Long-range correlations in amplitude variability of HF and LF components of heart rate variability.

For the assessment of autonomic nervous system activity based on heart rate variability (HRV) analysis, characteristics of high-frequency (HF; 0.15 to 0.4 Hz) and low-frequency (LF; 0.04 to 0.15 Hz) components have been widely employed. HF and LF band powers quantified by power spectral analysis have most commonly been used in the conventional studies; the physiological significance of these measures has also been extensively studied. However, nonlinear characteristics of HF and LF components have not been well established. In this paper, we investigated nonlinear properties of HF and LF components in 122 healthy subjects and 108 patients with congestive heart failure (CHF). By analyzing bandpass-filtered time series of HRV corresponding to HF and LF components, it is shown that amplitude variability of HF and LF components displays long-range correlation, which cannot be explained by linear HRV properties. Compared with the age-matched healthy control group, the CHF patients showed significantly decreased long range correlation of HF component amplitude variability. These findings suggest that nonlinear properties of HF and LF components provides some complementary information on HRV dynamics.