Infusion Pump

Abstract

A constant displacement infusion pump for administering medicinal fluid to a patient and means for controllably operating the pump such that the pump is caused to intermittently dispense medicinal fluid with the amount of each dosage dispensation variable in accordance with a first signal and the duration between successive dosage dispensations variable in accordance with a second signal.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to infusion pump apparatus of the type adapted to controllably administer medicinal fluid to a patient. In apparatus of this type, it is highly important to control the dispensation of medicinal fluid so that the proper dosage is administered over a period of time. In view of the seemingly innumerable types of medicine which can be intravenously injected into a patient, and the varying needs of individual patients, it is highly desirable to have a wide range in the dispensing capability of the pump, yet also ease and simplicity of adjustment over this range. At the same time, it is important to maintain accurate control over this range so that the proper dosage is always administered for the setting to which the unit is adjusted. Moreover, when the infusion pump is of the portable battery-operated type, it is also desirable to consume minimum power so that the unit can operate over relatively long time periods with assurance that the accuracy in the dispensing rate will be relatively unimpaired.

Accordingly, among the objects of the present invention are to provide infusion pump apparatus for controllably administering medicinal fluid to a patient: which has a wide range of fluid dispensation rates but which requires at most only two simple adjustments to deliver fluid at a selected rate; which is accurate and highly reliable; which when battery operated, consumes minimum power from the battery thereby prolonging battery life and maintaining accuracy of delivery; and which is all around a better unit than previous types of apparatus.

The foregoing objects along with additional objects and advantages of the invention accrue by providing a constant displacement infusion pump and means for controllably operating the pump such that the pump is caused to intermittently dispense dosages of medicinal fluid with the amount of each dosage dispensation variable in accordance with a first signal and the duration between successive dosage dispensations variable in accordance with a second signal.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing discloses preferred embodiments of the invention in accordance with the best mode presently contemplated for carrying out the invention.

FIG. 1 is a semi-schematic plan view of a portion of the infusion pump apparatus according to the present invention and having portions broken away.

FIG. 2 is a first form of drive arrangement for the infusion pump apparatus according to the invention and is to be taken in conjunction with FIG. 1.

FIG. 3 is a second form of drive arrangement for the infusion pump apparatus according to the invention and is to be taken in conjunction with FIG. 1.

FIG. 4 illustrates a waveform useful in understanding the operation of the drive arrangements of FIGS. 2 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the pumping mechanism 10 of the infusion pump apparatus of the present invention. A constant displacement infusion pump in the form of a syringe 12 is arranged to dispense medicinal fluid 14 via a flexible hose 16 and a needle 18. Hose 16 may be of sufficient length to enable needle 18 to be inserted into the vein of a patient at a location remote from syringe 12; this feature allows the infusion pump apparatus to be worn or carried by the patient as a portable unit with hose 16 being routed from the unit to the location where needle 18 is inserted into the patient's vein. Fluid 14 is dispensed from syringe 12 by means of a plunger 20. Plunger 20 is operated by rotating a lead screw 22 to advance a drive nut 24 axially along the screw. As nut 24 advances along screw 22, a flange 26 on the nut pushes plunger 20 into syringe 12 to thereby cause the syringe to dispense fluid 14 at a rate corresponding to the rate of travel of nut 24. Screw 22 is operatively coupled through a conventional gear reducer 28 and a conventional reversing clutch 30 to a drive shaft 32. As will be seen in greater detail hereinafter, shaft 32 is operated by either of the two forms of drive arrangements shown in FIGS. 2 and 3. Gear reducer 28 reduces the relatively high rpm of shaft 32 to turn screw 22 at a relatively low rpm. Clutch 30 permits the direction of rotation of screw 22 to be reversed so that after nut 24 has been advanced to discharge the contents of syringe 12, it can be retracted preparatory to refilling the syringe. From the foregoing description, it will be apparent that pumping mechanism 10 operates to administer fluid 14 to the patient at a rate directly proportional to the speed of shaft 32. Thus, as the speed of shaft 32 increases from zero rpm to maximum rpm, the rate of fluid delivery increases from zero to a maximum. Stated differently, the volume of fluid dispensed from syringe 12 with plunger 20 working against a full charge of fluid is directly proportional to the distance traveled by nut 24.

A first form of drive arrangement 34 for pumping mechanism 10 is shown in FIG. 2. Drive arrangement 34 comprises a D.C. motor 36 for rotating shaft 32 and a D.C. battery 38 for powering motor 36. An electronic circuit is also operatively associated with motor 36 and battery 38 for operating motor 36 in a fashion which, as will be seen later, provides great versatility in regulating the injection of fluid 14 into the patient. The circuit comprises a multivibrator stage 40, an emitter follower stage 42 and switching stages 44 and 46.

The circuit is connected across battery 38 through an on-off control switch 52 and a normally closed limit switch 54. Terminal 52a of switch 52 is connected to the positive terminal 38a of battery 38 and terminal 52b of switch 52 is connected to terminal 54a of switch 54. Terminal 54b of switch 54 is connected to the positive supply terminals of stages 40, 42, 44, 46. The negative terminal 38b of battery 38 is connected via ground to the negative supply terminals of stages 40, 42, 44 and to the negative armature terminal 36b of motor 36. Switch 54 is operatively associated with nut 24, and as can be seen in FIG. 1, is positioned to be tripped by flange 26 when the contents of syringe 12 have been dispensed. Accordingly, when switch 52 is operated from its broken line position to its solid line position, a circuit path is completed through switches 52 and 54, and the voltage of battery 38 is applied between terminals 54b of switch 54 and battery terminal 38b for delivery to the circuit. When switch 54 is tripped by nut 24 to operate switch 54 from its solid line position to its broken line position in FIG. 2, or when switch 52 is turned off, the circuit path is broken so that battery 38 is disconnected from terminals 54b and 38b.

Multivibrator 40 comprises a pair of identical NPN transistors 56, 58 having respective base terminals 56b, 58b, respective emitter terminals 56e, 58e, and respective collector terminals 56c, 58c. The positive and negative supply terminals of multivibrator 40 are designated 40a and 40b respectively. Emitter terminals 56e, 58e are connected to terminal 40b; collector terminals 56c, 58c through identical resistors 60, 62 respectively to terminal 40a; and base terminals 56b, 58b through identical capacitors 64, 66 respectively to collector terminals 58c, 56c respectively. A resistor 68 is connected between terminal 56c and terminal 56b. A fixed resistor 70 and a string of switched resistors 72 are serially connected between terminals 58b and 58c. String 72 consists of serially connected resistors 72a, 72b, 72c, 72d, 72e which are operatively connected with a seven position selector switch 74. Switch 74 comprises taps 74a, 74b, 74c, 74d, 74e, 74f, 74g and a wiper 74h which is connected to a common switch terminal 74j. Wiper 74h is selectively operable to connect terminal 74j to any of the seven taps 74a through 74g. Each resistor 72a through 72e is connected between successive taps 74a through 74f and the last two taps 74f, 74g are connected together and to one terminal of resistor 70. The other terminal of resistor 70 is connected to terminal 58b, and terminal 74j is connected to terminal 58c. With this arrangement as wiper 74h is operated from tap 74a to taps 74f and 74g, the total resistance between terminals 58c and 58b is selectively reduced from a maximum value to a minimum value. The maximum resistance value is equal to the sum of resistor 70 and resistors 72a through 72e; the minimum, the resistance of resistor 70 alone.

A steady state operating cycle of multivibrator 40 is as follows. With battery 38 connected to multivibrator 40, current flows in a loop from battery terminal 38a into multivibrator 40 via terminal 40a and from multivibrator 40 via terminal 40b to battery terminal 38b. The division of this current in the various circuit components of multivibrator 40 is such that transistors 56 and 58 are alternately conductive. For purposes of description, let it be assumed that transistor 56 has just become conductive and transistor 58 non-conductive. With transistor 58 non-conductive, there is no current flow from terminal 58c to terminal 58e. Upon conduction of transistor 56, the increasing current flow through its collector-emitter circuit from terminal 56c to terminal 56e simultaneously reduces the positive voltage at terminal 56c to just slightly above ground potential. At this time, there exists a voltage on capacitor 66 such that plate 66a is positive with respect to plate 66b. (Why this voltage exists will be seen later.) Upon conduction of transistor 56, a current path is created from terminal 40a through capacitor 62, through resistor string 72, through resistor 70, through capacitor 66, through terminals 56c and 56e, to terminal 40b. Battery 38 delivers current through this path in an attempt to reverse the polarity of the charge on capacitor 66 (i.e., attempts to make plate 66b positive with respect to plate 66a). The rate at which the voltage of capacitor 66 changes is a function of the capacitance of capacitor 66 and the resistance of the resistors in the current path through which the charging current for capacitor 66 flows (i.e., resistor 62, resistor 70, and the selected resistance of resistor string 72). Since battery 38 is attempting to charge capacitor 66 to the battery voltage, the sum of the collector-emitter voltage of transistor 56 (i.e., the voltage across terminals 56c and 56e) and the voltage across capacitor 66 reaches a point during charging of capacitor 66 where the resultant voltage at terminal 58b is slightly positive with respect to ground and causes transistor 58 to conduct. (For reasons which will soon become apparent, it is important to note that during the time transistor 56 was conductive, capacitor 64 has been charged by current flow from battery 38 through resistor 62 and the base-emitter circuit of transistor 56 so that plate 64a is positive with respect to plate 64b. ) Now current flow from terminal 58c to terminal 58e increases rapidly and the positive voltage at terminal 58c drops rapidly to just slightly above ground potential. However, since capacitor 64 has been charged as indicated above, the rapid fall in voltage at terminal 58c is coupled through the charged capacitor 64 causing a negative voltage to be applied to base terminal 56b and rendering transistor 56 non-conductive. Now with transistor 56 non-conductive and transistor 58 conductive, a current path is created from terminal 40a through resistor 60, through resistor 68, through capacitor 64, through terminals 58c and 58e, to terminal 40b. Since capacitor 64 at this time is charged with plate 64b negative with respect to plate 64a, current flows from battery 38 through this current path is an attempt to reverse the charge on capacitor 64 in the same fashion as described above in connection with capacitor 66 during the conduction of transistor 56. The rate at which the voltage of capacitor 64 changes is a function of the capacitance of capacitor 64 and the resistance of the two resistors 60 and 68 in the current path through which the charging current for capacitor 64 flows. Since battery 38 is attempting to charge capacitor 64 to the battery voltage, the sum of the collector-emitter voltage of transistor 58 and the voltage across capacitor 64 reaches a point during charging of capacitor 64 where the resultant voltage at terminal 56b is slightly positive with respect to ground causing transistor 56 to conduct. The resulting drop in the collector voltage at terminal 56c is coupled through capacitor 66 to turn off transistor 58, capacitor 66 having been charged through resistor 60 and the base-emitter circuit of transistor 58 during the time transistor 58 was conducting so that plate 66a is positive with respect to plate 66b. This completes one operating cycle of multivibrator 40. The cycle now repeats itself and continues to do so until either switch 52 or 54 is opened.

In light of the foregoing description, it is apparent that multivibrator 40 develops a positive square wave voltage at terminal 56c whose amplitude is slightly less than battery voltage. This waveform is illustrated as waveform W in FIG. 4, and it is to be understood that waveform W is not necessarily to any particular scale. When transistor 56 is conducting, waveform W is at its low level (approximately zero volts); and when transistor 56 is not conducting, at its high level (approximately battery voltage). The conducting period is designated T.sub.1 while the non-conducting period is designated T.sub.2. The duration of the time period T.sub.1 is a function of capacitor 66, resistor 62, resistor 70, and resistor string 72. The duration of the time period T.sub.2 is a function of capacitor 64 and resistors 60 and 68. By making resistor 68 much greater than resistor 60, resistor 70 much greater than resistor 62 and capacitors 64 and 66 equal, T.sub.1 becomes essentially a function of resistor 70 and the selected value of resistor string 72 while T.sub.2 becomes essentially a function of resistor 68. By making resistor 68 equal to resistor 70, T.sub.1 equals T.sub.2 whenever wiper 74h is operated to either tap 74f or 74g. As wiper 74h is operated away from taps 74g and 74f toward tap 74a, the increasing resistance which is inserted in series with resistor 70 causes T.sub.1 to increase with the maximum value thereof occurring when wiper 74h is operated to tap 74a. Because resistor 68 is fixed, T.sub.2 remains constant for all settings of switch 74.

Emitter follower stage 42 comprises an NPN transistor 78 whose base terminal 78b is connected through a resistor 80 to collector terminal 56c, whose collector terminal 78c is connected to terminal 54b and whose emitter terminal 78e is connected through a resistor 82 to ground. The emitter voltage of transistor 78 at terminal 78e follows the collector voltage of transistor 56 at collector terminal 56c to provide power amplification of waveform W without loading multivibrator 40. Thus, when the voltage at terminal 56c is high, the voltage at terminal 78e is also high; when the voltage at terminal 56c is low, the voltage at terminal 78e is also low.

Switching stage 44 comprises a transistor 84 whose base terminal 84b is connected through a resistor 86 to emitter terminal 78e, whose emitter terminal 84e is connected to ground and whose collector terminal 84c is connected to a switch 88. Transistor 84 operates as a switch to conduct when the emitter voltage of transistor 78 at terminal 78e is high, and to not conduct when the voltage at terminal 78e is low. Switch 88, like switch 74, has seven operating positions defined by taps 88a through 88g, a wiper 88h and a common terminal 88j. The first six of these taps 88a through 88f are connected together and collector terminal 84c can be connected to any tap 88a through 88f. The seventh tap 88g is connected to ground. When wiper 88h is operated to any one of its first six positions (i.e., taps 88a through 88f), terminal 84c is connected to terminal 88j; and when to the seventh position (tap 88g), terminal 88j is connected to ground. Wiper 88h is ganged with wiper 74h so that the two switches 74, 88 are operated in unison to corresponding taps.

Switching stage 46 comprises a PNP transistor 90 whose emitter terminal 90e is connected to terminal 54b, whose base terminal 90b is connected through a resistor 92 to terminal 88j of switch 88 and whose collector terminal 90c is connected through the series combination of a fixed resistor 94 and a variable resistor 96 to the positive armature terminal 36a of motor 36. With this arrangement, when switches 74 and 88 are operated to any one of their first six positions, the base circuit of transistor 90 is connected to the collector circuit of transistor 84, and transistor 90 conducts whenever transistor 84 conducts. When switches 74 and 88 are operated to their seventh position, transistor 90 is disconnected from transistor 84 and a ground is applied to the base of transistor 90 causing the transistor to continuously conduct. Resistor 94 limits the armature current flow to a maximum selected value, and hence, limits the motor speed to a corresponding maximum value. Resistor 96 is variable to vary the armature current downwardly from its maximum value and hence, vary the speed of motor 36 downwardly from its maximum value.

The operation of the infusion pump will now be apparent. The output waveform W developed by multivibrator 40 operates through the successive stages 42, 44, and 46 to cause transistor 90 to conduct during the time periods T.sub.2 and to not conduct during the time periods T.sub.1. The intermittent conduction of transistor 90 in turn causes current to be intermittently supplied from battery 38 to motor 36 in the form of square wave current pulses. Thus, motor 36 intermittently operates to intermittently dispense dosages of fluid 14 to the patient. Setting switches 74, 88 to taps 74a, 88a sets T.sub.1 to maximum. By also setting resistor 96 to maximum resistance, the speed of motor 36 during time T.sub.2 is a minimum. Accordingly, with these two adjustment settings, the rate of fluid dispensation from syringe 12 is a minimum. The rate can be increased by either operating switches 74, 88 in the direction away from taps 74a, 88a, by decreasing the resistance of resistor 96, or by adjusting both switches 74, 88 and resistor 96. When switches 74, 88 are set to taps 74g, 88g, the ground applied to base terminal 90b overrides the on-off type control of multivibrator 40 causing the motor to run continuously at the speed determined by resistor 96. By now setting resistor 96 to zero resistance, the maximum rate of fluid dispensation is achieved. Thus, it will be appreciated that the various possible settings of switches 74, 88 and resistor 96 cover a wide range in the dispensing capability of the apparatus with at most only two adjustments being necessary to select any possible dispensation rate. For example, it is possible to have the maximum dispensing rate 3,000 times as great as the minimum dispensing rate so that the present invention has the advantage of being able to administer medication over a long time period as well as a short time period.

After the contents of syringe 12 have been exhausted, nut 24 can be retracted by reversing clutch 30 and operating motor 36 at maximum speed. Suitable provision could be made for manually actuating screw 22 if desired.

It is preferable to calibrate the infusion pump apparatus so that required dispensation rates can be quickly set without need to empirically determine the dispensing rate for given settings of switches 74, 88 and resistor 96. The solid state circuit construction renders the apparatus highly reliable as well as highly accurate over this wide range of dispensing rates. It will be noted that the unit is efficiently designed for minimum power consumption so that when fluid is not being dispensed, motor 36 is not operated and so that multivibrator 40 draws only very small current. Moreover, the apparatus may be economically constructed and readily packaged for portable use by an ambulatory patient.

FIG. 3 discloses a drive arrangement 100 which is very similar to drive arrangement 34, and hence, need be described only insofar as it differs from drive arrangement 34. Accordingly, like parts in both FIGS. 2 and 3 are identified by like numerals. Drive arrangement 100 differs from drive arrangement 34 in the following respects. Switch 88 is omitted with terminal 84c of transistor 84 being connected directly to resistor 92. Resistor 96 is omitted with resistor 94 being connected directly to motor 36. A variable resistor 102 is connected in series with resistor 68 between terminals 56c and 56b of transistor 56. Drive arrangement 100 includes an additional battery 104. The way in which batteries 38, 104 are connected to motor 36 and to the electronic circuitry is somewhat different. Battery 38 is connected through switch 54 and switch 52 to emitter terminal 90e of transistor 90. Battery 104 is connected through an on-off switch 106 to terminal 40a of multivibrator 40 and to terminal 78c of transistor 78. Switch 106 is operative with switch 52, the two switches being either both closed or both open. With this arrangement, battery 38 powers essentially only motor 36, while battery 104 powers essentially only multivibrator 40 and emitter follower 42. Since battery 104 is thus isolated from motor 36, the voltage delivered by battery 104 to multivibrator 40 is independent of battery voltage drops which are likely to occur due to motor armature current when only a single battery is used. For a given adjustment setting, the bwo battery arrangement maintains high accuracy in the time periods T.sub.1 and T.sub.2 over a longer operating time.

The operation of drive arrangement 100 further differs from that of drive arrangement 34 in that resistor 102 replaces resistor 96 to control the amount of fluid dispensed during each dispensation from syringe 12. As resistor 102 is increased from zero resistance to maximum resistance, the duration of time period T.sub.2 is likewise increased to operate motor 36 for a longer time. Whereas drive arrangement 34 maintains the operating time of motor 36 constant while varying the motor speed, drive arrangement 100 varies the operating time of motor 36 while maintaining constant motor speed. Preferably, motor 36 is of a type which is relatively insensitive to variations in the voltage of battery 38 and hence, maintains a reasonably constant speed over the life of battery 38.

Claims

I claim:

1. In infusion pump apparatus for controllably administering the injection of medicinal fluid into a patient, the combination comprising infusion pump means for dispensing medicinal fluid, drive means comprising a D. C. motor, means operatively coupling said drive means with said pump means, operating means for operating said drive means, said operating means comprising first circuit means for alternately and repetitively generating first and second signals, each of said signals having a variable characteristic, and second circuit means operatively coupling said first circuit means and said drive means such that said drive means is operated in accordance with said first and second signals to cause the pump means to dispense dosages of medicinal fluid with the amount of each dosage dispensation variable in accordance with the characteristic of the first signal and the duration between successive dosage dispensations variable in accordance with the characteristic of the second signal, said first circuit means comprising means for repetitively generating a direct current of fixed duration and variable amplitude, with said amplitude representing the variable characteristic of said first signal and means for varying the duration between successive generations of said direct current, with said duration between successive generations of direct current representing the variable characteristic of said second signal and said second circuit means comprising means for supplying said direct current to said motor.

2. In infusion pump apparatus for controllably administering the injection of medicinal fluid into a patient, the combination comprising infusion pump means for dispensing medicinal fluid, drive means comprising a D. C. motor, means operatively coupling said drive means with said pump means, operating means for operating said drive means, said operating means comprising first circuit means for alternately and repetitively generating first and second signals, each of said signals having a variable characteristic, and second circuit means operatively coupling said first circuit means and said drive means such that said drive means is operated in accordance with said first and second signals to cause the pump means to dispense dosages of medicinal fluid with the amount of each dosage dispensation variable in accordance with the characteristic of the first signal and the duration between successive dosage dispensations variable in accordance with the characteristic of the second signal, said first circuit means comprising means for repetitively generating a direct current of variable duration and fixed amplitude, with said duration representing the variable characteristic of said first signal and means for varying the duration between successive generations of said direct current, with said duration between successive generations of said direct current representing the variable characteristic of said second signal and said second circuit means comprising means for supplying said direct current to said motor.

3. In infusion pump apparatus for controllably administering the injection of medicinal fluid into a patient, the combination comprising infusion pump means for dispensing medicinal fluid, drive means, means operatively coupling said drive means with said pump means, operating means for operating said drive means, said operating means comprising first circuit means for alternately and repetitively generating first and second signals, each of said signals having a variable characteristic, and second circuit means operatively coupling said first circuit means and said drive means such that said drive means is operated in accordance with said first and second signals to cause the pump means to dispense dosages of medicinal fluid with the amount of each dosage dispensation variable in accordance with the characteristic of the first signal and the duration between successive dosage dispensations variable in accordance with the characteristic of the second signal, said first circuit means comprising generating circuit means for generating a waveform alternating between high and low levels, said first signal corresponding to one of said levels and said second signal corresponding to the other of said levels.

4. The combination of claim 3 wherein said drive means comprises a D. C. motor.

5. The combination of claim 3 wherein said generating circuit means comprises means for generating a square wave waveform alternating between said high and low levels, said first signal corresponding to the duration of said square wave waveform at said one level, and said second signal corresponding to the duration of said square wave waveform at said other level.

6. The combination of claim 5 wherein said second circuit means comprises switching means responsive to one of said levels for operating said drive means.

7. In an infusion pump apparatus of the type wherein an infusion pump is controllably operated to controllably dispense fluid the combination comprising a D.C. motor, a D.C. battery, multivibrator circuit means for developing a square wave signal, including means for varying the length of time the square wave signal remains at one level, switching circuit means operably coupling said motor with said battery and responsive to said square wave signal for blocking current flow from the battery to the motor when the square wave signal is at the one level and for conducting current from the battery when the square wave signal is at the other level and means for varying a selected parameter of the current flow from the battery to the motor.

8. The combination of claim 7 wherein said means for varying a selected parameter of the current flow from the battery to the motor comprises means for varying the amplitude of said current.

9. The combination of claim 7 wherein said means for varying a selected parameter of the current flow from the battery to the motor comprises means for varying the duration of said current.

10. The combination of claim 7 wherein said means for varying a selected parameter of the current flow from the battery to the motor comprises variable resistance means operatively associated with said multivibrator circuit means for varying the length of time the square wave signal remains at the other level.

11. The combination of claim 7 wherein said means for varying a selected parameter of the current flow from the battery to the motor comprises variable resistance means operatively associated with said motor for varying the magnitude of current flow from the battery to the motor.

12. The combination of claim 7 wherein said means for varying the length of time the square wave signal remains at the one level comprises variable resistance means operatively associated with said multivibrator circuit means.

13. The combination of claim 7 wherein said multivibrator circuit means comprises first and second transistors, means operatively coupling the output of the first transistor with the input of the second transistor, means coupling the output of the second transistor with the input of the first transistor, said means for varying the length of time the square wave signal remains at the one level comprising variable resistance means operatively associated with one of said coupling means.

14. The combination of claim 13 wherein said means for varying a selected parameter of the current value from the battery to the motor comprises variable resistance means operatively associated with the other of said coupling means.

15. The combination of claim 7 further including a second D.C. battery, said second battery being operatively coupled with said multivibrator circuit means for supplying the power requirements of said multivibrator circuit means, said first battery being isolated from said multivibrator circuit means.