Exploiting Dual-Wavelength Depolarization of Skin-Tissues for Camera-Based Perfusion Monitoring

Perfusion index (PI), the ratio between variable pulsatile (AC) and non-pulsatile (DC) components in a photoplethysmographic (PPG) signal, is an indirect and non-invasive measure of peripheral perfusion. PI has been widely used in assessing sympathetic block success, and monitoring hemodynamics in anesthesia and intensive care. Based on the principle of dual-wavelength depolarization (DWD) of skin tissues, we propose to investigate its opportunity in quantifying the skin perfusion contactlessly. The proposed method exploits the characteristic changes in chromaticity caused by skin depolarization and chromophore absorption. The experimental results of DWD, obtained with the post occlusive reactive hyperemia test and the local cooling and heating test, were compared to the PI values obtained from the patient monitor and photoplethysmography imaging (PPGI). The comparison demonstrated the feasibility of using DWD for PI measurement. Clinical trials conducted in the anesthesia recovery room and operating theatre further showed that DWD is potentially a new metric for camera-based non-contact skin perfusion monitoring during clinical operations, such as the guidance in anesthetic surgery.