Noncontact Monitoring of Blood Oxygen Saturation Using Camera and Dual-Wavelength Imaging System

We present a noncontact method to monitor blood oxygen saturation (SpO₂). The method uses a CMOS camera with a trigger control to allow recording of photoplethysmography (PPG) signals alternatively at two particular wavelengths, and determines the SpO₂ from the measured ratios of the pulsatile to the nonpulsatile components of the PPG signals at these wavelengths. The signal-to-noise ratio (SNR) of the SpO₂ value depends on the choice of the wavelengths. We found that the combination of orange (λ = 611 nm) and near infrared (λ = 880 nm) provides the best SNR for the noncontact video-based detection method. This combination is different from that used in traditional contact-based SpO ₂ measurement since the PPG signal strengths and camera quantum efficiencies at these wavelengths are more amenable to SpO₂ measurement using a noncontact method. We also conducted a small pilot study to validate the noncontact method over an SpO₂ range of 83%-98%. This study results are consistent with those measured using a reference contact SpO₂ device (r = 0.936, p < 0.001). The presented method is particularly suitable for tracking one's health and wellness at home under free-living conditions, and for those who cannot use traditional contact-based PPG devices.