Patent ID: 7066177

Claim:
An exhalation valve for use with an exhalation port of a respiratory circuit, the exhalation valve comprising: a hermetically sealed gas chamber, a gas inlet for supplying gas to the gas chamber, and a membrane of flexible material defining at least part of a wall of the gas chamber, the membrane being situated, in use, adjacent to the exhalation port, and the membrane being deformable by a change in the pressure differential between the gas within the gas chamber and the gas within the exhalation port between an inoperative configuration and an operative configuration in which the membrane restricts the flow of gas from the exhalation port to a greater extent than in said inoperative configuration, wherein the membrane is inherently planar but is sized and mounted within the exhalation valve such that the surface area of that part of the membrane that spans the space within which it is held is greater than the cross-sectional area of that space and deformation of the membrane to its operative configuration occurs substantially without increase of the surface area of the membrane.