Plenum chamber insert for patient interface

A patient interface comprising:

• a plenum chamber pressurisable to a therapeutic pressure of at least 4 cmH2O greater than ambient air pressure, said plenum chamber including a plenum chamber port sized and structured to receive a flow of air at the therapeutic pressure for breathing by a patient;
• a seal-forming structure constructed and arranged to contact and seal against a region of the patient's face surrounding an entrance to the patient's airways, said seal-forming structure having a hole therein such that the flow of air at said therapeutic pressure is delivered to at least the patient's nares, the seal-forming structure constructed and arranged to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use;
• a positioning and stabilising structure configured to hold the seal-forming structure in a therapeutically effective position on the patient's head, the positioning and stabilising structure comprising a tie, the tie being constructed and arranged so that at least a portion of the tie overlies a region of the patient's head superior to the patient's corresponding otobasion superior in use;
• a plenum chamber insert configured to be positioned and retained within the plenum chamber and between the entrance to the patient's airways and the plenum chamber port;
• and
• a vent structure configured to allow a continuous flow of gases exhaled by the patient from an interior of the plenum chamber to ambient, said vent structure being sized and shaped to maintain the therapeutic pressure in the plenum chamber in use;
• wherein the plenum chamber insert has a plenum chamber insert port positioned in pneumatic communication with the plenum chamber port such that the flow of air at the therapeutic pressure passes through the plenum chamber insert port after passing through the plenum chamber port;
• wherein the plenum chamber insert has an exterior surface configured to be positioned adjacent to an interior surface of the plenum chamber;
• wherein when the plenum chamber insert is positioned and retained within the plenum chamber, a radial channel is formed by the interior surface of the plenum chamber and the exterior surface of the plenum chamber insert such that gas is able to pass between a patient-proximal side of the plenum chamber insert and a patient-distal side of the plenum chamber insert via the radial channel during use;
• and
• wherein the patient interface is configured to allow the patient to breathe from ambient through their mouth in the absence of a flow of pressurised air through the plenum chamber port, or the patient interface is configured to leave the patient's mouth uncovered.