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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The physiological effects of simultaneous exposures to heat and vibration

Determination of the effects of exposure to vibration on the body's ability to handle heat stress, and, if so, identification of the specific vibration parameters (frequency and intensity) for both whole-body (wbv) and segmental-body vibration (sbv) that would have the most detrimental effect on the body's ability to maintain thermal homeostasis were studied. Rectal and skin temperatures, heart rates, localized sweat rates, arm-segment blood perfusion rates, respiration rates, oxygen uptakes, and respiratory exchange ratios were measured in six men (22 to 33 yr) during simultaneous exposures to heat and vibration - either wbv or sbv, and during a heated 50 min recovery period. The heat conditions were T (sub db) = 43.5 + or - 0.5 C (mean + or S.E.M.), and RH = 20 + or - 4%. All vibration exposures were divided into two exposure conditions - identical frequencies but at a high intensity (HI) and a low intensity (LI) level. The HI wbv exposure was for 25 min/day at 5 Hz, 0.37 g-rms; 10 Hz, 0.46 g-rms; 16 Hz, 0.72 g-rms; 30 Hz, 1.40 g-rms; 80 Hz, 3.70 g-rms. The LI wbv exposure was for 2.5 hr/day at the same frequencies but at the following accelerations: 0.14 g-rms; 0.18 g-rms; 0.28 g-rms; 0.55 g-rms; 1.44 g-rms. During the sbv the subject stood and grasped a vibrating, in the Z-axis, hand grip with both hands.

Spaul, W. A.↗
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 NTRS1984

Increase in whole-body peripheral vascular resistance during three hours of air or oxygen prebreathing

Male and female subjects prebreathed air or 100% oxygen through a mask for 3.0 hours while comfortably reclined. Blood pressures, heart rate, and cardiac output were collected before and after the prebreathe. Peripheral vascular resistance (PVR) was calculated from these parameters and increased by 29% during oxygen prebreathing and 15% during air prebreathing. The oxygen contributed substantially to the increase in PVR. Diastolic blood pressure increased by 18% during the oxygen prebreathe while stystolic blood pressure showed no change under either procedure. The increase in PVR during air prebreathing was attributed to procedural stress common to air and oxygen prebreathing.

Waligora, J. M.↗
NASA NTRS1983

Cardiovascular responses to spaceflight

The cardiovascular system's adaptive changes during and after spaceflight are discussed. Cephalic fluid shifts are demonstrated by photographs along with calf girth and leg volume changes. Inflight measurements show an increase in average resting heart rate and systolic blood pressure, and a sympathetic-parasympathetic neural imbalance. Postflight findings include a small but reversible decrease in the left ventricular muscle mass. Since 1980, NASA's research has emphasized cardiovascular deconditioning and countermeasures: hemodynamic changes, endocrine and neurohumoral aspects, etiologic factors, and lower body negative pressure devices. Though human beings acclimate to the space environment, questions concerning the immediate and long-term aspects of spaceflight need to be answered for adequate planning of extended space missions.

Nicogossian, A.↗
NASA NTRS1984

Acute physiological responses of squirrel monkeys exposed to hyperdynamic environments

Physiological and behavioral responses to a hyperdynamic environment were examined in four adult male squirrel monkeys. After baseline monitoring at 1 G, monkeys were exposed to one of three conditions: (1) +2 Gz for 60 minutes, (2) +2.9 Gz max for 8 minutes (simulating Space Shuttle launch), or (3) +1.7 Gz max for 19 minutes (simulating Space Shuttle reentry). During all experimental conditions, heart rate rose, and colonic temperature began to decline within the first ten minutes of centrifugation and decreased by as much as 2 C in some instances. Behaviorally, during centrifugation, the monkeys seemed to exhibit drowsiness and fall asleep, an observation not made during the control period. It is concluded that primates are susceptible to acute hyperdynamic field exposure.

Fuller, C. A.↗
NASA NTRS1984

Cardiovascular responses during orthostasis - Effect of an increase in maximal O2 uptake

A study is described which tests the hypothesis that changes in aerobic activity (increases in maximum oxygen uptake) will reduce the effectiveness of cardiovascular reflexes to regulate blood pressure during orthostasis. The hypothesis was tested by measuring heart rate, blood pressure and blood volume responses in eight healthy male subjects before and after an eight-day endurance regimen. The results of the study suggest that the physiologic responses to orthostasis are dependent upon the rate of plasma volume loss and pooling, and are associated with training-induced hypervolemia. It is indicated that endurance type exercise training enhances cardiovascular adjustments during tilt. The implications of these results for the use of exercise training as a countermeasure and/or therapeutic method for the prevention of cardiovascular instability during orthostatic stress are discussed.

Convertino, V. A.↗
NASA NTRS1985

What Is Being Done to Control Motion Sickness?

AFT (Autogenic Feedback Training) involves practicing a series of mental exercises to speed up or slow down the control of autonomic activity. This produces a reduced tendency for autonomic activity levels to diverge from baseline (at rest) under stressful motion-sickness-inducing conditions. Subjects conditions. Subjects engaged in applying AFT exercises are required to closely monitor their own bodily sensations during motion-sickness-eliciting tests. These tests include the Coriolis Sickness Susceptibility Index (CSSI), which consists of sitting a subject into a rotating chair that moves at various speeds while a visual background turns at differing speeds and directions, and the Vertical Acceleration Rotation Device (VARD) test, which involves the placing of a subject in a drum that moves in an upward and downward motion until he or she is sick, while simultaneously monitoring the subject's vital signs. These tests provide investigators with evidence of slight changes in autonomic activities such as increases in heart rate, skin temperature, and sweat. All of these symptoms occur in subjects that experience bodily weakness or discomfort with the onset of motion sickness.

Hall, Y. D.↗
NASA NTRS1985

Hypothalamic, rectal, and muscle temperatures in exercising dogs - Effect of cooling

An experimental investigation of the mechanisms of performance prolongation during exercise is presented. Measurements were obtained of the rectal, muscle, and hypothalamic temperature of dogs during treadmill exercise at an ambient temperature of 22 + or - 1 C, with and without cooling by use of ice packs. In comparison with exercise without cooling, exercise with cooling was found to: (1) increase exercise duration from 90 + or - 14 to 145 + or - 15 min; (2) attenuate increases in hypothalamic, rectal and muscle temperature; (3) decrease respiratory and heart rates; and (4) lower blood lactic acid content. It is shown that although significant differences were found between the brain, core, and muscle temperatures during exercise with and without cooling, an inverse relation was observed between muscle temperature and the total duration of exercise. It is suggested that sustained muscle hyperthermia may have contributed to the limitation of working ability in exercise with and without cooling.

Kruk, B.↗
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 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 NTRS1986

Photoelectronic Monitor of Motion Sickness

Instrument includes gallium arsenide light-emitting diode (LED) and silicon phototransistor with infrared filter, all cast in single plastic housing. Housing attached to subject's face with transparent doublesided adhesive tape. LED directs pulses of infrared light to skin, which reflects them to phototransistor. Phototransistor produces signal that is processed by external circuits to yield plot of infrared reflectance with time. External circuits temperature-compensated and respond only to pulsed component of detector output, rejecting those components caused by stray light. Circuits also extract blood-volume pulse amplitude and heart rate.

Oman, C. M.↗
NASA NTRS1985

Effects of 9-hour time zone changes on fatigue and circadian rhythms of sleep/wake and core temperature

Physiological and psychological disruptions caused by transmeridian flights may affect the ability of flight crews to meet operational demands. To study these effects, 9 Royal Norwegian Airforces P3-Orion crewmembers flew from Norway to California (-9 hr), and back (+9 hr). Rectal temperature, heart rate and wrist activity were recorded every 2 min, fatigue and mood were rated every 2 hr during the waking day, and logs were kept of sleep times and ratings. Subjects also completed 4 personality inventories. The time-zone shifts produced negative changes in mood which persisted longer after westward flights. Sleep quality (subjective and objective) and duration were slightly disrupted (more after eastward flights). The circadian rhythms of sleep/wake and temperature both completed the 9-hr delay by day 5 in California, although temperature adjusted more slowly. The size of the delay shift was significantly correlated with scores on extraversion and achievement need personality scales. Response to the 9-hr advance were more variable. One subject exhibited a 15-hr delay in his temperature rhythm, and an atypical sleep/nap pattern. On average, the sleep/wake cycle (but not the temperature rhythm), completed the 9-hr advance by the end of the study. Both rhythms adapted more slowly after the eastward flight.

Gander, P. H.↗
NASA NTRS1985

General Automatic Components of Motion Sickness

A body of investigations performed in support of experiments aboard the space shuttle, and designed to counteract the symptoms of Space Adaptation Syndrome, which resemble those of motion sickness on Earth is reviewed. For these supporting studies, the automatic manifestations of earth-based motion sickness was examined. Heart rate, respiration rate, finger pulse volume and basal skin resistance were measured on 127 men and women before, during and after exposure to nauseogenic rotating chair tests. Significant changes in all autonomic responses were observed across the tests. Significant differences in autonomic responses among groups divided according to motion sickness susceptibility were also observed. Results suggest that the examination of autonomic responses as an objective indicator of motion sickness malaise is warranted and may contribute to the overall understanding of the syndrome on Earth and in Space.

Suter, S.↗
NASA NTRS1985

Stimulus specificity and individual stereotypy of autonomic responses to motion stressors

Motion sickness research shows a lack of agreement regarding the contribution of the autonomic nervous system (ANS). The resolution of this question is exigent for Space Adaptation Syndrome, zero gravity sickness. A case is drawn for the necessity to apply a methodological approach that incorporates: (1) standardization of parameters in relation to the individual differences in variability and prestimulus levels; (2) a concern for patterning of responses; and (3) the physiological association with subjective reports. Vasomotor, heart rate, respiration rate, skin conductance and subjective reports of malaise were collected from 22 subjects while participating in three motion stressors; vertical acceleration, Coriolis stimulation, and combined optokinetic and Coriolis stimulation. The results demonstrate that ANS response patterns can be separated into three mutually exclusive components: (1) a generalized response to motion sickness; (2) a stimulus specific response to the type of stressor being presented; and (3) individualized stereotypical response patterns that are associated with subjective reports of malaise.

Morgan, M. G.↗
NASA NTRS1985

Cardiovascular deconditioning during space flight and the use of saline as a countermeasure to orthostatic intolerance

Results are reported of trials with oral hydration by astronauts before reentry of the Orbiter. The experiments were run to evaluate hydration as a means of offsetting the loss of lower body negative pressure experienced after several days in space. The rehydration was carried out by 17 astronauts who ingested salt tablets and water prior to the end of the first eight STS mission orbital phases; nine astronauts abstained. Pulse and blood pressure data were collected from 1-2 hr post landing. Measurements were also made of the extent of cardiac deconditioning and the response to orthostatic stress (standing). Ingestion of the salt tablets reduced the heart rate response to stress an average of 29 percent. The statistical significance of the difference has encouraged adoption of the salt tablet countermeasure as an operational procedure by Shuttle astronauts.

Bungo, M. W.↗
NASA NTRS1985

Blood pressure and plasma renin activity as predictors of orthostatic intolerance

The effect of 3 h standing, followed by a period of head-up tilt (HUT) on physiological response (orthostatic tolerance, blood pressure and heart rate), as well as on plasma vasopressin (PVP) and renin activity (PRA) were studied in 13 dehydrated (to 2.4 pct loss of body weight) subjects. Seven subjects showed signs of orthostatic intolerance (INT), manifested by sweating, pallor, nausea and dizziness. Prior to these symptoms, the INT subjects exhibited lower systolic (SP) and pulse (PP) pressures, and an elevated PRA, compared to the tolerant (TOL) subjects. HUT has aggravated increases of RPA in the INT subjects and caused an increase, higher than in TOL subjects, in PVP, while rehydration has greatly attenuated the PVP response to the HUT and decreased the PRA response. It is concluded that dehydration, together with measurements of SP, PP and PRA, may serve as a means of predicting orthostatic intolerance and may provide a physiological model for studying the causes of intolerance.

Harrison, M. H.↗
NASA NTRS1985

The human cardiovascular system in the absence of gravity

The data collected from a Space Shuttle crew to investigate cardiovascular changes due to microgravity are presented. The experimental procedures which involved preflight, immediate postflight, and one week following postflight echocardiograms of 13 individuals are described. The immediate postflight results reveal a 20 percent decrease in stroke volume, a 16 percent decrease in left ventricular diastolic volume index (LVDVI), no change in systolic volume, blood pressure, or cardiac index, and a 24 percent increase in heart rate. One week later a 17 percent stroke volume increase, a 29 percent increase in cardiac index, and normal blood pressure, and LVDVI were observed. It is concluded that upon reexposure to gravity a readaptation process for the cardiovascular system occurs.

Bungo, M. W.↗
NASA NTRS1986

Bedrest-induced peak VO2 reduction associated with age, gender, and aerobic capacity

A study measuring the peak oxygen uptake (V02), heart rate (HR), and exercise tolerance time of 15 men of 55 + or - 2 yr and 17 women of 55 + or - 1 yr after 10 days of continuous bed rest (BR) is presented. The experimental conditions and procedures are described. Following BR a decrease in peak VO2 of 8.4 percent in men and 6.8 percent in women, a reduction in exercise tolerance time by 8.1 percent in men and 7.3 percent in women, and an increse in HR of 4.4 percent and 1.3 percent for men and women, respectively, are observed. These data are compared with data from Convertino et al. (1977) for men 21 + or - 1 yr and women 28 + or - 2yr. It is concluded that BR-induced aerobic deconditioning is independent of age and sex, since the relative decrease in peak V02 in the older and younger subjects and men and women are similar.

Convertino, V. A.↗