Calculating a Vagal Tone Index using Webcam Photoplethysmography

We propose a method which allows Heart Rate Variability (HRV) and Respiratory Sinus Arrhythmia (RSA) to be measured via a webcam. HRV and RSA provide an index of vagal tone, the activity level of the vagus nerve, which has a multitude of uses as a psychiatric research tool. The proposed Modified Eulerian Video Magnification (MEVM) algorithm amplifies signals from a video within a cardiac frequency range. This signal is used to obtain cardiac phase magnitude over time and thus construct inter-beat interval series (IBI), which can be processed to identify HRV and RSA. Results obtained agree with the gold standard (ECG) to within 2.5%.