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Postspaceflight orthostatic hypotension occurs mostly in women and is predicted by low vascular resistanceAbout 20% of astronauts suffer postspaceflight presyncope. We studied pre- to postflight (5- to 16-day missions) cardiovascular responses to standing in 35 astronauts to determine differences between 1) men and women and 2) presyncopal and nonpresyncopal groups. The groups were presyncopal women, presyncopal men, and nonpresyncopal men based on their ability to stand for 10 min postflight. Preflight, women and presyncopal men had low vascular resistance, with the women having the lowest. Postflight, women experienced higher rates of presyncope (100 vs. 20%; P = 0.001) and greater losses of plasma volume (20 vs. 7%; P < 0.05) than men. Also, presyncopal subjects had lower standing mean arterial pressure (P < or = 0.001) and vascular resistance (P < 0.05), smaller increases in norepinephrine (P < or = 0.058) and greater increases in epinephrine (P < or = 0.058) than nonpresyncopal subjects. Presyncopal subjects had a strong dependence on plasma volume to maintain standing stroke volume. These findings suggest that postflight presyncope is greatest in women, and this can be ascribed to a combination of inherently low-resistance responses, a strong dependence on volume status, and relative hypoadrenergic responses. Conversely, high vascular resistance and postflight hyperadrenergic responses prevent presyncope.
Document ID
20040088518
Acquisition Source
Johnson Space Center
Document Type
Reprint (Version printed in journal)
Authors
Waters, Wendy W.
(National Space Biomedical Research Institute, Baylor College of Medicine Houston, Texas 77030, United States)
Ziegler, Michael G.
Meck, Janice V.
Date Acquired
August 21, 2013
Publication Date
February 1, 2002
Publication Information
Publication: Journal of applied physiology (Bethesda, Md. : 1985)
Volume: 92
Issue: 2
ISSN: 8750-7587
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: M01 RR-08827
Distribution Limits
Public
Copyright
Other
Keywords
Flight Experiment
NASA Discipline Cardiopulmonary
manned
NASA Center JSC
short duration
STS Shuttle Project

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