Human lung ventilator system

A ventilator system for use in assisting a patient to breathe, comprising:

• gas control means for mixing and regulating the gas that is to flow to a patient and receiving the gas that flows from the patient, the gas control means including
• flow control means for mixing together controllable amounts of two gases to form a mixed gas that flows to the patient, the flow control means including a separate, independently controllable custom-calibrated rotary flow control valve for each of the two gases,
• ventilation tube means extending to the patient for conducting the mixed gas to the patient and for receiving exhaled gas from the patient, and
• positive end expiration pressure means for controllably maintaining a minimum pressure in the exhaled gas;
• and
• controller means for independently controlling the two rotary flow control valves, wherein the controller means includes
• a calibration table for each of the rotary flow control valves, the calibration table including a correlation of gas flow rate as a function of rotary flow control valve position relative to a rotary flow control valve zero flow position, and
• means for automatically and periodically determining the rotary flow control valve zero flow position corresponding to a zero flow of each of the rotary flow control valves.