A pressure driver for a ventilation system comprises a gas source, an inspiration flow control valve and a patient pressure sensor to form a closed loop control system. The inspiration flow control valve may be mounted within a housing and is operative to open and close in response to patient pressure measurements in order to produce a desired pressure at the patient. The pressure driver may further include a mixture control for allowing selective adjustment of the oxygen concentration in pressurized gas delivered to the patient. An oxygen mixer is connected between the gas source and the mixture control and is operative to deliver the desired mixture of oxygen and air to the inspiration flow control valve for delivery to the patient. An oxygen sensor monitors the oxygen concentration in the gas provided by the oxygen mixer.
