Abstract: An exhaust port assembly (10) for use in a system for delivering a flow of gas from a pressure generating device (4) to the airway of a patient includes a first member structured to be in communication with the flow of gas and a second member moveably coupled to the first member. The first member and the second member define a cross-sectional area of an exhaust port which is structured to allow the passage therethrough of exhaust gases (12) from the flow of gas. The second member is moveable among a first position in which the exhaust port has a first cross-sectional area and a second position in which the exhaust port has a second cross-sectional area different than the first cross-sectional area.