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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Skeletal abnormalities in rats induced by simulated weightlessness

A hypokinetic model has been developed which attempts to simulate the weightlessness experienced during space flight. Male rats were suspended from the model with a head-down tilt for a two-week period. Total mechanical unloading of the hind limbs and partial unloading of the fore limbs occurred. In comparison to pair-fed control rats, the skeletal alterations in the proximal tibial and humeral metaphyses of suspended rats were determined to be a diminished rate of longitudinal bone growth, a reduced mass of mineralized tissue, and an accumulation of marrow fat. Also, suspended rats exhibited decreased numbers of osteoblasts and increased numbers of osteoclasts immediately adjacent to the growth plate-metaphyseal junction at both skeletal sites. Although the reduction in mineralized tissue and the fat accumulation were more marked in the tibia, the skeletal changes in the proximal tibial and humeral metaphyses were generally comparable. The observed abnormalities may be due to mechanical unloading and/or a hypersecretion of corticosteroids.

Wronski, T. J.↗
NASA NTRS1982

Evaluation of the response of rat skeletal muscle to a model of weightlessness

Suspension of rats in a head-down tilt position such that their hind limbs are non-load bearing has been proposed as a model for weightlessness. Changes observed in metabolism, bone formation (Morey et al., 1979), and muscle catabolism (Mussachia et al., 1980) support the validity of the model. To further document this model, the effects of suspension on the mechanical, biochemical and histochemical characteristics of two hind limb skeletal muscles, the gastrocnemius and the soleus, are investigated.

Templeton, G. H.↗
NASA NTRS1983

Cardiovascular responses to hypogravic environments

The cardiovascular deconditioning observed during and after space flight is characterized in a review of human space and simulation studies and animal simulations. The various simulation techniques (horizontal bed rest, head-down tilt, and water immersion in man, and immobilization of animals) are examined, and sample results are presented in graphs. Countermeasures such as exercise regimens, fluid replacement, drugs, venous pooling, G-suits, oscillating beds, electrostimulation of muscles, lower-body negative pressure, body-surface cooling, and hypoxia are reviewed and found to be generally ineffective or unreliable. The need for future space experimentation in both humans and animals is indicated.

Sandler, H.↗
NASA NTRS1985

Regulation of hematopoiesis in rats exposed to antiorthostatic, hypokinetic/hypodynamia. I - Model description

The effect of a 7-day suspension in a jacket and harness with 20-deg head-down tilt on body weight, food and water consumption, and hematological parameters is investigated experimentally in male Sprague-Dawley rats weighing 150-175 g. The results are presented in graphs and compared with those for unsuspended controls and with published data on rats and humans exposed to microgravity in space flight. Suspended rats are found to have reduced red-blood-cell mass, erythropoiesis, plasma volume (leading to temporarily increased hematocrit), body weight, and food and water consumption; rightward-shifted oxyhemoglobin-dissociation curves; and unchanged platelet count, leucocyte count or PHA reactivity, and red-blood-cell shape distribution. Since many of these effects are also seen in space flight, the present experimental model is considered a promising technique for simulating the hematopoietic effects of microgravity at 1 g.

Dunn, C. D. R.↗
NASA NTRS1984

Cardiovascular and hormonal (aldosterone) responses in a rat model which mimics responses to weightlessness

Cardiovascular responses and fluid/electrolyte shifts seen during spaceflight have been attributed to cephalad redistribution of vascular fluid. The antiorthostatic (AO) rat (suspended, head-down tilt of 15-20 deg) is used to model these responses. This study documents that elevated blood pressures in AO rats are sustained for periods of up to seven days, compared with presuspension values. Increased blood pressures in AO rats suggests a specific response to AO positioning, potentially relatable to a cephalad fluid shift. To assess a role for hormonal regulation of sodium excretion, serum aldosterone levels were measured. Circulating aldosterone concentrations were seen to increase approximately 100 percent during seven days of AO suspension, concurrently with a pronounced natriuresis. These results suggest that aldosterone may not be involved in the long term regulation of increased Na(+) excretion in AO animals. These studies continue to show the usefulness of models for the development of animal protocols for space flight.

Musacchia, X. J.↗
NASA NTRS1985

Transient dehydration of lungs in tail-suspended rats

The fluid balance in the lungs of rats exposed to head-down tilt is examined. Six Munich-Wister rats were suspended for 7 days and 10 Sprague-Dawley rats for 14 days using the technique of Morey (1979). The water contents of the lungs of the suspended and a control group are calculated and compared. The data reveal that the two-days suspended rats had dehydrated lungs; however, the lungs of the 14-day suspended and control group rats were similar. It is noted that the dehydration in the 2-day suspended rats is caused by general dehydration not the head-tilt position.

Hargens, A. R.↗
NASA NTRS1986

Biomedical support of man in space

The effects of G and/or exercise on cardiopulmonary adjustments to stresses are studied. The control of the cardiopulmonary system is examined using simulated microgravity (recumbency, immersion, lower body positive pressure, and 6-deg head-down tilt) and increased acceleration. It is observed that at rest and during exercise in simulated zero-6 environments, the stroke volume and cardiac output are initially increased and then (after prolonged exposure) return to prezero-G levels. Cardiovascular responses to increased gravity (1, 2, and 3 G) at rest and during exercise are analyzed; a decrease in plasma volume resulting in decreases in stroke volume and cardiac output, and an increase in heart rate are detected.

Pendergast, D. R.↗
NASA NTRS1986

Microcirculatory fluid dynamics in weightlessness and simulated weightlessness

The method of Smith et al. (1985), which makes it possible to simultaneously measure the macrocirculation and microcirculation in an unanesthetized rat, was used to study the effect of acute hypokinesia on the rat microvascular system. The measurements yielded values of the length, diameter, and number of arteriolar and venular vessels; vascular patterns; branching ratios; and the amplitude and frequency of vasomotion. Early effects (30-60 min after the start of the head-down tilt) include a 10 percent increase in the diameter of arterioles, a slight increase of heart rate and mean arterial blood pressure, and an increase in the heart rate-pulse pressure product, with most of the changes returning to normal after 2-3 h. The baroreceptor reflex index was reduced by almost 50 percent for the first 2 h, but rebounded to almost 3 times the control value after 3 h. This indicates that, in spite of relatively small changes in gross hemodynamic parameters, the cardiovascular function is altered significantly during the acute phase of hypokinesia.

Hutchins, P. M.↗
NASA NTRS1984

Effect of antiorthostatic suspension on interferon-alpha/beta production by the mouse (41939)

Mice were suspended in a model that simulates the weightlessness that occurs during prolonged space flight. After one and two weeks of suspension in an antiorthostatic (head-down tilt) position, the mice were challenged with polyriboinosinic-polyribocytidylic acid to induce interferon-alpha/beta. Interferon production was severely reduced in mice that had been suspended. When mice were allowed to recover in cages for a week following removal from suspension, they recovered their full interferon-production capacity. Mice suspended in an orthostatic (horizontal) position did not have their interferon production capabilities affected, which indicates that stress per se was not a major component in the effects of antiorthostatic suspension on interferon induction.

Rose, Andrea↗
NASA NTRS1987

Enhancement of viral pathogenesis in mice maintained in an antiorthostatic suspension model - Coordination with effects on interferon production

Both rodents and men returning from spaceflight have exhibited alterations in immune responses and, in particular, interferon production. This work utilizes a model for antiorthostatic (20-deg head-down tilt), hypokinetic, hypodynamic suspension of mice that simulates some aspects of weightlessness. Female Swiss/Webster mice that are normally resistant to infection with the D variant of encephalomyocarditis virus showed a marked increase in susceptibility to infection when suspended. This correlated with a drop in interferom production. Control, orthostatically suspended mice (no tilt) showed no increase in susceptibility to the virus.

Gould, C. L.↗
NASA NTRS1990

Effect of simulated weightlessness on the postural response of microvascular cutaneous blood flow

The effect of simulated weightlessness (1 week of bed rest) on the response of cutaneous microcirculatory blood flow to postural changes was investigated by measuring rates of the cutaneous blood flow in the central forehead and in the dorsum of the left foot in subjects who were tested in -6 deg head-down tilt (HDT) and 60-deg head-up tilt (HUT) before and after the week of bed rest. It was found that, when the subjects were moved from HUT to HDT before the bed rest period, the forehead cutaneous blood flow increased (in comparison to no-tilt baseline), due to increased arterial pressure, by about 26 percent, and that the response was the same on the first and the second day after 1 week of bed rest. The cutaneous blood flow in the dorsum of the foot decreased by about 46 percent in response to tilting from HDT to HUT both before and after bedrest.

Aratow, M.↗
NASA NTRS1991

Light as a chronobiologic countermeasure for long-duration space operations

Long-duration space missions require adaptation to work-rest schedules which are substantially shifted with respect to earth. Astronauts are expected to work in two-shift operations and the environmental synchronizers (zeitgebers) in a spacecraft differ significantly from those on earth. A study on circadian rhythms, sleep, and performance was conducted by exposing four subjects to 6 deg head-down tilt bedrest (to simulate the effects of the weightless condition) and imposing a 12-h shift (6 h delay per day for two days). Bright light was tested in a cross-over design as a countermeasure for achieving faster resynchronization and regaining stable conditions for sleep and circadian rhythmicity. Data collection included objective sleep recording, temperature, heart rate, and excretion of hormones and electrolytes as well as performance and responses to questionnaires. Even without a shift in the sleep-wake cycle, the sleep quantity, circadian amplitudes and 24 h means decreased in many functions under bedrest conditions. During the shift days, sleepiness and fatigue increased, and alertness decreased. However, sleep quantity was regained, and resynchronization was completed within seven days after the shift for almost all functions, irrespective of whether light was administered during day-time or night-time hours. The time of day of light exposure surprisingly appeared not to have a discriminatory effect on the resynchronization speed under shift and bedrest conditions. The results indicate that simulated weightlessness alters circadian rhythms and sleep, and that schedule changes induce additional physiological disruption with decreased subjective alertness and increased fatigue. Because of their operational implications, these phenomena deserve additional investigation.

Samel, Alexander↗
NASA NTRS1987

Spacelab Life Sciences flight experiments: an integrated approach to the study of cardiovascular deconditioning and orthostatic hypotension

The microgravity environment of spaceflight produces rapid cardiovascular changes which are adaptive and appropriate in that setting, but are associated with significant deconditioning and orthostatic hypotension on return to Earth's gravity. The rapidity with which these space flight induced changes appear and disappear provides an ideal model for studying the underlying pathophysiological mechanisms of deconditioning and orthostatic hypotension, regardless of etiology. Since significant deconditioning is seen after flights of very short duration, muscle atrophy due to inactivity plays, at most, a small role. These changes in circulatory control associated with cephalad fluid shifts, rather than inactivity per se, are probably more important factors. In order to test this hypothesis in a systematic way, a multidisciplinary approach which defines and integrates inputs and responses from a wide variety of circulatory sub-systems is required. The cardiovascular experiments selected for Spacelab Life Sciences flights 1 and 2 provide such an approach. Both human and animal models will be utilized. Pre- and post-flight characterization of the payload crew includes determination of maximal exercise capacity (bicycle ergometry), orthostatic tolerance (lower body negative pressure), alpha and beta adrenergic sensitivity (isoproterenol and phenylephrine infusions), baroreflex sensitivity (ECG-gated, stepwise changes in carotid artery transmural pressure with a pneumatic neck collar), and responses to a 24 h period of 5 deg head-down tilt. Measurements of cardiac output (CO2 and C2H2 rebreathing), cardiac chamber dimensions (phased-array 2-dimensional echocardiography), direct central venous pressure, leg volume (Thornton sock), limb blood flow and venous compliance (occlusion plethysmography), blood and plasma volumes, renal plasma flow and glomerular filtration rates, and various hormonal levels including catecholamines and atrial natriuretic factor will also be obtained. The central venous catheter will be inserted immediately pre-launch and monitored with heart rate and blood pressure in-flight until cardiac output, respiratory gas exchange and quantitative 2D echocardiography measurements can be performed. In-flight hemodynamic measurements will be repeated at rest and during submaximal exercise daily and also during maximal exercise midway through the flight to document the timecourse and extent of cardiovascular changes in the payload crew. Parallel studies are planned for the animals. In addition to measurements of right atrial and aortic pressures and cardiac output, a dorsal micro-circulatory chamber will allow determinations of changes in capillary and venular architecture and function in six of the rats. The techniques and findings from many of the SLS-1 and 2 supporting studies have already yielded significant information about circulatory regulation in patients with both hypo- and hypertension. The flight experiments themselves will provide new data to test the validity of both animal and human models currently used for simulating the fluid shifts of a micro-gravity environment. The development of effective countermeasures, not only for short and long duration space travellers, but also for Earth-bound medical patients can then be physiologically based on experimental data rather than anecdote.

Non-NASA Center↗
NASA NTRS1971

Hydraulically operated tilt table

Table raises, lowers, or tilts test subject from vertical through an angle of 105 deg to a head-down position of 15 deg. Table is designed for medical center or laboratory use. Additional features are described.

Gause, R. L.↗
NASA NTRS1982

Short term /1 and 3 day/ cardiovascular adjustments to suspension antiorthostasis in rats

Antiorthostasis (AO) results in responses reflective of thoracic vessel loading. Initial findings included fluid and electrolyte shifts (diuresis and natriuresis) in AO but not in orthostatic (O) rats. This study aims at obtaining supportive evidence for cardiovascular responses, E.g., blood pressure and related parameters, in light of the original hypothesis. Tilting rats rapidly head-up from either horizontal (O) or head-down (AO) positions was used to assess cardiovascular sensitivities. O and AO rats were used after 1 or 3 days of suspension. Rats were controls (C), pre-tilted O and AO, tilted O and AO (rapid head-up 70-80 deg); post-tilted (to original postures). MAP in C rats was 108 +2 mmHg, in O, (117 + or - 1.02) and AO, (120 + or - 0.58). MAP, diastolic pressure (DP) and pulse pressure were consistently elevated in AO rats on day 3. With rapid head-up tilt, only MAP and DP showed significant increases. These changes were seen as cardiovascular responses to AO and support further use of this rat model for AO studies.

Musacchia, X. J.↗
NASA NTRS1989

Orthostatic responses following 30-day bed rest deconditioning with isotonic and isokinetic exercise training

The effects of intensive exercise training on tilt tolerance following deconditioning of astronauts were investigated by studying orthostatic responses of 19 subjects who underwent two intensive exercise-training regimens during 30 days of -6-deg head-down bed rest (BR). Subjects were divided into no-exercise control group, and two exercise groups, one performing isotonic (Quinton ergometer) exercises, the other doing isokinetic (Lido ergometer) exercises. A 60-deg head-up tilt test was administered on the control day 1 and BR day 30; the test was terminated at 60 min or when presyncopal signs and/or symptoms occurred. It was found that exercise training did not affect tilt tolerance significantly.

Greenleaf, J. E.↗
NASA NTRS1982

Hormonal changes in antiorthostatic rats

Hypokinesia, especially hypokinesia with negative tilt ('antiorthostatic hypokinesia'), mimics some of the effects of weightlessness. It is shown that cardiac output is increased during early exposure of rats to antiorthostatic hypokinesia. The increase of the stroke volume and of the cardiac output observed in the antiorthostatic hypokinetic rats is probably the consequence of a blood volume shift toward the chest brought forth by head-down positioning of the animals. It is also possible that struggling of the animals to escape from the harness and an increased metabolism contribute to the elevation of cardiac output. In order to study this hypothesis 'stress hormones' were measured in the antiorthostatic rats. Plasma levels of ACTH, corticosterone and prolactin were measured in the arterial blood (0.3 ml) sampled before, during and after hypokinesia from chronic aortic cannulas of the rats.

Popovic, V.↗
NASA NTRS1988

Biomedical support of man in space

In its broadest sense, biomedical support of man in space must not be limited to assisting spacecraft crew during the mission; such support should also ensure that flight personnel be able to perform properly during landing and after leaving the craft. Man has developed mechanisms that allow him to cope with specific stresses in his normal habitat; there is indisputable evidence that, in some cases, the space environment, by relieving these stresses, has also allowed the adaptive mechanisms to lapse, causing serious problems after re-entry. Inflight biomedical support must therefore include means to simulate some of the normal stresses of the Earth environment. In the area of cardiovascular performance, we have come to rely heavily on complex feedback mechanisms to cope with two stresses, often combined: postural changes, which alter the body axis along which gravitational acceleration acts, and physical exercise, which increases the total load on the system. Unless the appropriate responses are reinforced continuously during flight, crew members may be incapacitated upon return. The first step in the support process must be a study of the way in which changes in g, even of short duration, affect these responses. In particular we should learn more about effects of g on the "on" and "off" dynamics, using a variety of approaches: increased acceleration on one hand at recumbency, immersion, lower body positive pressure, and other means of simulating some of the effects of low g, on the other. Once we understand this, we will have to determine the minimal exposure dose required to maintain the response mechanisms. Finally, we shall have to design stresses that simulate Earth environment and can be imposed in the space vehicle. Some of the information is already at hand; we know that several aspects of the response to exercise are affected by posture. Results from a current series of studies on the kinetics of tilt and on the dynamics of readjustment to exercise in different postures will be presented and discussed.

NASA Discipline Cardiopulmonary↗