Abstract
Obstructive sleep apnea (OSA) is a common sleep disorder, and continuous positive airway pressure (CPAP) is the most effective treatment. Poor adherence is one of the major challenges in CPAP therapy. The recent boom of wearable optical sensors measuring oxygen saturation makes at-home multiple-night CPAP titrations possible, which may essentially improve the adherence of CPAP therapy by optimizing its pressure in a real-life setting economically. We tested whether the oxygen desaturations (ODs) measured in the arm muscle (arm_OD) by gold-standard frequency-domain multi-distance near-infrared spectroscopy (FDMD-NIRS) change quantitatively with titrated CPAP pressures in OSA patients together with polysomnography. We found that the arm_OD (2.08 ± 1.23%, mean ± standard deviation) was significantly smaller (p-value < 0.0001) than the fingertip OD (finger_OD) (4.46 ± 2.37%) measured by a polysomnography pulse oximeter. Linear mixed-effects models suggested that CPAP pressure was a significant predictor for finger_OD but not for arm_OD. Since FDMD-NIRS measures a mixture of arterial and venous OD, whereas a fingertip pulse oximeter measures arterial OD, our results of no association between arm_OD and finger_OD indicate that the arm_OD mainly represented venous desaturation. Arm_OD measured by optical sensors used for wearables may not be a suitable indicator of the CPAP titration effectiveness.
Highlights
Obstructive sleep apnea (OSA) is the most prevalent respiratory sleep disorder, occurring in 9–38% of the general population [1], and it is a high-risk factor for many diseases, such as cardio-/cerebrovascular diseases [2,3], periodontal disease [4] and type 2 diabetes [5]
Unlike the in-lab PSG fingertip pulse oximetry, in which the detector measures the light transmitted through the fingertip (i.e., transmission photoplethysmography (T-PPG)), these wearable devices assess the SpO2 or StO2 by measuring the changes in the backscattering light from the wrist or arm based on the modified Beer–Lambert law (MBLL) [25,26,27,28]
Fingertip SpO2 but not the arm StO2 reflects the reduction of desaturations during continuous positive airway pressure (CPAP) titration, probably because venous blood contributing to StO2 reduces the sensitivity of StO2 in response to CPAP pressures compared to SpO2
Summary
Obstructive sleep apnea (OSA) is the most prevalent respiratory sleep disorder, occurring in 9–38% of the general population [1], and it is a high-risk factor for many diseases, such as cardio-/cerebrovascular diseases [2,3], periodontal disease [4] and type 2 diabetes [5]. Unlike the in-lab PSG fingertip pulse oximetry, in which the detector measures the light transmitted through the fingertip (i.e., transmission photoplethysmography (T-PPG)), these wearable devices assess the SpO2 or StO2 by measuring the changes in the backscattering light from the wrist or arm based on the modified Beer–Lambert law (MBLL) [25,26,27,28]. That is, their light sources are usually two or more near-infrared light wavelengths mainly absorbed by oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (HHb) in biological tissues, and detectors are placed on the same side of the measured tissues because the wrist and arm are too thick to be penetrated by light. While wrist wearable devices mainly use reflectance photoplethysmography (R-PPG) or pulse oximetry [28,29,30], armbands are mainly based on simple continuous-wave near-infrared spectroscopy (CW-NIRS)
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