Patient interface device

A patient interface for sealed delivery of a flow of air at a continuously positive pressure with respect to ambient air pressure to an entrance to the patient's airways including at least an entrance of a patient's nares, wherein the patient interface is configured to maintain a therapy pressure in a range of about 4 cmH2O to about 30 cmH2O above ambient air pressure in use, throughout the patient's respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing, said patient interface comprising:

• a seal-forming structure to form a pneumatic seal with the entrance to the patient's airways;
• a positioning and stabilising structure to maintain the seal-forming structure in sealing contact with an area surrounding the entrance to the patient's airways while maintaining a therapeutic pressure at the entrance to the patient's airways;
• a plenum chamber pressurised at a pressure above ambient pressure in use;
• a connection port for the delivery of the flow of breathable gas into the patient interface;
• and
• a device having a predetermined surface area comprising at least one aperture having a predetermined size;
• the device positioned along a flow path of breathable gas to physically interfere with the flow;
• wherein the predetermined size of the at least one aperture and the predetermined surface area of the device are selected such that a predetermined amount of breathable gas flows through the at least one aperture;
• and
• wherein the device is heat non-absorbent and moisture non-absorbent and the device changes the flow of breathable gas flowing towards a mucosal surface of the patient's airways from a turbulent flow to a laminar flow by directing the predetermined amount of breathable gas through the at least one aperture such that a rate of heat and water loss from the mucosal surface is reduced.