Wearable device as good as polysomnography in estimating oxygen saturation during sleep

A wrist-worn reflectance-based pulse oximeter can measure oxygen saturation during sleep with reasonable accuracy and small error, according to a recent study.

“The major strength of this study is that it evaluated the performance of wrist-worn reflectance pulse oximetry when measuring oxygen saturation of patients with sleep apnoea and of some patients with profound desaturation,” the researchers said.

Ninety-seven adults (mean age 544.4 years, 76.3 percent men) participated in the study. Simultaneous oxygen saturation measurements were conducted using a reflectance pulse oximeter (Samsung Galaxy Watch 4) and polysomnography (transmittance-based pulse oximeter; reference standard). Device performance was primarily assessed as the root mean squared error (RMSE) and coverage rate.

Of the participants, 21, 23, and 35 had mild, moderate, and severe obstructive sleep apnoea (OSA), respectively; the remaining 18 participants were deemed to be healthy, with an apnoea-hypopnoea index (AHI) of 2.3/hour. In the healthy subgroup, oxygen saturation as measured by the Galaxy Watch ranging from 90 percent to 100 percent. [Sleep Health 2022;doi:10.1016/j.sleh.2022.04.003]

Of the 672.3 hours of recorded sleep time, only 490.8 hours had viable readings for both the wrist-worn device and polysomnography and were thus deemed eligible for analysis. The Galaxy Watch showed a coverage rate of 73.5 percent, with a data rejection rate of 26.5 percent.

Compared with the reference standard, the reflectance-based device had an RMSE of 2.3 percent calculated throughout the valid period, making it in-line with requirements set by both the Food and Drug Administration (FDA) and the International Organization for Standardization (ISO).

In addition, Bland-Altman density plot analysis revealed that the smartwatch agreed well with polysomnography, yielding a negligible mean bias of –0.16 percent.

The researchers then stratified the analysis according to OSA severity. In participants with AHI ≤60/hour, the wrist device still satisfied both FDA and ISO guidelines, with RMSE values of 1.65 percent, 1.76 percent, and 1.93 percent in normal, mild, and moderate OSA. However, in participants with severe OSA (AHI >60), RMSE increased to 2.93 percent, falling short of FDA and ISO standards. Coverage rate was likewise poorest in sever OSA patients at 64.29 percent.

“Although the Galaxy Watch 4 showed a relatively imprecise estimation of oxygen desaturation for participants with very severe OSA, it demonstrated generally good performance for the other three groups,” the researchers said.

“In the field of sleep medicine, the development of precise and convenient oxygen saturation measurements should be associated with the screening and monitoring of OSA,” they added.

“With improvements in accuracy and error correction algorithms of wrist-worn wearable devices, it is expected that future devices will provide more accurate and reliable information to patients and clinicians alike,” the researchers said.