GAS MIXING APPARATUS FOR A VENTILATOR

摘要

The gas mixing apparatus (10) provides the components of a breathing gas for mixing at approximately ambient atmospheric pressure, and regulates the pressure of a selected gas to approximately ambient atmospheric pressure for mixing with air at ambient atmospheric pressure. The gas mixing apparatus (10) includes a piston (26) disposed within a pump chamber (12). A flow limiting inlet (46) controls introduction of a first selected gas such as oxygen for mixing with a second selected gas such as air. The pressure of the first selected gas is limited to an acceptable maximum pressure, so that even if a valve (54) for admitting the first selected gas for mixing at ambient pressure fails, breathing gas will not be provided at an excessive pressure. A demand valve (68) is alternatively provided for reducing the pressure of the first selected gas supplied before mixing, but a pressure sensor (74) is also provided downstream of the demand valve (68) for detecting failure of the demand valve (68), to shut off the supply of the first selected gas to prevent overpressurization.