| 摘要 |
A device for providing a gas-air mixture to a patient in response to suction applied by the patient, comprising means defining an air inlet, a backward-facing step, an air passage for directing air past said backward-facing step, a non-return valve for controlling flow of air from said inlet to said air passage and a gas passage communicating with said air passage through at least one orifice adjacent to said backward-facing step.
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