Detrended fluctuation analysis of short-term heart rate variability in late pregnant women.

Spectral analysis of heart rate variability using short or long time series is a common method in the assessment of autonomic nervous activity. Nonlinear method such as detrended fluctuation analysis was proposed and proved to be useful for the possible non-stationary and nonlinear characteristics in the time series of heart period. In this study, we investigated the detrended fluctuation analysis and conventional heart rate variability measures in 16 late pregnant women before and 3 months after delivery and in 16 healthy controls. Global and discrete, short-term (< or =11 beats, alpha1) and long-term (>11 beats, alpha2), scaling exponent were calculated in detrended fluctuation analysis. We found that the late pregnant women have elevated global scaling exponent, elevated short-term scaling exponent and lower heart rate variability measures in the low and high frequency ranges than those of the healthy controls and 3 months after delivery. The deranged measures recovered 3 months after delivery. In addition, the detrended fluctuation scaling exponent did not correlate with most conventional time and frequency domain measures of heart rate variability. Our study suggested that the global and short-term detrended fluctuation scaling exponents might be new and independent measures of heart rate variability in late pregnancy, in addition to those conventional time and frequency domain measures.