Photoplethysmogram signal variability and repeatability assessment

A clinically practiced low cost, non-invasive physiological signal recorder, Photoplethysmogram (PPG) is a blood volume change monitoring method. Various parameters are analysed and used in establishing the PPG usage in physiological health monitoring. Currently our research team is in the pathway of establishing single pulse utilization in formulating PPG fitness index for cardiovascular risk assessment. Even though PPG is widely used by medical practioners and researchers there are many unknown issues concerning this method are yet to be explored. Pulses variability in a single recording session and repeatability of the PPG recording in health monitoring are being unexplored aspects. In our study we recorded PPG signals (from the finger) four times in resting conditions in the interval of 30 minutes. Two different evaluations were approached: (1) variability between pulses in single recording; (2) repeatability in one individual PPG signal in different recording (30 minutes apart). This study has produced repeatability coefficient, CR = 93.22±1.18 and variability coefficient, CV = 6.18 ± 1.51, which is a strong indicator for PPG establishment as a reliable physiological assessment method. The result suggested that single pulse quantification is suitable to be considered as a parameter in PPG assessment.