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

Purpose The increased physiological demand of pregnancy results in the 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. Methods Healthy nonpregnant (n = 18), pregnant (n = 14, 22-26 wk gestation), and postpartum women (n = 13, 12-16 wk postdelivery) underwent assessments of cardiac function and LV mechanics at rest, during a sustained isometric forearm contraction (30% maximum), and during low-intensity (LOW) and moderate-intensity (MOD) dynamic cycling exercise (25% and 50% peak power output). Significant differences (alpha = 0.05) were determined using ANCOVA and general linear model (resting value included as covariate). Results When accounting for higher resting cardiac output in pregnant women, pregnant women had greater cardiac output during isometric contraction (2.0 +/- 0.3 L center dot min(-1)center dot m(-1.83); nonpregnant, 1.3 +/- 0.2 L center dot min(-1)center dot m(-1.83); postpartum, 1.5 +/- 0.5 L center dot min(-1)center dot m(-1.83); P = 0.02) but similar values during dynamic cycling exercise (pregnant, LOW = 2.8 +/- 0.4 L center dot min(-1)center dot m(-1.83), MOD = 3.4 +/- 0.7 L center dot min(-1)center dot m(-1.83); nonpregnant, LOW = 2.4 +/- 0.3 L center dot min(-1)center dot m(-1.83), MOD = 3.0 +/- 0.3 L center dot min(-1)center dot m(-1.83); postpartum, LOW = 2.3 +/- 0.4 L center dot min(-1)center dot m(-1.83), MOD = 3.0 +/- 0.5 L center dot min(-1)center dot m(-1.83); P = 0.96). Basal circumferential strain was higher in pregnant women at rest, during the sustained isometric forearm contraction (-23.5% +/- 1.2%; nonpregnant, -14.6% +/- 1.4%; P = 0.001), and during dynamic cycling exercise (LOW = -27.0% +/- 4.9%, MOD = -27.4% +/- 4.6%; nonpregnant, LOW = -15.8% +/- 4.5%, MOD = -15.2% +/- 6.7%; P = 0.012); however, other parameters of LV mechanics were not different between groups. Conclusion The 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. In addition, 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.