Dual-ratio approach to pulse oximetry and the effect of skin tone

Pulsatile blood oxygen saturation ( ${\mathrm{SpO}}_2$ ) via pulse oximetry is a valuable clinical metric for assessing oxygen delivery. Individual anatomical features, including skin tone, may affect current optical pulse oximetry methods.

We developed an optical pulse oximetry method based on dual-ratio (DR) measurements to suppress individual anatomical confounds on ${\mathrm{SpO}}_2$ .

We designed a DR-based finger pulse oximeter, hypothesizing that DR would suppress confounds from optical coupling and superficial tissue absorption. This method is tested using Monte Carlo simulations and in vivo experiments.

Different melanosome volume fractions in the epidermis, a surrogate for skin tone, cause changes in the recovered ${\mathrm{SpO}}_2$ on the order of 1% in simulation and in vivo. Different heterogeneous pulsatile hemodynamics cause greater changes on the order of 10% in simulations. ${\mathrm{SpO}}_2$ recovered with DR measurements showed less variability than the traditional single-distance (SD) transmission method.

For the models and methods considered here, ${\mathrm{SpO}}_2$ measurements are strongly impacted by heterogeneous pulsatile hemodynamics. This variability may be larger than the skin tone bias, which is a known confound in ${\mathrm{SpO}}_2$ measurements. The partial suppression of variability in the ${\mathrm{SpO}}_2$ recovered by DR suggests the promise of DR for pulse oximetry.