A morphological approach to calculation of the second derivative of photoplethysmography

Many previous studies reported that the second derivative of photoplethysmography (SDPTG) is a rational indicator of arterial stiffness. In order to obtain the SDPTG, a photoplethysmography (PPG) and the second derivative operator are required. Since the PPG contain very high frequency components due to quantization effect, pulse signal smoothing has to be preceded before calculation of the second derivative. Over the past few years, several techniques have been proposed and applied for assessing the SDPTG. Although these techniques show high performance in assessment, they require higher order filters according to signal specifications, such as sampling rate. In order to complement this problem, we have proposed a linear fitting algorithm based on morphological approach and have compared performance of our proposed algorithm with that of previous algorithms. In performance evaluation, we can conclude that our proposed algorithm is reasonable to calculate the SDPTG waveform, which is similar to the waveform obtained by previous approach, with low computational complexity.