US3831596A - Control device for a respiratory apparatus - Google Patents

Abstract

Respiratory apparatus having an electromagnetically operated valve for controlling the flow of respirable gas from a source thereof to a mouthpiece has a control arrangement for opening and shutting the valve in accordance with pressure changes appearing during periods of inhalation and exhalation by a patient using the apparatus. Alternatively, the valve can be opened and shut according to a predetermined cycle.

Description

D United StatesPatent 1 1 1111 3,831,596 Cavallo Au 27 1974 [54] CONTROL DEVICE FOR A RESPIRATORY 3,357,428 12/1967 Carlson 137/4875 q q 3,456,643 7/1969 Koch 128/1458 APP TUS 3,508,542 4/1970 Browner 128/1422 Inventor: Roger Paul Charles Cavallo, 3,611,178 10/1971 McConnell 128/1422 Bourg-la-Reine, France 1 S th 1 M p F Primary ExaminerRichard A. Gaudet [73] Asslgnee yn e a ans rance Assistant Examiner-Henry J. Recla Flledi 1972 Attorney, Agent, or Firm-Karl F Ross; Herbert 211 App]. No.2 304,487 Dubno [52] U.S.Cl. ..128/145.8, 128/145.5 [57], ABS CT 51 11m. (:1A61m 16/00 Resplratory apparatus havlPg electromagnetlcally [58] Field of Search 128/1453 1463 1464 operated valve for controlling the flow of resplrable 128/146 51 5 1422 1423 gas from a source thereof to a mouthpiece has a con- 37 4 14 1 trol arrangement for opening and shutting the valve in accordance with pressure changes appearing during [561 References Cited periods of inhalation and exhalation by a patient using the apparatus. Alternatively, the valve can be opened UNITED STATES PATENTS and shut according to a predetermined cycle. 2,376,348 5/1945 Fox 128/1458 2,863,287 12/1958 Berkman 137/4875 10 Chums, 3 Drawing Flgures CONTROL DEVICE FOR A RESPIRATORY APPARATUS This invention relates to control devices for respiratory apparatus. Respiratory apparatus for assisting natural respiration is normally controlled to operate at a fixed frequency or rhythm by a clock mechanism operated electrically or pneumatically but this is not satisfactory when the respiratory rhythm of a patient to be treated is irregular.

The present invention concerns means for supplying air to patient according to the demand of his lungs, in other words means to control the apparatus by shutting air supply as soon as the lungs are full of air and by opening the air supply as soon as patient begins an inhalation.

A control device for a respiratory apparatus comprising a source of respirable gas connected to a mouthpiece by a conduit provided with a control valve, according to the invention includes a pressure sensor connected to said conduit between said valve and mouthpiece, said sensor comprising a housing closed by a membrane, the outer face of which exposed to ambient air is partly applied against a rigid sustaining member, a first detector of a predetermined outward distortion of said membrane for controlling closing of said valve and a second detector of a predetermined inner distrotion of said membrane for controlling opening of said valve. Thus owing to the membrane outer sustaining member, outward displacement of a given point on the membrane due to gas over pressure inflating the lungs and prevailing in the housing may be of the same order as inward displacement of the same point due to under pressure in said housing produced by the inhalation effort of the patient.

Preferably an adjustable flexible flat member is connected to a point of the flexible membrane, so as to respond to the flexure of the latter and both faces of the member are provided with strain gauges which are connected in a Wheatstone bridge with reference resistors. Hence by adjusting the initial shape of the member, the bridge may be exactly equilibrated when the same pressure prevails on both faces of the membrane, so that an over pressure in the housing provides a current of one direction in the bridge detecting diagonal and an under pressure a current of the other direction, in the same diagonal.

Thus the bridge arrangement is a part of the first and second detectors.

By comparison of each of both currents with respective adjustable thresholds, control of a flip-flop at predetermined amplitudes of the currents (i.e. definite levels of membrane distortions) may be obtained for the alternate control of the .valve.

In one particular form of the control device according to the invention the the flow control valve is electro-magnetically operated by one output of a flipflop device triggered by signals derived from the strain gauges.

For reasons of security after control of the valve to close position, the flip-flop is again triggered to control open position of the valve by the output of a timing device a predetermined time after closing of the valve.

For allowing the weak inhalation effort of the patient to entail a negative pressure in the conduit portion the flow control valve is adapted, when in its closed position, to place the pipe in communication with atmosphere via a light exhaust valve.

In a further embodiment of the apparatus, means are provided for operating the flip-flop according to a predetermined time cycle. Such means may comprise resistorcapacitor combinations of which the resistors are variable.

By way of example only, an embodiment of the invention will now be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a plan view of part of one embodiment,

FIG. 2 is a section on the line lI-Il of FIG. 1, and,

FIG. 3 is a circuit diagram partly in block or schematic form of the respiratory apparatus,

The component shown in FIGS. 1 and 2 is a pressure change detector and it comprises a flatcircular membrane 1 attached to aplate 2 concentrically with anap erture 3 in the latter. The membrane is clamped between the plate and a cup-shaped housing 4 attached to the plate byscrews 5 which also pass through the membrane adjacent its periphery.

Themembrane 1 is made of metal or of a plastic material, for example that known as Stabilene.

Theplate 2 is of laminated glass/resin construction and is extended to provide support for other components described below.

Extending externally of thehousing 4 and centrally from the base thereof is a coupling 4a by means of which connection is made to a pipe supplying a patient with respirable gas.

Connected to the center of themembrane 1 is one end of abolt 6 whose other end is fixed to aflexible strip 7 clamped cantilever fashion between small clamping plates 8 bolted toplate 2.. The free end of thestrip 7 rests resiliently on an adjustingscrew 9, which sets the zero position of thestrip 7, and of the membrane.

To the upper and lower faces of thestrip 7 arefixed strain gauges 10, 11 respectively. The gauges are connected in a Wheatstone bridge including reference resistors l2, 13 (FIG. 3) for supplying control signals.

Increase of pressure within thehousing 4 causes the central part only of themembrane 1 to flex upwardly as indicated by the dotted line la whereas a reduction in pressure below atmospheric causes the membrane to flex downwardly over a much greater area as indicated by the dotted line 1b. In this way, a pressure reduction which is only one tenth of the maximum pressure to which the membrane is likely to be exposed produces, in the strip 7 a flexure equal in amplitude but opposite in sense to that produced by that maximum pressure.

Amanometer 20 is joined tothepipe 18 as shown and the latter also has a branch connection to thehousing 4 via the coupling 4a.

In use, flexure of thestrip 7 causes signals to be transmitted from the bridge whose amplitude and polarity depend upon the extent to which and the direction in which the strip is flexed and thus, this flexure indicates the pressure in thehousing 4 and so in thepipe 18. Owing to thescrew 9 output of the bridge is adjusted to zero when both faces of the membrane are submitted to the same pressure.

The bridge output is applied to anamplifier 31 having thus one output on which appear positive signals representing positive pressure inhousing 4 and another output on which appear negative signals representing negative pressures in that housing. The two outputs are connected to respective differential amplifiers 32 32 B each with a reference input controlled by the respective potentiometers 33, 33

Amplifier 32, and its potentiometer 33,, are adapted to deal with positive pressures and by adjustment of the potentiometer 33,, can be set to deal with a range of from +100 mb as indicated by themanometer 20. This range is selected so that a supply pressure can be selected which suffices to fill the lungs of a patient without smothering him.

Amplifier 32 B and its potentiometer 33 are adapted to deal with negative pressures and by adjustment of the potentiometer 33,, can be set to deal with a range of pressures of from -1 mb to l0 mb which pressure can also be indicated bymanometer 20. In practice, the pressure is determined by the comfort of the patient in that a signal is emitted when the latter breathes undue without effort.

By means of the contact arms 26,,, 26 of a doublepole changeover switch, the outputs of the differential amplifiers 32,,, 32 can be applied to the inputs of an electronic flip-flop circuit represented byblock 34. The flip-flop has a single output corresponding with the output of amplifier 32,, which is used, after amplification bypower amplifier 35, to energise thewinding 16 and soopen valve 15.

The output ofdifferential amplifier 32A is also applied to atiming device 37 which, in response to an input, produces an output after a predetermined delay within the range of from 2 to seconds, for example 3 seconds. The output oftiming device 37 is connected to the output of differential amplifier 32 The general arrangement is such that when the predetermined positive pressure is reachedpipe 18, a signal is sent to the flip-flop 34 which responds by a change in its other stable state and as a result valve is closed. At the same time, thetiming device 37 is set into operation.

The patient then exhales and after a certain time inhales again providing a negative pressure inhousing 4 and this produces a signal that is applied via amplifier 32,, to the flip-flop 34 which switches to its other stable state with the result thatvalve 15 is opened.

In inhaling is insufficient to produce the necessary negative pressure or if the latter appears after the end of the predetermined delay to whichdevice 37 is set, the latter produces a signal atthe end of the delay and this causes flip-flop 34 to switch to its other state andvalve 15 opens. The cycle then repeats,timing device 37 being ready then to receive a further signal from amplifier 32,, when the pressure inpipe 18 again rises to the predetermined positive value.

It has already been stated thatvalve 15 is a three-way valve. In the open position ofvalve 15,pipe 18 is placed in communication withsource 14 only while in the closedposition source 14 is shut off frompipe 18 but the latter is placed in communication with the atmosphere via anoutlet 38 normally closed by alight exhaust valve 39, for example a flexible elastomeric disc with a central fastening positioning the valve overoutlet 38. Thus, whenvalve 15 closes, the positive pressure then existing inpipe 18flexes valve 39 away from theoutlet 38 and the pressure rapidly drops to ambient pressure. As the patient inhalesexhaust valve 39 is closed and negative pressure appears inpipe 18 andhousing 4.

The double pole switch can be manually actuated to disconnect the amplifiers 32,,, 32,, from the flip-flop 34 to connect the latter to capacitive devices 40,, 40,, which with theirrespective potentiometers 41 A and 41 3 convert the flip-flop into a multivibrator.

The setting of thepotentiometers 41 41 B is such that the ratio of the switching times of the multivibrator is 2:1 so that thevalve 15 is open and shut cyclically, the closed time being twice the open time, this giving a time period for expiration that is twice the time period for inhalation.

For medical use, the frequency of the multivibrator can be set to a value within the range 10-60 exhalations and inhalations per minute. However, for veterinary use, a wider range of variation may be required and in practice, the respiratory rhythm is adjustable within the range of from to per minute.

What 1 claim is:

1. A device for the control of a respiratory apparatus comprising:

a source of a respirable gas connected to a patient through a conduit provided with an electrically operated control valve;

control means for operating said valve, said control means including a housing communicating with said conduit between said valve and the patient, a flat membrane spanning said housing and having an outer face exposed to the atmosphere and an inner face exposed to the breathing air supplied to said patient, a flat generally rigid member disposed proximal to said outer face for securing said membrane and provided with a central aperture of a surface area substantially less than the area of said membrane, a rigid element connected to a central portion of said membrane, and a distortion detec tor connected to said element; and

electrical means connected to said detector and to said valve for supplying a valve-closing signal to said valve upon distortion of the membrane in the direction of said central aperture and; for supplying a valve-opening signal to the latter upon distortion of the membrane in the other direction.

2. The device defined inclaim 1, further comprising a flexible member overlying said membrane, said distortion detectors being formed as strain gauges applied to opposite faces of said flexible member and a wheatstone bridge circuit having reference resistors and said strain gauges connected therein.

3. The device defined inclaim 2 wherein said flexible member is a blade, further comprising means for clamping said blade at one end to said housing, adjustment means for varying the position of the opposite end of said blade with respect to the housing, and means connecting an intermediate location on said blade between said ends to said rigid element.

4. The device defined theclaim 3 wherein said rigid member is a wall of electrically insulating material carrying said detectors and said blade.

5. The device defined inclaim 1 wherein the firstmentioned and second electrical means are respective differential amplifiers having respective adjustable thresholds of opposite polarity, and a bistable flip-flop responsive to said differential amplifiers.

6. The device defined inclaim 1 wherein said valve is a three-way valve and in its closed position connects said conduit to the atmosphere through an adjust valve.

7. The device defined inclaim 6, further comprising a timing device for operating said valve independent of at least one of said detectors.

8. The device defined in claim ll, further comprising means for indicating visually the pressure in said conduit.

9. A device for the control of a respiratory apparatus comprising:

a source of a respirable gas connected to a patient through a conduit provided with an electrically operated control valve;

control means for operating said valve, said control means including a housing communicating with said conduit between said valve and the patient, a flat membrane spanning said housing and having an outer face exposed to the atmosphere and an inner face exposed to the breathing air supplied to said patient, a flat generally rigid member disposed proximal to said outerface for securing said membrane, a rigid element connected to a central portion of said membrane, and a distortion detector connected to said element; electrical means connected to said detector and to said valve for supplying a valve-opening signal to the latter upon distortion of the membrane in one direction; second distortion detector connected to said element for sensing deflection of said membrane in the opposite direction, and second electrical means responsive to said second detector and connected to said valve to apply a valve-closing signal to the latter, said control valve is electromagnetic, said detectors are strain gauges, and said electrical means include respective differential amplifiers having adjustable thresholds and connected to said strain gauges, a bistable flip-flop connected to said differential amplifiers and having an output applied to said valve, two resistor-capacitor combinations, each associated with said flip-flop, and switching means for selectively applying said resistorcapacitor combinations and said differential amplifiers to said valve for constituting a multivibrator from the flip-flop upon connection of a resistorcapacitor combination therewith.

10. The device defined inclaim 9, further comprising variable resistors in said resistor-capacitor combinations for determining the switching time of the multivi- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,831,596 DATED 27 August 1974 INVENTOR(S) Roger Paul Charles CAVALLO It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, afterline 1 insert:

-- Q ForeignApplication Priority Data 10 November 1971 FRANCE 71 40291 17 October 1972 FRANCE 72 36666 Erigned and Scaled this A ttest:

RUTH C. MASON C. MARSHALL DANN iltcsling ()jfr'zer (mnmissz'uncr uflarents and Trademarks

Claims (10)

1. A device for the control of a respiratory apparatus comprising: a source of a respirable gas connected to a patient through a conduit provided with an electrically operated control valve; control means for operating said valve, said control means including a housing communicating with said conduit between said valve and the patient, a flat membrane spanning said housing and having an outer face exposed to the atmosphere and an inner face exposed to the breathing air supplied to said patient, a flat generally rigid member disposed proximal to said outer face for securing said membrane and provided with a central aperture of a surface area substantially less than the area of said membrane, a rigid element connected to a central portion of said membrane, and a distortion detector connected to said element; and electrical means connected to said detector and to said valve for supplying a valve-closing signal to said valve upon distortion of the membrane in the direction of said central aperture and; for supplying a valve-opening signal to the latter upon distortion of the membrane in the other direction.

2. The device defined in claim 1, further comprising a flexible member overlying said membrane, said distortion detectors being formed as strain gauges applied to opposite faces of said flexible member and a wheatstone bridge circuit having reference resistors and said strain gauges connected therein.

3. The device defined in claim 2 wherein said flexible member is a blade, further comprising means for clamping said blade at one end to said housing, adjustment means for varying the position of the opposite end of said blade with respect to the housing, and means connecting an intermediate location on said blade between said ends to said rigid element.

4. The device defined the claim 3 wherein said rigid member is a wall of electrically insulating material carrying said detectors and said blade.

5. The device defined in claim 1 wherein the first-mentioned and second electrical means are respective differential amplifiers having respective adjustable thresholds of opposite polarity, and a bistable flip-flop responsive to said differential amplifiers.

6. The device defined in claim 1 wherein said valve is a three-way valve and in its closed position connects said conduit to the atmosphere through an adjust valve.

7. The device defined in claim 6, further comprising a timing device for operating said valve independent of at least one of said detectors.

8. The device defined in claim 1, further comprising means for indicating visually the pressure in said conduit.

9. A device for the control of a respiratory apparatus comprising: a source of a respirable gas connected to a patient through a conduit provided with an electrically operated control valve; control means for operating said valve, said control means including a housing communicating with said conduit between said valve and the patient, a flat membrane spanning said housing and having an outer face exposed to the atmosphere and an inner face exposed to the breathing air supplied to said patient, a flat generally rigid member disposed proximal to said outerface for securing said membrane, a rigid element connected to a central portion of said membrane, and a disTortion detector connected to said element; electrical means connected to said detector and to said valve for supplying a valve-opening signal to the latter upon distortion of the membrane in one direction; a second distortion detector connected to said element for sensing deflection of said membrane in the opposite direction, and second electrical means responsive to said second detector and connected to said valve to apply a valve-closing signal to the latter, said control valve is electromagnetic, said detectors are strain gauges, and said electrical means include respective differential amplifiers having adjustable thresholds and connected to said strain gauges, a bistable flip-flop connected to said differential amplifiers and having an output applied to said valve, two resistor-capacitor combinations, each associated with said flip-flop, and switching means for selectively applying said resistor-capacitor combinations and said differential amplifiers to said valve for constituting a multivibrator from the flip-flop upon connection of a resistor-capacitor combination therewith.

10. The device defined in claim 9, further comprising variable resistors in said resistor-capacitor combinations for determining the switching time of the multivibrator.

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