Ventilation to a patient is provided in response to patient effort. The free flow of gas from a piston, or similar air source, in response to patient inhalation is detected, the instantaneous rate and volume of flow are measured and the measurements are used as control signals to a drive motor for the...http://www.google.es/patents/US5107830?utm_source=gb-gplus-sharePatente US5107830 - Lung ventilator device
