Correlation analysis of heart rate variability between PPG and ECG for wearable devices in different postures

In this study, correlation of heart rate variability (HRV) results in different postures between ECG-based and PPG-based cardiac measurement devices is explored. Electrocardiogram (ECG) is one of the best indicators for the assessment of physical health and heart function, while photoplethysmography (PPG) uses light sensor to detect the change of blood volume in the vessel, and is thus less susceptible to power supply noise and electromagnetic interference. Our wearable prototype Z1 Wristband and commercially available Mio Alpha HR watch are chosen as the target PPG-based devices, while the medical 12-lead Poly-Spectrum-12/E ECG monitor is chosen as the target (benchmark) ECG-based device. The experimental results shows that in different postures, the HRV results of our Z1 prototype are of significant positive correlation with the HRV results of the ECG device (r>0.861, p<;0.01) where r and p represent the correlation coefficient and p-value in Pearson's correlation analysis. The performance of the Mio Alpha is slightly worse than our Z1 prototype. The HRV results of our Z1 prototype on the right hand and left hand also show a significant positive correlation (r>0.970, p<;0.01) which shows the feasibility of measurement with our Z1 via either right hand or left hand. The performance with the posture with hands in the same height of the heart is slightly better than that with hands drooping.