Prospective clinical validation of the Empatica EmbracePlus wristband as a reflective pulse oximeter

Abstract

Introduction: Respiratory diseases such as chronic obstructive pulmonary disease, obstructive sleep apnea syndrome, and COVID-19 may cause a decrease in arterial oxygen saturation (SaO₂). The continuous monitoring of oxygen levels may be beneficial for the early detection of hypoxemia and timely intervention. Wearable non-invasive pulse oximetry devices measuring peripheral oxygen saturation (SpO₂) have been garnering increasing popularity. However, there is still a strong need for extended and robust clinical validation of such devices, especially to address topical concerns about disparities in performances across racial groups. This prospective clinical validation aimed to assess the accuracy of the reflective pulse oximeter function of the EmbracePlus wristband during a controlled hypoxia study in accordance with the ISO 80601-2-61:2017 standard and the Food & Drug Administration (FDA) guidance.

Methods: Healthy adult participants were recruited in a controlled desaturation protocol to reproduce mild, moderate, and severe hypoxic conditions with SaO₂ ranging from 100% to 70% (ClinicalTrials.gov registration #NCT04964609). The SpO₂ level was estimated with an EmbracePlus device placed on the participant's wrist and the reference SaO₂ was obtained from blood samples analyzed with a multiwavelength co-oximeter.

Results: The controlled hypoxia study yielded 373 conclusive measurements on 15 subjects, including 30% of participants with dark skin pigmentation (V-VI on the Fitzpatrick scale). The accuracy root mean square (A_rms) error was found to be 2.4%, within the 3.5% limit recommended by the FDA. A strong positive correlation between the wristband SpO₂ and the reference SaO₂ was observed (r = 0.96, P < 0.001), and a good concordance was found with Bland-Altman analysis (bias, 0.05%; standard deviation, 1.66; lower limit, -4.7%; and upper limit, 4.8%). Moreover, acceptable accuracy was observed when stratifying data points by skin pigmentation (A_rms 2.2% in Fitzpatrick V-VI, 2.5% in Fitzpatrick I-IV), and sex (A_rms 1.9% in females, and 2.9% in males).

Discussion: This study demonstrates that the EmbracePlus wristband could be used to assess SpO₂ with clinically acceptable accuracy under no-motion and high perfusion conditions for individuals of different ethnicities across the claimed range. This study paves the way for further accuracy evaluations on unhealthy subjects and during prolonged use in ambulatory settings.

Keywords: FDA clearance; blood oxygen saturation; reflective pulse oximeter; respiratory disease; wearable device; wrist photoplethysmography.