Key result
Long-duration head-down bed rest altered cardiovascular function, including a 15% reduction in plasma volume and an increase in myocardial performance index (0.41 to 0.49 by day 7).
Why the study?
Does long-duration head-down bed rest alter cardiovascular structure and function?
Observational (n=13)
Does long-duration head-down bed rest alter cardiovascular structure and function?
Long-duration head-down bed rest induces cardiovascular structural and functional adaptations, primarily affecting lower body vasculature and decreasing cardiac function, similar to short-duration spaceflight.
Bed rest induces early cardiovascular changes; hypothesis-generating for spaceflight effects, needs confirmation in actual microgravity.
INTRODUCTION: Orthostatic hypotension is a serious risk for crewmembers returning from spaceflight. Numerous cardiovascular mechanisms have been proposed to account for this problem, including vascular and cardiac dysfunction, which we studied during bed rest. METHODS: Thirteen subjects were studied before and during bed rest. Statistical analysis was limited to the first 49-60 d of bed rest and compared to pre-bed rest data. Ultrasound data were collected on vascular and cardiac structure and function. Tilt testing was conducted for 30 min or until presyncopal symptoms intervened. RESULTS: Plasma volume was significantly reduced (15%) by day 7 of bed rest. Flow-mediated dilation in the leg was significantly increased at bed rest day 49 (6% from pre-bed rest). Arterial responses to nitroglycerin differed in the arm and leg, but did not change as a result of bed rest. Anterior tibial artery intimal-medial thickness markedly decreased at bed rest days 21 (21%), 35 (22%), and 49 (19%). Several cardiac functional parameters, including isovolumic relaxation time (73 ms to 85 ms at day 7) and myocardial performance index, were significantly increased (0.41 to 0.49 by day 7 of bed rest; indicating a decrease in cardiac function) during bed rest. There was a trend for decreased orthostatic tolerance following 60 d of bed rest (P = 0.1). DISCUSSION: Our data suggest that bed rest altered cardiovascular structure and function in a pattern similar to short-duration spaceflight. Additionally, the vascular alterations were primarily seen in the lower body, while vessels of the upper body were unaffected.
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Platts et al. (2009) conducted an observational in Cardiovascular adaptation to bed rest (n=13). Long-duration head-down bed rest vs. Pre-bed rest baseline was evaluated on Cardiovascular structure and function. Long-duration head-down bed rest altered cardiovascular function, including a 15% reduction in plasma volume and an increase in myocardial performance index (0.41 to 0.49 by day 7).
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