Directional thermistor assist sensing

In a respiratory ventilator, of the type having means for providing a predetermined respiratory reference pressure and means for providing a respiration assist cycle for a patient, a mechanism for controlling said assist cycle providing means, comprising:

• a housing having a chamber with first and second compartments;
• a restricted-diameter sensing tube adapted to communicate a patient-induced respiratory pressure to said first compartment;
• means for fluidly communicating said reference pressure to said second compartment;
• diaphragm means, in said chamber, for (a) dividing said chamber into said first and second compartments, and (b) providing a high-velocity, low volume flow of gas through said sensing tube in response to a patient-induced pressure differential between said first and second compartments, said flow of gas being in a first direction in response to an inhalation-induced pressure differential and in a second direction in response to an exhalation-induced pressure differential, the velocity and volume of said flow of gas being determined, at least substantially in part, by the restricted diameter of said sensing tube;
• temperature sensitive means in said sensing tube for producing variable electrical output signals in response to temperature changes in said sensing tube;
• heating means located in said sensing tube substantially adjacent to said temperature sensitive means for providing a reference temperature and producing first and second temperature in said sensing tube around said temperature sensitive means and thereby, producing first and second electrical signals, respectively, in response to the flow of gas in said first and second directions past said temperature sensitive means and heating means;
• discriminating means receiving said first and second electrical output signals and producing a triggering signal having a first value in response to said first electrical output signal and a second value in response to said second electrical output signal;
• and
• control means, receiving said triggering signal, for actuating said assist cycle providing means in response to said first value of said triggering signal, and for blocking the actuation of said assist cycle providing means in response to said second value of said triggering signal.

In a respiratory ventilator of the type having means for providing a respiratory assist cycle for a patient, and means for providing a predetermined respiratory reference pressure, a mechanism for controlling said assist cycle providing means, comprising:

• breathing conduit means adapted for fluid communication with the breathing passages of said patient;
• a first conduit fluidly communicating with said breathing conduit means and receptive to patient-induced inhalation and exhalation pressures therein;
• a second conduit receptive to said reference pressure;
• a restricted diameter sensing tube having a first end in fluid communication with said first conduit;
• pressure-sensitive means, coupled between a second end of said sensing tube and said second conduit, for producing a high velocity, low volume flow of gas through said sensing tube in a first direction in response to a first patient-induced pressure differential between said first and second conduits of a value representing the initiation of an inhalation effort by said patient, and in a second direction in response to a second patient-induced pressure differential between said first and second conduits representing the initiation of an exhalation effort by said patient, the velocity and volume of said flow of gas being determined, at least substantially in part, by the restricted diameter of said sensing tube;
• fluid flow responsive means in said sensing tube for producing a first output signal having a first predetermined output level in response to gas flow in said first direction and a second output signal having a second predetermined output level different from said first predetermined output level in response to gas flow in said second direction;
• discriminating means, receptive to said first and second output signals, for producing an enabling signal in response to said first output signal and a blocking signal in response to said second output signal;
• control means for actuating said assist cycle providing means in response to said enabling signal, and for blocking the actuation of said assist cycle providing means in response to said blocking signal.