Heat and moisture exchanger for patient interface

A patient interface comprising:

• a plenum chamber pressurisable to a therapeutic pressure of at least 4 cmH2O above ambient air pressure by a flow of air at the therapeutic pressure for breathing by a patient, the plenum chamber comprising a main frame and a removable frame that is removably connectable to the main frame, the main frame comprising two plenum chamber connectors, and each of the plenum chamber connectors being positioned on a corresponding lateral side of the main frame and configured to receive the flow of air at the therapeutic pressure;
• a seal-forming structure connected to the plenum chamber, the seal-forming structure being constructed and arranged to seal with a region of the patient's face at least partly surrounding an entrance to the patient's airways, the seal-forming structure having a sealing flange and a hole in the sealing flange to deliver the flow of air at the therapeutic pressure to at least the patient's nares, and the seal-forming structure being constructed and arranged to maintain the therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use;
• a positioning and stabilising structure comprising two conduits configured to hold the seal-forming structure in a therapeutically effective position on the patient's head, each of the conduits being configured to be positioned on a corresponding lateral side of the patient's head in use, and each of the conduits being configured to connect to a corresponding one of the two plenum chamber connectors;
• a vent structure comprising vent holes configured to allow a continuous flow of gas from an interior of the plenum chamber to ambient while the plenum chamber is pressurized by the flow of air at the therapeutic pressure and during inhalation, exhalation, and breath pause, and the vent holes being sized and shaped to maintain the therapeutic pressure in the plenum chamber in use;
• a material configured to adsorb water vapour from gases exhaled by the patient and desorb water vapour into the flow of air at the therapeutic pressure, the material being attached to the removable frame such that the removable frame and the material are removable from the main frame together, and the material being shaped and dimensioned to be positioned within the plenum chamber, when the removable frame is removably connected to the main frame, such that at least a portion of the flow of air at the therapeutic pressure entering the plenum chamber from the two plenum chamber connectors passes through the material before entering the patient's airways,
• wherein the vent holes are positioned such that, in use, a portion of the flow of air at the therapeutic pressure travels to ambient through the vent holes without passing through the material.