Heart rate variability in the acceleration photoplethysmogram at rest and after exercise—a preliminary study

There are a limited number of studies on heart rate variability (HRV) dynamics immediately after exercise. The electrocardiogram (ECG) may be used to measure HRV, however acquiring ECG signals from subjects undergoing exercise is not convenient. Many researchers have demonstrated that photoplethysmogram (PPG) signals offer an alternative method to measure HRV when ECG and PPG signals are simultaneously collected. However, we investigate a different approach to potentially show that the PPG signals can measure HRV without collecting ECG signals. Moreover, we explore the extraction of the most suitable HRV-parameters from short PPG signal recordings. Our preliminary results now motivate further studies that cross check HRV parameters extracted from both ECG and PPG. In this study, PPG signals from an existing database were used to determine a range of HRV indices, including the standard deviation of heart beat interval (SDNN) and the root-mean square of the difference of successive heart beats (rMSSD). Results from this study indicate that the use of the a–a interval, derived from the acceleration of PPG signals, show very promising results in determining the HRV statistical indices SDNN and rMSSD over 20-second PPG recordings. Moreover, post-exercise SDNN and rMSSD indices show negative correlation with age.