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Mechanism for negative water balance during weightlessness An hypothesisThe mechanism for the apparent decrease in body fluid volume in astronauts during spaceflight remains obscure. The widespread postulate that the hypohydration is the result of the Henry-Gauer reflex, a diuresis caused by inhibition of vasopressin secretion resulting from increased left and perhaps right atrial (central) venous pressure, has not been established with direct measurements on astronauts. An hypothesis is proposed to account for fluid-electrolyte shifts during weightlessness. A moderate but transient increase in central venous pressure occurs when orbit is entered that is insufficient to activate the Henry-Gauer reflex but sufficient to stimulate the release of atrial natriuretic peptides. Increased sodium excretion would facilitate some increased urinary water loss. The resulting relatively dilute plasma and interstitial fluids would cause fluid to shift into the cellular space, resulting in edema in the head and trunk and inhibition of thirst and drinking. Thus, the negative water balance in astronauts would be caused by a gradual natriuresis and diuresis coupled with reduced fluid intake.
Document ID
19860037926
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Greenleaf, J. E.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
August 12, 2013
Publication Date
January 1, 1986
Publication Information
Publication: Journal of Applied Physiology
Volume: 60
ISSN: 0161-7567
Subject Category
Aerospace Medicine
Accession Number
86A22664
Distribution Limits
Public
Copyright
Other

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