The TBT and SFT will be recorded and measured on frozen ultrasound images on performance of the MM with the tongue base positioned farthest away from the transducer (i.e. with the pharyngeal airway presumably decreased to its smallest caliber). The maximum TBT and SFT on the Muller's Maneuver (MM) were measured three times on three separate images, and the mean values, TBT (MM) and SFT (MM), will be obtained for analysis. The difference in TBT, TBT (difference), on eupneic breathing and the MM was defined as TBT (MM) - TBT (eupneic). The difference in SFT, SFT (difference), on eupneic breathing and the MM will be defined as SFT (MM) - SFT (eupneic). TBT (difference) and SFT (difference) will be computed for each participant for further analysis.