Detection of pulse-wave foot of photoplethysmography by projection mapping

The accurate detection of onset and pulse-peak fiducial points of photoplethysmograpy (PPG) is quite important to estimate the time delay from QRS complexes in electrocardiogram (ECG) for assessing diagnostic parameters concerning vascular aging and arterial stiffness. Although the pulse-peaks are easily resolved by the local maximum, the definition of beginning point of a PPG segment, i.e. a pulse-wave foot still remains in unclear. With this aim, we propose a new method of determining a foot point by projecting PPG signal onto the baseline based on angle between the minimum and maximum magnitude of the pulse wave in the considered PPG segment. In order to validate our proposed method, Pearson correlation coefficient was computed (r = 0.9806) between R-R peak interval in ECG and foot-foot segment in PPG and a paired Student's t test demonstrated that the difference between PPG pulse-wave foot-foot and RR peak was statistically insignificant.