Changes in autonomic nervous activity during pregnancy as a result of the standing test

Abstract

Purpose

In this study, we investigated the effects of standing tests on autonomic nervous activity during the early, middle, and final stages of pregnancy, to evaluate the mechanism of autonomic nervous system regulation by standing tests during pregnancy.

Methods

For 73 pregnant women, heart rate variability during a standing test was measured longitudinally during each pregnancy stage. Additionally, indicators of autonomic nervous activity, namely the total autonomic nervous system (CVRR), sympathetic nervous system (LF/HF), parasympathetic nervous system (CCVHF), and sympathetic/parasympathetic nervous systems (CCVLF) were assessed. Data obtained from four minutes in the sitting position, one minute immediately after standing (standing up), one minute from one to two minutes after standing (standing position), and one minute immediately after sitting (sitting down) were analyzed. A two-way analysis of variance and subtests were conducted using repeated measurements based on pregnancy stage and position.

Results

A main effect for pregnancy stage was found in LF/HF and CCVLF. A main effect for the standing test was observed in all indicators. Interaction was observed for indicators other than CCVHF. Multiple comparisons revealed that CVRR and CCVLF increased significantly (all, p<.001) when standing up compared with the sitting position during early, middle, and final stages; these values decreased in the standing position (only significant during the middle stage; in order, p=.004, .033) and increased significantly when sitting down (all, p<.001). Among the pregnancy stages, CCVLF in the sitting, standing up, and sitting down positions was significantly lower (p=.015, .032, .008) in the final stage than in the early stage. Furthermore, LF/HF increased significantly (early, middle stages, p<.001; final stage, p=.001) when standing up compared with when in the sitting position at each pregnancy stage. The value was significantly high in the standing position for the early and final stages (early, p<.001; final, p=.004), but it decreased in the middle stage to a value not significantly different from that in the sitting position. The value when standing up during the final stage was significantly lower (p=.015) compared with that in the middle stage. The CCVHF decreased when standing up compared with the sitting position in early, middle, and final stages (early, p=.001; middle, p<.001). It decreased significantly in the standing position (all, p<.001) and increased when sitting down (middle stage, p=.011; final stage, p<.001).

Conclusion

Effects of the standing test on autonomic nervous activity are not uniform in different pregnancy stages, and it is suggested that in the standing position during the middle stage, activity of the CVRR, LF/HF, CCVLF is suppressed. When standing up in the final stage of pregnancy, activity of the LF/HF, CCVLF is suppressed.