Facial video photoplethysmography for measuring average and instantaneous heart rate: a pilot validation study

Introduction Video photoplethysmography (vPPG) is a contactless optical technique of recording blood pulsations in the skin vasculature using a digital camera, which is increasingly used to measure or estimate various physiological parameters. Here, we evaluate the accuracy of heart rate (HR) measurements performed using facial vPPG technology Shen.AI Vitals and a smartphone camera. Methods We studied 35 healthy volunteers in a sitting position (median age 25 years, 17 females). Video recordings of participants’ faces were obtained using the front camera of a smartphone mounted on a tripod. In parallel, a 1-lead chest electrocardiogram (ECG) was recorded to obtain reference HR values (average value from the entire 60-second measurement and multiple values averaged over 10-second or 4-second periods during the measurement). Results The mean absolute errors were 0.1, 0.2, and 0.4 beats per minute (bpm) for HR averaged over 60-second, 10-second, and 4-second periods, respectively. The errors did not exceed 1 bpm in 100.0%, 99.8%, and 94.5% of cases, respectively. Regardless of the HR averaging time, the correlation between the vPPG-based and reference values was very strong (r > 0.99, P < 0.001). Conclusions In predominantly young, white, sitting subjects, the tested vPPG technology provided highly accurate HR values, both when averaging over 60 seconds as well as in the case of short-term averages over 10 seconds or instantaneous HR values averaged over 4 seconds. The results should be confirmed in a larger study with greater diversity in age, skin tone, and lighting conditions.