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Record Details

Record 47 of 1008
Influence of Gravity on Blood Volume and Flow Distribution
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Author and Affiliation:
Pendergast, D.(State Univ. of New York, Dept. of Physiology and Biophysics, Buffalo, NY United States)
Olszowka, A.(State Univ. of New York, Dept. of Physiology and Biophysics, Buffalo, NY United States)
Bednarczyk, E.(State Univ. of New York, Dept. of Nuclear Medicine, Buffalo, NY United States)
Shykoff, B.(State Univ. of New York, Dept. of Physiology and Biophysics, Buffalo, NY United States)
Farhi, L.(State Univ. of New York, Dept. of Physiology and Biophysics, Buffalo, NY United States)
Abstract: In our previous experiments during NASA Shuttle flights SLS 1 and 2 (9-15 days) and EUROMIR flights (30-90 days) we observed that pulmonary blood flow (cardiac output) was elevated initially, and surprisingly remained elevated for the duration of the flights. Stroke volume increased initially and then decreased, but was still above 1 Gz values. As venous return was constant, the changes in SV were secondary to modulation of heart rate. Mean blood pressure was at or slightly below 1 Gz levels in space, indicating a decrease in total peripheral resistance. It has been suggested that plasma volume is reduced in space, however cardiac output/venous return do not return to 1 Gz levels over the duration of flight. In spite of the increased cardiac output, central venous pressure was not elevated in space. These data suggest that there is a change in the basic relationship between cardiac output and central venous pressure, a persistent "hyperperfusion" and a re-distribution of blood flow and volume during space flight. Increased pulmonary blood flow has been reported to increase diffusing capacity in space, presumably due to the improved homogeneity of ventilation and perfusion. Other studies have suggested that ventilation may be independent of gravity, and perfusion may not be gravity- dependent. No data for the distribution of pulmonary blood volume were available for flight or simulated microgravity. Recent studies have suggested that the pulmonary vascular tree is influenced by sympathetic tone in a manner similar to that of the systemic system. This implies that the pulmonary circulation is dilated during microgravity and that the distribution of blood flow and volume may be influenced more by vascular control than by gravity. The cerebral circulation is influenced by sympathetic tone similarly to that of the systemic and pulmonary circulations; however its effects are modulated by cerebral autoregulation. Thus it is difficult to predict if cerebral perfusion is increased and if there is edema in space. Anecdotal evidence suggests there may be cerebral edema early in flight. Cerebral artery velocity has been shown to be elevated in simulated microgravity. The elevated cerebral artery velocity during simulated microgravity may reflect vasoconstriction of the arteries and not increased cerebral blood flow. The purpose of our investigations was to evaluate the effects of alterations in simulated gravity (+/-), resulting in changes in cardiac output (+/-), and on the blood flow and volume distribution in the lung and brain of human subjects. The first hypothesis of these studies was that blood flow and volume would be affected by gravity, but their distribution in the lung would be independent of gravity and due to vasoactivity changing vascular resistance in lung vessels. The vasodilitation of the lung vasculature (lower resistance) along with increased "compliance" of the heart could account for the absence of increased central venous pressure in microgravity. Secondly, we postulate that cerebral blood velocity is increased in microgravity due to large artery vasoconstriction, but that cerebral blood flow would be reduced due to autoregulation.
Publication Date: Jan 01, 1999
Document ID:
20000020560
(Acquired Mar 03, 2000)
Subject Category: AEROSPACE MEDICINE
Document Type: Conference Paper
Publication Information: Proceedings of the First Biennial Space Biomedical Investigators' Workshop; 297-299
Contract/Grant/Task Num: NAS9-16042; NAGW-3937
Financial Sponsor: NASA Johnson Space Center; Houston, TX United States
NASA; Washington, DC United States
Organization Source: State Univ. of New York; Buffalo, NY United States
Description: 3p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: BLOOD FLOW; BLOOD VOLUME; GRAVITATIONAL EFFECTS; AUTOMATIC CONTROL; BRAIN CIRCULATION; CARDIOVASCULAR SYSTEM; FLOW DISTRIBUTION; EXPERIMENTATION; ARTERIES; CARDIAC OUTPUT; CEREBRUM; BLOOD PRESSURE; HOMOGENEITY; PULMONARY CIRCULATION; STROKE VOLUME; VASOCONSTRICTION
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