A preliminary attempt to understand compatibility of photoplethysmographic pulse rate variability with electrocardiogramic heart rate variability

We investigated the difference between heart rate variability (HRV) derived from electrocardiogramic (ECG) signals and pulse rate variability (PRV) derived from photoplethysmographic (PPG) signals. Ten-minute recordings of finger and ear photoplethysmogram (PPG) and Lead I electrocardiogram (ECG) were collected in fourteen healthy subjects. In this study, analyses accounting for time and frequency domain, agreement, correlation coefficient and geometrical distribution were utilized to process the ear pulse rate variability (ePRV) and finger pulse rate variability (fPRV). The agreement analysis showed high degree of agreement (Bland-Altman ratio < 0.1) between ePRV or fPRV of PPG and HRV of ECG for all the parameters except the normal-to-normal (NN) range with a moderate agreement (0.1 < Bland-Altman ratio < 0.2). Highly significant (p < 0.001) correlations (0.97 < r <1) were found between HRV and ePRV or fPRV parameters except in the NN range, where the r values were 0.92 and 0.85, respectively. Also, the experimental results indicated that the frequency-domain parameters appeared inadequate in statistical analysis. Both fPRV and ePRV were acceptable surrogates for time-domain HRV study, especially when the ECG recording was unavailable and inconvenient. Photolethysmography could offer a simple and robust means to fulfill the requirements of rhythmical pulsation assessment.