Evaluation of skin pigmentation effect on photoplethysmography signals using a vascular finger phantom with tunable...

Photoplethysmography (PPG) is a widely used optical technique for the noninvasive monitoring of cardiovascular parameters. However, its accuracy may be affected by variations in skin pigmentation due to the strong absorption properties of melanin, particularly at visible wavelengths.

We aimed to investigate how skin tone influences PPG signal signals by developing a pulsatile vascular finger phantom with interchangeable skin layers, characterizing their optical properties across green, red, and infrared wavelengths and evaluating their impact on PPG signal features.

The finger phantom included three optically characterized, interchangeable skin layers representing pale, medium, and dark tones, as well as a custom-made silicone vessel embedded in an anatomically and mechanically characterized structure. PPG signals were recorded in reflectance mode using a custom-made finger clip probe in an in vitro cardiovascular system. Signal features, including signal-to-noise ratio, peak-to-peak amplitude, and area under the curve, were analyzed.

Analysis revealed statistically significant differences ( $p<0.001$ ) between skin tones, with signal degradation increasing with skin pigmentation.

These findings suggest there is a measurable impact of skin pigmentation on the PPG signal and highlight the need for further research to improve the equity of light-based sensing technologies across all populations. We provide an advancement for future work in developing in vitro models to assess optical sensing performance across diverse skin tones.