Muller's manoeuver is

Muller's manoeuvre: Used to find the level and degree of obstruction in sleep-disordered breathing. It is performed while using flexible nasopharyngoscope. First, the examiner sees the upper airways at rest and then during the time when the patient makes a maximal inspiratory effo with nose and mouth closed. The base of tongue, lateral pharyngeal wall and palate are examined for collapsibility and then rated from 0 (minimal collapse) to 4+ (complete collapse). Ref: Textbook of ENT, Dhingra; 6th edition; Pg no: 449