A CPAP system comprising: a mask provided to a patient in use, the mask including a breathing chamber and an inlet port; a flow generator in communication with the mask; and a positive pressure line connected to the inlet port and configured to provide positive pressure air from the flow generator to the mask; characterized in that: the mask comprises an access port, the CPAP system further comprises a vacuum or return line connected to the access port and provided to actively extract gas exhausted by the patient, wherein the positive pressure line includes an air delivery tube, and the vacuum or return line includes a relatively smaller tube which is spirally wound around the perimeter of the air delivery tube, the CPAP system further comprises a vent outlet in communication with the vacuum or return line to vent the gas exhausted by the patient, the vent outlet provided at a location that is remote from the mask, wherein the mask includes a nozzle assembly including a pair of nozzles provided to respective nares of the patient in use, and wherein the nozzle assembly includes a first end portion that is closed and a second end portion provided with an elbow, the nozzle assembly including a main body having a baffle (87, 87a) therein to define a first chamber in communication with the positive pressure line and a second chamber in communication with the vacuum line. a mask provided to a patient in use, the mask including a breathing chamber and an inlet port; a flow generator in communication with the mask; and a positive pressure line connected to the inlet port and configured to provide positive pressure air from the flow generator to the mask; characterized in that: the mask comprises an access port, the CPAP system further comprises a vacuum or return line connected to the access port and provided to actively extract gas exhausted by the patient, wherein the positive pressure line includes an air delivery tube, and the vacuum or return line includes a relatively smaller tube which is spirally wound around the perimeter of the air delivery tube, the CPAP system further comprises a vent outlet in communication with the vacuum or return line to vent the gas exhausted by the patient, the vent outlet provided at a location that is remote from the mask, wherein the mask includes a nozzle assembly including a pair of nozzles provided to respective nares of the patient in use, and wherein the nozzle assembly includes a first end portion that is closed and a second end portion provided with an elbow, the nozzle assembly including a main body having a baffle (87, 87a) therein to define a first chamber in communication with the positive pressure line and a second chamber in communication with the vacuum line. the mask comprises an access port, the CPAP system further comprises a vacuum or return line connected to the access port and provided to actively extract gas exhausted by the patient, wherein the positive pressure line includes an air delivery tube, and the vacuum or return line includes a relatively smaller tube which is spirally wound around the perimeter of the air delivery tube, the CPAP system further comprises a vent outlet in communication with the vacuum or return line to vent the gas exhausted by the patient, the vent outlet provided at a location that is remote from the mask, wherein the mask includes a nozzle assembly including a pair of nozzles provided to respective nares of the patient in use, and wherein the nozzle assembly includes a first end portion that is closed and a second end portion provided with an elbow, the nozzle assembly including a main body having a baffle (87, 87a) therein to define a first chamber in communication with the positive pressure line and a second chamber in communication with the vacuum line.