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Cardiovascular Adaptations to Long Duration Head Down Tilt Bed RestOrthostatic hypotension is a recognized risk for crewmembers returning from space. Numerous cardiovascular mechanisms have been proposed to account for this problem including vascular and cardiac dysfunction. We studied arterial and cardiac function in 6-degree head-down tilt bed rest, which is the most widely accepted ground-based analog of spaceflight. Eleven subjects are included in this study (8 men and 3 women). Data analysis was limited to the first 49 days, and compared to pre-bed rest baseline data. Using ultrasound, data was collected on arterial diameters and flows at baseline and during reactive hyperemia and following administration of nitroglycerin. Echocardiography was used to acquire information regarding systolic and diastolic function as well as ventricular mass and diameter. Plasma volumes were significantly decreased by 7 days of bed rest and stayed down through 49 days. There were no differences in reactive hyperemic response in the arm at any time point. However, the hyperemic response in the leg was significantly increased at day 49. Arterial responses to nitroglycerin did not change over the duration of bed rest (day effect) in either the arm or leg, but there was a significant difference between the arm and the leg responses. There was a marked decrease in anterior tibial intimal-medial thickness at days 21, 35 and 49. Several cardiac functional parameters including IVRT, Mitral e-wave, ejection time, velocity of circumferential shortening and myocardial performance index were significantly changed following 49 days of bed rest. These data show that some cardiovascular measures change during bed rest, while others do not. Further study is needed to determine if these measures can provide any insight into the effects of bed rest, or spaceflight, on human cardiovascular performance.
Document ID
20070006525
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Platts, Steven H.
(NASA Johnson Space Center Houston, TX, United States)
Meck, Janice V.
(NASA Johnson Space Center Houston, TX, United States)
Martin, David S.
(Wyle Labs., Inc. Houston, TX, United States)
Freeman-Perez, Sondra A.
(Wyle Labs., Inc. Houston, TX, United States)
Riberio, Christine
(Wyle Labs., Inc. Houston, TX, United States)
Garcia, Kathleen M.
(Wyle Labs., Inc. Houston, TX, United States)
Waters, Wendy W.
(Wyle Labs., Inc. Houston, TX, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2007
Subject Category
Aerospace Medicine
Meeting Information
Meeting: NASA Human Research Project Investigators Meeting
Location: League City, TX
Country: United States
Start Date: February 12, 2007
End Date: February 14, 2007
Sponsors: Universities Space Research Association
Distribution Limits
Public
Copyright
Other

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