Central regulation of 1/f fluctuations of heart rate variability in patients with coma

1/f-like fluctuations of the HR variability (HRV) and circadian or ultradian rhythms of the HR were studied in comatose patients to: (1) examine how the central nervous system affects the heart rate (HR) dynamics; and (2) evaluate the usefulness of spectral analysis of the HRV for the assessment of the comatose state. Circadian changes of the HRV were observed in the comatose state patients. The authors also detected an ultradian rhythm of the heart rate with a cycle length of 1000-2000 sec. The circadian and ultradian amplitude decreased in a brain-dead patient. The slope of the log-log scaled power spectrum of the HRV was -1.2 in a patient with locked-in syndrome and -2.06 in the brain-dead patient. There was a plateau in the power spectrum between 0.001-0.0005 Hz. The level of consciousness effect on the HR dynamics and the analysis of the 1/f fluctuation or the circadian changes of the HRV might afford one useful information for the evaluation of coma patients