CORRELATION ANALYSIS OF HEART RATE VARIABILITY BETWEEN PPG AND ECG COMPARED WITH A SMART PHOTONIC DEVICE IN SUPINE, SITTING, AND STANDING POSTURES

In this study, correlation of heart rate variability (HRV) results in supine, sitting, and standing with ECG-based, mobile Elite HRV app, and reflective photoplethysmographic (PPG) pulse measurement devices are explored. HRVs were analyzed with the means of the Poincaré plots. It is not yet clearly indicated whether HRV can be replaced by PRV which also could reflect changes in autonomic nervous function (ANS) and peripheral arterial elasticity. We synchronize electrocardiogram (ECG) signal for HRV and PPG for PRV at 1 kHz sampling frequency with 16 bit. ECG is the best indicator for the assessment of physical health and heart information [1, 2]. By using Photonic device such as PPG which uses light sensor to detect the change of blood volume in the peripheral vessel contains different information. Reflective PPG measurements are also less susceptible to power line noise and any electromagnetic interference [3]. A wearable smart mobile phone Elite HRV app (with BlueTooth) and a CorSense sensor was chosen in parallel with the lab made reflective PPG device. The lab made ECG amplifier was chosen as the reference ECG device. 

Participants were volunteers aged 22–79 years from the city and students at Oulu University, Oulu (Finland) to participate in 25 subjects during the year 2024, provided they did not have cardiac diseases or there were no other criteria for exclusion. The results show that in supine, sitting, and standing position (3x5min), the HRV results of the Elite HRV and the reflective PPG finger sensor are of significant positive correlation with the HRV results of the ECG device. Also between each test the blood pressure was measured. The Variance Inflation Factor (VIF) being over 100 for the young persons, while under 10 for the elderly persons. The VIF is equal to 1/(1-r) and r represents the linear correlation coefficient value. The VIF method is appropriate for validation of the regression model. 

The VIF is an integer number >2 (e.g. r=0,5) to 1000 compared to the decimal number (r<1 always), and VIF is easy-to-use. The Elite HRV app is also slightly better in many cases than the reflective PPG prototype. The HRV results of the PPG sensor on the right hand and the CorSense sensor on the left hand also show a significant positive correlation (VIF is under 10 for elderly, but over 100 for young) which could show the feasibility of parallel measurements with the reflective PPG and the CorSense sensor. The measurement performance at the supine position with hands at the same level of the heart is better compared with sitting or standing position as the ECG reference based on the VIF numbers. This is important as the consideration also when testing different aged subjects especially in the cases of elderly persons.