US3731679A - Infusion system - Google Patents

Abstract

A portable infusion system uses a disposable piston type syringe as a positive displacement pump. The syringe piston is reciprocally driven by a bidirectional DC motor under control of a battery powered circuit. Different selectable rates of pumping are maintained by controlling the width of bidirectional DC pulses coupled to the DC motor and by monitoring the motor back EMF during the off-time of the pulses. A disposable two-way valve connects the syringe pump with a fluid source and a catheter. Safety circuits protect against deleterious conditions such as the passage of an air bubble or an over-pressure condition.

Description

United States Patent 091 Wilhelmson et al.

[451 May 8, 1973 INFUSION SYSTEM [75] Inventors: Jack L. Wilhelmson, Fenton; Theodore E. Weichselbaum, St. Louis; Vernon F. Braun, Berkeley,

[21] Appl. No.: 81,926

[52] U.S. Cl......l28/214 F, 128/214 E, 128/DIG. 12, l28/DIG. l, l28/DIG. 13, 417/45, 417/411 [51] Int. Cl. ..A6lm 05/00 [58] Field oiSearch ..128/2l3,214R,214 E, 128/214 F, 214 B, 214.2, 218 R, 218 A, 230,

234, 273, DIG. 1, DIG. 12, DIG. 13, DIG. 3,

3,515,966 6/1970 De Valroger et al. ....417/411 X 3,648,694 3/1972 Mogos et al ..128/214 F FOREIGN PATENTS OR APPLICATIONS 232,476 2/1969 U.S.S.R ..128/214 E OTHER PUBLICATIONS Blum et al. A Method of Continuous Arterial infusion, Surgery, 1948, pp. 30-35.

Primary Examiner-Dalton L. Truluck Attorney-Hofgren, Wegner, Allen, Stellman & Mc- Cord [57] ABSTRACT A portable infusion system uses a disposable piston type syringe as a positive displacement pump. The syringe piston is reciprocally driven by a bidirectional DC motor under control of a battery powered circuit. Different selectable rates of pumping are maintained by controlling the width of bidirectional DC pulses coupled to the DC motor and by monitoring the motor back EMF during the off-time of the pulses. A disposable two-way valve connects the syringe pump with a fluid source and a catheter. Safety circuits protect against deleterious conditions such as the passage of an air bubble or an over-pressure condition.

10 Claims, 6 Drawing Figures PATENTEDHAY 81975 SHEET 1BF 3 INVENTORS flog Z Z/Ze/rrzao'n ile ATTORNEYS INFUSION SYSTEM This invention relates to an improved pumping system and an improved control circuit, particularly adapted for use in an infusion system.

During typical blood transfusions and intravenous injections, a solution bottle is usually hung above a patient to allow gravity feed of fluid through disposable venoclysis tubing to a catheter inserted in the vein of the patient. Transportation of the patient is difficult because the solution bottle must always be located above the patient, requiring an attendant to hold the solution bottle. Even when the patient is located in a hospital, periodic monitoring of the process is required, utilizing valuable personnel time. Despite periodic monitoring, certain malfunctions can occur which may go unattended for lack of a suitable indication of the malfunction. For example, during an injection, it is possible for a needle to become displaced from its position in a vein and become lodged in a muscle.

In accordance with the present invention, a novel portable positive displacement pumping system replaces the gravity feed system typically used for transfusions and injections. As a result, the solution bottle may be located at any reasonable height with regard to the patient. A novel battery powered control circuit for the pump system includes a number of safety circuits which automatically monitor for deleterious conditions, such as passage of air bubbles or the dislodgement of the intravenous needle into a muscle, eliminating the requirement that an attendant periodically monitor the process. Sterile conditions are easily maintained because the positive displacement pumping system uses a disposable syringe and a disposable twoway valve which can be discarded after use with each patient and replaced with a new sterile syringe and valve.

Some attempts have been made to use disposable piston type syringes for pumping fluids at fixed locations. For example, it has been proposed to drive the piston of a syringe by an AC motor connected to an external AC line source. To control the rate of pumping, adjustment is made of the length of the drive stroke for the piston. Such apparatus is not usable in an infusion system, since air bubbles may be passed to the patient, and other serious malfunctions might occur which could not be automatically cured. Also, such apparatus does not permit priming of the syringe, nor is accurate control possible, as is essential in an infusion system.

The applicants novel control circuit for driving the novel pumping system includes a unique DC motor drive which can be used to accurately drive loads other than pumps. The drive automatically compensates for variations in the load, long term aging of batteries for powering the control circuit, and detection of deleterious conditions associated with the driven load. Bidirectional motor movement is accomplished by a simple reversing circuit controlled by movement of the motor armature. The control circuit uses the known techniques of driving the DC motor by variable width pulses, and monitoring the back EMF across the motor during the off-time of the pulses to control the on-time width of the pulses. However, a pair of such circuits has heretofore been required when driving a motor in both forward and reverse directions. The applicants control circuit accomplishes the same degree of control while substantially simplifying the circuit.

One object of this invention is the provision of an improved infusion system in which the sterile parts in contact with the fluid being pumped are disposable and readily replaceable with new sterile parts.

Another object of this invention is the provision of an improved control circuit for driving a DC motor through a bidirectional cycle of operation.

Yet another object of this invention is the provision of improved pump means driven by a DC motor and feedback means for modifying the operation of a control circuit in accordance with external conditions related to the operation of the pump.

Further objects and features of the invention will be apparent from the following specification, and from the drawings, in which:

FIG. 1 is a perspective illustration of an infusion system incorporating the pumping system of the present invention;

FIG. 2 is an exploded view of the pumping system, with the syringe pump being illustrated for clarity as located on the opposite side of the pump housing shown in FIG. 1;

FIG. 3 is a partly plan and partly sectional view of a disposable valve with embedded electrodes;

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 3;

FIG. Sis a plan view taken along lines 55 of FIG. 4;

and

FIG. 6 is a schematic diagram of the control circuit for the pump system.

While an illustrative embodiment of the invention is shown in the drawings and will be described in detail herein, the invention is susceptible of embodiment in many different forms and it should be understood that the present disclosure is to be considered as an exemplitication of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.

GENERAL DESCRIPTION Turning to FIG. 1, a portable infusion system is illustrated for pumping fluids such as blood from asolution bottle 20 to acatheter 21 inserted into the vein of a patient. Fluid transfer is accomplished by a pumping apparatus 24 held by acaddy assembly 26 mounted to arail 28 of a bed for the patient. Thecaddy 26 also removably holds thesolution bottle 20, which can be located at any reasonable altitude with respect to the patient.

Solution bottle 20 is of conventional construction, and includes acap 30 having anair valve 31 and anoutput port 32 for fluid transfer.Disposable venoclysis tubing 34 couples theport 32 to aninput port 36 in a disposable two-way valve 40 which forms a part of the pump apparatus 24.

Pump apparatus 24 uses as a pump chamber a conventional disposable syringe 42 having aslidable piston 44 which can be reciprocated to pump fluid within a hollow syringe barrel coupled with the two-way valve 40 which includes an outlet oroutput port 46 connected byvenoclysis tubing 50 with aconventional Y connector 52 for medication introduction. The output of theY connector 52 is coupled by additional disposable venoclysis tubing 54 to thecatheter 21.

The control circuit for pump apparatus 24, seen in detail in FIG. 3, is completely contained within the housing for the pump apparatus, and can be either externally or internally powered. During a back stroke, in which thesyringe piston 44 is driven away from thevalve 40,input port 36 admits fluids from solution bottle into the syringe barrel. The valve inoutput port 46 is closed at this time. During a forward stroke, in whichpiston 44 is driven towards thevalve 40, theinput port 36 is closed and theoutput port 46 is opened, pumping the solution throughvenoclysis tubing 52 and 54 to thecatheter 21.

The novel pumping apparatus 24 is seen in exploded view in FIG. 2. A sterile, positive displacement pump is economically formed by using a conventional disposable syringe 42 in combination with a uniquedisposable valve 40, to be described. Syringe 42 includes agasket 70 fixedly mounted to thepiston 44 for movement within a hollow barrel 72 which has a single fluid opening terminating in aneedle connector 74. The syringe includes extendingfinger grip arms 76, which in the present invention are held by base means for the pump apparatus 24.

Syringe 42 andvalve 40 are removably held by housing means in order to allow disposal after use with each patient and replacement with a new presteriled syringe and valve. A lower moldedcase 90 includes a pair ofupstanding arms 92 each having aslot channel 94 which slidably receives one of theextensions 76 of the syringe.Lower case 90 also includes anupstanding post 100 having aconcave surface 102 for holding thevalve 40 when it is mated to the syringe 42, and for making electrical contact with electrodes embedded in the valve. A pair of femaleelectrical sockets 106 insurface 102 receive air bubble detector electrodes, as will appear, and a female socket 108 (not illustrated in FIG. 2), which may be separate fromcase 90 or similarly molded in a portion thereof, receives an over-pressure detector electrode. Thesockets 106 and 108 are connectedby wires to the circuit of FIG. 3 which is contained within thehollow case 90.

The mechanical drive arrangement forpiston 44 consists of abidirectional DC motor 120 having anarmature shaft 121 with anintegral motor gear 122. Themotor gear 122 meshes with anidler gear 126 rotatable about anidler shaft 128 rigidly attached to apinion gear 130. Thepinion gear 130 meshes with adrive gear 132 which is fixedly attached to theshaft ofajackscrew 134. Asyringe cylinder carrier 140 includes agripping head 142 having an opening therein for slidably receiving thehead 45 ofpiston 44. Thecarrier 140 has an internally threaded central opening for engaging the threads of thejackscrew 134 to cause the carrier to act as a drive nut on the jackscrew.

When DC motor 120 is energized by voltage of predetermined polarity, the two-stage spur reduction gears rotatejackscrew 134 and cause thecarrier 140 and attachedcylinder 44 to be driven in a forward stroke.Carrier 140 includes aprotrusion 150 with a permanent magnet which extends downward for magnetically actuating a sealed forwardstroke limit switch 152 and a sealed reversestroke limit switch 154, mounted to acircuit board 156 which contains the circuit of FIG. 3. Thecarrier 140 is driven in a forward stroke direction untilprotrusion 150 is directly overlimit switch 152, at which time the circuit of FIG. 3 reverses the polarity of voltage to DC motor in order to rotatearmature 121 in a reverse direction. The carrier andcylinder 44 are now longitudinally moved through a back stroke until the protrusion is directly overlimit switch 154, at which time the circuit of FIG. 3 again reverses the polarity of voltage toDC motor 120. While magnetically actuated proximity switches are preferred, a mechanical switch arrangement could alternately be used, actuated by mechanical engagement withprotrusion 150.

Power for theDC motor 120 and the control circuit is obtained from a self-contained DC power source, as a pair of series connectedDC batteries 160. Desirably,batteries 160 are rechargeable, sealed nickel-cadmium batteries which allow the pump apparatus to be powered either from an external AC source, or internally powered in order to allow the unit to be completely portable. If the unit is constructed for portable use only, thebatteries 160 may be conventional 1.5 volt D size. TheDC batteries 160 are housed within abattery retainer cylinder 162 molded inlower case 90. Electrical connection is made through abattery contact spring 164 and a contact on abattery retainer cap 165 which threads into the battery retainer cylinder wall to allow replacement of the batteries when necessary.

An upper case mates with thelower case 90 to enclose the drive train assembly and the batteries 1 60.Case 170 includes awindow 172 through which indicia on athumbwheel knob 174 may be observed in order to allow'operator selection of different rates of pumping fluid. Desirably, the indicia onwheel 174 directly indicate pump rate, such as one liter of fluid per one, two, three, etc., hours. A different range of pump rates may be provided by replacing syringe 42 with a syringe of different capacity, andknob 174 may be so marked with alternate indicia. A syringeprime switch 176 allows an operator to override the setting selected bywheel 174 in order to rapidly reciprocate thepiston 44 when first priming the syringe 42 to eliminate air bubbles. During the time theswitch 176 is actuated, the air bubble protector circuit is disabled.

Disposable Valve Assembly Thedisposable valve assembly 40 is illustrated in detail in FIGS. 3-5. The assembly is economically formed by using a pair of identically manufactured valve units mated in opposite fluid flow directions with a centralfluid channel unit 192 so that onevalve unit 190forms input port 36 and theother valve unit 190forms output port 46.

Eachvalve unit 190 includes a fluid input port having a taperedconical wall 194 which directs fluid to acheck valve 195 formed of flexible, resilient material such as rubber.Check valve 195 is formed by a hollow center portion with anintegral tapering nose 196 terminating in a rectangular slit opening 197 which passes fluid to an output port defined by atubular wall 200 which also serves to anchor the hollow center portion of the check valve. Thecheck valve 195 is of conventional construction and allows fluid flow in a direction from the input port defined byconical wall 194 to the output port defined by thetubular wall 200, but collapses to block fluid flow in an opposite direction.

The centralfluid channel unit 192 includes aninput fluid channel 202 into which is inserted the output port of thevalve unit 190 which formsinput port 36. Oppositeinput fluid channel 202 is an output fluid port orchannel 203 having a conical wall which receives the taperedsyringe connector 94. Contiguous withfluid channels 202 and 203 are anoutput fluid channel 204 and aclosed fluid channel 206.Channel 204 terminates in aneck portion 208 of reduced diameter which mates with the input port of thecheck valve 190 which serves as theoutput port 46 for passing fluid flow to the catheter.

To detect the presence of anair bubble in the fluid channel, a pair of metal rods orelectrodes 212 extend through the wall of the valve assembly and into thefluid channel 204. Theelectrodes 212 are spaced apart approximately 0.25 inches, and are placed ahead of the output functioningcheck valve 195. When fluid of 0.001 percent salinity or higher is present between theelectrodes 212, the fluid completes a resistance path of sufficiently low impedance to allow the circuit of FIG. 6 to continue to operate. When an air bubble of predetermined size passes the electrodes, the impedance rises and breaks the circuit to cause the forward stroke of the pump to terminate.

To detect an over-pressure condition, as is caused when the catheter becomes lodged in a muscle, theclosed fluid channel 206 forms a pressure detector. Acap 217 closes the end offluid channel 206, trapping air between thecap 217 and the fluid which enters thechannel 206. A single metal rod orelectrode 220 is embedded through the wall of the valve assembly and into thefluid channel 206. When an over-pressure condition occurs, the pressure of the fluid withincentral channel unit 192 further compresses the trapped air and allows fluid to further enter theclosed channel 206 until it contacts theelectrode 220, thereby completing a circuit through the fluid to one of theelectrodes 212 in order to indicate an over-pressure condition.

. Desirably,electrodes 212 and 220 are an integral part of thevalve assembly 40, rather than a part of the syringe 42. As a result, a conventional disposable syringe of low cost may be used as the pump. The valve assembly itself may be economically molded of plastic, except for the pair ofcheck valves 190 which may be molded of rubber. The externally extending ends of themetal electrodes 212 and 220 are directly inserted in thefemale sockets 106 and 108, respectively, as previously described.

Control Circuit The control circuit for the pump assembly is illustrated in detail in FIG. 5. DC power is provided between a DC potential line 248 and a source of reference potential orground 250. When external 115 volt AC is available, aplug 256 may be inserted into the external AC source so as to couple 115 volt AC to astepdown transformer 258. The transformer is connected through a full wave diode rectifier to aline 260 connectable through a socket with line 248. Therechargeable batteries 160 form a filter capacitor for the full wave rectified AC voltage, reducing the ripple of the voltage on DC line 248. If desired, an additional filter capacitor 262 may be provided. Thestepdown transformer 258 and full wave rectifier may be housed within theplug 256, and connected through a two'line cord to the socket receptacle on the pump assembly. When the pump assembly is to be used independent of the external AC source, the line plug is simply removed from the receptacle on the pump assembly, allowing the previously rechargedbatteries 160 to thereafter power the control circuit.

DC motor 120 is a shunt wound permanent magnet motor which rotates in a forward direction when current flows from a terminal 260 to a terminal 262, and rotates in a reverse direction when current flows from terminal 262 toterminal 260. As will appear, the motor is driven by pulses having a less than percent duty cycle. During the off-time of the pulses, the motor acts as a generator or tachometer, and the back EMF across the terminals is sensed and stored in order to control the duty cycle of the drive pulses.

An electronic reversing switch, includingtransistors 265, 266, 267, 268, 269, and 270 forms a double-pole, double-throw switch.Transistors 265 and 268 are synchronously driven conductive to pass current in a forward direction throughmotor 120. Alternatively,transistors 266 and 267 may be synchronously driven conductive to complete a reverse current path formotor 120 to drive the motor through its reverse or back stroke. Whentransistors 265 and 268 are on, current passes from apositive line 275 throughtransistor 265 toterminal 260 ofmotor 120, throughmotor 120 and out terminal 262 totransistor 268, and thence toground 250. When the forward limit of travel is reached, as indicated by the permanent magnet on protrusionactuating limit switch 154, a reversing switch driver, to be described, turnstransistors 265 and 268 off andtransistors 266 and 267 on. Current then flows from thepositive line 275 throughtransistor 266 to terminal 262, and thence throughmotor 120 and outterminal 260 totransistor 267 and thence toground 250.

The reversing switch driver, consisting oftransistors 280, 281, 282, and 283, acts as a regenerative bistable switch useful to obtain the heavy drive capability which is necessary when using low supply voltage, such as 3.0 volts from the pair ofbatteries 160.Transistors 280 and 283 drive each other into saturation whenmagnetic protrusion 150 actuates switch 152 at the end of a back stroke, grounding the base oftransistor 282. Alternatively,transistors 282 and 281 drive each other into saturation whenmagnetic protrusion 150 actuates theswitch 154, grounding the base oftransistor 283 at the forward stroke limit of travel.

When transistor 281 saturates, current flows from its emitter to base and through aresistor 290 to the base oftransistor 267 to provide drive for the reversing switch. At the same time, the voltage at the collector of transistor 281 rises to the potential ofline 275, back biasingtransistors 269 and 265.Transistor 282 is also saturated at this time, causing current to flow through the emitter-base oftransistor 266, through aresistor 292 and via aline 293 to the collector oftransistor 282 and thence toground 250. This provides drive for the other half of the reversing switch. Since the collector voltage oftransistor 282 is at approximately ground potential, no current flows through aresistor 295 totransistor 270, nortransistor 268. When the opposite stable state of the bistable is set bymagnetic protrusion 150,transistors 280 and 283 act similar to the above described operation fortransistors 281 and 282, providing drive fortransistors 265 and 269, andtransistors 268 and 270, as will be explained with reference to the bubble detector circuit.

During the forward stroke,transistor 270 is driven on by pulses having approximately a 25 percent duty cycle. For one circuit which was constructed, the drive pulses for minimum motor speed had a four millisecond on-time out of a sixteen millisecond interval, producing a sixty hertz frequency. The duty cycle during the forward stroke is adjustable, as will appear, and is controlled by a forward stroke control.

The reverse stroke always occurs at maximum speed sincetransistors 266 and 267 are fully saturated during reverse motor movement. As the DC voltage frombat teries 160 slowly drops with age and use, lesser voltage is passed through thereverse stroke transistors 266 and 267to theDC motor 120, resulting in a decreased speed of movement. As will appear, a battery voltage variation compensation circuit is responsive to decreased battery voltage to decrease the off-time of the pulses controlled by the forward stroke control, thus increasing speed in the forward stroke in order to maintain the selected rate of pumping.

The forward stroke control includestransistors 300, 301, 302, 303, and 304, connected basically as an unsymmetrical astable multivibrator. To allow selection of different rates of pumping,thumbwheel knob 174 is connected to thewiper 310 of multi-position switches 312.Wiper 310 is connected to any one of a plurality ofresistors 315 each having a different resistance value. A master OFFswitch 316 when actuated connects thewiper 310 to DC line 248, viaprime switch 176. When thethumbwheel 174 is rotated to cause thewiper 310 ofswitch 312 to contact oneparticular resistor 315, a path is formed from DC line 248, through actuatedswitch 316 andunactuated switch 176 towiper 310, and thence through the selectedresistor 315 to the emitter oftransistor 300. The collector oftransistor 300 is connected through acapacitor 317 and thence through the collector-emitter oftransistor 301 toground 250. The duty cycle of the pulse coupled totransistor 270 is determined by the capacitance ofcapacitor 317, the selected value ofresistor 315, and the voltage at the base of transistor 300 (from the velocity feedback circuit as will appear).

The on-time of the duty cycle is determined by thetime period transistors 301 and 303 are saturated andtransistors 302 and 304 are turned off.Transistor 300 acts as a controlled current source that dischargescapacitor 317 during the time it holdstransistor 304 turned off. Whentransistor 301 turns on, transistor 303 is turned on by current flowing from its base and through aresistor 320 and conductingtransistor 301 toground 250. Transistor 303 drivestransistor 270 of the reversing switch driver through aresistor 322. Thus, the on-time of the duty cycle which controls the forward stroke of the motor is determined by saturation of transistor 303.

The off-time of the duty cycle is controlled by satura tion oftransistor 304, at whichtime transistors 301 and 303 are turned off. This off-time is determined by the capacitance value of acapacitor 325, the voltage to which thecapacitor 325 is allowed to charge during the prior on-time, and the resistance values of a pair of series connectedresistors 327 and 328. The allowable voltage to whichcapacitor 325 is allowed to charge is set by the battery voltage variation compensation circuit, to be explained.

The detailed operation of the forward stroke control circuit is as follows. Assumetransistor 301 has just turned on withcapacitor 317 fully charged andcapaci tor 325 fully discharged. Whentransistor 301 saturates, the negative terminal ofcapacitor 317 has a negative voltage equal to the supply potential. For this example, it will be assumed that the supply potential frombatteries 160 is at maximum potential, or 3.0 volts. Current now flows from the +3.0 volt supply and throughswitches 316, 176 and 310 to the selectedresistor 315 and thence throughtransistor 300 to dischargecapacitor 317. When the negative terminal ofcapacitor 317 reaches 1.2 volts (the base-emitter drop oftransistors 302 and 304),transistors 302 and 304 are turned on, turningtransistor 301 off and rechargingcapacitor 317 to supply voltage through aresistor 330.Capacitor 325 discharges through theseries resistors 327 and 328 until the base-emitter voltage oftransistor 301 is reached, at whichtime transistor 301 turns on and the cycle is repeated.

During the forward stroke, the pulse coupled to the DC motor has an approximately 25 percent off-time at the maximum infusion rate selectable byswitch 310. Due to mechanical inertia, the motor continues to turn and generates a back EMF proportional to the angular velocity of the armature. This voltage is sensed by a velocity feedback circuit and stored in order to controltransistor 300 and adjust the on-time of the pulses to compensate for variations in load. Thus, various fluids and syringes may be used without effecting to any significant extent the calibration ofthumbwheel knob 174.

During the forward stroke,transistor 265 is on, connectingterminal 260 to the supply voltage atline 275. During the off portion of the forward stroke pulse,transistor 270 is off, blockingtransistor 268 and disconnectingground 250 from the motor terminal 262. The back EMF across the motor terminal is now coupled through aresistor 335 and a pair of series connecteddiodes 336 and 337 to a capacitor 340 connected toground 250. The capacitor 340 charges to a potential that is the sum of the supply voltage and the voltage generated by the motor.

During the on-time of the forward stroke control,transistor 270 is driven into conduction, drivingtransistor 268 into conduction and hence connecting motor terminal 262 to approximately ground potential, back biasing thediodes 336 and 337. The voltage charge across capacitor 340 is now used to control the base drive oftransistors 300, establishing ,an on-time duration proportional to the voltage across the capacitor. A resistor 342 allows the voltage across capacitor 340 to slowly leak off. Since the emitter oftransistor 300 is referenced to the DC supply voltage, the current throughtransistor 300 is dependent solely on the back EMF across the DC motor, eliminating the effect of supply voltage variations.

The control circuit also includes a number of special circuits described in the following sections.

Bubble Detector The bubble detector circuit includes thebubble detector electrodes 212 andtransistors 350 and 351.

When fluids having a conductivity equal to a salinity of 0.001 percent or greater are present betweenelectrodes 212 which are spaced 0.25 inches apart, the resistance therebetween is on the order of 200 kilohms orv lower. This causes current to flow from thesupply line 275, through the emitter-base oftransistor 350, through aresistor 352, as 10 kilohms, to oneelectrode 212 and thence through the fluid to theother electrode 212 to charge acapacitor 353, as 1.0 microfarads.Capacitor 353 is discharged by the forward stroke control circuit through adiode 355. The time constants are chosen such thatcapacitor 353 is never charged to more than 0.1 volts unless the forward stroke control circuit fails. If the forward stroke control circuit fails in such a way that the forward stroke would be at full supply voltage across themotor 120,capacitor 353 charges to supply voltage and turnstransistor 350 off.

A This terminates operation. Thus, the patient is protected from excessive infusion rates which otherwise might be caused by failure of critical parts in the circuit. The current passing through the fluid is on the order of 10 microamps or less thereby creating no hazard of electrolysis or other hazard to the patient.

The current that chargescapacitor 353 causes a current of at least 200 times magnitude to flow from the supply, through the emitter-collector oftransistor 350, through aresistor 357 and into the base oftransistor 351. Thisforward biases transistor 351, creating a path to ground through thetransistor 351 and aresistor 358 connected to the base oftransistor 269, thereby allowing drive fortransistors 269 and 265 to flow when thetransistors 269 and 265 are turned on by the reversing switch driver circuit. When an air bubble or cavity is present between theelectrodes 212, the current path is broken andtransistor 351 is biased off. Therefore, themotor 120 stos on the forward stroke.Prime switch 176 in the forward stroke control circuit is used to override this shut-off during syringe priming.

The combination of the bubble detector circuit and the placement of theelectrodes 212 and 220 in the two-way valve assembly 40 creates a fail safe apparatus which detectsair leaks caused by a defect in the pump assembly itself. Referring to FIG. 4, theelectrodes 212 are located in the pressure side of the fluid channel, between the pair ofcheck valves 195. Should themetal electrodes 212 not be completely surrounded by the plastic material forming the wall of the valve channel, as might occur due to dropping of the valve assembly, for example, an air passageway or void would be created which would allow air to seep from the atmosphere into thefluid channel 204. If theelectrodes 212 were located ininput port 36 upstream of thecheck valve 195, the electrode located furthest downstream could leak air during a back stroke operation. 1f the bubble should pass thecheck valve 195, it would escape detection by the bubble detector circuit.

To prevent such an occurrence, theelectrodes 212 are located in a region which has high pressure during a forward stroke. During the forward stroke, the pressure inchannel 204 is in excess of atmospheric pressure, therefore an air passageway adjacent eitherelectrode 212 merely causes fluid to seep out of thechannel 204, but does not create an air bubble within the channel. During the back stroke, a low pressure region is formed influid channel 204, allowing air to seep from the atmosphere into thechannel 204. Regardless of theelectrode 212 which leaks air, the bubble will travel upstream towards thepump port 203, so that the bubble will again have to pass theelectrodes 212 during the forward stroke. This allows the air bubble to be detected in the same manner as if the bubble had been drawn in from the fluid supply.

The bubble detector control circuit serves the dual purposes of providing a safety device to prevent accidental passage of an air bubble, and also automatically shuts off the pumping apparatus when all the fluid in the solution bottle is used up. At the end of the supply of fluid, air is introduced into the solution bottle and is pumped to thevalve assembly 40. When the air reaches the point where the twosensing electrodes 212 are placed, the current path is broken and motor operation is terminated, turning off the pumping system.

Battery Voltage Variation Compensation This circuit, consisting oftransistors 370 and 371, is responsive to decreases in the battery voltage to decrease the off-time of the pulses in the forward stroke control. As previously described, the back stroke is not controlled and will vary in speed with voltage variations. The time lost on the back stroke is gained by speeding up the motor on the forward stroke.

Transistor 371 acts as an ideal diode, establishing a reference voltage of approximately 0.6 volts at its collector, which is coupled in series through aresistor 376 and aresistor 377 to a line coupled throughswitch 316 with the positive potential line 248. In shunt withresistors 376 and 377 andtransistor 371 is aresistor 380 in series with the emitter oftransistor 370, and aresistor 382 in series between the collector oftransistor 370 andground 250. The collector oftransistor 370 is directly coupled to the junction betweentransistor 304 andcapacitor 325. As the battery supply voltage lowers, the current throughresistor 380 changes linearly. This causes the collector voltage oftransistor 370 to rise linearly at a rate established by the ratio ofresistor 380 toresistor 382 and aresistor 384 in series between the collectors oftransistors 303 and 304. The voltage at the base oftransistor 370 also varies, but at reduced ratio.

For the particular motor driven mechanism which was constructed, the circuit constants were chosen so that the voltage on the collector oftransistor 370 and hence alsotransistor 304 lowered as the battery voltage lowered by a ratio of 1.5, that is, 0.1 volt battery variation produced 0.15 volts less charge oncapacitor 325. While this ratio produced the correct compensation, other ratios may be utilized for other loads driven by the motor. The range of the battery voltage compensation circuit is such that battery voltages down to approximately 2.0 volts may be tolerated, representing a decrease of 33 percent from the full battery voltage of 3.0 volts.

For the circuit constants disclosed above, a battery supply voltage of less than 2.0 volts indicates that the batteries must be replaced or recharged in order to maintain the calibrated accuracy of the pumping apparatus. A low battery indicator circuit is formed by integratedcircuit NOT gates 390 and 391 for energizing a lowbattery indicator lamp 393. When the supply voltage is above 2.0 volts, a divider formed byresistors 395 and 396 in series betweenground 250 and the supply line viaswitch 316 and line 248 produces a voltage above 0.8 volts at the junction betweenresistors 395 and 396 which causesNOT gate 390 to saturate, turningNOT gate 391 off and thus maintaining thelamp 393 off. When the supply voltage drops to 2.0 volts,gate 390 turns off, causinggate 391 to turn on and hence energize thelamp indicator 393. Theindicator lamp 393 is desirably located beneath a window in the upper case of the pump assembly so as to be visible by an operator.

Over-Pressure Detector This circuit is formed byintegrated circuit gates 400, 401 and atransistor 372.Gates 400 and 401 are connected to form a bistable multivibrator. During normal operation (no over-pressure condition), gate 401 is on andtransistor 372 is off. To insure this state, acapacitor 405 is made five times as large as a capacitor 406. When the control circuit is first energized, thecapacitor 405 holds one input ofgate 400 low long enough to set the bistable with gate 401 saturated andgate 400 off.

When fluid reacheselectrode 220, indicating an over-pressure condition, a circuit path is formed from one input ofgate 400 to thesupply voltage line 275 viatransistor 350 and theelectrode 212 connected throughresistor 352 to the base thereof, saturatinggate 400 and turning gate 401 off. This turnstransistor 372 on, turning offtransistor 351 which in turn opens the bias path fortransistors 269 and 265. This stops the system on the forward stroke. The over-pressure detector circuit may be reset by turning the control circuit off and back on, causingcapacitor 405 to again saturate gate 401.

Bubble and Over-Pressure Indicator This circuit consists oftransistors 310 and 41 1 which control energization of a visual indicator, such as a light emitting diode (LED) 413. Desirably, a light emitting diode is used rather than an incandescent lamp due to its low power consumption. When an air bubble or an over-pressure condition is detected by the circuits previously described,transistor 351 is turned off. This in turn biases offtransistor 410, ungrounding ajunction formed between aresistor 415 and adiode 416 connected in series between the anode ofLED 413 and the base of transistor 41]. The transistor 41] is thus forward biased, creating a current path for theLED 413 to ground through aresistor 420 and the collector-emitter junction, of the conductingtransistor 411. TheLED 413 is located adjacent a jewel lens mounted incase 170 in order to give a visual indication ofa circuit shutoff caused by the detectm of an air bubble or an overpressure condition.

For some applications, it may be desirable to include less than the number of individual circuits described above, or to include various combinations thereof, as will be apparent to one skilled in the art.

We claim:

1. In a portable infusion system for transferring fluid from a fluid source to a catheter, a positive displacement pumping system having disposable parts, comprising: a self-contained source of DC power; disposable syringe means having a barrel and a piston movable in said barrel along a path to move fluid within the barrel, said barrel having a fluid passage opening; disposable valve means having a pump port in fluid communication with said passage opening, input port means connected with said fluid source for passing fluid to said barrel, and output port means for connection with said catheter for passing fluid to said catheter; base means removably holding said syringe means and said valve means to allow disposal after use with a patient; a holding member removably connected to said piston and mounted on said base for reciprocal movement along said path; motor means energized by said DC power source for reciprocating said holding member and said piston, said motor means including gear means connected to said holding member to effect reciprocal movement of said holding member in response to rotation of said gear means, and a DC motor for rotating said gear means, means for selecting one of a plurality of rates of pumping including generator means for generating DC drive pulses having different duty cycles selectable to effect different rates of pumping, circuit means for coupling said DC drive pulses to said DC motor, and voltage variation compensation means including means responsive to decreasing voltage from said DC power source for increasing the duty cycle of at least some of said DC drive pulses.

2. The system of claim 1 wherein said DC motor is a bidirectional DC motor having an armature shaft rotatable in opposite directions when opposite polarity current is coupled to the DC motor, said gear means converting rotational movement of said armature shaft into translational movement which drives said holding member, and circuit means for periodically reversing the polarity of current passed from said DC power source to said DC motor.

3. The system of claim 1 wherein said valve means ineludes sensing means for detecting the presence of an air bubble, and safety means responsive to detection of an air bubble for terminating the operation of said motor means.

4. The system of claim 1 including over-pressure means for detecting when the pressure of fluid passed to said catheter exceeds a predetermined maximum, and indicator means actuated when said predetermined maximum is exceeded for providing an alarm indication.

5. In an infusion system for transferring fluid to catheter means, a pumping system comprising a source of fluid capable of passing electricity, a valve assembly having a fluid channel with an outlet adapted for connection with the catheter means for directing the flow of said fluid to the catheter means, fluid pump means including a chamber connected in fluid communication with said fluid source and said fluid channel, and drive means in said chamber actuable to effect movement of fluid from said fluid source and pump fluid through said fluid channel to the catheter means, unidirectional valve means connected in fluid communication with said fluid channel to permit fluid flow from said fluid channel to the catheter and prevent fluid flow from the catheter to said fluid channel, said fluid channel including a fluid passageway having a fluid opening contiguous with said fluid channel for admitting fluid into said passageway a distance determined by the pressure of the fluid in said fluid channel, and a pair of electrode means located within said fluid channel and having extensions connectable with an external circuit, at least one of said pair of electrode means being located in said passageway a predetermined distance from said fluid opening so that the presence of fluid at said last named electrode means indicates a predetermined fluid pressure condition.

6. The pumping system of claim further including third electrode means in said channel adjacent the other of said pair of electrodes, nd circuit means responsive to the presence of an air bubble between said third and other electrode means to provide a signal indicative thereof.

7. The pumping system ofclaim 5 wherein said fluid passageway has a closed end opposite said fluid opening for trapping a compressible gas between said closed end and the fluid admitted trough said fluid opening, said last named electrode means being surrounded by said compressible gas when the pressure of fluid in said fluid channel means is less than said predetermined pressure condition.

8. In an infusion system for transferring fluid to catheter means, a pumping system comprising a source of fluid capable of conducting electricity, a syringe having a barrel and a reciprocal plunger slidable in said barrel for moving fluid into and out of said barrel, a valve assembly having a fluid source inlet connected to said source of fluid, a pressure fluid inlet-connected to said syringe barrel and in fluid communication with said fluid source inlet, and a channel connected in fluid communication with said pressure fluid inlet and having an outlet connectable with the catheter, first valve means connected in fluid communication with said source of fluid to pennit fluid flow from said source to said syringe barrel and to prevent return fluid flow from said syringe barrel to said fluid source, second valve means connected in fluid communication with said channel to permit fluid flow from said channel to the catheter and prevent return fluid flow from the catheter to said channel, and means for reciprocating said plunger to draw fluid from said source into said barrel through said pressure fluid inlet during movement thereof in one direction and supply pressurized fluid to said channel from said barrel during movement thereof in the opposite direction to transfer the fluid to the catheter, said valve assembly including a pressure chamber connected at one end in fluid communication with said channel and closed at the opposite end thereof, an electrode within said chamber, gas disposed in said chamber normally between said electrode and said one end to prevent contact between said fluid and said electrode, said gas being compressible to permit said fluid to contact said electrode upon the occurrence of fluid pressure in said channel of a predetermined value, and circuit means connected with said electrode for detecting the contact between the fluid and said electrode.

9. The infusion system of claim 8 wherein said circuit means includes a second electrode disposed in said channel incontact with the fluid therein.

10. The infusion system of claim a further including a pair of closely spaced electrodes in said channel and normally bridged by the fluid to normally provide a predetermined value of impedance between said pair of electrodes, and circuit means connected to said pair of electrodes and responsive to a change in said value of impedance upon the occurrence of the presence of an air bubble between said electrodes to interrupt the reciprocation of said plunger.

Claims (10)

1. In a portable infusion system for transferring fluid from a fluid source to a catheter, a positive displacement pumping system having disposable parts, comprising: a self-contained source of DC power; disposable syringe means having a barrel and a piston movable in said barrel along a path to move fluid within the barrel, said barrel having a fluid passage opening; disposable valve means having a pump port in fluid communication with said passage opening, input port means connected with said fluid source for passing fluid to said barrel, and output port means for connection with said catheter for passing fluid to said catheter; base means removably holding said syringe means and said valve means to allow disposal after use with a patient; a holding member removably connected to said piston and mounted on said base for reciprocal movement along said path; motor means energized by said DC power source for reciprocating said holding member and said piston, said motor means including gear means connected to said holding member to effect reciprocal movement of said holding member in response to rotation of said gear means, and a DC motor for rotating said gear means, means for selecting one of a plurality of rates of pumping including generator means for generating DC drive pulses having different duty cycles selectable to effect different rates of pumping, circuit means for coupling said DC drive pulses to said DC motor, and voltage variation compensation means including means responSive to decreasing voltage from said DC power source for increasing the duty cycle of at least some of said DC drive pulses.

2. The system of claim 1 wherein said DC motor is a bidirectional DC motor having an armature shaft rotatable in opposite directions when opposite polarity current is coupled to the DC motor, said gear means converting rotational movement of said armature shaft into translational movement which drives said holding member, and circuit means for periodically reversing the polarity of current passed from said DC power source to said DC motor.

3. The system of claim 1 wherein said valve means includes sensing means for detecting the presence of an air bubble, and safety means responsive to detection of an air bubble for terminating the operation of said motor means.

4. The system of claim 1 including over-pressure means for detecting when the pressure of fluid passed to said catheter exceeds a predetermined maximum, and indicator means actuated when said predetermined maximum is exceeded for providing an alarm indication.

5. In an infusion system for transferring fluid to catheter means, a pumping system comprising a source of fluid capable of passing electricity, a valve assembly having a fluid channel with an outlet adapted for connection with the catheter means for directing the flow of said fluid to the catheter means, fluid pump means including a chamber connected in fluid communication with said fluid source and said fluid channel, and drive means in said chamber actuable to effect movement of fluid from said fluid source and pump fluid through said fluid channel to the catheter means, unidirectional valve means connected in fluid communication with said fluid channel to permit fluid flow from said fluid channel to the catheter and prevent fluid flow from the catheter to said fluid channel, said fluid channel including a fluid passageway having a fluid opening contiguous with said fluid channel for admitting fluid into said passageway a distance determined by the pressure of the fluid in said fluid channel, and a pair of electrode means located within said fluid channel and having extensions connectable with an external circuit, at least one of said pair of electrode means being located in said passageway a predetermined distance from said fluid opening so that the presence of fluid at said last named electrode means indicates a predetermined fluid pressure condition.

6. The pumping system of claim 5 further including third electrode means in said channel adjacent the other of said pair of electrodes, and circuit means responsive to the presence of an air bubble between said third and other electrode means to provide a signal indicative thereof.

7. The pumping system of claim 5 wherein said fluid passageway has a closed end opposite said fluid opening for trapping a compressible gas between said closed end and the fluid admitted trough said fluid opening, said last named electrode means being surrounded by said compressible gas when the pressure of fluid in said fluid channel means is less than said predetermined pressure condition.

8. In an infusion system for transferring fluid to catheter means, a pumping system comprising a source of fluid capable of conducting electricity, a syringe having a barrel and a reciprocal plunger slidable in said barrel for moving fluid into and out of said barrel, a valve assembly having a fluid source inlet connected to said source of fluid, a pressure fluid inlet connected to said syringe barrel and in fluid communication with said fluid source inlet, and a channel connected in fluid communication with said pressure fluid inlet and having an outlet connectable with the catheter, first valve means connected in fluid communication with said source of fluid to permit fluid flow from said source to said syringe barrel and to prevent return fluid flow from said syringe barrel to said fluid source, second valve means connected in fluid communication with said channel to permit fluId flow from said channel to the catheter and prevent return fluid flow from the catheter to said channel, and means for reciprocating said plunger to draw fluid from said source into said barrel through said pressure fluid inlet during movement thereof in one direction and supply pressurized fluid to said channel from said barrel during movement thereof in the opposite direction to transfer the fluid to the catheter, said valve assembly including a pressure chamber connected at one end in fluid communication with said channel and closed at the opposite end thereof, an electrode within said chamber, gas disposed in said chamber normally between said electrode and said one end to prevent contact between said fluid and said electrode, said gas being compressible to permit said fluid to contact said electrode upon the occurrence of fluid pressure in said channel of a predetermined value, and circuit means connected with said electrode for detecting the contact between the fluid and said electrode.

9. The infusion system of claim 8 wherein said circuit means includes a second electrode disposed in said channel in contact with the fluid therein.

10. The infusion system of claim 8 further including a pair of closely spaced electrodes in said channel and normally bridged by the fluid to normally provide a predetermined value of impedance between said pair of electrodes, and circuit means connected to said pair of electrodes and responsive to a change in said value of impedance upon the occurrence of the presence of an air bubble between said electrodes to interrupt the reciprocation of said plunger.

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