A respiratory treatment device comprising: a housing enclosing at least one chamber a chamber inlet configured to receive exhaled air into the at least one chamber at least one chamber outlet configured to permit exhaled air to exit the at least one chamber an exhalation flow path defined between the chamber inlet and the at least one chamber outlet a restrictor member positioned in the exhalation flow path, the restrictor member moveable in response to a flow of exhaled air along the exhalation flow path between a closed position, where the flow of exhaled air along the exhalation flow path is restricted, and an open position, where the flow of exhaled air along the exhalation flow path is less restricted and, a variable nozzle positioned in the exhalation flow path such that the exhalation flow path passes through an orifice of the variable nozzle, wherein a size of the orifice is configured to increase in response to the flow of exhaled air through the orifice.
