Engineering topics

Charles, John B.

Publications and source records attributed to Charles, John B..

54 records · Page 3

NASA NTRS1993

Countermeasure for reducing post-flight orthostatic intolerance: Lower Body Negative Pressure (LBNP) experiment E140

Investigators have shown that after 1-2 weeks of bed rest ingestion of 1000 ml of a salt water solution during 4 hours of continuous exposure to 30 mm Hg of lower body negative pressure will protect plasma volume and orthostatic function for up to 24 hours. We hypothesize that a similar countermeasure will reduce the effects of fluid loss induced by headward fluid shift during space flight. The objective of this flight experiment is to evaluate the efficacy of the proposed countermeasure in reversing these effects on the cardiovascular system. Lower Body Negative Pressure (LBNP) involves exposing the legs and lower abdomen to reduced air pressure. The LBNP device is an air-tight chamber that seals the subject's waist to enclose the lower body. As used in this experiment, LBNP provides both the candidate treatment as well as the means of assessing the effectiveness of the treatment.

Charles, John B.↗

NASA NTRS1993

Cerebral blood velocity and other cardiovascular responses to 2 days of head-down tilt

Spaceflight induces a cephalad redistribution of fluid volume and blood flow within the human body, and space motion sickness, which is a problem during the first few days of space flight, could be related to these changes in fluid status and in blood flow of the cerebrum and vestibular system. To evaluate possible changes in cerebral blood flow during simulated weightlessness, we measured blood velocity in the middle cerebral artery (MCA) along with retinal vascular diameters, intraocular pressure, impedance cardiography, and sphygmomanometry on nine men (26.2 +/- 6.6 yr) morning and evening for 2 days during continuous 10 deg head-down tilt (HDT). When subjects went from seated to head-down bed rest, their heart rate and retinal diameters decreased, and intraocular pressures increased. After 48 h of HDT, blood flow velocity in the MCA was decreased and thoracic impedance was increased, indicating less fluid in the thorax. Percent changes in blood flow velocities in the MCA after 48 h of HDT were inversely correlated with percent changes in retinal vascular diameters. Blood flow velocities in the MCA were inversely correlated (intersubject) with arterial pressures and retinal vascular diameters. Heart rate, stroke volume, cardiac output, systolic arterial pressure, and at times pulse pressure and blood flow velocities in the MCA were greater in the evening. Total peripheral resistance was higher in the morning. Although cerebral blood velocity is reduced after subjects are head down for 2 days, the inverse relationship with retinal vessel diameters, which have control analogous to that of cerebral vessels, indicates cerebral blood flow is not reduced.

Frey, Mary A. B.↗

NASA NTRS1992

Short-duration spaceflight impairs human carotid baroreceptor-cardiac reflex responses

The effect of a spaceflight on the vagally mediated baroreceptor-cardiac reflex responses of humans were investigated by measuring the responses (provoked by neck pressure changes) in supine position and the heart rate and blood pressure in the supine and standing positions in 16 astronauts before and after 4- to 5-day long Space Shuttle missions. The results showed that exposures to spaceflight resulted in reduced baseline levels of the vagal-cardiac outflow and the vagally mediated responses to changes of the arterial baroreceptor input and that these changes contribute to postflight reductions of astronauts' ability to maintain standing arterial pressures.

Fritsch, Janice M.↗

NASA NTRS1992

Cardiovascular orthostatic function of Space Shuttle astronauts during and after return from orbit

Routine entry, landing, and seat egress after Space Shuttle flights is observed to be associated with drops in blood pressure and increases in heart rate that indicate that the cardiovascular system is performing at its maximum capacity in a large fraction (30 percent) of the study population. It is not apparent that adequate cardiovascular reserve capacity remains to accommodate unaided emergency egress after either current or extended space flights.

Charles, John B.↗

NASA NTRS1992

Responses to graded lower body negative pressure after space flight

Lower body negative pressure tests (0 to -60 mm Hg) were administered 2-3 times preflight and 4 times postflight (L0 to L7), to evaluate the effect of space flight on orthostatic responses. This paper presents preliminary findings from the first 4 crew members who have completed this protocol. Overall the results suggest a greater orthostatic strain lasting approximately two days postflight, that may have been due to enhanced pooling of blood in body regions other than the calf.

Fortney, Suzanne M.↗

NASA NTRS1992

Saline ingestion during lower body negative pressure as an end-of-mission countermeasure to post-space flight orthostatic intolerance

Lower body negative pressure (LBNP) in conjunction with saline ingestion can protect astronauts against post-space flight orthostatic intolerance. LBNP was used for both treatment and testing. The treatment was 4 hours of lower body decompression at 30 mm Hg below ambient pressure. One liter of water and 8 g of salt were ingested during the first hour. The treatment was evaluated by comparing heart rate (HR) and blood pressure (BP) responses to test decompressions on the days before and after treatment. It is concluded that cardiovascular responses to step-wise decompression duplicated Skylab findings. BP was maintained, but HR responses to each step were progressively greater in-flight than preflight. After the 4-hour treatment HR responses were closer to preflight values.

Charles, John B.↗

NASA NTRS1992

The effects of in-flight treadmill exercise on postflight orthostatic tolerance

In-flight aerobic exercise is thought to decrease the deconditioning effects of microgravity. Two deconditioning characteristics are the decreases in aerobic capacity (maximum O2 uptake) and an increased cardiovascular response to orthostatic stress (supine to standing). Changes in both parameters were examined after Shuttle flights of 8 to 11 days in astronauts who performed no in-flight exercise, a lower than normal volume of exercise, and a near-normal volume of exercise. The exercise regimen was a traditional continuous protocol. Maximum O2 uptake was maintained in astronauts who completed a near-normal exercise volume of in-flight exercise. Cardiovascular responses to stand test were equivocal among the groups. The use of the traditional exercise regimen as a means to maintain adequate orthostatic responses produced equivocal responses. A different exercise prescription may be more effective in maintaining both exercise capacity and orthostatic tolerance.

Siconolfi, Steven F.↗

NASA NTRS1991

Blood and urine responses to ingesting fluids of various salt and glucose concentrations

To compensate for the reduced blood and fluid volumes that develop during weightlessness, the Space Shuttle crewmembers consume salt tablets and water equivalent to 1 l of normal saline, about 2 hrs before landing. This paper compares the effects on blood, urine, and cardiovascular variables of the ingestion of 1 l of normal (0.9 percent) saline with the effects of distilled water, 1 percent glucose, 0.74 percent saline with 1 percent glucose, 0.9 percent saline with 1 percent glucose, and 1.07 percent saline. It was found that the expansion of plasma volume and the concentration of urine were greater 4 hrs after ingestion of 1.07 percent saline solution than after ingestion of normal saline and that the solutions containig glucose did not enhance any variables as compared with normal saline.

Frey, Mary A.↗

NASA NTRS1991

Orthostatic function during a stand test before and after head-up or head-down bedrest

The effects of head-down or head-up bedrest at -5, +10, +20, or +42 deg (simulating 0, 1/6, 1/3, and 2/3 g, respectively) for 6 hrs on four different days on the orthostatic tolerance were investigated by measuring relevant physiological reactions to orthostatic test taken before and after bedrest sessions. The multivariate analysis of variance statistical analyses indicates that there was no angle effect on any of the cardiovascular parameters monitored during the last 3 min of the stand test, suggesting that partial gravity loads would have no effect on the cardiovascular deconditioning exhibited postflight. There was, however, a significant elevation in the heart rate post-bedrest, and the heart rate increased on standing. Results from the stand test pre- and post-bedrest at -5 deg (but not at +10, +20, and +42 deg) were similar to those observed after space flight.

Lathers, Claire M.↗

NASA NTRS1991

Acute hemodynamic response to weightlessness during parabolic flight

The effect of a short exposure to weightlessness on hemodynamic parameters of humans was investigated in seven subjects flown aboard the KC-135 aircraft. Particular attention is given to the relationships among various hemodynamic responses to hypergravic and hypogravic states, observed for four different postures: semisupine, supine, standing, and sitting. Results are presented on changes in the thoracic fluid index, heart rate, cardiac index, and the coefficient of variation of the R-R intervals. High values of the coefficient of variation were found at the onset of 0-G, suggesting that vagal cardiac neural activity increases in all positions except supine (where a small decrease was registered).

Mukai, Chiaki N.↗

NASA NTRS1991

Changes in total body water during spaceflight

Total body water (TBW) changes occurring in humans as a consequence of prolonged exposure to microgravity were measured in five male crewmembers of Space Shuttle missions STS-61C and STS-26. It was found that the inflight mean TBW values were significantly different from the preflight and postflight values, while the preflight TBW values were not significantly different from the postflight values. It was also found that individuals may differ in the rate at which they respond to weightlessness. Of the three crewmen who reported experiencing no symptoms of space motion sickness (SMS), two had not exhibited a decrease of TBW at the time of measurements (24 hrs after launch), while the two crewmen who reported SMS of intermediate severity showed a decrease of several kg by 24 hrs, suggesting that dehydration might be an important factor affecting the rate of TBW decrease.

Leach, Carolyn S.↗

NASA NTRS1991

Cardiovascular adaptation to spaceflight

Data are presented on the rate of adaptation of the human cardiovascular system to conditions of spaceflight, with particular attention given to data obtained during spaceflight in the U.S. Space Shuttle Program. It is pointed out that many of the cardiovascular changes that occurred during spaceflights that lasted from 2 to 11 days can be traced directly to changes in the body fluid volume. The beneficial effects of a fluid loading countermeasure (oral rehydration) and of the supine body position on the heart rate during the spaceflight are demonstrated. It is noted that, after hours or a few days of spaceflight, a state of adaptation is reached, in which the subject is well adapted and appropriately hydrated for the weightless environment. However, the return to the normal gravity of the earth leaves the individual especially sensitive to orthostatic stress.

Charles, John B.↗

NASA NTRS1991

Echocardiographic evaluation of the cardiovascular effects of short-duration spaceflight

Results are presented of echocardiographic investigations and hemodynamic measurements performed on 24 astronauts before and after short-duration (4-5 days) spaceflight, including data on the heart rate, blood pressure, and cardiac volumes. Cardiovascular changes which were found to occur after 4-5 day long spaceflight included decreased the left ventricular end-diastolic volume and the stroke volume indices, with a compensatory increased heart rate and the cardiac output being maintained; in addition, altered total peripheral vascular resistance was found to occur, with an apparent reduction in the ability to augment the peripheral vascular tone upon assuming the standing position. These cardiovascular characteristics normalized within 48 hrs of landing.

Mulvagh, Sharon L.↗

NASA NTRS1991

Echocardiography in the flight program

Observations on American and Soviet astronauts have documented the association of changes in cardiovascular function during orthostasis with space flight. A basic understanding of the cardiovascular changes occurring in astronauts requires the determination of cardiac output and total peripheral vascular resistance as a minimum. In 1982, we selected ultrasound echocardiography as our means of acquiring this information. Ultrasound offers a quick, non-invasive and accurate means of determining stroke volume which, when combined with the blood pressure and heart rate measurements of the stand test, allows calculation of changes in peripheral vascular resistance, the body's major response to orthostatic stress. The history of echocardiography in the Space Shuttle Program is discussed and the results are briefly presented.

Charles, John B.↗

NASA NTRS1991

Spectral analysis of resting cardiovascular variables and responses to oscillatory LBNP before and after 6 degree head dowm bedrest

A major focus of our research program is to develop noninvasive procedures for determining changes in cardiovascular function associated with the null gravity environment. We define changes in cardiovascular function to be (1) the result of the regulatory system operating at values different from 'normal' but with an overall control system basically unchanged by the null gravity exposure, or (2) the result of operating with a control system that has significantly different regulatory characteristics after an exposure. To this end, we have used a model of weightlessness that consisted of exposing humans to 2 hrs. in the launch position, followed by 20 hrs. of 6 deg head down bedrest. Our principal objective was to use this model to measure cardiovascular responses to the 6 deg head down bedrest protocol and to develop the most sensitive 'systems identification' procedure for indicating change. A second objective, related to future experiments, is to use the procedure in combination with experiments designed to determine the degree to which a regulatory pathway has been altered and to determine the mechanisms responsible for the changes.

Knapp, Charles F.↗

NASA NTRS1991

Mathematical modeling of acute and chronic cardiovascular changes during Extended Duration Orbiter (EDO) flights

The purpose of NASA's Extended Duration Orbiter program is a gradual extension of the capabilities of the Space Shuttle Orbiter beyond its current 7-10 day limit on mission duration, as warranted by deepening understanding of the long-term physiological effects of weightlessness. Attention is being given to the cardiovascular problem of orthostatic tolerance loss due to its adverse effects on crew performance and health during reentry and initial readaptation to earth gravity. An account is given of the results of the application of proven mathematical models of circulatory and cardiovascular systems under microgravity conditions.

White, Ronald J.↗

NASA NTRS1991

Cardiovascular physiology in space flight

The effects of space flight on the cardiovascular system have been studied since the first manned flights. In several instances, the results from these investigations have directly contradicted the predictions based on established models. Results suggest associations between space flight's effects on other organ systems and those on the cardiovascular system. Such findings provide new insights into normal human physiology. They must also be considered when planning for the safety and efficiency of space flight crewmembers.

Charles, John B.↗

NASA NTRS1990

Computer simulation of cardiovascular changes during extended duration space flights

The application of mathematical modeling and computer simulation to the study of spaceflight cardiovascular changes is examined using a multicompartment representation model of the entire human cardiovascular system including its control elements. The model simulates the beat-to-beat dynamic responses of the cardiovascular system to orthostatic stresses. Simulation results pertaining to long-term space flight, the combined effect of +G(z) and blood volume loss, and the effect of anti-G suit inflation are discussed, including past results on the original version of the model which has been used in a number of analysis applications at NASA. New results pertain to analysis of cardiovascular changes in extended duration space flights and demonstrate the use of this model in evaluation of physiological factors that contribute to orthostatic intolerance following an exposure to weightlessness, in particular, blood volume loss and changes in the sensitivity of baroreceptors.

Srinivasan, R. Srini↗