CA1224101A - Precision medication dispensing system and method - Google Patents
Precision medication dispensing system and methodInfo
- Publication number
- CA1224101A CA1224101A CA000444215A CA444215A CA1224101A CA 1224101 A CA1224101 A CA 1224101A CA 000444215 A CA000444215 A CA 000444215A CA 444215 A CA444215 A CA 444215A CA 1224101 A CA1224101 A CA 1224101A
- Authority
- CA
- Canada
- Prior art keywords
- medication
- pressure
- outlet
- pumping chamber
- flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
- A61M5/14244—Pressure infusion, e.g. using pumps adapted to be carried by the patient, e.g. portable on the body
- A61M5/14276—Pressure infusion, e.g. using pumps adapted to be carried by the patient, e.g. portable on the body specially adapted for implantation
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
- A61M5/172—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body electrical or electronic
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D7/00—Control of flow
- G05D7/06—Control of flow characterised by the use of electric means
- G05D7/0617—Control of flow characterised by the use of electric means specially adapted for fluid materials
- G05D7/0629—Control of flow characterised by the use of electric means specially adapted for fluid materials characterised by the type of regulator means
- G05D7/0676—Control of flow characterised by the use of electric means specially adapted for fluid materials characterised by the type of regulator means by action on flow sources
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
- A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
- A61M5/142—Pressure infusion, e.g. using pumps
- A61M5/14244—Pressure infusion, e.g. using pumps adapted to be carried by the patient, e.g. portable on the body
- A61M2005/14264—Pressure infusion, e.g. using pumps adapted to be carried by the patient, e.g. portable on the body with means for compensating influence from the environment
Abstract
Abstract of the Disclosure The implantable device includes a medication reser-voir, a pulsatile pump and an absolute pressure transducer.
The pumping pressure wave developed in the pumping chamber is measured by the absolute pressure transducer whose output is used to adjust the pulsing rate of the solenoid operated pump so that the programmed time averaged rate of infusion of medication into the body is precisely maintained throughout all operating temperature and pressure conditions.
The pumping pressure wave developed in the pumping chamber is measured by the absolute pressure transducer whose output is used to adjust the pulsing rate of the solenoid operated pump so that the programmed time averaged rate of infusion of medication into the body is precisely maintained throughout all operating temperature and pressure conditions.
Description
PRECISION MEDICATION DISPENSING SYSTEM AND METHOD
The present invention relates to implantable medica-tion infusion systems and methods, and, more particularly, to so-called pulsatile systems and methods in which medication is dispensed to the body during short dispensing periods separated by relatively long intervals between such dispensing periods.
Many implantable devices in the prior art have employed so-called pulsatile medication dispensing system.
Examples of such pulsatile dispensing systems are shown in Summers Patent No. 3,527,220; Ellinwood Patent No. 3,692,027, Ellinwood Patent No. 3,9~3,060, Thomas et al Patent No.
3,963,380; Haerten et al Patent No. 4,077,405; Ellinwood Patent No. 4,146,029, Moody et al Patent No. 4,152,098; Franetzki et al Patent No. 4~191,181; Portner Patent No. 4,265,241; and Dorman International Publication No. WO 81/00209.
Some of these pulsatile systems have used inlet and outlet check valves in connection with a pumping chamber, the pump element acting to withdraw a metered amount of me~ication from a reservoir during the intake stroke of the pump and dispensing this metered amount of medication to an outlet catheter during the return stroke of the pump element. In such arrangements, the outlet:check valve closes and the inlet chec~ valve opens on the intake stroke of the pump so that medication can be drawn from the reservoir into the pumping chamber~
In other pulsatile systems, an outlet flow restric-tion device has been employed instead of an outlet check valve, for example, in Haerten et al Patent No. 4,077,405. In such devices compliance of the pumping chamber prevents the accurate dispensing of a fixed amount of medication for each stroke of ~, ~
the pump, because the pressure head across the pump will vary with different operating conditions. Variations in the pres-sure head across the pump will produce corresponding variations in the bolus volume of medication forced through the restrictor during the medication dispensing periods. Such variations in pressure head can occur due to changes in altitude and tempera-ture of the person carrying the implanted device, since the pressure within the body, i.e. the pressure at the outlet of the flow restrictor, varies with changes in altitude, and the pressure at the pump inlet varies with changes in temperature of the medication reservoir.
It is an object of the present invention to provide a new and improved pulsatile medication infusion system and method whereby an outlet flow restrictor may be used and the time averaged rate of infusion of medication into the body may be very accurately controlled under all operating condi-tions.
It is another object of the present invention to provide a new and improved pulsatile medication infusion system in which the exact amount of medication dispensed during each dispensing period is measured and compared with a reference value, the output of such comparator being employed to vary the timing between dispensing periods so that the overall time averaged rate of infusion corresponds to said reference value.
It is a further object of the present invention to provide a new and improved pulsatile medication dispensing system wherein the accurate measurement of the amount of medi-cation dispensed through a flow restriction device during each medication dispensing period is obtained by measuring the chanye in pressure in the pumping chamber during the medi-cation dispensing period, converting said pressure measurementinto a corresponding flow through said flow restrictor, and integrating said value representing flow to obtain a measure-ment of the total volume of medication dispensed during the dispensing period.
It is another object of the present invention to provide an integrated inlet check valve and solenoid pump arrangement wherein the loading on the inlet check valve has a substantial value between medication dispensing periods, but this loading force is removed at the beginning of the pumping period so that it does not interfere with the operation of the inlet check valve during the intake stroke of the pump.
It is a further object of the present invention to provide a new and improved integral check valve and solenoid pump arrangement wherein the increased loading on the inlet check valve is obtained by employing the inlet check valve as a stop Eor the spring biased armature oE a solenoid operated pump.
Briefly considered, the present invention provides an implantable device which includes a medication reservoir, a solenoid pump arrangement, and an outlet ~low restrictor connected between the:pumping chamber and the catheter which infuses medication into the body. An absolute pressure trans-ducer is included in the implantable device and is conne~ted to the pumping chamber so that its electrical output measures the instantaneous pumping pre~ssure transient which is produced within the pumping chamber during medication dispensing periods~
Since the pressure at the inlet o~ the ~low restrictor falls to catheter outlet pressure in the intervals between medication dispensing periods, this pressure transducer also measures the internal body pressure at the catheter outlet during such intervals. The output of the pressure transducer is then employed to provide both a measurement of the body pressure during intervals between medication dispensing periods and the variation in pressure within the chamber during a medica-S tion dispensing period.
By subtracting the body pressure, or base line pres-sure, which is obtained during the intervals between medication dispensing periods from the amplitudes of the pumping pressure transient at various points along this transient during a medication dispensing periodl a series of differential pressure measurements are developed which represent the differential pressure across the flow restrictor and catheter at various points during the medication dispensing period. These differ-ential pressure signals are then converted to a corresponding flow through the ~low restrictor and the individual samples are accumulated, or integrated to provide an output signal accurately representing the total volume supplied to the catheter outlet during each medication dispensing period.
A reference signal is developed corresponding to a desired volume of medication to be dispensed during each dis-pensing period and the precisely measured volume which is obtained by means of the above-described pressure transducer is then compared with this reference signal to provide an error signal. The error signal is then used to control the time period between successive medication dispensing periods so that the average rate of infusion of medication dispensing periods is maintained at the value called for by the reference signal.
A common problem with the usage of pressure trans-ducers in long life installations is drift of the transducerzero set point. It is of special concern in implantable devices because it is not possible to periodically recalibrate the pressure transducer. An important advantage of the subject invention is that it automatically provides compensation for any transducer drift that might occur, since the same trans-ducer is used to measure the baseline (body) pressure and thepump pressure transient. Since the electronics substract the baseline pressure from the transient pressure, an output drift common to both o these outputs is nulled-out. Typically, output drift applies throughout the entire output range of a pressure transducer, so the present invention provides a very effective means to eliminate the effect of output drift of the absolute pressure transducer.
In accordance with a further aspect of the invention the solenoid pump includes a bipole solenoid coil which is included in a magnetic circuit including a movable armature which is spring biased against an inlet check valve which ls provided between the medication reservoir an~ the pumping chamber. The biased armature thus provides a substantial loading force on the inlet check valve during periods between medication dispensing periods so as to prevent leakage from the body into the pumping chamber and hence into the reservoir.
However, soon after the solenoid coil is energized the armature is lifted off of the inIet check valve and removes its loading force so that the inlet check valve can open ko permit with-drawal of a predetermined small amount of medication from thereservoir into the pumping chamber.
The invention both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:
4~
FIG. 1 is a block diayram of an implantable medication infusion system embodying the features of the present inven-tion;
FIG. 2 is a block diagram of a portion of the elec-tronic circuitry of the implantable device of FIG. l;
FIG. 3 is a graph of the pumping chamber pressure transient which is produced in the system of FIG. l; and FIG. 4 is a graph o~ the drug bolus size which is produced at different pressure heads across the pump (from the medication reservoir to the outlet of the catheter) due to the intrinsic compliance of the pump.
Referring now to FIG. 1, the implantable device 10 of the present invention is therein illustrated as comprising a medication reservoir 12 which can be refilled while the device 10 remains implanted by insertiny a hypodermic needle into an entry septum 14 and supplying medication through a ~ill filter 16 and a fill check valve indicated generally at ~ diaphragm 20 is provided as one wall of the reservoir 12 and the chamber 22 behind the diaphragm 20 is filled with a ~luid which is in a two-phase ~gas and liquid) state at body temperature to maintain a reference pressure within the reservoir 12 which is slightly less than a chosen minimum body pressure, i.e. the body pressure which may occur when the patient who carries the implanted device 10 is a at a designated maximum altitude.
The reservoir 12 communicates with an integral inlet check valve and solenoid pump arrangement indicated generally at 24 through the conduit 26. The outlet of the integral unit 24 is connected through a conduit 13 to a flow restriction device indicated generally at 15, the output of flow restric-tion device 15 being connected to a catheter 17 which is employed to dispense medication into a desired portion of the body in which the implantable device 10 is implanted.
An inlet check valve 28 is mounted so as normally to close the conduit 26. A solenoid coil 30 which is mounted in a magnetic structure or housing 32 which includes a central core portion 34 and an annular outer wall portion 36, is arranged to attract a movable armature 38 when the coil 30 is energized so as to lift the armature 38 upwardly into engage-ment with the bottom surface 40 of the outer rim portion 36 of the housing 32. The armature is mounted within the housing 32 for limited vertical movement by means of the Belleville washer 42 which is positioned between the inner wall 36 and an annular flange portion 44 provided near the center of the armature 38. A central stud 46 which is threaded into the center of the armature 38 and extends downwardly therefrom is provided wi~h a transversely extending head portion 48 which normally rests on the top surface of the inlet check valve 28 ancl is connected to a bellows 58 which extends between the.
head portion 48 and a plate 49 so that the portion 48 forms a movable wall portion o a pumping chamber 60.
A coil spring 50 is positioned between a member 52, which is threaded into the housing 32, and the upper surface of the armature 38 so as to provide an additional biasing force which urges the armature downwardly so that the head portion 48 is biased into engagement with the inlet check valve 28 and provides an initial loading force of substantial value for this inlet check valve.
A flexible member 5~ which may be in the form of a multi-fingered spider, is connected between the main housing 5~ of the implantable device and the central portion of the inlet check valve 28 so as to maintain this check valve in ~4~
registration with the conduit 26 during opening and closing thereof.
When the solenoid coil 30 is energized it lifts khe armature 38 upwardly and removes the loading force thereof from the inlet check valve 28. At the same time the head portion 48 is moved upwardly and the bellows 58 compressed so that the volume of the pumping chamber 60 is increased. As soon as the head portion ~8 is lifted off of the upper end of the check valve 128, this inlet check valve remains biased to its closed position only by the relatively small biasing force provided by the mounting member 54 thereof and as soon as the differential pressure across this check valve increases slightly and exceeds the cracking pressure of this valve, the inlet valve 28 opens and admits medication into the pumping chamber 60. ~his increase is differential pressure across khe inlet valve 28 occurs as soon as the solenoid 30 is energized and the head portion 48 and bello~s 58 start to move upwardly.
Accordingly, the inlet valve efectively moves upwardly with the bellows 58 when the solenoid coil 30 is energized.
When the coil 30 is energized the upward mbvement of the armature 38 is very fast and fluid cannot immediately enter the pumping chamber until the inlet valve 28 is opened.
Accordingly, it is necessary that the effective diameter of the inlet valve 28 be at least as grea-t as and preferably greater than the effective diameter of the bellows so that as the inlet valve 28 moves upwardly it displaces a volume at least equal to the increase in volume produced by upward move-ment of the bellows. For example, if the effective diameter of the bellows 58, i.e. the diameter half way between the inner and outer diameters of the convolutions of the bellows, ~4~
is 0.160 inches the effective diameter of the ir.let valve 28 is preferably in the order of 0.20 inches.
If the effective diameter of the inlet valve 28 is smaller than the effective diameter of the bellows 58, the pressure within the pumping chamber 60 will become so greatly reduced during the initial portion o the intake stroke that vaporization and cavitation within the pumping chamber will occur. For example, if we assume that the bellows 58 has an eEfective diameter of 0.16 inches and is moved upwardly 0.003 inches when the coil 30 is energized and the e~fective diameter of the inlet valve 28 is assumed to be one half that of the bellows 58, i.e. 0.08 inches, the area of the inlet valve 28 will be 1/4 that of the bellows 58 and the inlet valve 28 would have to move up a distance of 0.012 inches to displace an amount of fluid equal to the increase in vol~me due to compres-sion of the bellows. However, upward movement oE the inlet valve 2~ is limited by the head portion 48 to 0.003 inches so that the pressure within the chamber 60 will be drasticall~
reduced and cause vaporization of the fluid and improper opera-tion of the pump.
The inlet check valve 28 returns to its initialclosed position after a volume of medication equal to that of the compression of the bellows 58 (typically one microliter) flows into the pumping chamber 60 and increases the~pumping chamher pressure to reduce the pressure differential across the inlet check valve 28 to its reseat value.
It should be noted that the motions of the small solenoid operated bellows 58 and the inlet check valve 28 during the intake stroke of the solenoid actuated pump, are quite ast. For example, the upward motion o~ the bellows 58 when the coil 30 is energized will take typically on the order of 0.001 seconds. The inlet check valve 28 will follow this upward movement of the bellows 58 and then takes a substantially longer time, in the order of 0.005 seconds to settle back into its seat as fluid flows into the chamber 60 and increases the pumpiny chamber pressure.
The outlet restrictor 15 which is connected to the outlet of the pumping chamber, is quite small and may be equiva-lent to a 0.001 inch diameter thin plate orifice, as will be described in detail hereinafter. Accordingly, such a flow restriction device allows only negligible backflow into the pumping chamber 60 during the extremely fast intake stroke of the pump.
Following closure of the inlet check valve 28, the solenoid coil is de-energized and the mechanical spring forces of the deflected Belleville washer 42, the spring 50, and the compressed bellows 5~, acting on the effective area of the head portion 48, increase the pumpiny chamber pressure above the bod~ pressure at the catheter outlet. This forces medica-tion from the pumping chamber 60 through the outlet restrictor 15 and out the catheter 17. ThiS exhaust strGke occurs very slowly relative to the previous intake stroke and its rate is determined by the pumping chamber pressure level, the outlet restrictor size and the body pressure at the catheter outlet.
After the solenoid bellows 58 extends and the sole-noid armature reaches its de-energized position on top of the inlet check valve 28, the pumping chamber pressure equalizes to the catheter outlet (body) pressure and infusion of medica-tion ceases.
Flow restriction device 15 which is provided at the pumping chamber outlet, has substantial resistance to the flow of medication in its reverse direction, and can also have substantial restriction in its forward direction.
Accordingly, the flow restriction device 15 prevents back10w of any significance during the solenoid bellows intake stroke.
Although the restrictor 15 can be a conventional orifice, such as a thin plate orifice, it preferably comprises another type of fluid restrictor, such as a series of chemically milled plates of irregular shape which provide a long tortuous flow passage which provides a high pressure drop while having a relatively large flow area. Such a device has a flow passage size which is larger than that of a thin plate orifice and hence will not as readily plug with contamination in the medi-cation. In the alternative, a length of capillary tubing may act as the restrictor 15. In this connection it will be under-stood that in some instances the catheter itself may act as an additional outlet restrictor depending upon the internal diameter and length of the catheter.
After the exhaust stroke has been completed and medication has been forced out of the catheter 17 a medication dispensing period is completed. Subsequent medication dispens~
ing periods are repeated, by successive energizations of the solenoid coil 30, so as to provide a desired average flow rate of medication out of the catheter 17. However, it will be understood that with normal rates of flow of medication, the intervals between medication dispensing periods are quite long as compared to the medication dispensing periods them-selves. For example, the medication dispensing period may last for 0.08 seconds, whereas the time interval to the next medication dispensing period may be six seconds or longer.
With such a long time period between medication dispensing periods, the flow restrictor 15 permits the pressure at the inlet conduit 14 of the flow restrictor 15 to fall to 3L2~9~31 4~B~I
body pressure. Accordingly, when the patient who carries the implanted device changes altitude, as for example when he goes from sea level to ten thousand feet altitude, his body pressure changes substantially with the result that the operating conditions of the medication dispensing pump 24 are changed substantially. In the case of sea level operation the base line pressure, i.e. the pressure between medication dispensing periods will be substantially higher than it is when the patient is at ten thousand feet altitude causing the pressure head across the pump to increase.
As indicated in FIG. 4, when the pressure head across the pump increases the volumetric efficiency of the pump decreases due to the compliance of the components of the pump, particularly the elastomer valve seat of the inlet valve 28 and the bellows 48, so that the pump will infwse a smaller sized bolus of medicatlon during the medication dispensing period. Also, the temperature reservoir 12 will affect the inlet pressure to the pump and hence the volumet~ic efficiency thereof so that the bolus size will change. For example, the pressure at the outlet of the reservoir 12 may change from 7 to 10 psi with a variation in body temperature of from 94 F.
to 104 F. Accordingly, if a patient carrying the implanted device 10 is at 10,000 feet altitude and has a body temperature of 104 F. the pressure head across the pump is 10 psia. on the inlet and 10.1 psia. on the outlet, i.e. a pressure head of 0.1 psi., which accordingly to FIG. 4 would produce a bolus size of 1.0 microliter. On the other hand, if the patient is at sea level and his body temperature is 94 F. the pressure head across the pump would be 7.0 psia. at the inlet and 14.7 psia. at the outlet, i.e. a pressure head of 7.7 psi. which according to FIG. 4 would produce a bolus size of approximately 0.9 microliters each medication dispensing period. While the above examples are worst-case conditions, it is nevertheless evident that a fixed timing rate of six seconds will not result in a desired average rate of ~low of medication into the body under different operating conditions which affect the volumetric efficiency of the pump due to the compliance of various compo-nents theLeof. In addition, variations in manu~acturing toler-ances of the extremely small components of the integral inlet check valve and solenoid pump 24 can cause variations in the actual volume of medication dispensed during each medication dispensing period. AlSo, life and wear caused variations may also introduce further changes in the volume of medication dispensed each time the solenoid coil 30 is energized.
In accordance with an important aspect of the present invention, the pressure within the pumpiny chamber 60 is measured by means of an absolute pressure transducer 70, and the output o thls pressure transducer is employed to control the timing of solenoid coil actuations so as to maintain a programmed, time averaged rate of flow of medication into the body. More particularly, the pressure transducer 70 provides an output signal which is proportional to the instantaneous pressure existing in the pumping chamber 60 during the entire medication dispensiny period. This pumping pressure transient 72, which is shown in FIG. 3, includes an initial negative going portion 74 corresponding to -the decrease in pressure within the chamber 60 during the solenoid bellows intake stroke and a positive portion 76 of much longer duration during which time the pressure in the pumping chamber 60 gradually decreases Erom an initial high value during the time when medication is forced through the flow restriction de~ice 15 and the catheter 17 into the body. The pressure in the pumping chamber 60 1~2~
then falls to a base line value 78 which is equal to body pressure, due to the equalization of pressure through the flow restriction device 15, and remains at this base line value for approximately si~ seconds or longer until the next medication period. If, for example, the patient is at sea level, the base line pressure 78 will be 14.7 psia., as shown in FIG. 3.
It will thus be seen that the pumping pressure tran-sient 72 lasts for only a brief interval of approximately 0.08 seconds, while the time interval between medication dis-pensing periods is in the order of six seconds or longer.
Since the base line pressure 78 corresponds to the body pres-sure at the outlet of the flow restriction device 15 duriny the medication dispensing period, this base line pressure may be subtracted from the instantaneous value o~ the pressure pumping transient 72 so as to provide a~ accurate measure o~
the differential pressure Across the flow restriction device 15 and catheter 17 during the medication dispensing period.
Then, the differential pressure vs. flow rate characteristic of the flow restricting device 15 and catheter 17 can be employed to provide an accurate measure of the actual flow of medication through the flow restriction device 15 and catheter 17 at various times during the pumping transient 72. By inte-grating these instantaneous flow rates, an output signal may ~5 be developed which is accurately proportional to the total volume of medication actually dispensed during a medication dispensing period. Furthermore, this output signal will reflect all changes in mechanical and operating condition variables which influence the volume of medication dispensed.
Accordingly, this output signal may be compared to a programmed reference signal, which represents a desired volume of medica-tion to be dispensed at the catheter outlet during each dis-pensing period at a nominal rate of occurrence of said dispens-ing periods, and the resultant error signal may be employed to vary the timing of coil actuations from this nominal rate so that a desired time averaged rate of infusion into the body is maintained despite changes in any or all of these variables.
As stated above, this variation or "trimming" of the interval between pumping periods, is necessary to achieve accurate medication infusion dosage in accordance with program-med requirements throughout the range of operating pressures and temperatures of an implanted system which determine the pump pressure head and efficiency of the pump, as shown in FIG. 4. This range of operating conditions includes reservoir lS pressure variations due to temperature changes that in turn change the vapor pressure of the material in the chamber 22.
Also, changes in the reservoir diaphragm pressure as medication is displaced from the reservoir 12 may influence the volume of medication dispensed. Body pressure relative to ambient variations, as well as ambient pressure variations primarily due to altitude changes, mav also affect the volume of medica-tion dispensed.
Referring now to FIG. 2, a portion of the electronic circuitry included in the implanted device lO is shown in this figure, whereby the output of the pressure transducer may be employed to control the time periods between actuations of the solenoid coil 30 so as to provide a desired time averaged rate of infusion of medication into the body. More particularly~
the output of the pressure transducer 70 is supplied to an analog to digital converter 73 which converts the analog elec-trical output of the pressure transducer 70 into a corresponding ~z~
digital signal. Since the output of the pressure transducer 70 may be somewhat non-linear, it is desirable to correct the output of this transducer so that an extremely accurate measurement of the volume of medication dispensed during a particular medication dispensing period is obtained. To this end, the output of the analog-to-digital converter 73 is connected to a transducer calibration lookup table 75 which provides a correction which is unique to the particular pres-sure transducer 70 which is used in the implanted device 10.
More particularly, the output of the transducer calibration lookup table 75 provides a corrected digital output which is linear with respect to pressure~
As discussed generally heretofore, the output of the pressure transducer 70 measures body pressure during the intervals between medication dispensing periods, i.e. during the base line portion 78 of the pressure transducer OtltpUt shown in FIG. 3. This is because the flow restriction device 15, unlike an outlet check valve, permits the inlet pressure in the conduit 13, and hence the pressure in the pumping chamber 60 measured by the pressure transducer 70, to fall to body pressure during the relatively lon~ intervals between medication dispensing periods.
The base line pressure 78, which is equal to body pressure, is sampled and stoxed in a sample and hold circuit 77 which is controlled to sample the output of the pressure transducer 70 at some convenient point during the interval between medication dispensing periods, preferably immediately before or immediately after a dispensing period.
The body pressure (PO) which is stored in the sample and hold circuit 77 is then subtracted from the pumping pres-sure transient (Pl) in a subtractor 79. The subtractor 79 ~4~
samples the pumping pressure transient 72 at a sufficiently high rat~e that a number of samples of the differential pres-sure across the flow restriction device 15 is obtained during both the negative portion 74 of the pumping pressure transient and the positive portion 76 thereof. Preferably, the pumping pressure transient 72 is sampled at the appro~imate rate of 1000 samples per second. By storing the base line pressure (PO) and subtracting it from the pumping pressure transient 72, a large number of samples is obtained representing the actual differential pressure across the flow restrictor 15 at successive times during a medication dispensing period.
The output of the subtractor 7g is then supplied to a restrictor differential pressure versus flow rate lookup table 80. This lookup table provides an output signal propor-tional to the flow rate through ~he flow restrictor 15 (andcatheter 17 if necessary) for each particular Yalue of difer-ential pressure across this flow restrictor. Accordingl~, for each sample of di~ferential pressure developed by the subtractor 79, a corresponding output is developed at the output of the lookup table 80 which converts this differential pressure into a corresponding ~low rate through the flow res-trictor 15. The resulting flow rates, which are both negative during the negative portion 74 of the pumping transient, and are positive during the positive pumping portion 76 thereof, are summed in a total flow accumulator 82 so as to provide an output signal which is proportional to the actual volume of medication which flows through the flow restrictor 15 during a particular medication dispensing period.
In order to establish a nominal rate of occurrence of dispensing periods, i.e. actuations of the solenoid coil 30, a timer 84 is provided which controls a solenoid pulse generator 86 which in turn supplies a pulse of current to the solenoid coil 30 of th~ appropriate duration to attract the armature 38 and introduce the desired amount of medication into the pumping chamber 60. As discussed generally hereto-fore, this timer may control the generator 8~ to produce medi-cation dispensing periods at the nominal rate of one every six seconds, for example. Under these nominal conditions the integral valve and pump 24 may produce, for example, one micro-liter of medication which is dispensed to the body every six seconds. However, it will be understood that any desired time averaged rate of infusion of medication into the body may be established by any suitable programmable arrangement~
For example, the rate of infusion of medication into the body may be programmed to substantially increase during mealtimes in the case of the infusion of insulin into the body.
The electronic circuitry for establishing a desired rate of infusion may be of any suitable type such as a micro-processor, which is included within the implanted device 10 and provides a programmed reference signal which is supplied to the input terminal 88 connected to one input of a comparator 90. The other input of the comparator 90 is connected to the output of the accumulator 82 which represents the actual volume of medication dispensed during a particular m~dication dispens-ing periods.
The reference signal 88 represents a desired vol~me of medication to be dispensed to the catheter outlet at a nominal rate of occurrence of say, six seconds. I the actual volume of medication dispensed does not equal the programmed reEerence value on the input terminal 88, an error signal is developed in the output of the comparator 90 which is supplied to the timer 84 and is employed to vary the rate of occurrence of pulses developed by the timer in the correct direction to hold the time averaged rate of infusion of medication into the body at the desired value.
For example, if the total volume signal developed by the accumulator ~2 is larger than the reference signal on the input terminal 88, thus indicating that a larger than desired volume of medication has been dispensed during that particular medication dispensing period, the frequency of the timer 84 is decreased so that a longer time interval ensues be~ore the next medication dispensing period. Accordingly, the average rate of infusion of medication when measured over at a number of medication dispensing periods is thus automa-tically adjusted so that the rate of infusion is equal to the desired value represented by the reference signal on the input te~minal 7~.
On the other hand, if th~ actual volume measured by the accumulator 82 is less than the desired amount, the output of the comparator 90 will increase the frequency of the timer 84 so that a shorter time interval elapses before the next medication dispensing period. Accordingly, the time averaged rate of infusion of medication, when measured over a number of medication periods, wilI be brought back to the desired value represented by the signal on the terminal 8~. It will thus be seen that with the apparatus of the present invention, a precise time averaged rate of infusion of medication into the body can be provided under programmed control and taking into account all of the mechanical and operating condition variables which tend to influence the volume of medication dispensed by the pumping unit 24.
While the arrangement of the present invention has been illustrated in FIG. 2 as operatin~ on a digital basis, which is most suitable for microprocessor applications, it will also be understood that the output of the pressure trans-ducer can be employed on an analog basis to provide the above-described feedback compensation for variations in the total flow of medication during each medication dispensing period.
More particularly, it is only necessary to store the analog value of the output of the pressure transducer 70 during the base line portion 78 and then compare this stored value with the analog value of the pumping pressure transient 72 at a relatively high sampling rate during this pumping pressure transient and then su~tract the stored base line value there-from. The resultant differential pressure signal may then be converted into a corresponding flow rate signal corresponding to the actual flow throuyh the flow restrictor 15 at that differential pressure and the output thereof integrated to provide an output signal proportional to the total volume of medication Elowing through the restrictor 15 during that par-ticular medication dispensing period, as will be readily under-stood by those skilled in the art.
While there have been illustrated and described various embodiments of the present invention, it wiIl be apparent that various changes and modifications thereof will occur to those skilled in the art. It is intended in the appended claims to cover all such changes and modificatio~s as fall within the true spirit and scope of the present inven-tion.
What is claimed as new and desired to be secured by Letters Patént of the C ~ is:
" .. ...
The present invention relates to implantable medica-tion infusion systems and methods, and, more particularly, to so-called pulsatile systems and methods in which medication is dispensed to the body during short dispensing periods separated by relatively long intervals between such dispensing periods.
Many implantable devices in the prior art have employed so-called pulsatile medication dispensing system.
Examples of such pulsatile dispensing systems are shown in Summers Patent No. 3,527,220; Ellinwood Patent No. 3,692,027, Ellinwood Patent No. 3,9~3,060, Thomas et al Patent No.
3,963,380; Haerten et al Patent No. 4,077,405; Ellinwood Patent No. 4,146,029, Moody et al Patent No. 4,152,098; Franetzki et al Patent No. 4~191,181; Portner Patent No. 4,265,241; and Dorman International Publication No. WO 81/00209.
Some of these pulsatile systems have used inlet and outlet check valves in connection with a pumping chamber, the pump element acting to withdraw a metered amount of me~ication from a reservoir during the intake stroke of the pump and dispensing this metered amount of medication to an outlet catheter during the return stroke of the pump element. In such arrangements, the outlet:check valve closes and the inlet chec~ valve opens on the intake stroke of the pump so that medication can be drawn from the reservoir into the pumping chamber~
In other pulsatile systems, an outlet flow restric-tion device has been employed instead of an outlet check valve, for example, in Haerten et al Patent No. 4,077,405. In such devices compliance of the pumping chamber prevents the accurate dispensing of a fixed amount of medication for each stroke of ~, ~
the pump, because the pressure head across the pump will vary with different operating conditions. Variations in the pres-sure head across the pump will produce corresponding variations in the bolus volume of medication forced through the restrictor during the medication dispensing periods. Such variations in pressure head can occur due to changes in altitude and tempera-ture of the person carrying the implanted device, since the pressure within the body, i.e. the pressure at the outlet of the flow restrictor, varies with changes in altitude, and the pressure at the pump inlet varies with changes in temperature of the medication reservoir.
It is an object of the present invention to provide a new and improved pulsatile medication infusion system and method whereby an outlet flow restrictor may be used and the time averaged rate of infusion of medication into the body may be very accurately controlled under all operating condi-tions.
It is another object of the present invention to provide a new and improved pulsatile medication infusion system in which the exact amount of medication dispensed during each dispensing period is measured and compared with a reference value, the output of such comparator being employed to vary the timing between dispensing periods so that the overall time averaged rate of infusion corresponds to said reference value.
It is a further object of the present invention to provide a new and improved pulsatile medication dispensing system wherein the accurate measurement of the amount of medi-cation dispensed through a flow restriction device during each medication dispensing period is obtained by measuring the chanye in pressure in the pumping chamber during the medi-cation dispensing period, converting said pressure measurementinto a corresponding flow through said flow restrictor, and integrating said value representing flow to obtain a measure-ment of the total volume of medication dispensed during the dispensing period.
It is another object of the present invention to provide an integrated inlet check valve and solenoid pump arrangement wherein the loading on the inlet check valve has a substantial value between medication dispensing periods, but this loading force is removed at the beginning of the pumping period so that it does not interfere with the operation of the inlet check valve during the intake stroke of the pump.
It is a further object of the present invention to provide a new and improved integral check valve and solenoid pump arrangement wherein the increased loading on the inlet check valve is obtained by employing the inlet check valve as a stop Eor the spring biased armature oE a solenoid operated pump.
Briefly considered, the present invention provides an implantable device which includes a medication reservoir, a solenoid pump arrangement, and an outlet ~low restrictor connected between the:pumping chamber and the catheter which infuses medication into the body. An absolute pressure trans-ducer is included in the implantable device and is conne~ted to the pumping chamber so that its electrical output measures the instantaneous pumping pre~ssure transient which is produced within the pumping chamber during medication dispensing periods~
Since the pressure at the inlet o~ the ~low restrictor falls to catheter outlet pressure in the intervals between medication dispensing periods, this pressure transducer also measures the internal body pressure at the catheter outlet during such intervals. The output of the pressure transducer is then employed to provide both a measurement of the body pressure during intervals between medication dispensing periods and the variation in pressure within the chamber during a medica-S tion dispensing period.
By subtracting the body pressure, or base line pres-sure, which is obtained during the intervals between medication dispensing periods from the amplitudes of the pumping pressure transient at various points along this transient during a medication dispensing periodl a series of differential pressure measurements are developed which represent the differential pressure across the flow restrictor and catheter at various points during the medication dispensing period. These differ-ential pressure signals are then converted to a corresponding flow through the ~low restrictor and the individual samples are accumulated, or integrated to provide an output signal accurately representing the total volume supplied to the catheter outlet during each medication dispensing period.
A reference signal is developed corresponding to a desired volume of medication to be dispensed during each dis-pensing period and the precisely measured volume which is obtained by means of the above-described pressure transducer is then compared with this reference signal to provide an error signal. The error signal is then used to control the time period between successive medication dispensing periods so that the average rate of infusion of medication dispensing periods is maintained at the value called for by the reference signal.
A common problem with the usage of pressure trans-ducers in long life installations is drift of the transducerzero set point. It is of special concern in implantable devices because it is not possible to periodically recalibrate the pressure transducer. An important advantage of the subject invention is that it automatically provides compensation for any transducer drift that might occur, since the same trans-ducer is used to measure the baseline (body) pressure and thepump pressure transient. Since the electronics substract the baseline pressure from the transient pressure, an output drift common to both o these outputs is nulled-out. Typically, output drift applies throughout the entire output range of a pressure transducer, so the present invention provides a very effective means to eliminate the effect of output drift of the absolute pressure transducer.
In accordance with a further aspect of the invention the solenoid pump includes a bipole solenoid coil which is included in a magnetic circuit including a movable armature which is spring biased against an inlet check valve which ls provided between the medication reservoir an~ the pumping chamber. The biased armature thus provides a substantial loading force on the inlet check valve during periods between medication dispensing periods so as to prevent leakage from the body into the pumping chamber and hence into the reservoir.
However, soon after the solenoid coil is energized the armature is lifted off of the inIet check valve and removes its loading force so that the inlet check valve can open ko permit with-drawal of a predetermined small amount of medication from thereservoir into the pumping chamber.
The invention both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:
4~
FIG. 1 is a block diayram of an implantable medication infusion system embodying the features of the present inven-tion;
FIG. 2 is a block diagram of a portion of the elec-tronic circuitry of the implantable device of FIG. l;
FIG. 3 is a graph of the pumping chamber pressure transient which is produced in the system of FIG. l; and FIG. 4 is a graph o~ the drug bolus size which is produced at different pressure heads across the pump (from the medication reservoir to the outlet of the catheter) due to the intrinsic compliance of the pump.
Referring now to FIG. 1, the implantable device 10 of the present invention is therein illustrated as comprising a medication reservoir 12 which can be refilled while the device 10 remains implanted by insertiny a hypodermic needle into an entry septum 14 and supplying medication through a ~ill filter 16 and a fill check valve indicated generally at ~ diaphragm 20 is provided as one wall of the reservoir 12 and the chamber 22 behind the diaphragm 20 is filled with a ~luid which is in a two-phase ~gas and liquid) state at body temperature to maintain a reference pressure within the reservoir 12 which is slightly less than a chosen minimum body pressure, i.e. the body pressure which may occur when the patient who carries the implanted device 10 is a at a designated maximum altitude.
The reservoir 12 communicates with an integral inlet check valve and solenoid pump arrangement indicated generally at 24 through the conduit 26. The outlet of the integral unit 24 is connected through a conduit 13 to a flow restriction device indicated generally at 15, the output of flow restric-tion device 15 being connected to a catheter 17 which is employed to dispense medication into a desired portion of the body in which the implantable device 10 is implanted.
An inlet check valve 28 is mounted so as normally to close the conduit 26. A solenoid coil 30 which is mounted in a magnetic structure or housing 32 which includes a central core portion 34 and an annular outer wall portion 36, is arranged to attract a movable armature 38 when the coil 30 is energized so as to lift the armature 38 upwardly into engage-ment with the bottom surface 40 of the outer rim portion 36 of the housing 32. The armature is mounted within the housing 32 for limited vertical movement by means of the Belleville washer 42 which is positioned between the inner wall 36 and an annular flange portion 44 provided near the center of the armature 38. A central stud 46 which is threaded into the center of the armature 38 and extends downwardly therefrom is provided wi~h a transversely extending head portion 48 which normally rests on the top surface of the inlet check valve 28 ancl is connected to a bellows 58 which extends between the.
head portion 48 and a plate 49 so that the portion 48 forms a movable wall portion o a pumping chamber 60.
A coil spring 50 is positioned between a member 52, which is threaded into the housing 32, and the upper surface of the armature 38 so as to provide an additional biasing force which urges the armature downwardly so that the head portion 48 is biased into engagement with the inlet check valve 28 and provides an initial loading force of substantial value for this inlet check valve.
A flexible member 5~ which may be in the form of a multi-fingered spider, is connected between the main housing 5~ of the implantable device and the central portion of the inlet check valve 28 so as to maintain this check valve in ~4~
registration with the conduit 26 during opening and closing thereof.
When the solenoid coil 30 is energized it lifts khe armature 38 upwardly and removes the loading force thereof from the inlet check valve 28. At the same time the head portion 48 is moved upwardly and the bellows 58 compressed so that the volume of the pumping chamber 60 is increased. As soon as the head portion ~8 is lifted off of the upper end of the check valve 128, this inlet check valve remains biased to its closed position only by the relatively small biasing force provided by the mounting member 54 thereof and as soon as the differential pressure across this check valve increases slightly and exceeds the cracking pressure of this valve, the inlet valve 28 opens and admits medication into the pumping chamber 60. ~his increase is differential pressure across khe inlet valve 28 occurs as soon as the solenoid 30 is energized and the head portion 48 and bello~s 58 start to move upwardly.
Accordingly, the inlet valve efectively moves upwardly with the bellows 58 when the solenoid coil 30 is energized.
When the coil 30 is energized the upward mbvement of the armature 38 is very fast and fluid cannot immediately enter the pumping chamber until the inlet valve 28 is opened.
Accordingly, it is necessary that the effective diameter of the inlet valve 28 be at least as grea-t as and preferably greater than the effective diameter of the bellows so that as the inlet valve 28 moves upwardly it displaces a volume at least equal to the increase in volume produced by upward move-ment of the bellows. For example, if the effective diameter of the bellows 58, i.e. the diameter half way between the inner and outer diameters of the convolutions of the bellows, ~4~
is 0.160 inches the effective diameter of the ir.let valve 28 is preferably in the order of 0.20 inches.
If the effective diameter of the inlet valve 28 is smaller than the effective diameter of the bellows 58, the pressure within the pumping chamber 60 will become so greatly reduced during the initial portion o the intake stroke that vaporization and cavitation within the pumping chamber will occur. For example, if we assume that the bellows 58 has an eEfective diameter of 0.16 inches and is moved upwardly 0.003 inches when the coil 30 is energized and the e~fective diameter of the inlet valve 28 is assumed to be one half that of the bellows 58, i.e. 0.08 inches, the area of the inlet valve 28 will be 1/4 that of the bellows 58 and the inlet valve 28 would have to move up a distance of 0.012 inches to displace an amount of fluid equal to the increase in vol~me due to compres-sion of the bellows. However, upward movement oE the inlet valve 2~ is limited by the head portion 48 to 0.003 inches so that the pressure within the chamber 60 will be drasticall~
reduced and cause vaporization of the fluid and improper opera-tion of the pump.
The inlet check valve 28 returns to its initialclosed position after a volume of medication equal to that of the compression of the bellows 58 (typically one microliter) flows into the pumping chamber 60 and increases the~pumping chamher pressure to reduce the pressure differential across the inlet check valve 28 to its reseat value.
It should be noted that the motions of the small solenoid operated bellows 58 and the inlet check valve 28 during the intake stroke of the solenoid actuated pump, are quite ast. For example, the upward motion o~ the bellows 58 when the coil 30 is energized will take typically on the order of 0.001 seconds. The inlet check valve 28 will follow this upward movement of the bellows 58 and then takes a substantially longer time, in the order of 0.005 seconds to settle back into its seat as fluid flows into the chamber 60 and increases the pumpiny chamber pressure.
The outlet restrictor 15 which is connected to the outlet of the pumping chamber, is quite small and may be equiva-lent to a 0.001 inch diameter thin plate orifice, as will be described in detail hereinafter. Accordingly, such a flow restriction device allows only negligible backflow into the pumping chamber 60 during the extremely fast intake stroke of the pump.
Following closure of the inlet check valve 28, the solenoid coil is de-energized and the mechanical spring forces of the deflected Belleville washer 42, the spring 50, and the compressed bellows 5~, acting on the effective area of the head portion 48, increase the pumpiny chamber pressure above the bod~ pressure at the catheter outlet. This forces medica-tion from the pumping chamber 60 through the outlet restrictor 15 and out the catheter 17. ThiS exhaust strGke occurs very slowly relative to the previous intake stroke and its rate is determined by the pumping chamber pressure level, the outlet restrictor size and the body pressure at the catheter outlet.
After the solenoid bellows 58 extends and the sole-noid armature reaches its de-energized position on top of the inlet check valve 28, the pumping chamber pressure equalizes to the catheter outlet (body) pressure and infusion of medica-tion ceases.
Flow restriction device 15 which is provided at the pumping chamber outlet, has substantial resistance to the flow of medication in its reverse direction, and can also have substantial restriction in its forward direction.
Accordingly, the flow restriction device 15 prevents back10w of any significance during the solenoid bellows intake stroke.
Although the restrictor 15 can be a conventional orifice, such as a thin plate orifice, it preferably comprises another type of fluid restrictor, such as a series of chemically milled plates of irregular shape which provide a long tortuous flow passage which provides a high pressure drop while having a relatively large flow area. Such a device has a flow passage size which is larger than that of a thin plate orifice and hence will not as readily plug with contamination in the medi-cation. In the alternative, a length of capillary tubing may act as the restrictor 15. In this connection it will be under-stood that in some instances the catheter itself may act as an additional outlet restrictor depending upon the internal diameter and length of the catheter.
After the exhaust stroke has been completed and medication has been forced out of the catheter 17 a medication dispensing period is completed. Subsequent medication dispens~
ing periods are repeated, by successive energizations of the solenoid coil 30, so as to provide a desired average flow rate of medication out of the catheter 17. However, it will be understood that with normal rates of flow of medication, the intervals between medication dispensing periods are quite long as compared to the medication dispensing periods them-selves. For example, the medication dispensing period may last for 0.08 seconds, whereas the time interval to the next medication dispensing period may be six seconds or longer.
With such a long time period between medication dispensing periods, the flow restrictor 15 permits the pressure at the inlet conduit 14 of the flow restrictor 15 to fall to 3L2~9~31 4~B~I
body pressure. Accordingly, when the patient who carries the implanted device changes altitude, as for example when he goes from sea level to ten thousand feet altitude, his body pressure changes substantially with the result that the operating conditions of the medication dispensing pump 24 are changed substantially. In the case of sea level operation the base line pressure, i.e. the pressure between medication dispensing periods will be substantially higher than it is when the patient is at ten thousand feet altitude causing the pressure head across the pump to increase.
As indicated in FIG. 4, when the pressure head across the pump increases the volumetric efficiency of the pump decreases due to the compliance of the components of the pump, particularly the elastomer valve seat of the inlet valve 28 and the bellows 48, so that the pump will infwse a smaller sized bolus of medicatlon during the medication dispensing period. Also, the temperature reservoir 12 will affect the inlet pressure to the pump and hence the volumet~ic efficiency thereof so that the bolus size will change. For example, the pressure at the outlet of the reservoir 12 may change from 7 to 10 psi with a variation in body temperature of from 94 F.
to 104 F. Accordingly, if a patient carrying the implanted device 10 is at 10,000 feet altitude and has a body temperature of 104 F. the pressure head across the pump is 10 psia. on the inlet and 10.1 psia. on the outlet, i.e. a pressure head of 0.1 psi., which accordingly to FIG. 4 would produce a bolus size of 1.0 microliter. On the other hand, if the patient is at sea level and his body temperature is 94 F. the pressure head across the pump would be 7.0 psia. at the inlet and 14.7 psia. at the outlet, i.e. a pressure head of 7.7 psi. which according to FIG. 4 would produce a bolus size of approximately 0.9 microliters each medication dispensing period. While the above examples are worst-case conditions, it is nevertheless evident that a fixed timing rate of six seconds will not result in a desired average rate of ~low of medication into the body under different operating conditions which affect the volumetric efficiency of the pump due to the compliance of various compo-nents theLeof. In addition, variations in manu~acturing toler-ances of the extremely small components of the integral inlet check valve and solenoid pump 24 can cause variations in the actual volume of medication dispensed during each medication dispensing period. AlSo, life and wear caused variations may also introduce further changes in the volume of medication dispensed each time the solenoid coil 30 is energized.
In accordance with an important aspect of the present invention, the pressure within the pumpiny chamber 60 is measured by means of an absolute pressure transducer 70, and the output o thls pressure transducer is employed to control the timing of solenoid coil actuations so as to maintain a programmed, time averaged rate of flow of medication into the body. More particularly, the pressure transducer 70 provides an output signal which is proportional to the instantaneous pressure existing in the pumping chamber 60 during the entire medication dispensiny period. This pumping pressure transient 72, which is shown in FIG. 3, includes an initial negative going portion 74 corresponding to -the decrease in pressure within the chamber 60 during the solenoid bellows intake stroke and a positive portion 76 of much longer duration during which time the pressure in the pumping chamber 60 gradually decreases Erom an initial high value during the time when medication is forced through the flow restriction de~ice 15 and the catheter 17 into the body. The pressure in the pumping chamber 60 1~2~
then falls to a base line value 78 which is equal to body pressure, due to the equalization of pressure through the flow restriction device 15, and remains at this base line value for approximately si~ seconds or longer until the next medication period. If, for example, the patient is at sea level, the base line pressure 78 will be 14.7 psia., as shown in FIG. 3.
It will thus be seen that the pumping pressure tran-sient 72 lasts for only a brief interval of approximately 0.08 seconds, while the time interval between medication dis-pensing periods is in the order of six seconds or longer.
Since the base line pressure 78 corresponds to the body pres-sure at the outlet of the flow restriction device 15 duriny the medication dispensing period, this base line pressure may be subtracted from the instantaneous value o~ the pressure pumping transient 72 so as to provide a~ accurate measure o~
the differential pressure Across the flow restriction device 15 and catheter 17 during the medication dispensing period.
Then, the differential pressure vs. flow rate characteristic of the flow restricting device 15 and catheter 17 can be employed to provide an accurate measure of the actual flow of medication through the flow restriction device 15 and catheter 17 at various times during the pumping transient 72. By inte-grating these instantaneous flow rates, an output signal may ~5 be developed which is accurately proportional to the total volume of medication actually dispensed during a medication dispensing period. Furthermore, this output signal will reflect all changes in mechanical and operating condition variables which influence the volume of medication dispensed.
Accordingly, this output signal may be compared to a programmed reference signal, which represents a desired volume of medica-tion to be dispensed at the catheter outlet during each dis-pensing period at a nominal rate of occurrence of said dispens-ing periods, and the resultant error signal may be employed to vary the timing of coil actuations from this nominal rate so that a desired time averaged rate of infusion into the body is maintained despite changes in any or all of these variables.
As stated above, this variation or "trimming" of the interval between pumping periods, is necessary to achieve accurate medication infusion dosage in accordance with program-med requirements throughout the range of operating pressures and temperatures of an implanted system which determine the pump pressure head and efficiency of the pump, as shown in FIG. 4. This range of operating conditions includes reservoir lS pressure variations due to temperature changes that in turn change the vapor pressure of the material in the chamber 22.
Also, changes in the reservoir diaphragm pressure as medication is displaced from the reservoir 12 may influence the volume of medication dispensed. Body pressure relative to ambient variations, as well as ambient pressure variations primarily due to altitude changes, mav also affect the volume of medica-tion dispensed.
Referring now to FIG. 2, a portion of the electronic circuitry included in the implanted device lO is shown in this figure, whereby the output of the pressure transducer may be employed to control the time periods between actuations of the solenoid coil 30 so as to provide a desired time averaged rate of infusion of medication into the body. More particularly~
the output of the pressure transducer 70 is supplied to an analog to digital converter 73 which converts the analog elec-trical output of the pressure transducer 70 into a corresponding ~z~
digital signal. Since the output of the pressure transducer 70 may be somewhat non-linear, it is desirable to correct the output of this transducer so that an extremely accurate measurement of the volume of medication dispensed during a particular medication dispensing period is obtained. To this end, the output of the analog-to-digital converter 73 is connected to a transducer calibration lookup table 75 which provides a correction which is unique to the particular pres-sure transducer 70 which is used in the implanted device 10.
More particularly, the output of the transducer calibration lookup table 75 provides a corrected digital output which is linear with respect to pressure~
As discussed generally heretofore, the output of the pressure transducer 70 measures body pressure during the intervals between medication dispensing periods, i.e. during the base line portion 78 of the pressure transducer OtltpUt shown in FIG. 3. This is because the flow restriction device 15, unlike an outlet check valve, permits the inlet pressure in the conduit 13, and hence the pressure in the pumping chamber 60 measured by the pressure transducer 70, to fall to body pressure during the relatively lon~ intervals between medication dispensing periods.
The base line pressure 78, which is equal to body pressure, is sampled and stoxed in a sample and hold circuit 77 which is controlled to sample the output of the pressure transducer 70 at some convenient point during the interval between medication dispensing periods, preferably immediately before or immediately after a dispensing period.
The body pressure (PO) which is stored in the sample and hold circuit 77 is then subtracted from the pumping pres-sure transient (Pl) in a subtractor 79. The subtractor 79 ~4~
samples the pumping pressure transient 72 at a sufficiently high rat~e that a number of samples of the differential pres-sure across the flow restriction device 15 is obtained during both the negative portion 74 of the pumping pressure transient and the positive portion 76 thereof. Preferably, the pumping pressure transient 72 is sampled at the appro~imate rate of 1000 samples per second. By storing the base line pressure (PO) and subtracting it from the pumping pressure transient 72, a large number of samples is obtained representing the actual differential pressure across the flow restrictor 15 at successive times during a medication dispensing period.
The output of the subtractor 7g is then supplied to a restrictor differential pressure versus flow rate lookup table 80. This lookup table provides an output signal propor-tional to the flow rate through ~he flow restrictor 15 (andcatheter 17 if necessary) for each particular Yalue of difer-ential pressure across this flow restrictor. Accordingl~, for each sample of di~ferential pressure developed by the subtractor 79, a corresponding output is developed at the output of the lookup table 80 which converts this differential pressure into a corresponding ~low rate through the flow res-trictor 15. The resulting flow rates, which are both negative during the negative portion 74 of the pumping transient, and are positive during the positive pumping portion 76 thereof, are summed in a total flow accumulator 82 so as to provide an output signal which is proportional to the actual volume of medication which flows through the flow restrictor 15 during a particular medication dispensing period.
In order to establish a nominal rate of occurrence of dispensing periods, i.e. actuations of the solenoid coil 30, a timer 84 is provided which controls a solenoid pulse generator 86 which in turn supplies a pulse of current to the solenoid coil 30 of th~ appropriate duration to attract the armature 38 and introduce the desired amount of medication into the pumping chamber 60. As discussed generally hereto-fore, this timer may control the generator 8~ to produce medi-cation dispensing periods at the nominal rate of one every six seconds, for example. Under these nominal conditions the integral valve and pump 24 may produce, for example, one micro-liter of medication which is dispensed to the body every six seconds. However, it will be understood that any desired time averaged rate of infusion of medication into the body may be established by any suitable programmable arrangement~
For example, the rate of infusion of medication into the body may be programmed to substantially increase during mealtimes in the case of the infusion of insulin into the body.
The electronic circuitry for establishing a desired rate of infusion may be of any suitable type such as a micro-processor, which is included within the implanted device 10 and provides a programmed reference signal which is supplied to the input terminal 88 connected to one input of a comparator 90. The other input of the comparator 90 is connected to the output of the accumulator 82 which represents the actual volume of medication dispensed during a particular m~dication dispens-ing periods.
The reference signal 88 represents a desired vol~me of medication to be dispensed to the catheter outlet at a nominal rate of occurrence of say, six seconds. I the actual volume of medication dispensed does not equal the programmed reEerence value on the input terminal 88, an error signal is developed in the output of the comparator 90 which is supplied to the timer 84 and is employed to vary the rate of occurrence of pulses developed by the timer in the correct direction to hold the time averaged rate of infusion of medication into the body at the desired value.
For example, if the total volume signal developed by the accumulator ~2 is larger than the reference signal on the input terminal 88, thus indicating that a larger than desired volume of medication has been dispensed during that particular medication dispensing period, the frequency of the timer 84 is decreased so that a longer time interval ensues be~ore the next medication dispensing period. Accordingly, the average rate of infusion of medication when measured over at a number of medication dispensing periods is thus automa-tically adjusted so that the rate of infusion is equal to the desired value represented by the reference signal on the input te~minal 7~.
On the other hand, if th~ actual volume measured by the accumulator 82 is less than the desired amount, the output of the comparator 90 will increase the frequency of the timer 84 so that a shorter time interval elapses before the next medication dispensing period. Accordingly, the time averaged rate of infusion of medication, when measured over a number of medication periods, wilI be brought back to the desired value represented by the signal on the terminal 8~. It will thus be seen that with the apparatus of the present invention, a precise time averaged rate of infusion of medication into the body can be provided under programmed control and taking into account all of the mechanical and operating condition variables which tend to influence the volume of medication dispensed by the pumping unit 24.
While the arrangement of the present invention has been illustrated in FIG. 2 as operatin~ on a digital basis, which is most suitable for microprocessor applications, it will also be understood that the output of the pressure trans-ducer can be employed on an analog basis to provide the above-described feedback compensation for variations in the total flow of medication during each medication dispensing period.
More particularly, it is only necessary to store the analog value of the output of the pressure transducer 70 during the base line portion 78 and then compare this stored value with the analog value of the pumping pressure transient 72 at a relatively high sampling rate during this pumping pressure transient and then su~tract the stored base line value there-from. The resultant differential pressure signal may then be converted into a corresponding flow rate signal corresponding to the actual flow throuyh the flow restrictor 15 at that differential pressure and the output thereof integrated to provide an output signal proportional to the total volume of medication Elowing through the restrictor 15 during that par-ticular medication dispensing period, as will be readily under-stood by those skilled in the art.
While there have been illustrated and described various embodiments of the present invention, it wiIl be apparent that various changes and modifications thereof will occur to those skilled in the art. It is intended in the appended claims to cover all such changes and modificatio~s as fall within the true spirit and scope of the present inven-tion.
What is claimed as new and desired to be secured by Letters Patént of the C ~ is:
" .. ...
Claims (35)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a system for infusing medication into a body, the combination of, a medication reservoir, a flow restriction means having an outlet For infusing medication into the body, metering means connected between said reservoir and the inlet of said flow restrict on means for periodically supplying a small portion of the medication in said reservoir to the inlet of said flow restriction means during successive spaced apart dispensing periods, means for measuring the exact amount of medication supplied to said flow restriction outlet during each dispensing period, and means responsive to said measuring means for varying the time between successive dispensing periods so as to maintain the rate of infusion of medication into the body at a desired value, measuring means including a pressure transducer for developing a signal corresponding to the pressure transient developed at said inlet of said flow restriction means during each of said dispensing periods.
2. The combination of claim 1, wherein said flow restriction means allows the pressure at the inlet thereof to become equal to the pressure at said outlet in the intervals between dispensing periods, and means for period-ically sampling the output of said pressure transducer during one of said dispensing periods and subtracting from each sample the output of said pressure transducer during said intervals to obtain successive samples representing the differential pressure across said flow restriction means during said one dispensing period.
3. The combination of claim 2, wherein the output of said pressure transducer is subject to drift and said differential pressure samples are compensated for such drift by subtracting the output of the pressure transducer during the interval between dispensing periods from the output of the pressure transducer during one of the dispensing periods.
4. The combination of claim 2, which includes means for converting said differential pressure samples into signals representing the corresponding flow of medication through said flow restriction means, and means responsive to said signals for developing an output signal representing the total volume of medication supplied to said outlet during each of said dispensing periods.
5. In a system for infusing medication into a body, the combination of, a medication reservoir, a medication outlet for infusing medication into the body, positive displacement pump means connected between said reservoir and said outlet and including a pumping chamber and a pump element movable through a predetermined stroke within said chamber to force medication from said reservoir into said medication outlet, means for developing an electrical signal which varies in accordance with the instantaneous pressure within said pumping chamber, means controlled by said electrical signal for varying the rate at which said pump is actuated so as to maintain a predetermined average rate of flow of medication to said outlet, a flow restrictor positioned between said pumping chamber and said outlet, said flow restrictor allowing the pressure within said pumping chamber to become equal to the pressure at said outlet in the intervals between strokes of said pump element and a pressure transducer for measuring the absolute pressure within said pumping chamber and developing said electrical signal, whereby said electrical signal includes a base line portion proportional to the pressure at said outlet during said intervals and a pumping pressure transient portion which varies in accordance with variations in to pressure within said chamber during pumping strokes of said pump element.
6. The combination of claim 5, which includes means for storing a value proportional to said base line portion of said electrical signal, and means for periodically subtracting said base line value from the instantaneous value of said electrical signal during said pumping pressure transient portion of said electrical signal to obtain successive values of the differential pressure across said flow restrictor during said pumping pressure transient, and means controlled by said successive differential pressure values for calculating the actual flow of medication to said outlet during said pumping pressure transient.
7. The combination of claim 6, which includes means for developing a reference signal corresponding to a desired flow of medication to said outlet, and means jointly responsive to said successive differential pressure values and said reference signal for controlling the rate at which said pump element is actuated so as to maintain the flow of medication to said outlet at said desired value.
8. The combination of claim 7, which includes means for converting said successive differential pressure values into corresponding rates of flow through said restrictor, and means for integrating said successive converted flow rates to obtain an output corresponding to the total volume of medication supplied to said outlet during one stroke of said pump element.
9. In a system for infusing medication into a body, the combination of, a medication reservoir, a medication outlet for infusing medication into the body, positive displacement pump means connected between said reservoir and said outlet and including a pumping chamber and a pump element movable through a predetermined stroke within said chamber to force medication from said reservoir into said medication outlet, means for measuring the volume of medication pumped to said outlet on each stroke of said pump element, means controlled at least in part by said measuring means for varying the rate at which said pump element is stroked to maintain the volume of medication supplied to said outlet per unit of time at a predetermined value, a pressure transducer for developing an electrical signal corresponding to the pressure transient developed within said pumping chamber during one stroke of said pump element, means for generating successive signals corresponding to the flow of medication to said outlet during successive portions of said pressure transient, and means responsive to said successive signals for developing an output signal corresponding to the total volume of medication supplied to said outlet during said one stroke of said pump element.
10. The combination of claim 9, which includes means for integrating said successive signals to obtain said output signal.
11. In a system for infusing medication into a body, the combination of, a medication reservoir, a medication outlet for infusing medication into the body, positive displacement pump means connected between said reservoir and said outlet and including a pumping chamber and a pump element movable through a predetermined stroke within said chamber to force medication from said reservoir into said medication outlet, means for measuring the volume of medication pumped to said outlet on each stroke of said pump element, means controlled at least in part by said measuring means for varying the rate at which said pump element is stroked to maintain the volume of medication supplied to said outlet per unit of time at a predetermined value, a flow restrictor connected between said pumping chamber and said outlet, said flow restrictor allowing the pressure within said pumping chamber to become equal to the pressure at said outlet in the intervals between strokes of said pump element.
12. The combination of claim 11, which includes a pressure transducer for developing an electrical signal corresponding to the pressure transient developed within said pumping chamber during one stroke of said pump element, means for generating a series of signals corresponding to the differential pressure across said flow restrictor at different points along said pressure transient, means responsive to each of said series of differential pressure signals for developing a signal representing the corresponding flow of medication through said flow restrictor, and means responsive to said series of flow signals for developing an output signal representing the total volume of medication supplied to said outlet during said one stroke of said pump element.
13. The combination of claim 12, wherein said series of flow signals are digital signals, and accumulator means for summing said series of flow signals to provide said output signal.
14. The combination of claim 11, which includes a pressure transducer for developing an electrical signal corresponding to the pressure transient developed within said pumping chamber during one stroke of said pump element, means responsive to said electrical signal for generating a differential pressure signal which varies in accordance with the differential pressure across said flow restrictor during said pressure transient, means for converting said different pressure signal into a corresponding flow rate signal whose amplitude varies in accordance with variations in flow through said flow restrictor during said pressure transient, and means for integrating said flow rate signal, thereby to provide an output signal representing the total volume of medication supplied to said outlet during said one stroke of said pump element.
15. The combination of claim 12, which includes means for actuating said pump element at a variable rate, means for generating a reference signal corresponding to a desired flow of medication to said outlet, means for comparing said reference signal with said output signal to develop an error signal corresponding to the difference therebetween, and means controlled by said error signal for varying the rate of actuation of said pump element by said actuating means to maintain said desired flow of medication to said outlet.
16. In a system for infusing medication into a body, the combination of, a medication reservoir, a medication outlet for infusing medication into the body, positive displacement pump means connected between said reservoir and said outlet and including a pumping chamber and a pump element movable through a predetermined stroke within said chamber to force medication from said reservoir into said medication outlet, means for actuating said pump element at a variable rate, means for generating a reference signal corresponding to a desired flow of medication to said outlet, means for developing a control signal representing the flow of medication to said outlet on each stroke of said pump element, said means for developing a control signal including a pressure transducer for developing an electrical signal corresponding to the pumping pressure transient developed within said pumping chamber during one stroke of said pump element, means for comparing said reference signal and said output signal to develop an error signal corresponding to the difference therebetween, and means controlled by said error signal for varying the rate of actuation of said pump element by said actuating means to maintain said desired flow of medication to said outlet.
17. The combination of claim 16, which includes pressure transducer calibration means for modifying said electrical signal to correct for non-linearity in the output of said pressure transducer.
18. The combination of claim 16, which includes A/D converter means for developing a digital signal corresponding to the output of said pressure transducer.
19. The combination of claim 18, which includes transducer calibration means connected to the output of said A/D converter means to correct for non-linearity in the output of said pressure transducer.
20. The combination of claim 16, which includes a flow restrictor connected between said pumping chamber and said outlet, said flow restrictor allowing the pressure within said pumping chamber to become equal to the pressure at said outlet in the intervals between strokes of said pump element.
21. The combination of claim 20, which includes means for storing a value corresponding to the pressure in said pumping chamber during said intervals.
22. The combination of claim 21, which includes means for periodically subtracting said stored value from the output of said pressure transducer during said pressure transient to obtain a succession of signals representing the differential pressure across said flow restrictor at different times during said pressure transient.
23. The combination of claim 22, which includes means for converting said succession of signals into signals representing the flow rate through said restrictor corresponding to each of said differential pressure signals.
24. The combination of claim 23, which includes means for combining said flow rate signals to provide said output signal.
25. The combination of claim 21, which includes means for periodically sampling said pressure transient to provide successive values corresponding to the amplitude of said pressure transient relative to said stored value at different -times during said pressure transient.
26. The combination of claim 25, which includes means controlled by said successive values for developing said output signal.
27. The combination of claim 16, which includes a flow restrictor connected between said pumping chamber and said outlet, said flow restrictor permitting the pressure within said pumping chamber to become equal to the pressure at said outlet in the intervals between strokes of said pump element, means for developing a first signal corresponding to the pressure in said chamber during said intervals, means for developing a second signal which varies in accordance with variations in the pressure within said chamber during strokes of said pump element, and means responsive to said first and second signals for developing said control signal.
28. In a system for infusing medication into a body, the combination of, a reservoir of medication, a pumping chamber, a medication outlet, an inlet valve between said reservoir and said pumping chamber and including a fixed valve seat and a movable valve element, a movable member forming a wall portion of said pumping chamber and positioned adjacent said movable valve element, an armature connected to said movable member, means for biasing said armature in the direction to urge said movable member into engagement with said movable valve element and said movable valve element into engagement with said valve seat, thereby normally to provide a substantial closing force for said inlet valve, and electromagnetic means for attracting said armature and moving said movable element away from said movable valve element and in the direction to increase the volume of said pumping chamber thereby to remove said closing force from said inlet valve and permit medication to flow from said reservoir into said pumping chamber, wherein said armature is a flat disc and said biasing means comprises a spring positioned between said disc and a fixed support member.
29. In a system for infusing medication into a body, the combination of, a reservoir of medication, a pumping chamber, a medication outlet, an inlet valve between said reservoir and said pumping chamber and including a fixed valve seat and a movable valve element, a movable member forming a wall portion of said pumping chamber and positioned adjacent said movable valve element, an armature connected to said movable member, means for biasing said armature in the direction to urge said movable member into engagement with said movable valve element and said movable valve element into engagement with said valve seat, thereby normally to provide a substantial closing force for said inlet valve, and electromagnetic means for attracting said armature and moving said movable element away from said movable valve element and in the direction to increase the volume of said pumping chamber thereby to remove said closing force from said inlet valve and permit medication to flow from said reservoir into said pumping chamber, said system including a housing within which said reservoir and pumping chamber are located, said armature comprising a flat disc which is mounted in said housing for movement in said direction, and said biasing means comprising a spring positioned between said disc and said housing.
30. In a system for infusing medication into a body, the combination of, a reservoir of medication, a pumping chamber, a medication outlet, an inlet valve between said reservoir and said pumping chamber and including a fixed valve seat and a movable valve element, a movable member forming a wall portion of said pumping chamber and positioned adjacent said movable valve element, an armature connected to said movable member, means for biasing said armature in the direction to urge said movable member into engagement with said movable valve element and said movable valve element into engagement with said valve seat, thereby normally to provide a substantial closing force for said inlet valve, and electromagnetic means for attracting said armature and moving said movable element away from said movable valve element and in the direction to increase the volume of said pumping chamber thereby to remove said closing force from said inlet valve and permit medication to flow from said reservoir into said pumping chamber, wherein said armature is a flat disc, said movable member comprises a pin connected to said disc at the center thereof and having a head portion positioned within said pumping chamber, and a flexible member connected between said head portion and the adjacent wall of said pumping chamber so that said head portion forms a movable wall portion of said pumping chamber.
31. The combination of claim 30, wherein said flexible member is a metal bellows.
32. In a system for infusing medication into a body, the combination of, a reservoir of medication, a pumping chamber, a medication outlet, an inlet valve between said reservoir and said pumping chamber and including a fixed valve seat and a movable valve element, a movable member forming a wall portion of said pumping chamber and positioned adjacent said movable valve element, an armature connected to said movable member, means for biasing said armature in the direction to urge said movable member into engagement with said movable valve element and said movable valve element into engagement with said valve seat, thereby normally to provide a substantial closing force for said inlet valve, and electromagnetic means for attracting said armature and moving said movable element away from said movable valve element and in the direction to increase the volume of said pumping chamber thereby to remove said closing force from said inlet valve and permit medication to flow from said reservoir into said pumping chamber, wherein said electro-magnetic means comprises a magnetic core, a coil mounted on said core, said armature being mounted to complete a magnetic flux path with said core, and being moved in response to energization of said coil.
33. In a system for infusing medication into a body, the combination of, means defining a pumping chamber including a movable wall portion biased to an initial position, a movably mounted armature connected to said movable wall portion, electromagnetic means including a coil for moving said armature so that the volume of said pumping chamber is altered, a reservoir of medication, conduit means inter-connecting said reservoir and said pumping chamber and including a check valve operative when open to permit flow of medication from said reservoir to said pumping chamber and blocking such flow when closed, means for applying a pulse of current to said coil so that said armature is moved in a direction to increase the volume of said pumping chamber by moving said movable wall portion away from said initial position against the force of said biasing means, the resultant drop in pressure in said pumping chamber when said armature is moved in said direction being sufficient to cause said check valve to open, a medication outlet, and flow restriction means for connecting said pumping chamber to said medication outlet, said check valve closing when the differential pressure thereacross reaches a pre-determined value, said biasing means acting after said check valve is closed to force medication through said flow restriction means to said outlet.
34. The system of claim 33, which includes pressure transducer means for developing an electrical signal which varies in accordance with the pressure within said pumping chamber, and means controlled by said electrical signal for varying the rate at which pulses are applied to said coil so as to maintain a predetermined rate of flow of medication to said outlet.
35. In a system for infusing medication into a body, the combination of, means defining a pumping chamber including a movable wall portion biased to an initial position, a coil, means for applying pulses of current to said coil, electromagnet-ic means for moving said wall portion in the direction to increase the volume of said pumping chamber when said current pulses are applied to said coil, a medication reservoir, a check valve positioned between said pumping chamber and said reservoir, said check valve being operative when open to permit flow of medication to said pumping chamber and blocking such flow when closed, a medication outlet for infusing medication into the body, a flow restrictor connected between said pumping chamber and said outlet for restricting the flow of medication to said outlet, said flow restrictor allowing the pressure within said pumping chamber to become equal to the pressure at said outlet in the intervals between said current pulses, said biasing means acting after said check valve closes to increase the pressure in said pumping chamber and force medication through said flow restrictor to said outlet, pressure transducer means for developing an electrical signal which varies in accordance with the pressure within said pumping chamber, and means controlled by said electrical signal for controlling the rate at which said current pulses are applied to said coil so as to maintain a predetermined average flow of medication to said outlet.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/453,594 US4486190A (en) | 1982-12-27 | 1982-12-27 | Precision medication dispensing system and method |
| US453,594 | 1982-12-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1224101A true CA1224101A (en) | 1987-07-14 |
Family
ID=23801195
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000444215A Expired CA1224101A (en) | 1982-12-27 | 1983-12-23 | Precision medication dispensing system and method |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4486190A (en) |
| EP (1) | EP0112585B1 (en) |
| CA (1) | CA1224101A (en) |
| DE (1) | DE3371171D1 (en) |
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| US4231354A (en) * | 1978-07-14 | 1980-11-04 | Howmedica, Incorporated | Pulsatile blood pumping apparatus and method |
| SE426783B (en) * | 1978-10-19 | 1983-02-14 | Figueiredo Nuno R M | DEVICE FOR AUTOMATIC CONTROL OF THE INFUSION FLUID IN AN INFUSER |
| US4360019A (en) * | 1979-02-28 | 1982-11-23 | Andros Incorporated | Implantable infusion device |
| US4373527B1 (en) * | 1979-04-27 | 1995-06-27 | Univ Johns Hopkins | Implantable programmable medication infusion system |
| US4299220A (en) * | 1979-05-03 | 1981-11-10 | The Regents Of The University Of Minnesota | Implantable drug infusion regulator |
| AR221767A1 (en) * | 1979-07-13 | 1981-03-13 | Univ Minnesota | A MEDICAL DEVICE FOR INFUSION OF DRUGS IN THE BODY OF AN ANIMAL |
| DE2937066A1 (en) * | 1979-09-13 | 1981-03-26 | Clinicon International Gmbh, 6800 Mannheim | DOSING DEVICE |
| DE3035670A1 (en) * | 1980-09-22 | 1982-04-29 | Siemens AG, 1000 Berlin und 8000 München | DEVICE FOR INFUSING LIQUIDS IN HUMAN OR ANIMAL BODIES |
| US4391598A (en) * | 1981-04-28 | 1983-07-05 | Quest Medical, Inc. | Intravenous drug additive delivery system with electronic control |
-
1982
- 1982-12-27 US US06/453,594 patent/US4486190A/en not_active Expired - Fee Related
-
1983
- 1983-12-23 CA CA000444215A patent/CA1224101A/en not_active Expired
- 1983-12-27 DE DE8383113157T patent/DE3371171D1/en not_active Expired
- 1983-12-27 EP EP83113157A patent/EP0112585B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0112585B1 (en) | 1987-04-29 |
| US4486190A (en) | 1984-12-04 |
| DE3371171D1 (en) | 1987-06-04 |
| EP0112585A1 (en) | 1984-07-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |