 Methods Detailed clinical history and physical examination will be performed before natural sleep endoscopy. A 2-hour fast will be required. During both natural sleep and propofol-induced sleep, pharyngeal pressure will be measured using a pressure-tipped catheter model TC-500XG; Millar.The nasopharynx will be numbed with xylocaine 10 and oxymetazoline 0.05, the catheter will be passed through a nasal mask into one nostril, and placed at the tongue base as confirmed by visual inspection of the oropharynx.A 2.8mm pediatric bronchoscope Olympus will be passed through the mask and into the other nostril. A nasal mask will be fitted and a heated pneumotachograph with differential pressure transducer connected to the mask will quantify airflow. The endoscope will be located at velopharynx, lateral wall of the pharynx and 2 cm above tongue and epiglottis.The VOTE Endoscopic Classification will be used to describe site and configuration of pharyngeal collapse in each study. The study will be scored by two experienced investigators, blind to the patient identification and type of study natural sleep or drug-induced. Propofol-induced sleep will be performed at the operating room before surgery. 