Phase synchronization of arterial pressure and heart rate as a measure of baroreflex activity

Phase differences between signals resulting from band-pass digital filtering of mean arterial pressure and heart rate were calculated using analytic signal approach. Frequency dependencies of phase synchronization index were obtained for 11 subjects in supine and vertical positions. It was shown that at the frequency of Meyer waves (about 0.1 Hz) phase synchronization index was sufficiently higher for head-up position, whereas at high frequency (respiratory waves) it did not depend on the body position.