An apparatus for delivering a flow of breathable gas to an airway of a user, the apparatus comprising: a plenum chamber, the plenum chamber adapted for coupling with a respiratory pressure therapy device to receive a supply of breathable gas to the plenum chamber, the plenum chamber further adapted to couple with the airway of the user； and one or more exhaust vents (3400, 3456), the one or more exhaust vents coupled with the plenum chamber to permit a flow of exhaust gas from a cavity of the plenum chamber； wherein the one or more exhaust vents are configured to change a direction of exhaust flow relative to the plenum chamber in accordance with orientation of the plenum chamber. The vent allows for unobstructed flow from the mask if the wearer rolls over and blocks the open vent during sleep.
