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{Ballaji2020-wp,

title = {A textile sleeve for monitoring oxygen saturation using 

 multichannel optical fibre photoplethysmography},

author = {Hattan K Ballaji and Ricardo Correia and Serhiy Korposh and Barrie R Hayes-Gill and Francisco U Hernandez and Byron Salisbury and Stephen P Morgan},

year  = {2020},

date = {2020-11-01},

journal = {Sensors (Basel)},

volume = {20},

number = {22},

pages = {6568},

publisher = {MDPI AG},

abstract = {Textile-based systems are an attractive prospect for wearable 

 technology as they can provide monitoring of key physiological 

 parameters in a comfortable and unobtrusive form. A novel system 

 based on multichannel optical fibre sensor probes integrated 

 into a textile sleeve is described. The system measures the 

 photoplethysmogram (PPG) at two wavelengths (660 and 830 nm), 

 which is then used to calculate oxygen saturation (SpO2). In 

 order to achieve reliable measurement without adjusting the 

 position of the garment, four plastic optical fibre (POF) probes 

 are utilised to increase the likelihood that a high-quality PPG 

 is obtained due to at least one of the probes being positioned 

 over a blood vessel. Each probe transmits and receives light 

 into the skin to measure the PPG and SpO2. All POFs are 

 integrated in a stretchable textile sleeve with a circumference 

 of 15 cm to keep the sensor in contact with the subject's wrist 

 and to minimise motion artefacts. Tests on healthy volunteers 

 show that the multichannel PPG sensor faithfully provides an 

 SpO2 reading in at least one of the four sensor channels in all 

 cases with no need for adjusting the position of the sleeve. 

 This could not be achieved using a single sensor alone. The 

 multichannel sensor is used to monitor the SpO2 of 10 

 participants with an average wrist circumference of 16.0 $±$ 

 0.6 cm. Comparing the developed sensor's SpO2 readings to a 

 reference commercial oximeter (reflectance Masimo Radical-7) 

 illustrates that the mean difference between the two sensors' 

 readings is -0.03%, the upper limit of agreement (LOA) is 

 0.52% and the lower LOA is -0.58%. This multichannel sensor 

 has the potential to achieve reliable, unobtrusive and 

 comfortable textile-based monitoring of both heart rate and SpO2 

 during everyday life.},

keywords = {multichannel, oxygen saturation, photoplethysmography, plastic   optical fibre, textile, wearable technology},

pubstate = {published},

tppubtype = {article}

}