Hyperspectral imaging photoplethysmography: insights into the signals' origin and usage

This work explores the hyperspectral characteristics of imaging photoplethysmography (iPPG) to (1) deepen the understanding of iPPG signals' origin, and (2) assess iPPG's capacity to capture the peripheral perfusion. Our analyses are based on an experimental study employing a hyperspectral snapshot camera for iPPG and laser speckle contrast imaging (LSCI) at the forearm. We demonstrate a pronounced correlation between the wavelength-dependent normalized AC component from iPPG and the extinction coefficient of oxyhemoglobin (r = 0.975). Further, we show iPPG's ability to explain LSCI (linear mixed models' β up to 0.692). Considering the entire optical spectrum, our results support blood volume changes as a dominant factor for iPPG signals' generation and demonstrate iPPG's capacity to monitor peripheral perfusion.