Nasal interface

1. A nasal interface configured to provide a flow of respiratory gases to a user in use, the nasal interface comprising:

a headgear including a strap configured to support the nasal interface against a user in use; and

a nasal cannula assembly including a nasal cannula body and a frame that provides support to the nasal cannula assembly, the nasal cannula assembly comprising:

first and second nasal prongs, each of the first and second nasal prongs configured to extend into a user's nostril in use;

a manifold including an inlet connected to a conduit configured to provide respiratory gases to the inlet, the manifold connecting the inlet to the first and second nasal prongs such that gases flow from the conduit, into the nasal cannula body through the inlet, and through the manifold to exit each of the first and second nasal prongs to enter the user's nostrils;

first and second side arms extending from first and second lateral sides of the nasal cannula assembly;

a bridging portion extending between and connected to the first and second side arms;

an expiratory flow passage defining an expiratory flow direction with a cross sectional shape transverse to the expiratory flow direction, the expiratory flow passage defined between the bridging portion and the inlet, the cross sectional shape of the expiratory flow passage having at least first, second, and third sides, the first side defined by the inlet and being concave, the second and third sides having straight portions adjacent to the first side; and

a filter material disposed in the expiratory flow passage.

2. The nasal interface according to claim 1 , wherein the nasal cannula body is resilient, flexible, and pliable, and wherein the filter material comprises noise suppression media configured to attenuate sound.

3. The nasal interface according to claim 1 , wherein the concave first side of the expiratory flow passage is spaced from the first side arm by the straight portion of the second side of the expiratory flow passage.

4. A nasal interface configured to provide a flow of respiratory gases to a user in use, the nasal interface comprising:

a headgear including a strap configured to support the nasal interface against a user in use; and

a nasal cannula assembly including a nasal cannula body and a frame supporting the nasal cannula body, the nasal cannula assembly comprising:

first and second nasal prongs, each of the first and second nasal prongs configured to extend into a user's nostril in use;

a manifold including an inlet connected to a conduit configured to provide respiratory gases to the inlet, the manifold connecting the inlet to the first and second nasal prongs;

first and second side arms extending from first and second lateral sides of the nasal cannula assembly; and

a bridging portion extending between and connected to the first and second side arms, the bridging portion and the inlet defining at least a portion of an expiratory flow passage, wherein the portion of the expiratory flow passage defines an expiratory flow direction with a cross sectional shape transverse to the expiratory flow direction, the inlet defining a concave portion of the cross sectional shape.

5. The nasal interface according to claim 4 , additionally comprising a filter material in the expiratory flow passage.

6. The nasal interface according to claim 5 , wherein the filter material comprises noise suppression media.

7. The nasal interface according to claim 6 , wherein the expiratory flow passage comprises at least first, second, and third sides, the first side comprising the concave portion, the second and third sides having straight portions adjacent to the first side.

8. The nasal interface according to claim 7 , wherein the expiratory flow passage is disposed between the first and second side arms.

9. The nasal interface according to claim 8 , wherein the inlet defines a portion of an inspiratory flow passage, the filter material being disposed in a portion of the expiratory flow passage that is parallel to the inspiratory flow passage.

10. The nasal interface according to claim 7 , wherein the first side arm is connected to the bridging portion at a first connection point positioned adjacent a lateral side of the expiratory flow passage.

11. The nasal interface according to claim 5 , wherein the filter material is configured to attenuate sound.

12. The nasal interface according to claim 4 , wherein the nasal cannula body is pliable, resilient, and flexible.

13. The nasal interface according to claim 4 , wherein the manifold connects the inlet and the first and second nasal prongs such that gases flow into the nasal cannula body through the inlet, through the manifold to each of the first and second nasal prongs and to enter the user's nostrils.

14. A nasal interface configured to provide a flow of respiratory gases to a user in use, the nasal interface comprising:

a nasal cannula assembly comprising:

first and second nasal prongs, each of the first and second nasal prongs configured to extend into a user's nostril in use;

first and second side arms extending from first and second lateral sides of the nasal cannula assembly;

a bridging portion extending between and connected to the first and second side arms; and

an expiratory flow passage defined at least in part by a portion of the bridging portion extending between the first and second side arms, the expiratory flow passage defining an expiratory flow direction with a cross sectional shape transverse to the expiratory flow direction, a portion of the cross sectional shape being concave.

15. The nasal interface according to claim 14 , additionally comprising a filter material in the expiratory flow passage.

16. The nasal interface according to claim 15 , wherein the filter material comprises noise suppression media.

17. The nasal interface according to claim 14 , wherein the nasal cannula assembly comprises a cannula body and a frame including an inlet connected to a conduit configured to provide respiratory gases to the inlet.

18. The nasal interface according to claim 14 , wherein the first and second side arms comprise a flexible material.

19. The nasal interface according to claim 17 , wherein the expiratory flow passage is defined between the bridging portion and the inlet.

20. The nasal interface according to claim 17 , wherein the expiratory flow passage is defined by both the bridging portion and the inlet.

21. The nasal interface according to claim 15 , wherein the nasal cannula assembly comprises an inlet defining a portion of an inspiratory flow passage, the filter material being disposed in a portion of the of the expiratory flow passage that is parallel to the inspiratory flow passage.

22. The nasal interface according to claim 15 , wherein the filter material is configured to attenuate sound.