Investigation of Heartbeat Rate Variability Under Physical Stress Using a Smartphone Camera

In this paper, we propose a new method to calculate the heartbeat rate (HR) of humans using an ordinary smartphone with a build-in camera and a flashlight. Based on this proposed method, the PPG signal is passed through a bandpass filter (BPF), which rejects DC component and high-frequency artifacts, and then, the local peaks (heart beats) are identified using the Gradient and the Local Maximum method. The time intervals between successive peaks are curve-fitted to a normal distribution from which we extract the mean and the standard deviation. The mean corresponds to the average heartbeat rate during the monitoring interval, and the standard deviation is correlated with the physical stress experienced by the human being during the same interval. Our investigation shows that the more physically stressed the body, the smaller the standard deviation and the higher the HR.