Expiratory limb for a breathing circuit

1. A breathing circuit component comprising:

a patient end for connecting to a patient interface component,

a gases-source end comprising a gases-source end connector configured for receiving inspiratory gases and for delivering a bulk flow of expired gases thereto;

an outer conduit, insufficiently sturdy to be self-supporting, extending from the patient end to the gases-source end;

lateral reinforcement configured to support the outer conduit and reinforce the outer conduit against contraction;

longitudinal reinforcement, distinct from the lateral reinforcement, configured to support the outer conduit and reinforce the outer conduit against stretching, and

an inner conduit continuously extending within said outer conduit from the patient end to the gases-source end, thereby completely dividing said breathing circuit component into

an inner gases passageway, within said inner conduit, configured to carry the inspiratory gases from the gases-source end connector to a patient and

an outer gases passageway, between said inner conduit and said outer conduit, configured to carry the bulk flow of the expired gases from the patient to the gases-source end connector, the complete division of the outer gases passageway from the inner gases passageway configured to reduce the possibility of rebreathing expiratory gases by the patient during use,

wherein substantially all of said outer conduit comprises a material that allows the passage of water vapor from said outer gases passageway to ambient air without allowing the passage of liquid water or the bulk flow of the expired gases, such that the outer conduit reduces relative saturation in the bulk flow of the expired gases to reduce rain out along the outer conduit when in use.

2. The breathing circuit component of claim 1 wherein said outer conduit includes at least one helically wound polymer tape or strip, all of said at least one strip being of a material that allows the passage of water vapor without allowing the passage of liquid water or respiratory gases, respective edges of adjacent turns of said at least one strip being adjoining or overlapping and bonded.

3. The breathing circuit component of claim 2 , wherein said lateral reinforcement is a helical bead disposed over said adjoining or overlapping edges between said adjoining turns of said at least one strip.

4. The breathing circuit component of claim 1 wherein said material includes at least one longitudinal strip extending parallel to an axis of said outer conduit, edges of said at least one longitudinal strip adjoining or overlapping to form an enclosed tube and bonded.

5. The breathing circuit component of claim 1 , further comprising at least one of:

an inspiratory flow director for directing at least the bulk of an inspiratory air flow to said inner gases passageway, and

an expiratory flow director for directing at least the bulk of an expiratory flow to said outer gases passageway.

6. The breathing circuit component of claim 1 , wherein said longitudinal reinforcement includes a plurality of longitudinally extending threads spaced around the perimeter of the outer conduit, each of said plurality of threads aligned substantially parallel with the overall axis of said outer conduit.

7. The breathing circuit component of claim 1 , wherein the material is a hydrophilic polyester block copolymer.

8. The breathing circuit component of claim 1 , wherein the outer conduit further comprises a heater wire.

9. The breathing circuit component of claim 1 , wherein the inner conduit further comprises a heater wire.

10. The breathing circuit component of claim 1 , wherein the lateral reinforcement comprises a helical bead or a series of annular beads or ribs distributed over the length of the outer conduit.