Effects of pregnancy and chronic exercise on maternal cardiac structure and function

This study examined the interactive effects of pregnancy and aerobic condit ioning on maternal cardiac structure and function. Effects of closely monit ored cycle ergometer conditioning were studied during the second (TM2) and third trimesters (TM3) in 22 previously sedentary pregnant women (exercised group, EG) and a nonexercising pregnant control group with similar charact eristics (CG, n = 19). Subjects were studied in the resting state by two-di mensional echocardiography and during cycle ergometer exercise at three ste ady-state power outputs at the start of TM2 (ENTRY), at the end of TM2 and TM3 (postconditioning), and 3-4 months postpartum (NPR, nonpregnant referen ce, CG only). Aerobic conditioning did not increase left ventricular dimens ions beyond those attributable to pregnancy itself. In addition, in contras t with previous studies of nonpregnant women, physical conditioning during pregnancy did not reduce heart rate (HR) in the resting state. During exerc ise, the slope of the HR versus oxygen uptake ((V)over dot O-2) regression decreased significantly between preconditioning and the end of TM3 in the E G, suggesting that training-induced reductions in HR become more evident wi th increasing exercise intensity. Also, significant reductions in oxygen pu lse ((V)over dotO(2)/HR) were observed at all three work rates in the CG, b ut not in the EG. These findings support the hypothesis that the cardiovasc ular effects of aerobic conditioning are obscured by more powerful effects of pregnancy in the resting state but become "unmasked" during strenuous ex ercise.