Abstract 3640: Cardiac Atrophy in Women After 8 Weeks of Bed Rest Deconditioning

Background : Chronic exposure to microgravity by bed rest or spaceflight induces cardiac atrophy which leads to reduced standing stroke volume and orthostatic intolerance. However despite the fact that orthostatic intolerance appears worse in female astronauts as well as patient populations, most previous high resolution studies of cardiac morphology after microgravity were performed only in men. Since female athletes have less physiological hypertrophy than male athletes, we reasoned that they also might have less physiological cardiac atrophy after bed rest.

Methods : Magnetic resonance imaging (MRI) was performed in 24 healthy young women (32.1± 4yr.) to measure LV and 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 (N=8) or 2 control groups consisting of a) exercise training using supine treadmill running within lower body negative pressure plus resistive training (N=8); or b) protein supplementation (N=8; 0.6g/kg increase in protein long chain amino acids).

Results : After sedentary bed rest without nutritional protein supplementation, there were significant reductions in LV (2.2 ± 0.2 to 2.0 ± 0.2 g/kg, P=0.001) and RV masses (0.8 ± 0.1 to 0.6 ± 0.1 g/kg, P<0.001), similar to what has been observed previously in men (8.0% Perhonen

; : –653 ). In contrast, there were significant increases in LV (1.9 ± 0.4 to 2.3 ± 0.3 g/kg, P<0.001) and RV masses (0.7 ± 0.1 to 0.8 ± 0.2 g/kg, P=0.002) in the exercise trained controls. Protein supplementation led to an intermediate phenotype with no change in LV or RV mass after bed rest.

Conclusions : Cardiac atrophy occurs in women similar to men following sedentary long term HDT bed rest. However, exercise training and to a lesser extent protein supplementation prevent the cardiac atrophy associated with microgravity simulated by strict bed rest.