Heart Rate Spectral Analysis for Assessing Autonomic Neuropathy

Abstract In this paper we apply spectral analysis methods to the heart rate variability signal to assess the autonomic nervous regulation system in both normal subjects ancl patients affected by autonomic neuropathy. Traditional methods for investigating the degree of impairment of the autonomic heart rate regulation system make use of external or self-evoked inputs, which perturb the biological system producing changes in heart rhythm and arterial pressure. Different clinical tests allow to quantify separately sympathetic and parasympathetic activity. The use of power spectral analysis of the heart rate variability signal is an appealing methodology for quantifying the activity of the autonomic nervous system since it can be performed at rest due to the natural “spectral” separation of the sympathetic and parasympathetic control systems. While the first regulatory mechanism acts at the low frequency band of approximately on cycle every ten seconds, the parasympathetic control can act two or three times faster producing rhythmic changes in heart rate of a few seconds. Results show in normal patients a significant reduction of parasympathetic activity in standing position with respect to supine, and in patients affected by severe autonomic neuropathy an overall reduction of power at all frequencies. For autonomic patients there are no significant differences following postural changes. From this study a working hypothesis emerges, concerning pronounced impairment of the sympathetic system as well as the parasympathetic one in autonomic neuropathy, which requires further investigation.