US3543752A - Infusion apparatus - Google Patents

Description

United States Patent Holger Hesse,

Lyngby Carl Sloth, Copenhagen Valby, and Asger Brendstrup, Glostrup, Denmark; 460,302

June .1, 1965 Dec. 1, 1970 said Sloth and Brendstrup assignors to said Hesse; Ruth Leo Hesse, heiress and executrix of the estate of said Holger Hesse, deceased.

Inventors App]. No. Filed Patented Assignee Priority June 1, 1964 Great Britain INFUSION APPARATUS 16 Claims, 9 Drawing Figs.

Int.Cl A61m 5/00 Field olSearch 128/213,

[56] References Cited UNITED STATES PATENTS 2,625,933 1/1953 Salisbury 128/2142 2,689,565 9/1954 Gobel 128/2142 2,693,801 11/1954 Foreman 128/214 2,705,493 4/1955 Malmros et al. 23/2585 2,835,252 5/1958 Mauchel 128/214 2,847,008 8/1958 Tayloreta1 23/2585 2,927,582 3/1960 Berkman et a1... 23/2585 3,014,481 12/1961 Rumble et alQ.... 128/214 3,052,238 9/1962 Broman et a1. 128/214 Primary Examiner-Dalton L. Truldck Attorney-Spencer and Kaye ABSTRACT: An apparatus for performing continuous infusion of liquids into blood vessels or muscles of animal or human bodies over an extended period of time with a desired degree of dosage exactitude. The apparatus has a treating liquid container, a pump, an infusion cannula adapted to be inserted in the body of the animal or person to be treated, a gas bubb1e-collecting vessel and safety means responsive to the presence of a predetermined volume of accumulated gas in the collecting vessel.

Patnted Dec. 1, 1970 Sheet 1 off:

L NORMAL START STOP ? WARNING min.

f zwvzzmons.

Holger Hesse Carl Sloth Asger Brendstrup ATTORNEYS,

Patented Dec. 1,1970 3,543,752

Sheet 3 of5 FIG. 3

- INVENTORS. Holger Hesse Curl Sloth Asger Brendstr up eat/i214 ATTORNEYS,

Patented Dec. 1,1970 3,543,752

Sheet 5 015 INVENTORS. Holger Hesse Curl Sloth Asger Brendsrrup ATTORNEYS,

. XNFUSION APPARATUS The present invention is concerned with ofliquids into veins, arteries or muscles of animal or human bodies over a longer period of time with more'or less exact dosage of the quantities of liquid infused per time unit. Among the numerous fields in which a reliable method of this type will be applicable the following may be mentioned; pharmaceutical examinations; control of supply requirements concerning a drug or other required substance; positive or negative control of metabolic, such as kidney functions; continual medicament administration for therapeutic purposes; performance of intravenous anesthesia; so-called extra corporal circulation", heart-lung machines and artificial kidneys.

in any application of an apparatus of this type precautions must be taken to prevent air bubbles from entering-the body of the patient via the attached infusion apparatus.

Methods and apparatus are known for preventing airfrom entering into blood transfusion tubing systems when the blood container is running empty. However.- so' far no satisfactory system has been proposed to prevent bubbles from forming and migrating in systems in which the liquid is continuously pressed into the blood vessels or tissue of an animal or an human body under positive pressure such as by means of a pump or syringe. The difficulty in constructing a satisfactory device for this purpose is in part due to the necessity to have all mechanical devices sterilized before use and to be assembled under sterile conditions and to the fact that valves must be used to direct the liquid from the container to the pumping devices and the patient respectively, these factors involving risks of leaks by bad connections so that bubbles of air entering into the system may pass from the system into the body of the animal or person treated.

Various means have been proposed for the purpose of detecting individual air bubbles while passing through a tubing system of the type here in question. For example, electrodes may beprovided in such a way that an air bubble passing through the system will interrupt the fluid connection between them; a photoelectric device may be provided to detect air bubbles passing; another control factor that may beused for this purpose is the dielectric value that may be changed by the passage of airbubbles between condenser plates. In all these cases a new difficulty will arise when air is present in the form of minute bubbles which individually may not beharmful but which may coalesce somewhere in the system to form bubbleslarge enough to involve fatal risks when entering into important arteries in the brain or other critical places in the body. This problem is not satisfactorily solved by so constructing the apparatus that a warning or control signal is produced by any minute air bubble appearing in the system because the high signalling frequency that may be caused thereby, in particular during startup, is definitely undesirable in connection with a continuous medical treatment.

It is a purpose of the invention to solve these and related problems previously encountered in connection with permanent infusion systems.

Basically an apparatus for performing continuous infusion 'of liquids into blood vessels or muscles. of animal or human bodies over a longer period of time with a desired degree of exactitude of dosage comprises: A treating liquid supply container, a pump, such as a power-operated piston pump, and an infusion cannula adapted to inserted into the body of the animal or person to be treated. The above-mentioned parts are mutually connected by conduits or tubes which to. the extent necessary are provided with valves. In accordance with the basic feature of the invention the apparatus further comprises a closed gas bubble-collecting vessel having a liquid. inlet connected to said liquid pump and a liquid outlet connected to said cannula, the apparatus further including safety means responsive to the presence of a predetermined accumulated gas volume in said bubble-collecting vessel to produce a warning or control signal or to positively interrupt flow of liquid to said cannula. I

An apparatus constructed according to this principle will promptly and safely react to the presence-of dangerous gas volumes in the system while being unsensitive to the casual appearance of small air bubbles.

While any type of valve may be usedin an apparatus of the type here in question the use of squeeze valves closing soft conduits by external compression is preferred for reasons of sterility and security. Such valves have no parts in communication with the inner sterile surfaces of the system and accordingly do not require sterilization when the apparatus is transferred from one patient to another. The use of squeeze valves also facilitates disassembly of the tubing system for cleaning or replacement.

One important aspect of thisinvention is the possibility of using cheap plastic, tubing inthe connections between the various vessels and the pump and cannula enabling such tubing to be simply discarded after use and saving a critical cleaning procedure before renewed use of the machine. This feature is of particular interest in combination with the use of squeeze valves consisting of pressure elements compressing the soft and resilient plastic tubing against a rigid stationary base.

A squeeze valve in combination with resilient tubing has the further advantage of reacting immediately in contrast to e.g. ball valves which will allow some liquid to pass in the reverse direction before closing completely whereby dosage may become uncertain.

A system designed in accordance with the present invention is suited to operate in a more or less automatic way which is desirable in normal clinical routine where the operators may not be fully qualified technicians.

In view of the great risks involved and, particularly, in order to safeguard against fatal failure of the electronic system an electronically controlled system according to the present inventionmay be providedwith an automatic checking device periodically checking the electronic system and, in the case of a breakdown or improper function, stopping operation with or without emission of a warning-signal. The basic feature of the present invention, viz. the provision of the closed bubble-collecting vessel, permits introduction of a beneficial time factor in the operation ofthe device, by so dimensioning said vessel and so predetermining said critical volume of accumulated gas that the'volume of treating liquid present in the bubble-collecting vessel at anytime is sufficient to maintain safe operation during extended intervals of time between, for example, issuance of a warning signal and final automatic stopping of the operation or between successive checking cycles of the automatic checking device.

The above and other objects and advantages of the invention will appear from the following detailed description by reference to the enclosed drawings of an infusion apparatus and some alternative details thereof embodying the basic and some subsidiary features of the invention.

In the drawings FIG. 1 is a front view representation showing the parts visible and accessible on the front side of the mounting panel of an infusion apparatus for medical purposes with attached liquid supply container and cannula.

FIG. 2 is a rearview rear view representation, showing the mechanism for operating the pump or syringe feeding the infusion liquid under pressure. 7

FIG. 3 is a 'schematic representation showing the mechanism for operating the various squeeze'valves which close soft conduits by external pressure.

FIG. 4 illustrates an alternative, purely mechanically operating embodiment of the bubble-collecting vessel and safety means therein.

FIGS 5a, 5b and 5c illustrate three embodiments of the signalling mechanism cooperating with the bubble-collecting vessel, each adapted to be used in place of the float-operated mechanisms of respectively FlGS. I and 4.

FIGS. 6a and 6b illustrate a modification of the photoelectrio device forming part of the apparatus shown in FIG. 1.

Attached to the front side of a vertically disposed panel of the support structure S of the medical infusion apparatus schematically shown in FlG. i is a liquid pump orsyringe 28 from filled with a supply of treating liquid is provided independently of the support structure S in an elevated-position in relation to pump 28.Container 21 is in communication withinlet port 26 of thepump 28 by alength 22 of flexible, resiliently compressible tubing of a cheap disposable plastic material. A squeeze valve comprising a laterallyshiftable pressure element 23 and a cooperating stationaryrigid base 24 is shown in its closing position in whichtubing 22 is compressed between thepressure element 23 and thebase 24.

Also attached to the support structure S of the apparatus is a cylindrical bubble-collectingvessel 35 having atransparent sidewall 155 and hermetically sealing top andbottom walls 42 and 70.Outlet port 29 of thepump 28 is connected to aninlet port 71 in the bottom wall 70 ofvessel 35 by alength 30 of flexible, resiliently compressible tubing ofthe above-mentioned type, a squeeze valve comprising a laterallyshiftable pressure element 32 and a cooperating stationary rigid base 31 being shown in its opening position in whichtubing 30 is resiliently expanded between thepressure element 32 and the base 31. An outlet port 72 in bottom wall 70 ofvessel 35 is connected by alength 37 of flexible, resiliently compressible tubing of the above-mentioned disposable type to an infusion cannula 40, a squeeze valve comprising a laterally shiftable double-acting,pressure element 153 and a cooperating stationaryrigid base 38 being shown in its opening position in .whichtubing 37 is resiliently expanded between the left-hand portion ofpressure'element 153 and thebase 38.

The portions of thetubings 22 and 37 shown in broken lines and extending between, on the'one hand,container 21 and squeeze valve 23-24 and, on the other hand, between cannula 40 and squeeze valve 153-38 are not clamped to the support structure S of the apparatus and have a length permitting free relative movement of the apparatus proper in relation to thesupply container 21 and of the cannula 40 in relation to the apparatus whereas the remaining tubing portions passing through the squeeze valves to and from the various outlets and inlets squeeze valve above are clamped to the support structure S in any suitable way to hold them fixed squeeze valvein relation to the valves and outlet and inlet connections.

Connected to an outlet intop wall 42 ofvessel 35 is a venting conduit consisting of a length ill of the above-mentioned tubing material communicating with a collectingbottle 45 via a squeeze valve comprising the previously mentioneddoubleacting pressure element 153 and a cooperating stationary rigid base 4 3 the squeeze valve being shown in its closing position in which tubing 31 is compressed between the right-hand portion ofpressure element 153 and thebase 43. The normal disposition of the double-actingpressure element 153 and the cooperatingbases 3% and 43 as schematically indicated in FIG. 1 is such that-one of the two squeeze valves is open when the other one is closed.

As shown in FIG. 2, the pump orsyringe 28 is suspended on anupper bracket 53 which in turn is suspended on the forwardly extending arm of a two-armed lever E51 journaled in an aperture in the support structure S with the other arm extending to the rear for a purpose to be described later. The lower end of piston rod. 27 is connected by means of a threadedpin 52 to the upper side of a horizontal lifting platform which extends fromia position below thesyringe 28 on the front side of the apparatus through an elongated aperture in the support structure S to a position behind the support structure S where it is firmly connected to a verticallyreciprocatable operating mass 92 resting with its lower end on the free forward end of acam lever 93 pivoted for vertical swinging movement at its rear end in the support structure S and supported by a rotatable cam 94' carried by a shaft which is an extension of shaft 302 shown in FIG. 3 or is driven in unison therewith. Owing to the considerable weight (about l kg) ofmass 92 the suction stroke ofpump 2% will be gravityoperated. the stroke length being adjustable by means of an adiusting device schematically shown in FlG. l and shown in its proper functional position in FIG. 2, said adjusting device comprising a bracket Kill horizontally extending from support structure S to a position below platform as, a stroke-length limiting adjusting 'screw "90 extending vertically throughbracket 101 towards the underside of said platform 56 and a fixingscrew 91 extending through bracket Mil into engagement with adjusting screw 9b to fix the same in any position of adjustment.

To avoid contamination or jamming due to thickening of adhering liquid die portions of thepiston rod 27 extending downwardly frompump 28 towards platform $0 are protected by an extensible bellows 13b.

The maximum filling volume ofpump 28 permitted by the stroke-length adjusting device is indicated by apointer 103 carried by platform dd on a scale 162 provided on the front side of the support structure S.

The various squeeze valves shown in FIG. 1 are operated by means of a mechanism schematically shown in FIG. 3. A motor and reduction gear unit 301 drives a shaft 362 which may also be the shaft carrying cam 9 Shaft 302 further carries twocams 303 and 304 each adapted to cooperate with one ofsqueeze'valve pressure elements 23 and E32, these latter elements here being shown in the form of knee levers journaled in the support structure S and biased by tension springsj323 and 332 respectively into engagement with therespective conduits 22 and 30 supported onbases 24 and 31 respectively. The shape and disposition oi"cams 303 and 3% is such thatpressure element 32 is lifted bycam 304 against the action ofspring 332 out of engagement withconduit 30 resting against base 31 whilepressure element 23 is out of contact withcarn 303 and is held byspring 323 in closing contact withconduit 22 resting on base 2d, conditions being obviously reversed after 180 turn of the shaft 302. Arelease lever 3% is adapted upon depression of its one end by means of a key A accessible for manual operation from the front side of the apparatus simultaneously to hold, by means of pin and slot connections, both pressure elements out of squeezing contact with therespective conduits 22 and 34) independently of the angular positions ofcams 363 and 304.

The double-acting pressure element i539 of the squeeze valves acting onconduits 37 and 41 extending between, on the one hand, thevessel 35 and the cannula 4t} and, on the other hand, the vessel :35 and the venting bottle as is represented in FIG. 3 in the form of an knee lever journaled in the support structure S and having one arm urged by atension spring 353 into normalclosing contact'with conduit 41 resting againstbase 43. A key 5 accessible for manual operation from the front side of the apparatus is provided to act on the free arm of lever H53 to swing it against the action ofspring 3% to a position in which conduit 4'1 is temporarily allowed to open andconduit 37 is compressed againstbase 38.

in order to fill to system described above with treating liquid from thecontainer 21 key A is manually operated whereby bothconduits 22 and 30 are opened whileconduit 37 is normally open andconduit 41 normally closed by the double-actingpressure element 153 as long as key B is not operated.

Liquid from thecontainer 211 is freely flowing through the system to the cannula 40 and will eventually emerge therefrom. Due to the presence of accumulated air and the closing ofsqueeze valve 43vessel 35 will not be completely filled during this phase. The electronic or other safety system to be described later will respond to the presence of an excessive air volume invessel 35 and will not permit the apparatus to be started for infusion treatment. The operator will now operate key l3 and the resulting changeover of the doubleacting pressure element 153 will close theconduit 37 leading to the cannula 4d while opening the conduit ti to ventvessel 3 and permit the liquid fromcontainer 21 to fillvessel 35 completely, the complete filling being evidenced by discharge of liquid from conduit d-ll into ventingbottle 45. Now key B is released and as there is no volume of accumulated air in thevessel 35 the safety system. will no longer prevent the apparatus from being started by operation of start button 262. Key A may be coupled to key id to be held operated until key The system also comprises means safeguarding against buil-.

dup of a super-pressure, e.g. due to kinking inconduit 37 leading to the cannula or obstruction of .the cannula port, or

against other faults due to jamming of the pump piston in the pump cylinder, such jamming causing undue upward thrust during the pumping stroke and undue shortening'of the stroke length during the filling stroke. in all such cases the pumpcylinder carrying bracket 53 will be exposed to extraordinary strains in either direction which by the swinging suspension ofbracket 53 onlever 151 maybe used to operate a warning or control system such as shown in FIG. 2. The free rear end oflever 151 is biased by meansofopposed springs 152 and 154 to a neutral position maintained under the thrust and pulling strains appearing during normal pumpoperation. When thrust or pulling strains become strong enough to overcome the balancing action ofsprings 154 and 152 respectively the respective one of two opposedelectrical contacts 215 and 216 will be operated to produce a warning or control signal.

Further visible on the front side of theapparatus are a stop button 204 and signallinglamps 217 and 218, green light fromlamp 217 indicating normal operation and red light fromlamp 218 indicating an emergency state or stop due to faults. The

control system may further comprise a counter 112 indicating operating time or number of drive shaft revolutions and thereby total volume of liquid pumped.

Now turning to the safety device incorporated into the apparatus in accordance with the present invention reference is first made to the combined photoelectric and float arrangement shown in FIG. 1. Anopaque float 85 is provided in thevessel 35. At any liquid level corresponding to accumulated air volumes less than a predetermined volume thefloat 85 is supported on a level in which it intercepts a beam of light from alamp 211 which otherwise would pass through adiaphragm 156, diametrically through the air-filledupper part 80 ofvessel 35, through anotherdiaphragm 157andonto aphotoelectric element 21%; When due to excessive accumulation of air inspace 80float 85 has been lowered sufficiently to allow the light beam fromlamp 211 to reach element 210 a circuit into which this element is connected will be caused to produce a warning or control signal, involving for examplelighting ofred lamp 218 and simultaneous or subsequent stopping of motor 301, either measurepossibly being accompanied by the emission of an acoustic warning signal. An electronic circuit suitable to respond in such or a similar way to the operation ofelement 210 due to illumination fromlamp 211 can be designed by any expert on the electronic field.

FIG. 4 illustrates a safety device of a purely mechanical character. The air-collectingvessel 435 shown there may be substituted for vessel shown in FIG. 1 by connecting itslower outlet 472 viaconduit 37 to cannula 40 and by connecting inlet 471 viaconduit 30 to pumpoutlet 29 or directly to the outlet ofvessel 21 for gravity supply of liquid. Upper outlet Ml serves as a vent. A float 385 is provided withinvessel 435. Bothvessel 435 and float 485 have conical end portions connected by a cylindrical intermediate portion, the opposite ends of the float being provided with upper and lower hemispherical valve elements 4% and 405 adapted'to beseated on correspondingseats 406 and 407 provided within vessel 335 around the inner ends of vent outlet 441 andliquid outlet 472. Thefloat 485 will be in the position shown in which it opens liquid outlet 4'72 and closes vent outlet 441 as long as the volume of accumulated air invessel 435 is less than a predetermined volume. In the presence of said predetermined volume of accumulated air the liquid level will'be so low that the lloat closesliquid outlet 472 and opens vent M1. Excess air will now be discharged, the liquid level will rise and the float will be restored to the position shown in which liquid is fed to the cannula.

Alternative embodiments of thesafety device on an electric or electronic basis are illustrated in FlGS. 5a. 5b and 5c. ln all the three FIGS. the air bubble-collecting vessel is only schematically shown without liquid or-vent connections.

As shown in H6. So anupper electrode 501 is provided invessel 535 A substantially on or slightly above the liquid level corresponding to the presence of said predetermined accumulated air or gas volume. Anotherelectrode 502 is disposed further down in thevessel 535 A. A circuit for producing a warning or control signal comprises a signalling device AA and a transistor or electronic tube 533 the base or grid of which is negatively biased in acircuit including electrodes 501 and 502. when the liquid level is depressed by accumulated air below electrode 591 the connection between electrodes 50] and 502 will be broken and the negative bias will be removed fromelement 503 causing the main circuit to actuate the signalling device AA.

As shown in FIG. 5b threeelectrodes 504, 505 and 506 are provided withinvessel 535 B in an equilaterally triangular dis tribution with thetop electrode 504 disposed substantially on or slightly above the liquid level corresponding to the presence of said predetermined accumulated air or gas volume andthe twoother electrodes 505 and 506 disposed on a common lower level. Theelectrodes 504, 505 and 506 are connected in a bridge circuit comprising a signalling device AB emitting 'a warning or control signal in response to unbalance in the bridge circuit. While the bridge is in equilibrium as long as all the electrodes are submerged, the bridge will be unbalanced and the signalling device actuated by an accumulation of air depressing the liquid level belowtop electrode 50 causing the resistance R, between the top and bottom electrodes to increase while the resistance R between the two bottom electrodes remains unchanged.

The embodiment illustrated .in FIG. 5c also makes use of a bridge circuit comprising a signalling device AC emitting a warning or control signal in response to unbalance in the bridge circuit. One bridge arm comprises a condenser C having a constant value which is'the same as the value of a condenser C, in another bridge arm, this latter condenser C, being formed by condenser plates 507-and 508 disposedon the same level withinvessel 535 C and the liquid dielectric between said plates. Theplates 507 and 508 extend downwardly substantially from the liquid level corresponding to said predetermined accumulated air or gas volume. It the liquid level is further depressed by accumulation of air or gas some portions of thecondenser plates 507 and 508 will emerge from the liquid whereby the value of condenser C, will be changed, the equilibrium of the bridge circuit will be disturbed and the signalling device AC will be actuated.

FIGS. 6a and 6b are schematic top views illustrating an electro-optical embodiment of the safety device according to the invention.

Disposed to one side of the transparent air orgas bubblecollecting vessel 635 is anelectric lamp 611 radiating a beam of light towards the vessel substantially on the liquid level withinvessel 635 corresponding to the presence of said predetermined accumulated air or gas volume. Opposite tolamp 611 and on the same level there is disposed aphotoelectric element 610 connected in a circuit (not shown and obvious to the expert) which is inactivated as long as thephotoelectric element 610 is exposed to concentrated illumination fromlamp 611 and which will be caused to produce a warning or control signal when the electric condition of said element is changed by interruption of said concentrated illumination. The central portion of the beam emitted fromlamp 611 is prevented from passing through the central area of saidvessel 635 and reachingelement 610 by ascreening element 612. However, as long as there is a column of liquid in saidvessel 635 above said critical level the portions of the beam passing outwardly of the screening element and going through the outer portions of thc vest -c1635 and the liquid therein will be deflected and concentrated onto thephotoelectric element 610 as shown in H6. 6b thus inactivating the circuit. lf due to the presence of an increased volume of air withinvessel 635 no light-deflecting liquid column will be disposed in the path of the beam from lamp dill no light will be-focussed onto element ell) and the circuit will respond to the change electrical state of element dill by producing a warning or control signal.

Other electrical, electro-optical and equivalent embodiments of the safety device will be readily apparent to the expert and are intended to be comprised by the attached claims.

We claim:

l. An apparatus for performing continuous infusion of liquids into veins, arteries, and muscles of living bodies, comprising a treated liquid supply container, liquid-feeding pump means having an inlet and an outlet, a closed gas bubble-collecting vessel having an inlet and an outlet, an infusion cannula adapted to be inserted into the body to be treated, liquid conduits connecting respectively said supply container with the inlet of said liquid-feeding pump means, the outlet of said pump means with the inlet of said gas bubble-collecting vessel and the outlet of said gas bubble-collecting vessel with said cannula, first control valve means inserted between said liquid supply container and the inlet of said pump means, and second control valve means inserted between the outlet of said pump and the inlet of said bubble-collecting vessel, safety means responsive to the presence of a' predetermined accumulated gas volume in said bubble-collecting vessel to produce a control signal for indicating the presence of said predetermined gas volume, said first and second control valve means being adapted to be operated in timed relation to the operation of said pump to open during the suction action of said pump means said first control valve means while closing said second control valve means and to close during discharge action of said pump said first control valve means while opening said second control valve means, a liquid-collecting vessel, a liquid conduit connecting said collecting vessel and said gas bubblecollecting vessel, and double-acting valve means for closing said conduit to said collecting vessel and for simultaneously opening said conduit between said gas bubble-collecting vessel and said cannula and for opening said conduit to said liquid collecting vessel while simultaneously closing said conduit to said cannula.

2. The apparatus as claimed in claim 1 in which both said liquid inlet and outlet are provided 'near the'bottom of said bubble-collecting vessel.

3. The apparatus as claimed in claim 1 in which third control valve means are provided between the outlet of said bubble-co1lecting vessel and said cannula.

4. The apparatus as claimed in claim 1 wherein said liquid conduits are made of resiliently deformable material, and said control valve including a squeezing means for closing said conduits by compression and allowing them to resiliently open upon the release of said compression.

5. The apparatus as claimed in claim 4 in which said liquid conduits are in the form of disposable plastic tubing and that said control valve means are pressure elements movable to compress such tubing between a stationary support and an edge on the element.

6. The apparatus as claimed in claim l wherein said pump means is a piston pump.

7. The apparatus as claimed in claim 6 wherein the volume of liquid present in said bubblecollecting vessel in the presence of said predetermined accumulated gas volume is greater than the volume of liquid fed during one discharge stroke of said piston pump.

8. The apparatus as claimed in claim l wherein said safety means includes a float valve provided within said bubble-collecting vessel, and means mounting said float valve to close the outlet of said vessel leading to said cannula when at least said predetermined accumulated gas volume is present and for leaving said outlet open when said predetermined accumulated gas volume is not present.

9. An apparatus as claimed in claim 1 wherein said safety means include a float provided within the bubble-collecting vessel, photo electric means including a light beam positioned to be interrupted by said float in one position, and not to be interrupted in another position, and means for producing a control signal in response to a change in said float from said one position to said other position. t

it). The apparatuses claimed in claim ll wherein said safety means include an electronic circuit actuatable to cause a control signal to be produced, said circuit comprising a pair of spaced contacts disposed one above the other within said bubbio-collecting vessel, the upper one of said contacts being disposed substantially on a liquid level corresponding to said predetermined accumulated gas volume whereby the circuit between said upper and lower contacts is closed through said liquid only when there is an accumulated gas volume less than said predetermined accumulated gas volume in said vessel.

ii. The apparatus as claimed in claim 1 wherein said safety means include an electrical bridge circuit adapted to be unbalanced causing a warning or control signal to be produced, said bridge circuit including spaced contacts each connected to a different bridge arm and one disposed above any other of said contactswvithin said bubble-collecting vessel, said upper one of said contacts being disposed substantially on the liquid level corresponding to said predetermined accumulated gas volume to be in circuit-balancing connection with any other of said contacts through said liquid only when there is an accumulated gas volume less than said predetermined accumulated gas volume in said vessel.

12. The apparatus as claimed in claim 1; wherein said safety means include an electrical bridge circuit adapted to be unbalanced causing a control signal to be produced, said bridge in one arm comprising a constant value capacitor and then in another arm capacitor means comprising spaced condenser plates disposed within said bubble-collecting vessel such as to extend downwardly from the liquid level corresponding to said predetermined accumulated gas volume and spaced from each other a distance corresponding to the presence of a bridgebalancing dielectric liquid layer between said plates only as long as the plates are fully submerged in said liquid.

13. The apparatus as claimed in claim ll wherein said bubisle-collecting vessel has transparent wall portions in the range of the interface between the liquid and said predetermined accumulated gas volume, said safety means including a light source disposed externally adjacent to said transparent wall portions, an electronic circuit including a photosensitive device responsive to the interruption of a focused beam of incident light from said light source to cause the circuit to produce a' control signal, said photosensitive device being disposed externally adjacent to said transparent wall portions and substantially opposite to said light source, a light obstructing member disposed between said light source and transparent wall portions acting to prevent light from said source from falling onto said photosensitive device directly through said transparent wall portions, said light source and photosensitive device being disposed on such a level relative to said transparent wall portions that a liquid column will be disposed in the path of the light only when the liquid level corresponds to accumulated gas levels less than said predetermined accumulated gas level, said light source, light obstructing member and photosensitive device being optically disposed so that light passing from the light source passed said light obstructing .member and through said transparent wall portions and a column of liquid enclosed therein will be focused onto said photosensitive device to hold said circuit unaffected.

14. The apparatus as claimed in claim 1 wherein said safety means include electrical means for cutting off the power supply to said pumping means, and automatic checking device for periodically checking the electric elements of said safety means and in the case of a breakdown or an improper function to stop operation of the apparatus.

R5. The apparatus as claimed in claim l including means responsive to said control signal from said safety means for interrupting operation of said pump.

16. The apparatus as claimed in claim l including means responsive to said control signal from said safety means for producing warning signals perceptible to a human being.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,543,752 D d December lst, 1970 Inve t (s)Holger Hesse, Carl Sloth and Asger Brendstrup It; is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 9 change "Leo" to Lea Column 1,line 2 after "with" insert -infusion-; line 62 after "adapted to" insert be-.Column 2, line 54 after "FIG. 1 is a" insert schematical; line 58, change "rearview" to schematical-.Column 3 line 39 change "squeeze valve" to mentioned; line 40 change "fixed squeeze valve" to in fixed positions;line 43, change to 4l. Column 4 line 61, after "valve" insert 153- Signed and sealed this 6th day of April 1971.

(SEAL) Attest:

EDWARD I-I.FLETCHEIR,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents l FORM PC1-1050 (10-69) i i i i i i

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