Validation of a Smart Ring Oximeter in Individuals With Dark Skin Pigment

To evaluate a ring wearable's accuracy in the measurement of oxyhemoglobin saturation measured by pulse oximeter (SpO₂) compared to a simultaneous SaO₂ obtained from arterial blood gases (ABGs) because oximeters may overestimate oxyhemoglobin saturation in darkly pigmented individuals resulting in occult hypoxemia.

Circul+ (Bodimetrics), with a form factor of a ring, measures several variables for cardiorespiratory assessment (SpO₂, movement, and heart rate). The design ensures that measurements are made on the palmar surface of the digit, where there is generally less pigment. Twenty-four healthy participants (8 Black, 16 non-Black) had catheters inserted into their radial arteries during the timeframe between August 2020 and January 2022. They were administered nitrogen-rich air that made them hypoxic in steps to an SaO₂ of 70%. ABGs was sampled at various levels of hypoxia, and simultaneous readings were obtained from the Circul+. We compared SpO₂ from Circul with measurement of ABGs by a medical grade blood gas analyzer.

There was excellent correlation between SaO₂ measured by the ring oximeter and ABGs in both Black (y = 1.0174x - 1.573; R ² = 0.9414) and Non-Black (y = 1.0209x - 2.5607; R ² = 0.9207) participants. No differences were found in comparing the intercept and slopes of the regressions. At ABG of 70% and 100%, the SaO₂ measured by the ring was calculated to be 69.6% and 100.2% for the Black participants and 68.9% and 99.5% for the non-Black participants. Bland-Altman analysis found a bias (deviation from the mean) of 0.0 for the Black participants and -0.7% for the non-Black participants.

Results from this study confirmed that Circul+ oximetry accuracy seems to be independent of skin tone, perhaps because measurements are made on the palmar surface of the digit, where there is generally less pigment.