Extraction of the Mayer wave component in blood pressure from the instantaneous phase difference between electrocardiograms and photoplethysmograms

To analyze the human baroreflex function noninvasively, a beat-by-beat blood pressure signal is often measured by tonometry or plethysmogram using continuous blood pressure sensors. However, these sensors are too expensive and bulky to be used for home healthcare or telemedicine. On the other hand, it is well known that the pulse transmission time (PTT) is strongly correlated with the beat-by-beat blood pressure, especially in the Mayer wave-related frequency band (0.05-0.15 Hz). To obtain a new physiological parameter with a higher correlation with blood pressure in this band compared with that obtained using the PTT alone, we proposed the samephase temporal difference (SPTD) based on electrocardiogram and photoplethysmogram signals. By examining 94 healthy subjects using a combination of SPTD and conventional PTT, it was revealed that the correlation with blood pressure for 25 subjects could be improved using the SPTD instead of the PTT, by applying the criterion of the ratio of their powers. However, for 7 subjects, the correlation decreased.