RGB Camera-based Simultaneous Measurements of Percutaneous Arterial Oxygen Saturation, Tissue Oxygen Saturation, Pulse Rate, and Respiratory Rate

We propose a method to perform simultaneous measurements of percutaneous arterial oxygen saturation ( ), tissue oxygen saturation ( ), pulse rate (), and respiratory rate () in real-time, using a digital red-green-blue (RGB) camera. Concentrations of oxygenated hemoglobin ( ), deoxygenated hemoglobin ( ), total hemoglobin ( ), and were estimated from videos of the human face using a method based on a tissue-like light transport model of the skin. The photoplethysmogram (PPG) signals are extracted from the temporal fluctuations in , , and using a finite impulse response (FIR) filter (low and high cut-off frequencies of 0.7 and 3 Hz, respectively). The is calculated from the PPG signal for . The ratio of pulse wave amplitude for and that for are associated with the reference value of measured by a commercially available pulse oximeter, which provides an empirical formula to estimate from videos. The respiration-dependent oscillation in was extracted from another FIR filter (low and high cut-off frequencies of 0.05 and 0.5 Hz, respectively) and used to calculate the . experiments with human volunteers while varying the fraction of inspired oxygen were performed to evaluate the comparability of the proposed method with commercially available devices. The Bland-Altman analysis showed that the mean bias for , , , and were -1.4 (bpm), -1.2(rpm), 0.5 (%), and -3.0 (%), respectively. The precisions for , , , and were ±3.1 (bpm), ±3.5 (rpm), ±4.3 (%), and ±4.8 (%), respectively. The resulting precision and RMSE for were pretty close to the clinical accuracy requirement. The accuracy of the is considered a little less accurate than clinical requirements. This is the first demonstration of a low-cost RGB camera-based method for contactless simultaneous measurements of the heart rate, percutaneous arterial oxygen saturation, and tissue oxygen saturation in real-time.