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Is there resetting of central venous pressure in microgravity?In the early phase of the Space Shuttle program, NASA flight surgeons implemented a fluid-loading countermeasure in which astronauts were instructed to ingest eight 1-g salt tablets with 960 ml of water approximately 2 hours prior to reentry from space. This fluid loading regimen was intended to enhance orthostatic tolerance by replacing circulating plasma volume reduced during the space mission. Unfortunately, fluid loading failed to replace plasma volume in groundbased experiments and has proven minimally effective as a countermeasure against post-spaceflight orthostatic intolerance. In addition to the reduction of plasma volume, central venous pressure (CVP) is reduced during exposure to actual and groundbased analogs of microgravity. In the present study, we hypothesized that the reduction in CVP due to exposure to microgravity represents a resetting of the CVP operating point to a lower threshold. A lower CVP 'setpoint' might explain the failure of fluid loading to restore plasma volume. In order to test this hypothesis, we conducted an investigation in which we administered an acute volume load (stimulus) and measured responses in CVP, plasma volume and renal functions. If our hypothesis is true, we would expect the elevation in CVP induced by saline infusion to return to its pre-infusion levels in both HDT and upright control conditions despite lower vascular volume during HDT. In contrast to previous experiments, our approach is novel in that it provides information on alterations in CVP and vascular volume during HDT that are necessary for interpretation of the proposed CVP operating point resetting hypothesis.
Document ID
20040087791
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Convertino, V. A.
(U.S. Army Institute of Surgical Research Fort Sam Houston, TX 78234, United States)
Ludwig, D. A.
Elliott, J. J.
Wade, C. E.
Date Acquired
August 21, 2013
Publication Date
July 1, 2001
Publication Information
Publication: Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology
Volume: 8
Issue: 1
ISSN: 1077-9248
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Cardiopulmonary
NASA Center ARC
Non-NASA Center

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