Spectral analysis of heart rate fluctuations. A non-invasive, sensitive method for the early diagnosis of autonomic neuropathy in diabetes mellitus

Early detection and a quantitative evaluation of the degree of diabetic autonomic neuropathy were performed in 23 diabetic patients and 22 controls by computerized spectral analysis of beat-to-beat R-R interval variations on a continuous electrocardiogram. Simultaneous recording of cardiac and respiratory activity, R-wave detection by a fast peak detection algorithm and spectrum computation by Fast Fourier transform enabled the study of the power spectrum of heart rate fluctuations. The power of fluctuations at different frequencies is the result of sympathetic and vagal input into the sinoatrial node: this input is derived from vasomotor, baroreceptor and respiratory control loops. A marked reduction in the power of heart rate (HR) fluctuations, at all frequencies, was found in the diabetic patients as compared to controls. This indicates a depression of both parasympathetic and sympathetic activity. The difference was especially pronounced in subjects below age 65. The lowest activity was found in diabetics with concomitant peripheral neuropathy. The method described here is simple, objective, quantitative and very sensitive. It may facilitate the screening of diabetic patients for autonomic neuropathy and enable a convenient quantitative follow-up.