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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Vestibular selection criteria development

The experimental elicitation of motion sickness using a short arm centrifuge or a rotating chair surrounded by a striped cylindrical enclosure failed to reveal any systematic group or consistent individual relationship between changes in heart rate, blood pressure, and body temperature and the appearance of symptoms of motion sickness. A study of the influence of vision on susceptability to motion sickness during sudden stop simulation shows that having the eyes open during any part of the sudden stop assessment is more stressful than having them closed throughout the test. Subjects were found to be highly susceptible to motion sickness when tested in free fall and in high force phases of flight. The effect of touch and pressure cues on body orientation during rotation and in parabolic flight are considered as sensory as well as motor adaptation.

Lackner, J. R.↗
NASA NTRS1980

Cardiovascular responses to static exercise in distance runners and weight lifters

Three groups of athletes including long-distance runners, competitive and amateur weight lifters, and age- and sex-matched control subjects have been studied by hemodynamic and echocardiographic methods in order to determine the effect of the training programs on the cardiovascular response to static exercise. Blood pressure, heart rate, and double product data at rest and at fatigue suggest that competitive endurance (dynamic exercise) training alters the cardiovascular response to static exercise. In contrast to endurance exercise, weight lifting (static exercise) training does not alter the cardiovascular response to static exercise: weight lifters responded to static exercise in a manner very similar to that of the control subjects.

Longhurst, J. C.↗
NASA NTRS1980

Renal responses to central vascular expansion are suppressed at night in conscious primates

The renal and hemodynamic responses of squirrel monkeys to central vascular volume expansion induced by lower body positive pressure (LBPP) during the day and night are investigated. Twelve unanesthetized animals trained to sit in a metabolism chair in which they were restrained only at the waist by a partition separating upper and lower body chambers were subjected to 4 h of continuous LBPP during the day and night, and hemodynamic, urinary and drinking data were monitored. LBPP during day and night is found to induce similar increases in central venous pressure, rises in heart rate and elevations in mean arterial blood pressure. However, although daytime LBPP induced a significant increase in urine flow and sodium excretion, a marked nocturnal inhibition of the renal response to LBPP is observed. Analysis of the time course and circadian regulation patterns of the urinary responses suggests that several separate efferent control pathways are involved.

Kass, D. A.↗
NASA NTRS1981

Effects of antiorthostatic bedrest on the cardiorespiratory responses to exercise

The cardiorespiratory changes in exercise performance induced by horizontal and antiorthostatic bed rest are compared in order to determine the physiological changes occurring in the antiorthostatic position and their degree of similarity to those observed in weightlessness. Systolic and diastolic pressures, heart rates, maximum oxygen uptake, ventilation volume during and following 5 min of submaximal exercise in the supine position and body weight and composition were determined in subjects before and following 7 days of bed rest in the horizontal or 6-deg head-down positions. Bed rest is found to result in a general decrease in exercise tolerance as indicated by cardiorespiratory parameters in both groups, with the 6-deg head-down treatment causing greater cardiovascular deconditioning. When compared with space flight data, the antiorthostatic position is shown to simulate the effects of weightlessness more effectively than horizontal bed rest

Convertino, V. A.↗
NASA NTRS1981

Beat-by-beat stroke volume assessment by pulsed Doppler in upright and supine exercise

The instantaneous stroke volume (SV) and cardiac output (Q) in eight male subjects during steady-state supine (S) and upright (U) exercises at 300 kpm/min is assessed by a 3.0-MHz pulsed Doppler echocardiograph. The mean transients in heart rate (HR), SV, and Q for each posture were determined and the center-line blood velocities obtained in the ascending aorta. Results show that the mean supine values for SV and Q at rest and exercise were 111 ml and 6.4 l/min and 112 ml and 9.7 l/min, respectively. The corresponding results for U were 76 ml and 5.6 l/min and 92 ml and 8.4 l/min, respectively. The values compare favorably with previous studies utilizing invasive procedures. The transient response of Q following the onset of exercise in U was about twice as fast as in S because of the rapid and almost immediate upsurge in SV. The faster rise in aortic flow in U with exercise represented and additional volume (184 ml) of blood passing through the aorta compared with S in the first 20 exercises. It is suggested that the rapid mobilization of pooled venous blood from the leg veins during U was responsible for the increased blood flow.

Loeppky, J. A.↗
NASA NTRS1981

Exercise training hypotension - Implications for plasma volume, renin, and vasopressin

The relation of changes in plasma volume, plasma renin activity and arginine vasopressin to changes in resting blood pressure during exercise training is investigated. Resting supine, sitting, and standing systolic and fifth-phase diastolic blood pressures were measured in ten men before and after an eight-day training period on a cycle ergometer in either a hot (39.8 C) or cool (23.8 C) environment, and compared with plasma volume, renin and vasopressin levels, heart rates, maximal oxygen uptakes, rectal temperatures and sweat rates. Following acclimatization, resting supine and sitting diastolic pressures are observed to decrease by 6 and 9 mm Hg, respectively, while no significant changes are found in the diastolic pressures of the control group or the systolic pressures of either group. Resting plasma volume is found to increase by 12.2% in the controls and by 17.6% after acclimatization following the exercise training. Results suggest that the resting hypotension produced is not attributable to changes in resting plasma volume, renin or vasopressin, although heat acclimatization, which leads to large decreases in plasma volume and increases in vasopressin and renin activity, may be useful in the treatment of hypertension.

Greenleaf, J. E.↗
NASA NTRS1981

Personal miniature electrophysiological tape recorder

The use of a personal miniature electrophysiological tape recorder to measure the physiological reactions of space flight personnel to space flight stress and weightlessness is described. The Oxford Instruments Medilog recorder, a battery-powered, four-channel cassette tape recorder with 24 hour endurance is carried on the person and will record EKG, EOG, EEG, and timing and event markers. The data will give information about heart rate and morphology changes, and document adaptation to zero gravity on the part of subjects who, unlike highly trained astronauts, are more representative of the normal population than were the subjects of previous space flight studies.

Green, H.↗
NASA NTRS1982

The effects of horizontal body casting on blood volume, drug responsiveness, and +Gz tolerance in the rhesus monkey

To simulate the weightless condition, eight rhesus monkeys, instrumented with solid-state pressure transducers, were horizontally restrained in body casts for 28 days. Blood volume decreased an average of 13% after 14 days of restraint, due mainly to a drop in plasma volume. Aortic pressure and heart rate responses to norepinephrine and phenylephrine decreased after 14 days of restraint. The monkeys did not show a statistically significant decreased tolerance to a 90 deg sudden upright tilt after horizontal restraint. During the fifth week of casting, four animals were subjected to +Gz acceleration tests on a centrifuge. The acceleration tolerance of the casted monkeys was significantly reduced compared to four similarly instrumented control animals. These findings indicate that the cardiovascular deconditioning associated with simulated weightlessness results from an inability to maintain central blood volume during orthostatic stress.

Dickey, D. T.↗
NASA NTRS1982

Modulation of human sinus node function by systemic hypoxia

The present study was conducted to determine whether bradycardia develops during systemic hypoxia in supine conscious human volunteers when respiratory frequency and tidal volume are maintained at constant levels. The obtained results suggest that mild hypoxia provokes cardioacceleration in humans, independent of changes of ventilation or baroreflex responsiveness. The earliest cardioacceleration is more prominent in the inspiratory than in the expiratory phase of respiration, and occurs with very small reductions of arterial oxygen saturation. Moderate systemic hypoxia dampens fluctuations of heart rate during the respiratory cycle.

Eckberg, D. L.↗
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

Measurement of cardiopulmonary performance during acute exposure to a 2440-m equivalent atmosphere

Each of 20 subjects (ranging in age from 18 to 38 years, 15 being male, five female) was given two Bruce Protocol symptom-limited maximum treadmill stress tests, breathing sea-level compressed air (20.9% O2) for one test and a 2440-m equivalent (15.5% O2) for the other. A significant difference was found to exist between measured VO2 max (p less than 0.0002) and exercise time (p less than 0.0004) for the two conditions. No significant differences were observed in heart rate or the recovery time to a respiratory quotient of less than 1. Hemoglobin saturation, as measured by an ear oximeter, averaged 95% for sea-level and 91% for the 2440-m equivalent gases. These results support a 2440-m equivalent contingency atmosphere in the Space Shuttle prior to donning a low-pressure suit for the purpose reducing nitrogen washout times.

Levitan, B. M.↗
NASA NTRS1982

Changes in blood volume and response to vaso-active drugs in horizontally casted primates

Experiments were performed on horizontally casted primates (male rhesus monkeys) in order to note changes in blood volume caused by horizontal restraint, to compare orthostatic tolerance before and after casting using the responses to upright tilting, to begin to uncover the cardiovascular and neural mechanisms involved in deconditioning, and to compare the data with that obtained from bed-rested human subjects and from humans exposed to weightlessness. Bolus injections of norepinephrine of 2.0 microgram/kg, phenylephrine of 4.0 microgram/kg, and nitroprusside of 2.0 microgram/kg were administered; and aortic pressure and heart rate were recorded during the injections. The results indicate that the horizontally casted primate is a valid animal model for studying the effects of simulated zero-G on the human cardiovascular system.

Dickey, D. T.↗
NASA NTRS1982

Effect of physical training in cool and hot environments on +Gz acceleration tolerance in women

Acceleration tolerance, plasma volume, and maximal oxygen uptake were measured in 15 healthy women before and after submaximal isotonic exercise training periods in cool and hot environments. The women were divided on the basis of age, maximal oxygen uptake, and +Gz tolerance into three groups: a group that exercised in heat (40.6 C), a group that exercised at a lower temperature (18.7 C), and a sedentary control group that functioned in the cool environment. There was no significant change in the +Gz tolerance in any group after training, and terminal heart rates were similar within each group. It is concluded that induction of moderate acclimation responses without increases in sweat rate or resting plasma volume has no influence on +Gz acceleration tolerance in women.

Brock, P. J.↗
NASA NTRS1982

Influences of horizontal hypokinesia on performance and circadian physiological rhythms in female humans

Eight females from 35-45 yr of age were subjected to seven days of ambulatory control, seven days of bed rest, and a five day recovery period, with 30 min of centrifugation on day seven of bedrest to determine the effects of weightlessness on the circadian rhythms of females in that age group. Heart rate and rectal temperature (RT) were monitored and each subject was tested in a flight simulator twice a day in conditions of varying levels of turbulence. The flight simulations were run during the morning and acrophase of the circadian RT and performance errors wery monitored for 6 min. No significant differences were detected in the group performance data pre-, during, and post-bedrest, although better performance in the simulator was observed after the centrifuge exposure. An RT phase shift was statistically significant between pre- and during bedrest stages.

Winget, C. M.↗
NASA NTRS1982

Instantaneous stroke volume in man during lower body negative pressure /LBNP/

Results of an examination of the instantaneous time course of the stroke volume (SV) and cardiac output (Q) in response to the onset and release of -50 torr lower body negative pressure (LBNP) are reported. Six male subjects were sealed into a LBNP box up to the iliac crest while being monitored by echocardiograph for centerlamina blood velocity, fluid displacement, stroke volume, heart rate, and leg volume. Particular use was made of pulsed ultrasonic Doppler velocity meters for measuring the blood velocities and flow dynamics. Measurements were made of the subjects continuously beginning from 20 sec prior to and one min after LBNP onset and release. A linear fall in the SV was observed with LBNP at 49% of the baseline value after 33 sec. A 62% drop, the lowest, was detected after 8 min of LBNP. The leg volume was inversely related to Q for the duration of the experiment.

Loeppky, J. A.↗
NASA NTRS1982

Antiorthostatic hypokinesia and circulation in the rat

Circulatory mechanisms that occur during exposure to head-down hypokinesia as well as during readaptation to control conditions were studied on unanesthetized unrestrained Sprague-Dawley rats exposed to hypokinesia for seven days. The heart rate was slightly elevated, and the right atrial pressure increased to 4 mm Hg, but returned to 0 mm Hg after three days of exposure. Mean arterial blood pressure decreased from 118 to 100 mm Hg during early exposure to antiorthostatic hypokinesia. Cardiac output and stroke volume of resting rats increased during early exposure to hypokinesia but decreased continuously during the next seven days. The results indicate that antiorthostatic hypokinesia induces circulatory changes similar to those seen in astronauts after several days of exposure to 0 g forces.

Popovic, V.↗
NASA NTRS1983

Evaluation of a Reverse Gradient Garment for prevention of bed-rest deconditioning

A Reverse Gradient Garment (RGG) was used to intermittently induce venous pooling in the extremities of a magnitude similar to that seen in going from a lying to standing position during the course of a 15-d period of horizontal bed rest. Venous pooling failed to improve bed-rest-induced losses in +2.5 Gz and +3.0 Gz centrifugation tolerance or to prevent increased heart-rate responses to lower-body negative pressure (LBNP). Four subjects served as controls, four were treated. Tests during the 7-d recovery period showed fluid/electrolyte and body composition values to have returned to pre-bed-rest levels with continued depression of acceleration tolerance times (56% decreased at +2.5 Gz and 74% decreased at +3.0 Gz compared to pre-bed-rest levels) and exaggerated blood insulin response on glucose tolerance testing (blood insulin for treated group increased 95% at 1 h before bed rest and 465% during recovery). This study demonstrates that the physiologic changes after bed rest persist for significant periods of time. Acceleration tolerance time proved to be a sensitive test for the deconditioning process.

Sandler, H.↗
NASA NTRS1983

Cardiovascular responses to exercise as functions of absolute and relative work load

The roles of absolute and relative oxygen uptake (VO2 and percent of muscle group specific VO2-max) as determinants of the cardiovascular and ventilatory responses to exercise over a wide range of active muscle mass are investigated. Experiments were conducted using four types of dynamic exercise: one-arm curl, one-arm cranking, and one and two-leg cycling at four different relative work loads (25, 50, 75, and 100 percent of VO2-max) for the corresponding muscle group. Results show that VO2 during maximal one-arm curl, one-arm cranking, and one-leg cycling averaged 20, 50, and 75 percent, respectively, of that for maximal two-leg cycling. Cardiac output was determined to be linearly related to VO2 with a similar slope and intercept for each type of exercise, and the heart rate at a given percent VO2-max was higher with larger active muscle mass. It is concluded that the cardiovascular responses to exercise was determined to a large extent by the active muscle mass and the absolute oxygen uptake, with the principal feature appearing to be the tight linkage between systematic oxygen transport and utilization.

Lewis, S. F.↗