Commercial smartwatch with pulse oximeter detects short-time hypoxemia as well as standard medical-grade device: Validation study

Jakub Rafl, Thomas E Bachman, Veronika Rafl-Huttova, Simon Walzel, Martin Rozanek, Jakub Rafl, Thomas E Bachman, Veronika Rafl-Huttova, Simon Walzel, Martin Rozanek

Abstract

Objective: We investigated how a commercially available smartwatch that measures peripheral blood oxygen saturation (SpO2) can detect hypoxemia compared to a medical-grade pulse oximeter.

Methods: We recruited 24 healthy participants. Each participant wore a smartwatch (Apple Watch Series 6) on the left wrist and a pulse oximeter sensor (Masimo Radical-7) on the left middle finger. The participants breathed via a breathing circuit with a three-way non-rebreathing valve in three phases. First, in the 2-minute initial stabilization phase, the participants inhaled the ambient air. Then in the 5-minute desaturation phase, the participants breathed the oxygen-reduced gas mixture (12% O2), which temporarily reduced their blood oxygen saturation. In the final stabilization phase, the participants inhaled the ambient air again until SpO2 returned to normal values. Measurements of SpO2 were taken from the smartwatch and the pulse oximeter simultaneously in 30-s intervals.

Results: There were 642 individual pairs of SpO2 measurements. The bias in SpO2 between the smartwatch and the oximeter was 0.0% for all the data points. The bias for SpO2 less than 90% was 1.2%. The differences in individual measurements between the smartwatch and oximeter within 6% SpO2 can be expected for SpO2 readings 90%-100% and up to 8% for SpO2 readings less than 90%.

Conclusions: Apple Watch Series 6 can reliably detect states of reduced blood oxygen saturation with SpO2 below 90% when compared to a medical-grade pulse oximeter. The technology used in this smartwatch is sufficiently advanced for the indicative measurement of SpO2 outside the clinic.

Trial registration: ClinicalTrials.gov NCT04780724.

Keywords: Apple Watch; Wearables; hypoxemia; hypoxic gas mixture; oxygen saturation; pulse oximetry; reflectance mode.

Conflict of interest statement

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

© The Author(s) 2022.

Figures

Figure 1.
Figure 1.
Differences between simultaneous SpO2 readings of the smartwatch (Apple Watch 6) and oximeter (Masimo Radical-7) across different ranges of oxyhemoglobin saturation. Pooled SpO2 measurements were analyzed for all participants grouped. The solid line is the mean difference of the measurements (bias). Dashed lines are the 95% limits of agreement. The area of markers is proportional to the number of measurements.
Figure 2.
Figure 2.
The time courses of the mean of all smartwatch SpO2 measurements (Apple Watch 6) and the mean of all oximeter SpO2 measurements (Masimo Radical-7) across all 24 participants. Data are mean ± SEM.

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