Patient interface

1. A patient interface comprising:

a plenum chamber pressurisable to a therapeutic pressure of at least 6 cmH 2 O above ambient air pressure, said plenum chamber including a plenum chamber inlet 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 form a seal with a region of the patient's face surrounding an entrance to the patient's airways, 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 to provide a force 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 overlies a region of the patient's head superior to an otobasion superior of the patient's head in use; and

a vent structure 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 patient interface is configured to allow the patient to breath from ambient through their mouth in the absence of a flow of pressurised air through the plenum chamber inlet port, or the patient interface is configured to leave the patient's mouth uncovered,

wherein the seal-forming structure further comprises a patient-contacting surface configured to engage the patient's facial skin to form a seal and a posterior opening formed in the patient-contacting surface, the posterior opening configured to provide the flow of air at said therapeutic pressure to the patient's nares, and

wherein the seal-forming structure includes a support structure extending from a first location on the patient contacting surface to a second location on an interior surface of the seal-forming structure, the support structure and the interior surface forming a continuous loop, and

wherein a superior portion of the seal-forming structure is structured to engage the patient's nose inferior to the patient's nasal bone.

2. The patient interface of claim 1 , wherein the seal-forming structure further comprises an anterior opening formed in a non-patient contacting surface and an anterior tie that spans the anterior opening, and

wherein a first end of the support structure is connected to the anterior tie.

3. The patient interface of claim 2 , wherein the seal-forming structure further comprises an edge bounding the posterior opening in the patient contacting surface, and

wherein a second end of the support structure is connected to the patient contacting surface at a superior region of the edge.

4. The patient interface of claim 1 , wherein the support structure has a length in an undeformed state that is greater than a linear distance from the first location to the second location.

5. The patient interface of claim 1 , wherein the support structure is configured to be positioned adjacent to or in contact with the patient's columella during use.

6. The patient interface of claim 1 , wherein the support structure is curved along a longitudinal axis of the support structure in an undeformed state.

7. The patient interface of claim 1 , wherein the support structure has a different thickness than the patient-contacting surface.

8. The patient interface of claim 1 , wherein the support structure is thicker than the patient-contacting surface.

9. The patient interface of claim 1 , wherein the support structure does not extend completely across the posterior opening.

10. The patient interface of claim 1 , wherein the seal-forming structure at least partly forms a gas chamber, and

wherein in an undeformed state the support structure extends into the gas chamber.

11. The patient interface of claim 1 , wherein the support structure has a variable thickness in a longitudinal direction.

12. The patient interface of claim 1 , wherein the support structure has an increased thickness adjacent the first location and/or the second location.

13. The patient interface of claim 1 , wherein a portion of the support structure is curved away from the patient's nose along a longitudinal axis of the support structure in an undeformed state.

14. The patient interface of claim 1 , wherein the seal-forming structure further comprises an undercushion that supports the patient contacting surface.

15. The patient interface of claim 14 , wherein an inferior portion of the seal-forming structure includes the undercushion and the superior portion of the seal-forming structure does not include the undercushion.

16. The patient interface of claim 14 , wherein the undercushion is structured to only support the patient contacting surface against the patient's lip superior.

17. The patient interface of claim 1 , wherein the superior portion of the seal-forming structure is structured to engage the patient's nose inferior to the patient's pronasale.

18. The patient interface of claim 1 , wherein an inferior portion of the seal-forming structure is structured to engage the patient's lip superior such that the seal-forming structure does not extend beyond the lip superior to the patient's upper vermilion.