CA1307178C - Programmable valve pump - Google Patents

Abstract

PROGRAMMABLE VALVE PUMP
Abstract An implantable valve accumulator pump comprises a drug reservoir (18) maintained at constant pressure vapor. The medication metering assembly comprises a fixed volume accumulator (30) positioned between a pair of valves (26,28). The valves alternately open and close to admit medication from the reservoir into the accumulator and to dispense a precise volume spike to an outlet catheter (36). In order to mimimize dead volume and insure complete discharge, the accumulator employs a titanium diaphragm (90) seated in one position by a recessed stop and in the discharge position by a spacer plate (98) having a grooved pattern. The unit is externally programmed.

Description

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p~OCRAMMABLE V~LVE PUM,æ

Thi~ invention relates to an implant~ble infuslon pump fo~
tlle di~penging of infusate. In p~rticular, it relates to a pump operating at positive pressure which is programmable to dispense medication in accordance with dif~erent specified flow rates.
Implantable infusion pumps are currently used for a variety of medical purposes. Typical o~ such commercially acceptable device~ are the IN~USAID Model 100 and 400 devices. Such devices are implantable in the human body and rely on a liquid/
vapor e~lilibrium to maintain constant pres~ure Otl the drug which i8 hou~d therein oo that the drug flow3 through a capillary in order to malntain 3 constant flow rate. Such devlces are characterized by "constant flow" and are used in a variety of medical appl1cation~, for example, to di~pense chemotherapy at a relatively constant flow rate. As b~ckgrotlnd to the INFUSAID
Model 100 and ~00 devices, are U.S. patelltR 3,731,681 and 4,496, 343 .
There are a variety of medical conditiolls wllere a patient requ~res an adju tmeDt in the dosage and as such, constant flow pumps are inadequate. A typical example iB diabetes where the guantity of medication, such as in~ulin, to be lnfu~cd varies due 4 _ , _ :

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to requirements of the patient. Fl~lctllations can occur on a daily ba~1~ or more randomly as ~ ~unction of the ingestion of food. It is known that the amoul-t of medication to be infused per unit of time should be adjusted at certain time intervals. A
patients re~uirements may fluctuate at either set, known rates or vary abnormally, for e~ample, ~y tlle inge~tion of food or other transitory condition~. Those conditions require the admini~tratlon of a bolus dose of infusate. The daily administration of insulin requir~s a basal dose that is supplanted by bolus doses, for example, at meal times. The d~fference in flow rates between tlle basal and bolu~ dose3 may be guite large, the bolus dose several orders of magnitude larger than the basal dose. Consequently, to achieve proper flow rates over the ~pectrum of desired rates, such a device mu~t have the ability to continually infuse at very low rate~ yet provlde periodically a ~ubstantially increased flow rate.
Within the repo~ted literature, a number of implantable programmable concepts have been di~closed. Typical are U.S.
Patent3 3,894,538; 4,077,405; and 4,443,218. A category of programmable pumps i~ so-called negative pressure pumps typified by U.S. Pat~nts 4,482,346 and 4,486,190. These devices are ~olenoid act~vated negative pressure device~. In those systems a diaphraqm storage chamber maintain~ the drug to be infused. A
diaphragm ~eparates the drug from propellant, normally Freon maintained at negative pressure. The ~olenoid is activated 7~

driving an armature and a bellows p~lmping element. The displacement of the a~mature opens a c]-~ck valve which draws drucJ
from the storage chamber into a ~ownstream pu~ping chamber. A
re~triction i8 u~ed to prevent backflow in the outlet during thi~
~hort period. When the pump chamber i.s full, the check valve clQses and the solenoid is deenergized. A ~pring force i8 uYed to displace the bellows into the ~hamber thereby pumping the drug through a restrictor and into the patient. The bellows armature assembly come~ to re.st on the check valve to insure that no bac~flow occur~ during the rest peLiod. such a system operates at negative pressure to insure no forward flow duriny thi~ rest period, that is the drug chamber pres~ure is below body pressure.
Such negative pres~ure ystems suffer from several ~lgnificant dlsadvantages. First, the ingestion of air into the system wlll ~top the drug flow proces~. Consequently, such devlces req~ire expensive fill and empty ~y~tems for recycling of the implantable device. A more prflctical and serious problem i~
that spacial handling i8 required for the devices themselves.
The drugs uced with such devices must be vacuum conditioned thereby requiring that special steps be taken by those who in many cases are medical technicians and are technically unnophisticated. The drugs must also be packaged and shipped with special care to maintain ~uch vacuum conditioning.
Consequently, these devices, while offering theoretical advantage~, in practice suffer from s~gnificant di~advantages.

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~ ~ ~ 7~t78 5~80-~80 A second lass o~ devlce is khe so-called positive pressure pumps which are used in combination with an accumulator pump. Typical are U.s. Patents 4,221,219; 4,299,220; and 4,447,224. S~ch devices operate at positive pressure thereby eliminating the problems of prior art neyative pressure devices.
Because the drug chamber is maintained above body pressure, there is, however, a remote potential for an overdose of drug should all the valves in-line with the output fall open at the same time. An extremely high degree of safety, however, may be achieved in such systems by the use of redundant or fall-safe valves togethex with the addition of sensor/shut-down circuits. Such, however, results in significant cost increases which are added to the system.
Reference is made to U.S. Patent 4,525,165. This patent employs a series of pump and accumulator elements between the drug chamber and the outlet. Medication is drawn out of the chamber by a pump and delivered to a bellows accumulator. This system is not only complex but cannot accurately meter doses given the variable volume of the bellows.
To deal with these situations where deficiencies exist within prior art devices, U.S. Patent 4,714,462 commonly assigned, deals specifically with a programmable positive displacement system having a pumping chamber which is placed in the path of fluid communication between the pressurized drug reservoir and a flow restrictor. By use of external `B

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programming, the device can be u.sed to expel infusate from the pumping chamber at varying rates. Wllile .such sy~tems provide advantages over the prior art, a need exist~ to define a ~ystem which i~ simple in operation yet provides the ability to accurately meter dosage. System ~implification by the elimination o bellows chambers, implantable solenoid~ and the like with their attendant power requirements, repre3ent a ~tanding requirement for reliability and ea~e of operation of such implantable device~.
While not implantable device.~, there exlst~ in separate art, techniques for di~pensing fl~id~ by intravenous administration.
Representative are U.S. Patents 4,121,584; 4,261,356 and 4,262,824. These devices employ a valved accumulator metering system from a hydrostatic source llsing a gravity feed. The problem3 inherent in implantable technology are not recoynized or addres3ed. There 18 similarity in the concept of using a metering chamber that i8 valved a~ in the ca~e of the '219 patent with a diaphragm, but the application to implant~ble device is not stated nor recognized in the indu~try.

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The invention is an implantable infusion apparatus including a sealed housing having an inlet septum, a rechargeable positive pressure infusate reservoir in said housing, character-ized in that there is provided metering means in said housing receiving infusate from said reservoir, said metering means comprising first and second valves and a fixed volume accumulator positioned in fluid communication with each of said valves, electronic means in said housing for controlling the operation of said valves, such that when a first of said valves is open, infusate flows from said reservoir into said accumulator to fiil said accumulator and when the second valve is open and the first valve closes, infusate flows from said accumulator and an outlet in fluid communication with said metering means to dispense infusate to a site in a living body, whereby infusate dispensed in a series of predetermined volume spikes, the frequency of said spikes determined by the cycling rate of said first and second valves.
Given the recognized shortcomings in the prior art, the invention to provide a positive pressure programmable valve pump that is implantable into a living body. It includes a system which utilizes the valved accumulator to precisely deliver small quantities of a drug at programmed rates. Consequently, reliability and simplicity of the system is a primary aspect of this invention in its preferred embodiments. The device operates at positive pressure thereby removing the problems of handling and potential failure modes which are inherent in negative pressure systems.

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~3~ 8 64680-~o The apparatus has four basic components. The first is the rechargeable, constant pressure drug reservoir ln series with a bacteria/air filter. The second major assembly is an electronically controlled metering assembly comprising the two normally closed valves adjacent and opposite to the fixed volume accumulator. The third fundamental concept used in the system is an outlet catheter. These three components comprise the implantable aspect of the pump. The fourth aspect is the external programmer.
In accordance with this invention, initial 'Ipumping'l is provided by the reservoir which is used to fill the accumulator to its fi~ed volume. The accumulator is then "dumped" via the - 6a -' '' ' . ` , ;' ' ' ' ~'7~ 7~

di~charge catheter to the desired infusion site. In accordance with thi~ invention, a pre~sure which i~ intermediate between the reservoir and the outlet i~ maintained behind the accumulator 80 that it fill~ and emptie3 completely and r~pidly. The accumulator i~ alternately filled and emptied by the alternate switching of the valves. The rate of qwitching therefore governs the rate of pump~ng and thus the delivery rate.
Valve control i5 provided in the implantable pump by means of an on-board proces~ing system and power supply. The processor i~ externally acce~ed through a telemetry link which can be u~ed to both program the pump operation and obtain diagnostic information a~ to the operation of the device.
In accordance with ba~ic implantable pump technology, the pump reservoir may be refilled periodically and can ~e acce~ed transcutaneou~ly by means of the re~ervoir qeptum. That i~, in accordance with known techniques~ a streqsed ela~tomerlc ~eal may be punctured with a qpecially shaped needle. The ~eptum is ~elf healing for a defined number of punctures. Reservoir pre~sure i~
provided by a moderately high vapor pressure fluid in a two-phase equilibrium. Such 18 known in the context of existing constant flow implantable device~. Pressure iq recharged at each refill since the vapor i8 reconden~ed.

. , ' :' ' ~7:~d8 Fig. 1 is a sc~ematic dia~ram showing the complete sy~tem and a schematic diagram of the ~low;
Fiq. 2A is a schematic diagram iLlustrAting the pumping cycle of the accumulator;
Fig. 2B i~ a time--flow r~te chart of the delivery schedule of the ~ystem;
Fig. 3 i~ a cutaw~y side elevation of the ba~ic constructio of the lmplantable pump portlon of t'ne sy~tem;
Fig. 4 i~ a cutaway schematic vl~w of the valve/accumulator meterlng ~ystem in accordance with thl~ invention;
Flgs. 5A and 58 are ~ldo and top vlews of the accumulator and in Fig. SB a top view of the ~pacer plate component of the accumulator; and Fig. 6 la a cutaway ~ide view of the swltch accumulator.

Referring no~ to Fig. 1, ~chematic diagram of t'ne essential a~pect.s of this invention is depicted. The invention is a positive pressure programmable valve p~lmp comprising a constant pres~ure drug reser~oir 10 which is refillable by means of a ~eptum 12. Such devices are ~nown, for example, the INFUSAID

Model 100 and 400 devices. Those .~y~tems compri~e a sealed hou3ing 14 containing a bellows element 16 having a chamber 18 comprisinq the drug re~ervoir. The bellow.s 16 ~eparate~ the hou~ing into a s~cond zone 20 normally filled with a two-phase fluid which has a ~ignificant vapor pre~sure at body temperature.
Thu~, as the 1uld v~porize~, it compresses the bellows 16 and urges the contents of the reservoir 18 thLough an outlet leading to an infusion ~ite. During the proces~ of refilling, the chamber 18 vla the septum 12, the two-pha~e fluid i8 pres~urized condensing a portion of the vapor and returning it to its liquid phase. As indicated, such basic constant pre3sure devices are known ~n the art as de~cribed in U.S. Patents 3,731,681 and 4,221,219.
Typically, the re~ervoir 18 ha~ a volume of approximately 2Sml and the pressurization maintained in the system i8 approximately 23.2psia. A ~ideport 27 can be u~ed for direct bolu~ in~ections. SideportR are u~ed in the INFUSAID Model 400 and described in U.S. Patent 4,496,343.
An outlet 22, from the re~ervoir 1~ delivers infu6ate from the reservoir via a bacterial filter 24 to the electronically controlled mstering as3embly.
In accordance with this invention, tlle metering a~s~mbly compri~es two normally closed valves 26, 28, which are posikioned on the inlet and outlet ~ide~ of an accumulator 30. The accumulator operates at a constant volume, very low, in the range . .
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of 1~1 pres~urized typically to 19.2p~ia. The valve~ 26 and 28 a~ controll~d ~lectronically vi~ a module 32 which i8 programmed utllizlng an external programmer 34. Flg. 1 illu~trate~ 1n a chain lina, the pump envelope Which Bepara~es the elec~ronlcs 32, that i~ the sy~tem which i~ implanted, from the external pro~rammer 34. The programmer can employ known technology for exampl~ tha~ di8clo~ed in the above co-pendlng application which ie incorporated herein by reference.
The programmer 34 i8 a hand held unit using a touch ~creen.
It provide~ a data transfer link to the electronics 32 implanted a~ a part of the device (~ee Fig. 3). In a memory, th~
programmer 34 maintains a patient hi~tory based on storage of real time data. Data as to device ~tatus, such a8 battery condition, dlagnostic~ on valve current, prescrlption in use ~nd th~ like ar~ retained. The external programmer also has diff~rent interrogation modes such as lnitial calibration and prot~cted mod~c ~or technician u~e.
Th~ outlet from th~ accumulator 30 i8 via a catheter 36 which delivers the infusate to the 6ite in the body to which drug delivery i~ required. A8 ~ndicated by the arroW in Fig. 1, the delivery of infusate occur~ at the infusion Bite below the accumulator pre3sure forcing di~charge through the cathe~er.
Thi~ pressure may be atmospheric ~typically 14.7p8ia) or ~ardiovascular pre~ure~ slightly above atmospher~c, e.g.
17.6p~ia arterlal.

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Refarring now to Flg. 2A, the pumping cycle i~ Achematically lllu~trated. The ~alient aspect~ of thl~ sectlon of the sy~t0m ~ompri~s the valv~s 26, 2~ ~nd th~ ~ccumulator 30. The flr0 ~tap i~ one where both valve~ 26 and 28 are clo~ed and the accumulator 30 18 empty. Infusate is delivered from the reservoir 18 through conduit 22 and filter 24 to fill the accumulator 30. Thu8, as a second ~tep in the operatlon the valve 26 i~ opened whlle valve 28 i~ closed to fill the accwmulator to it~ fix~d volume. The third step i8 then to clo~e both valves 26 and 28 wlth the accumulator now ull. The final ztep in the accumulator cycle i8 the opening of valve 28 while ~alve 26 remains cloced to empty the accumulator throu~h the catheter 36. Conseguently, th~ accumulator is alternately filled and emptied by the switchi~g action of the valves. A pressure int~rmodi~t~ betw~en that of the reaervoir and the outlet i8 maintained ~ehind the ac~umulator ~o that it fills and emptle~
completely and rapldly. The rate of switching of the valve~
thereore governs the rate of pumping and accordingly determines the delivery rate of infusate.
Referring to Fig. 2B an example of the delivery rate of thi~
3ystsm i~ illu#trated. Fig. 2B is a chart plotting a flow rate in ths y-axis again~t time in the x-axi~. The output of the pump i~ periodic a~d iB a function of the frequency of the valve cycle. Thu~, the fa~ter the valve cycle, the greater the number of accumulator di~chargeB p~r unit time- Each dl~charge iB ln the form of a volume ~plke.

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In ~ig. 2B a change from a basal rate to a desired bolus rate, that i 8 an increase in flow rate above the basal rate, i5 illustrated by means of the square wave on the left-hand portion of the time chart. Thi3 would be the programmed bolus flow into the electronics package 32. The pump, to e~tablish the requlred bolu~ flow rate, would increa~e the frequency of the discharge spike~ by varying it~ pump cycle during the bolus period a illustrated in the center of Fig. 2B. The total number of spike~
are integrated over time ~o that the flow rate volume replicates that required by the desired bolus flow rate. The output through the catheter 36 to the bloodstream i8 illustrated in the right-hand portion of Fig. 2B.
By integrating the volùme of the pump over time, given the number of pump cycle~, and the volume of each discharge, digital basal and bolu3 rate~ clo~ely replicating the required values, that i8 flow rates having the required amplitude over the required time, are delivered. With su~ficiently cho~en accumulator volume, drug concentration and di~charge rate, the delivery site can filter the output to achieve a desired "contlnuou~" and ba~al dosage.
Referring now to Fig. 3, the implantable portion of the ~y~tem i8 illuRtrated in cro~s section. The implantable portion of the reservolr ~ystem lO comprises a housing 14 having therein all of the e~sential elements comprising the reservoir 18, the Freon two-pha~e pressurlzing chamber 20, the electronlcs module `' ~~ ` . ~: ' . :
' ' ~L3~7~'7~3 in location 32, and the accumulator valve a~pects of th~ sy~tam hou~ed in location 33. The pump reservoir 18 is periodically accessed transcutaneou~ly via the reservoir 3eptum 12. The ~eptum i~ a stre~ed ~la~tomer seal which may be punctured with a ~pecifically shaped needle. It is ~elf-~ealing for a finite number of puncture~. As in the case of known sy~tems, reservoir pressure is provided by a moderately high vapor pre~ure fluid maintained in a two-phase equilibrium. Freon i8, a~ mentioned, a typical material. Pressure in the ~y~tem i~ recharged with each refill since the Freon vapor i~ recondensed.
As illustrated in Fiy. 3, the mechanical construction of the device comprise~ a hollow disk-shaped housing generally made of two components. That is, the hou3ing 14 comprises a lower saction 40 and an upper or cover 6ection 42. The two main cavitie~ of the sy~tem are separated by a solid base plate 44 which define~ the central core of the unit. The lower cavity i~
subdivided lnto two chambers 18 and 20 by mean3 of the bellows 16. Chamber 18 contains the drug while Chamber 20 contalns the Ereon pressur~zation sy~tem. During manuacture, a relatively small amount of the volatile fluid, typically Freon, iB injected into the region 20 via a ~mall fill tube not illustrated. The Freon then comes to a two-pha~e equilibrium within thi~ chamber.
The vapor pres3ure is determined by the equilibrium pres~ure and remalns constant for constant pump temperature and quasi-static volume change~ of the bellows 16. The magnitude of the storage `:

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re~ervoir pres~ur~ ia th~n the sum of this vapor pressure and the mechanical pressure which i~ associated with the spring rate of the bellows 16.
The central core region contains the needle piercing septum through which drug i B injected into the chambPr 18. The septum includes a needle-stop 46. The needle-stop i8 a non-metallic cup which is ueed to ~upport the needle and llmit its travel yet at the ~ame time prevent damage to the needle tip. When the needle i~ removed, drug is sealed in the reservoir 18.
Thu~, the needle, not illustrated, p~ncture~ the septum 12 and comes to rest on the stop 46. Drug i8 then dispensed into chamber 48 and via flow pa~sages S0, ia delivered into the re~ervoir 18. A check valve 52 may optionally be u~ed in the inlet. Thu~, as illustrated by the flow arrows in Fig. 3, drug d~livered into the chamber 48 passe~ through the through-hole~ S0 and, if in place, the increa~ed pre~sure of the fluid or the force of the needle pushing down on the needle stop 46 opens th~
check valve 52 to deliver drug into the chamber 1~.
The system includes within the hou ing 14, the electronics cavity 32 containing the nece~ary microprocessor electronic3 and battery. Battery life is sufficient to power the device during it~ normal intended implantable life. The housing 14 includes within the central core region the two valves 26 and 28 and the accumulator 30. The valves 26 and 28 comprise two miniature soIenoid valves which are lntimately connected to the accumulator ~3~)7~

30. The valves 26 and 28, to be disc~ ed hereln are man~factured by Wilson G~eatbatch Comp~ny ~nd illustrated in detail in Fig. 4. It i.~ to be llnderstood that such valves are commercially available. The valve.~ hermetically isolate the fluid sides of the valve rom the electrical side of the valve.
Fig. 3 lllu~trate~ by arrow~ the flow configuration from the chamber 18 to the outlet catheter 36. The drug, from chamber 18, pa~es through circular opening~ 54 thro~tgh the annular filter assembly 56. The filter 56 i3 in~erposed between the base plate 44 and a backing plate 57 and i8 sealed at it3 radially inward and outward points by means of annular seals 60 and 62. The drug then passing through the filter 56 i~ ~ub;ect to valve action by valve 26 filling the accumulator 30 and then dumped via valve 28 ~nto ths outlet port 64. A rlght angle connector 66, locked into the outlet port and 6ealed via 0-ring~ 68 and 70, couple~ the hou3ing 14 to the catheter 36.
Referring now to Flg. 4, the detall 8 of the valve/
accumulator metering assembly are depicted. Valves 26 and 28 are miniature solenoid valve~ attached to the accumulator 30 by means of a weld point 72. Valves are dispo~ed in a side-by-~ide arrangemant having ~olenold a~semblie~ 74 and applicable input power via laads 76. The valve~ are operably powered to drive a , working plunger 78 bia3ed by mean~ of spring 80. The working plun~er and return ~pring a~sembly are i~olated from the solenold~ by me~ns of an isolation diaphragm 82. Thi~ i~olation : - 15 -. .

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diaphragm i9 a welded metal diaphragm ~andwiched between both sides, that i~ the electrical side and the fluid side of the system. The diaphragm B2 doe~ not tran~mit pres~ure to the wor~ing plunger 78 therefore the only pre~.~ure differentlal which oppose~ valve motion i~ that which is acros~ the valve seat area.
The flow path i~ illustrated by the arrow~ in Fig. 4. At the input conduit 54, the nominal pressure of the infusate i~
23.2psia. With valve 26 in the open position, drug i8 delivered upward-through the valve ~eat 84 ~shown closed in Fig. 4), into the accumulator flow passage 86. As can be seen from Fig. 4, the configuration minlmizes the Sotal volume and any possible ~tagnant flow pa~sages which exist between the valvP seat~. The area between the valvs seat~ comprises the accumulator storage ~pace. Con~equently, to minimize entrapped air, a low "dead volume" i~ de~igned into the ~ystem. Dead volume i~ tho non-compliant volume between khe valve ~eat~, that i~ the area between seats which defineQ the accumulator flow passage 86 and the non-compliant portton of the accumulator chamber 102. The val~e ~eat~ are ~llu6trated ~t the points 84. The dead volume betwoen the valve seats 84 ~not including the compliant accumulator volume which 18 nominally 1~1~ i9 in the range of 4.9 - 8.4~1. When cloQed, the accumulator 30 i8 i~olated. When opened, the valves allow fluid commun~cation to be e3tabli~hed between the accumulator and the inlet conduit 54 or the outlet conduit 55.

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~1 3~ 78 R~ferring now to Figs. 5A and 5B, detaila of the accumulator ara depicted. The accumulator comprlses a diaphra~m 90, a bac~ing plate 92, an end cap 94, a fill tube 96, and a ~pacer pl~t~ 98.
~ he accumul~tor and ~t~ diaphragm are a key component in thl~ Byst2m. The diaphragm gO, as lllustrated in Flg. 5B, iB a circular di~k of a thin metal ~heet. Preferably titanium may ~e ussd. The disk is ~elected to have a diamet~r and thickne~ of virtually negligible ~pr~ng r~te over the d~slred range of deflectlon. Thus, the diaphragm acts a~ a compllant, flexible wall which ~parates fluid from the environment behlnd it.
The upward motion of the diaphragm 90 i8 limited by the backing plate 92. Backing plate 92 i~ a metal plug of the same matorial and diameter a3 that of the diaphragm 90. It iB
provlded with ~ ahallow concave profilo manufactured into ~t~
low~r ~urface. Thi~ ~urface 100 act~ as a conto~ret Btop for the diaphragm 90. Dimensiona of the contour are chosen to match the general profile of ths diaphragm 90, when it i8 deflected by a predetermined fixed volume (e.g. 1~1). Thi~ predetermined fixed volume i8 the volume de~ired to be metered, that i~ the volume of one discharge ~pike a~ illustrated in Fig~ 2.
The ~acking plate 92 act~ a~ a mechanical 3top which limit~
the motlon of the dlaphragm after the accumulator cavity 102 hac been illed to a apecified volume. Tha contour of the plate iB
de8igned ao that it contacta as much of the surface of the .. .... .

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diaphragm when the volume in chamber 102 has been reached. This surface on the backing plate 92 then rlqidly ~tops ~11 portions of thQ diaphragm from moYing and for any further increa~e ln pree~ur~ the volume of the accumulator in zone 102 will not ch~nge. A~ long a~ the operating pre~ure of the pump iB higher than ~h3 pre~ure re~uired to fill the ~ccumulator (ts b~
di~cu~sed herein) the accumulator wlll then ~lways store, i~ zona 102, th~ samo volume irre~pectlve of oper~tlng pre~ure variation~. The ability to store and dlscharge the ~ame volume repeatedly over a very lar~ number of cycles irrespectiv~ of pump pre~ure, represent~ an important advantage over other implantable pumps in which the dlscharge rate ~ 8 a function of the pre~ure generated by the two-phase fluid. Thi3 is because pres~ure changes a~ociated with two-pha~ f luid pumps are a function of pump temp~rature. If the u~er i8 in an envlronment where there is a ~ignificant temperatura change at kln ~urface, for sxample during swimming, the pressure of the device will change.
Pre~surQ differential across the diaphragm 90 determines whether it fille or emptle~ On the non-fluld side, th~ pro~ure effects both kh~ fill and ~mpty differential~. Thia pre~ure mu~t be lower than the main re~ervoir pre~sure yet higher than the catheter outlet pres~ure. Consequently, the backfill prossure which exl3ts on th~ ~ide of the diaphragm 90 opposlte that of th~ accumulator zone 102 must be controlled at a value 13()7~7~3 which allows for complete fllling yet guarantees complete emptying of the accumulator for any normal variation~ in r~ervoir or outlet pr2~sure. S-lch a pre~sure can be cho~en and maintained by controlli~g the pre~sure in chamber 104 and having it ma~ntained in fluid communicatlon with the backside of the diaphragm g0. The endcap 94 i8 used to cover this chamber. A
fill tube 96 is u-~ed to charge the chamber 104 with an inert gas such as Argon maintained at 19.2p~ia. Thq volume defined in the chamber 104 is chosen to be large enough 30 that any variation~
in the total volume due to diaphragm displacement will have negligible effect on the backfill pres~ure. Once chamber 10~ has been filled with a pres~urized gas, the fill tube 96 i~ sealed by welding. The tube 96 i8 cho~en to have a ~mall in~ida diameter 80 that change~ in its length during weldlng or rework will not oignificantly effect the chamber volume and consequently, the backflll preasure.
Fig~. 5A and 5B illustrate the details of the ~pacer plate 98. The spacer plate perform~ three ma~or function3. Fir~t, it support~ the diaphragm 90 during discharge. Secondly, it provide~ pa~ages as illustrated in Fig. 5B to enhance fluid flow and thirdly it provides a technique for mounting the completed and tested units to the valve ~uba~sembly. In the same manner that the backlng plate 92 supports the diaphragm during filling o the accumulator chamber 102, the spacer 98 i~ u~ed to limit ~iaphragm motion during discharge. The ~pacer plate, however, .; .
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~L30'7~7~3 need not be conto~red becau~e lt support~ the unRtreased, that i~
the flat po~ition of tho diaphragm whlch i~ e~tabli~hed dur~ng welding. The continuou~ contoured ~urface desirable to u~e as a mechanical stop on the ga~-filled ~ide of the dlaphragm, that i8 in chamber 104, 1~ unde~rable on the 1uld side. Intimate contact of two relatively flat surfac2G with a liquid int~rface wlll create a ~uction effect which makes the ~eparation of thoae surfaces dlff~cult. Thi8 ~uc~ion effect ca~ b0 overcome by the addition of a checkerboard groove pattern a~ illu~trated in Fig.
5B. A aerle~ of orthogonal checkerboard grooves 105 are provided on the surface of the spacer plate 98. Additionally, a circumferential groove 106 i~ provided to e~tablish fluid commun1catlon between th~ inlet 58 and the outlet 59.
~onsequently, the ~pacer plate 98 definea flow path~ comprising an annular p~th along g~oove 106 and an orthogonal flow path along groove~ 105. The grooving i8 de~lgned to permit complete free flow of 1uid underneath the flattened diaphragm.
Additionally, the groove~ as3iat in wa~hing of ~rea~ which might otherwise remaln atagnant. Dimenslons of the groove~ may be cho~n to provlde an appr~ci~ble aurface to support the diaphragm, that i8 th~ rectangle~ 107 between the groove~ lOS but malntain the accumulator dead volume at a minimum level. A
grooved ~pac~r plate al80 promotes the rapld filllng and emptying o the accumulator æone 102 which in turn mlnimizes the time and therefore the ~ner~y nece~aary to hold either valv~ open. It can ~3~

be appreclated that decreased valve energy regulrement~ in such a ~y~tom materi~lly lncr~aa~ tho llfe of th~ pump since the overall 2nergy requirements of ~he ~ystem are decreased.
The bottom of the spacer plate 98 contains two counter boree 58'and 59' to ma~ with the valv~ which are llluatrated in Flg.
4. The bottom ~urface 108 of the epacer plat~ 98 ~ B controlled to be flat and have a ~mooth surface finiah which will mate wlth tho 3urface of the eame quality on the valve subaasembly. It i~
at this point that the weld 72 i~ made. Such again guarantees a minimum dead volume between parts and the min~mum ~pace for air entrapment. Tha geometry of the outer flange 110 matche~ the mating plate from ths valve~ and permits a hermetic weld 7 around the rlm.
Referring now to Fig. 6, a modified accumulator i~ dPpicted.
Flg. 6 illustrat~ a modification which utilize~ the 8amo basic alemants o the accumulator illu~trated in Flgs. 5A and 5B but ~mploy~ an electrical swltch to Mignal the level of volume wlthin the accumulator. This dual function provide~ an important safety feature which can indicate the pre~ence of leak~ in the valve 8eat8 and accumulator weldn or, sticklng of the valve~. Because thi~ inventton uti lize8 po~itive pressure, fallure of one or both valve ~eats will lead to improper do~lng of the re3ervoir content~. A ~wltch accumulator can then be u~ed to ~ense condition~ which are ~ug~e~tive of vslve mal unction and warn the pump to ~ignal operator and dl~continue do~lng.

~L3~

The operating principles of the switch accumulator illu~trated in Elg. 6 are ldenti~al to tho~e of the accumul~tor illustrated in Figs. SA and 5B. One modification, however, is that the contour has been moved to the spacer plate and that the backing plate surface 92 i8 now manufactured flat. In Fig. 6, those elements which are common to the accumulator design in Fig.
5 are given like identification n~lmbers. The backing plate co~,prises three elements that are used to electrically i~olate the center of the plate from the diaphragm 90 and yet maintain the ability to store a sealed volume of inert qas. In the conflguration of Fig. 6, the endcap 94 and fill tube 96 have a dual function, that of chamber cover and electrical lead. The l~ad llO i~ ~hown ~chematically attached to a flange 112 forming a portion of the endcap a~embly. A ceramic cup 113 l~ lined wlth a metal lll to provlde a conducive path between stop 114 and lead 110. The diaphragm is used as a moving ~wltch contact.
That is, a full diaphragm will ~hort the lead to ground via the metallized ceramic 111 on the in~ide of the ceramlc cup 113 and conductive stop 114. Thu~, a signal ia issued indicating that the accumulator i8 full, diaphragm in the upward po~ition. Thi~
.signal can be ~en~ed by the electronic~ ~ust prior to opening or ~u~t following the relea~e of either valve. Con~equently, by determining conditlons during the sense period and by the ~witch otate, a variety of diagnostic determinations can be made.

i3071~3 For example, during a sense period ju3t prior to the inlet opening, if an open ~witch condition 0xists, then the system is functioning properly. If, however, the switch state is closed then, it can be determined that there i8 a leak in the inlet valve 26. During the ~ame period ~ust prior to pulRing the outlet, to release infu~ate from the accumulator, if an open switch eXi3t8, then a leak exists in the outlet valve. s~at or one of the valve or accumulator welds. If, however, the switch lllustrated in Flg. 6 i~ closed d~1ring the outlet 3en~e perlod, the system i~ deemed to be functio1ling properly. In a similar manner, by ~enaing durinq the inlet portion of the cycle, but immediately following relea~e, an open condition in the ~witch will indicate that the inlet did not open or that there i8 a leak in an accumulator or valve weld. Howev~r, sensing the ~wltch atato as clo~ed during the ~ame period, deem~ the ~ystem to be working in an acceptable configuration. Thus, by utilizlng a switch ac~umulator, a relatively large amount of information can b~ obtained about the ~tatus of the valve seats or metering sy~tem hermeticity. By repeatedly pul~ing the valve, the failure mode can be determined to be repeatable or simply artifact.
While not illustrated, it i~ also pos~ible to have an audiotran~ducer which will ~iynal the u~er in the ca~e of failure of one or both of the valv~ in the pump.
A3 can be ~een by this invention then, a programmable pump exlst~ which operates at positive pre~sure~ and accurately ~30~

control4 the flow rate by metering di~crete and repeatable volumes through a microaccumulator. The accumulator is filled and amptied by alternately cycling two control vaIve~ which are in Yerie~ with the accumulator. Thus, by setting the cycling rate of the valves, the pump di~pen~ing rate may be controlled.
The accumulator its~lf operates at a pres~ure which i~
intarmadiate between the pump re~ervoir pre~ure and the outlet pressure. Thi~ de~ign pressure, when taken in conjunction with t~e negligible internal ~pring rate, guarantees a complete illing and emptying of the ~y~tem. The volume, however, i8 repeatedly demonstrated, that is repeatedly di pénsed and the valve energy requirements may be minimized. Given the design of t~e valves them~elves, minimum dead volume and flow through occur. Thi~ minimizes the danger of entrapped air or stagnant flow in the ~ystem.
It is apparent that modifications of this de~ign and of preferred embodiment~ therein may be made without departing from the e~sentlal ~cope o thls invention. Having de~cribed my invent~on, I claim:

,

Claims (11)

1. An implantable infusion apparatus including a sealed housing having an inlet septum, a rechargeable positive pressure infusate reservoir in said housing, characterized in that there is provided metering means in said housing receiving infusate from said reservoir, said metering means comprising first and second valves and a fixed volume accumulator positioned in fluid communication with each of said valves, electronic means in said housing for controlling the operation of said valves, such that when a first of said valves is open, infusate flows from said reservoir into said accumulator to fill said accumulator and when the second valve is open and the first valve closes, infusate flows from said accumulator and an outlet in fluid communication with said metering means to dispense infusate to a site in a living body, whereby infusate dispensed in a series of predetermined volume spikes, the frequency of said spikes determined by the cycling rate of said first and second valves.

2. The device of claim 1, wherein said first and second valves are positioned side-by-side in fluid isolation with each other, each of said valves having a conduit to said accumulator that may be opened or closed by a valve member and, said accumulator having an inlet aligned with one of said conduits and an outlet aligned with the other of said conduits.

3. The device of claim 1, wherein said accumulator comprises an end cap, a backing plate having a recessed contoured surface, an inextensible diaphragm, and a spacer plate, said diaphragm sandwiched between said backing plate and said spacer plate.

4. The device of claim 3, wherein said backing plate contains a recess, and recess covered by said end cap, means to fill said recess with a fluid under pressure and conduit means in said backing plate to establish fluid communication between said recess and one side of said diaphragm to bias said diaphragm.

5. The device of claim 3, wherein said contoured surface defines a stop for said diaphragm when said accumulator has been filled with infusate whereby said contoured surface contacting substantially the entire surface of said diaphragm to limit any change in the stored volume of the accumulator irrespective of changes in pressure of infusate delivered from the reservoir to said accumulator.

6. The device of claim 5, wherein said spacer plate comprises a groove pattern confronting said diaphragm to provide fluid flow for complete discharge of infusate from said accumulator.

7. The device of claim 6, wherein said spacer plate further comprises inlet and outlet ports, an annular groove between said inlet and outlet and said groove pattern comprises a series of orthogonal grooves surrounded by said annular groove.

8. The device of claim 5, further comprising a conductive stop for said diaphragm, said backing plate comprising a conductively lined ceramic cup, and electrical means providing an output to determine the position of said diaphragm.

9. The device of claim 1, further comprising programmer means external to said housing for interrogating and programming said electronic means.

10. The device of claim 1, further comprising an outlet catheter attached to said housing, said outlet catheter including a connector lockably insertable into said outlet port.

11. The device of claim 1, further comprising a sideport for the direct injection of a drug into said outlet.