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Hoffler, G. W.

Publications and source records attributed to Hoffler, G. W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Evidence for increased beta-adrenoreceptor responsiveness induced by 14 days of simulated microgravity in humans

We studied hemodynamic responses to alpha- and beta-receptor agonists in eight healthy men before and after 14 days of 6 degrees head-down tilt (HDT) to test the hypothesis that increased adrenoreceptor responsiveness is induced by prolonged exposure to simulated microgravity. Steady-state infusions of isoproterenol (Iso) at rates of 0.005, 0.01, and 0.02 microgram.kg-1.min-1 were used to assess beta 1- and beta 2-adrenoreceptor responsiveness. Infusions of phenylephrine (PE) at rates of 0.25, 0.50, and 1.00 microgram.kg-1.min-1 were used to assess responsiveness of alpha 1-vascular adrenoreceptors. Slopes calculated from linear regressions between Iso and PE doses and changes in beat-to-beat heart rate, blood pressure, and leg vascular resistance (occlusion plethysmography) for each subject were used as an index of alpha- and beta-adrenoreceptor responsiveness. HDT increased the slopes of heart rate (1,056 +/- 107 to 1,553 +/- 83 beats micrograms-1.kg-1.min-1; P = 0.014) and vasodilation (-469 +/- 111 to -1,446 +/- 309 peripheral resistance units.microgram-1.kg-1.min-1; P = 0.0224) to Iso infusion. There was no alteration in blood pressure or vascular resistance responses to PE infusion after HDT. Our results provide evidence that simulated microgravity causes selective increases in beta 1- and beta 2-adrenoreceptor responsiveness without affecting alpha 1-vascular adrenoreceptor responses.

NASA Discipline Cardiopulmonary↗
NASA NTRS1996

Evidence for Increased Beta-Adrenoreceptor Responsiveness Induced by 14 Days of Simulated Microgravity in Humans

We studied hemodynamic responses to alpha and beta receptor agonists in 8 healthy men ( 38+- 2 yrs) before and after 14 days of 6 degree head-down tilt (HDT) to test the hypothesis that increased adrenergic responsiveness is induced by prolonged exposure to microgravity. Immediately following a 30-min baseline period, a steady-state infusion of isoproterenol (ISO) was used to assess beta 1- and beta 2-adrenergic responsiveness. ISO was infused at three graded constant rates of 0.005, 0.01 and 0.02 ug/kg/min. After heart rate and blood pressure had been allowed to return to baseline levels following ISO infusion graded infusion of phenylephrine (PE) was used to assess responsiveness of alpha I-vascular receptors. PE was infused at three graded constant rates of 0.25, 0.50 and 1.00 ug/kg/min. Each infusion interval for both drugs was 9 min. During the infusions, constant monitoring of beat-to-beat blood pressure and heart rate was performed and leg blood flow was measured with occlusion plethysmography at each infusion level. The slopes calculated from linear regressions between ISO and PE doses and changes in heart rate, blood pressure, and leg vascular resistance for each subject were used to represent alpha- and beta- adrenoreceptor responsiveness. Fourteen days HDT increased the slopes of heart rate (1056 +- 107 to 1553 +- 83 beats/ug/kg/min; P= 0.014) and vasodilation (-469ft +- 111 to -l446 +- 309 PRU/ug/kg/min; P =0.0224) to ISO infusion. There was no alteration in blood pressure or vascular resistance responses to PE infusion after HDT. Our results provide evidence that microgravity causes selective increases in beta 1- and beta 2-adrenergic responsiveness without affecting alpha 1-vascular responses.

CARDIOVASCULAR SYSTEM↗
NASA NTRS1995

Increased beta-adrenergic responsiveness induced by 14 days exposure to simulated microgravity

Increased sensitivity of end-organ responses to neuroendocrine stimuli as a result of prolonged exposure to the relative inactivity of microgravity has recently been hypothesized. This notion is based on the inverse relationship between circulating norepinephrine and beta-adrenoreceptor sensitivity. The beta-adrenoreceptor activity is reduced in individuals who have elevated plasma norepinephrine as a result of regular exposure to upright posture and physical exercise. In contrast, adrenoreceptor hypersensitivity has been reported in patients with dysautonomias in which circulating catecholamines are absent or reduced. Taken together, these studies and the observation that circulating plasma norepinephrine has been reduced during spaceflight and in groundbased simulations of microgravity prompt the suggestion that adrenoreceptor hypersensitivity may be a consequence of the adaptation to spaceflight. We conducted an experiment designed to measure cardiovascular responses to adrenoreceptor agonists in human subjects before and after prolonged exposure to 6 deg head-down tilt (HDT) to test the hypothesis that adaptation to microgravity increases adrenoreceptor responsiveness, and that this adaptation is associated with reduced levels of circulating norepinephrine.

Convertino, V. A.↗
NASA NTRS1993

Hemodynamic and hormonal responses to lower body negative pressure in men with varying profiles of strength and aerobic power

Hemodynamic, cardiac, and hormonal responses to lower-body negative pressure (LBNP) were examined in 24 healthy men to test the hypothesis that responsiveness of reflex control of blood pressure during orthostatic challenge is associated with interactions between strength and aerobic power. Subjects underwent treadmill tests to determine peak oxygen uptake (VO2max) and isokinetic dynamometer tests to determine knee extensor strength. Based on predetermined criteria, subjects were classified into one of four fitness profiles of six subjects each, matched for age, height, and body mass: (a) low strength/average aerobic fitness, (b) low strength/high aerobic fitness, (c) high strength/average aerobic fitness, and (d) high strength/high aerobic fitness. Following 90 min of 0.11 rad (6 degrees) head-down tilt (HDT), each subject underwent graded LBNP to -6.7 kPa or presyncope, with maximal duration 15 min, while hemodynamic, cardiac, and hormonal responses were measured. All groups exhibited typical hemodynamic, hormonal, and fluid shift responses during LBNP, with no intergroup differences between high and low strength characteristics. Subjects with high aerobic power exhibited greater (P < 0.05) stroke volume and lower (P < 0.05) heart rate, vascular peripheral resistance, and mean arterial pressure during rest, HDT, and LBNP. Seven subjects, distributed among the four fitness profiles, became presyncopal. These subjects showed greatest reduction in mean arterial pressure during LBNP, had greater elevations in vasopressin, and lesser increases in heart rate and peripheral resistance. Neither VO2max nor leg strength were associated with fall in arterial pressure or with syncopal episodes. We conclude that interactions between aerobic and strength fitness characteristics do not influence responses to LBNP challenge.

Norepinephrine/blood↗
NASA NTRS1992

Cardiovascular physiology - Effects of microgravity

Experiments during spaceflight and its groundbase analog, bedrest, provide consistent data which demonstrate that numerous changes in cardiovascular function occur as part of the physiological adaptation process to the microgravity environment. These include elevated heart rate and venous compliance, lowered blood volume, central venous pressure and stroke volume, and attenuated autonomic reflex functions. Although most of these adaptations are not functionally apparent during microgravity exposure, they manifest themselves during the return to the gravitational challenge of earth's terrestrial environment as orthostatic hypotension and instability, a condition which could compromise safety, health and productivity. Development and application of effective and efficient countermeasures such as saline "loading," intermittent venous pooling, pharmacological treatments, and exercise have become primary emphases of the space life sciences research effort with only limited success. Successful development of countermeasures will require knowledge of the physiological mechanisms underlying cardiovascular adaptation to microgravity which can be obtained only through controlled, parallel groundbased research to complement carefully designed flight experiments. Continued research will provide benefits for both space and clinical applications as well as enhance the basic understanding of cardiovascular homeostasis in humans.

Convertino, V.↗
NASA NTRS1992

Effect of breakfast on selected serum and cardiovascular variables

In view of the objections of many subjects to overnight fasting prior to their blood being drawn for analyses, the effect of eating breakfast on the results of subsequent blood analyses of selected blood constituents and on cardiovascular variables was investigated in 47 men and 34 women who were subjected to blood analyses on two occasions, one week apart: once fasting and once after breakfast. Results suggest that subjects need not fast overnight before blood is being drawn for determinations of the HDL-C levels, hemoglobin, hematocrit, total cholesterol, or phosphorus. However, based on other studies, it is suggested breakfast should not have a high content of fat.

Frey, Mary A. B.↗
NASA NTRS1990

Responses of women to orthostatic and exercise stresses

The results are presented from a special physiological study of women at the Johnson Space Center in 1976 to 1977. Its purpose was to establish a large (98 subjects) database from normal working women. The data sets are medical historical, clinical, anthropometric, and stress response statistics useful for establishing medical criteria for selecting women astronauts. Stressors were lower body negative pressure and static standing (both orthostatic) and treadmill exercise (ergometric). Data shown are original individual values with analyses and subsets, and statistical summaries and correlations relating to human responses to microgravity. Similarities appear between the characteristics of women in this study and those of women astronauts currently flying in Shuttle crews.

Hoffler, G. W.↗
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 NTRS1981

Logic-controlled occlusive cuff system

An occlusive cuff system comprises a pressure cuff and a source of regulated compressed gas feeding the cuff through an electrically operated fill valve. An electrically operated vent valve vents the cuff to the ambient pressure. The fill valve is normally closed and the vent valve is normally open. In response to an external start signal, a logic network opens the fill valve and closes the vent valve, thereby starting the pressurization cycle and a timer. A pressure transducer continuously monitors the pressure in the cuff. When the transducer's output equals a selected reference voltage, a comparator causes the logic network to close the fill valve. The timer, after a selected time delay, opens the vent valve to the ambient pressure, thereby ending the pressurization cycle.

Baker, J. T.↗
NASA NTRS1979

Skylab medical data evaluation program (SMEDEP)

A day-by-day summary of selected data collected during the experiment is presented. The clinical and environmental data are presented in a mission-day format along with a tabulation of biomedical measurements whose values exceed three standard deviations from the preflight measurements.

Hoffler, G. W.↗
NASA NTRS1977

Changes in the Achilles tendon reflexes following Skylab missions

Postflight measurements of Achilles tendon reflex duration on Skylab crewmen indicate a state of disequilibrium between the flexor and extensor muscle groups with an initial decrease in reflex duration. As the muscles regain strength and mass there occurs an overcompensation reflected by increased reflex duration. Finally, when a normal neuromuscular state is reached the reflex duration returns to baseline value.

Baker, J. T.↗
NASA NTRS1977

Lower body negative pressure: Third manned Skylab mission

The objective of the Skylab Lower Body Negative Pressure experiment was to determine the extent and the time course of changes in orthostatic tolerance during the weightlessness of space flight and to determine whether in-flight data from the experiment would be useful in predicting the postflight status of orthostatic tolerance. Compared to preflight results, lower body negative pressure produced exaggerated blood pressure and heart rate responses during the first in-flight test of the Skylab 2 crewmen and showed no clear-cut trend toward preflight levels during the 28-day flight. During the second manned mission, Skylab 3, similar exaggeration of blood pressure and heart rate responses occurred during the first in-flight test. Again no definite trend toward preflight values could be seen during the first 28 days but cardiovascular responses to lower body negative pressure appeared to become more stable by the sixth to eighth week of flight. In general, the test results in-flight served to predict quite well the orthostatic tolerance of the individual crewmen in the immediate postflight period.

Johnson, R. L.↗
NASA NTRS1977

Vectorcardiographic results from Skylab medical experiment M092: Lower body negative pressure

Electrocardiographic interval changes suggesting effects of increased vagal tone were observed early in some Gemini crewmembers. Preflight versus postflight amplitude differences appeared in electrocardiograms of several of the early Apollo crewmembers. In preflight and postflight crew evaluations of the last three Apollo flights, quantitative postflight vectorcardiographic changes were for the first time determined in American space crews. Changes not considered related to heart rate were mainly those of increased P and QRS vector magnitudes and orientation shifts. But since most of these postflight findings resembled those observed with the orthostatic stress of lower body negative pressure, it was inferred then that upon their return from space, these Apollo astronauts exhibited exaggerated responses to orthostasis in the vectorcardiogram as well as in measures of cardiovascular hemodynamics.

Hoffler, G. W.↗
NASA NTRS1977

Anthropometric changes and fluid shifts

In an effort to obtain the most comprehensive and coherent picture of changes under weightlessness, a set of measurements on Skylab 2 was initiated and at every opportunity, additional studies were added. All pertinent information from ancillary sources were gleaned and collated. On Skylab 2, the initial anthropometric studies were scheduled in conjunction with muscle study. A single set of facial photographs was made in-flight. Additional measurements were made on Skylab 3, with photographs and truncal and limb girth measurements in-flight. Prior to Skylab 4, it was felt there was considerable evidence for large and rapid fluid shifts, so a series of in-flight volume and center of mass measurements and infrared photographs were scheduled to be conducted in the Skylab 4 mission. A number of changes were properly documented for the first time, most important of which were the fluid shifts. The following description of Skylab anthropometrics address work done on Skylab 4 primarily.

Thornton, W. E.↗
NASA NTRS1977

Evaluation of the electromechanical properties of the cardiovascular system after prolonged weightlessness

Devices and techniques for measuring and analyzing systolic time intervals and quantitative phonocardiograms were initiated during Apollo 17. The data show that the systolic time interval from Apollo 17 crewmen remained elevated longer postflight than the response criteria of heart rate, blood pressure, and percent change in leg volume all of which had returned to preflight levels by the second day postflight. Although the systolic time interval values were only slightly outside the preflight fiducial limits, this finding suggested that: the analysis of systolic time intervals may help to identify the mechanisms of postflight orthostatic intolerance by virtue of measuring ventricular function more directly and, the noninvasive technique may prove useful in determining the extent and duration of cardiovascular instability after long duration space flight. The systolic time intervals obtained on the Apollo 17 crewmen during lower body negative pressure were similar to those noted in patients with significant heart disease.

Bergman, S. A., Jr.↗
NASA NTRS1977

Determination of cardiac size from chest roentgenograms following Skylab missions

The majority of crewmembers who exhibited postflight decreases in the cardiac silhouette size also showed a decreased orthostatic tolerance to lower body negative pressure. Similar findings were also reported by the Soviet investigators following 30-day bedrest studies and in cosmonauts upon return from space missions. Further radiological data from all three Skylab manned missions are presented and the physiological factors possibly involved in the cardiac silhouette changes are discussed.

Nicogossian, A. E.↗
NASA NTRS1976

Occlusive-cuff controller

Device can be automatically set to supply desired amount of pressure for given time and may be triggered manually or from patient's electrocardiograph.

Baker, J. T.↗