Oxygen blending in a piston ventilator

A method of blending oxygen with breathable gas in a piston ventilator comprising the steps of:

• providing a pressurized source of oxygen and a piston ventilator, said ventilator including a piston and cylinder assembly having a reciprocating piston shiftable within a cylinder during a retracting gas intake stroke and a protracting gas expelling stroke to define therebetween a variable volume chamber, a first path for fluidically connecting said oxygen source to said piston and cylinder assembly to deliver oxygen to said chamber, said first path including a flow sensor and a first oxygen control valve, a patient circuit located fluidically downstream from said piston and cylinder assembly for delivering breathable gas to a patient, and a controller connected to said piston and cylinder assembly, said flow sensor and said first control valve;
• retracting said piston within said cylinder to intake breathable gas into said chamber;
• monitoring the position of said piston within said cylinder during retraction;
• delivering a signal to said controller from said piston and cylinder assembly representative of said position of the piston;
• delivering oxygen from said source through said first path to said chamber of said piston ventilator during retraction of said piston;
• monitoring a flow of oxygen past said flow sensors along said first path;
• delivering a signal to said controller from said flow sensor representative of an amount of oxygen flowing past the flow sensor;
• calculating in said controller the amount of oxygen delivered to said chamber of said piston and cylinder assembly from said first path during retraction of the piston based on said signal from said flow sensor;
• comparing said calculated amount of delivered oxygen to a preselected value corresponding to a target amount of oxygen desired to be delivered to said piston and cylinder assembly based on the piston position signal and calculating a difference between the calculated amount and the preselected value;
• generating a control signal in said controller corresponding to said calculated difference and delivering said control signal to said oxygen control valve;
• and
• adjusting the flow of oxygen to be delivered to said chamber through said oxygen control valve responsive to said control signal.