Publications

@article{Swamy2025-po,

title = {Pulse oximeter bench tests under different simulated skin tones},

author = {Suvvi K Narayana Swamy and Chenyang He and Barrie R Hayes-Gill and Daniel J Clark and Sarah Green and Stephen P Morgan},

doi = {10.1007/s11517-024-03091-2},

year  = {2025},

date = {2025-07-01},

urldate = {2025-07-01},

journal = {Med. Biol. Eng. Comput.},

volume = {63},

number = {7},

pages = {1931\textendash1942},

publisher = {Springer Science and Business Media LLC},

abstract = {Pulse oximeters\' (POs) varying performance based on skin tones 

 has been highly publicised. Compared to arterial blood gas 

 analysis, POs tend to overestimate oxygen saturation (SpO2) 

 values for people with darker skin (occult hypoxemia). The 

 objective is to develop a test bench for assessing commercial 

 home and hospital-based POs in controlled laboratory conditions. 

 A laboratory simulator was used to mimic different SpO2 values 

 (~ 70 to 100%). Different neutral density and synthetic melanin 

 filters were used to reproduce low signal and varying melanin 

 attenuation levels. Six devices consisting of commercial home (Bioligh},

keywords = {Melanin, Occult hypoxemia, oxygen saturation, Pulse oximeter, Racial bias, Skin colour, Transmission-mode},

pubstate = {published},

tppubtype = {article}

}

@article{Narayana_Swamy2024-la,

title = {Exploring the bias: how skin color influences oxygen saturation  readings via Monte Carlo simulations},

author = {Suvvi K Narayana Swamy and Chong Liu and Ricardo Correia and Barrie R Hayes-Gill and Stephen P Morgan},

doi = {10.1117/1.JBO.29.S3.S33308},

year  = {2024},

date = {2024-06-01},

urldate = {2024-06-01},

journal = {J. Biomed. Opt.},

volume = {29},

number = {Suppl 3},

pages = {S33308},

publisher = {SPIE-Intl Soc Optical Eng},

abstract = {Significance: Our goal is to understand the root cause of 

 reported oxygen saturation ( SpO 2 ) overestimation in heavily 

 pigmented skin types to devise solutions toward enabling equity 

 in pulse oximeter designs. Aim: We aim to gain theoretical 

 insights into the effect of skin tone on SpO 2 - R curves using 

 a three-dimensional, four-layer tissue model representing a 

 finger. Approach: A finger tissue model, comprising the 

 epidermis, dermis, two arteries, and a bone, was developed using 

 a Monte Carlo-based approach in the MCmatlab software. Two skin 

 tones-light and dark-were simulated by adjusting the absorption 

 and scattering properties within the epidermal layer. Following 

 this, SpO 2 - R curves were generated in various tissue 

 configurations, including transmission and reflection modes 

 using red and infrared wavelengths. In addition, the influence 

 of source-detector (SD) separation distances on both light and 

 dark skin tissue models was studied. Results: In transmission 

 mode, SpO 2 - R curves did not deviate with changes in skin 

 tones because both pulsatile and non-pulsatile terms experienced 

 equal attenuation at red and infrared wavelengths. However, in 

 reflection mode, measurable variations in SpO 2 - R curves were 

 evident. This was due to differential attenuation of the red 

 components, which resulted in a lower perfusion index at the red 

 wavelength in darker skin. As the SD separation increased, the 

 effect of skin tone on SpO 2 - R curves in reflection mode 

 became less pronounced, with the largest SD separation 

 exhibiting effects similar to those observed in transmission 

 mode. Conclusions: Monte Carlo simulations have demonstrated 

 that different light pathlengths within the tissue contribute to 

 the overestimation of SpO 2 in people with darker skin in 

 reflection mode pulse oximetry. Increasing the SD separation may 

 mitigate the effect of skin tone on SpO 2 readings. These trends 

 were not observed in transmission mode; however, further planned 

 research using more complex models of the tissue is essential.},

keywords = {Melanin, Monte Carlo, Occult hypoxemia, oxygen saturation, pulse   oximeter, Racial bias, skin color, transmission mode},

pubstate = {published},

tppubtype = {article}

}

@article{Setchfield2024-kl,

title = {Effect of skin color on optical properties and the implications  for medical optical technologies: a review},

author = {Kerry Setchfield and Alistair Gorman and A Hamish R W Simpson and Michael G Somekh and Amanda J Wright},

doi = {10.1117/1.JBO.29.1.010901},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {J. Biomed. Opt.},

volume = {29},

number = {1},

pages = {010901},

abstract = {Significance: Skin color affects light penetration leading to 

 differences in its absorption and scattering properties. COVID-19 

 highlighted the importance of understanding of the interaction of 

 light with different skin types, e.g., pulse oximetry (PO) 

 unreliably determined oxygen saturation levels in people from 

 Black and ethnic minority backgrounds. Furthermore, with 

 increased use of other medical wearables using light to provide 

 disease information and photodynamic therapies to treat skin 

 cancers, a thorough understanding of the effect skin color has on 

 light is important for reducing healthcare disparities. Aim: The 

 aim of this work is to perform a thorough review on the effect of 

 skin color on optical properties and the implication of variation 

 on optical medical technologies. Approach: Published in vivo 

 optical coefficients associated with different skin colors were 

 collated and their effects on optical penetration depth and 

 transport mean free path (TMFP) assessed. Results: Variation 

 among reported values is significant. We show that absorption 

 coefficients for dark skin are ∼6% to 74% greater than for 

 light skin in the 400 to 1000 nm spectrum. Beyond 600 nm, the 

 TMFP for light skin is greater than for dark skin. Maximum 

 transmission for all skin types was beyond 940 nm in this 

 spectrum. There are significant losses of light with increasing 

 skin depth; in this spectrum, depending upon Fitzpatrick skin 

 type (FST), on average 14% to 18% of light is lost by a depth 

 of 0.1 mm compared with 90% to 97% of the remaining light being 

 lost by a depth of 1.93 mm. Conclusions: Current published data 

 suggest that at wavelengths beyond 940 nm light transmission is 

 greatest for all FSTs. Data beyond 1000 nm are minimal and 

 further study is required. It is possible that the amount of 

 light transmitted through skin for all skin colors will converge 

 with increasing wavelength enabling optical medical technologies 

 to become independent of skin color.},

keywords = {absorption and scattering   coefficients, Fitzpatrick skin type scale, medical wearables, optical coherence tomography, optical imaging, photodynamic therapy, Racial bias, skin, transmission},

pubstate = {published},

tppubtype = {article}

}