Feasibility of Remote Pulse Transit Time Estimation Using Narrow-band Multi-wavelength Camera Photoplethysmography

Contact-free remote sensing is showing increasing potential for real-life use, especially for screening applications (e.g., thermal cameras to detect fever). We investigated the feasibility of estimating pulse transit time (PTT) – a marker known to be highly correlated with blood pressure – in a remote way from a single measuring site, using just a single modified RGB camera. We replaced the default infrared (IR) filter with a narrow-band triple-bandpass filter allowing us to remotely measure the PTT between green and near-infrared (NIR) wavelengths. Such a filter minimizes the inter-channel influence and band overlap, while also leveraging the non-traditional NIR information. We based the PTT measurements on the fact that different wavelengths penetrate to different skin layers. This allowed for the capture of slightly delayed blood pulses corresponding to different wavelengths and skins depth. Our early observations in 5-subject small-scale experiment show relatively consistent temporal delays between the waveforms from different wavelengths in accordance with expectations and related work. These early results show promise for further research in remote multi-wavelength PTT and blood pressure (BP) estimation, while also highlighting important fundamental and technical challenges to be considered.