Abstract
Heart rate variability (HRV) parameters have been considered as useful noninvasive tools for assessing cardiac autonomic nervous function. Moreover, it has also been shown that abnormality in a HRV parameter is associated with increased mortality risk in patients with cardiovascular diseases. In such HRV parameters, frequency domain measures, such as high-frequency (HF) and low-frequency (LF) components, are well established and widely used for quantifying autonomic function. For instance, HF power and LF/HF ratio have been regard as indices to quantify sympathetic and parasympathetic activity (or sympathovagal balance), respectively. However, it has been pointed out that such conventional measures are not enough to provide insights into autonomic dysfunction associated with mortality risk. To overcome this difficulty, we here show that HF and LF components of HRV have as-yet-unknown nonlinear characteristics, such as long-range temporal correlations in the amplitude envelope and heterogeneity of the amplitude, and that those characteristics are associated with mortality risk in patients with congestive heart failure.
