US3834382A

US3834382A - Fluidic respirator control system with patient triggering response means

Info

Publication number: US3834382A
Application number: US00286293A
Authority: US
Inventors: W Lederman; A Pawlak
Original assignee: Johnson Service Co
Current assignee: Johnson Service Co; Johnson Controls International Inc
Priority date: 1972-09-05
Filing date: 1972-09-05
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10

Abstract

A respirator unit has patient triggering control means with an isolating fluidic repeater connected to an operational amplifying circuit employing a summing impact modulator and a feedback network. Two cascaded stages of differentiation connect the amplifying circuit to an output logic gate for controlling a control oscillator to initiate an inhalation cycle. An inhibit circuit includes a pair of pressure taps connected to spaced points on the flow line. Fluidic repeaters connect the taps to a fluidic comparator. A fluidic time delay means is connected to the output of the comparator and connected in common to the output logic gate to inhibit the triggering control means during the exhalation cycle. The fluidic oscillator includes a flip-flop circuit with output lines interconnected to control the exhalation and inhalation valves between the fluid air-oxygen mixer source and the patient. Inhalation and exhalation time adjustment means are provided. A positive pressure cutoff circuit includes a fluidic amplifier which produces a logic on-off type signal in accordance with the magnitude of patient pressure and is connected to the oscillator to terminate the inhalation cycle and initiate the exhalation cycle. An automatic selection switch means is provided to selectively deactivate the inhalation and exhalation time adjustment, and the triggering control means to control the respirator operating mode.

Description

United States Patent 1191 Lederman et al.

[ Sept. 10, 1974 FLUIDIC RESPIRATOR CONTROL SYSTEM WITH PATIENT TRIGGERING RESPONSE MEANS [75] Inventors: Warren A. Lederman, Wauwatosa;

Alfred J. Pawlak, Milwaukee, both of Wis.

[73] Assignee: Johnson Service Company,

Milwaukee, Wis.

[22] Filed: Sept. 5, 1972 [21] Appl. No.: 286,293

[52] US. Cl. 128/145.8, 137/624.ll [51] Int. Cl A6lm 16/00 [58] Field of Search 128/1455, 145.6, 145.8,

[56] References Cited UNITED STATES PATENTS 5/1972 Peters 3,662,751 5/1972 Barclow .L 128/ 145.8 3,669,108 6/1972 Sundblom '128TF45I8 3,753,436 8/1973 Bird 128/1458 Primary ExaminerRichard A. Gaudet Assistant Examiner-G. F. Dunne Attorney, Agent, or Firm-Andrus, Sceales, Starke & Sawall [57] ABSTRACT A respirator unit has patient triggering control means with an isolating fluidic repeater connected to an operationalamplifying circuit employing a summing impact modulator and a feedback network. Two cascaded stages of differentiation connect the amplifying circuit to an output logic gate for controlling a control oscillator to initiate an inhalation cycle. An inhibit circuit includes a pair of pressure taps connected to spaced points on the flow line. Fluidic repeaters connect the taps to a fluidic comparator. A fluidic time delay means is connected to the output of the comparator and connected in common to the output logic gate to inhibit the triggering control means during the exhalation cycle. The fluidic oscillator includes a flipflop circuit with output lines interconnected to control the exhalation and inhalation valves between the fluid air-oxygen mixer source and the patient. Inhalation and exhalation time adjustment means are provided. A positive pressure cutoff circuit includes a fluidic amplifier which produces a logic on-off type signal in accordance with the magnitude of patient pressure and is connected to the oscillator to terminate the inhalation cycle and initiate the exhalation cycle. An automatic selection switch means is provided to selectively deactivate the inhalation and exhalation time adjustment, and the triggering control means to control the respirator operating mode.

14 Claims, 3 Drawing Figures FLUIDIC RESPIRATOR CONTROL SYSTEM WITH PATIENT TRIGGERING RESPONSE MEANS BACKGROUND OF THE INVENTION This invention relates to a respirator control system and particularly to a fluidic control system havinga patient triggering means interconnected to permit control of the respirator in accordance with the breathing of the patient.

In the treatment of patients, particularly under certain emergency conditions, it is necessary to assist the breathing of the patient by providing a source of oxygen and air. Respirators are well-known and have been applied in inhalation therapy in emergency vehicles, doctors offices, clinics and hospitals to provide a mixture of air and oxygen to the patient under various controlled modes. A respirator control therefore desirably provides a plurality of different modes of operation to permit use of a single respirator for the various patients. In a first mode, normally identified as an assistor mode, the patients breathing cycle is detected and interconnected into the system to control the operation of the respiratory device. A second controller mode is also normally provided in which the respirator cycle is operated automatically and independently of the patients effort to breathe. Finally, a combined mode may respond to a patient who does not breathe voluntarily within a prescribed limit to create a forced breathing control cycle.

As a respirator system is basically a fluid supply system, the relatively recent fluidic art is particularly useful and adapted for a control of the respirator. Both private, governmental and institutional agencies and organizations have developed various control systems, many-of which include the above three modes of operation. In addition, they may provide a positive pressure cutoff feature to automatically terminate the inhalation phase of the breathing cycle at a selected inhalation pressure level. For example, in the assistor mode, the system may respond to the rate of change of the inhalation pressure such that the initial inhalation portion of the breathing cycle actuates the respirator to establish its inhalation operation.

A patients breathing pattern may be either positive or negative pressure breathing. Positive pressure breathing is identified with exhalation to a pressure above atmosphere or ambient, whereas negative pressure exhalation is identified with corresponding exhalation to a pressure slightly below atmosphere and ambiem, with creation of a slight vacuum condition in the patient. When a patient exhales, the ambient pressure thus will finally reach a steady state pressure level identified as the end expiratory pressure which will be somewhere within the negative to positive pressure range. Normally, the pressure is approximately within the range of a minus centimeters of water to a plug 10 centimeters of water. Patient triggering systems are interconnected with positive pressure breathing on either an intermittent or a continuous basis. In intermittent positive pressure breathing inhalator units, the patient exhales to an ambient or atmospheric pressure. However, exhalation pressures may include a range over a relatively negative to a positive exhalation presthe exhalation cycle. The pause may well produce a decrease in the ambient pressure during the exhalation cycle. If the triggering circuit responds to the pressure changes, the apparatus may respond to this pause and prematurely establish an inhalation cycle mode during actual exhalation. Although time delay means can be employed, breathing patterns are so erratic that it is very difficult, if not impossible, to adjust the time delay characteristic to accommodate the breathing of various emphysema patients and the like. Further, the respiratory apparatus obviously requires'the design of a very reliable system which can accurately sense the breathing cycle and provide the necessary reinforcements and assistance in a predetermined pattern.

SUMMARY OF THE PRESENT INVENTION The present invention is particularly directed to a sensitive, reliable fluidic respirator control and particularly to a control employing fluidic sensing and control means.

Generally, in accordance with the present invention the patient triggering control means is provided and interconnected to establish a control of the operation of the respirator in accordance with the patients breathing cycle and in particular based on the flow direction with respect to the auxiliary breathing apparatus. A flow direction means is interconnected to the main respirator system to establish a control signal in accordance with the direction of flow with respect to the patient. The'flow related signal inhibits a control means during the exhalation cycle to positively prevent the creation of an inhalation cycle. In a particularly novel and practical aspect of this invention, a pressure sensing means is coupled to the flow line and monitors the pressure drop between selected, spaced points within the flow line with the output of the sensing means connected to the patient triggering control means.

The patient triggering control means is also connected to such flow means and provides an output for actuating .the flow means in accordance with the movement of the patients breathing faculties with an interconnection between the sensing means and the patient triggering control means for selectively inhibiting such triggering control means during predetermined flow conditions.

In accordance with a more particular aspect of the present invention, the sensing flow line is connected to the respirator with a pair of pressure taps connected to spaced points on the flow line and with the pressure signals connected to a differential pressure response means, preferably a fluidic comparator connected to the taps by separate fluidic repeaters. Each fluidic repeater is a diaphragm unit which defines a dead-ended input chamber for positioning of a diaphragm with respect to an exhaust nozzle in an output chamber. The output chamber is also connected to a regulated supply such that the pressure in the output chamber is directly related to the position of the diaphragm. The diaphragm is further resiliently biased to a first level to establish a continuous positive output pressure signal regardless of the magnitude of the pressure in the flow line and the direction of the signal. The resilient setting further establishes a corresponding bias output level from the two repeaters in the absence of flow from or in the flow line. A fluidic amplifier or comparator preferably in the form of a summing impact modulator having a pair of opposed nozzles is connected to the output of the two fluidic repeaters. The output of the impact modulator is connected to a fluidic time delay means and a suitable logic means to establish an inhibit signal. This signal is applied to the triggering control means to inhibit the triggering control means during the exhalation portion of the cycle or the like.

The patient'triggering control means is also a fluidic circuit constructed in accordance with a further aspect of is n s g w i s t a is teasers! in qgnr 'rT c fed to sense the breathing cycle of the patient by connection to the respirator output system. The fluidic repeater isolates the respirator from the fluidic control system and maintains a positive output pressure signal over the complete operating range of the respirator. The output of the fluidic repeater is amplified and differentiated to sense the rate of change of the patient conditions with the output interconnected to establish the inhibit signal.

In a particularly novel and satisfactory system, the output of the fluidic repeater is connected to an operational amplifying circuit including a summing impact modulator and in particular to one of the nozzles of a summing impact modulator. A feedback network is connected to the opposite nozzle of the impact modulator and to the output of the modulator through a diaphragm amplifier. This system is preferably connected such that under steady state conditions the feedback network is such as to actuate the diaphragm amplifier to establish a maximum output. The output magnitude or level is established by the resistive network of the feedback unit or the feedback circuit. A drop in the input signal as a result of a drop in ambient pressure from the patient reduces the output of the impact modulator allowing the diaphragm amplifier to reduce the output pressure accordingly. The amplified output is transmitted to the differentiator of the circuit.

The differentiator means is preferably two stages of differentiation and each is similarly constructed with a summing impact modulator having opposed nozzles connected in common through suitable resistors as an input and with a differentiating capacitor means con nected in the connection to one of the nozzles. The two stages of differentiation have been found to be quite significant in providing reliable response and in particular in minimizing and establishing a constant sensitivity over the negative to positive pressure range of ambient pressures. Thus, the initial or DC level changes with ambient pressure levels. Even though the operational amplifier has a constant gain, the magnitude of the pressure will vary and thus increase, for example, with increased ambient. The output of the differentiator drives a logic gate having a fixed cutoff pressure level and, consequently, a DC shifting level could result in the corresponding triggering signal. The second differentiator significantly reduces the variation in DC level or the effect of the variation of the DC level.

The basic respirator control can advantageously employ a variable pulse width fluidic oscillator having a pair of NOR gate means interconnected to define a flipflop circuit with output lines interconnected to control the exhalation and inhalation valves between the fluid air-oxygen mixer source and the patient. 'A separate in halation time adjustment means and exhalation time adjustment means are provided and each includes a capacitive timing means and adjustable restrictor to ground to permit variation and adjustment of the particular time. The output of the time adjustment means is connected to the input of a related gate of the flipflop oscillator circuit to provide the desired flip-flop response time. In addition, the output of the triggering control means is interconnected to the one gate such that when the patient inhales slightly the associated triggering signal is set or reset with the flip-flop circuit thereby establishing an inhalation cycle.

In addition, apositive pressure cutoff circuit includes a fluidic amplifier preferably a summing impact modulator having a nozzle connected to sense the flow and the direction of flow. An opposing nozzle or input of the fluidic comparator is connected to an adjustable set pressure source such that the output of the amplifier is a logic on-off type signal in accordance with the magnitude of the patient pressure. The output is suitably amplified and connected to the said gate of the oscillator. It thus responds to a particular inhalation pressure to set the flip-flop circuit or to trigger the oscillator to terminate the inhalation cycle and initiate the exhalation cycle for a portion of the cycle. The system is provided with an automatic selection switch means in the form of a suitable fluid pulse signal generator which is selected having a plurality of output lines selectively generating signals to establish an assister mode, a controller mode or an assister-controller mode. Thus, in the assister mode the output is connected to deactivate the automatic inhalation and exhalation time adjustment controls with the patient initiating the inhalation cycle through the patient triggering control. The inhalation phase of the cycle is terminated by the positive pressure cutoff circuit. The patient exhales and in response to the patients demand, the respirator subsequently recycles to establish the inhalation phase of the cycle. In the controller mode, the patient triggering or control means is inhibited and the system operates under the complete control of the oscillator with the inhalation and exhalation time adjustment controls. The positive pressure cutoff circuit is still active when provided. Thus, automatic respiration is achieved by the low frequency variable pulse width oscillator. The oscillator provides for control of the respiration rate and the inhalation and exhalation ratio through the timing adjustments. The inhalation time of the oscillator thus mainly functions as an override control such that in the case of a malfunction wherein the set pressure is not attained, the oscillator will automatically cycle.

The third combination mode is an interconnected active combination of the controller and assister modes. Thus, a patient normally controls the breathing cycle so long as he is able. If he is unable, however, the oscillator will take over to assert and maintain automatic operation. Thus, in this mode the pulse signal generator is essentially turned off and no circuits are inhibited.

Further, the invention is found to provide reliable fluidic control or respirator control and in particular a fluidic control system which will operate over a wide range including negative and positive ambient or exhalation breathing pressures and, furthermore, responds to various breathing rates in a reliable manner such that it can be readily applied to special inhalation therapy such as that required by emphysema patients and the like.

BRIEF DESCRIPTION OF THE DRAWINGS The drawingsfurnished herewith illustrate the best mode presently contemplated by the inventor for carrying out the subject invention with the above advantages and features clearly disclosed as well as others which will be readily understood by those skilled in the art from the description of such embodiment.

In the drawings:

FIG. 1 is a block diagram of a respirator unit constructed in accordance with the teaching of the present invention;

FIG. 2 is a fluidic circuit schematic of the portion of the system shown in FIG. 1 illustrating the fluidic oscillator and positive pressure cutoff in a preferred construction of this invention; and

FIG. 3 is a fluidic circuit schematic of the portions illustrating the flow sensing means and the patient control means in a preferred construction of the present invention.

DESCRIPTION OF ILLUSTRATED EMBODIMENT Referring to the drawing and particularly to FIG. 1, a respirator 1 is diagrammatically illustrated connected to provide air to a patients lungs 2 from a conventional air-oxygen mixer source 3. The flow means includes a connecting inhalation control valve 4 which may be of any suitable construction such as a conventional pneumatically responsive mushroom valve. An exhalation valve 5 is connected downstream of the valve 4 and couples the flow means to the lung 2 with a regulated discharge means for exhaust of expired air from lung 2.

The valve means 4 and 5 are operated to establish posi-- tive supply of the air-oxygen fluid medium from the mixer 3 to the lung 2 during one portion of the cycle identified as the inhalation portion of the breathing cycle, and conversely are actuated to permit exit of the fluid in the lung 2 during the opposite or exhalation portion via the exhalation valve 5. Such valving structure is well-known in the art and consequently has been diagrammatically illustrated and no further description thereof is given other than as required to thoroughly illustrate and describe the preferred illustrated embodiment of the present invention.

Thus, the valves 4 and 5 are actuated from the output of an oscillator 6 which includes

individual output lines

7 and 8 connected respectively to the valves 4 and 5. This provides for the alternate and the opposite operation of the

valves

4 and 4 to provide for the inhalation and exhalation cycling. A diaphragm amplifier 9 is shown connected in line 8 to provide sufficient pressure for reliable operation of the exhalation valve 5 in synchronism with the turning on and off of the fluid source 3. A positive pressure cutoff circuit 10 is connected via a line 11 to the oscillator 6. The cutoff circuit 10 is also connected via a sensing line 12 to the patient pressure tap associated with the valve 4 and thus provides an output signal directly in accordance with the magnitude of the patient pressure with respect to the lung 2. The cutoff circuit 10 is a pressure sensitive circuit which responds to a predetermined inhalation set pressure to establish an output signal at line 11 to terminate the inhalation cycle and automatically operate the system to open the valve 5 for the exhalation period or cycle. The inhalation phase of the cycle is initiated automatically by the oscillator 6 or in response to the output of a patient control means or trigger circuit means 14 having an input line 14a connected to the patient pressure tap and particularly in the illustrated embodiment of the invention to the common flow sensing line 12. The output of the patient control means 14 is connected as an input to the oscillator 6 via the line 13 which actuatesthe oscillator to provide signals at

lines

7 and 8 to initiate the inhalation phase of the cycle.

A selection switch unit 15 is connected to selectively connect the control means 14 into the circuit. Thus, the selection switch unit 15 may be a three-position pulse signal generator having a first position output terminal 16 connected to the oscillator 6. In this mode of operation, a signal deactivates the automatic cycling of the oscillator 6 and maintains the control from the control unit 14 and the positive oscillator cutoff unit 10. Thus, the patient initiates the inhalation phase of the cycle which is terminated by the unit 10 after which the patient exhales. The inhalation cycle is again triggered by thecontrol unit 14.

The selection unit 15 has a second position output terminal 17 which is connected to deactivate the patient control unit 14. In this mode of operation, the patient control unit 14 is cut out while the oscillator 6 is allowed to function in an automatic and repetitive manner to continuously cycle for inhalation and exhalation.

In a third position, the selection switch unit 15 is set to a dead output terminal 18 and neither of the circuits 6 or 14 are inhibited. Consequently, the system operates under a joint control, with the patient providing the control to the extent possible. In the event the patient cannot or does not control the cycle, the oscillator 6 automatically establishes a corresponding inhalationexhalation cycling.

In addition and in accordance with a teaching of the present invention, a flow direction sensor 19 is interconnected to the flow line 12 through a pair of spaced coupling lines 20-20a to continuously monitor the direction of flow through the line 12 by monitoring the pressure drop between the connecting points or positions. The output of the flow direction sensor 19 is connected via an output line 21' to the patient control unit 14 and is operative to inhibit the patient control unit 14 during a portion of the breathing cycle. In particular, the flow direction sensor is connected to inhibit the patients control unit 14 during the exhalation cycle. This is very significant when the unit is applied to inhalation therapy in which the patients breathing is erratic and relatively slow, such as emphysema patients and the like. As previously discussed, such patients exhale very slowly and may even pause during the exhalation which may be accompanied with a decrease in the ambient pressure and triggering of the patient triggering control unit 14 with premature initiation of a new inhalation cycle. Although timing means can be employed to insert a delay and thereby compensate for hesitations, the type, variety and lengthof hesitations are not uniform and it is very difficult and practically impossible to preadjust and select the magnitude of the time delay to accommodate breathing of various emphysema patients. The flow direction sensor 19 of the present invention however continuously monitors the portions of the breathing cycle with a full range of ambient pressures encountered in the usual respirator application.

Thus, the present aspirator as shown in block diagram in FIG. 1 can be applied as a general inhalation therapy applicator for standard and emergency procedures and will provide a reliable sensitive control for all normal applications. The system is preferably a pure fluidic control and includes an operating supply 22 of air or similar fluid medium for operating of the several components. The supply 22 is interconnected to the several active components through a pressure regulator valve 23 to establish highly regulated output pressures of a suitable'level for. the various components. Thus, the oscillator 6 and positive pressure cutoff unit are connected to the regulator valve 23 through a suitable adjustable pin valve 24 to produce a suitable pressure level for these components. In a practical application, this section is operated at relatively low pressures, for example, 2% psig. Similarly, an adjustable pin valve 25 in series with a pair of paralleled fixed resistors 26 are shown connecting the output of the regulator supply 23 to the flow direction sensor 19 and the patient control unit 14 to establish a suitable operating pressure, for example, 7 /2 psig. In addition, the three-way valve 27 has a supply connection to the output of the regulator 23 to produce a relatively high operating pressure of the order of 20 psig which is selectively applied to the air-oxygen mixer source 3 in synchronism with the establishment of the inhalation cycle. Thus, the valve includes an input control connected to the exhalation control line 8 via a line 27a. The exhalation valve 5 and the mixer source 3 are therefore operated in synchronism to provide for the desired inhalation-exhalation cycle connection of the respirator.

As more clearly shown in FIG. 2, the oscillator 6 is a variable pulse width generator producing a low frequency square wave output of opposite phase at the

lines

7 and 8. The illustrated oscillator 6 includes a setreset flip-flop unit 28 consisting of apair of multiple input NOR gates 29 and 30, with their outputs interconnected to each others inputs. The output of the gate 29 is connected directlyto the exhalation valve control line 8 and through a fluid inverting gate 31 to the inhalation control valve line 7. The

gates

29, 30 and 31 may be of any suitable construction, for example, as shown in U.S. Pat. No. 3,604,962.

The cycling of the oscillator is further controlled through a pair of time

adjustment feedback circuits

32 and 33 which, in the illustrated embodiment of the invention, respectively control the inhalation time and the exhalation time of cycle. Thus, each circuit is similarly constructed and that of the inhalation time 32 is described as providing an input signal or feedback signal to an input 34 of the gate 29. A capacitor 35 is connected to receive a signal from the output of the gate 29 and is connected to ground 36 through a variable resistor 37. The capacitor 35 is connected to the output of the gate 29 through a logic inverter 38 in a connecting line 39 to maintain a proper logic signal condition. The NOR logic output signal is invertedand transmitted to the capacitor 35 to establish a timed signal depending upon the bleed characteristic of the resistor 37. This signal is transmitted through a diaphragm amplifier 40 and a two input gate 41 to the input terminal 34. Feedback is prevented through a check valve 42. This establishes an inhalation time adjustment control to maintain the flip-flop circuit 28in a set condition until the capacitor 35 discharges to the switching level. This, in turn, transmits a signal from the gate 30 to the exhalation time adjustment circuit which includes a capacitor 43 similarly connected into the circuit, as shown by corresponding primed numbers, to maintain that condition for a predetermined time.

Thus, once the flip-flop circuit is actuated, the feedback from

circuit

32 or 33 maintains the set or reset condition for a predetermined time period after which the circuit will switch to the opposite condition. The variable pulse width oscillator 6 thus continues to operate with the inhalation and the exhalation time periods separately adjustable to maintain a corresponding forced control of the valves 4 and 5 under the operation as described.

As previously noted, the selection switch means 15 includes an output terminal 16 connected to the oscillator 6 to inhibit the normal automatic timed functioning. In the illustrated embodiment, the second input of each of the two input NOR gates 41 and 41' have the second inputs connected via

lines

44 and 45 to the terminal 16. The

circuits

32 and 33 are thus inactivated andthe forced operation is inhibited, without however preventing operation of the set-reset flip-flop circuit 28 as presently described to initiate an inhalation cycle in response to the output of the control unit 14 in connection with the system shown in FIG. 3. The initiation of the cycle is created as the result of the input signal from unit 14 and particularly the connection of line 13 to input terminal 46 of gate 30. In FIG. 2, the termination of the inhalation phase of the cycle is produced by a signal from the positive pressure cutoff unit 10 applied to a second input terminal. Cutoff unit 10 in FIG. 2 includes a fluidic comparator in the form of an impact modulator 48 having one side connected to compare the pressure in the flow line 12 with a set pressure. Impact modulator 48 is diagrammatically shown with a first nozzle 49 connected in series with a check valve 50 to the line 12. The opposite nozzle 51 is connected to a pressure regulator 52 having an adjustable control 53 for varying of the preset pressure signal applied to the nozzle 51. A sjitable meter 54 is provided to allow the operator to set the pressure at any desired pressure level. After the person initiates the inhalation phase of the cycle, a positive pressure signal will be established at nozzle 49 establishing a corresponding flow stream which is compared with the stream from the nozzle 51 within a collector 55. At a selected set pressure, the output switches from essentially zero to a maximum or high level to produce a rapidly changing signal. The output may be suitably amplified by a pair of NOR

fluidic amplifiers

56 and 57 to establish a corresponding logic output signal at line 1 1. The positive pressure cutoff unit 10 thus functions in essence as a conventional electronic Schmitt trigger type circuit to provide a rapidly changing signal at line 11. Line 11 in turn is connected to the input line 47 of the gate 29 to trigger the flip-flop circuit 28 to terminate inhalation. The patient then exhales untill the end expiratory pressure is established. At the end expiratory pressure, the patient can slightly inhale which will activate the oscillator 6 through the patient control unit 14.

Referring particularly to FIG. 3, the illustrated patient control unit 14 includes a fluidic repeater 59 which is connected via line 14a to sense the pressure in the flow line 12 to provide a positive output pressure signal over the complete total operating ambient pressure range and isolate the fluidic control circuit from the respirator flow system. The output of the fluidic repeater S9 is applied to an amplifying stage 60, the output of which is connected to a pair of series connected cascaded

differentiators

61 and 62, the output of which is a pulse signal which is coupled through a multiple input NOR gate 63 to the line 13 for triggering of the variable pulse width oscillator 6. The NOR gate 63 is a suitable fluidic device such as shown in the US. Pat. No. 3,614,962 having a fixed input pressure cutoff such that a corresponding pressure at any of the inputs establishes a logic zero output. The illustrated fiuidic repeater 59 may correspond to that shown in US. Pat. No. 3,662,779 and includes a convoluted diaphragm 64 defining a dead ended input chamber 65 connected to line 14a. The opposite side of the diaphragm forms a wall of an output chamber 66 which is connected to the regulated supply 22 via suitable coupling restrictor 67. An exhaust nozzle 68 is selectively opened and closed in accordance with the positioning of the diaphragm 64 to thereby regulate the back pressure in the output chamber 66 and the output pressure supplied to the amplifying stage 60. The repeater 59 is adjustably resiliently loaded by a suitable spring means 69 to establish an initial bias level on the unit which maintains a positive pressure output in chamber 66 for both the negative and the positive pressures encountered in line 12 from the respirator unit. Repeater 59 thus has an isolating dead-ended input means and a positive pressure output adjustment means.

The output is applied to stage 60 which includes a fluidic amplifier 70 shown as an impact modulator having a first nozzle connected to the output chamber 66 and thus establishing a signal stream in accordance with the back pressure in chamber 66. The output line 71 of the impact amplifier is connected to a diaphragm amplifier 72 which is similar in construction to the fluidic repeater and selected to have a relatively low gain characteristic. Thus, the input chamber of the diaphragm amplifier 72 is dead-ended while the nozzle in the output chamber is connected to the supply line through similar fluid restrictor 73. The output line 74 from the amplifier is connected to the differentiating stage 61 and to a paralleled resistance feedback network 75 to establish the input to the opposed or second nozzle of the fluidic amplifier 70. The illustrated work includes a fixed resistor 77 such as a crimped copper restrictor connected in parallel with a fixed restrictor 78 in series with an adjustable pin valve 79. The setting of the pin valve 79 controls the gain of the operational rate of change of the ambient pressure as reflected at the repeater 59. Thus, increasing of the resistance of valve 79 will increase the gain to make the circuit more sensitive and responsive to slower rates of change of the ambient pressure.

Pin valve 79 is shown coupled to an adjustable control unit 80 which may include a push and turn-control knob 81. Pushing inwardly on the knob 81 engages a clutch mechanism 82 to couple the input of the pin valve 79 to the rotating knob 81. This also may actuate a pushbutton pulse signal generator 83 to transmit a signal via a line 84 to the NOR gate 63 to disable the patient triggering circuit during the adjustment period.

The amplified output is transmitted and coupled by a coupling restrictor 85 to the first differentiator stage 61. The differentiator stage 61 is shown as a fluidic circuit including an impact modulator 86 connected as the active element with the opposed nozzles connected in common to the coupling restrictor 85 through individual coupling restrictors87 and 88. In addition, a capacitor 89 is connected in the line to the independent input nozzle of the modulator 86 to establish a selected time delay. A drop in the ambient pressure associated withthe end of the exhalation cycle is transmitted to stage 61 with the independent nozzle pressure momentarily higher than the dependent nozzle. During the time delay period, the impact modulator 61 will establish an output which is directly related to the difference between the independent and the dependent pressure which in turn is directly related to the degree of amplification provided by the operational amplifying stage 60. The output of the differentiator thus responds to a slower rate of change of ambient pressure with the increasing amplifier gain.

The output is coupled via a coupling restrictor 90 to the second differentiator stage 62 constructed in the. same manner as the first differentiator stage except that the capacitor is connected in the line to the dependent nozzle. The output of the second differentiator stage is coupled through a suitable fluidic logic converter 92 to the input terminal 93 of the NOR gate 63.

The two-stage differentiation minimizes the effect of DC level or starting point drift. Thus, as previously noted, the ambient or starting point pressure level may vary somewhere within a known pressure range. As the ambient pressure increases, the output pressure level of the operational amplifying stage 60 correspondingly increases. The second differentiator stageminimizes the variations associated with drift conditions and in effect significantly reduces the variation in the output signal to gate 63 with DC level input variation. The output amplifying stage 60 thus will exhibit a change in output pressure over the range of ambient pressures or the span of the sensitivity adjustment. The first differentiator thus sees a corresponding change in pressure and the output varies slightly. However, the second stage sees only this slight variation and not the total variation of the output of the amplifier 60 and consequently its output will shift minimally with normal variation in the output of the amplifier. For example, in an actual construction, the output of the amplifying state 60 varied approximately 2 to 3 psig over the range of the ambient pressures. The first differentiator output varied by a related few inches of water. The output of second differentiator stage 62 which only saw this slight variation at its input was shifted very minimally and by a generally corresponding reduced amount.

Thus an appropriate rate of change of the sensed pressure is detected by the operational amplifier 60 and the differentiator stages 61 and 62 which supply a trigger signal via the gate 63 to initiate an inhalation cycle. In the illustrated embodiment of the invention, a disable input 94 of gate 63 is connected directly to the output terminal 17 of the selection switch means 15. When the selection switch means 15 is set to the controller position, a signal is impressed upon the NOR gate 63 to positively prevent cutoff and transmission of an output signal from the control unit 14 to the oscillator 6, thereby preventing the oscillator control from being triggered by the control unit 14.

In addition, when the control unit 14 is connected into the circuit the flow direction sensor 19 is interrelated and coupled through the Nor gate 63 to prevent spurious and erroneous triggering by the patient control unit 14 during the exhalation cycle or portion of the breathing cycle. Thus, a significant reduction in the exhalation rate or a pause in the exhalation process creates a decrease in the ambient pressure which might be detected by the control unit 14 as a termination period.

This is prevented in the present invention by the sensor 19 which includes a means for monitoring the pressure drop in a portion of the flow line 12.

In particular in the illustrated embodiment of the invention,

repeaters

95 and 96, similar to the repeater 59, have a dead ended input chamber 97 connected one each to the respective lines 20. As

repeaters

95 and 96 correspond, repeater 95 is described and the corresponding elements of repeater 96 are identified by corresponding primed numbers. Repeater 95 includes a diaphragm 98 and an adjustable set-point spring 99 in the input chamber to providesetting of a constant bias level. The

repeaters

95 and 96 are set to provide a balanced output with no flow through the line 12. The output chamber of the fluidic repeater 95 is connected to the regulated supply valve 23 with an exhaust nozzle 100 to ground or reference. The output line 101 is connected'as a first input to a summing impact modulator 102. The output line 103 of repeater 96 is connected to the opposite nozzle of modulator 102. The connecting lines 101 and 103 include the restrictors 104 and 105, with the restrictor-104 made adjustable to provide accurate adjustment of the signals to the summing impact modulator 102 in the absence of flow in the line 12.

The repeaters function in essentially the same manner as does repeater 59 to permit maintaining positive output pressure signals to the system and to isolate the fluidic circuitry contained in the flow direction sensor 19 from the ambient pressure. Thus any expired air which contains contaminants is not transmitted into the fluidic circuitry.

The output of the summing impact modulator 102 is amplified in the illustrated embodiment of the invention by a pair of cascaded Nor

gate amplifiers

106 and 107 via an output line 108 to an input terminal 109 of the four input Nor gate 63. A time delay capacitor 110 is connected to the output line 108 to maintain the transmission of the output signal during the exhalation cycle and in particular assure that a momentary expiratory pressure changedoes not enable the gate 63. The inhibit circuitry is therefore responsive to the particular portion of the breathing cycle during which it is desired to positively inhibit the initiation of inhalation. Consequently the time delay inserted into the circuit does not have to accommodate various pauses and the like or respond to the rate of exhalation. There is no need therefore to adjust the magnitude of the time delay to accommodate the various breathing conditions and characteristics of different patients. The illustrated flow direction sensor 19 operates over the full range of the ambient pressure encountered by a respirator in normal usage.

Thus, in operation, the flow sensor 19 responds to the relative pressure at the two pressure sensing lines and 20a. Thus, if the patient is exhaling, flow through line 12 from the first line 20 to the second line 20a and consequently the pressure on line 20 is greater than that at line 20a. On the other hand, if the patient is inhaling, there is an opposite flow direction and the pressure at the line 20a is greater than at the line 20. These two pressures are sensed by the special repeaters 9.5

and 96. In the absence of flow, the signal input pressures will be equal and with the bias levels of the repeaters properly adjusted, equal outputs are supplied to the impact modulator 102 which will be balanced and therefore not yield an output signal. When the patient exhales such that the signal at line 20 is greater than at line 20a, a pressure imbalance occurs across the impact modulator which generates a positive output signal. When the patient inhales, the pressure condition is reversed and the pressure imbalance is reversed and the summing impact modulator does not register or create an output. The output is therefore a logic signal directly related to the direction of flow.

Thus, when the patient exhales, an output signal of sufficient amplitude to inhibit the output of the patient triggering circuit 14 is created. When the patient inhales, no such signal occurs. Further, when the patient is exhaling, a timed delay is, in the illustrated embodiment, introduced during exhalation as a result of the charging of capacitor 110. This maintains the inhibit circuit until such time as a steady stage exhalation pressure level is reached such that momentary hesitations in the exhalation cycle will not result in a false release of the inhibit circuitry andpermit the accidental and erroneous triggering.

Thus, the present invention provides reliable selectively regulated control independent of the ambient pressure and essentially independent of the exhalation characteristic of the patient to thereby permit reliable application of the respirator to various patients.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims, particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim: I

1. A respirator having a fluid source coupled to a valved flow means for carrying fluid to and from a patient, comprising a patient triggering circuit means for initiating the inhalation phase of the breathing cycle in response to inhalation flow by the patient, flow sensing means coupled to said valved means for detecting exhalation flow, said sensing means including a flow line having a flow in accordance with the direction of flow of said fluid with respect to the patient, a pressure sensing means coupled to said flow line and monitoring the pressure drop between two selected spaced points in said flow line, and coupling means connecting said pressure sensing means to said patient triggering circuit to inhibit the triggering circuit during exhalation flow.

2. A respirator control apparatus coupling a respirator having a fluid medium source and a valved control means for carrying fluid to and from a patient and establishing regulated breathing assistance for the patient through a flow means of the respirator, comprising flow sensing means having a flow line means connected to said flow means of the respirator and having flow in accordance with the direction of flow of said fluid in said flow means, and having monitoring means for connection to spaced points of the flow line means and establishing a signal in accordance with the pressure differ ential between said points and thereby the direction of flow of fluid with respect to the patient, a patient triggering control means having output means for connection to the flow means for actuating the flow means in accordance with the movement of the patients breathing faculties, and means connecting said sensing means to said control means to selectively inhibit said control means.

3. The respirator control apparatus of claim 2 wherein said flow sensing means includes a first pressure tap means connected to said flow line adjacent said respirator, a second pressure tap means connected to said flow line downstream of said first pressure tap means to define with said first tap means a pressure drop sensing means, and a first and a second fluidic repeater connected to the corresponding first and second pressure tap means to isolate the sensing means of the breathing flow means and establish a pair of positive pressure signals over the operating range of the respirator,

4. The respirator control apparatus of claim 3 wherein each repeater includes a diaphragm defining a closed input chamber and an output chamber, said output chamber being connected to a regulated supply and having an exhaust nozzle selectively opened and closed by the position of the diaphragm, means resiliently preloading the diaphragm to maintain a positive output pressure signal over the complete operating range of the respirator, and a fluidic comparator means establishing a selected output in response to flow associated with patient exhalation and a zero output associated with patient inhalation.

5. The respirator control apparatus of claim 4 having a time delay capacitor means connected to the output of the fluidic comparator means to inhibit the triggering control-means until a stable exhalation period is created. 7

6. The respirator control apparatus of claim 4 operable over an ambient pressure range of l cm of H 0 to +10 cm of H 0 and wherein said repeater diaphragm includes an annular convolution and is preloaded by an adjustable spring means to maintain said positive output pressure signal over said pressure range, said fluidic comparator including an impact modulator having a pair of opposed nozzle means connected respectively one each to each of said output chambers and establishing said selected output, fluidic logic amplifiers connected to the output of the impact modulator, a time delay capacitor means connected to the output of the amplifiers, said triggering control means including a fluidic Nor gate having a first input connected to said capacitor means and to said modulator to inhibit the triggering control means until a stable exhalation period is created.

7. The respirator control apparatus of claim 2 wherein said triggering control means includes a diaphragm fluidic repeater having a deadended input chamber connected to said flow sensing line and an output chamber with an exhaust means regulated by a common chamber diaphragm, an operational amplifier including a fluidic amplifier means connected to the output of the repeater and a feedback network including adjustable resistance means connected to said fluidic amplifier means, a first fluidic differentiator connected to the output of said fluidic amplifier means, a second fluidic differentiator connected to the output of the first differentiator, a logic gate connected to the output of said second differentiator to control the flow means.

8. The respirator of claim 7 including a diaphragm amplifier having a deadended input chamber connected to the output of the fluidic amplifier means and an output chamber connected to said feedback network and to said first fluidic differentiator.

9. The respirator of claim 2 wherein the flow means includes inhalation valve means and exhalation valve means and a fluidic variable pulse width oscillator coupled to alternately activate the inhalation valve means and the exhalation valve means, said oscillator having an inhalation time adjustment means and an exhalation time adjustment means, each of said adjustment means including a capacitive means and an adjustable bleed restrictor means connected to said capacitive means.

10. The respirator of claim 9 whereinsaid fluidic variable pulse width oscillator includes a pair of Nor gates connected to define a fluidic flip-flop circuit with a pair of output lines connected to the opposite of said gates and to alternately activate the inhalation valve means and the exhalation valve means, said inhalation time adjustment means and exhalation time adjustment means being connected to said Nor gates to actuate said flip-flop circuit.

11. The respirator of claim 9 having a positive pressure cutoff means connected to said flow line and to a set pressure source means and connected to said oscillator to terminate the inhalation cycle at a selected inhalation pressure, and said triggering control means connected to said oscillator to initiate the inhalation phase of the breathing cycle.

12. The respirator of claim 11 having a selector switch means connected to said oscillator and to said triggering control means and having a first position to inhibit the inhalation adjustment means and the exhalation adjustment means and having a second position inhibiting the triggering control means and a third noninhibiting position.

13. The respirator control apparatus of claim 2 operable over an ambient pressure range of -10 cm of H 0 to +10 cm of H 0 and having a first pressure tap means connected to said flow line adjacent said respirator, a second pressure tap means connected to said flow line downstream of said first pressure tap means, a first and a second fluidic repeater connected to the corresponding first and second pressure tap means, each repeater including a diaphragm having an annular convolution and defining a closed input chamber and an output chamber, said output chamber being connected to a regulated supply and having an exhaust nozzle selectively opened and closed by the position of the diaphragm, a spring means resiliently preloading the diaphragm to maintain a positive output pressure signal over the complete operating range of the respirator, a fluidic comparator including an impact modulator having a pair of opposed nozzle means connected respectively one each to each of said output chambers and establishing a selected output in response to flow associated with patient exhalation and a zero output associated with patient inhalation, fluidic logic amplifying gate means connected to the output of the comparator, a time delay capacitor means connected to the output of the gate means, said triggering control means including an output fluidic Nor" gate having a first input connected to said capacitor means and to gate means to inhibit the triggering control means during the exhalation cycle, said triggering control means including a third fluidic repeater corresponding to said first and second repeaters and having an input chamber connected to said flow sensing line, an operational amplifier including a fluidic impact modulator having first and second nozzle means in opposed relation with the first nozzle means connected to the output of the third repeater and the second nozzle means connected to a feedback network, said feedback network including adjustable pin valve means, a diaphragm amplifier having a deadended input chamber connected to the output of the impact modulator and an output chamber connected to said feedback network, a first fluidic differentiator including an impact modulator with a pair of opposed nozzles connected in common to the output of said last-named diaphragm amplifier and having a fluidic capacitor between one of said nozzles and the common connection, a second fluidic differentiator having a corresponding impact modulator to said first and having a common connection to the output of the first differentiator and having a fluidic capacitor in the connection to the opposite one of said nozzle means, and a logic inverter gate connecting the output of said second differentiator to a second input of said output fluidic NOR gate. a

14. The respirator of claim 13 wherein the flow means includes inhalation valve means and exhalation valve means and including a fluidic variable pulse width oscillator having a pair of NOR gates connected to define a fluidic flip-flop circuit with a pair of output lines connected to one of said gates and coupled to alternately activate the inhalation valve means and the exhalation valve means, said oscillator having an inhalation time adjustment means and an exhalation time adjustment means, each of said adjustment means including a capacitive means and an adjustable bleed restrictor means connected to said capacitive means, a positive pressure cutoff means including an impact modulator connected to said flow line and to a set pressure source means and connected to a first of said gates of said oscillator to terminate the inhalation cycle at a selected inhalation pressure, said triggering control means having said output fluidic Nor gate means connected to the second of said gates of said oscillator to initiate an inhalation cycle, and a selector switch means connected to said oscillator and to said triggering control means and having a first position to inhibit the inhalation adjustment means and the exhalation adjustment means and having a second position inhibiting the triggering control means and a third non-inhibiting position, said selector switch means being constructed to establish fluidic control signals, said oscillator and triggering control means having logic gates, said switch means being connected to said logic gates for selective inhibiting of said oscillator and said triggering control means.

Claims

2. A respirator control apparatus coupling a respirator having a fluid medium source and a valved control means for carrying fluid to and from a patient and establishing regulated breathing assistance for the patient through a flow means of the respirator, comprising flow sensing means having a flow line means connected to said flow means of the respirator and having flow in accordance with the direction of flow of said fluid in said flow means, and having monitoring means for connection to spaced points of the flow line means and establishing a signal in accordance with the pressure differential between said points and thereby the direction of flow of flUid with respect to the patient, a patient triggering control means having output means for connection to the flow means for actuating the flow means in accordance with the movement of the patient''s breathing faculties, and means connecting said sensing means to said control means to selectively inhibit said control means.

3. The respirator control apparatus of claim 2 wherein said flow sensing means includes a first pressure tap means connected to said flow line adjacent said respirator, a second pressure tap means connected to said flow line downstream of said first pressure tap means to define with said first tap means a pressure drop sensing means, and a first and a second fluidic repeater connected to the corresponding first and second pressure tap means to isolate the sensing means of the breathing flow means and establish a pair of positive pressure signals over the operating range of the respirator.

5. The respirator control apparatus of claim 4 having a time delay capacitor means connected to the output of the fluidic comparator means to inhibit the triggering control means until a stable exhalation period is created.

6. The respirator control apparatus of claim 4 operable over an ambient pressure range of -10 cm of H2O to +10 cm of H2O and wherein said repeater diaphragm includes an annular convolution and is preloaded by an adjustable spring means to maintain said positive output pressure signal over said pressure range, said fluidic comparator including an impact modulator having a pair of opposed nozzle means connected respectively one each to each of said output chambers and establishing said selected output, fluidic logic amplifiers connected to the output of the impact modulator, a time delay capacitor means connected to the output of the amplifiers, said triggering control means including a fluidic ''''Nor'''' gate having a first input connected to said capacitor means and to said modulator to inhibit the triggering control means until a stable exhalation period is created.

10. The respirator of claim 9 wherein said fluidic variable pulse width oscillator includes a pair of ''''Nor'''' gates connected to define a fluidic flip-flop circuit with a pair of output lines connected to the opposite of said gates and to alternately activate the inhalation valve means and the exhalation valve means, said inhalation time adjustment means and exhalation time adjustment means being connected to said ''''Nor'''' gates to actuate said flip-flop circuit.

12. The respirator of claim 11 having a selector switch means connected to said oscillator and to said triggering control means and having a first position to inhibit the inhalation adjustment means and the exhalation adjustment means and having a second position inhibiting the triggering control means and a third non-inhibiting position.

13. The respirator control apparatus of claim 2 operable over an ambient pressure range of -10 cm of H2O to +10 cm of H2O and having a first pressure tap means connected to said flow line adjacent said respirator, a second pressure tap means connected to said flow line downstream of said first pressure tap means, a first and a second fluidic repeater connected to the corresponding first and second pressure tap means, each repeater including a diaphragm having an annular convolution and defining a closed input chamber and an output chamber, said output chamber being connected to a regulated supply and having an exhaust nozzle selectively opened and closed by the position of the diaphragm, a spring means resiliently preloading the diaphragm to maintain a positive output pressure signal over the complete operating range of the respirator, a fluidic comparator including an impact modulator having a pair of opposed nozzle means connected respectively one each to each of said output chambers and establishing a selected output in response to flow associated with patient exhalation and a zero output associated with patient inhalation, fluidic logic amplifying gate means connected to the output of the comparator, a time delay capacitor means connected to the output of the gate means, said triggering control means including an output fluidic ''''Nor'''' gate having a first input connected to said capacitor means and to gate means to inhibit the triggering control means during the exhalation cycle, said triggering control means including a third fluidic repeater corresponding to said first and second repeaters and having an input chamber connected to said flow sensing line, an operational amplifier including a fluidic impact modulator having first and second nozzle means in opposed relation with the first nozzle means connected to the output of the third repeater and the second nozzle means connected to a feedback network, said feedback network including adjustable pin valve means, a diaphragm amplifier having a deadended input chamber connected to the output of the impact modulator and an output chamber connected to said feedback network, a first fluidic differentiator including an impact modulator with a pair of opposed nozzles connected in common to the output of said last-named diaphragm amplifier and having a fluidic capacitor between one of said nozzles and the common connection, a second fluidic differentiator having a corresponding impact modulator to said first and having a common connection to the output of the first differentiator and having a fluidic capacitor in the connection to the opposite one of said nozzle means, and a logic inverter gate cOnnecting the output of said second differentiator to a second input of said output fluidic NOR gate.

14. The respirator of claim 13 wherein the flow means includes inhalation valve means and exhalation valve means and including a fluidic variable pulse width oscillator having a pair of NOR gates connected to define a fluidic flip-flop circuit with a pair of output lines connected to one of said gates and coupled to alternately activate the inhalation valve means and the exhalation valve means, said oscillator having an inhalation time adjustment means and an exhalation time adjustment means, each of said adjustment means including a capacitive means and an adjustable bleed restrictor means connected to said capacitive means, a positive pressure cutoff means including an impact modulator connected to said flow line and to a set pressure source means and connected to a first of said gates of said oscillator to terminate the inhalation cycle at a selected inhalation pressure, said triggering control means having said output fluidic ''''Nor'''' gate means connected to the second of said gates of said oscillator to initiate an inhalation cycle, and a selector switch means connected to said oscillator and to said triggering control means and having a first position to inhibit the inhalation adjustment means and the exhalation adjustment means and having a second position inhibiting the triggering control means and a third non-inhibiting position, said selector switch means being constructed to establish fluidic control signals, said oscillator and triggering control means having logic gates, said switch means being connected to said logic gates for selective inhibiting of said oscillator and said triggering control means.