Camera-Based Bi-Modal PPG-SCG: Sleep Privacy-Protected Contactless Vital Signs Monitoring

The monitoring of respiratory rate (RR), heart rate (HR), heart rate variability (HRV), and blood pressure (BP) during sleep allows for a comprehensive evaluation of sleep quality, facilitating the understanding and improvement of a person's sleep health. Contactless physiological monitoring using cameras has gained popularity recently due to its convenient, infection-free, continuous, and versatile nature. However, the privacy concerns limit the application of camera-based solutions in sleep monitoring setups. This study proposes a novel hybrid setup that integrates camera-based seismocardiography (CamSCG) and photoplethysmography (CamPPG) for contactless measurement of RR, HR and HRV during sleep while simultaneously estimating BP. For the proximal SCG, we employed camera-based laser speckle vibrometry to measure cardiac motions from the chest, and benchmarked it with a millimeter-wave radar (RFSCG). For the distal PPG, a defocused camera was utilized to measure pulse signals from the facial skin while protecting privacy. In this setup, we analyzed the single-modality in measuring RR, HR and HRV, and established two bi-modalities (CamSCG-CamPPG and RFSCG-CamPPG) to measure Pulse Transit Time (PTT) features for BP calibration. The benchmark involving 19 subjects highlights the potential of camera-based bimodal SCG-PPG for privacy-protected vital signs monitoring during sleep.