Sequential analysis of heart rate variability, blood pressure variability and baroreflex sensitivity in healthy pregnancy.

OBJECTIVE

The aim of this study was to demonstrate the temporal profile of changes in heart rate variability (HRV), blood pressure variability (BPV), and cardiac baroreflex sensitivity (BRS) during the course of a healthy pregnancy.

MATERIALS AND METHODS

This was a longitudinal study during which autonomic variability parameters (HRV, BPV, BRS) were assessed in 66 pregnant women at 11-13, 20-22 and 30-32 weeks of gestation. A lead II electrocardiogram tracing and beat-to-beat blood pressure were recorded with the subject breathing spontaneously in the supine position. Changes in the parameters were analyzed using repeated measures analysis of variance.

RESULTS

Overall HRV (SDNN; standard deviation of all NN intervals) was found to decrease significantly over the course of pregnancy (p < 0.05). Similarly, indices which represent the parasympathetic component of these variables (SDSD [standard deviation of differences between adjacent NN intervals]; pNN50 [NN50 count {number of pairs of adjacent NN intervals differing by more than 50 ms} divided by the total number of all NN intervals]; high-frequency [HF] power) were also found to decrease significantly from the first to third trimester of pregnancy (p < 0.05). Low-frequency (LF) power increased over the course of pregnancy (p < 0.05). The LF/HF ratio increased significantly from first to third trimester of pregnancy (median: 0.66 [first trimester] vs.1.02 [second] vs. 0.91 [third]; p < 0.05) Overall BPV increased during the course of pregnancy, with a significant rise in the HF component of BPV and a significant fall in the LF component of BPV with advancing gestation (p < 0.05). BRS decreased over the course of pregnancy (median: 16.31, interquartile range [IQR] 11.04-23.13 [first trimester] vs. 11.42, IQR 8.54-19.52 [second] vs. 8.84, IQR 7.15-12.45 [third] ms/mmHg; p < 0.05).

CONCLUSION

Pregnancy is associated with decreased vagal and increased sympathetic modulation of cardiac autonomic tone with advancing gestation, together with increased BPV. The reduction in cardiac BRS may play a role in increasing BPV and decreasing HRV over the course of pregnancy.