Engineering Papers⌕ Search

Engineering topics

Greenleaf, J. E.

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

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Muscle ultrastructural changes from exhaustive exercise performed after prolonged restricted activity and retraining in dogs

The effect of exhaustive treadmill exercise on ultrastructural changes in the quadriceps femoris muscle was studied in 7 normal, healthy dogs, before and after restricted activity (RA), and following a subsequent 2 month treadmill exercise retraining period for the 5 mo group. Mean time to exhaustion in the 2 mo group decreased from 177 + or - 22 min before to 90 + or - 32 min after RA. Retraining increased tolerance to 219 + or - 73 min; 24 pct. above the before RA and 143 pct. above the after RA time. After RA exhaustion time in the 5 mo group was 25 and 45 min. Before RA, pre-exercise muscle structure was normal and post exercise there was only slight swelling of mitochondria. After RA, pre-exercise, numerous glycogen granules and lipid droplets appeared in the muscle fibers, mitochondria were smaller, and sarcoplasmic reticulum channels widened; post exercise these changes were accentuated and some areas were devoid of glycogen, and there was fiber degradation. After 5 mo RA pre-exercise there were more pronounced changes; mitochondria were very small and dense, there were many lipid droplets, myofibrils were often separated, and the fibers appeared edematous and degenerating; post exercise the sarcoplasmic reticulum was swollen, no glycogen was present, and there was marked swelling and deformation of mitochondria. After retraining, both pre-exercise and post exercise there was still evidence of fiber degeneration. Thus, susceptibility of active skeletal muscle structures and subcellular elements, e.g., mitochondria, to the action of damaging factors occurring during exhaustive exercise is enhanced considerably by prolonged disuse.

Nazar, K.↗
NASA NTRS1989

Exercise-training protocols for astronauts in microgravity

Based on physical working requirements for astronauts during intra- and extravehicular activity and on the findings from bed-rest studies that utilized exercise training as a countermeasure for the reduction of aerobic power, deterioration of muscular strength and endurance, decrements in mood and cognitive performance, and possibly for bone loss, two exercise protocols are proposed. One assumes that, during microgravity, astronaut exercise physiological functions should be maintained at 100 percent of ground-based levels. The other assumes that maximal aerobic power in flight can be reduced by 10 percent of the ground-based level.

Greenleaf, J. E.↗
NASA NTRS1989

Work capacity during 30 days of bed rest with isotonic and isokinetic exercise training

Results are presented from a study to determine whether or not short-term variable intensity isotonic and intermittent high-intensity isokinetic short-duration leg exercise is effective for the maintenance of peak O2 (VO2) uptake and muscular strength and endurance, respectively, during 30 days of -6 deg head-down bed rest deconditioning. The results show no significant changes in leg peak torque, leg mean total work, arm total peak torque, or arm mean total work for members of the isotonic, isokinetic, and controls groups. Changes are observed, however, in peak VO2 levels. The results suggest that near-peak variabile intensity, isotonic leg excercise maintains peak VO2 during 30 days of bed rest, while peak intermittent, isokinetic leg excercise protocol does not.

Greenleaf, J. E.↗
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 NTRS1988

Physiology of prolonged bed rest

Bed rest has been a normal procedure used by physicians for centuries in the treatment of injury and disease. Exposure of patients to prolonged bed rest in the horizontal position induces adaptive deconditioning responses. While deconditioning responses are appropriate for patients or test subjects in the horizontal position, they usually result in adverse physiological responses (fainting, muscular weakness) when the patient assume the upright posture. These deconditioning responses result from reduction in hydrostatic pressure within the cardiovascular system, virtual elimination of longitudinal pressure on the long bones, some decrease in total body metabolism, changes in diet, and perhaps psychological impact from the different environment. Almost every system in the body is affected. An early stimulus is the cephalic shift of fluid from the legs which increases atrial pressure and induces compensatory responses for fluid and electrolyte redistribution. Without countermeasures, deterioration in strength and muscle function occurs within 1 wk while increased calcium loss may continue for months. Research should also focus on drug and carbohydrate metabolism.

Greenleaf, J. E.↗
NASA NTRS1988

Effect of longitudinal physical training and water immersion on orthostatic tolerance in men

The effect of six months of moderately intense aerobic training on 60-deg head-up tilt tolerance was assessed before and after 6 hrs of water-immersion deconditioning by comparing the orthostatic and fluid-electrolyte-endocrine responses of five male subjects before and after these tests. It was found that six months of training has no significant effect on 60-deg head-up tilt tolerance. Thus, during pretraining, the water immersion tilt-tolerance was found to decrease from about 74 min before to 34 min after water immersion, while during posttraining, water immersion tilt tolerance decreased from 74 min to 44 min. Fluid-electrolyte-endocrine responses were also essentially the same during all four tilts. Plasma volume decreased by 9.0 to 12.6 percent; plasma sodium and osmotic concentrations were unchanged; and serum protein and plasma renin activity increased.

Greenleaf, J. E.↗
NASA NTRS1988

Effect of lower-body positive pressure on postural fluid shifts in men

The effect of the lower-body positive pressure (LBPP) on the orthostatic fluid and protein shifts were investigated in five men during combined tilt-table/antigravity suit inflation and deflation experiments. Changes in the mass densities of venous blood and plasma were measured and the values were used to calculate the densities of erythrocytes, whole-body blood, and shifted fluid. It was found that the application of 60 mm Hg LBPP during 60-deg head-up tilt prevented about half of the postural hemoconcentration occurring during passive head-up tilt.

Hinghofer-Szalkay, H.↗
NASA NTRS1987

Continuous monitoring of blood volume changes in humans

Use of on-line high-precision mass densitometry for the continuous monitoring of blood volume changes in humans was demonstrated by recording short-term blood volume alterations produced by changes in body position. The mass density of antecubital venous blood was measured continuously for 80 min per session with 0.1 g/l precision at a flow rate of 1.5 ml/min. Additional discrete plasma density and hematocrit measurements gave linear relations between all possible combinations of blood density, plasma density, and hematocrit. Transient filtration phenomena were revealed that are not amenable to discontinuous measurements.

Hinghofer-Szalkay, H.↗
NASA NTRS1987

Measurement of Human Blood and Plasma Volumes

Report reviews techniques for measuring blood-plasma volume in humans. Common technique of using radioactive iodine isotope to label plasma albumin involves unwarranted risks from low-level radiation. Report emphasizes techniques using Evans-blue-dye (T-1824) labeling of albumin, hematocrit or hemoglobin/hematocrit measurements, or blood densitometry. In Evans-blue-dye technique, plasma volume determined from decrease in dye concentration occurring after small amount of dye solution injected into circulatory system. Subjection of Evans blue dye to test for carcinogenicity gave negative results.

Greenleaf, J. E.↗
NASA NTRS1987

Early Fluid and Protein Shifts in Men During Water Immersion

High precision blood and plasma densitometry was used to measure transvascular fluid shifts during water immersion to the neck. Six men (28-49 years) undertook 30 min of standing immersion in water at 35.0 +/- 0.2 C; immersion was preceded by 30 min control standing in air at 28 +/- 1 C. Blood was sampled from an antecubital catheter for determination of Blood Density (BD), Plasma Density (PD), Haematocrit (Ht), total Plasma Protein Concentration (PPC), and Plasma Albumin Concentration (PAC). Compared to control, significant decreases (p less than 0.01) in all these measures were observed after 20 min immersion. At 30 min, plasma volume had increased by 11.0 +/- 2.8%; the average density of the fluid shifted from extravascular fluid into the vascular compartment was 1006.3 g/l; albumin moved with the fluid and its albumin concentration was about one-third of the plasma protein concentration during early immersion. These calculations are based on the assumption that the F-cell ratio remained unchanged. No changes in erythrocyte water content during immersion were found. Thus, immersion-induced haemodilution is probably accompanied by protein (mainly albumin) augmentation which accompanies the intra-vascular fluid shift.

Hinghofer-Szalkay, H.↗
NASA NTRS1986

Thermoregulatory responses to heat and vibration in men

The effect of vibration on thermoregulatory responses was studied in heat-acclimated men exposed suddenly to simultaneous heat and whole body vibrations (WBVs) at two intensity levels, each at graded frequencies between 5 and 80 Hz. The mean rectal temperature (Tre) became elevated more quickly in the WBV exposures than in the controls (heat exposure alone). Both intensity- and frequency-dependent WBV relationships were recorded in localized blood flows and in sweat rates. Thus, vibration appears to reduce the efficiency of the cooling mechanisms during a heat exposure.

Spaul, W. A.↗
NASA NTRS1986

Mechanism for negative water balance during weightlessness An hypothesis

The mechanism for the apparent decrease in body fluid volume in astronauts during spaceflight remains obscure. The widespread postulate that the hypohydration is the result of the Henry-Gauer reflex, a diuresis caused by inhibition of vasopressin secretion resulting from increased left and perhaps right atrial (central) venous pressure, has not been established with direct measurements on astronauts. An hypothesis is proposed to account for fluid-electrolyte shifts during weightlessness. A moderate but transient increase in central venous pressure occurs when orbit is entered that is insufficient to activate the Henry-Gauer reflex but sufficient to stimulate the release of atrial natriuretic peptides. Increased sodium excretion would facilitate some increased urinary water loss. The resulting relatively dilute plasma and interstitial fluids would cause fluid to shift into the cellular space, resulting in edema in the head and trunk and inhibition of thirst and drinking. Thus, the negative water balance in astronauts would be caused by a gradual natriuresis and diuresis coupled with reduced fluid intake.

Greenleaf, J. E.↗
NASA NTRS1986

Water and electrolytes

It has been found that the performance of the strongest and fittest people will deteriorate rapidly with dehydration. The present paper is concerned with the anatomy of the fluid spaces in the body, taking into account also the fluid shifts and losses during exercise and their effects on performance. Total body water is arbitrarily divided into that contained within cells (cellular) and that located outside the cells (extracellular). The anatomy of body fluid compartments is considered along with the effects of exercise on body water, fluid shifts with exercise, the consequences of sweating, dehydration and exercise, heat acclimatization and endurance training, the adverse effects of dehydration, thirst and drinking during exercise, stimuli for drinking, and water, electrolyte, and carbohydrate replacement during exercise. It is found that the deterioration of physical exercise performance due to dehydration begins when body weight decreases by about 1 percent.

Greenleaf, J. E.↗
NASA NTRS1986

Effect of hydration on some orthostatic and haematological responses to head-up tilt

Experiments were undertaken to determine the effects of hydration status on: (1) orthostatic responses, and on (2) relative changes in intravascular volume and protein content, during 70 deg head-up tilt (HUT). Six men underwent 45 min of HUT, preceded by 45 min supine, first dehydrated, and again 105 min later after rehydration with water. Heart rate was consistently lower following rehydration (p less than 0.01), while supine diastolic pressure was higher (p less than 0.02). Systolic pressure fell during dehydrated HUT (p less than 0.01), but not during rehydrated HUT. Postural haemoconcentration, which was reduced after rehydration (p less than 0.001), was accompanied by a decrease in intravascular albumin content (p less than 0.05). Two subjects experienced severe presyncopal symptoms during dehydrated HUT, but not during rehydrated HUT. Thus, it appears that rehydration after fluid restriction improves orthostatic tolerance. Furthermore, extravascular hydration status may be more important than intravascular hydration status in determining orthostatic tolerance.

Harrison, M. H.↗
NASA NTRS1986

Effect of posture on arterial baroreflex control of heart rate in humans

The effects of blood-volume redistribution induced by postural changes on baroreflex activity are investigated. The central blood volume and baroreceptor functions of ten males between 23-51 years old were examined while they were in the head-up tilt (HUT), head-down tilt (HDT), and supine positions. It is observed that during HDT at 15 deg the pulse interval over the first five cardiac cycles following neck suction onset is 51 + or - 18 ms longer, at 30 deg it is 61 + or - 20 ms longer, and at 45 deg it is 74 + or - 35 ms longer than at supine; during HUT at 15 deg the pulse interval is 25 + or - 9 ms shorter than when supine, but for the 30 and 45 deg there is no significant difference in pulse interval detected. The data reveal that posture does modify arterial baroreflex control of heart rate.

Harrison, M. H.↗
NASA NTRS1985

Mechanisms for negative water balance during weightlessness Immersion or bed rest?

Results of bedrest and water immersion studies are of interest when formulating an hypothesis to explain inflight changes in water and electrolyte metabolism. A comparison of the two techniques is made, and it is found that the time course of fluid-electrolyte responses with bedrest occur more slowly than during weightlessness and faster with immersion. Hence, the head-down bedrest is the more appropriate model for simulation studies. The facts lead to the following hypothesis: Because of the head-ward shift of fluid , there is a transient elevation of central venous pressure upon reaching weightlessness that is not sufficiently intense to significantly activate the vasopressin-diuresis mechanism. But the increased pressure is of significant intensity to release atrial natriuretic peptides. A hypotonic fluid moving into the cells contributes to edema and inhibits thirst. In this manner, astronauts gradually lose body water as a result of slightly increased urinary sodium coupled with decreased fluid intake. These responses continue until a new fluid-electrolyte steady state is attained at a reduced level of total body water.

Greenleaf, J. E.↗
NASA NTRS1985

Plasma volume methodology: Evans blue, hemoglobin-hematocrit, and mass density transformations

Methods for measuring absolute levels and changes in plasma volume are presented along with derivations of pertinent equations. Reduction in variability of the Evans blue dye dilution technique using chromatographic column purification suggests that the day-to-day variability in the plasma volume in humans is less than + or - 20 m1. Mass density determination using the mechanical-oscillator technique provides a method for measuring vascular fluid shifts continuously for assessing the density of the filtrate, and for quantifying movements of protein across microvascular walls. Equations for the calculation of volume and density of shifted fluid are presented.

Greenleaf, J. E.↗