Cardiac atrophy in women following bed rest

1 Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, and 2 Division of Cardiology, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas; 3 Division of Physical Performance and Development, University of New Mexico, Albuquerque, New Mexico; 4 Department of Clinical, Technological and Morphological Sciences, and Division of Internal Medicine, University of Trieste, Trieste, Italy; and 5 Department of Orthopaedic Surgery, University of California, San Diego, California Submitted 14 October 2006 ; accepted in final form 15 March 2007 Both chronic microgravity exposure and long-duration bed rest induce cardiac atrophy, which leads to reduced standing stroke volume and orthostatic intolerance. However, despite the fact that women appear to be more susceptible to postspaceflight presyncope and orthostatic hypotension than male astronauts, most previous high-resolution studies of cardiac morphology following microgravity have been performed only in men. Because female athletes have less physiological hypertrophy than male athletes, we reasoned that they also might have altered physiological cardiac atrophy after bed rest. Magnetic resonance imaging was performed in 24 healthy young women (32.1 ± 4 yr) to measure left ventricular (LV) and right ventricular (RV) mass, volumes, and morphology accurately before and after 60 days of 6° head-down tilt (HDT) bed rest. Subjects were matched and then randomly assigned to sedentary bed rest (controls, n = 8) or two treatment groups consisting of 1 ) exercise training using supine treadmill running within lower body negative pressure plus resistive training ( n = 8), or 2 ) protein (0.45 g·kg –1 ·day –1 increase) plus branched-chain amino acid (BCAA) (7.2 g/day) supplementation ( n = 8). After sedentary bed rest without nutritional supplementation, there were significant reductions in LV (96 ± 26 to 77 ± 25 ml; P = 0.03) and RV volumes (104 ± 33 to 86 ± 25 ml; P = 0.02), LV (2.2 ± 0.2 to 2.0 ± 0.2 g/kg; P = 0.003) and RV masses (0.8 ± 0.1 to 0.6 ± 0.1 g/kg; P < 0.001), and the length of the major axis of the LV (90 ± 6 to 84 ± 7 mm. P < 0.001), similar to what has been observed previously in men (8.0%; Perhonen MA, Franco F, Lane LD, Buckey JC, Blomqvist Zerwekh JE, Peshock RM, Weatherall PT, Levine BD. J Appl Physiol 91: 645–653, 2001). In contrast, there were no significant reductions in LV or RV volumes in the exercise-trained group, and the lengt