A Multi-wavelength Photoplethysmography System for Sleep Quality Monitoring

This study proposes an intraoral, wearable, and noninvasive consumer electronics system based on the measurement of photoplethysmography (PPG) signals from the oral cavity for monitoring sleep quality. The system consists of a dual-channel PPG sensor and a Bluetooth module integrated with the microprocessor. It is experimentally demonstrated that the PPG signals measured by the proposed intraoral wearable system have a relatively identical morphology, i.e., baseline, frequency, and detectable peaks, as those recorded by an FDA-approved home sleep test module, which places at the conventional anatomical site, i.e., the fingertip. Thanks to the high quality of the captured PPG signals, the apnea-hypopnea index (AHI) can be calculated as an indicator of sleep quality. A comparison between the AHI values estimated by the FDA-approved home test and our proposed sleep monitoring system confirms that our monitoring device and its implemented algorithm can accurately predict the AHI. Therefore, the proposed sleep monitoring system can be integrated with a common oral appliance to monitor the efficacy of oral appliance therapy on a regular basis.