Decreased cardiac parasympathetic nerve activity of pregnant women during foot baths.

AIM This study aimed to examine the effect of foot baths on the cardiac parasympathetic outflow of five pregnant (31-32 weeks; mid-pregnancy) women and 16 non-pregnant women. METHODS The cardiac parasympathetic outflow was assessed by using the respiratory variability of the R-R interval under controlled breathing according to three different methods: (i) respiratory sinus arrhythmia; (ii) a respiratory-synchronized component of the power spectrum of R-R interval variability with a fast Fourier transform; and (iii) a high-frequency component (HF at 0.15-0.40 Hz) of the power spectrum of R-R interval variability with a maximum entropy method. RESULTS The rate and amplitude of spontaneous respiration and arterial blood pressure at rest were the same between the non-pregnant and pregnant women. However, the baseline R-R interval was shorter and the respiratory-synchronized and HF components of the power spectrum of R-R interval variability were smaller in the pregnant women, indicating a decreased baseline cardiac parasympathetic outflow with mid-pregnancy. Although a foot bath for 15 min did not significantly affect the systemic hemodynamics and body temperature of both groups, the foot bath reduced the respiratory arrhythmia and the respiratory-synchronized and HF components of the power spectrum of R-R interval variability in both groups. The reduction in the respiratory R-R interval became more prominent in the pregnant group. CONCLUSION A foot bath, used as part of midwives' daily nursing care, is able to decrease the cardiac parasympathetic outflow of pregnant women.