Validation of the Withings ScanWatch as a Wrist-Worn Reflective Pulse Oximeter: Prospective Interventional Clinical Study

Abstract

Background: A decrease in the level of pulse oxygen saturation as measured by pulse oximetry (SpO2) is an indicator of hypoxemia that may occur in various respiratory diseases, such as chronic obstructive pulmonary disease (COPD), sleep apnea syndrome, and COVID-19. Currently, no mass-market wrist-worn SpO2 monitor meets the medical standards for pulse oximeters.

Objective: The main objective of this monocentric and prospective clinical study with single-blind analysis was to test and validate the accuracy of the reflective pulse oximeter function of the Withings ScanWatch to measure SpO2 levels at different stages of hypoxia. The secondary objective was to confirm the safety of this device when used as intended.

Methods: To achieve these objectives, we included 14 healthy participants aged 23-39 years in the study, and we induced several stable plateaus of arterial oxygen saturation (SaO2) ranging from 100%-70% to mimic nonhypoxic conditions and then mild, moderate, and severe hypoxic conditions. We measured the SpO2 level with a Withings ScanWatch on each participant's wrist and the SaO2 from blood samples with a co-oximeter, the ABL90 hemoximeter (Radiometer Medical ApS).

Results: After removal of the inconclusive measurements, we obtained 275 and 244 conclusive measurements with the two ScanWatches on the participants' right and left wrists, respectively, evenly distributed among the 3 predetermined SpO2 groups: SpO2≤80%, 80%<SpO2≤90%, and 90%<SpO2. We found a strong association and a high level of agreement between the measurements collected from the devices, with high Pearson correlation coefficients of r=0.944 and r=0.954 on the correlation plots, low Pearson correlation coefficients of r=0.083 (P=.17) and r=0.23 (P=.001) on Bland-Altman plots, biases of 0.98% (95% CI 0.65-1.32) and 1.56% (95% CI 1.24-1.87), and root mean square errors of 2.97% and 3.00% from the participants' right and left hands, respectively.

Conclusions: In conclusion, the Withings ScanWatch is able to measure SpO2 levels with adequate accuracy at a clinical grade. No undesirable effects or adverse events were reported during the study.

Trial registration: ClinicalTrials.gov NCT04380389; https://ichgcp.net/clinical-trials-registry/NCT04380389.

Keywords: COPD; COVID-19; SpO2; Withings ScanWatch; accuracy; connected watch; neural network; oximeter; oxygen; pulse oxygen saturation; reflective pulse oximeter; respiratory; respiratory disease; safety; sleep apnea syndrome; validation; wearable.

Conflict of interest statement

Conflicts of Interest: Both authors are employees of Withings, which manufactures ScanWatch, the connected watch studied in this article.

©Romain Kirszenblat, Paul Edouard. Originally published in the Journal of Medical Internet Research (https://www.jmir.org), 26.04.2021.

Figures

Figure 1

Absorption spectra of oxygenated and deoxygenated hemoglobin. Licensed from Adrian Curtin/CC BY-SA. Hb: deoxygenated hemoglobin; HbO2: oxygenated hemoglobin.

Figure 2

Comparison of SpO2 measured by the ScanWatch and hemoximeter for one subject. SpO2: pulse oxygen saturation as measured by pulse oximetry.

Figure 3

Front view (left) and back view (right) of the Withings ScanWatch.

Figure 4

Correlation plots for the Withings ScanWatches versus the ABL90 hemoximeter from the participants’ right (A) and left (B) hands.

Figure 5

Bland-Altman plots for the Withings ScanWatches and the ABL90 hemoximeter from the participants’ right (A) and left (B) hands. BFSL: best fit straight line.

Figure 6

SpO2 measured by ScanWatch and a finger pulse oximeter during apnea/hypopnea events.