Wearable Upper Arm SpO<sub>2</sub> Sensor for Wellness Monitoring
Matti Kinnunen, Mohammad H. Behfar, Nuutti Santaniemi, Tuomas Happonen, Dung Nguyen, Joni Kilpijärvi, Tommi Jaako, Jukka Happonen, Monica K. Russell, Christian A. Clermont, Michael J. Asmussen, Trevor A. Day, Markus Tuomikoski, Jussi Hiltunen
Abstract
<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Objective:</i> This paper describes the full development of a sensor for measuring optical heart rate (OHR) and blood oxygen saturation (SpO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>). <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Methods:</i> A wearable sensor with a new type of skin compatible dispensed lens was designed and manufactured. All critical optical components, light emitting diodes (LEDs) and photodiode (PD) were close to skin and gave maximum light intensity due to minimal loss in the lens structure. Lens and optical components formed a thin monolithic structure. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Results:</i> Suppressed crosstalk between LED and PD was achieved by using two types of dispensed material: light blocking and transparent. High signal to noise ratio (SNR) and amplitude in the alternating current (AC) part of the photoplethysmography (PPG) signal were achieved. User comfort was achieved by having a small sensor located on the upper arm. When re-training the algorithm from our first iteration, the multiwavelength PPG sensor showed an SpO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RMSE of 2.61% with a 7-second average analysis for 25 participants. The average RMSE of heart rate over all 25 participants was 1.6 ± 1.1%. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Conclusion:</i> This study demonstrates a sensor with a clinical grade SpO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> measurement and a highly accurate OHR measurement that is also comfortable and easy to wear. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Significance:</i> A dispensing method provides a new way of manufacturing sensor elements for wearable sensors with increased performance with reduced crosstalk.