Circadian changes of heart rate variability

The assessment of circadian changes of autonomic nervous activities by using spectral analysis of the heart-rate variability (HRV) during 24-hour electrocardiogram is described. Forty-five subjects (ages 20-81) and one patient (37-year-old male) who died suddenly during sleep were examined (sudden cardiac death: SCD). Spectral analysis of the HRV using the fast Fourier transform (FFT) has been used for the assessment of autonomic nervous activity (ANA). Respiratory peaks were most frequently observed at night. Marked day-to-day variations were observed in the respiratory peak of the HRV in the SCD patient. The respiratory peak disappeared during the night in the SCD patient one week before death. The fluctuations of heart rate were 1/f² at ages between 20 and 40, and 1/f^z at ages between 60 and 80. The mean slopes of the HRV at ages between 30 and 39 were -1.83 (ranges: -153 and -2.29). In the SCD patient, on the other hand, this value gradually increased from -2.13 (one month before SCD) to -1.05 (one week before SCD). Thus the assessment of circadian and day-to-day variation of the ANA might provide useful information for the identification of SCD-prone patients