Efficient estimation of the heart period power spectrum suitable for physiologic or pharmacologic studies.

Abstract The standard deviation of the normal RR intervals (SDNN) computed over 24 hours predicts mortality after myocardial infarction. 1 The power spectrum of heart period or of instantaneous heart rate, calculated over intervals of 2 to 15 minutes, is used to assess autonomie nervous system activity: Energy in the 0.04- to 0.15-Hz band reflects both parasympathetic and sympathetic activity, and energy in the 0.15- to 0.40-Hz band reflects pure parasympathetic activity. 2 The prognostic significance of 24-hour SDNN has stimulated interest in computing heart period power spectra for 24-hour periods. Previous computational approaches to the 24-hour heart rate power spectrum used the fast Fourier transform (FFT) to analyze the entire 24-hour period in toto. 3,4 We report a practical approach for computing heart period or heart rate power spectra over 24-hour periods by analyzing the data in 5-minute segments. This approach has the advantages of permitting physiologic and pharmacologic studies and requiring fewer assumptions in dealing with "noisy" or arrhythmic segments.