A respiratory treatment device comprising: a housing enclosing a plurality of chambers; a first opening in the housing configured to transmit air exhaled into and air inhaled from the housing ; a second opening in the housing configured to permit air exhaled into the first opening to exit the housing ; a third opening in the housing configured to permit air outside the housing to enter the housing upon inhalation at the first opening ; an exhalation flow path defined between the first opening and the second opening , and an inhalation flow path defined between the third opening and the first opening ; a vane in fluid communication with the exhalation flow path and the inhalation flow path , the vane being operatively connected to a restrictor member and configured to reciprocate between a first position and a second position in response to a flow of air along the exhalation flow path or the inhalation flow path ; and the restrictor member positioned along the exhalation flow path and the inhalation flow path , the restrictor member being movable in response to a flow of air along the exhalation flow path , during a single period of exhalation, or the inhalation flow path , during a single period of inhalation, repeatedly between a closed position, where the flow of air along the exhalation flow path or the inhalation flow path is restricted, and an open position, where the flow of exhaled air along the exhalation flow path or the inhalation flow path is less restricted; wherein the third opening comprises a one-way inhalation valve configured to permit air outside the housing to enter the housing upon inhalation at the first opening , wherein the second opening comprises a one-way exhalation valve configured to permit air exhaled into the housing to exit the housing upon exhalation at the first opening , and characterised in that a cross-sectional area of the second opening is selectively adjustable to control a resistance to the flow of air therethrough. a housing enclosing a plurality of chambers; a first opening in the housing configured to transmit air exhaled into and air inhaled from the housing ; a second opening in the housing configured to permit air exhaled into the first opening to exit the housing ; a third opening in the housing configured to permit air outside the housing to enter the housing upon inhalation at the first opening ; an exhalation flow path defined between the first opening and the second opening , and an inhalation flow path defined between the third opening and the first opening ; a vane in fluid communication with the exhalation flow path and the inhalation flow path , the vane being operatively connected to a restrictor member and configured to reciprocate between a first position and a second position in response to a flow of air along the exhalation flow path or the inhalation flow path ; and the restrictor member positioned along the exhalation flow path and the inhalation flow path , the restrictor member being movable in response to a flow of air along the exhalation flow path , during a single period of exhalation, or the inhalation flow path , during a single period of inhalation, repeatedly between a closed position, where the flow of air along the exhalation flow path or the inhalation flow path is restricted, and an open position, where the flow of exhaled air along the exhalation flow path or the inhalation flow path is less restricted; wherein the third opening comprises a one-way inhalation valve configured to permit air outside the housing to enter the housing upon inhalation at the first opening , wherein the second opening comprises a one-way exhalation valve configured to permit air exhaled into the housing to exit the housing upon exhalation at the first opening , and characterised in that a cross-sectional area of the second opening is selectively adjustable to control a resistance to the flow of air therethrough. <EOS>