Wavelet Phase Coherence Between the Microvascular Pulse Contour and the Respiratory Activity

A wavelet phase coherence (WPC) analysis was conducted in order to evaluate the time-phase relationships between the respiratory activity and the pulse of the peripheral perfusion. The investigation involved a group of 21 young healthy subjects, aged from 20 to 30 years. Cutaneous perfusion was measured by laser Doppler flowmetry, while breathing was simultaneously monitored with a wearable chest band. A multi-Gaussian modeling algorithm was used to decompose the pulse waveform thus enabling the separate characterization of the forward-travelling systolic pulse and the diastolic components arising from vascular impedance mismatch. The WPC between model-derived shape features and the breathing rhythm was assessed, to determine whether their characteristic oscillations were somehow synchronized. In 17 subjects a significant degree of phase coherence was detected in the respiratory frequency band for the area beneath the diastolic phase of the cardiac pulse. This result indicates that the microvascular reflection waves exhibit a marked periodicity linked to the breathing activity.