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 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 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 therein to define a first chamber in communication with the positive pressure line and a second chamber in communication with the vacuum line. <EOS>