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Deterioration of left ventricular chamber performance after bed rest : "cardiovascular deconditioning" or hypovolemia?BACKGROUND: Orthostatic intolerance after bed rest is characterized by hypovolemia and an excessive reduction in stroke volume (SV) in the upright position. We studied whether the reduction in SV is due to a specific adaptation of the heart to head-down tilt bed rest (HDTBR) or acute hypovolemia alone. METHODS AND RESULTS: We constructed left ventricular (LV) pressure-volume curves from pulmonary capillary wedge pressure and LV end-diastolic volume and Starling curves from pulmonary capillary wedge pressure and SV during lower body negative pressure and saline loading in 7 men (25+/-2 years) before and after 2 weeks of -6 degrees HDTBR and after the acute administration of intravenous furosemide. Both HDTBR and hypovolemia led to a similar reduction in plasma volume. However, baseline LV end-diastolic volume decreased by 20+/-4% after HDTBR and by 7+/-2% after hypovolemia (interaction P<0.001). Moreover, SV was reduced more and the Starling curve was steeper during orthostatic stress after HDTBR than after hypovolemia. The pressure-volume curve showed a leftward shift and the equilibrium volume of the left ventricle was decreased after HDTBR; however, after hypovolemia alone, the curve was identical, with no change in equilibrium volume. Lower body negative pressure tolerance was reduced after both conditions; it decreased by 27+/-7% (P<0.05) after HDTBR and by 18+/-8% (P<0.05) after hypovolemia. CONCLUSIONS: Chronic HDTBR leads to ventricular remodeling, which is not seen with equivalent degrees of acute hypovolemia. This remodeling leads to a greater decrease in SV during orthostatic stress after bed rest than hypovolemia alone, potentially contributing to orthostatic intolerance.
Document ID
20040112492
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Perhonen, M. A.
(Institute for Exercise and Environmental Medicine, Presbyterian Hospital and University of Texas Southwestern Medical Center Dallas, Texas, United States)
Zuckerman, J. H.
Levine, B. D.
Blomqvist, C. G.
Date Acquired
August 21, 2013
Publication Date
April 10, 2001
Publication Information
Publication: Circulation
Volume: 103
Issue: 14
ISSN: 0009-7322
Subject Category
Aerospace Medicine
Funding Number(s)
CONTRACT_GRANT: MO1-RR00633
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Cardiopulmonary
Clinical Trial
Non-NASA Center

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