Eumelanin and Pheomelanin Modelling in Optical Oximetry Using Pulse Oximetry (for 540 nm and 660 nm): DC Component

Oximetry is used to quantify the presence of oxygen in soft tissues. It can be expressed as, for example, tissue oxygen saturation (StO₂), arterial oxygen saturation (SaO₂) and pulsatile oxygen saturation (SpO₂), among others. Non-invasive medical devices are used to estimate (SaO₂). Their accuracy is compromised in individuals with highly pigmented skin. The aim of this initial work is to go back few steps into the understanding of the light absorption for the DC component in pulse oximeters, by using a mixtures model for different hypothetical scenarios of normoxia and hyperoxia. Under hypoxic states, an initial and simple multi-wavelength approach could be established to identify the impact of eumelanin (EuM) and pheomelanin (PhM), which are directly related to skin pigmentation in dark skin colour individuals. We used public spectra for water (H₂O), haemoglobin (HHb), oxy-haemoglobin (HbO₂), eumelanin and pheomelanin, to create 1000 possible absorption combinations. These spectra simulations were used to understand the hypothetical limits, across a 450-800 nm wavelength range. These results have outlined the maximum oxy-haemoglobin concentrations that can be detected without interfering with eumelanin and pheomelanin. This initial and simple approach helped us to understand how eumelanin and pheomelanin absorption interferes and overlaps with low oxy-haemoglobin, which is a key biomarker for oxygen quantification in pulse oximeters and other non-invasive biomedical devices.