 Methods: OSA patients referred to surgical treatment lateral pharyngoplasty will be enrolled in this study. Natural sleep endoscopy will be performed at the sleep lab during the night. Propofol induced sleep will be performed at the operating room before surgery. The VOTE velum, oropharyngeal lateral walls, tongue base and epiglottis classification will be used to compare site and configuration of collapse between studies. Peak inspiratory flow will also be compared between studies. 