Multiwavelength Photoplethysmography and Bioimpedance Multimodal Signal Analysis above the Radial Artery on the Wrist

As wearable devices continue to advance, the implementation of additional sensors and device health monitoring capabilities has become integral to their development. To explore noninvasive health monitoring capabilities, in this study, we developed a multimodal system consisting of multiwavelength photoplethysmography (PPG), and bio-impedance (Bio-Z) used to extract signals simultaneously from the wrist above the radial artery. We then evaluated the systolic rising edges of each modality and the systolic temporal peak-to-peak separation between the Bio-Z and PPG signals. The preliminary results show a signal time delay with a correlation to penetration depth between the systolic peaks across modalities within and across subjects. The trend showed the systolic peak of Bio-Z arriving first, with PPG systolic peaks arriving milliseconds after in the order of infrared, red, and green, each with its own time delay and decreasing slope intensity, likely resulting from differences in light penetration depth and impedance changes due to continuum mechanics associated with the cardiac pulse wave.