Closed loop control in a piston ventilator

In a piston ventilator having a piston motor for driving a piston to deliver gas at a gas pressure and flow to a patient circuit, a control circuit comprising:

• a pressure sensor coupled with the patient circuit and operable for sensing the gas pressure therein and for producing sensor signals representative thereof;
• a motor controller coupled with the piston motor for receiving motor control signals and for operating the piston motor in accordance therewith;
• and
• a digital processor under computer program control coupled with said motor controller and coupled with said pressure sensor for receiving and processing said pressure signals for determining the gas flow amount from said piston necessary so that said gas pressure substantially conforms to a predetermined set point pressure, and for producing motor control signals representative of said gas flow amount and delivering said motor control signals to said motor controller for driving said piston to produce said gas flow amount, said digital processor being programmed to determine said set point pressure as one of a plurality of sequential set point pressures on a pressure trajectory determined as a function of a predetermined rate of rise between a beginning pressure and a target pressure wherein said beginning pressure is the pressure in the patient circuit at the beginning of patient inspiration.