Temporal contribution of body movement to very long-term heart rate variability in humans

A newly developed, very long-term(similar to 7 days) ambulatory monitoring system for assessing beat-to-beat heart rate variability (HRV) and body mov ements (BM) was used to study the mechanism(s) responsible for the long-per iod oscillation in human HRV. Data continuously collected from five healthy subjects were analyzed by 1) standard auto- and cross-spectral techniques, 2) a cross-Wigner distribution (WD; a time-frequency analysis) between BM and HRV for 10-s averaged data, and 3) coarse-graining spectral analysis fo r 600 successive cardiac cycles. The results showed 1) a clear circadian rh ythm in HRV and BM, 2) a 1/f(beta)-type spectrum in HRV and BM at ultradian frequencies, and 3) coherent relationships between BM and HRV only at spec ific ultradian as well as circadian frequencies, indicated by significant ( P < 0.05) levels of the squared coherence and temporal localizations of the covariance between BM and HRV in the cross-WD. In a single subject, an ins tance in which the behavioral (mean EM) and autonomic [HRV power >0.15 Hz a nd mean heart rate (HR)] rhythmicities were dissociated occurred when the i ndividual had an irregular daily life. It was concluded that the long-term HRV in normal humans contained persistent oscillations synchronized with th ose of BM at ultradian frequencies but could not be explained exclusively b y activity levels of the subjects.