Relationship between power spectral densities of P-P and R-R intervals

To investigate the role of the peripheral effector for the generation of heart rate variability, the relationship among the P-P, R-R, P-R, and R-P intervals were compared on five healthy male subject in the supine position. During supine rest, electrocardiogram was monitored, and P-P, R-R, P-R, and R-P intervals were measured. Power spectral densities (PSD) were estimated by using direct method for successive 256 intervals. PSDs were integrated at the low (PSDLF; 0.05-0.15 cycle/beat) and high (PSDHF; 0.20-0.40 cycle/beat) frequency bands. Mean interval times of P-P, R-R, R-P, and P-R intervals were 827 +/- 40, 827 +/- 40, 357 +/- 34, 170 +/- 19 msec, respectively. PSDLFS of P-P, R-R, R-P, and P-R intervals were 15677 +/- 2771, 15566 +/- 2815, 15345 +/- 2767, 1491 +/- 255 msec2/c/b, respectively. PSDHFS of P-P, R-R, R-P, and P-R intervals were 13289 +/- 3602, 12918 +/- 3897, 12558 +/- 3630, 2758 +/- 517 msec2/c/b, respectively. The PSD of P-R intervals showed white noise. These results might suggest that the periodic fluctuation would be formed at or above the sinoatrial node.