Abstract:
Embodiments of medical infusion pumps are provided that include structural elements for providing sources of compliance within a fluid path within the pump. Some preferred embodiments provide implantable infusion pumps with compliance positioned between an exit port of a pumping mechanism and an outlet (e.g. an opening in a catheter) of the infusion pump. Other embodiments provide compliance in fluid path in proximity to entrance port of the pumping mechanism. Insertion of compliance in a flow path that is down stream of the pumping mechanism may aid in minimizing negative effects associated with attempting to force fluid through a restricted flow path that is further down-stream, such as that offered by a catheter or other outlet component. Insertion of compliance before the pumping mechanism may aid in reducing negative effects associated with an up stream restricted flow path, such as that which might be offered by a rigid filter located between the reservoir and the pumping mechanism. Several structural components, assemblies, or configurations may be used as sources of compliance. For example, compressible structures (e.g. pillows, drums) are used within a side port of the infusion pump. The compressible structures may quickly distort to accommodate for a large impulse of fluid into the flow path that can not otherwise be readily dealt with. The compression, in turn, results in a restoring force being exerted that returns the structure substantially to its original volume so as to slowly force fluid from the flow path.

Description:
PRIORITY CLAIM 
     This application claims priority to U.S. Provisional Application No. 60/089,719, filed Jun. 18, 1998, the full disclosure of which is hereby incorporated by reference as if set forth herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to medical infusion devices that are intended to deliver, in a controlled manner, desired quantities of a fluid to a patient, more particularly this invention relates to the utilization of compliant structures within such medical devices. 
     BACKGROUND 
     Both external and internally implanted infusion pumps are generally known in the art for use in delivering a selected fluid to the body of a patient (i.e. body of a person or animal being treated or benefited by the fluid) in a scheduled or preprogrammed manner. Such fluids include drugs, medications, proteins, e.g. insulin, or the like. Programmable medication infusion pumps offer significant potential advantages to patients who are required to comply with a long-term medication treatment regimen. Such pumps can operate automatically, with little or no patient intervention, to administer an important medication such as insulin to a diabetic patient on a regular basis. 
     Implantable infusion pumps typically include an internal fluid chamber or reservoir for receiving and storing a supply of the selected fluid (e.g. drug, medication, protein such as insulin) a miniature pump mechanism, programmable control means (e.g. electrical circuit possibly including telemetry elements for communication with an external programming device) for operating the pump mechanism to deliver discrete doses of the fluid from the internal reservoir to a desired region within the body. These pumps typically deliver medication to the body through a catheter connected to an output port of the pump mechanism. A refill port is typically provided on the pump to permit transcutaneous needle access for purpose of periodically refilling the pump reservoir with a fresh supply of fluid. Some implantable infusion pumps include a side port that is connected to the output port of the pump mechanism and to a first end of the catheter. The side port may be used in a process of flushing residue from the catheter, flushing the pump, and or to determine pump stroke volume. 
     Various infusion pumps, associated components and processes, for example, are described in the various patent publications listed in Table 1, the disclosures of which are hereby incorporated herein by reference. The brief description of each publication is provided in Table 1 to aid the reader in finding specific types of teachings. It is not intended that the incorporation of subject matter be limited to those topics specifically indicated, but instead the incorporation is to include all subject matter found in these publications. The teachings in these incorporated publications may be combined with the teachings herein in many ways. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Pat. Pub. No. 
                   
               
               
                 (US if not indicated 
               
               
                 other wise) 
               
               
                 Issue Date 
               
               
                 Inventor(s) 
                 Brief Description of Subject Matter Disclosed in Each Publication 
               
               
                   
               
             
             
               
                 4,373,525 
                 A change in the internal pressure of the fluid-infusion tube of a peristaltic fluid- 
               
               
                 Feb. 15, 1983 
                 infusion pump due to occlusion in the fluid-infusion tube is detected through a 
               
               
                 Fischell 
                 change in the diameter of the fluid-infusion tube. The occlusion is detected by 
               
               
                   
                 detection of the change in the distance between the opposite wall portions of the 
               
               
                   
                 tube. 
               
               
                 4,482,346 
                 An integral valve and pumping unit is provided for infusing medication into the 
               
               
                 Nov. 13, 1984 
                 body which employs only one moving part. This pumping unit is connected to the 
               
               
                 Reinicke 
                 medication supply reservoir through a first flow restriction device which has no 
               
               
                   
                 moving parts but has directional flow characteristics so that liquid medication can 
               
               
                   
                 flow readily from the reservoir to the pumping unit but flow from the pumping 
               
               
                   
                 unit to the reservoir encounters a relatively high resistance. A second flow 
               
               
                   
                 restriction device is connected between the pumping unit and the outlet catheter 
               
               
                   
                 which is employed to infuse medication into the body, this second flow restriction 
               
               
                   
                 device likewise having no moving parts and offering relatively little resistance to 
               
               
                   
                 liquid flow from the pumping unit to the catheter while having relatively high 
               
               
                   
                 resistance to flow in the opposite direction. The valve portion of the integral 
               
               
                   
                 valve-pump unit ensures that no liquid can flow either from the reservoir to the 
               
               
                   
                 catheter or vice versa, when the pumping unit is inoperative or when the reservoir 
               
               
                   
                 is being filled. 
               
               
                 4,486,190 
                 The implantable device includes a medication reservoir, a pulsatile pump and an 
               
               
                 Dec. 4, 1984 
                 absolute pressure transducer. The pumping pressure wave developed in the 
               
               
                 Reinicke 
                 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. 
               
               
                 4,525,165 
                 An apparatus for fluid handling and delivery in a medication infusion system is 
               
               
                 Jun. 25, 1985 
                 disclosed. The apparatus generally contains a pulsatile pump in combination with 
               
               
                 Fischell 
                 at least an accumulation flow restrictor. The pulsatile pump is economical in 
               
               
                   
                 electrical consumption by virtue of the use of a spring force pumping action. The 
               
               
                   
                 accumulator flow restrictor smooths the output from the pulsatile pump so that 
               
               
                   
                 medication is delivered in a manner compatible with human or animal body 
               
               
                   
                 needs. As an example, for infusion of medication such as insulin, the medication 
               
               
                   
                 infusion system can provide an infusion flow profile which mimics that of insulin 
               
               
                   
                 production in a normal person. 
               
               
                 4,561,443 
                 A two-way coherent inductive communications link between an external 
               
               
                 Dec. 31, 1985 
                 transceiver and an internal transceiver located in a biologically implanted 
               
               
                 Hogrefe et al. 
                 programmable medical device. Digitally formatted command data and 
               
               
                   
                 programming data is transmitted to the implanted medical device by frequency 
               
               
                   
                 shift keying the inductive communications link. Internal transceiver is powered by 
               
               
                   
                 the inductive field between internal and external transceivers. Digitally formatted 
               
               
                   
                 data is transmitted to external transceiver by internal transceiver amplitude 
               
               
                   
                 modulating inductive field. Immediate verification of the establishment of a 
               
               
                   
                 reliable communications link is provided by determining existence of frequency 
               
               
                   
                 lock and bit phase lock between internal and external transceivers. 
               
               
                 4,573,994 
                 Apparatus and method for filling, or refilling, the internal reservoir of a 
               
               
                 Mar. 4, 1986 
                 medication infusion system, wherein filling or refilling is permitted only when a 
               
               
                 Fischell et al. 
                 means for injecting medication is properly positioned relative to the reservoir. 
               
               
                   
                 Prior to filling or refilling, a pressure integrity check can be made to help assure 
               
               
                   
                 that injected medication enters the reservoir without leakage. Additionally, 
               
               
                   
                 flushing of a portion or all of the medication reservoir can be accomplished if 
               
               
                   
                 desired. Medication is introduced to and is stored in the reservoir at a pressure 
               
               
                   
                 below ambient body pressure. 
               
               
                 4,604,090 
                 An implantable medication infusion device wherein a generally cylindrical 
               
               
                 Aug. 5, 1986 
                 manifold is employed having a shallow recess on one face thereof. A flexible 
               
               
                 Reinicke 
                 diaphragm is positioned to form with the face of said manifold a medication 
               
               
                   
                 reservoir. A circular cover member is positioned over the diaphragm to form with 
               
               
                   
                 said diaphragm a pressure stabilizing chamber within which is positioned a two- 
               
               
                   
                 phase fluid for maintaining a constant pressure on said diaphragm. A permanent 
               
               
                   
                 magnet is positioned at the center of said diaphragm and is movable therewith. A 
               
               
                   
                 Hall effect transducer positioned on said manifold opposite said permanent 
               
               
                   
                 magnet is employed continuously to measure the position of said diaphragm and 
               
               
                   
                 provide an indication of the amount of medication in said reservoir. A method of 
               
               
                   
                 filling and sealing the pressure stabilizing chamber which insures that a small 
               
               
                   
                 bubble of two-phase fluid is present in said chamber at all times. An inlet filter is 
               
               
                   
                 positioned between the medication reservoir and an inlet check valve to act as a 
               
               
                   
                 bubble trap during the intake stroke of a pulsatile pumping unit also mounted in 
               
               
                   
                 the manifold. 
               
               
                 4,619,653 
                 A medication infusion system provides redundant safety and includes condition 
               
               
                 Oct. 28, 1996 
                 detecting and informational alarm signal generating apparatus for indicating if (1) 
               
               
                 Fischell 
                 a fluid leak occurs in different portions of the system; (2) a programmable input 
               
               
                   
                 from a patient or physician would result in exceeding a safe dosage limit; (3) the 
               
               
                   
                 reservoir containing medication has been filled; (4) the intended medication 
               
               
                   
                 pumping does not correlate with the pumping actually effected; (5) battery 
               
               
                   
                 voltage is low; (6) the medication reserve is low; and (7) the system has been 
               
               
                   
                 switched off. The apparatus may provide subcutaneous electrical, thermal, or 
               
               
                   
                 audible stimulation to the patient and also provides a signal which a physician 
               
               
                   
                 may monitor. The stimulation may be coded to separately identify each above- 
               
               
                   
                 listed deviation in nominal system performance. In addition, the number of 
               
               
                   
                 medication requests are correlated with actual medication dispensing to assure 
               
               
                   
                 proper operation. An identification scheme is provided which matches the patient 
               
               
                   
                 with his or her corresponding medication. 
               
               
                 4,731,051 
                 An implantable programmable infusion pump (IPIP) is disclosed and generally 
               
               
                 Mar. 15, 1988 
                 includes: a fluid reservoir filled with selected medication; a pump for causing a 
               
               
                 Fischell et al. 
                 precise volumetric dosage of medication to be withdrawn from the reservoir and 
               
               
                   
                 delivered to the appropriate site within the body; and, a control means for 
               
               
                   
                 actuating the pump in a safe and programmable manner. The control means 
               
               
                   
                 includes a microprocessor, a permanent memory containing a series of fixed 
               
               
                   
                 software instructions, and a memory for storing prescription schedules, dosage 
               
               
                   
                 limits and other data. The microprocessor actuates the pump in accordance with 
               
               
                   
                 programmable prescription parameters and dosage limits stored in the memory. A 
               
               
                   
                 communication link allows the control means to be remotely programmed. The 
               
               
                   
                 control means incorporates a running integral dosage limit and other safety 
               
               
                   
                 features which prevent an inadvertent or intentional medication overdose. The 
               
               
                   
                 control means also monitors the pump and fluid handling system and provides an 
               
               
                   
                 alert if any improper or potentially unsafe operation is detected. 
               
               
                 5,514,103 
                 An implantable medication infusion pump is provided of the type having a 
               
               
                 May 7, 1996 
                 pressure reservoir with a selected pressure fluid therein for maintaining liquid 
               
               
                 Srisathapat et al. 
                 medication in an adjacent medication chamber under a substantially constant 
               
               
                   
                 pressure. The reservoir comprises a hollow structural enclosure defined by at least 
               
               
                   
                 one movable wall and adapted to be filled with a selected quantity of the pressure 
               
               
                   
                 fluid, particularly such as a selected fluorocarbon in a liquid-vapor state. The 
               
               
                   
                 movable wall of the pressure reservoir is shared with and defines one side of the 
               
               
                   
                 medication chamber, with the pressure fluid undergoing appropriate change of 
               
               
                   
                 state to expand or contract the pressure reservoir in a manner maintaining the 
               
               
                   
                 medication under substantially constant pressure. The improved pressure 
               
               
                   
                 reservoir includes an internal spacer element to prevent contraction of the 
               
               
                   
                 pressure reservoir beyond a minimum volume at least slightly greater than the 
               
               
                   
                 liquid state volume of the pressure fluid therein. With this construction, at least 
               
               
                   
                 some pressure fluid within the pressure reservoir remains in a vapor state at all 
               
               
                   
                 times. 
               
               
                 5,527,307 
                 A medication infusion pump is provided of the type adapted for implantation into 
               
               
                 Jun. 18, 1996 
                 the body of a patient, and for programmable delivery of a selected medication 
               
               
                 Srisathapat et al. 
                 through a catheter to the patient over an extended period of time. A side port 
               
               
                   
                 assembly is mounted quickly and easily onto the pump and defines a flow path 
               
               
                   
                 through which the medication is discharged to the catheter. The side port 
               
               
                   
                 assembly includes an access port to permit transcutaneous needle access to the 
               
               
                   
                 discharge flow path, in combination with a check valve to prevent backflow 
               
               
                   
                 within the discharge flow path. The discharge side access port can be used to 
               
               
                   
                 flush residue from the catheter, or in combination with a primary refill port on the 
               
               
                   
                 pump to flush the pump and/or to determine actual pump stroke volume. 
               
               
                 5,167,633 
                 An improved and simplified pressure reservoir is provided for use with an 
               
               
                 Dec. 1, 1992 
                 implantable medication infusion pump to maintain a selected medication in liquid 
               
               
                 Mann et al. 
                 form with a pump housing under a substantially constant pressure. The pressure 
               
               
                   
                 reservoir comprises a hollow structural enclosure having at least one flexible 
               
               
                   
                 resilient wall and is adapted to be filled with a selected quantity of a pressure 
               
               
                   
                 fluid, such as a selected fluorocarbon in a liquid-vapor state, prior to mounting of 
               
               
                   
                 the reservoir as a structural unit into the infusion pump housing. Within the pump 
               
               
                   
                 housing, the flexible reservoir wall defines one side of a medication chamber, 
               
               
                   
                 with the pressure fluid undergoing appropriate change of state to expand or 
               
               
                   
                 contact the reservoir in a manner maintaining the medication under a substantially 
               
               
                   
                 constant pressure. The improved reservoir can be provided in a variety of 
               
               
                   
                 structural shapes and/or utilized in pump housings of various size and shape to 
               
               
                   
                 permit the pump size to be reduced, or, in the alternative, to increase pump 
               
               
                   
                 medication capacity without increasing pump housing size. 
               
               
                 5,176,644 
                 An implantable medication infusion pump is provided which utilizes an improved 
               
               
                 Jan. 5, 1993 
                 and simplified pressure reservoir to maintain a selected medication in liquid form 
               
               
                 Srisathapat et al. 
                 within a pump housing under a substantially constant pressure. The pressure 
               
               
                   
                 reservoir comprises a hollow structural enclosure having at least one flexible 
               
               
                   
                 resilient wall and is adapted to be filled with a selected quantity of a pressure 
               
               
                   
                 fluid, such as a selected fluorocarbon in a liquid-vapor state, prior to mounting of 
               
               
                   
                 the reservoir as a structural unit into the infusion pump housing. Within the pump 
               
               
                   
                 housing, the flexible reservoir wall defines one side of a medication chamber, 
               
               
                   
                 with the pressure fluid undergoing appropriate change of state to expand or 
               
               
                   
                 contract the reservoir in a manner maintaining the medication under a 
               
               
                   
                 substantially constant pressure. The improved reservoir can be provided in a 
               
               
                   
                 variety of structural shapes and/or utilized in pump housings of various size and 
               
               
                   
                 shape to permit the pump size to be reduced, or, in the alternative, to increase 
               
               
                   
                 pump medication capacity without increasing pump housing size. 
               
               
                 5,197,322 
                 An improved process and related apparatus are provided for filling a pressure 
               
               
                 Mar. 30, 1993 
                 reservoir of an implantable medication infusion pump with a selected pressure 
               
               
                 Indravudh 
                 fluid, wherein the pressure reservoir is separated by a movable wall from an 
               
               
                   
                 adjacent medication chamber. The improved filling process includes vacuum- 
               
               
                   
                 draw filling of the pressure reservoir with relatively purified pressure fluid in 
               
               
                   
                 liquid state. The specific quantity of pressure fluid within the pressure reservoir is 
               
               
                   
                 thereafter calibrated by filling the adjacent medication chamber with a calibration 
               
               
                   
                 fluid at a predetermined positive pressure, thereby expelling excess pressure fluid 
               
               
                   
                 from the pressure reservoir. The pressure reservoir is then sealed and the 
               
               
                   
                 performance characteristics thereof are tested under simulated implantation 
               
               
                   
                 conditions to confirm the capability of the pressure reservoir to maintain 
               
               
                   
                 medication within the medication chamber under substantially constant pressure 
               
               
                   
                 conditions. 
               
               
                 5,257,971 
                 A method is provided for reconditioning a medication infusion pump by removal 
               
               
                 Nov. 2, 1993 
                 of accumulated medication deposits and the like to restore pump performance 
               
               
                 Lord et al. 
                 without requiring surgical removal of an implanted pump from a patient. The 
               
               
                   
                 reconditioning process comprises sequential delivery of a buffer solution and a 
               
               
                   
                 rinse solution to internal pump flow passages. The rinse solution is effective to 
               
               
                   
                 dissolve medication deposits and the like within narrow pump flow passages 
               
               
                   
                 before the rinse solution is neutralized by intermixing with the buffer solution. 
               
               
                   
                 Dissolution of accumulated medication deposits results in restoration of pump 
               
               
                   
                 performance substantially to original product specifications. 
               
               
                 5,328,460 
                 Apparatus located in an implantable medication infusion pump for quickly and 
               
               
                 Jul. 12, 1994 
                 easily detecting a condition adversely affecting medication delivery in the 
               
               
                 Lord et al. 
                 implantable medication infusion pump is disclosed which can reliably detect 
               
               
                   
                 occurrences including an occluded catheter, the presence of air in the pumping 
               
               
                   
                 mechanism, and the failure of the pumping mechanism. The system uses the 
               
               
                   
                 amplitude of an acoustic signal generated by operation of the pumping 
               
               
                   
                 mechanism as compared with a baseline signal to detect an encapsulated or 
               
               
                   
                 occluded catheter or air in the fluid line. In addition, the system can detect a 
               
               
                   
                 partially encapsulated or occluded catheter by detecting repeated downward slope 
               
               
                   
                 patterns during repetitive, closely spaced pumping cycles. 
               
               
                 5,462,525 
                 An infusion pump for delivering a selected medication to a patient is provided 
               
               
                 Oct. 31, 1995 
                 with an inductance flow sensor for monitoring and verifying delivery of 
               
               
                 Srisathapat et al. 
                 medication in response to pump operation. The flow sensor comprises a compact 
               
               
                   
                 inductor coil wrapped about a pump discharge conduit, in combination with a 
               
               
                   
                 magnetically attractable core pin disposed within the discharge conduit for 
               
               
                   
                 movement to a position within the inductor coil in response to pump outflow. A 
               
               
                   
                 control circuit operates with minimal power requirements to monitor coil 
               
               
                   
                 inductance changes as a result of core pin displacement to confirm medication 
               
               
                   
                 delivery to the patient in response to pump operation. A magnet mounted at one 
               
               
                   
                 end of the inductor coil draws and retains the core pin at a position retracted from 
               
               
                   
                 the coil in the absence of pump outflow. 
               
               
                 5,466,218 
                 A medication infusion pump is provided of the type adapted for implantation into 
               
               
                 Nov. 14, 1995 
                 the body of a patient, and for programmable delivery of a selected medication 
               
               
                 Srisathapat et al. 
                 through a catheter to the patient over an extended period of time. A side port 
               
               
                   
                 assembly is mounted quickly and easily onto the pump and defines a flow path 
               
               
                   
                 through which the medication is discharged to the catheter. The side port 
               
               
                   
                 assembly includes an access port to permit transcutaneous needle access to the 
               
               
                   
                 discharge flow path, in combination with a check valve to prevent backflow 
               
               
                   
                 within the discharge flow path. The discharge side access port can be used to 
               
               
                   
                 flush residue from the catheter, or in combination with a primary refill port on the 
               
               
                   
                 pump to flush the pump and/or to determine actual pump stroke volume. 
               
               
                 5,785,681 
                 A flow rate controller is provided for regulating the flow rate of medication 
               
               
                 Jul. 28, 1998 
                 delivered to a patient by an implantable medication infusion pump of the constant 
               
               
                 Indravudh 
                 flow type, to minimize or prevent flow rate increases attributable to fluctuations 
               
               
                   
                 in ambient pressure. The infusion pump comprises an implantable pump housing 
               
               
                   
                 with a pressurized medication reservoir therein for continuous flow delivery to the 
               
               
                   
                 patient through a baseline flow path including a restrictor such as a capillary tube. 
               
               
                   
                 The controller comprises a pressure responsive control valve for connecting a 
               
               
                   
                 secondary restrictor such as an additional capillary tube in series with the baseline 
               
               
                   
                 flow path, to prevent undesired increase in the medication flow rate in the event 
               
               
                   
                 that the patient temporarily encounters a high altitude ambient pressure. 
               
               
                 5,797,733 
                 An electromagnetic pump comprising a housing having fluid receiving and 
               
               
                 Aug. 25, 1998 
                 pumping chambers in communication with an inlet and outlet, respectively, an 
               
               
                 Falk et al. 
                 electromagnet carried by the housing external to the fluid chambers thereof, and 
               
               
                   
                 an armature movable in the housing having a pole portion magnetically attracted 
               
               
                   
                 by the electromagnet and a piston portion to force fluid out of the chambers and 
               
               
                   
                 through the pump outlet. A path provides controlled bypass for bubbles in the 
               
               
                   
                 fluid around the armature piston portion between the fluid pumping chamber and 
               
               
                   
                 the fluid receiving chamber only during the return stroke of the armature. Fluid 
               
               
                   
                 inertia is reduced by an outlet orifice in the path of fluid flow from the pump 
               
               
                   
                 outlet and by a bypass orifice for fluid flow in the bypass path, the orifices being 
               
               
                   
                 provided either individually or in combination depending upon the fluid flow 
               
               
                   
                 characteristics of the system including the pump. An accumulator in the fluid 
               
               
                   
                 flow path between the pump outlet and a catheter leading away from the pump 
               
               
                   
                 alleviates inertial and viscous effects arising from the catheter. The armature pole 
               
               
                   
                 portion has a fluid-contacting section of material which is compatible with and 
               
               
                   
                 corrosion resistant to the fluid, which can be a body of magnetic material within a 
               
               
                   
                 titanium enclosure or a body of chrome-molybdenum-iron alloy. The check valve 
               
               
                   
                 and inlet are so arranged that the pump displacement can be reduced without 
               
               
                   
                 reducing the bubble pumping capability of the pump. 
               
               
                 WO 98/19627 
                 A medication infusion pump is provided for use in the delivery of a selected 
               
               
                 May 14, 1998 
                 medication to a patient, wherein the pump includes internal surface coatings 
               
               
                 Van Antwerp et al. 
                 defining protein stable surfaces. In accordance with the invention, hydrophilic 
               
               
                   
                 internal surface and related coating methods are provided to reduce or eliminate 
               
               
                   
                 accumulation of medication deposits which can otherwise occur when handling 
               
               
                   
                 complex protein-based medication. Preferred hydrophilic pump surfaces include 
               
               
                   
                 hydrophilic surfactant (PEO) or (PEG) coatings which exhibit very low protein 
               
               
                   
                 adsorption characteristics. Several methods are disclosed for producing such 
               
               
                   
                 coatings, including direct surface modification, covalent and non-covalent 
               
               
                   
                 attachment of polymers, and covalent attachment through a saline primer. 
               
               
                   
               
             
          
         
       
     
     Operation of these pumps may be effected by a combination of flow resistance within a fluid path and a characteristic known as “compliance”. Flow resistance is related to how much pressure is required to make a desired quantity of fluid flow through the path in a given time period. Compliance is related to how a fluid path, as defined by the structural body forming the path or a part of the path, expands, contracts or deflects under an environmental input, such as, for example, a pressure load from a pulse stroke from an infusion pump mechanism that is intended to deliver an amount of medication to a catheter. 
     If a particular flow path (e.g. path from pump mechanism output port to distal end of a catheter) has little or no compliance, any attempt to move fluid into the flow path (e.g. at the pump mechanism output port) will only occur to the extent that substantially an equivalent amount of fluid will be moved out of the flow path (e.g. out of the distal end of the catheter). On the other hand, if a flow path offers a large amount of compliance, a fluid may be easily pushed into one end of the flow path, during a specified time period, with little or no fluid exiting the other end of the flow path during that time period. 
     In some pump designs too little compliance may influence the infusion pump&#39;s performance by offering increased resistance of flow at the inlet of the flow path (e.g. output port of the pump mechanism). If a significant amount of resistance is offered, the infusion pump mechanism may deliver less fluid, than predicted, for each pump stroke. It is further known that excessive compliance may influence the infusion pump mechanism&#39;s performance by offering insufficient resistance to flow at the inlet of the flow path (e.g. output port of the pump mechanism). If an insufficient amount of resistance is offered, it may result in delivery of more fluid, than predicted, with each stroke. Either situation may provide incorrect dosing of the fluid, which may have long term and short term health effects for a patient being treated by the fluid. 
     In some pump designs, especially with implantable pumps, low power consumption is of importance so that battery life is not prematurely reduced below an acceptable level and that useful life of the pump is of reasonable length. In electromagnetic pumps, such as those described in U.S. Pat. No. 5,797,733, as referenced in Table 1, it is desirable that the electromagnetic coil be activated for only for a short period of time, with only a limited amount of power so as to minimize battery drain. However, if an inappropriate amount of compliance exists, a piston that is used to force fluid from a fluid reservoir may not travel an intended length and thus may not cause a desired amount of material to be dispensed. 
     In the &#39;733 patent, as illustrated in FIG. 4 of this referenced patent, it is proposed that an accumulator  436  form a portion of the flow path between the outlet tube  430  of the pump  420  and the catheter  440 . It is proposed that this accumulator be in the form of a small compliant element. It is indicated that the accumulator  436  can comprise a small length of Silicone rubber tubing, i.e. about ½ inch in length and {fraction (1/32)} inch inner diameter. 
     Among other things, the &#39;733 patent further indicates that 
     “ . . . a small accumulator is provided downstream of the pump outlet orifice large enough to contain the pulse volume of the pump with a reasonable pressure rise. The catheter diameter may then be small enough to ensure that the flow through the accumulator catheter combination is critically damped and no flow oscillations occur which might otherwise draw additional flow through the pump check valves. It is desirable that the accumulator be small enough so that a significant pressure rise occurs during the pump stroke. The back pressure build-up serves the purpose of preventing a large pulse volume when the supply pressure exceeds the delivery pressure.” 
     However, even with some recognition of a need for an appropriate amount of compliance in the pump system, a need continues to exist in the art for improved methods of and apparatus for supplying compliance within infusion pump systems and particularly within implantable systems. 
     The use of silicone as a source of compliance within a fluid path, and especially for long term use, has many shortcomings: (1) It is subject to swelling, leakage, and change of mechanical properties, as it is permeable to water, air, and various other substances, such as preservatives that may be used with various types of insulin; (2) The compliance of silicone is based on its flexibility as opposed to its compressibility; (3) It is a hydrophobic material can aggravate physical instability of some drugs, e.g. insulin, which can lead to precipitation and build up of the drug within the system; (4) If exposed to body fluids, hard tissue may build up on the tubing to reduce its compliance with the progression of time; (5) If exposed to ambient pressure within the body, unintentional discharge of fluid may occur as a result of an impact, other significant pressure increase, or shock to the source of compliance; (6) If used within a portion of the system subject to high pressure flushing, the silicone may rupture. 
     SUMMARY OF THE DISCLOSURE 
     In view of the shortcomings noted above, it is a first object of the present invention to provide a source of compliance that is not permeable to fluids that it may come into contact with. 
     It is a second object of the present invention to provide a source of compliance that is compressible. 
     It is a third object of the invention to provide a source of compliance that is less likely to cause physical instability of the drugs that it will come into contact with, e.g. insulin. 
     It is a fourth object of the invention to provide a source of compliance that is less variable with the passage of time. 
     It is a fifth object of the invention to provide a source of compliance that is less likely to cause unintentional discharge of fluid into the body of a patient. 
     It is a sixth object of the invention to provide a source of compliance that is not subject to damage as a result of exposure to high pressures that might occur, for example, during a flushing operation, or the like. 
     It is intended that each of the above noted objects of the invention, as well as any other objects of the invention set forth explicitly or implicitly herein, be pursued alone, or in various combinations, by different aspects of the invention. It is further intended that additional objects of the invention provide infusion pumps that pursue or address one or more of the above noted objects of the invention alone or various combinations. 
     A first aspect of the invention provides an infusion pump for delivering a fluid to the body of a patient, including: (1) a pumping mechanism having a fluid entrance port and fluid exit port for transferring fluid from the entrance port to the exit port, (2) a reservoir for containing the fluid, the reservoir connected to the entrance port of the pumping mechanism by a first fluid path, (3) an outlet connected to the exit port of the pumping mechanism along a second fluid path for supplying fluid from the reservoir to the body of a patient, (4) a control device for controllably operating the pumping mechanism, (5) a source of compliance in communication with fluid along the first or second fluid paths for providing a source of compliance for fluid in proximity to the entrance port of the pump mechanism or for fluid exiting the exit port of the pumping mechanism, respectively. The source of compliance includes a structure selected from the group of (a) a compressible structure, (b) an expandable structure, (c) a non-permeable structure, and (d) a structure located within a flow path defined by a substantially non-compliant material. 
     A second aspect of the invention a method for infusing a fluid into a body of a patient, including: (1) providing fluid to a reservoir within an infusion device, (2) controlling a pumping mechanism having a fluid entrance port and fluid exit port for transferring fluid from the entrance port to the exit port, (3) directing a fluid from the reservoir to the entrance port of the pumping mechanism along a first fluid path, (4) directing fluid to an outlet connected to the exit port of the pumping mechanism along a second fluid path for supplying to the body of a patient, (5) operating the pumping mechanism in a controlled manner, (6) supplying a source of compliance in communication with fluid along the first or second fluid paths for providing a source of compliance for fluid in proximity of the entrance port of the pump mechanism or for fluid exiting the exit port of the pumping mechanism, respectively. The source of compliance includes a structure selected from the group of (a) a compressible structure, (b) an expandable structure, (c) a non-permeable structure, and (d) a structure located within a flow path defined by a substantially non-compliant material. 
     A third aspect of the invention provides an infusion pump for delivering a fluid to the body of a patient, including: (1) a pumping means having a fluid entrance port and fluid exit port for transferring fluid from the entrance port to the exit port, (2) a means for containing a fluid to be dispensed connected to the entrance port of the pumping means by a first fluid path, (3) an outlet means connected to the exit port of the pumping mechanism along a second fluid path for supplying fluid from the reservoir to the body of a patient, (4) a means for controllably operating the pumping mechanism, (5) a compliance means in communication with fluid along the first or second fluid paths for providing a source of compliance for fluid in proximity to the entrance port of the pump mechanism or for fluid exiting the exit port of the pumping mechanism, respectively. The compliance means includes a structure selected from the group of (a) a compressible structure, (b) an expandable structure, (c) a non-permeable structure, and (d) a structure located within a flow path defined by a substantially non-compliant material. 
     A fourth aspect of the inventions provides a compliance mechanism for use with a pump mechanism in an infusion pump that is intended to deliver a predetermined amount of fluid through an outlet from operation of the pump mechanism. The compliance mechanism includes at least one pillow. The at least one pillow includes a pair of diaphragms that are hermetically sealed to enclose a known volume of a gas or other compressible substance. The at least one pillow is positioned to be in fluid communication with fluid in the infusion pump. 
     A fifth aspect of the invention a compliance mechanism for use with a pump mechanism in an infusion pump that is intended to deliver a predetermined amount of fluid through an outlet from operation of the pump mechanism. The compliance mechanism includes a drum member including a pair of diaphragms that are hermetically sealed to open ends of a stand off member. 
     The drum encloses a trapped volume of gas or other compressible substance and is positioned to be in fluid communication with the fluid in the infusion pump. 
     A sixth aspect of the invention provides a compliance mechanism for use with a pump mechanism in an infusion pump that is intended to deliver a predetermined amount of fluid through an outlet from operation of the pump mechanism. The compliance mechanism includes (1) at least one diaphragm, and (2) a body having a cavity with at least one opening, wherein the at least one diaphragm is hermetically sealed to close off the at least one opening in the cavity. The diaphragm is positioned to be in fluid communication with the fluid in the infusion pump. 
     A seventh aspect of the invention provides an infusion pump for delivering a fluid to the body of a patient, including: (1) a reservoir for containing a fluid to be dispensed, (2) an outlet for supplying fluid from the reservoir to the body of a patient, (3) a pumping mechanism for transferring fluid from the reservoir to the outlet (4) a programmable control device, including an electrical circuit, for controllably operating the pumping mechanism, and (5) a compressible structure in communication with fluid in the infusion pump for providing a source of compliance within the infusion pump. 
     While certain aspects of the invention have been noted above, other aspects will be apparent to those of skill in the art upon study of the teachings herein. As noted above, it is not intended that each aspect of the invention simultaneously address all of the objectives set forth above. Each aspect of the invention may address a single one of the objectives or alternatively may address a combination of two or more objectives. 
     Some preferred embodiments provide implantable infusion pumps with sources of compliance positioned between an exit port of a pumping mechanism and an outlet (e.g. an opening in a catheter) of the infusion pump. Other embodiments provide compliance for fluid in an entrance port of the pumping mechanism. Insertion of compliance in a flow path that is down stream of the pumping mechanism may aid in minimizing negative effects associated with attempting to force fluid through a restricted flow path that is further down-stream, such as that offered by a catheter or other outlet component. Insertion of compliance before the pumping mechanism may aid in reducing negative effects associated with an up stream restricted flow path, such as that which might be offered by a rigid filter located between the reservoir and the pumping mechanism. Several structural components, assemblies, or configurations are used as sources of compliance. For example, compressible structures (e.g. pillows, drums) are used within a side port of the infusion pump. The compressible structures may quickly distort to accommodate for a large impulse of fluid into the flow path that can not otherwise be readily dealt with. The compression, in turn, results in a restoring force being exerted that returns the structure substantially to its original volume so as to slowly force fluid from the flow path. 
     Thus, some embodiments of the present invention provide an attachable, field replaceable catheter assembly with controlled compliance characteristics for use with an implantable infusion pump that attempts to deliver an amount of fluid in a short time period. However, to minimize energy consumption, it is typically desired to operate the pumping mechanism over a time period that is significantly less than that necessary to delivery a desired volume of fluid from an outlet of the infusion pump. The supplied compliance aids in ensuring that a desired amount of fluid is deliver for each operation of the pumping mechanism (e.g. each stroke of an electromagnetically driven piston). 
     According to one embodiment of the invention, a compliance mechanism is used with a pump mechanism in an infusion pump to aid in delivering a desired or predetermined amount of fluid through a catheter. The compliance mechanism includes a plurality of diaphragms used in the formation of at least one pillow. Each of the at least one pillows is formed from a pair of diaphragms that are hermetically sealed to enclose a known volume of a gas. The at least one pillow is preferably located within a fluid path that is separated from an exit port of the pump mechanism by a small amount of flow impedance, or resistance, so as to minimize the effects of flow resistance in the catheter. 
     In some embodiments, the compliance mechanism includes a support component to protect the at least one pillow from collapse beyond its structural limits during the pump stroke or during a flush out operation. Further embodiments provide pillows which can accommodate pressures up to about −8 to about 300 psi. Still further embodiments, form the diaphragms from a metallic material, such as titanium or the like, a metallic composite, or Halar film. 
     Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of embodiments of the invention will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the several figures: 
     FIG. 1 is a perspective view illustrating an implantable medication infusion pump equipped with a side port assembly; 
     FIG. 2 is a fragmented exploded perspective view depicting connection of the side port assembly onto the implantable infusion pump; 
     FIG.  3 ( a ) is a top plan view of an attachable field replaceable side port/catheter assembly. 
     FIG.  3 ( b ) is a cross-sectional view of the attachable field replaceable side port/catheter assembly as shown in FIG.  3 ( a ). 
     FIG. 4 is a side perspective view of a side port as shown in FIGS.  3 ( a ) and  3 ( b ). 
     FIG. 5 is a perspective cross-sectional view of the side port, as shown in FIG. 4, showing one proposed site for the improved compliance mechanism. 
     FIG.  6 ( a ) is a top perspective view of a pillow for use as a compliance mechanism in accordance with an embodiment of the present invention. 
     FIG.  6 ( b ) is a perspective cross-sectional view of the pillow for use as the compliance mechanism as shown in FIG.  6 ( a ). 
     FIG.  7 ( a ) is a perspective cross-sectional view of an attachable field replaceable side port/catheter assembly using a compliance mechanism in accordance with an embodiment of the present invention. 
     FIG.  7 ( b ) is an enlarged perspective partial cross-sectional view of the compliance mechanism shown in FIG.  7 ( a ). 
     FIG.  8 ( a ) is a perspective view of a central flow support structure for use with a preferred embodiment of the compliance structure as show in FIGS.  7 ( a ) and  7 ( b ). 
     FIG.  8 ( b ) is a perspective view of a peripheral flow support structure for use with a preferred embodiment of a compliance structure as show in FIGS.  7 ( a ) and  7 ( b ). 
     FIG.  9 ( a ) is a perspective cross-sectional view of alternative support components that include the pillow assembly for another embodiment of the compliance mechanism shown in FIGS.  7 ( a ) and  7 ( b ). 
     FIG.  9 ( b ) is a perspective view of alternative support components that include the pillow assembly for another embodiment of the compliance mechanism shown in FIGS.  7 ( a ) and  7 ( b ). 
     FIG. 10 is a perspective cross-sectional view of an attachable field replaceable side port assembly that utilizes a filter support component that integrates the filter and support functions with the compliance mechanism in accordance with another embodiment of the present invention. 
     FIG.  11 ( a ) is a perspective view of a compliance mechanism in accordance with still another embodiment of the present invention. 
     FIG.  11 ( b ) is an exploded perspective view of the components forming the compliance mechanism of FIG.  11 ( a ). 
     FIG.  12 ( a ) is a perspective view of a support structure for use with the compliance mechanism of FIGS.  11 ( a ) and  11 ( b ). 
     FIG.  12 ( b ) is a perspective view of the compliance mechanism of FIG.  11 ( a ) positioned between two support structures like those shown in FIG.  12 ( a ). 
     FIG. 13 shows a partial cross-sectional view of a compliance mechanism in accordance with another embodiment of the present invention. 
     FIG. 14 shows a partial cross-sectional view of a compliance mechanism in accordance with yet another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to some preferred embodiments of the invention, an implantable infusion pump is provided that includes a number of functionally related elements or assemblies: (1) an outer shell or housing, (2) a fluid reservoir located entirely within or forming part of the housing, (3) an inlet orifice functionally connected to the reservoir for allowing fluid to be supplied from outside the housing to the reservoir for filling the reservoir when the fluid supply gets low or is depleted, (4) a pumping mechanism, located entirely within or forming part of the housing, transfers fluid from an entrance port of the mechanism to an exit port of the mechanism, (5) a fluid flow path connecting the reservoir to the entrance port for a pumping mechanism, (6) an outlet that has an opening for dispensing fluid from the infusion pump to a desired location within the body of a patient, (7) a fluid flow path connecting the exit port to the outlet, (8) a mechanism and/or circuit for controlling the operation of the pumping mechanism to controllably dispense fluid from the infusion pump to the body of the patient. Filters may be included at any of various locations in the system, for example, between the inlet and the reservoir and/or between the reservoir and the entrance port of the pumping mechanism, and/or between the exit port of the mechanism and the outlet of the system. 
     The entrance port of the pump mechanism and exit port of the pump mechanism may be located within the mechanism assembly as opposed to defining an inlet or outlet of the assembly itself. The exit port of the mechanism is located at position within the fluid path for which the fluid has been acted on by the pumping mechanism to place it down-stream of the active part of the mechanism. The exit port may be defined by a check valve that allows fluid to leave the active portion of the mechanism on it down-stream path to the pump outlet but will not allow fluid flow in the reverse direction. The entrance port of the mechanism is located at a position within the fluid path for which fluid located up-stream of the position has not yet been acted upon or is in position set be forced through the exit port during a next operation of the mechanism. In the case of a piston pump, fluid located up-stream of the piston may be considered to have not yet reached the entrance port. 
     A fluid region may be considered to be in proximity to another fluid region (regardless of spatial separation) when a relatively small impedance exists in the flow path that connects the two regions. A relative small impedance may in turn be considered that which allows a desired amount (e.g. 50%-200% of the desired pump volume, more preferably 100%) to be transferred during a period of time (e.g. the time associated with pumping) between the two regions when experiencing a pressure no greater than the peak pressure induced in the fluid in the pump mechanism during pumping. A fluid region may be considered removed from another fluid region (regardless of spatial separation) when relatively large flow impedance exists between the two regions. The relatively large impedance may be considered anything greater than the relative small impedance. Alternatively, the relatively large impedance may be considered an amount that is at least two, five or even ten times larger than the relatively small impedance. 
     In some embodiments an infusion pump may include a main pump body with an attached side port and catheter. FIGS. 1 and 2 provide an overview of such an infusion pump. As illustrated, an implantable fluid infusion pump  10  comprises a substantially sealed housing  12  encasing a fluid storage reservoir  14  and an appropriate pump mechanism  16  for delivering discrete doses of a selected fluid through a catheter  18  to a patient. Catheter  18  may be fitted through shell  30  by a strain relief fitting  40 . The pump  10  is equipped with a discharge side access port  20  which can be used to flush or clean accumulated particle-like residues from the catheter  18 , and/or from internal pump flow passages. The pump housing  12  comprises a hermetically sealed case formed from a biocompatible material, such as titanium or titanium alloy. A primary inlet or refill port  22  is provided on the pump housing  12  to receive a hypodermic needle  24  to permit transcutaneous refilling of the medication storage reservoir  14  within the pump housing. During normal operation, the pump mechanism  16  within the housing  12  is programmably operated by an appropriate control circuit  26  to deliver the medication via the catheter  18  in accordance with individual patient requirements. 
     Over a period of time, particle-like deposits form the fluid can accumulate within the catheter  18 , and also within internal flow passages of the pump  10 . These medication deposits are believed to consist primarily of protein and other organic constituents, particularly when relatively complex and/or protein-based medications such as insulin are used. These accumulated deposits can eventually interfere with accurate pump operation and, in some instances, occlude the catheter  18 . 
     A compact side port assembly  28  may be provided and may include discharge side access port  20 . This side access port  20  permits facilitated flushing of particle-like deposits from the catheter  18 . In addition, the side access port  20  can be used in combination with the primary refill port  22  to flush and clean residue from internal pump flow passages. 
     As shown, the side port assembly  28  comprises a relatively small, substantially half-circle case, body, or shell  30  adapted for facilitated interconnection between a pump mechanism exit port  32  and the catheter  18 . Body  30  may be formed from a plastic or other material that is substantially non-compliant. As shown, the pump mechanism exit port  32  includes a discharge tube  34  which projects outwardly a short distance from one edge of the pump housing  12 , and disposed within a generally cylindrical mounting lug  36  having a flanged end  38 . The side port assembly has an inboard side or face adapted for flush-fit mounting against the side edge of the pump housing  12 . A fitting and seal members provide sealed engagement between the discharge tube  34  and the side port. When the side port is fitted to the housing and engaged with the discharge tube an open slot in the housing shell  30  is aligned generally with the mounting lug  36 , at a location behind the flanged end  38 . A fork-shaped lock clip  42  includes a pair of generally parallel legs  44  for slide-fit reception through a slot in body  30  behind the flange lug end  38 , for locking the side port assembly onto the pump housing  12 . 
     A more detailed description of the overall construction and operation of implantable infusion pumps of the general type described above is provided in previously referenced U.S. Pat. Nos. 5,527,307; 4,373,527; and 4,573,994. 
     In the case of an external pumping device, as contemplated by some preferred embodiments, an inlet for refilling the reservoir and a reusable reservoir may be replaced by a disposal and replaceable reservoir that functionally connects to the pumping mechanism. 
     According to some preferred embodiments, the process utilized in supplying the desired fluid to the body of the patient includes a number of acts: (1) providing fluid to a reservoir within an infusion device, (2) directing fluid from the reservoir to an entrance port of a pumping mechanism along a first fluid path, (3) controlling a pumping mechanism to transfer fluid from a an entrance port of the mechanism to an exit port of the mechanism, (4) directing fluid, along a second fluid path, from the exit port of the mechanism to an outlet that releases the fluid into the body of the patient. 
     As shown in some of the drawings, a preferred embodiment of the invention locates one or more sources of compliance in an improved side port assembly that includes an attachable, field replaceable catheter for use with a high impulse-type delivery pump mechanisms (e.g. a mechanism that transfers fluid from an entrance port to an exit port by movement of a piston that is driven by a magnetic force from an electromagnet). As noted above, some preferred embodiments of the invention involve implantable infusion pumps that are placed inside the human body. Still, as noted above, further embodiments may be used with other types of infusion pumps, such as external pumps or the like, which may benefit from use of controlled compliance due to interaction between the infusion pump and the catheter. 
     Additionally, some preferred embodiments of the side pump/catheter assembly provide adequate protection from pressure extremes that may occur from changes in altitude, manufacturing testing, flushing, refilling, purging, and cleaning, or the like. 
     A preferred side port/catheter assembly  28 ′ includes a body portion  30 , a catheter  18 , a strain relief fitting  40 , a side port to housing seal  54 , a locking clip  42 , a filter assembly  56 , and a valve/catheter interface assembly  58  (that can close the catheter inlet when the catheter is removed from the side port) as shown in FIGS.  3 ( a ) and  3 ( b ). As indicated in  3 ( b ) the catheter may be removable from the side port with a valve closing the side port when the Because of the fluid restriction offered by the catheter portion  18  (including the diameter of the lumen and the catheter length), it has been found that a compliance control device is more preferably located between the exit port of pump mechanism and the catheter portion  18  of the side port/catheter assembly  28 ′. Preferred locations are shown as those between points  50  and  52  of FIG.  3 ( b ). However, in alternative embodiments, other suitable locations may be used. As it is intended that a desired amount of fluid be driven out of the exit port of the pump mechanism, the choice for placement and quantity of compliance is dependent on several factors: (1) the available, or desired, pumping force that is exerted on the fluid by the mechanism, (2) the desired duration of pumping, and (3) the impedance of the flow path between the exit port of the mechanism and the outlet of the system. The location and amount of compliance preferably allows a full stroke of fluid to be released from the pump mechanism to the exit port without excess electrical power consumption. It is known that the shorter the electrical impulse supplied to an electromagnetically driven pump mechanism the less drain on the power supply. Thus, if appropriate system compliance is present, minimal power consumption can be achieved while still delivering a desired amount of fluid in a desired amount of time. The compliance should be sufficiently large to allow the pump mechanism to transfer an appropriate amount of fluid without fighting unproductive back pressure while having compliance low enough that it offers sufficient force to drive stored liquid from the fluid path beyond the exit port out of the output orifice between successive pulse operations. 
     In some preferred embodiments, a compliance mechanism  100  is located below side access port  20 , below septum  62 , and filter  64 , as well as below a spacer element  66  between the filter  14  and body  30 , as indicated in FIG.  5 . 
     A first preferred embodiment of a compliance mechanism  100 , as shown in FIGS. 6-7, is a pillow assembly  106 , that uses a plurality of diaphragms  104  coupled together to form gas filled pillows  106  or cushions, with predictable compliance properties within the implantable infusion pump environment. In preferred embodiments, the pillow assembly  106  uses diaphragms  104  as shown in FIG. 6 that hermetically encloses a volume, e.g. preferably known volume) of a known gas  108 , such as air, Argon, Helium, Nitrogen, mixtures or pure gases, Freon (including Freon  113 ), or the like, between two diaphragms  104  that are welded and sealed together. The volume of gas  108  is preferably controlled such that at high pressure extremes the internal to external pressure equalization occurs at a condition which does not exceed elastic limit of the pillow or the yield strength of the chosen diaphragm material. In this way, the compliance mechanism  100  becomes self-supporting at high pressure extremes and does not collapse or degrade. In particular embodiments, the compliance mechanism  100  is formed from two or more pillows  106  (see FIG. 7) using the diaphragms  104 , as shown in FIG.  6 . In FIG. 7, filter  64  is held above the source of compliance by support  68 . A spacer may be placed above the lower portion of filter  64  to prevent the filter or compliance members from being damaged by a hypodermic needle. In preferred embodiments, air is used since it has an increasing pressure curve as the pillow  106  and the diaphragms are compressed. However, Freon  113 , or the like, may also be used to take advantage of its relatively linear or flat pressure curve, and the feature that upon full compression, the Freon  113  will become a liquid to prevent over compression of the pillows  106  and diaphragms  104  beyond the structural limits of the materials that they are formed from. 
     In some preferred embodiments, the diaphragms  104  are formed from a protein and bio-compatible material, such as titanium, titanium alloys, stainless steel, MP35N, Nitinol, or the like, that are hermetically joined together by a method such as TIG welding, laser welding or the like. Inclusion of appropriate trace materials, such as helium, helium radioisotopes or the like, within the known volume of gas  108  during the welding process allows for easy detection and inspection of whether the diaphragms  104  are hermetically sealed after welding. In alternative embodiments, other suitable materials for the diaphragm  104  may be used, such as Halar Film (ethelyne-chlortriflouroethelyne copolymer (ECTFE)), plastic composites, laminates or the like may be used. In addition other methods of sealing the diaphragms  104  together may be used, such as adhesives, or the like. In some preferred embodiments, three pillows  106  are used to form the compliant member  100 . However, in alternative embodiments, more or less pillows  106 , or a bellows, may be used, with the selection being dependent on the characteristics of the implantable infusion pump mechanism and the compliance characteristics of the catheter portion  12  and catheter assembly  10 . 
     In still further preferred embodiments the pillows, diaphragms, or other components forming the source of compliance may be supplied with a protein stabilized surface coating for those portions of the surface that will be in contact with the fluid (e.g. coating over a titanium substrate). Such coatings are described in WO 98/19627 and include such things as hydrophilic polymers, proteins, or polyurethane. 
     Further embodiments of the compliance mechanism  100  in the assembly may require the addition of a structural “support” component such as central flow support  120  in FIG.  8 ( a ), peripheral flow support  122  in FIG.  8 ( b ) to facilitate reception and flow of the fluid received during each stroke of the infusion pump mechanism. As shown in FIGS.  9 ( a ) and  9 ( b ), the pillow assemblies  106  may also be included and formed in an interior recess or cavity in the support member  124 . The use of supports may increase the life of the compliance mechanism  100 . In other embodiments, the support member may be omitted and a hanging filter component  64 ′ may include additional support structures  126 , as shown in FIG. 10, to integrate the filter and support functions to retain the filter component  64 ′ in position during pump strokes, cleaning, refilling, purging or the like. 
     A second embodiment of a compliance mechanism  150 , as shown in FIG. 11, utilizes a drum assembly  152  with predictable compliance properties in the implantable infusion pump environment. The drum assembly  152  uses diaphragms  106 , as described above in the first embodiment. This embodiment uses an internal spacer structure (e.g. over pressure star  154 ) within a stand off collar  156  between diaphragms  106  to provide support to the diaphragms during compression to substantially inhibit the compression of the diaphragms  106  beyond structural limits. In alternative embodiments, different shaped spacer structures  154  may be used, and the number of spacer structures  154  and diaphragms  106  may be increased. In alternative embodiments, the standoff collar may be omitted, if sufficient seal and structural support is provided by the body  30  of the implantable infusion pump. These embodiments may also use supports  160  to further enhance the durability of the compliance mechanisms, as shown in FIG.  12 . Further alternatives may use a variation of the filter support shown in FIG.  10 . 
     FIG. 13 shows a partial cross-sectional view of a compliance mechanism  200  in accordance with another embodiment of the present invention. The compliance mechanism  200  includes a channel  202  that extends to the exterior surface of the body  30 . The exterior opening of the channel  202  is covered by a diaphragm  204  that provides sufficient deflection upon receipt of an impulse from the pump medication. In preferred embodiments, the diaphragm  204  may be made out of similar materials and have similar properties to the diaphragms  104  described above. Preferably, the diaphragm is welded, or attached by adhesives to the body  30 . In alternative embodiments, other suitable materials, such as plastic, Halar, composites or the like may be used. In preferred embodiments, the fluid acts upon the diaphragm to cause deflection and the diaphragm is non-permeable to the fluid. However, in alternative embodiments, the compliance mechanism  200  may include an additional diaphragm (not shown) to close off the channel  202 , and the enclosed space between the diaphragms may be filled with gases as described above. The enclosed area may be filled with a liquid, particularly when the lower surface of diaphragm  204  is adjacent to a volume of gas. 
     FIG. 14 shows a partial cross-sectional view of a compliance mechanism  300  in accordance with yet another embodiment of the present invention. . The compliance mechanism  300  includes a cavity  302  that does not extend to the exterior surface of the body  30 . The cavity  302  has an opening at the support member  120  that is covered by a diaphragm  304  that provides sufficient deflection upon receipt of an impulse from the pump medication. In preferred embodiments, the diaphragm  304  may be made out of similar materials and have similar properties to the diaphragms  104  described above. Preferably, the diaphragm is welded, or attached by adhesives to the body  30 . In alternative embodiments, other suitable materials, such as plastic, Halar, composites or the like may be used. 
     In other embodiments, the source of compliance may be located within the main enclosure of the infusion port as opposed to in a side port assembly. 
     In the previously discussed embodiments, the source of compliance was placed in position primarily to provide a space for fluid to occupy as a result of significant local pressure increases that may accompany the operation of a pumping mechanism. The pumping mechanism attempts to transfer or force a desired quantity of fluid from an entrance port of the pump mechanism to an exit port of the pump mechanism, in a short period of time (e.g. around 1.5 millisecond or less). Typically, the volume of fluid to be transferred is greater than what can be forced through the outlet of the system in the short time period, as such a pressure sensitive compliant device is used to provide a temporary storage location and a longer term fluid displacement force than provided by the pump mechanism. In this regard it is desired that the compliant assembly or member be able to operate elastically under pressures as high as about 300 psig. Of course, the actual pressure range and limit may be more or less than this value depending on system configuration and to what processes the source of compliance may be subjected. 
     In contrast to the previous embodiments where a pressure increase must be elastically accommodated by the source of compliance, other embodiments may require the source of compliance to operate elastically under decreases in pressure and thus to temporarily remove volume from a region of the flow path and to exert a long term force to pull fluid into the region. Such negative pressure (e.g. pressures below ambient) environments may temporarily occur in fluid regions that are up-stream of the entrance port of the pump mechanism. As the pump mechanism operates and transfers fluid from the entrance side to the exit side, the volume of fluid that is desired to be transferred may be greater than what can be transferred from the reservoir to the entrance port of the mechanism in the short period of time allowed (approximately 1.5 millisecond or less). The decreased pressure on the entrance side may be so great as to limit the ability of the pump mechanism to supply the desired amount of fluid. This is particularly true when a rigid, low flow filter, or other flow restrictor, separates the entrance port from the reservoir. If the source of compliance is to be utilized in such environments it is preferred that it be able to operate elastically within the pressure range that might be encountered (e.g. down to −8 psig). 
     As such, in certain embodiments it may be advantageous to place a source of controlled compliance in communication with a portion of the fluid path that is located up stream of the pump mechanism. In particular, it may be advantageous to place the source of compliance along the fluid path between the reservoir and an entrance port to the pumping mechanism. Even more particularly, the source of compliance may be located between a the entrance port of the pump mechanism and a rigid filter component that may be used to form a barrier over which a substantial pressure can built up during operation of the pumping mechanism. 
     In still further additional embodiments, the diaphragms  104  and pillow assembly  100  may be replaced with other resilient devices, such as elastic materials, foam, or the like, which provide compressibility or be deflectable particularly when they are of a material or coated with a material that is non-permeable to the fluid, fluids, or gases that they may come into contact with. 
     In some preferred embodiments as discussed above, the source of compliance preferably includes unitary structures or assemblies that are compressible, expandable, non-permeable to fluids encountered (e.g. gases or liquids), and/or are located within a flow path defined at least in part by a substantially non-compliant material. In some preferred embodiments the amount of compliance provided by the source of compliance may be within a range of about 10% to about 200%, more preferably between about 20% to about 130%, of the intended volume of fluid to be delivered by a single operation of the pump mechanism when experiencing a pressure in the range of 5 to 200 psig, more preferably between 10 to 100 psig. The relationship between compliant volume and pressure is more particularly based on an anticipated peak transient pressure exerted by the pump during pumping, length of time associated with pumping, that amount of impedance between the exit port of the pumping mechanism and the pump outlet, and the volume of fluid that is desired to be dispensed. Based on consideration of these issues, one of ordinary skill in the art may, at least, empirically determine an appropriate amount of compliance to add to a particular system. In some preferred embodiments a compliance of about 0.5 microliters at about 20 psig is considered appropriate when the desired pump volume is about 0.5 microliters. This amount of compliance, may for example, be offered by one or more pillows or drums (e.g. 2 or 3 pillows) 
     As noted above, if a catheter lumen is small and restrictive or if other restrictions exist in the flow path, an electromagnetic piston pump mechanism may not be able to push or pull the full stroke into the catheter or other restricted region in the very short time of piston action (e.g. of less than about 1.5 millisecond). To obviate the resulting problems in fluid delivery a controlled source of compliance is added to the system so that the fluid may be stored in the first millisecond and then made to flow under the lower force offered by the source of compliance during subsequent milliseconds. 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. For example, while examples of self contained controllable sources of compliance have been explicitly disclosed herein, other self contained sources of compliance will be apparent to those of skill in the art after reviewing the teachings herein. Alternative sources of compliance might have adjustable compliance, e.g. a source that includes a clamping mechanism that can change the effective compliance of the source by varying its maximum size volume. 
     The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.