Comparison of valley-to-valley and peak-to-peak intervals from photoplethysmographic signals to obtain heart rate variability in the sitting position

Photoplethysmographic (PPG) signals have been considered as a promising approach to obtain heart rate variability (HRV). In the study, we used RR intervals (RRI) of electrocardiograph (ECG) as a standard to compare the accuracy of valley-to-valley intervals (VVI) and peak-to-peak intervals (PPI) from PPG for HRV analysis in the sitting position. The PPG and the ECG signals were recorded simultaneously from 20 subjects. The PPI and VVI time series were derived from the PPG signal and RRI time series were from the ECG signals. For each interval time series, 9 HRV indices were calculated. The correlation and linear regression analysis were performed to assess the consistency. The results showed that for all indices, the correlation coefficients between VVI and RRI reached 0.979±0.025 and the determination coefficients R²>0.94, which were higher than the corresponding parameters between PPI and RRI. The results suggest that for PPG signals, VVI is more reliable than PPI for HRV analysis in the sitting position.