Expiratory limb for a breathing circuit

1. A limb for a breathing circuit comprising:

an inlet,

an outlet, and

an enclosing wall defining a substantially singular exhalation flow passage between said inlet and said outlet, at least a region of said enclosing wall being of a material that allows the passage of water vapour without allowing the passage of liquid water or respiratory gases

a water vapour flow path from said exhalation flow passage to ambient air through said material, and

wherein said limb is an expiratory limb of the breathing circuit.

2. A limb for a breathing circuit as claimed in claim 1 wherein said material is selected from:

(a) hydrophilic thermoplastics,

(b) perfluorinated polymers,

(c) woven treated fabrics.

3. A limb for a breathing circuit as claimed in claim 1 wherein said material is a perfluorinated polymer membrane.

4. A limb for a breathing circuit as claimed in claim 1 wherein said material is a hydrophilic polyester block copolymer.

5. A limb for a breathing circuit as claimed in claim 1 wherein said flow passage is a conduit and said region or regions is or are distributed over the length of said conduit.

6. A limb for a breathing circuit as claimed in claim 5 wherein said region or regions are elongate and run at least a substantial part of the length of said conduit.

7. A limb for a breathing circuit as claimed in claim 5 including a series of said regions spaced along the length of said conduit.

8. A limb for a breathing circuit as claimed in claim 5 wherein said conduit including said regions is extruded.

9. A limb for a breathing circuit as claimed in claim 8 wherein the entire of said extruded conduit is of a material that allows the passage of water vapour without allowing the passage of liquid water or respiratory gases.

10. A limb for a breathing circuit as claimed in claim 8 wherein said regions of a material that allows the passage of water vapour without allowing the passage of liquid water or respiratory gases are one or more longitudinal strips running the complete length of said conduit.

11. A limb for a breathing circuit as claimed in claim 5 wherein said conduit includes at least one helically wound polymer tape or strip, part or all of said strip being of a material that allows the passage of water vapour without allowing the passage of liquid water or respiratory gases, respective edges of adjacent turns of said strip being adjoining or overlapping and bonded.

12. A limb for a breathing circuit as claimed in claim 11 including lateral reinforcement against crushing wherein said lateral reinforcement is a helical bead disposed over said adjoining or overlapping edges between turns of strip.

13. A limb for a breathing circuit as claimed in claim 5 wherein said conduit includes at least one longitudinal strip, part or all of said strip being of a material that allows the passage of water vapour without allowing the passage of liquid water or respiratory gases, said strip or strips extending parallel to the axis or said conduit, edges of said strip or strips adjoining or overlapping to form an enclosed tube and bonded.

14. A limb for a breathing circuit as claimed in claim 5 wherein said conduit is a blown film tube of a material that allows the passage of water vapour without allowing the passage of liquid water or respiratory gases.

15. A limb far a breathing circuit as claimed in any one of claims 10 to 14 including lateral reinforcement against crushing.

16. A limb for a breathing circuit as claimed in claim 15 wherein said lateral reinforcement includes a plurality of annular corrugations distributed over the length of said conduit.

17. A limb for a breathing circuit as claimed in claim 15 wherein said lateral reinforcement is a helical bead or a series of annular ring beads or ribs distributed over the length of said conduit.

18. A limb for a breathing circuit as claimed in claim 4 wherein said lateral reinforcement is a skeletal reinforcing structure within said conduit.