Contactless Vital Sign Monitoring in Emergency Settings: A Factorial Study of Camera Position and Motion Using rPPG

Reliable acquisition of vital signs is essential in prehospital emergency care; however, conventional contact-based sensors may delay assessment, cause patient discomfort, increase cross-contamination risk, and perform poorly during motion. To address these limitations, this study developed a body-worn smart camera system for paramedics incorporating a remote photoplethysmography (rPPG)-based signal-processing algorithm to estimate heart rate (HR), oxygen saturation (SpO2), and blood pressure (BP) in real time from subtle facial blood volume fluctuations. The system was evaluated in a repeated-measures full-factorial experiment with three adults under varying lighting, camera positions, and stabilization conditions. Performance was assessed using mean absolute error (MAE) relative to contact-based reference devices. HR (MAE: 1.20–5.60 bpm) and SpO2 (MAE: 0.93–3.00%) showed relatively small errors relative to the reference measurements across the tested conditions, whereas BP estimation showed larger errors (SYS: 5.00–14.20 mmHg; DIA: 3.87–11.60 mmHg), indicating the need for further algorithm refinement. The head-mounted configuration provided the best performance (HR MAE: 1.96 bpm). These preliminary findings support the technical feasibility of a wearable, contactless rPPG-based vital sign monitoring system under the tested conditions, while identifying BP estimation as the primary target for future improvement. Further validation in larger and more diverse populations is required before clinical or prehospital applicability can be established.