Gas flow control method in a blower based ventilation system

A method of controlling a gas flow rate from a medical ventilator system, including the steps of:

• providing a medical ventilator having a variable speed blower, an air hose, an electronic control system, an air flow transducer and a pressure transducer;
• connecting the air hose of the medical ventilator to a patient's lungs;
• repeatedly blowing air from the running fan through the air hose and into the patient's lungs;
• monitoring the air flow through the air hose using the air flow transducer;
• monitoring the pressure within the air hose using the pressure transducer;
• calculating a desired fan speed using the electronic controller based upon signals from the air flow transducer and the pressure transducer;
• and
• adjusting the variable speed fan to the desired fan speed.

A method of controlling the rate of gas flow induced for inspiration by a fan including a fan outlet in a medical ventilator system, including the steps of:

• setting a target gas flow rate;
• setting a time span for the gas flow rate;
• calculating a first fan speed to induce the target flow rate within the time span;
• adjusting the fan to the first fan speed;
• measuring a first gas flow rate at the fan outlet at the conclusion of the time span;
• measuring a first back pressure at the fan outlet at the conclusion of he time span;
• calculating a second fan speed based on the first flow rate and the first back pressure to correct for the difference between the first flow rate and the target gas flow rate;
• and
• adjusting the fan to the second fan speed.

A system for controlling the gas flow induced by a medical ventilator comprising:

• a variable speed motor connected to a fan having a fan outlet;
• a first transducer configured to measure the pressure at the fan outlet and to generate an electrical signal indicative of the pressure;
• a second transducer configured to measure the rate of gas flow at the fan outlet and to generate an electrical signal indicative of the gas flow rate;
• an electronic feedforward control circuit configured to receive the electrical signal from the first transducer and to generate a signal indicative of an adjustment to the speed of the variable speed motor;
• an electronic feedback control circuit configured to receive the electrical signal from the second transducer and to output a signal indicative of an adjustment to the speed of the variable speed motor;
• and
• an electronic motor controller configured to vary the speed of the variable speed motor and to receive the signals generated by the feedforward controller and the feedback controller.