Unobtrusive Reflectance Photoplethysmography for Detecting and Severity Grading of Sleep Apnea via Oxygen Desaturation Index

TL;DR

This study demonstrates that unobtrusive wrist and upper arm reflectance PPG devices can effectively estimate oxygen desaturation index, serving as a reliable surrogate for sleep apnea severity assessment, potentially simplifying diagnosis.

Contribution

It introduces a wearable reflectance PPG method for sleep apnea detection, comparing measurement sites and validating ODI as a predictor of apnea severity.

Findings

Upper arm ODI predicts moderate/severe sleep apnea with 86% accuracy.

Wrist ODI is less reliable for sleep apnea diagnosis.

Upper arm measurement shows high sensitivity and acceptable specificity.

Abstract

Sleep apnea is a common chronic sleep-related disorder which is known to be a comorbidity for cerebro- and cardio-vascular disease. Diagnosis of sleep apnea usually requires an overnight polysomnography at the sleep laboratory. In this paper, we used a wearable device which measures reflectance photoplethysmography (PPG) at the wrist and upper arm to estimate continuous SpO2 levels during sleep and subsequently derive an oxygen desaturation index (ODI) for each patient. On a cohort of 170 patients undergoing sleep apnea screening, we evaluated whether this ODI value could represent a surrogate marker for the apnea-hypopnea index (AHI) for the diagnosis and severity assessment of sleep apnea. As the ODI was simultaneously obtained at the fingertip, upper arm and wrist, we compared ODI diagnostic performance depending on the measurement location. We then further evaluated the accuracy of ODI as a direct predictor for moderate and severe sleep apnea as defined by established AHI thresholds. We found that ODI values obtained at the upper arm were good predictors for moderate or severe sleep apnea, with 86% accuracy, 96% sensitivity and 70% specificity, whereas ODI values obtained at the wrist were less reliable as a diagnostic tool.