An Analysis of Phase Relationships between Oscillatory Processes in the Human Cardiovascular System

Abstract—The phase relationships between heart rate variability, respiration, forearm skin blood flow oscillations (according to laser Doppler flowmetry), and finger-pad tissue blood volume oscillations (according to photoplethysmography) were analyzed in relatively healthy volunteers at rest. The degree of synchronization between phases of analyzed signals was estimated based on the value of the phase wavelet coherence function. A significant phase synchronization was detected between forearm skin blood flow oscillations and finger-pad tissue blood volume oscillations in the low frequency region (0.0095–0.1 Hz) and at the frequency of heart rate of ~ 1 Hz. At a respiration rate of ~0.3 Hz, differences were detected in the phase synchronization of peripheral hemodynamic oscillations (blood volume and blood flow) with both heart rate variability and respiration. For finger-pad tissue blood volume oscillations, a high phase synchronization with both heart rate variability and respiratory rate was observed; for forearm blood flow oscillations, low phase synchronization occurred in both cases.