Regulation of a propellant gas flow

Apparatus for regulating the volume of a breathing gas delivered to a patient during an inhalation phase of a respiratory cycle, said respiratory cycle also having an expiration phase, said apparatus employing propellant gas from a propellant gas source and comprising:

• a propellant gas chamber;
• supply conduit means extending from the propellant gas source to said propellant gas chamber for providing a flow of propellant gas from the gas source to said propellant gas chamber;
• discharge conduit means for discharging propellant gas from said propellant gas chamber;
• a second gas chamber containing breathing gas and separated by a wall from said propellant gas chamber, said wall being movable responsive to the pressure of the propellant gas in said propellant gas chamber for altering the volume of said second gas chamber, said second gas chamber delivering breathing gas to the patient in the inhalation phase and receiving gas expired by the patient in the expiration phase as a result of the supply and discharge of propellant gas to and from the propellant gas chamber;
• a controllable pressure regulator interposed in said supply conduit means and having an input connected to the propellant gas source and an output coupled to said propellant gas chamber for discharging gas at a pressure determined by the pressure regulating action of said controllable pressure regulator;
• means interposed in said supply conduit means, said means sensing and responding to the flow of propellant gas through said supply conduit means for measuring a selected physical property of the flowing propellant gas indicative of the amount of gas delivered to said propellant gas chamber;
• and
• control means coupled to said controllable pressure regulator and said measuring means for operating said controllable pressure regulator responsive to the measurement of said selected physical property to regulate propellant gas pressure to establish a desired propellant gas flow magnitude to the propellant gas chamber during the inhalation phase.