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Enabling Continuous Wearable Reflectance Pulse Oximetry at the Sternum.

Michael ChanVenu G GantiJ Alex HellerCalvin A AbdallahMozziyar EtemadiOmer T Inan
Published in: Biosensors (2021)
In light of the recent Coronavirus disease (COVID-19) pandemic, peripheral oxygen saturation (SpO 2 ) has shown to be amongst the vital signs most indicative of deterioration in persons with COVID-19. To allow for the continuous monitoring of SpO 2 , we attempted to demonstrate accurate SpO 2 estimation using our custom chest-based wearable patch biosensor, capable of measuring electrocardiogram (ECG) and photoplethysmogram (PPG) signals with high fidelity. Through a breath-hold protocol, we collected physiological data with a wide dynamic range of SpO 2 from 20 subjects. The ratio of ratios (R) used in pulse oximetry to estimate SpO 2 was robustly extracted from the red and infrared PPG signals during the breath-hold segments using novel feature extraction and PPG green -based outlier rejection algorithms. Through subject independent training, we achieved a low root-mean-square error (RMSE) of 2.64 ± 1.14% and a Pearson correlation coefficient (PCC) of 0.89. With subject-specific calibration, we further reduced the RMSE to 2.27 ± 0.76% and increased the PCC to 0.91. In addition, we showed that calibration is more efficiently accomplished by standardizing and focusing on the duration of breath-hold rather than the resulting range in SpO 2 . The accurate SpO 2 estimation provided by our custom biosensor and the algorithms provide research opportunities for a wide range of disease and wellness monitoring applications.
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