Engineering Papers⌕ Search

Engineering topics

Greenleaf, J. E.

Publications and source records attributed to Greenleaf, J. E..

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Body water compartments during bed rest: Evaluation of analytical methods

Nine healthy young men were studied to determine the reproducibility and interchangeability of the use of radio-iodinated human serum albumin and Evans Blue dye for estimating plasma volume, sodium bromide for extracellular fluid volume, and deuterium oxide for total body water volume. All subjects were tested in a semibasal condition and allowed to rest for at least 30 min. after arriving at the laboratory. The results indicate that there was uniform distribution of I131 and Evans Blue dye 10 min. after injection and of NaBr and D2O 3 hours after oral ingestion; the buildup of residual tracer did not interfere appreciably with the measurement of either or Evans Blue spaces when they are administered at equal intervals, and the buildup of background tracer after ingestion of NaBr and D2O once per week for three consecutive weeks did not affect the accuracy of the measurement. It was found that I131 and Evans Blue may be used interchangeably for estimating plasma volume; for estimating bromide and D2O spaces, one 3-hour equilibrium blood sample gives results similar to the extrapolation of multiple samples.

Young, H. L.↗
NASA NTRS1973

Changes in total plasma content of electrolytes and proteins with maximal exercise.

To determine to what extent the increases in concentration of plasma proteins and electrolytes with short maximal work were a result of hemoconcentration, the changes in plasma volume and total content of the plasma constituents were simultaneously evaluated. The results obtained from six human subjects indicated that in comparison to preexercise values there was a net decrease in total content of plasma protein, sodium, and chloride in the first 2 min of the postexercise period, due primarily to a significant loss (13-15%) of plasma fluid. The total plasma potassium content was increased immediately after exercise but was significantly below the preexercise plasma content after 2 min of recovery.

Van Beaumont, W.↗
NASA NTRS1973

Blood electrolytes and exercise in relation to temperature regulation in man.

It is shown that the body temperature rise during physical exercise is a regulated process and is not due to a failure of heat-dissipating mechanisms. Core and skin temperatures do not provide sufficient information to account for the control of sweating during exercise. Evidence is presented that suggests an association between equilibrium levels of rectal temperature and the osmotic concentration of the blood with essentially no influence from variations in plasma volume.-

Greenleaf, J. E.↗
NASA NTRS1973

Blood electrolytes and exercise in relation to temperature regulation in man

Current knowledge and theories about the relation of blood electrolytes and exercise to thermoregulation in man are reviewed. It is shown that the elevation of body temperature during physical exercise is a regulated process and is not due to a failure of the heat dissipating mechanisms. Core and skin temperatures do not provide sufficient information to account for the control of sweating during exercise. Evidence is presented that suggests an association between equilibrium levels of rectal temperature and the osmotic concentration of the blood with essentially no influence of variations in plasma volume.

Greenleaf, J. E.↗
NASA NTRS1972

Disproportional changes in hematocrit, plasma volume, and proteins during exercise and bed rest.

The interrelationships between the changes in plasma volume, hematocrit, and plasma proteins during muscular exercise and bed rest were investigated. Proportionally, the changes in hematocrit are always smaller than the changes in plasma volume. For this reason changes in the concentration of blood constituents can only be quantitated on the basis of plasma volume changes. During short periods of intensive exercise, there was a small loss of plasma proteins. With prolonged submaximal exercise there was a net gain in plasma protein, which contributes to stabilization of the vascular volume. Prolonged bed rest induced hypoproteinemia; this loss of plasma protein probably plays an important role in recumbency hypovolemia.

Van Beaumont, W.↗
NASA NTRS1972

External auditory canal temperature as an estimate of core temperature.

Measurement of rectal (T sub re), auditory canal (T sub ac), positioned 8 to 10 mm from the tympanic membrane, and mean skin temperature (mean T sub sk) in five men during various exercise regimens at an ambient temperature (T sub a) of 25 C (phase one) and in two men during rest and exercise at 5, 15, 25, and 35 C T sub a (phase two). The purpose was to determine if T sub ac can be used as an accurate estimate of core temperature. Previous observations that T sub ac was highly correlated with T sub re but T sub ac was consistently lower than T sub re are confirmed; the mean difference varied from 0.4 C at rest to 1.1 C at the end of exercise. It is concluded that auditory canal temperature cannot be utilized as an estimate of core temperature, but T sub ac may be used to estimate mean body temperature where very accurate measurements are not required.

Greenleaf, J. E.↗
NASA NTRS1972

+Gz tolerance after 14 days bed rest and the effects of rehydration.

Measurement of the reduction in centrifugation tolerance after two weeks of bedrest with moderate daily exercise, with an attempt to determine if rehydration improves +Gz tolerance. There were significant reductions in +Gz tolerance during bedrest periods at three acceleration levels. Rehydration resulted in a significant increase in tolerance at 2.1G but it did not restore tolerance to control levels. Rehydration did not affect tolerance at 3.2G and 3.8G.

Greenleaf, J. E.↗
NASA NTRS1972

Comparative changes in plasma protein concentration, hematocrit and plasma volume during exercise, bedrest and + Gz acceleration.

Discussion of experiments which indicate that under conditions of a constant red cell volume the proportional changes in hematocrit and plasma volume during exercise are never equal. On the basis of direct measurements and calculated changes of plasma volume it is concluded that during maximal exercise there is a small loss of protein from the plasma. It is clear that changes in content of blood constituents can only be evaluated correctly after determination of changes in plasma volume.

Van Beaumont, W.↗
NASA NTRS1972

Maximal Oxygen Uptake, Sweating and Tolerance to Exercise in the Heat

The physiological mechanisms that facilitate acute acclimation to heat have not been fully elucidated, but the result is the establishment of a more efficient cardiovascular system to increase heat dissipation via increased sweating that allows the acclimated man to function with a cooler internal environment and to extend his performance. Men in good physical condition with high maximal oxygen uptakes generally acclimate to heat more rapidly and retain it longer than men in poorer condition. Also, upon first exposure trained men tolerate exercise in the heat better than untrained men. Both resting in heat and physical training in a cool environment confer only partial acclimation when first exposed to work in the heat. These observations suggest separate additive stimuli of metabolic heat from exercise and environmental heat to increase sweating during the acclimation process. However, the necessity of utilizing physical exercise during acclimation has been questioned. Bradbury et al. (1964) have concluded exercise has no effect on the course of heat acclimation since increased sweating can be induced by merely heating resting subjects. Preliminary evidence suggests there is a direct relationship between the maximal oxygen uptake and the capacity to maintain thermal regulation, particularly through the control of sweating. Since increased sweating is an important mechanism for the development of heat acclimation, and fit men have high sweat rates, it follows that upon initial exposure to exercise in the heat, men with high maximal oxygen uptakes should exhibit less strain than men with lower maximal oxygen uptakes. The purpose of this study was: (1) to determine if men with higher maximal oxygen uptakes exhibit greater tolerance than men with lower oxygen uptakes during early exposure to exercise in the heat, and (2) to investigate further the mechanism of the relationship between sweating and maximal work capacity.

Greenleaf, J. E.↗
NASA NTRS1971

Exercise temperature regulation in man in the upright and supine positions.

Rectal, auditory canal, and mean skin temperatures and various metabolic measurements were taken on subjects during 70-min exercise periods, in the upright and supine positions, on a bicycle ergometer. The results indicate nonlinear relationships between sweating and core skin temperatures and suggest the action of undefined thermal and/or nonthermal inputs in the control of exercise temperature regulation.

Greenleaf, J. E.↗