Method and apparatus for triggering the inspiratory phase of a respirator

• US 3,896,800 A
• Filed: 07/27/1973
• Issued: 07/29/1975
• Est. Priority Date: 07/27/1973
• Status: Expired due to Term

• Current Assignee: Anthony B. Cibulka
• Original Assignee: Anthony B. Cibulka
• Inventors: Cibulka, Anthony B.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Recla, Henry J.
• Application Number:
  US05/383,422
• Time in Patent Office: 732 Days
• Field of Search: 128/145.8,142,142.3,142.2,142.4,145.5,145.6,146.4,146.5,188,196,197,202
• US Class Current: 128/204.26
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/022 Control means therefor

Abstract

A method and apparatus are herein disclosed for triggering the inspiratory phase of a respirator in response to an inhalation attempt on the part of a patient being '"'"''"'"''"'"''"'"'breathed.'"'"''"'"''"'"''"'"' The invention is used on respirators where a positive end expiratory pressure is provided the patient at the end of his exhalation, that is, the patient is prevented from exhaling completely by the respirator retaining a net positive pressure within the patient'"'"''"'"'s lungs. To sense an inhalation attempt in such respirators and to simultaneously distinguish such an attempt from a leak in the patient'"'"''"'"'s breathing line, a patient trigger system is provided which generates an output signal in response to differential pneumatic inputs including a variable reference pressure input and a breathing line pressure input. The reference pressure input comprises a delayed breathing line pressure which is communicated to the triggering device during a portion of a patient'"'"''"'"'s exhalation phase so that the reference pressure closely approaches and tracks the breathing line pressure toward the end of the exhalation phase. At this point, an inhalation attempt even on the part of a feeble patient is operable to trigger the system which, in turn, shifts the respirator into an inspiratory assistor mode. The net operative result of such a triggering system is the generation of an appropriate output signal only in response to breathing line pressure decay '"'"''"'"''"'"''"'"'rates'"'"''"'"''"'"''"'"' associated with a patient'"'"''"'"'s attempt to inhale.

Claims

1. A method for triggering a respirator from an expiratory phase into an inspiratory phase to force gas to a patient through a breathing line comprising the steps of:

monitoring the pressure within the patient breathing line during the expiratory phase;

sensing the pressure within the patient breathing line during a period which commences a predetermined time period after commencement of the expiratory phase, and triggering the respirator into the inspiratory phase upon said patient'"'"''"'"'s attempting to breathe while preventing triggering due to pressure declines generated by leaks from said system, by effecting said triggering when a drop in said sensed pressure over a sub-interval of said period exceeds a minimum predetermined value; and

disabling said triggering irrespective of the level of said sensed pressure where the average rate of pressure decline over said subinterval is less than a second pre-determined value.

2. A method according to claim 1 wherein said step of sensing the rate of pressure drop is carried out during a period commencing 0.2 - 0.5 seconds after commencement of the expiratory phase and ending at the time the respirator is actuated into the inspiratory phase.

3. A method for triggering a respirator from an expiratory phase into the inspiratory phase to force gas to a patient through a patient breathing line comprising the steps of:

monitoring the pressure within the patient breathing line to provide a first monitored pressure, modifying the first monitored pressure with respect to time to provide a modified pressure whereby the modified pressure substantially tracks the first monitored pressure at low rates of change in the first monitored pressure, and sensing a predetermined minimum pressure differential between said first monitored pressure and said modified pressure to actuate the respirator into an inspiratory phase.

4. A method according to claim 3 including the step of providing a pressure differential responsive means operatively associated with the respirator and wherein:

said step of monitoring the first pressure within the patient breathing line includes the step of communicating the patient breathing line pressure with the pressure differential responsive means as a first input thereto, said step of modifying the first monitored pressure to provide a modified pressure includes the step of communicating the patient breathing line pressure with the pressure differential responsive means through a restricted passageway, as a second input thereto during a portion of the expiratory phase, and said step of sensing a predetermined minimum pressure differential to actuate the respirator into the inspiratory phase comprises the step of triggering the respirator by the operation of the pressure differential responsive means when the predetermined minimum pressure differential is sensed between the first input and the second input.

5. A pressure differential triggering system for shifting a respirator from an expiratory phase into an inspiratory phase in response to a patient'"'"''"'"'s effort to inhale, said system comprising:

a patient breathing line providing communication between the patient and the respirator, first and second enclosed chambers, a flexible diaphragm positioned between said first and second chambers and adapted to be flexed in response to a minimum predetermined pressure differential between the pressure in said first chamber and the pressure in said second chamber, means for communicating the pressure in said patient breathing line to said first chamber, modifying means adapted to sense the pressure in said patient breathing line and communicate as a reference pressure to said second chamber, a modified pressure which substantially tracks the patient breathing line presSure communicated to said first chamber, whereby said modified pressure in said second chamber lags the patient breathing line pressure in said first chamber with respect to time and rapid changes in pressure in said patient breathing line cause said minimum predetermined pressure differential between said first and second chambers to flex said diaphragm, and means to sense the flexing of said diaphragm to provide an inspiratory phase triggering signal to the respirator.

6. The improvement according to claim 5 wherein said modifying means communicates the modified pressure to the second chamber only during a portion of the expiratory phase and comprises a switching valve:

said switching valve being operated by a valve actuating means, and said valve actuating means being operable to place said switching valve into a position communicating the modified pressure with the second chamber during a period commencing 0.2 - 0.5 seconds after commencement of the expiratory phase and terminating upon the commencement of the next inspiratory phase.

7. The improvement according to claim 6 wherein said modifying means includes a pneumatic resistor restricting communicating the pressure sensed in the breathing line with the second chamber.

8. In a respirator for supplying gas to a patient and having inspiratory and expiratory phases, the respirator being adapted to retain a predetermined positive gas pressure within the patient at the end of the expiratory phase and having switching means to switch the respirator from the expiratory phase to the inspiratory phase, the improvement comprising:

a patient breathing line for supplying gas from the respirator to the patient;

means to monitor the pressure in the patient breathing line during the expiratory phase, means to sense the pressure in said patient breathing line during a period which commences a predetermined time period after commencement of the expiratory phase; and

means to trigger the respirator into the inspiratory phase upon said patient'"'"''"'"'s attempting to breathe, said means preventing triggering due to pressure declines generated by leaks from said system by effecting said triggering where a drop in said sensed pressure over a sub-interval of said period exceeds a minimum predetermined value; and

said means further, disabling said triggering irrespective of the level of said sensed pressure where the average rate of pressure decline over said sub-interval is less than a second predetermined value.

9. Apparatus for triggering a respirator from an expiratory phase into an inspiratory phase of a breathing cycle in reponse to an effort on the part of a patient to inhale comprising, in combination:

a patient breathing line communicating between the respirator and the patient, pressure differential responsive means, means for communicating the pressure in said breathing line to said pressure differential responsive means as a first input thereto, means for modifying the pressure in said patient breathing line and communicating the modified pressure to said pressure differential responsive means only during a portion of an expiratory phase, as a second input to said pressure differential responsive means, said modifying means retarding any pressure variations of the second input with respect to time, whereby the modified pressure comprising the second input lags out of phase with respect to the pressure in the breathing line comprising the first input, and means responsive to a predetermined minimum pressure differential between said first input and said second input in said pressure differential responsive means to trigger the respirator from the expiratory phase into the inspiratory phase.

10. Apparatus according to claim 9 wherein said pressure differential means comprises a housing, a flexible diaphragm separating said housing into a first chamber for receiving said first input and a second chamber for receiving said second input, And wherein said flexible diaphragm flexes in response to the predetermined rate of pressure drop in said first input to trigger the respirator into an inspiratory phase.

11. Apparatus according to claim 10 wherein said means for modifying the pressure in said patient breathing line and communicating the modified pressure to said pressure differential responsive means operates only during a portion of an expiratory phase and comprises a switching valve:

said switching valve being operated by a valve actuating means, and said valve actuating means being operable to switch said switching valve into a position communicating the second input with said pressure differential responsive means during a period commencing 0.2 - 0.5 seconds after commencement of the expiratory phase and terminating upon the commencement of the next inspiratory phase.

12. Apparatus according to claim 10 wherein said modifying means includes a pneumatic resistor restricting a gas passageway formed by said means for providing the second input to said pressure differential responsive means.

13. Apparatus according to claim 11 wherein said modifying means includes a pneumatic capacitor comprising a variable chamber in communication with said second chamber, said variable chamber adapted to be reduced in volume in response to a decrease in said second pressure input.