A Single-Channel Acoustic Method for Portable Diagnosis of Sleep Apnea

Background: Sleep apnea is a very common disease with serious health consequences. It affects approximately 85% of adults, most of whom remain undiagnosed, which puts them at risk of car accidents, because of sleepiness, and hypertension, heart failure, and stroke. The objective of this thesis was to develop a single-channel device for portable monitoring of sleep apnea that uses breath sounds collected via a microphone placed in front of the nose and mouth. Methods: Project 1: Frequency characterization was used to identify the basic components of the respiratory cycle, i.e., inspiration and expiration. Project 2: Inspiratory sounds were used to determine upper airway narrowing by means of Linear Predictive Coding (LPC), which was validated against objective measures of upper airway resistance. Project 3: An algorithm to calculate the frequency of apneas and hypopneas per hour (apnea-hypopnea index or AHI) was developed and validated against polysomnography in 50 subjects during sleep. Project 4: Finally, a self contained device was then developed and evaluated in 49 subjects in the home setting, 11 of whom used the device on 2 different nights. Results: Project 1: Inspiratory and expiratory phases had characteristically different spectra that allowed them to be distinguished with up to 97% correct classification. Project 2: LPC coefficients were found to be modulated by the ensuing of upper airway narrowing. Project 3: AHI determined by acoustic analysis showed up to 94% correlation with PSG and up to 90% diagnostics accuracy. Project 4: In the home unattended setting, the overall rating for ease-of-use was excellent and the success rate of independent use was 94%. The portable device showed excellent performance with very high signal-to-noise ratio of 31.7 dB. The intra-subject 2-night AHI scores were reproducible in 9 out of 11 (82%) home subjects, which is well within reported inter-night variability. Conclusion: Acoustic analysis of breath sounds is a powerful tool for characterization of respiratory patterns including upper airway narrowing and accurate identification of apneas and hypopneas as compared with the current gold standard. This technology can be packaged in a compact device that can be used independently and reliably in the home environment.Ph