Performance of Wearable Pulse Oximetry During Controlled Hypoxia Induction

Abstract Oxygen saturation is a crucial metric used for monitoring patients with lung disease or other conditions who are at risk of hypoxemia. Recently, consumer wearable devices began incorporating oxygen saturation measurement tools, widening their use among individuals with lung disease. However, their performance has not been well characterized, particularly during blood oxygen desaturation, due to limitations in collecting comparison arterial blood gas measurements during exercise-induced hypoxemia. To address this knowledge gap, we performed a controlled oxygen desaturation study in nine healthy participants to mimic exercise-induced hypoxemia, reducing the blood oxygen saturation levels from 100% to 60% using a gas delivery system. We conducted a comparative analysis of the displayed oxygen saturation readings of both the Masimo MightySat Rx finger pulse oximeter and Apple Watch Series 7 with arterial blood oxygen saturation readings obtained from arterial blood gas samples. Both the Masimo MightySat Rx pulse oximeter and the Apple Watch Series 7 tended to overestimate the oxygen saturation. The Masimo pulse oximeter readings were more likely to fall within the acceptable error range than the Apple Watch (49.03% compared to 32.14%). Notably, both devices have limitations under low oxygen saturation levels (<88%) with an error of 1.96% and 4.99% for the Masimo and Apple Watch, respectively. Among the oxygen desaturation measurements at a desaturation rate larger than two percent per minute, a rate which is clinically correlated to sleep apnea, both devices increased their error slightly by 0.29% and 1.80% respectively for the Masimo and Apple Watch. However, no statistically significant increase was found. Author Summary Blood oxygen saturation (SpO 2 ) is an important measurement for monitoring patients with acute and chronic conditions that are associated with hypoxemia, including chronic obstructive pulmonary disease (COPD), heart failure, and sleep apnea. While smartwatches may provide a novel method for continuous and unobtrusive SpO 2 monitoring, it is necessary to understand their accuracy and limitations to ensure that they are used in a fit-for-purpose manner, especially under conditions of low oxygen saturation.