Comparison of methods for determining pulse arrival time from Doppler and photoplethysmography signals

The aim of this study was to compare three foot-finding methods applied to ultrasound Doppler and photoplethysmographic (PPG) signals: maximum 1^st derivative, maximum 2^nd derivative and an `intersecting tangents´ method. The pulse arrival times of each method were compared. Also the precision of each method was evaluated by comparing instantaneous cardiac periods derived using each method from simultaneous Doppler and PPG with a reference measurement: the R-R interval calculated from a simultaneously recorded ECG. The results show that the maximum 1st derivative method produced significantly larger pulse arrival times than the other two methods. The intersecting tangents method produced greatest precision for cardiac periods compared with ECG than maximum 1^st or 2^nd derivatives for both Doppler (r² = 0.975) and PPG (r² = 0.987) signals.