Positioning and stabilising structure for a patient interface

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 a 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 a patient's respiratory cycle, while the patient is sleeping, to ameliorate sleep disordered breathing;

• said patient interface comprising:
• a plenum chamber pressurisable to a therapeutic pressure of at least 6 cmH2O 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 a 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 an entrance to 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 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 air, 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 breathe from the ambient air through the patient's mouth in the absence of the flow of air through the plenum chamber inlet port, or the patient interface is configured to leave the patient's mouth uncovered;
• wherein the positioning and stabilising structure comprises:
• a knitted ring strap portion having a superior portion configured to overlay the parietal bones of the patient's head in use and having an inferior portion configured to overlay or lie inferior to the occipital bone of the patient's head in use, the ring strap portion defining a loop and having an inside periphery and an outside periphery;
• and
• a pair of upper strap portions, each configured to connect between the ring strap portion and a cushion assembly in use on a respective side of the patient's head superior to the otobasion superior;
• wherein the ring strap portion comprises a first knit structure forming a first portion extending along at least a portion of the outside periphery of the ring strap portion,
• wherein the ring strap portion comprises a second rigidised knit structure forming a second rigidised portion provided proximate the inside periphery of the ring strap portion, and
• wherein the first knit structure is a different knit structure than the second rigidised knit structure, and the first portion has increased stretchability as compared to the second rigidised portion.