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Results for “Weightlessness Countermeasures”

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At least 73 records · Page 4Linked to original sources
PubMed1997

Analysis of heart rate variability and its application.

Heart rate variability (HRV) has considerable potentials in assessing the role of autonomic nervous system fluctuations in healthy individuals and patients. This paper reviews the analytical methods of HRV and its application. HRV is a useful parameter for predicting cardiac risk after acute myocardial infarction, and an early warning sign of diabetes neuropath in clinical medicine. In space medical studies, HRV analysis have been used to assess changes in autonomic regulation after weightlessness or simulated weightlessness, evaluate tolerance in various stress test, study regulatory mechanisms of cardiovascular system, and assess the effect of countermeasure against weightlessness.

Aerospace Medicine↗
PubMed2001

[Counteraction effect of intermittent -Gx on changes of responsiveness of basilar artery in tail-suspended rats].

OBJECTIVE: To investigate counteracting effects of intermittent -Gx exposure on changes of responsiveness of basilar artery in tall-suspended rats. METHOD: Rats tail-suspended for 3 wk were daily subjected to 1 h 1.5 G or 2.6 G centrifugation, simulating -Gx exposure of various G values. Responses of perfused isolated basilar arterial rings to KCl was examined. RESULT: Maximal isometric contractile response to KCl were significantly enhanced in arterial rings isolated from 3 wk tail-suspended rats as compared with that from simultaneous control rats (P < 0. 05). However, maximal isometric contractile responses to KCl of arterial rings isolated from 3 wk tail-suspended plus daily -Gx exposure rats were no difference as compared with that from simultaneous control rats, and were significantly decreased (P < 0.05) as compared with that from 3 wk tail-suspended rats. CONCLUSION: Daily intermittent -Gx exposure as a countermeasure to prevent the effects of simulated weightless on changes in responsiveness of basilar artery from tail-suspended rats was valid.

Animals↗
PubMed2001

Modern view on the short-arm centrifuge as a potential generator of artificial gravity in piloted missions.

The problem of artificial gravity (AG) in long-term missions is one of the hottest, as the existing countermeasures do not fully cope with the negative consequences of weightlessness. From two variants of AG creation--rotation of space systems around of their mass center or short radius centrifuge (SAC)--the preference is given to SAC, as technically easier variant for realization. However, the rotation of a person on SAC can cause not only positive, but also negative effects. The purpose of the present study was to perform the analysis of data of researches on a problem of AG generated by a of SAC, executed in Russia during last 20 years, and to state modern views on application of SAC as a mean of AG creation in long piloted missions.

Adaptation, Physiological↗
PubMed1999

Relatively shorter but intensive isotonic exercise in legs prevented the decrease in maximal aerobic power after 20 days of head down tilt bed rest in man.

As a countermeasures for the decrease in maximal oxygen uptake (VO2max) during prolong simulated weightlessness, it has been suggested that intensive isotonic legs exercise was useful. The reason is possibly that a dynamic and intensive resistance exercise training makes to maintain not only the volume of exercising muscles but also cardiac output. For the reason, it has been studied the effects of 3 different exercise training on VO2max during simulated weightlessness.

Bed Rest↗
PubMedDate not supplied

Biomedical aspects of artificial gravity.

Artificial gravitv generated by spacecraft rotation may prove a universal countermeasure against adverse effects of weightlessness in the future. The paper summarizes the results of ground-based biomedical investigations of artificial gravity and flight experiments aboard Soviet biosatellites Cosmos-782 and Cosmos-936. It is believed that at the present stage the major goal of such investigations is to determine the minimum efficient value of artificial gravity in long-term flights which may eliminate adverse effects of prolonged weightlessness. In ground-bound studies the highest priority should be given to the development of methods on increasing human tolerance to the rotating environment.

Adaptation, Physiological↗
PubMedDate not supplied

Artificial gravity--head movements during short-radius centrifugation: influence of cognitive effects.

Short-radius centrifugation is a potential countermeasure against the effects of prolonged weightlessness. Head movements in a rotating environment, however, induce serious side effects: inappropriate vestibular ocular reflexes (VOR), body-tilt illusions and motion sickness induced by cross-coupled accelerations on a rotating platform. These are well predicted by a semicircular canal model. The present study investigates cognitive effects on the inappropriate VOR and the illusory sensations experienced by subjects rotating on a short-radius centrifuge (SRC). Subjects (N=19) were placed supine on a rotating horizontal bed with their head at the center of rotation. To investigate the extent to which they could control their sensations voluntarily, subjects were asked alternatively to "fight" (i.e. to try to resist and suppress) those sensations, or to "go" with (i.e. try to enhance or, at least, acquiesce in) them. The only significant effect on the VOR of this cognitive intervention was to diminish the time constant characterizing the decay of the nystagmus in subjects who had performed the "go" (rather than the "fight") trials. However, illusory sensations, as measured by reported subjective intensities, were significantly less intense during the "fight" than during the "go" trials. These measurements also verified an asymmetry in illusory sensation known from earlier experiments: the illusory sensations are greater when the head is rotated from right ear down (RED) to nose up (NU) posture than from NU to RED. The subjects habituated, modestly, to the rotation between their first and second sequences of trials, but showed no better (or worse) suppression of illusory sensations thereafter. No significant difference in habituation was observed between the "fight" and "go" trials.

Adaptation, Physiological↗
PubMedDate not supplied

Countermeasure of the negative effects of weightlessness on physical systems in long-term space flights.

The system of countermeasure of microgravity effects has been developed in Russia that allowed to perform safely long-term space flights. This system that includes different means and methods such as special regimens of physical exercises, axial loading ("Pingiun") and antigravity suits, low body negative pressure device (LBNP, "Chibis") and "cuffs" and others has been used with certain variations at certain stages of flight in 27 successfully accomplished space flights that lasted from 60 to 439 days. The pre-, in- and postflight studies performed in 57 crew members of these flights have shown that the system of countermeasure is effective in preventing or diminishing to a great extent almost all the negative effects of weightlessness in flights of a year and more duration and that the intensity and duration of changes recorded in different body systems after flights do not correlate significantly to flight durations, correlating strongly to the volume and intensity of physical exercises used during flight and especially during concluding stage of it.

Aerospace Medicine↗
PubMed1991

Carotid-cardiac baroreflex: relation with orthostatic hypotension following simulated microgravity and implications for development of countermeasures.

In a series of studies, we have examined the effects of exposure to simulated microgravity, varying states of vascular volume, and acute exercise on the function of the carotid-cardiac baroreflex in man. In the first study, exposure to simulated microgravity (6 degrees headdown bedrest) reduced the sensitivity and buffer capacity of the vagal baroreceptor-cardiac reflex mechanisms and this impaired baroreflex function was associated with orthostatic hypotension. Since the reduction in plasma volume during BR was not correlated with impaired baroreflex function, a second study was conducted which demonstrated that the carotid-cardiac baroreflex response was not affected by either acute hypovolemia or hypervolemia. These results suggest that acute fluid replacement prior to reentry may not reverse impaired baroreflex function associated with postflight hypotension. In a third study, we demonstrated that one bout of maximal exercise increased baroreflex sensitivity and buffer capacity through 24 h post-exercise. These baroreflex changes were opposite to those observed following BR. Taken together, these data suggest that the contributions of reduced blood volume and impaired carotid-cardiac baroreflex function to orthostatic hypotension following exposure to microgravity are probably separate and additive; maximal exercise in addition to fluid replacement may provide an acute effective countermeasure against postflight hypotension.

Adult↗
PubMed2001

Bed-rest studies for the International Space Station.

The microgravity experienced during space flight induces physiological changes that affect astronauts' health and performance. Simulations such as prolonged bed rest can mimic some of these changes and provide study conditions that are more accessible than during space flight itself. Previous studies, including several long and short-term bed-rest campaigns supported by ESA, have yielded significant medical data on the physiological changes induced by space flight. These data are being used extensively to study the effects of various countermeasures on those physiological changes.

Bed Rest↗
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↗
PubMed2006

Gravity replacement during running in simulated microgravity.

INTRODUCTION: During treadmill exercise on the International Space Station (ISS), a restoring load from a subject load device (SLD) is applied through a shoulder-and-waist harness to pull the exercising crewmember toward the treadmill surface. The capacity of this arrangement to provide 1-g-like reaction forces may be critical for effective use of the treadmill as a countermeasure to musculoskeletal changes during prolonged spaceflight. This study in simulated microgravity evaluated the comfort and function during running of the ISS harness used with a new SLD in a system that allows more even distribution of the load between the waist and shoulders. METHODS: Using a zero-gravity locomotion simulator, 12 subjects completed three 5-min running trials at a constant speed (3.35 m x s(-1)) using three SLD loads [50%, 75%, and 100% of bodyweight (BW)] presented at random and a shoulder-to-waist loading ratio of 50:50. Subjective ratings of discomfort, ground reaction forces (GRFs), and SLD loads were collected. RESULTS: A load of 100% BW resulted in similar GRF profiles (peak and rate of change of force) to those reported for 1-g running over ground and were also comfortably tolerated (mean Borg scale rating 3.9/10). DISCUSSION: With an appropriate harness and SLD system, 1-g-like GRF profiles can be generated at the feet during simulated microgravity running. Such forces can be achieved with a level of discomfort rated better than "somewhat uncomfortable," suggesting that running with 1-g loads could be an effective component of musculoskeletal countermeasures during long-duration spaceflight.

Adult↗
PubMed2004

Human adductor muscles atrophy after short duration of unweighting.

The purpose of this study was to investigate the effect of 20 days of bed rest (BR) on the physiological cross-sectional area (PCSA) of the adductor (AD) muscle group. Five healthy men and five healthy women were kept on a horizontal bed for 20 days. To calculate the PCSA of the AD muscle group, transaxial magnetic resonance imaging of the right thigh was acquired four times for each of the subjects: (1) pre BR, (2) on the tenth day of BR, (3) post BR, and (4) 1 month after BR. Overall, the PCSA measurements of the AD muscle group and its individual muscles were significantly decreased on the tenth day of BR and at post BR; however, they had recovered to the baseline within 1 month of the reambulation period. The amount and pattern of relative change in the PCSA measurements of the AD muscle group were similar to those of the knee extensor (KE) and knee flexor (KF) muscle groups studied previously. These results suggested that the AD muscle group showed an atrophic response that was similar to the KE and KF muscle groups after unweighting; therefore, we should pay much more attention to the AD muscle group when considering countermeasures for future human spaceflight projects.

Adult↗
PubMedDate not supplied

Muscle atrophy associated with microgravity in rat: basic data for countermeasures.

Morphological, contractile properties and myosin heavy chain (MHC) composition of rat soleus muscles were studied after 2 weeks of unloading (HS) and after 2 weeks of HS associated with selective deafferentation (HS + DEAF) at the level L4 and L5. The same significant reductions in muscle mass and tetanic tension were found after HS and HS + DEAF. However, the transformation of the slow-twitch soleus muscle towards a faster type characterized by a decrease in twitch time parameters and an increase in fast-twitch type MHC isoforms in HS did not appear in HS + DEAF conditions. Our results also showed that a pattern similar to firing rate of motoneurones innervating slow-twitch muscles inhibited the slow to fast fiber changes observed during HS. Nevertheless, neither the loss of mass or force output in the HS muscles were prevented by electrostimulation. Immobilization in a stretched position during HS maintained the muscle wet weight, mechanical and electrophoretical characteristics close to control values. We concluded that the decrease in mechanical strains imposed on the muscle during unloading was the main factor for the development of atrophy, while the kinetic changes might be predominantly modulated by the nervous command. These basic data suggested that some experimental conditions such as electrostimulation or stretching, could participate in countermeasure programmes.

Afferent Pathways↗
PubMed1999

Angiotensin-(1-7) antagonist [D-Ala7-Ang-(1-7);A-779] attenuates post-suspension hypotension in Sprague-Dawley rats.

Cardiovascular deconditioning manifested by reduction in mean arterial pressure (MAP) and cardioaccleration are usually observed in astronauts during standing postflight. The head-down tilt (HDT) rat model with "unloaded" hindlimbs has been extensively studied because some of the observed responses mimic observations made during exposure to microgravity. Angiotensin-(1-7) is a biologically active component of the renin-angiotensin system that acts to oppose the pressor and proliferative actions of Angiotensin II. It produces a hypotensive response by either stimulating production of vasodilator prostaglandins (i.e., prostacyclin), increasing nitric oxide or both. In the present study, we have evaluated the role of a specific inhibitor of Ang-(1-7), D-Ala7-Ang-(1-7)[A-779], as a countermeasure against post-suspension hypotension.

Angiotensin II↗
PubMed2005

Countermeasure for space flight effects on immune system: nutritional nucleotides.

Microgravity and its environment have adverse effects on the immune system. Abnormal immune responses observed in microgravity may pose serious consequences, especially for the recent directions of NASA for long-term space missions to Moon, Mars and deep Space exploration. The study of space flight immunology is limited due to relative inaccessibility, difficulty of performing experiments in space, and inadequate provisions in this area in the United States and Russian space programs (Taylor 1993). Microgravity and stress experienced during space flights results in immune system aberration (Taylor 1993). In ground-based mouse models for some of the microgravity effects on the human body, hindlimb unloading (HU) has been reported to cause abnormal cell proliferation and cytokine production (Armstrong et al., 1993, Chapes et al. 1993). In this report, we document that a nutritional nucleotide supplementation as studied in ground-based microgravity analogs, has potential to serve as a countermeasure for the immune dysfunction observed in space travel.

Animals↗
PubMed1996

Regional blood flow in microgravity: adaptation and deconditioning.

The objectives were to evaluate cardiac and peripheral changes induced by microgravity with and without countermeasures (CM), to assess the peripheral response to orthostatic tests (tilt, LBNP). Inflight or HDT, we used echography and Doppler to assess the left heart function and the peripheral arteries. We studied the cardiovascular system during 1) 21-d and 25-d spaceflights without CM, 2) 14.d spaceflight with "bracelets" CM, 3) 28-d HDT with and without LBNP, and 4) 30-d HDT with and without Exercise+LBNP. Similar peripheral circulation changes were noticed in both astronauts and HDT subjects without CM. There was a decrease in renal, cerebral, and femoral vascular resistances and maintenance of cerebral flow at rest, and a lack of increase in lower limb vascular resistance and abnormal flow redistribution during orthostatic tests. Conversely, with CM at rest, cerebral and renal vascular resistances stayed elevated and femoral resistance decreased, but less than without countermeasures. Lower limb vascular resistance increased normally, peripheral flows were adequately redistributed during orthostatic tests, and no orthostatic intolerance was observed. This confirms the efficiency of countermeasures (LBNP, exercise, cuffs) in preserving the vasomotor tone in most peripheral areas at rest and reducing the development of orthostatic intolerance.

Adaptation, Physiological↗