2.2. Polysomnography for diagnosis of obstructive sleep apnea

A day after the definite diagnosis of OSA based on polysomnography at the sleep center, the patients were scheduled to receive DISE and surgical interventions for OSA. During examination, the results of EEG, submental electromyography, and electrooculography were reviewed. In addition, nasal/oral airflow and oxygen saturation were measured and recorded by standard techniques. All results were scored and interpreted by a certified and experienced sleep medicine physician. Sleep stage was determined and the severity of sleep-disordered breathing was assessed based on the number of apnea/hypopnea episodes. OSA and obstructive hypopnea were defined separately according to previous study, namely, the cessation of airflow for at least 10 seconds with a corresponding respiratory effort and an abnormal respiratory event accompanied by at least 30% reduction in thoracoabdominal movement or airflow when compared with the baseline, which lasts for at least 10 seconds and is associated with ≥4% oxygen desaturation.^[19] Besides, the apnea–hypopnea index (AHI) was calculated by the definition of the total number of apnea and hypopnea episodes per hour of electroencephalographic sleep, while obstructive sleep apnea/hypopnea syndrome was defined as an AHI of >5 events per hour. Respiratory events of central origin were all excluded for severity classification.^[20]