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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Erythropoietic effects of space flight

Various factors which are important in the regulation of erythropoiesis have been studied in dehydrated mice in the belief that some information would be gained relevant to the erythropoietic effects of space flight. Dehydration reduced the plasma volume and, because changes in red cell volume were minimal, the hematocrit was elevated. Thus a state of relative erythrocytosis was produced. Understanding of the mechanism whereby these changes decreased red cell production is uncertain and appears to differ somewhat from the erythroid suppression seen following elevation of the hematocrit in animals with an absolute erythrocytosis. It is suggested that factors outside of the normal erythropoietic control pathway (such as energy balance) may play an important role in the decrease in red cell volume seen in man following space flight.

Dunn, C. D. R.↗
NASA NTRS1980

Exercise training-induced hypervolemia - Role of plasma albumin, renin, and vasopressin

The purpose of the present study was twofold: (1) to determine the rate of induction and decay of exercise-training hypervolemia with a short-duration high-intensity training regimen; and (2) to assess the protein, osmotic, and endocrine responses that contribute to that mechanism. The test subjects were eight volunteer, healthy, trained college men (20-22 yr) engaged in isotonic exercise on a bicycle ergometer. Factors associated with plasma hypervolemia during training are identified. The results suggest that an efficient procedure for increasing plasma volume is the daily performance of high-intensity isotonic leg exercise for 2 h/day.

Convertino, V. A.↗
NASA NTRS1982

Induced venous pooling and cardiorespiratory responses to exercise after bed rest

Venous pooling induced by a specially constructed garment is investigated as a possible means for reversing the reduction in maximal oxygen uptake regularly observed following bed rest. Experiments involved a 15-day period of bed rest during which four healthy male subjects, while remaining recumbent in bed, received daily 210-min venous pooling treatments from a reverse gradient garment supplying counterpressure to the torso. Results of exercise testing indicate that while maximal oxygen uptake endurance time and plasma volume were reduced and maximal heart rate increased after bed rest in the control group, those parameters remained essentially unchanged for the group undergoing venous pooling treatment. Results demonstrate the importance of fluid shifts and venous pooling within the cardiovascular system in addition to physical activity to the maintenance of cardiovascular conditioning.

Convertino, V. A.↗
NASA NTRS1982

Fluid shifts and erythropoiesis - Relevance to the 'anemia' of space flight

To model the fluid shifts thought to occur in man during space flight, cephalic fluid shifts have been induced in man subjected to horizontal or headdown bedrest, in squirrel monkeys exposed to lower body positive pressure, and in rats subjected to antiorthostatic hypokinesia. The influence on erythropoiesis of such fluid redistribution has been studied. Only in man did a cephalic fluid shift consistently and significantly lead to a plasma volume reduction and an increased hematocrit. Although there was evidence for erythrosuppression and the subjects were 'anemic' at the end of the study, serum erythropoietin titers remained normal throughout bedrest. The erythrosuppression probably did not arise due to the increased hematocrit but may have been related to P50 shifts or the loss of body weight. Each model appeared to reproduce different parts of man's physiological response to weightlessness and promises to be useful in unraveling the etiology of the 'anemia' of space flight.

Dunn, C. D. R.↗
NASA NTRS1983

Drinking and water balance during exercise and heat acclimation

The interactions between fluid intake and balance, and plasma ion, osmotic, and endocrine responses during dehydration produced by exercise in cool and warm environments during acclimation are explored. Two groups of five male subjects performed 8 days of ergometer exercise in hot and thermoneutral conditions, respectively. The exercise trials lasted 2 hr each. Monitoring was carried out on the PV, osmotic, sodium, and endocrine concentrations, voluntary fluid intake, fluid balances, and fluid deficits. A negative correlation was observed between the plasma sodium and osmolality during acclimation. The presence of hypervolemia during acclimation is suggested as a cause of drinking, while the vasopressin concentration was not found to be a significant factor stimulating drinking. Finally, the predominant mechanism in fluid intake during exercise and heat exposure is concluded to be the renin-angiotensin II system in the presence of reductions in total body water and extracellular plasma volumes.

Greenleaf, J. E.↗
NASA NTRS1982

Electromagnetic radiation from beam-plasma instabilities

The mechanism by which unstable electrostatic waves of an electron-beam plasma system are converted into observed electromagnetic waves is of great current interest in space plasma physics. Electromagnetic radiation arises from both natural beam-plasma systems, e.g., type III solar bursts and kilometric radiation, and from man-made electron beams injected from rockets and spacecraft. In the present investigation the diagnostic difficulties encountered in space plasmas are overcome by using a large laboratory plasma. A finite diameter (d approximately equal to 0.8 cm) electron beam is injected into a uniform quiescent magnetized afterglow plasma of dimensions large compared with electromagnetic wavelength. Electrostatic waves grow, saturate and decay within the uniform central region of the plasma volume so that linear mode conversion on density gradients can be excluded as a possible generation mechanism for electromagnetic waves.

Stenzel, R. L.↗
NASA NTRS1984

Numerical study of two-dimensional non-plane MHD wave propagation in a supersonic, superalfvenic magnetohydrodynamic flow

The features of a 2.5-dimensional time-dependent MHD numerical code used to simulate the propagation of finite amplitude MHD waves through an inhomogeneous, supersonic superalfvenic medium are described. Basic equations for conservation of mass, momentum, and free energy in a unit volume plasma gas and for magnetic induction are defined. Initial conditions are functions of the radial coordinates and disturbances are introduced at the lower boundary. A set of finite difference equations based on a Lax-Wendroff scheme is used for the simulation. The model is applied to analyzing a solar flare shock wave in steady-state and global transient conditions while propagating at 1 AU heliolongitude.

Han, S. M.↗
NASA NTRS1985

Research opportunities in loss of red blood cell mass in space flight

Decreases of red blood cell mass and plasma volume have been observed consistently following manned space flights. Losses of red cell mass by United States astronauts have averaged 10 to 15% (range: 2 to 21%). Based on postflight estimates of total hemoglobin, Soviet cosmonauts engaged in space missions lasting from 1 to 7 months have exhibited somewhat greater losses. Restoration of red cell mass requires from 4 to 6 weeks following return to Earth, regardless of the duration of space flight.

Talbot, J. M.↗
NASA NTRS1985

Reversal ion source - A new source of negative ion beams

A new type of ion source utilizing beams of electrons and target molecules, rather than a diffuse, volume plasma, is described. The source utilizes an electrostatic electron 'mirror' which reverses trajectories in an electron beam, producing electrons at their turning point having a distribution of velocities centered at zero velocity. A gas which attaches zero-velocity electrons is introduced at this turning point. Negative ions are produced by an attachment or dissociative attachment process. For many of the thermal electron-attaching molecules the cross sections can be quite large, varying as the inverse square root of the electron energy or just the s-wave threshold law. The efficiency and current density of the ion source for production of Cl(-) through the large, thermal energy attachment process is estimated. It is argued that the source can be used for the production of negative ions through attachment resonances located at higher energies as well.

Orient, O. J.↗
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 NTRS1985

Response to muscular exercise following repeated simulated weightlessness

The effects of 10-d 6-deg-head-down bed rest (BR1), 14 d of recovery, another 10 d bed rest (BR2), and another 14-d recovery on the cardiovascular response to a graded supine cycle ergometer test (4 min unloaded 60-rpm pedaling followed by 15-W/min increasing work load to volitional fatigue) are investigated experimentally in seven male nonsmokers of mean age 41 yrs, mean weight 80.2 kg, mean height 178 cm, and mean body fat content 22.3 percent. Ergometer tests are performed before BR1, after BR1 and BR2, and 14 d after BR2. The results are presented in tables, and it is found that the significantly decreased maximum-O2-uptake, gas-exchange-aerobic-threshold, and plasma-volume responses and the increased submaximal and maximal heart rates observed (relative to pre-BR1 levels) after BR1 and BR2 return to pre-BR1 values 14 d after BR2. It is inferred that 14 d of mild exercise are adequate for recovery from even repeated exposure to this type of simulated weightlessness.

Convertino, V. A.↗
NASA NTRS1985

Effect of hand-arm exercise on venous blood constituents during leg exercise

Contributions by ancillary hand and arm actions to the changes in blood constituents effected by leg exercises on cycle ergometer were assessed. Static or dynamic hand-arm exercises were added to the leg exercise (50 percent VO2 peak)-only control regimens for the subjects (19-27 yr old men) in the two experimental groups. Antecubital venous blood was analyzed at times 0, 15, and 30 min (T0, T15, and T30) for serum Na(+), K(+), osmolality, albumin, total CA(2+), and glucose; blood hemoglobin, hematocrit, and lactic acid; and change in plasma volume. Only glucose and lactate values were affected by additional arm exercise. Glucose decreased 4 percent at T15 and T30 after static exercise, and by 2 percent at T15 (with no change at T30) after dynamic arm exercise. Conversely, lactic acid increased by 20 percent at T30 after static exercise, and by 14 percent by T15 and 6 percent at T30 after dynamic arm exercise. It is concluded that additional arm movements, performed usually when gripping the handle-bar on the cycle ergometer, could introduce significant errors in measured venous concentrations of glucose and lactate in the leg-exercised subjects.

Wong, N.↗
NASA NTRS1986

Bedrest in healthy women: Effects of menstrual function and oral contraceptives

With the development of the space shuttle program, space flight for the first time is available to individuals who have not been specially selected and trained to be astronauts. In addition, women are being actively recruited into the space program, both as mission specialists and as career astronauts. One purpose of this project was to examine some of the physiological responses of women to a simulated weightlessness program (12 day horizontal bedrest), to compare their responses to those reported in men during similar programs, and to test whether menstrual function might alter some of the physiological changes which occur during bedrest, specifically changes in the plasma volume, exercise tolerance, and venous compliance before and after bedrest.

Fortney, Suzanne M.↗
NASA NTRS1989

Fluid/electrolyte and endocrine changes in space flight

The primary effects of space flight that influence the endocrine system and fluid and electrolyte regulation are the reduction of hydrostatic gradients, reduction in use and gravitational loading of bone and muscle, and stress. Each of these sets into motion a series of responses that culminates in alteration of some homeostatic set points for the environment of space. Set point alterations are believed to include decreases in venous pressure; red blood cell mass; total body water; plasma volume; and serum sodium, chloride, potassium, and osmolality. Serum calcium and phosphate increase. Hormones such as erythropoietin, atrial natriuretic peptide, aldosterone, cortisol, antidiuretic hormone, and growth hormone are involved in the dynamic processes that bring about the new set points. The inappropriateness of microgravity set points for 1-G conditions contributes to astronaut postflight responses.

Huntoon, Carolyn Leach↗
NASA NTRS1991

Effects of Weightlessness on Human Fluid and Electrolyte Physiology

The changes that occur in human fluid and electrolyte physiology during the acute and adaptive phases of adaptation to spaceflight are summarized. A number of questions remain to be answered. At a time when plasma volume and extracellular fluid volume are contracted and salt and water intake is unrestricted. ADH does not correct the volume deficit and serum sodium decreases. Change in secretion or activity of a natriuretic factor during spaceflight is one possible explanation. Recent identification of a polypeptide hormone produced in cardiac muscle cells which is natiuretic, is hypotensive, and has an inhibitory effect on renin and aldosterone secretion has renewed interest in the role of a natriuretic factor. The role of this atrial natriuretic factor (ANF) in both long- and short-term variation in extracellular volumes and in the inability of the kidney to bring about an escape from the sodium-retaining state accompanying chronic cardiac dysfunction makes it reasonable to look for a role of ANF in the regulation of sodium during exposure to microgravity. Prostaglandin-E is another hormone that may antagonize the action of ADH. Assays of these hormones will be performed on samples from crew members in the future.

Leach, Carolyn S.↗
NASA NTRS1991

Changes in body fluid compartments during a 28-day bed rest

Serial isotope measurements were used to obtain measurements of the body fluid responses of 10 22-29-year-old men during 28 d of simulated microgravity (bed rest). The subjects were maintained on a controlled metabolic diet for 7 d before the study, during 14 d of ambulatory control, 28 d of horizontal bed rest, and 14 d of ambulant recovery. Fluid compartments were measured on control days 1 and 9, bed rest days 2, 14, and 28, and recovery days 7 and 14. By day 2 of bed rest, plasma volume and extracellular volume (ECV) decreased significantly by an average 209 and 533 ml, respectively. Red cell volume and total body water (TBW) decreased more slowly, with average losses of 128 and 1316 ml, respectively, after 28 d of bed rest. Early in the bed rest, TBW loss was mostly from the ECV. Thereafter, the TBW deficit was derived from the intracellular compartment, which decreased an average of 838 ml after 28 d. These results suggest losses from all fluid compartments during bed rest, with no evidence of restoration of ECV after 1-2 weeks.

Fortney, Suzanne M.↗
NASA NTRS1991

Exercise training - Blood pressure responses in subjects adapted to microgravity

Conventional endurance exercise training that involves daily workouts of 1-2 hr duration during exposure to microgravity has not proven completely effective in ameliorating postexposure orthostatic hypotension. Single bouts of intense exercise have been shown to increase plasma volume and baroreflex sensitivity in ambulatory subjects through 24 hr postexercise and to reverse decrements in maximal oxygen uptake and syncopal episodes following exposure to simulated microgravity. These physiological adaptations to acute intense exercise were opposite to those observed following exposure to microgravity. These results suggest that the 'exercise training' stimulus used to prevent orthostatic hypotension induced by microgravity may be specific and should be redefined to include single bouts of maximal exercise which may provide an acute effective countermeasure against postflight hypotension.

Convertino, Victor A.↗
NASA NTRS1992

Vascular uptake of rehydration fluids in hypohydrated men at rest and exercise

The purpose of this study was to formulate and to evaluate rehydration drinks, which would restore total body water and plasma volume (PV), for astronauts to consume before and during extravehicular activity, a few hours before reentry, and immediately after landing. In the first experiment (rest, sitting), five healthy men (23-41 yr), previously dehydrated for 24 hr., drank six (1a, 2, 4, 5, 6, 7) fluid formulations (one each at weekly intervals) and then sat for 70 min. Pre-test PV were measured with Evans blue dye and changes in PV were calculated with the hematocrit-hemoglobin transformation equation. This rest experiment simulated hypohydrated astronauts preparing for reentry. The second experiment (exercise, supine) followed the same protocol except four healthy men (30-46 yr) worked for 70 min. in the supine position on a cycle ergometer at a mean load of 71+/-1 percent of their peak aerobic work capacity. This exercise experiment simulated conditions for astronauts with reduced total body water engaging in extravehicular activity.

Greenleaf, J. E.↗