The dynamics of autonomic nervous system activity and hemodynamic changes in pregnant women

The purpose of this research was to assess the dynamics of autonomic nervous system(ANS) and hemodynamic activity changes during uncomplicated pregnancy.

We enrolled 36 pregnant women (mean age 29 ± 4.8 years) and a control group of 10 non-pregnant women (mean age 25.9 ± 0.88 years). The examination was performed in the 1st, 2nd, and 3rd trimester. Continuous registration of BP, ECG, and cardioimpedance was performed with Task Force Monitor 3040i. ANS activity was measured using the following parameters: HRV, BPV, BRS at rest, and in response to autonomic tests.

Compared to the 1st trimester, an increase in HR (73 vs. 92 bpm; p < 0.001) and mean BP (80 vs. 85 mmHg, p < 0.01) was observed in the 3rd trimester. In the 1st trimester, the BRS of pregnant women was insignificantly higher than in the controls (24.8 vs. 22.3 ms/mmHg); subsequently, it decreased significantly, to 13.4 ms/mmHg in the 3rd trimester (p = 0.0004). An increase in nLF (39.57 ± 13.75 vs. 58.73 ± 15.55; p = 0.001) and LF/HF ratio (1.03 ± 0.76 vs. 1.85 ± 0.8; p < 0.00002) was revealed in HRV analysis conducted in the 3rd trimester, as compared to the 1st tri- mester, along with a decrease in nHF (60.43 ± 13.71 vs. 41.26 ± 15.55; p < 0.001). An increase in LF/HF-sBPV (1.05 ± 0.48 vs. 1.58 ± 0.44; p = 0.01) was recorded in BPV analysis at rest in the 3rd trimester as compared to the respective 1st trimester value.

Our findings suggest that pregnancy is associated with dynamic changes in autonomic balance, namely doubled dominance of the sympathetic component. Hypervolemia seems the major factor responsible for autonomic and hemodynamic changes observed during pregnancy, as it causes an increase in BP and simultaneous decrease in BRS.