Maternal cardioautonomic responses during and following exercise throughout pregnancy

Pregnancy is a significant physiological stressor that alters autonomic nervous system control. While previous research has documented shifts toward sympathetic dominance at rest, it remains unclear how these regulatory mechanisms operate during and immediately following exercise. The authors aimed to determine if gestation alters cardiovagal baroreflex gain (BRG) and heart rate variability (HRV) during an incremental peak exercise test and the subsequent active recovery phase.

Researchers recruited 43 pregnant women (distributed across the first, second, and third trimesters) and 20 nonpregnant (NP) controls. All participants underwent an incremental peak exercise test on a recumbent cycle ergometer. The authors measured beat-by-beat blood pressure and heart rate throughout the session. Specifically, they assessed BRG (using the sequence method to track changes in blood pressure and R-R intervals) and HRV (using RMSSD, a common index of parasympathetic activity) at three distinct states: rest, steady-state light exercise, and active recovery.

The study confirmed that resting cardiovagal baroreflex gain and heart rate variability decrease as pregnancy progresses, with third-trimester women showing significantly lower values than nonpregnant controls. However, the study challenged the assumption that this blunting would severely impair exercise recovery. During exercise, all groups showed reduced HRV and BRG compared to rest. Crucially, during active recovery, the pregnant groups did not show the further blunting of HRV and BRG that was observed in the nonpregnant control group. This suggests that the cardioautonomic system in pregnant women is surprisingly resilient during the recovery period following strenuous activity.

These findings offer clinical reassurance that pregnant women retain adequate cardioautonomic control to handle acute cardiovascular stress. The data suggest that, despite the lower baseline capacity associated with pregnancy, the autonomic nervous system does not show an increased risk of failure or extreme dysregulation in the immediate aftermath of peak exertion. Understanding these dynamics is vital for developing safe prenatal exercise guidelines and identifying mechanisms behind pregnancy-related issues like orthostatic intolerance.