Abstract:
An improved implantable valve accumulator pump for the delivery of medication is disclosed. The implantable pump comprises a pressurized drug reservoir. The medication metering assembly comprises a fixed volume accumulator positioned between a pair of valves. The valves alternately open and close to admit medication from the reservoir into the accumulator and to dispense a precise volume pulse to an outlet catheter. In order to improve the pump&#39;s accuracy and to increase pumping volume while optimizing the pump&#39;s overall size and energy usage a two way diaphragm accumulator is used. The unit can be externally programmed or can be used in a fixed rate configuration that is never programmed but set at the factory or in the current programmable configuration.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 11/906,826 (issuing as U.S. Pat. No. 8,273,058), filed Oct. 4, 2007, the entire contents of both of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    This invention is a direct improvement over the technology of U.S. Pat. Nos. 4,838,887 and 5,049,141, the disclosures of which are hereby incorporated by reference. U.S. Pat. Nos. &#39;887 and &#39;141 describe a programmable valve pump overcoming many of the problems of the prior art employing an accumulator with a diaphragm that deflects in one direction when filling with medication and returning to a non-deflected state when emptying the accumulator. This is demonstrated in  FIG. 2A  of each of these patents. In each case, initial “pumping” is provided by the reservoir which is used to fill the accumulator to its fixed volume. A pressure which is intermediate between the reservoir and the outlet is maintained behind the accumulator so that it fills and empties completely and rapidly. The accumulator is alternately filled and emptied by the alternate switching of the valves. The rate of switching governs the rate of pumping and thus the delivery rate. 
         [0003]    Switching is accomplished by onboard electronics powered by an internal battery. Once the battery is depleted, or if the battery is rechargeable and it cannot be recharged to an operational level, such devices need to be explanted and replaced with a new device. Extending the life of the pump through energy efficiency is critical in the design of such devices. Energy efficiency can be achieved by increasing the fixed volume pumped. Increasing the volume pumped can be achieved by increasing the size of the accumulator in diameter and/or height. However, increased accumulator size can create performance degradation of the existing designs. For example, a higher accumulator requires the accumulator diaphragm to deflect further. This increase in deflection creates a corresponding increase in diaphragm spring force. This in turn would have a cascading effect on design including the need to increase the intermediate accumulator and reservoir pressures and to increase the robustness of the pumps design and materials due to the increased pressure. These changes would adversely affect the size and weight of the implant, which by design, should be as small and light as practicable and would also adversely affect manufacturing costs and efficiencies. They would also adversely affect the filling pressure of the pump, would require the diaphragm to be prohibitively thin, making it hard to manufacture and to meet the life expectancy requirement for such a device. In addition, a one-way accumulator limits the maximum pulse size of drug delivery. 
         [0004]    An object of this invention is to affect energy efficiency, increase fixed volume pumping and pump performance through a new accumulator design while minimizing the aforesaid adverse effects. The new design employs a “Two Way Diaphragm” that deflects in two directions. 
       SUMMARY 
       [0005]    The problems of the prior art have been overcome by the present invention, which provides an infusion apparatus comprising a metering assembly that includes a valve accumulator pump, the infusion apparatus being implantable into a living body. More specifically, the invention relates to an infusion apparatus and to a metering assembly including a valve accumulator device for such apparatus that delivers precise amounts of medication or other fluid at programmed rates. The valve accumulator pump comprises two valves in fluid communication with a fixed volume accumulator. The valves alternately open and close to admit medication from an infusate reservoir into the accumulator and to dispense a precise volume pulse to an outlet catheter or the like. In order to improve the accuracy of the pump and to increase pumping volume while optimizing the overall size and energy usage of the pump, a two-way diaphragm accumulator is used. 
         [0006]    In certain embodiments, the accumulator includes a chamber housing a diaphragm. The diaphragm provides a barrier between a gas portion of the chamber, and a liquid (infusate) portion of the chamber. When the chamber is devoid of liquid (e.g., the infusate has been discharged), the diaphragm is in a resting position. Upon opening the inlet valve, infusate under pressure enters the fluid portion of the chamber and urges the diaphragm against the bias of the gas in a first (e.g., upward) direction to fill the chamber with infusate. The inlet valve is then closed, and upon opening the outlet valve, the gas urges the diaphragm in a second (e. g., downward) direction, forcing the infusate out of the chamber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary aspects of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention. 
           [0008]      FIG. 1  is a schematic diagram of an infusion device in accordance with certain embodiments of the present invention; 
           [0009]      FIG. 2  is a schematic diagram of a having a two way diaphragm in accordance with certain embodiments of the present invention; 
           [0010]      FIG. 3  is a top view of a spacer plate in accordance with certain embodiments of the present invention; 
           [0011]      FIG. 4  is a cross-sectional view of an accumulator in accordance with certain embodiments of the present invention; and 
           [0012]      FIG. 5  is an exploded perspective view of an accumulator in accordance with certain embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    As seen in  FIG. 1 , the infusion apparatus of the present invention includes a metering assembly having a programmable valve accumulator pump  30 , an infusate reservoir  10  that can be conventional and well-known in the art, and an external programmer  34 . Those skilled in the art will appreciate that an external programmer is not necessary; for example, the device could be used in a fixed rate configuration that is never programmed but is preset. The reservoir  10  is a sealed housing  14  that contains bellows  16  that includes an internal volume that contains the medicament or other fluid to be infused. The reservoir is preferably rechargeable such as via septum  12 . External of the bellow is a chamber  20  that contains a fluid, such as a two-phase fluid having a significant vapor pressure at normal body pressure so that it compresses the bellows and causes the fluid in the bellows to exit the outlet of the housing  14 . The outlet communicates with the metering assembly, such as via a bacterial filter  24 , the metering assembly generally comprising an accumulator  30  and an inlet valve  26  and an outlet valve  28  in fluid isolation from the inlet valve. Preferably the metering assembly is electronically controlled in accordance with convention. 
         [0014]    Turning now to  FIGS. 4 and 5 , accumulator  30  is shown. The accumulator  30  includes a housing  50 , that together with cap  51  defines a sealed gas chamber  52 . The cap  51  is attached to the housing  50  by any suitable means, such as laser welding. A suitable gas is sealed, under positive pressure, in the gas chamber  52 . The gas chamber  52  is in fluid communication with diaphragm chamber  57  via a port  55  in the housing  50 . The bottom surface of the housing  50  is configured and positioned to serve as a mechanical stop for the diaphragm  50  when the diaphragm  50  is in the up (fill) position. 
         [0015]    Affixed to the housing  50  is a faceplate  56 . Preferably the edges of the diaphragm  40  are sandwiched between the housing  50  and faceplate  57  as shown, and the assembly is sealed, such as by laser welding. The volume between the housing  50  and faceplate  57 , containing the diaphragm  40 , defines the diaphragm chamber  57 . The diaphragm  40  thus provides a barrier, separating the gas side (e.g., above the diaphragm) from the fluid side (e.g., below the diaphragm) in the accumulator  30 . Faceplate  56  also includes a fluid inlet port  58  that provides fluid communication between inlet valve  26  and the diaphragm chamber  57 , and fluid outlet port  59  that provides fluid communication between outlet valve  28  and the diaphragm chamber  57 . 
         [0016]    Turning now to  FIG. 2 , the operation of the accumulator assembly is shown schematically. A normally closed inlet valve  26  is in fluid communication with the inlet port  58  of the accumulator  30  (and the outlet of the reservoir  10  via line  22 ). A normally closed outlet valve  28  is in fluid communication with the outlet port  59  of the accumulator  30 . Miniature solenoid valves are suitable. Preferably the valves  26 ,  28  are controlled electronically, such as through a module programmed by an external programmer  34  ( FIG. 1 ). The outlet of the accumulator  30  communicates with a catheter or the like via line  36  that delivers the infusate to the delivery site in the patient in a conventional manner. 
         [0017]    The diaphragm  40 , as illustrated in  FIGS. 2 and 4 , is a circular disk of a thin metal sheet. Preferably titanium may be used, although other materials also may be suitable as determined by those skilled in the art. The disk is selected to have a diameter and thickness of low spring rate over the desired range of deflection. Thus, the diaphragm acts as a compliant, flexible wall which separates fluid from the environment behind it. The upward and downward motions of the diaphragm  40  are limited by the bottom surface of the housing  50 , and the top surface of the faceplate  56 , each of which serves as a mechanical stop for the diaphragm, depending on whether the diaphragm chamber  57  is filled with infusate or is empty of infusate. Thus, these surfaces are provided with a shallow concave profile manufactured into its diaphragm contact surface. This surface acts as a contour stop for the diaphragm. Dimensions of the contour are chosen to match the general profile of the diaphragm when it is deflected or biased by a predetermined fixed volume. This predetermined fixed volume is the volume desired to be metered from the accumulator (e.g., 2 μl) 
         [0018]    Deflection of the diaphragm  40  occurs in both the upward and downward direction. The fixed volume pumped is essentially twice that pumped by a diaphragm of the same size that is only deflected in one direction in the same accumulator package configuration. Thus, the Two Way Diaphragm permits the optimization of accumulator size and energy utilization to increase fixed volume pumping and to conserve battery energy. The first step in the  FIG. 2  pumping cycle shows the accumulator  30  in a state where both the inlet valve  26  and the outlet valve  28  are closed, and the diaphragm chamber  57  of the accumulator is empty (i.e., devoid of infusate fluid). In this condition, preferably the diaphragm  40  is firmly held against the spacer  70  by the gas and is substantially flat; it is not being urged or deflected in either an upward or downward direction (it is noted that the accumulator pressure is generally less than the reservoir pressure and diaphragm spring force and greater than the catheter outlet pressure). The second step in the cycle shows the accumulator  30  after the inlet valve  26  has been opened (maintaining the outlet valve  28  closed). The infusate fluid overcomes the bias of the pressurized gas against the diaphragm  40 , and deflects the diaphragm  40  upward, thereby filling the diaphragm chamber  57  with fluid from the reservoir  10 . The third step in the cycle is the closing of the inlet valve  26  once the diaphragm chamber  57  has been filled to its fixed or desired volume. The fourth step in the cycle is the opening of the outlet valve  28  (while maintaining the inlet valve  26  in the closed position) to empty the diaphragm chamber  57  through the catheter  36 , wherein the diaphragm  40  deflects downward as a result of the bias from the gas pressure in the gas chamber  52  and in the gas side of the diaphragm chamber  57 . Accordingly, the diaphragm  40  deflects in a first direction during the filling operation of the accumulator  30 , as infusate fluid under pressure forces the diaphragm upwards against the mechanical stop of the bottom surface of the housing  50 , overcoming the pressure exerted by the gas in the accumulator. The diaphragm also deflects in a second direction during the emptying of the accumulator  30 , past its flat, resting point position, as the pressurized gas in the accumulator forces the diaphragm downward against the mechanical stop of the top surface of the faceplate  56 . The two-way deflection allows twice the volume to be delivered during a single pumping cycle compared to conventional designs, using the substantially same amount of energy. Preferably the first and second directions of deflection of the diaphragm are opposite directions. The accumulator  30  thus stores and discharges predetermined volume spikes of infusate at a frequency defined by the cycling rate of the inlet and outlet valves. 
         [0019]    Since the metering assembly controls the flow of fluid from the reservoir and does not rely on constant pressure to initiate flow, although a two-phase liquid can be used in the reservoir, a one-phase gas is suitable as well. Suitable gasses include inert gases such as argon, helium and nitrogen, mixtures thereof, and air. 
         [0020]      FIGS. 5A and 5B  of the &#39;887 patent illustrate the details of the spacer plate utilized between the medication accumulation chamber and the accumulator valves. As disclosed in the &#39;887 patent, the continuous contoured surface desirable to use on the gas-filled side of the diaphragm is undesirable on the fluid side. Intimate contact of two relatively flat surfaces with a liquid interface will create flow restrictions when the accumulator is emptied as the plates move toward each other and during filling when the plates move away from each other. This adverse effect was designed to be overcome by the addition of a checkerboard groove pattern as illustrated in  FIG. 5B  of the &#39;887 patent. Additionally, a circumferential groove was incorporated in the design to establish fluid communication between the inlet and the outlet valves. Objects of the design were to: permit complete free flow of fluid underneath the flattened diaphragm; assist in washing of areas which might otherwise remain stagnant, and; maintain the accumulator dead volume at a minimum level. 
         [0021]    U.S. Pat. No. 5,049,141 introduced an improved spacer plate design as illustrated in  FIGS. 5A and 5B  of that patent, the purpose of which was to reduce the diaphragm contact area with the plate. It was found that the prior art&#39;s use of a checkerboard groove provided too much surface contact area and therefore large molecule drugs could be crushed at the plate and diaphragm contact points resulting in the creation of drug residue. The prior art checkerboard design also created areas where the drug could stagnate and particles and air bubbles could be trapped. The &#39;141 patent introduced an improved spacer plate design utilizing concentric circumferential grooves to establish fluid communication between the inlet and outlet valves and for fluid communication with the trough and a design that would reduce the diaphragm and plate contact area. 
         [0022]    The spacer  70  in accordance with certain embodiments of the present invention improves upon the prior art with a design that maximizes the wash out of fluid and minimizes dead volume. Channels in the spacer are designed to create a flow path that allows the fluid to exit the accumulator quickly (e. g., the channel flow restriction is kept large enough to allow the accumulator to empty in a short period of time). It was found that the multiple annular grooves of the prior art provided multiple sites for stagnant fluid and air encapsulation resulting in dead volume and a degradation of pumping accuracy. As seen in  FIGS. 3 and 5 , the spacer  70  of the present invention includes an annular groove  54  intersected by (and thereby in fluid communication with) a trough  53  connecting the inlet and outlet valves wherein the volume of the space created by the annular and trough grooves permits the dead volume in the grooves and outlets to be equal to or less than about 5% of the total volume discharged by the accumulator. Preferably only a single annular groove  54  is provided, and it is interior to the inlet and outlet apertures respectively communicating with the inlet and outlet valves, such that the diameter of the annular groove  54  is smaller than the length of the trough  53 . The groove  54  thus provides an annular flow path, and the trough  53  provides a lateral flow path between the inlet and outlet of the accumulator. Fluid in the groove  54  thus communicates with the inlet and outlet of the accumulator only through communication with the trough  53 . The remaining peripheral surface of the space plate  50  is preferably flat. The new design flow path configuration and placement also allows for the fluid to flow out of the accumulator without adversely affecting the empty time.