation of body segment positions and joint angular displacements. Phase-plane plots of knee, hip, and ankle angular velocities compared with the corresponding joint angles were used to describe the lower limb kinematics during jump landings. The position of the whole-body center of mass (COM) was also estimated in the sagittal plane using an eight-segment body model. Four of nine subjects exhibited expanded phase-plane portraits postflight, with significant increases in peak joint flexion angles and flexion rates following space flight. In contrast, two subjects showed significant contractions of their phase-plane portraits postflight and three subjects showed insignificant overall changes after space flight. Analysis of the vertical COM motion generally supported the joint angle results. Subjects with expanded joint angle phase-plane portraits postflight exhibited larger downward deviations of the COM and longer times from impact to peak deflection, as well as lower upward recovery velocities. Subjects with postflight joint angle phase-plane contraction demonstrated opposite effects in the COM motion. The joint kinematics results indicated the existence of two contrasting response modes due to microgravity exposure. Most subjects exhibited "compliant" impact absorption postflight, consistent with decreased limb stiffness and damping, and a reduction in the bandwidth of the postural control system. Fewer subjects showed "stiff" behavior after space flight, where contractions in the phase-plane portraits pointed to an increase in control bandwidth. The changes appeared to result from adaptive modifications in the control of lower limb impedance. A simple 2nd-order model of the vertical COM motion indicated that changes in the effective vertical stiffness of the legs can predict key features of the postflight performance. Compliant responses may reflect inflight adaptation due to altered demands on the postural control system in microgravity, while stiff behavior may result from overcompensation postflight for the presumed reduction in limb stiffness inflight.

Acceleration↗
PubMed1997

Comparison of ground-based and space flight energy expenditure and water turnover in middle-aged healthy male US astronauts.

Energy requirements during space flight are poorly defined because they depend on metabolic-balance studies, food disappearance, and dietary records. Water turnover has been estimated by balance methods only. The purpose of this study was to determine energy requirements and water turnover for short-term space flights (8-14 d). Subjects were 13 male astronauts aged 36-51 y with normal body mass indexes (BMIs). Total energy expenditure (TEE) was determined during both a ground-based period and space flight and compared with the World Health Organization (WHO) calculations of energy requirements and dietary intake. TEE was not different for the ground-based and the space-flight periods (12.40 +/- 2.83 and 11.70 +/- 1.89 MJ/d, respectively), and the WHO calculation using the moderate activity correction was a good predictor of TEE during space flight. During the ground-based period, energy intake and TEE did not differ, but during space flight energy intake was significantly lower than TEE; body weight was also less at landing than before flight. Water turnover was lower during space flight than during the ground-based period (2.7 +/- 0.6 compared with 3.8 +/- 0.5 L/d), probably because of lower fluid intakes and perspiration loss during flight. This study confirmed that the WHO calculation can be used for male crew members' energy requirements during short space flights.

Adult↗
PubMed2001

[Mechanisms reducing orthostatic stability of humans in long-term space flight].

Investigations conducted in and following space flights showed consistent decreases in cosmonauts' orthostatic stability due to the effects of long-term microgravity. Degree of this orthostatic disturbance depends on many factors prime of which is adequacy of countermeasures and least consequential is length of space flight, personal features, and others. Shifts in initial circulatory status and establishment of a new level of circulation and functioning of the other body systems in microgravity appear to play the central role in loss of orthostatic stability. The paper contains an in-depth analysis of processes occurring in human body during long-term stay in microgravity impacting orthostatic stability post flight.

Astronauts↗
PubMed2001

[G-tolerance of female cosmonauts during descent in space flights of 8 up to 169 days in duration].

Investigations into g-tolerance of female cosmonauts during descent in space flights of varying duration are topical for the present day, as there are little data on this issue. Tolerance of +Gz-loads during descent was analyzed based on the data about 4 female cosmonauts in 5 space flights. The space flights were conventionally divided into short- (8-16 days) and long-term (169 days). In two space flights (16 and 169-d long), tubeless anti-g suit Centaur was warn during descent. In these space flights, g-tolerance of females was quite satisfactory advocating for the possibility for women to fly to space without any constraints. When the anti-g suit was not used, female physiological systems were stressed heavier than male. The spacesuit smoothed away this difference. Our results evidence a distinct positive effect of wearing the anti-g suit by female cosmonauts during descent as it reduces stress to their physiological systems.

Adaptation, Physiological↗
PubMed1997

Neuromuscular activation patterns during treadmill walking after space flight.

Astronauts adopt a variety of neuromuscular control strategies during space flight that are appropriate for locomoting in that unique environment, but are less than optimal upon return to Earth. We report here the first systematic investigation of potential adaptations in neuromuscular activity patterns associated with postflight locomotion. Astronaut-subjects were tasked with walking on a treadmill at 6.4 km/h while fixating a visual target 30 cm away from their eyes after space flights of 8-15 days. Surface electromyography was collected from selected lower limb muscles and normalized with regard to mean amplitude and temporal relation to heel strike. In general, high correlations (more than 0.80) were found between preflight and postflight activation waveforms for each muscle and each subject: however relative activation amplitude around heel strike and toe off was changed as a result of flight. The level of muscle cocontraction and activation variability, and the relationship between the phasic characteristics of the ankle musculature in preparation for toe off also were altered by space flight. Subjects also reported oscillopsia during treadmill walking after flight. These findings indicate that, after space flight, the sensory-motor system can generate neuromuscular-activation strategies that permit treadmill walking, but subtle changes in lower-limb neuromuscular activation are present that may contribute to increased lower limb kinematic variability and oscillopsia also present during postflight walking.

Adaptation, Physiological↗
PubMed2006

[Bone loss and bone metabolism in astronauts during long-duration space flight].

Significant bone loss is one of the most serious medical concerns during long-duration space flight. This article provides the results of bone loss and bone metabolism obtained from American and Russian long-duration human space flight. Bone loss in astronauts before and after long-duration space flight was evaluated by dual energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). DXA revealed bone loss at rates of 0.9%/month in the lumbar spine and 1.5%/month in the femoral neck. QCT revealed cortical, trabecular and integral BMD in the femoral neck at rates of 0.5%/month, 2.5%/month, and 1.5%/month, respectively. Biochemical markers of bone resorption increased during space flight and several months after landing. Bone formation marker was unchanged during space flight, but since 3 weeks after landing it was significantly higher than before flight. A calcium kinetics study confirmed that bone resorption increased, and intestinal calcium absorption decreased during space flight.

Absorptiometry, Photon↗
PubMed1986

A review of the psychological aspects of space flight.

Instances of overt, serious functional impairment of space crews caused by adverse psychologic responses have not been scientifically documented. However, transient disorientation, spatial illusions, and visual disturbances as well as anomalous myopias, sleep disturbances, and instances of substandard performance have been described. Moreover, anecdotal information describes significant psychologic aberrations in space flight. Adequate scientific data are lacking for optimal psychological and psychophysiological methods for crew selection, training, and performance evaluation, for identifying key psychosocial factors for crew compatibility, cohesiveness, and productivity, and for determining the effects of space flight on perceptual, intellectual, and motor skills. The ad hoc Working Group, convened to review psychological aspects of space flight, favored establishment of a comprehensive research and development program to address the deficiencies identified in the study.

Behavior↗
PubMed1992

Some medical aspects of an 8-month's space flight.

In 1984 a 237-day space flight was performed on board the orbital complex Salyut-7-Soyuz-T with the crew members Leonid D. Kizim (Commander), Vladimnir A. Solovyov (Flight-Engineer), and Oleg Yu. Atkov (Cosmonaut Researcher). The major medical task was to continue the study of the acute stage of adaptation to weightlessness, phenomenology and mechanisms of changes in hemodynamics, metabolism and other functions. During flight, echocardiographic and biochemical measurements, vestibular and sensory studies were conducted extensively. In 1988-1989, the fourth prime crew performed its flight on the Mir orbital station. The crew consisted of: A.A. Volkov (Commander, Cr), S.K. Krikalyov (Flight-Engineer, FE) who were launched together with J.L. Cretien on November 26, 1988 as well as V.V. Polyakov (physician, cosmonaut-researcher, CP) who was in orbit until August 29, 1988 as a member of the third and fourth expeditions. Cr and FE remained in orbit for 151 days and CP for 421 days. Now we have 4 people experiencing 8 months space flight. The countermeasures included regular exercises on a treadmill and bicycle ergometer, use of G-suits and lower body negative pressure (LBNP) training at the final stage. The cosmonauts exercised for a hour twice a day for 3 days on end and then had an "active rest" day. On the recovery day the cosmonauts were recommended to take water-salt supplements according to the following protocol: 2.7 g NaCl in 300 ml liquid during lunch and dinner plus 1.8 g NaCl in 150 ml liquid immediately before they began preparing for the descent (after they donned their space suits). During re-entry the cosmonauts had an anti-G suit on (without bladders).

Adaptation, Physiological↗
PubMed2005

Interventions to prevent bone loss in astronauts during space flight.

This paper reviews the interventions to stabilize calcium balance and bone metabolism and prevent bone loss in astronauts during space flight. Weightlessness during space flight results in calcium, vitamin D, and vitamin K deficiency, increases urinary calcium excretion, decreases intestinal calcium absorption, and increases serum calcium level, with decreased levels of serum parathyroid hormone and calcitriol. Bone resorption is increased, whereas bone formation is decreased. The loss of bone mineral density (BMD) in the spine, femoral neck and trochanter, and pelvis is 1.0-1.6% per month. High calcium intake and vitamin D supplementation during space flight does not affect bone metabolism, but prevents an elevation of serum calcium level through increased calcitriol level, while vitamin K counteracts the reduction in bone formation. However, there are no data to show the efficacy of pharmaceutical agents for prevention of development of osteoporosis in astronauts during flight, although the preventative effect of bisphosphonates, testosterone, and vitamin K2 on cancellous bone loss in the tibia or BMD loss in the hindlimb was reported in tail-suspended mature rats. It still remains uncertain whether these agents can prevent cortical bone loss caused by weightlessness in tail-suspended rats. Therefore, in addition to calcium, vitamin D, and vitamin K supplementation, agents that have both potent anti-resorptive and anabolic effects on cancellous and cortical bone may be needed to stabilize calcium balance and bone metabolism and prevent bone loss in astronauts during space flight.

Aerospace Medicine↗
PubMed2003

[Development of medical monitoring and support in the practice of manned space flight].

The astronaut medical monitoring and support is an important part of space operational medicine. With the rapid development of the cause of China's manned space flight, the astronaut medical monitoring and support work has also made considerable progress since 1990s. Space operational medicine is responsible for the medical monitoring and support during astronaut selection and training as well as during the space flight. It's a severe challenge for mid-long term space flight to assure astronauts in sound body and mind and have good working capability. On the basis of the medical monitoring and support in short-term space flight, we should carry out the research of space operational medicine.

Aerospace Medicine↗
PubMed2005

Use of animal models for space flight physiology studies, with special focus on the immune system.

Animal models have been used to study the effects of space flight on physiological systems. The animal models have been used because of the limited availability of human subjects for studies to be carried out in space as well as because of the need to carry out experiments requiring samples and experimental conditions that cannot be performed using humans. Experiments have been carried out in space using a variety of species, and included developmental biology studies. These species included rats, mice, non-human primates, fish, invertebrates, amphibians and insects. The species were chosen because they best fit the experimental conditions required for the experiments. Experiments with animals have also been carried out utilizing ground-based models that simulate some of the effects of exposure to space flight conditions. Most of the animal studies have generated results that parallel the effects of space flight on human physiological systems. Systems studied have included the neurovestibular system, the musculoskeletal system, the immune system, the neurological system, the hematological system, and the cardiovascular system. Hindlimb unloading, a ground-based model of some of the effects of space flight on the immune system, has been used to study the effects of space flight conditions on physiological parameters. For the immune system, exposure to hindlimb unloading has been shown to results in alterations of the immune system similar to those observed after space flight. This has permitted the development of experiments that demonstrated compromised resistance to infection in rodents maintained in the hindlimb unloading model as well as the beginning of studies to develop countermeasures to ameliorate or prevent such occurrences. Although there are limitations to the use of animal models for the effects of space flight on physiological systems, the animal models should prove very valuable in designing countermeasures for exploration class missions of the future.

Animals↗