A 90-Min Cardiac Biorhythm Methodology and Data Analysis Using Modified Periodograms and Complex Demodulation

Since the discovery of an approximate 90-min oscillation in rapid eye movement (REM) or dream sleep, much interest has been expressed in the physiological and behavioral parameters associated with this phenomenon. One of the often stated theories is that this 90-min rhythm is an endogenous biorhythm present throughout the 24-h day, perhaps representing a rest-activity cycle of the nervous system. An approximate 90-min biorhythm in resting human heart rate is assessed and described using the techniques of periodogram analysis and complex demodulation. The techniques employed found evidence for this rhythm in all subjects; in-addition, the amplitude of the 90-min ultradian rhythm seemed to be modulated by a circadian (24-h) rhythm. However, the modulating circadian rhythm was not usually phase locked to the circadian rhythm fixed by the waking/sleeping cycle of each subject.