Assessment of autonomic function using complex demodulation and posture entrainment techniques: an application to normal subjects and diabetic patients.

The assessment of autonomic nervous systems (sympathetic and parasympathetic) using the method of complex demodulation and posture entrainment are presented. The heart rate variability signals were derived from the ECG of normal subjects and diabetic patients in both supine and standing positions. The method of complex demodulation is employed on the heart rate variability data for both groups. Two significant bands in the heart rate variability spectrum were investigated by this technique. The amplitude of the high frequency band (0.181-0.4 Hz) showed the parasympathetic changes in normal subjects and, to a lesser extent, in the diabetic patients. The amplitude of the low frequency band (0.03-0.15 Hz) showed the influence of sympathetic changes in both groups. The complex demodulation method indicated the effect of high frequency and low frequency bands on both divisions of autonomic function in regulating the heart rate variability in both normal subjects and diabetic patients. In the supine position, the parasympathetic and sympathetic were balanced. On standing (posture entrainment), the high frequency band showed a decrease in amplitude due to decreased parasympathetic activity, while the low frequency band showed an increase in amplitude, which indicated an increase in sympathetic activity. These patterns were repeated in both normal subjects and diabetic patients. It seems that the use of posture entrainment combined with the complex demodulation method is significant to characterize, assess and quantify the autonomic function in health and disease.