Beat-by-beat variability of the delays between the R peak and the pressure wave onset in a peripheral artery

The delay between the R peak in ECG (electrocardiography) and the pressure wave onset point (T_RD) in a peripheral artery is proposed as a variability signal, in addition to the classical ones relating to heart rate (HR) and arterial pressure (AP) variability. In five hypertensive subjects, who underwent routine ECG and AP monitoring under various autonomic stimuli, it is shown that T_RD duration can be determined by beat-by-beat measurement with a good precision. The spectral analysis of T_RD variability revealed a dominant high-frequency component in correspondence to the respiratory frequency, which remained almost stable under the various maneuvers. This high-frequency oscillation displayed a high and stable coherence with systolic AP variability, with a constant phase opposition. The results may provide further insight into the modulation mechanisms of respiration in connection with AP