Cardiac Responses to Submaximal Isometric Contraction and Aerobic Exercise in Healthy Pregnancy

PURPOSEThe increased physiological demand of pregnancy results in profound adaptation of the maternal cardiovascular system, reflected by greater resting cardiac output and left ventricular (LV) deformation. Whether the increased resting demand alters acute cardiac responses to exercise in healthy pregnant women is not well understood. METHODSHealthy non-pregnant (n=18), pregnant (n=14, 22-26 weeks gestation) and postpartum women (n=13, 12-16 weeks post-delivery) underwent assessments of cardiac function and LV mechanics at rest, during a sustained isometric forearm contraction (30% maximum) and during low- (LOW) and moderate-intensity (MOD) dynamic cycling exercise (25 and 50% peak power output). Significant differences (α=0.05) were determined using ANCOVA and general linear model (resting value included as covariate). RESULTSWhen accounting for higher resting cardiac output in pregnant women, pregnant women had greater cardiac output during isometric contraction (2.0±0.3; non-pregnant1.3±0.2; postpartum1.5±0.5 L.min/m, P=0.02), but similar values during dynamic cycling exercise (pregnantLOW2.8±0.4, MOD3.4±0.7, non-pregnantLOW2.4±0.3, MOD3.0±0.3, postpartumLOW2.3±0.4, MOD3.0±0.5 L.min/m, P=0.96). Basal circumferential strain was higher in pregnant women at rest, during the sustained isometric forearm contraction (-23.5±1.2%, non-pregnant-14.6±1.4%, P=0.001) and during dynamic cycling exercise (LOW-27.0±4.9, MOD-27.4±4.6%; non-pregnantLOW-15.8±4.5, MOD-15.2±6.7%, P=0.012), however other LV mechanics parameters were not different between groups. CONCLUSIONThe results support that the maternal heart can appropriately respond to additional cardiac demand and altered loading experienced during acute isometric and dynamic exercise, although subtle differences in responses to these challenges were observed. Additionally, the LV mechanics that underpin global cardiac function are greater in pregnant women during exercise, leading to the speculation that the hormonal milieu of pregnancy influences regional deformation.