OBJECTIVE

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

PATIENTS AND METHODS

Circul+ (Bodimetrics), with a form factor of a ring, measures several variables for cardiorespiratory assessment (SpO, 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 SaO of 70%. ABGs was sampled at various levels of hypoxia, and simultaneous readings were obtained from the Circul+. We compared SpO from Circul with measurement of ABGs by a medical grade blood gas analyzer.

RESULTS

There was excellent correlation between SaO measured by the ring oximeter and ABGs in both Black ( = 1.0174 - 1.573;  = 0.9414) and Non-Black ( = 1.0209 - 2.5607;  = 0.9207) participants. No differences were found in comparing the intercept and slopes of the regressions. At ABG of 70% and 100%, the SaO 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.

CONCLUSION

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.