Servo-controlled demand regulator for respiratory ventilator

A demand regulator for delivering breathable gas to a living subject capable of spontaneous respiration, comprising:

• first means for alternately receiving a supply of breathable gas from a source and delivering all or part of said received supply to said subject;
• second means for supplying a reference pressure;
• pressure transducing means, having first and second pressure inputs, and receptive to said reference pressure and the airway proximal pressure of said subject, for producing an electronic signal having a value proportional to the difference between said reference pressure and said airway proximal pressure, said electronic signal having a first polarity when said airway proximal pressure is less than said reference pressure in response to an inhalation effort by said subject, and a second polarity when said airway proximal pressure is greater than said reference pressure in response to an exhalation effort by said subject;
• third means, responsive to said electronic signal, for (a) producing a first output signal when said electronic signal has said first polarity and a value greater than a predetermined threshold value indicative of a threshold level differential between said airway proximal pressure and said reference pressure, said first output signal having a value substantially proportional to the value of said electronic signal, (b) producing a second output signal when said electronic signal has a value substantially equal to said threshold value, and (c) producing a third output signal when said electronic signal has said second polarity or when said electronic signal remains substantially at said threshold value for a predetermined time interval, whichever first occurs;
• fourth means, for (a) actuating said first means in a first mode in response to said first output signal so as to deliver gas to said subject at a rate which is substantially proportional to the absolute value of said first output signal, (b) ceasing the actuation of said first means in response to said second output signal, and (c) actuating said first means in a second mode in response to said third output signal so as to receive a fresh supply of gas from said source;
• an exhalation valve;
• first conduit means for transmitting gas from said first means to said subject during said first mode;
• second conduit means for transmitting exhaled gas from said subject to said exhalation valve during said second mode, said second conduit means being receptive to said airway proximal pressure;
• first pressure communication means for communicating said airway proximal pressure from said second conduit means to said first pressure input;
• and
• second pressure communication means for communicating said reference pressure from said second means to said second pressure input.

A respiratory ventilator, of the type including breathable gas supply means, exhalation valving means, conduit means adapted for transmitting breathable gas to a patient during inhalation and for transmitting exhaled gas from said patient to said exhalation valving means, and gas-delivery means for alternately receiving gas from said gas supply means during exhalation and delivering said received gas to said conduit means during inhalation, wherein the improvement comprises:

• first means for supplying a reference pressure;
• transducing means, having a first pressure input in fluid communication with said conduit means and a second pressure input in fluid communication with said first means, for producing an analog signal having a value proportional to the difference between said reference pressure and the pressure in said conduit means, said analog signal having a first polarity when said pressure in said conduit means is less than said reference pressure in response to an inhalation effort by said patient, and a second polarity when said pressure in said conduit means is greater than said reference pressure in response to an exhalation effort by said patient;
• first control means, responsive to said analog signal, for (a) producing a first control signal when said analog signal has said first polarity and a value greater than a predetermined threshold value indicative of a threshold level differential between said pressure in said conduit means and said reference pressure, said first control signal having a value substantially proportional to the value of said analog signal, (b) producing a second control signal when said analog signal has a value substantially equal to said threshold value, and (c) producing a third control signal when said analog signal has said second polarity or when said analog signal remains substantially at said threshold value for a predetermined time interval, whichever first occurs;
• second control means, responsive to said analog signal, for (a) producing a fourth control signal in response to selectable instances of said first polarity in said analog signal, and (b) substantially simultaneously disabling said first control means;
• and
• actuation means for (a) actuating said gas-delivery means in a first mode in response to said first control signal so as to deliver gas to said conduit means at a ratio which is substantially proportional to the absolute value of said first control signal, (b) ceasing the actuation of said gas-delivery means in response to said second control signal, (c) actuating said gas-delivery means in a second mode in response to said third control signal so as to receive a fresh supply of gas from said source, and (d) actuating said gas-delivery means in a third mode in response to said fourth control signal so as to deliver gas to said conduit means at a predetermined rate.

A method of operating a piston or a bellows to deliver breathable gas to a subject capable of spontaneous breathing during a period of inhalation by said subject, and to receive a fresh supply of said gas from a source thereof during a period of exhalation by said subject, said method comprising the steps of:

• (1) supplying a reference pressure;
• (2) comparing the airway proximal pressure of said subject to said reference pressure;
• (3) actuating said piston or bellows so as to deliver said gas to said subject at a rate which is substantially proportional to the difference between said airway proximal pressure and said reference pressure when said reference pressure exceeds said airway proximal pressure by at least a predetermined pressure differential indicative of an inhalation attempt by said subject;
• (4) actuating said piston or bellows so as to receive a fresh supply of gas from said source when said airway proximal pressure exceeds said reference pressure, thus indicating an exhalation effort by said subject;
• (5) selecting predetermined ones of said inhalation attempts in accordance with a predetermined program;
• and
• (6) actuating said piston or bellows so as to deliver said gas to said subject at a predetermined rate in response to the detection of said selected inhalation attempts.