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Article

In-Ear SpO2: A Tool for Wearable, Unobtrusive Monitoring of Core Blood Oxygen Saturation

1
Department of Electrical and Electronic Engineering, Imperial College London, London SW7 2AZ, UK
2
Imperial Centre for Cardiac Engineering, Imperial College London, London SW7 2AZ, UK
3
National Heart and Lung Institute, Faculty of Medicine, Imperial College London, London SW3 6LY, UK
*
Author to whom correspondence should be addressed.
Sensors 2020, 20(17), 4879; https://doi.org/10.3390/s20174879
Received: 5 August 2020 / Revised: 24 August 2020 / Accepted: 24 August 2020 / Published: 28 August 2020
(This article belongs to the Section Wearables)
The non-invasive estimation of blood oxygen saturation (SpO2) by pulse oximetry is of vital importance clinically, from the detection of sleep apnea to the recent ambulatory monitoring of hypoxemia in the delayed post-infective phase of COVID-19. In this proof of concept study, we set out to establish the feasibility of SpO2 measurement from the ear canal as a convenient site for long term monitoring, and perform a comprehensive comparison with the right index finger—the conventional clinical measurement site. During resting blood oxygen saturation estimation, we found a root mean square difference of 1.47% between the two measurement sites, with a mean difference of 0.23% higher SpO2 in the right ear canal. Using breath holds, we observe the known phenomena of time delay between central circulation and peripheral circulation with a mean delay between the ear and finger of 12.4 s across all subjects. Furthermore, we document the lower photoplethysmogram amplitude from the ear canal and suggest ways to mitigate this issue. In conjunction with the well-known robustness to temperature induced vasoconstriction, this makes conclusive evidence for in-ear SpO2 monitoring being both convenient and superior to conventional finger measurement for continuous non-intrusive monitoring in both clinical and everyday-life settings. View Full-Text
Keywords: SpO2; hearables; wearable health; hypoxia; sleep apnea; covid-19 SpO2; hearables; wearable health; hypoxia; sleep apnea; covid-19
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MDPI and ACS Style

Davies, H.J.; Williams, I.; Peters, N.S.; Mandic, D.P. In-Ear SpO2: A Tool for Wearable, Unobtrusive Monitoring of Core Blood Oxygen Saturation. Sensors 2020, 20, 4879. https://doi.org/10.3390/s20174879

AMA Style

Davies HJ, Williams I, Peters NS, Mandic DP. In-Ear SpO2: A Tool for Wearable, Unobtrusive Monitoring of Core Blood Oxygen Saturation. Sensors. 2020; 20(17):4879. https://doi.org/10.3390/s20174879

Chicago/Turabian Style

Davies, Harry J., Ian Williams, Nicholas S. Peters, and Danilo P. Mandic. 2020. "In-Ear SpO2: A Tool for Wearable, Unobtrusive Monitoring of Core Blood Oxygen Saturation" Sensors 20, no. 17: 4879. https://doi.org/10.3390/s20174879

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