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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Effects of simulated increased gravity on the rate of aging of rats - Implications for the rate of living theory of aging

It was found that the rate of aging of 17 month old rats which had been exposed to 3.14 times normal gravity in an animal centrifuge for 8 months was larger than that of the controls as determined by the apparently elevated lipofuscin content in heart and kidney, reduced numbers and increased size of mitochondria of heart tissue, and inferior liver mitochondria respiration. Steady-state food intake per day per kg body weight, which is presumably proportional to rate of living or specific basal metabolic expenditure, was found to be about 18 percent higher than in the controls after an initial 2 month adaptation period. Although half of the centrifuged animals lived only a little shorter than the controls (average about 343 vs. 364 days on the average, statistically nonsignificant), the remaining half (longest survivors) lived on the centrifuge an average of 520 days (range 483-572) compared to an average of 574 days (range 502-615) for the controls, computed from the onset of centrifugation, or 11 percent shorter. These findings indicate that a moderate increase of the level of basal metabolism of young adult rats adapted to hypergravity compared to controls in normal gravity is accompanied by a roughly similar increase in the rate of organ aging and reduction of survival, in agreement with Pearl's (1928) rate of living theory of aging, previously experimentally demonstrated only in poikilotherms.

Economos, A. C.↗
NASA NTRS1985

Transducers For Heat Research

Series of transducers with seven different configurations enable measurement of forces and displacements in heart wall. New transducers small, cause minimal perturbation of heart function and attached and detached without causing excessive tissue damage. All units implanted or removed during single heartbeat, permitting rapid relocation for detail mapping.

Feldstein, C.↗
NASA NTRS1984

Amplitude distributions of the spider heartpulse in response to gravitational stimuli

The arachnid Nuctenea sclopetaria (Clerck) which possesses a neurogenic heart, measuring the heartbeat is under efferent control through a dorsal nerve arising from a brain center is discussed. It was shown that the heartrate of this spider is also modulated by an afferent input associated with small increments of gravity. A compressive force on the order of 40 micron is sufficient to elicit a threshold change in heart rate for a typical (100mg) spider. This obtains in a hyper-Gz field less than 1.001. The functional relationship between gravity and heartrate is logarithmic between the absolute threshold and at least 1.5 Gz. A model was proposed in which equilibrium and movement are maintained by changes in blood pressure. It is concluded that the arachnid equilibrium system is like a weight detector which employs a hydraulic compensatory mechanism.

Finck, A.↗
NASA NTRS1985

Exercise thermoregulation in men after 6 hours of immersion

The present investigation is concerned with thermoregulation at rest and during exercise after water-immersion deconditioning, giving particular attention to the effects of fluid shifts and negative water balance on sweat rate and rectal temperature. Six healthy males 20-35 years old were used in the experiments. Rectal and mean skin temperature, skin heat conductance, heart rate, and total body sweat rate were measured during 70 min of supine leg exercise at 50 percent of peak O2 uptake. The data were taken after a 6-h control period in air and after immersion to the neck in water (34.5 C) for 6 h after overnight food and fluid restriction. Attention is given to end exercise heart rates and data during exercise. The obtained results suggest that, compared with control responses, the equilibrium level of core temperature during submaximal exercise is regulated at a higher level after immersion.

Greenleaf, J. E.↗
NASA NTRS1984

Role of cardiac volume receptors in the control of ADH release during acute simulated weightlessness in man

Hemodynamic responses and antidiuretic hormone (ADH) were measured during body position changes, designed to induce central blood volume shifts in ten cardiac and one heart-lung transplant recipients, to assess the contribution of cardiac volume receptors in the control of ADH release during the initial acute phase of exposure to weightlessness. Each subject underwent 15 min of a sitting-control period (C) followed by 30 min of 6 deg headdown tilt (T) and 30 min of resumed sitting (S). Venous blood samples and cardiac dimensions were taken at 0 and 15 min of C; 5, 15, and 30 min of T; and 5, 15, and 30 min of S. Blood samples were analyzed for hematocrit, plasma osmolality, plasma renin activity (PRA), and ADH. Heart rate and blood pressure were recorded every two min. Plasma osmolality was not altered by posture changes. Mean left ventricular end-diastolic volume increased (P less than 0.05) from 90 ml in C to 106 ml in T and returned to 87 ml in S. Plasma ADH was reduced by 20 percent (P less than 0.05) with T, and returned to control levels with S. These responses were similar in six normal cardiac-innervated control subjects. These data may suggest that cardiac volume receptors are not the primary mechanism for the control of ADH release during acute central volume shifts in man.

Convertino, V. A.↗
NASA NTRS1985

Cardiac reserve during weightlessness simulation and shuttle flight

Bedrest deconditioning is suspected to reduce cardiac function. However, quantitation of subtle decreases in cardiac reserve may be difficult. Normal subjects show considerable variability in heart rate response, reflected by a relatively broadband interbeat interval power spectrum. We hypothesized that the deconditioning effects of bedrest would induce narrowing of this spectrum, reflecting a reduction in the autonomically-modulated variability in heart rate. Ten aerobically conditioned men (average 35-50 years) underwent orthostatic tolerance testing with lower body negative pressure pre-bedrest and after 10 days of bedrest, while on placebo and after intravenous atropine. Spectra were derived by Fourier analysis of 128 interbeat interval data sets from subjects with sufficient numbers of beats during matched periods of the protocol. Data suggest that atropine unmasks the deconditioning effect of bedrest in athletic men, evidenced by a reduction in interbeat interval spectral power compared with placebo. Spectral analysis offers a new means of quantitating the effects of bedrest deconditioning and autonomic perturbations on cardiac dynamics.

Goldberger, A. L.↗
NASA NTRS1986

Cardiovascular dynamics associated with tolerance to lower body negative pressure

The purpose of this investigation was to identify cardiovascular responses associated with tolerance to lower body negative pressure (LBNP). Eighteen men, ages 29-51 years, were categorized as high (HT) or low (LT) LBNP-tolerant based on a graded presyncopal-limited LBNP exposure criterion of -60 mm Hg relative to ambient pressure. Groups were matched for physical characteristics and pre-LBNP cardiovascular measurements, with the exceptions of greater (p less than 0.05) end-diastolic volume and cardiac output in the HT group. During peak LBNP, cardiac output was similar in both groups, although the HT group displayed a greater heart rate (p less than 0.05). In both groups, venous return appeared to limit cardiac output resulting in decreased arterial pressure. Tolerance to LBNP did not appear solely dependent on the absolute amount of blood pooled in the legs since the HT group demonstrated a greater (p less than 0.05) peak LBNP-induced increase in midthigh-leg volume. Greater tolerance to LBNP was associated with a larger pre-LBNP cardiac output reserve and higher compensatory increases in heart rate and peripheral resistance.

Sather, T. M.↗
NASA NTRS1986

Cardiovascular responses of women to lower body negative pressure

The effects of lower body negative pressure (LBNP) on the cardiovascular response of 20 women between 23-43 years are evaluated. Calf circumference and cardiovascular data were recorded for women in the follicular and luteal phases of the menstrual cycle at -30, -40, and -50 mm Hg LBNP. The data reveal that the two menstrual phases did not cause differences in the way women respond to LBNP. It is observed that during LBNP calf circumference is enlarged; transthoracic impedance, and heart rate are increased; stroke volume, left ventricular ejection time, the Heather Index of contractility and systolic pressure, and cardiac output are reduced; and total peripheral resistance is elevated. The experimental data are compared to Montgomery et al. (1979). It is noted that the response of women to -50 mm Hg LBNP is similar to that of men; however, women adapt to stresses on the cardiovascular system with greater heart rate adjustments.

Frey, M. A. B.↗
NASA NTRS1987

Measurement of pilot workload

A multistage process for evaluating the workload of a five-minute segment of flight including approach and landing for a typical transport aircraft was described. The goal of the analysis was to compare the workload of the two pilots. Four types of measurement techniques were suggested: Analytic (a preliminary task and time line analysis identified task requirements and target performance levels); Performance (flight path control, communications, and interval production); Physiological (heart rate and heart rate variability); and Subjective ratings (a multidimensional technique developed at NASA Ames).

Hart, Sandra G.↗
NASA NTRS1987

Echocardiographic evaluation of Space Shuttle crewmembers

Echocardiographic measurements of left ventricular volume were obtained from 17 members of four Space Shuttle crews before and after 5- to 8-day space flights. Measurements obtained 1 h after landing indicated increases in the heart rate (HR), mean arterial pressure, and systemic vascular resistance values. On the other hand, the end-diastolic volume index (EDVI) fell 17 ml/sq m, and the stroke volume index (SVI) fell 15 ml/sq m. Measurements taken 1-2 weeks later demonstrated that the HR values returned to normal, but the EDVI and SVI values remained significantly below preflight levels, despite the ability of the subjects to ambulate and exercise. The results indicate that a space flight induces significant changes in heart volume affecting the left-ventricle function. It is suggested that the prolonged recovery period is related to the high level of aerobic conditioning in these subjects.

Bungo, M. W.↗
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 NTRS1988

Voice stress analysis

In a study of the validity of eight candidate voice measures (fundamental frequency, amplitude, speech rate, frequency jitter, amplitude shimmer, Psychological Stress Evaluator scores, energy distribution, and the derived measure of the above measures) for determining psychological stress, 17 males age 21 to 35 were subjected to a tracking task on a microcomputer CRT while parameters of vocal production as well as heart rate were measured. Findings confirm those of earlier studies that increases in fundamental frequency, amplitude, and speech rate are found in speakers involved in extreme levels of stress. In addition, it was found that the same changes appear to occur in a regular fashion within a more subtle level of stress that may be characteristic, for example, of routine flying situations. None of the individual speech measures performed as robustly as did heart rate.

Brenner, Malcolm↗
NASA NTRS1987

Inflight evaluation of pilot workload measures for rotorcraft research

The effectiveness of heart-rate monitoring and the NASA TLX workload rating scale (Hart et al., 1985) in measuring helicopter-pilot workloads is investigated experimentally. Four NASA test pilots flew two 2-h missions each in an SH-3G helicopter, following scenarios with takeoff, hover, cross-country, and landing tasks; pilot performance on the tasks undertaken near the landing area was measured by laser tracking. The results are presented in graphs and discussed in detail, and it is found that the TLX ratings clearly distinguish the flight segments and are well correlated with the performance data. The mean heart rate (measured as interbeat interval) is correlated (r = -0.69) with the TLX workload, but only the standard deviation of the interbeat interval is able to distinguish between flight segments; the correlation between standard deviation and TLX ratings is negative but not significant.

Shively, Robert J.↗
NASA NTRS1988

Association of sex and age with responses to lower-body negative pressure

The effects of age and sex on the human-body responses to -50 torr LBNP were investigated in subjects who have undergone LBNP tests at the Kennedy Space Center. The comparison of results obtained on women and age-matched men indicated that men had larger relative increases in calf circumference and greater increases in peripheral resistance during the exposure to LBNP than the women; on the other hand, women displayed greater increases in thoracic impedance and heart rate. The comparison of the results on men of different ages (between 29 and 56 y) indicated that older subjects had greater increases in peripheral resistance and less heart rate elevation in response to LBNP. It is suggested that the age-related circulatory differences were due to a reduction in vagal response and a switch to predominant sympathetic nervous system influence in older men.

Frey, Mary Anne Bassett↗
NASA NTRS1987

Fractals in physiology and medicine

The paper demonstrates how the nonlinear concepts of fractals, as applied in physiology and medicine, can provide an insight into the organization of such complex structures as the tracheobronchial tree and heart, as well as into the dynamics of healthy physiological variability. Particular attention is given to the characteristics of computer-generated fractal lungs and heart and to fractal pathologies in these organs. It is shown that alterations in fractal scaling may underlie a number of pathophysiological disturbances, including sudden cardiac death syndromes.

Goldberger, Ary L.↗
NASA NTRS1989

Adjustment of sleep and the circadian temperature rhythm after flights across nine time zones

The adjustment of sleep-wake patterns and the circadian temperature rhythm was monitored in nine Royal Norwegian Airforce volunteers operating P-3 aircraft during a westward training deployment across nine time zones. Subjects recorded all sleep and nap times, rated nightly sleep quality, and completed personality inventories. Rectal temperature, heart rate, and wrist activity were continuously monitored. Adjustment was slower after the return eastward flight than after the outbound westward flight. The eastward flight produced slower readjustment of sleep timing to local time and greater interindividual variability in the patterns of adjustment of sleep and temperature. One subject apparently exhibited resynchronization by partition, with the temperature rhythm undergoing the reciprocal 15-h delay. In contrast, average heart rates during sleep were significantly elevated only after westward flight. Interindividual differences in adjustment of the temperature rhythm were correlated with some of the personality measures. Larger phase delays in the overall temperature waveform (as measured on the 5th day after westward flight) were exhibited by extraverts, and less consistently by evening types.

Gander, Philippa H.↗
NASA NTRS1989

Gravitational biology and the mammalian circadian timing system

Using published reports, this paper compares and contrasts results on the effects of altered gravitational fields on the regulation in mammals of several physiological and behavioral variables with the circadian regulation of the same variables. The variables considered include the temperature regulation, heart rate, activity, food intake, and calcium balance. It is shown that, in rats, the homeostatic regulation of the body temperature, heart rate, and activity becomes depressed following exposure to a 2 G hyperdynamic field, and recovers within 6 days of 1 G condition. In addition, the circadian rhythms of these variables exhibit a depression of the rhythm amplitude; a recovery of this condition requires a minimum of 7 days.

Fuller, Charles A.↗
NASA NTRS1990

Human exercise capabilities in space

Maintenance of rest and exercise performance are prime requirements for all astronauts during flight, not only for maintaining day-to-day productivity, but also for coping with unlikely emergencies. Indirect estimates of submaximal work capacity (oxygen uptake) made from changes in the heart rates of 27 Apollo astronauts (less than 15-day flights) indicated a reduction in work capacity (maximal oxygen uptake) of 17 to 21 percent. This percentage decrease was similar to that measured in middle-aged men after 21 to 30 days of -6 deg head-down bed-rest deconditioning without exercise training. Heart-rate changes during submaximal exercise in the nine Skylab astronauts suggested that they were better able to maintain their work capacity because of longer and more intensive in-flight exercise training. The strength of the flexor and extensor muscle groups decreased by 2 to 9 percent in the elbow and by 6 to 20 percent in the knee in the Skylab astronauts, also similar to the decreases in men undergoing 30 days of bed-rest deconditioning. Exercise protocols have been devised that result in maintenance of work capacity and muscular strength during 30 to 49 days of bed-rest deconditioning.

Greenleaf, John E.↗