US 20040065615 A1
An implantable infusion pump to deliver stored infusate to a desired fluid delivery site. The pump includes a collapsible fluid chamber. The pump can include a multi-stage filtration system to filter micro-emboli as well as larger particles that are inadvertently introduced into the pump system. An external member can receive the pump and provide a medium to include additional, interactive components, e.g., a bolus port, as well as provide a versatile suture structure to enable the pump to be properly secured within an implantation site. To improve volumetric efficiency, the pump can further incorporate an outlet flow passage within a movable wall of the fluid chamber.
1. A filter system for an infusion pump implantable in a living body to filter emboli from an infusate, the filter system comprising:
a micro-filter stage to filter sub-micron emboli from an infusate; and
a particulate filter stage to filter particles greater than 1 micron from the infusate,
wherein the particulate filter stage is arranged relative to the micro-filter stage so as to operatively receive infusate filtered by the micro-filter.
2. A filter system in accordance with
3. A filter system for an infusion pump for delivering an infusate to a living body, the filter system comprising:
a first filter stage to filter the infusate; and
a second filter stage to filter the infusate,
wherein the first filter stage is disposed in an infusate flow path of said infusion pump upstream from said second filter stage, and wherein said first filter stage provides a smaller filter pore size than that provided by said second filter stage.
4. The filter system of
5. The filter system of
6. The filter system of
7. The filter system of
8. The filter system of
9. The filter system of
10. The filter system of
11. The filter system of
12. The filter system of
13. An elastomer member for implantation within a living body, the member comprising:
a first portion to receive an implantable infusion device;
a second portion to receive a bolus port; and
an enlarged skirt, extending substantially around a perimeter of the member, adapted to receive and retain a suture to secure the member at an implantation site.
14. A member in accordance with
15. A member in accordance with
16. A member in accordance with
17. A member in accordance with
18. A member in accordance with
19. A member to receive an implantable infusion device, which includes a fluid output, for implantation in a living body, the member comprising:
a first mating surface to receive a housing of an implantable infusion device; and
a second mating surface to receive a bolus port.
20. A member in accordance with
21. A member in accordance with
22. A member in accordance with
23. A member in accordance with
24. A member in accordance with
25. A member in accordance with
26. A member in accordance with
27. An elastomer member for implantation within a living body, the member comprising:
a first portion to engage an implantable infusion device for attachment thereto;
a second portion to receive a suture to secure the implantable infusion device at an implantation site, said second portion comprising said elastomer to prevent the in-growth of tissue at an area of said suture.
28. The member of
29. The member of
30. The member of
31. The member of
32. The member of
33. The member of
34. The member of
35. The member of
a third portion to engage a delivery catheter.
36. The member of
 The present application is a divisional of co-pending and commonly IMPLANTABLE INFUSION PUMP assigned U.S. patent application Ser. No. 09/755,894 entitled “IMPLANTABLE INFUSION PUMP,” filed Jan. 4, 2001, the disclosure of which is hereby incorporated herein by reference.
 The present invention concerns an implantable infusion pump, and in particular, an implantable infusion pump as well as independent components therefor that enable securing the pump within a living body, multi-stage filtration, and protection of a fluid-delivery catheter in and about the pump housing while improving volumetric efficiency of the pump configuration.
 The present invention relates to an implantable infusion pump for infusing drugs or other chemicals or solutions into a body wherein the infusion pump is implanted, Further, in at least one embodiment, the present invention relates to an implantable infusion pump that compensates for changes in both ambient pressure and ambient temperature so as to accurately control the flow rate of infusates from the implantable infusion pump into the body.
 Infusion pump designs were rarely seen in medical literature until the 1950s. Most of these early infusion pumps were extracorporeal devices of various designs. One such device included a reciprocating air pump driven by an electric motor. Yet another design considered comprised a metal housing for a glass syringe and a compression chamber fed by a tank of nitrogen gas. Yet another such infusion pump included a motorized syringe pump which included an electric motor connected to the worm drive that moved a syringe plunger by a gear box. The gears were interchangeable such that replacement of the gears permitted different delivery rates. Yet another infusion pump included a syringe plunger driven by a rider on a threaded shaft. While this is but a sampling of such devices, it should be appreciated that numerous other designs were considered and used for extracorporeal infusion devices.
 Modem constant-flow implantable infusion devices, or implantable pumps, for delivering an infusate (e.g., medicaments, insulin, etc.) commonly have a rigid housing that maintains a collapsible infusate reservoir. The housing includes a needle-penetrable septum that covers a reservoir inlet. A flow passage is provided between the reservoir and an exterior surface of the device, such flow passage includes, or defines, a restrictor to establish a maximum output infusate flow rate. At the flow passage outlet, a flexible delivery catheter is provided.
 Practically, such a device is implanted at a selected location in a body so that (i) the inlet septum is proximate to the patient's skin and (ii) a distal end of the catheter is positioned at a selected delivery site. Infusate can then be delivered to the infusion site by forcing such fluid from the device reservoir. When the infusate reservoir becomes empty, the reservoir is refillable through the septum inlet by injecting a new supply of infusate through the apparatus' inlet septum. Due to the location of the device in relation to the skin of the patient, injection can be readily accomplished using a hypodermic needle (or cannula).
 Infusate is expelled from the reservoir to an infusion site by collapsing the reservoir. While some infusion pumps use an electrically powered mechanism to force infusate from the reservoir, other such devices commonly use a two-phase fluid, or propellant, that is contained within the rigid housing and is further confined within a fluid-tight space adjacent to the infusate reservoir.
 The propellant is both a liquid and a vapor at patient physiological temperatures, e.g., 98.6° F., and theoretically exerts a positive, constant pressure over a full volume change of the reservoir, thus effecting the delivery of a constant flow of infusate. More particularly, when the infusate reservoir is expanded upon being refilled, the propellant is compressed, where a portion of such vapor reverts to its liquid phase and thereby recharges the vapor pressure power source of the pump. The construction and operation of implantable infusion pumps of this type are described in detail, for example, in U.S. Pat. Nos. 3,731,681 and 3,951,147.
 Gas-driven infusion pumps typically provide a cost-effective means to deliver a consistent flow of infusate throughout a delivery cycle. Notwithstanding, the rigid housing of the gas-driven infusion pump allows both environmental temperature and atmospheric pressure to affect an output fluid flow. With some drugs, particularly those having small therapeutic indices, such changes in drug infusion rates are undesirable and, in certain situations, unacceptable.
 Circumstances readily exist where either environmental temperature or pressure can rapidly change a significant amount. For example, in regard to temperature, an internalized pump pressure can change as much as 0.5 psi for each 1° F. change in body temperature. Thus, for example, assuming a pump driving force of 8 psi at 98.6° F., a twenty-five percent (25%) increase in pressure and drug flow rate can result from a fever of only 102.6° F.
 An even more serious situation results from changes in atmospheric pressure. Although minor variations in atmospheric pressure at any given location on earth does not significantly affect delivery flow rates, with modem modes of transportation, a patient can rapidly change altitude during travel, such as when traveling in the mountains or when traveling by plane.
 Again, the rigid housing of the conventional, gas-driven infusion pump is intended to produce a constant internal pressure (at constant temperature) independent of the external pressure. Largely due to compliance by the lungs and venous circulatory system, hydrostatic pressure within the human body closely follows atmospheric pressure. The net effect is a pressure differential across the fluid flow restrictor of infusion pump (typically a capillary tube or the like) which changes linearly with external pressure. Consequently, a delivered infusate flow rate can increase as much as forty percent (40%) when a patient takes a common commercial airline flight.
 A viable solution to address changes in atmospheric conditions for constant-flow infusion pumps is disclosed in U.S. Pat. No. 4,772,263, herein incorporated by reference in its entirety. Specifically, in place of the conventional rigid enclosure that maintains a two-phase fluid, the disclosure teaches forming the fluid reservoir between a rigid portion (which maintains at least the inlet septum and the restrictor) and a flexible drive-spring diaphragm. The diaphragm is exposed to the body of the patient and “senses” internal body pressure so as to compensate for changes in the internal body pressure caused by changes in atmospheric pressure and temperature.
 While the disclosure of U.S. Pat. No. 4,772,263 provides a foundational description for a pump having a drive-spring diaphragm capable of constant-flow delivery, such patent does not fully consider alternatives for restrictor and/or flow passage outlet placement that may provide for a safer practical configuration as well as capitalize on the unique structure of the drive-spring diaphragm.
 Moreover, U.S. Pat. No. 4,772,263 is silent to a means to incorporate a conventional bolus port with its unique drive-spring diaphragm design. A bolus port enables direct infusion of a fluid through the delivery catheter. A bolus port is typically a separate septum that is in fluid communication with an outlet of an associated infusion pump and a delivery catheter therefor. Typically, certain one-way valving structures can prevent fluid that is injected through the bolus port from flowing upstream to the infusate reservoir of the infusion pump.
 The present invention relates to an infusion pump for implantation in a living body. The infusion pump includes a housing having a fluid chamber, wherein the housing includes a spring-energy source for driving an infusate (e.g., medicaments, insulin, etc.) out of the fluid chamber and compensating for changes in internal body pressure and/or internal body temperature. The housing further includes an inlet conduit in communication with the fluid chamber and an outlet conduit in communication with the fluid chamber that leads to an infusion site in the body. A self-sealing, penetrable member is provided in the inlet conduit to facilitate periodic refilling of the drug chamber when the infusion pump is implanted. The spring-energy source allows a pressure differential between the fluid chamber and the internal body pressure to remain constant and unaffected by changes in body temperature or atmospheric pressure.
 In accordance with one aspect of the present invention, the spring-energy source is a spring diaphragm that forms a flexible, exterior rear wall of the fluid chamber that operatively applies pressure on a fluid solution stored in the fluid chamber equivalent to a predetermined constant force collectively exerted by the spring diaphragm and an internal body pressure of the patient.
 In accordance with another aspect of the present invention, an infusion pump for implantation in a living body has a variable-volume fluid chamber, a housing, and a driving spring. An inlet conduit of the pump includes a self-sealing penetrable member and extends between a surface of the housing and the fluid chamber. An outlet conduit of the pump communicates with the fluid chamber and is connectable to a delivery catheter. In addition to the driving spring being adapted to supply a principle force to drive a fluid stored in the fluid chamber into the body, the driving spring also includes the outlet conduit, which enters, passes through, and exits the driving spring.
 Another aspect of the present invention is directed to an implantable pump having a housing, an outlet conduit, and a multi-stage filter system. The housing defines a variable-volume fluid chamber to store infusate. The outlet conduit is in communication with the fluid chamber and connectable to a delivery catheter. The multi-stage filter system, positioned within the outlet conduit, filters infusate prior to delivery via the delivery catheter.
 Another aspect of the present invention is directed to an implantable pump that includes a housing having both a collapsible fluid chamber to store infusate and an energy source to collapse the fluid chamber. The pump further includes an inlet conduit and an outlet conduit. The inlet conduit, having a self-sealing penetrable member positioned therein, is located at a first position relative to the housing and in communication with the fluid chamber. The outlet conduit is in communication with the fluid chamber and connectable to a delivery catheter. The pump further includes a member having (i) a first mating surface to receive the housing and (ii) a reinforced-elastomer suture structure, extending substantially about a perimeter of the member, to receive and maintain applied sutures to secure the pump within a living body.
 Another aspect of the present invention is directed to an implantable pump that includes a bolus port and a housing having a collapsible fluid chamber to store infusate and an energy source to collapse the fluid chamber. The pump further includes an inlet conduit and an outlet conduit. The inlet conduit, having a self-sealing penetrable member positioned therein, is located at a first position relative to the housing and in communication with the fluid chamber. The outlet conduit is in communication with the fluid chamber. The pump further includes a member having (i) a first mating surface to receive the housing and (ii) a bolus port receptacle, having an inlet and an outlet, to receive the bolus port, wherein the outlet is connectable to a delivery catheter. A connection conduit operatively couples the inlet of the bolus port receptacle and the outlet conduit.
 An object of the present invention is to provide an implantable infusion pump having an outlet flow passage that is protected by the upper housing and is removed from potential damage during a refill operation.
 Another object of the present invention is to provide an implantable infusion pump having a drive-spring diaphragm with an outlet flow passage that passes through the drive-spring diaphragm.
 Another object of the present invention is to provide a suture structure that receives and is attachable to an infusion pump, wherein this structure enables a received infusion pump to be conveniently secured at an implantation site.
 Another object of the present invention is to provide a structure that receives and is attachable to an infusion pump and that facilitates a fluid connection between the infusion pump and a bolus port.
 Another object of the present invention is to provide a two-stage filtration system for an implantable infusion pump, wherein a first stage functions to filter micro-emboli and a second stage functions to filter greater particulate matter.
 Other objects and advantages of the present invention will be apparent to those of ordinary skill in the art having reference to the following specification together with the drawings.
 The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
 For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
FIG. 1 is a perspective view of a conventional embodiment of a spring-driven infusion pump;
FIG. 2 is a sectional view of the infusion pump shown in FIG. 1, wherein certain portions are being shown diagrammatically;.
FIG. 3 is a force/deflection curve for the spring-energy source of the present invention, wherein this curve illustrates a constant force over a predetermined range of spring deflection;
FIG. 4 is a sectional view of one embodiment of a conventional single conical spring-energy source in accordance with the present invention;
FIG. 5 is a sectional view of an infusion pump in accordance with the present invention;
FIG. 6A illustrates a side view of the spring diaphragm for the infusion pump of FIG. 5, FIG. 6B illustrates a plan view of such spring diaphragm, and FIG. 6C provides a partial sectional view of an inlet to the outlet passage of the spring diaphragm of FIG. 6B taken along line 6C-6C thereof;
FIG. 7 illustrates a bottom view of the spring diaphragm for the infusion pump of FIG. 5 connected to a delivery catheter;
FIGS. 8a and 8 b illustrate a second stage of a filter system in accordance with the present invention;
FIG. 9 is a perspective, exploded assembly view of the infusion pump of FIG. 5 and a boot incorporating a suture structure and a bolus port receptacle;
FIG. 10 is a sectional view of the boot of FIG. 9 taken along line 10-10 thereof;
FIG. 11 is a partial sectional view of a bolus port positioned within the bolus port receptacle of the boot of FIGS. 9 and 10; and
FIG. 12 is a partial sectional view of a pump assembly in accordance with one aspect of the present invention.
 As a foundation for a detailed description of the present inventions set forth in this disclosure, reference will first be made to that known in the art, and in particular, that generally disclosed in U.S. Pat. No. 4,772,263.
 Referring now to the drawings, there is illustrated in FIGS. 1 and 2 an embodiment of an implantable infusion pump in accordance with at least one aspect of the present invention, the pump being generally designated by the reference numeral 20. The pump 20 has a housing 22 with top and bottom wall portions 24, 26 interconnected by a side wall portion 28 forming a hardened outer shell structure. The expressions “top” and “bottom” are relative and refer only to positions that are generally shown in the drawings.
 The top wall portion 24 is constructed of a hardened, non-reactive material, e.g., stainless steel, titanium, etc. In contrast, the bottom wall portion 26 includes a flexible spring diaphragm 25 which cooperates with the remainder of the housing to define a variable-volume, fluid-tight drug chamber 30 for holding insulin, a drug solution or other chemicals or solutions to be infused into an infusion site of a patient's body where the delivery catheter is implanted. The outside surface of the spring diaphragm 25 is exposed to the body and “senses” an internal body pressure so as to compensate for changes in such internal body pressure caused by changes in atmospheric pressure and temperature. The flexible spring diaphragm 25 communicates the internal body pressure to the drug chamber 30.
 Notwithstanding the spring diaphragm 25, the infusion pump 20 further includes those features required of an implantable and refillable infusion pump. An inlet conduit 32 extends from the exterior of the housing 22 to the variable-volume, collapsible drug chamber 30 so as to provide for fluid communication from outside the housing 22 to the drug chamber 30. An upper end of the inlet conduit 32 includes a self-sealing, penetrable member or septum 34, suitably positioned therein to provide a fluid-tight seal and yet enable the refilling of the drug chamber 30 by injection. An outlet passage 36 leads from the drug chamber 30 to the exterior of the housing 22 to provide for outflow of drug solution from the drug chamber 30 to the exterior of the housing 22. The outlet passage 36 is illustrated as including a suitable filter 38 for filtering out bacteria and trapped gas, which might be inadvertently introduced into the infusion pump 20 during the manufacturing or the refilling process.
 Interconnected to an outer end of the outlet passage 36 by a suitable connector 40 is a flow restrictor 42, or in this instance, capillary tubing, which serves as a flow regulating element. The capillary tubing 42 might be interconnected at an opposite end to a rubber catheter or the like that leads to the site of infusion in the body.
 For controlling a rate of delivered flow, the most readily adjustable parameters are (i) the restrictor (i.e., the length and diameter of the capillary) and (ii) the viscosity of the infusate. Addressing the former, the flow rate through the flow restrictor 42 is governed by the Poisseuille equation:
 Q=flow (ml/sec),
 r=radius of restrictor passage (cm),
 μ=viscosity (poise),
 ΔP=pressure (dynes/cm2), and
 L=restrictor length (cm).
 Several feet of capillary tubing 42 is typically required, for example, 0.5-100 feet, and preferably, 20-100 feet, and more preferably, 50-100 feet.
 As illustrated, the capillary tubing 42 might be wrapped about the housing 22 in a groove 44 and suitably secured by a material compatible with body fluids. It will be appreciated that other types of structures or devices might be used to provide for drug output or outflow resistance; for example, spiral groove plate, etched glass, steel capillary tubing, silica chip, etc. Moreover, the resistance elements may number more than one, as in the case of more than one site of infusion.
 The outer surface of the top wall portion 24 of the housing 22 is preferably shaped to allow easy identification of the inlet conduit 32 (see also FIG. 5) and suitably protected with a layer of metal or the like to be protected from needle damage during the process of refilling the drug chamber 30. The bottom wall portion 26 and side wall portion 28 might also be similarly protected by a metal layer. As another alternative, the spring diaphragm 25 may include an integrated material (e.g., Kevlar™ [DuPont Corp., Wilmington, Del.]) to assist in preventing aberrational needle-penetrations during refill operations.
 It will be appreciated that the overall design of the infusion pump 20 of the present invention can be more compact and have higher volumetric efficiency than gas-driven pumps since there is no second chamber and the outer shell structure of the infusion pump serves a dual purpose as the infusate-driving energy source and the protective shell.
 In the embodiment of the infusion pump shown in FIGS. 1 and 2, the spring diaphragm 25 is formed of a series of nested conical sections 48 interconnected by stiff cylindrical ring sections 50 so as to form a substantially flat spring diaphragm. The conical sections 48 are constructed of an elastomer with a low elastic constant, and the ring sections 50 are preferably constructed of metal with a high elastic constant. The preferred construction technique is to mold the metal ring sections 50 into an elastomer structure forming the conical sections 48. If necessary, the inner surface of the spring diaphragm 25 can be coated with a plastic liner or provided with a thin metal liner to resist drug action on the elastomer and reduce gas diffusion from the body into the drug chamber 30.
 This arrangement of conical sections 48 and ring sections 50 provide a spring diaphragm 25 with a useful range of movement or stroke. Moreover, by separating the single conical spring into a nested series of conical sections interconnected by relatively stiff cylindrical ring sections, a substantially flat spring diaphragm having an effective stroke or range of movement in the substantially flat portion of the force/deflection curve shown in FIG. 3 is achievable. The flat portion of the curve of FIG. 3 is a constant force region that can be used to produce a constant pressure over a range of displacement volume and is desirable region of operation.
 The spring diaphragm 25 can be extended beyond its nested position when assembled such that the spring diaphragm 25 is therefore under stress. The initial displacement is selected to bring the pressure or force exerted by the spring diaphragm 25 to the flat portion of the force/displacement curve illustrated of FIG. 3. Appreciably, the functional volume of the infusion pump 20 is that displacement which takes place over this substantially flat region of the force/deflection curve.
 To limit the filling of the infusion pump to a desired displacement of the spring diaphragm 25, a telescoping section 54 can be interconnected to the spring diaphragm 25 and extend into the inlet conduit 32. When the telescoping section 54 is fully extended, collar portion 56 cooperates with a collar portion 58 of the inlet conduit 32 to prevent the spring diaphragm 25 from traveling more than the desired distance. As illustrated, the telescoping section 54 is interconnected to a substantially flat portion 60 of the spring diaphragm. The telescoping section 54, thus limits the stroke of the spring diaphragm 25 as indicated generally by the arrows 62 and causes the filling back pressure to increase rapidly, thereby reducing the risk of damaging the spring diaphragm 25 or causing errors in a drug flow rate due to excess pressure in the drug chamber.
 An alternative design of the spring diaphragm 25 can take the form of a single Belleville washer, as generally shown in FIG. 4. Not unlike the first spring diaphragm 25 discussed above, a Belleville washer with the proper selection of cone angle and thickness can yield a desired force displacement curve in accordance with FIG. 3. If a strong material like titanium is used, cone height must be very small, i.e., 10 to 20 thousandths of an inch, so as to provide force in the range suitable for infusion pumps, e.g., 4 to 15 psi. This range of heights, which constitutes the effective stroke of a spring diaphragm 35 that includes a single conical spring, is too small to be practical for use in infusion pumps. In order to retain a flat pressure curve and achieve a longer stroke or range of movement of the spring diaphragm 25, a spring material with a lower elastic constant should be used, for example, plastics and elastomers. When low elastic materials are used, the thickness of the conical section can be increased and the cone angle made larger. Accordingly, it is preferred that the spring material used should also have a much greater percent elongation in the elastic region of its stress strain curve. This allows the spring diaphragm 25 to have a much longer range of travel in the substantially flat portion of the curve shown in FIG. 3.
 No matter which diaphragm design is employed, it will be appreciated that the shape and thickness of the spring diaphragm 25 may vary in order to exhibit the required force/deflection characteristics.
FIG. 5 illustrates another embodiment of the pump 20 that includes a single conical spring diaphragm 25. The pump 20 of this embodiment is shown in an expended or collapsed state (i.e., substantially no infusate within the fluid chamber 30). In reference to the drawings, the same numerical designations are used to represent like structure between the disclosed embodiments. Accordingly, when this embodiment includes structure substantially identical to that of the embodiment of FIGS. I and 2, description of such structure will not be repeated.
 The top wall portion 24 offers a simplified configuration over that used for the embodiment shown in FIGS. 1 and 2. Specifically, the top wall portion 24 does not function as a manifold for the outlet passage 36 and related structure, rather the outlet passage 36 is formed in and passes through the spring diaphragm 25. This allows the pump restrictor and delivery catheter connector 40, which is an extension of the outlet passage 36, to be positioned away from the upper surface of the pump 20, thus avoiding the exposure of this sensitive structure from potential damage during a refilling procedure. As will be discussed in greater detail below, this embodiment incorporates a filter system 38 and a flow restrictor 42 within the internalized outlet passage 36.
 For one structural arrangement, the inlet conduit 32 is defined by a needle stop 32 a that includes at least one aperture 32 b. The needle stop 32 a is formed from a hardened material, e.g., stainless steel, titanium, etc. The needle stop 32 a receives and holds a resilient material 32 c, which serves to effectively stop a needle (not shown) that is inserted through the septum 34 and avoid damage through its contact with the lowest portion of the needle stop 32 a. The needle stop 32 a is held in place by a retaining structure 32 d, which is secured (e.g., welded) to an undersurface of the top wall portion 24. Although FIG. 5 illustrates (and the above description discusses) the use of the resilient material 32 c, it should be appreciated that the resilient material 32 c is not critical to the present invention, whereas the needle stop 32 a can be provided without the resilient material 32 c (FIG. 12).
FIGS. 6A and 6B further illustrate the spring diaphragm 25 of this embodiment. FIG. 6A is a side view of the spring diaphragm 25 and is consistent with the sectional view shown in FIG. 5. FIG. 6B is a plan view, which better illustrates the structure of the spring diaphragm 25, including a central portion 29 that can closely receive the needle stop 32 a (FIG. 5), the outlet passage 36, the outlet passage inlet 27 (FIG. 6C), and the delivery catheter connector 40.
 Operatively, infusate is injected using a needle (not shown) into the inlet conduit 32. The injected infusate passes from the inlet conduit 32 into the fluid chamber 30 via the at least one aperture 32 b. Infusate within the fluid chamber 30 enters the outlet passage 36 through the outlet passage inlet 27, which can interface with the aperture 32 b in even a collapsed state (see FIG. 6c).
 Embedding the outlet passage 36 within the spring diaphragm 25 creates a more compact overall pump design, allows the outlet passage 36 to be made using a basic molding process, and eliminates the need for a separate manifold to house a restrictor and/or filter, such as shown in FIG. 1. Accordingly, this embodiment exhibits greater volumetric efficiency, lower weight, ease of assembly, and requires no substantive change in the overall shape of the pump 20. Moreover, an embedded outlet passage 36 minimizes the occurrence of extreme stretching, compressing, flexing, or kinking of component couplings and joints.
 As but one fabrication example, the spring diaphragm 25 is fabricated by first supporting tubing (e.g., silicone tubing) on a flexible mandrel (not shown) within the cavity of a spring mold (not shown). The tubing is selected based largely on its inner diameter-the inner diameter should accommodate a bacteriostatic filter therein but still allow adequate flow thereabout. The mandrel holds the tubing in accordance with a desired shape relative to the final spring diaphragm 25. In this particular example, the mandrel maintains the tubing in a gentle spiral that extends substantially from a top surface of the spring diaphragm (i.e., outlet passage inlet 27) to a position slightly beyond (preferably, 0.1″-1.0″) the lower surface thereof (i.e., connector 40). A liquid elastomer (e.g., silicone rubber) is then injected into the mold cavity in and about the supported tubing. Consequently, the supported tubing is integrated with the spring diaphragm 25 during vulcanization. The flexible mandrel is then removed, thus leaving a hollow tubular channel within the wall of the spring diaphragm 25. The portion of the tubing that extends from the lower surface of the formed spring diaphragm 25 is adapted to be connected to (i) a delivery catheter 70 or (ii) tubing for connection to additional pump structure (e.g., a bolus port).
 It should be appreciated that the specific technique utilized to form the internalized outlet passage 36 is not critical to this invention.
 As may be seen in both the configurations of FIGS. 2 and 5, it is preferred that an inner surface 52 of the top wall portion 24 be configured to have a somewhat convoluted shape so as to allow the spring diaphragm 25 to nest into the complimentary shape of the inner surface 52. This enables the spring diaphragm 25 to expel substantially all of the drug solution from the fluid chamber 30 during an infusate delivery cycle.
 As stated before, it is intended that the outlet passage 36 include both a filter 38 and a flow restrictor 42.
 In regard to the filter 38, it is a requirement that drug infusion pumps include a means of micro-filtering infusates in order to insure their sterility. While a preferred filter structure would be sintered metal due to its durability, sintered metal filters are not currently available with a micro-filtration pore size. Consequently, filters with sub-micron pore size are conventionally fabricated from organic polymers such as polysulfone, Nylon®, polytetrafluoroethlyene, and cellulose acetate. These organic-based filters are not as durable as metal filters and are more likely to shed particles large enough to partially or completely obstruct some part of the pump flow path, valve seats, and interstices. Modem implantable infusion pumps have flow paths that range in size from 5 microns to 50 microns.
 In addition to the concern of filter break up, it is necessary to filter potentially damaging particles that may be introduced during the manufacturing process. First, silicone rubber, which can be used extensively in the fabrication of the present invention, has the propensity to attract electrostatically charged particles. It is more common than not that silicone rubber parts of the pump 20 will carry and introduce 5-25 micron particles into the pump system that can individually cause device failure. Second, particle control is an issue with respect to the sequence in which the pump 20 is assembled. The microbial filter 38 a (e.g., 0.2 micron polysulfone tubular fiber) can be installed within the outlet passage 36 at a relatively early stage of the manufacturing process, but the flow restrictor 42 is fabricated, inspected, and installed at a relatively later stage. The practical concern is that system-harmful particles may be introduced into the pump system, downstream of the microbial filter 38 a, despite the strictest of particle control standards and measures.
FIG. 7 illustrates a bottom view of the spring diaphragm 25 of this embodiment, which illustrates the position of both the micro-filter stage 38 a and the particle filter stage 38 b of the multi-stage filtration system 38, wherein the particle filter stage 38 b is downstream of the micro-filter stage 38 a. The micro-filter stage 38 a is a filter with sub-micron pore size and is preferably fabricated from conventional, organic polymers such as polysulfone, Nylon®, polytetrafluoroethlyene, cellulose acetate, or the like. The particle filter stage 38 b is illustrated in FIGS. 8a and 8 b.
 In FIG. 8a, the restrictor 42-particle filter stage 38 b assembly is generally shown. In particular, a delivery catheter 70 is positioned through the catheter connector 40 and into the outlet passage 36. The union between the connector 40 and the delivery catheter 70 is reinforced with a sleeve 74. The delivery catheter 70 and/or the sleeve 74 are held in place by an adhesive, friction, mechanical fastener, or the like.
 A tubing section 72 extends from a proximal end of the delivery catheter 70. A particle filter 38 b is fixed to a proximal end of the tubing section 72 so as to cover the inlet to the lumen of the tubing section 72. While the particle filter 38 b can assume any structure capable of preventing at least a 20 micron or greater particle from entering the lumen of the tubing section 72, it is preferred that the particle filter 38 b take the form of a sintered, stainless steel mesh. In one embodiment, the mesh of the particle filter 38 b is arranged so as to prevent the passage of particles having a size of approximately 20 microns or greater. More preferably, the mesh prevents the passage of particles having a size of approximately 10 microns or greater. Most preferably, however, the mesh prevents the passage of particles having a size of approximately 5 microns or greater. The particle filter 38 b is fixed to the tubing section 72 by adhesive, friction, mechanical fasteners, or the like.
FIG. 8b illustrates a partial sectional view of the structure shown in FIG. 8a. Capillary tubing, or the restrictor 42, shares and extends between the lumens of the delivery catheter 70 and the tubing section 72. Adhesive may be used to fix the relative positions of the delivery catheter 70, tubing section 72, and the restrictor 42. The restrictor 42 is preferably formed from a relatively short length of tubing (e.g., 0.1 cm-3.0 cm) of a prescribed inner diameter (e.g., 10 microns, 15 microns, 20 microns, 25 microns, 30 microns). The restrictor 42 may be fabricated from of a variety of medical grade materials, including silica. Furthermore, it is preferred that a proximal end of the restrictor 42 be treated with trimethychlorosilane or a functionally similar substance.
 The concerns of particle control are not limited to the pump 20 of the present invention. Accordingly, the multi-stage filtration system 38 is suitable and particularly applicable to any implantable infusion pump or like device.
 At the site of implantation, modern implantable infusion pumps are sutured to nearby tissue to insure their desired placement. Conventional implantable infusion pumps include three or four suture rings (i.e., eyelets), formed of metal or the like, fixed to a side-surface of the respective housings. The suture rings are equally spaced about the housings' perimeter. While suture rings typically offer a suitable means in which to secure an implantable pump, their circumferential placement often constrains pump/suture placement. Accordingly, it is perceived that a need exists for a structure that allows a physician to readily place a suture at largely any position about the pump.
FIG. 9 illustrates an elastomer-reinforced boot 80 in accordance with one aspect of the present invention. The boot 80 has an interior surface 83 that receives the pump 20 and specifically the upper wall portion 24 of the housing 22. The lip 84 of the boot 80 functions to contact the upper-most part of the upper wall portion 24 and insure that the boot 80 is properly positioned relative to the pump 20. Although the boot 80 could function without the lip 84 or the lip 84 could be arranged as to alternatively contact the lower wall portion 26, it is preferred that the lip 84 be configured in accordance with that illustrated in FIGS. 9 and 12. The boot 80 can be fixed to the pump 20 using an adhesive, friction, mechanical fasteners, or the like.
 A suture pad 82 extends substantially about the circumference of the boot 80. While the boot 80 is preferably fabricated from a medical grade elastomer, e.g., silicone rubber, silicone rubber cannot alone resist normal forces and stresses concentrated at the sutures sites. Accordingly, a reinforcing material 82 a is embedded within the boot 80 (FIG. 10).
 In a preferred embodiment, the reinforcing material 82 a is a polyester mesh, but it should be understood that the reinforcing material 82 a could also be a metal mesh, fabric, or the like. Notwithstanding the “open” structure of these examples, the reinforcing material 82 a is preferably encapsulated within the elastomer material of the boot 80 to prevent the in-growth of tissue in the reinforcing material 82 a. Otherwise, if the reinforcing material 82 a is exposed, tissue can grow in and about such a structure, which could make any pump revision (i.e., replacement) unnecessarily complicated and more traumatic to the surrounding tissue.
 While the reinforcing material 82 a may certainly be used throughout the entire structure of the boot 80, it is satisfactory and more convenient for fabrication to incorporate the reinforcing material 82 a only in the suture pad 82. Moreover, although the suture pad 82 can assume an inclined form (i.e., forming a truncated conical form), embedding the reinforcing material 82 a can be more consistently achieved when the suture pad 82 remains substantially flat. The reinforcing material 82 a spans continuously (or substantially continuously) about the circumference of the boot 80, thus providing the greatest potential for desirable suture placement.
 The illustrated embodiment of the boot 80 includes a bolus port receptacle 86 adapted to receive a bolus port 90. As illustrated in FIG. 11, the bolus port 90 is constructed in a manner generally consistent with the refill port (i.e., inlet conduit 32) of the pump 20. The bolus port 90 is defined by a needle stop 92 a that includes at least one aperture 92 b. The needle stop 92 a is formed from a hardened material, e.g., stainless steel, titanium, etc. The needle stop 92 a receives and holds a resilient material 92 c, which serves to effectively stop a needle (not shown) that is inserted through the septum 94 and avoid damage through its contact with the lowest portion of the needle stop 92 a. A retaining structure 92 d holds the septum 94 relative to the needle stop 92 a. The bolus port 90 is secured within the bolus port receptacle 86 using adhesive, friction, mechanical fasteners, or the like.
 While not critical to the invention, the septum 94 and the resilient material 92 c are intended to occupy a significant majority of the volume defined by the needle stop 92 a. If this configuration is adopted, this arrangement: (i) minimizes a potential fluid volume within the bolus port 90 and (ii) creates a “keyed” space 96 that can only be accessed by a special needle that has a discharge aperture alignable with the space 96.
 The bolus port receptacle 86 of the boot 80 is positioned between, and is in fluid communication with, an inlet 86 a and an outlet 86 b. A groove 86 c is formed in and follows at least a portion of the perimeter of the bolus port receptacle 86. It is preferred that the groove 86 c be aligned with the inlet 86 a and the outlet 86 b, thereby creating a continuous flow path. The groove 86 c may be formed about 360° of the interior surface of the receptacle 86 with one aperture 92 b formed in the needle stop 92 a. Alternatively, the groove 86 c may be formed about only 180° of the interior surface of the receptacle 86 with two oppositely positioned apertures 92 b formed in the needle stop 92 a (FIGS. 10 and 11). Alternatively, to further minimize the potential volume of the groove 86 c, the groove 86 c may be formed about only 90° of the interior surface of the receptacle 86 with at least two apertures 92 b formed in the needle stop 92 a. Notwithstanding, for each of the above options, it is possible to have only a single aperture 92 b between the bolus port 90 and the groove 86 c so as to prevent the possibility of infusate (from the fluid chamber 30) flowing through the bolus port 90.
 The bolus port receptacle 86 is connected to the output from pump 20 via a tubing extension 98. The tubing extension 98 extends between the connector 40 and the inlet 86 a and is held in place by adhesive, friction, mechanical fasteners, or the like.
 While the boot 80 described and illustrated includes a bolus port receptacle 86, it is should be understood that inclusion of the bolus port receptacle 86 is not a requirement of the present invention but an option. Rather, if a bolus port is believed to not be needed for a particular application, the boot 80 can be formed without the receptacle 86. For this configuration, the delivery catheter 70 would be connected directly to the connector 40. Also, it should be further understood that the boot 80 may serve as a medium to collectively arrange a pump and, for example, a bolus port; however, other means or structure other than the suture pad 82 could be provided to enable the assembly to be secured within an implantation site.
 While not shown, it should be further appreciated that as an alternative to the boot 80 receiving the pump 20 within an interior surface 83 of the boot 80, at least the suture pad 82 of the boot 80 could be integrated between upper and lower halves of the pump 20.
 It will be appreciated that the drug infusion site must be considered in the design of the infusion pump. For example, if the catheter must deliver an infusate into the relatively high pressure of the arterial system, a pump pressure will need to be greater to maintain the same error limits that can be obtained when delivering infusate for other operative purposes, e.g., intravenously, intraperitoneally.
 Moreover, although preferred embodiments of the present inventions have been described above, it will be appreciated that other pressure compensating mechanisms in accordance with the principles of the present invention might be utilized. In particular, other constant force spring arrangements might be utilized as an infusate drive source.
 It is to be understood that even though the above numerous characteristics and advantages of the invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principle of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
 Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.