Abstract:
A programmable implantable pump is disclosed. The pump includes an implantable pump and a hermetically sealed module. The module provides for varying flow rates of fluid being dispensed from the pump or may provide for a constant flow rate of such fluid. In the case of varying flow rate capabilities, the module preferably includes one or more sensors to determine information relating to the pressure of the fluid, electronics for analyzing the pressure information and determining the flow rate of the fluid, and a mechanism for physically altering the flow rate. Methods of dispensing a medicament to a patient utilizing such a system are also disclosed, as are variations of the pump system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 13/338,673, filed Dec. 28, 2011, the disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to implantable devices, more particularly, programmable implantable pumps allowing for variable flow rates in delivering medication or other fluid to a selected site in the body of a patient. 
         [0003]    Implantable pumps have been well known and widely utilized for many years. Typically, pumps of this type are implanted into patients who require the delivery of active substances or medication fluids to specific areas of their body. For example, patients that are experiencing severe pain may require pain killers daily or multiple times per day. Absent the use of an implantable pump or the like, a patient of this type would be subject to one or more painful injections of such medication fluids. In the case of pain associated with more remote areas of the body, such as the spine, these injections may be extremely difficult to administer and particularly painful for the patient. In certain instances, proper application of such medication may be impossible. Furthermore, attempting to treat conditions such as this through oral or intravascular administration of medication often requires higher doses of medication and may cause severe side effects. Therefore, it is widely recognized that utilizing an implantable pump may be beneficial to both a patient and a treating physician. 
         [0004]    Many implantable pump designs have been proposed. For example, commonly invented U.S. Pat. No. 4,969,873 (“the &#39;873 patent”), the disclosure of which is hereby incorporated by reference herein, teaches one such design. The &#39;873 patent is an example of a constant flow pump, which typically includes a housing having two chambers, a first chamber for holding a specific medication fluid to be administered and a second chamber for holding a propellant. A flexible membrane preferably separates the two chambers such that expansion of the propellant in the second chamber pushes the medication fluid out of the first chamber. It is to be understood that the propellant typically expands under normal body temperature. This type of pump also typically includes an outlet opening connected to a catheter for directing the medication fluid to the desired area of the body, a replenishment opening for allowing for refill of the medication fluid into the first chamber and a bolus opening for allowing the direct introduction of a substance through the catheter without introduction into the first chamber. Both the replenishment opening and the bolus opening are typically covered by a septum that allows a needle or similar device to be passed through it, but which properly seals the opening upon removal of the device. As pumps of this type provide a constant flow of medication fluid to the specific area of the body, they must be refilled periodically with the proper concentration of medication fluids suited for extended release. 
         [0005]    Although clearly beneficial to patients and doctors that utilize them, constant flow pumps generally have one major problem, i.e., that only a single flow rate can be achieved from the pump. Thus, implantable pumps have also been developed, which allow for variable flow rates of medication therefrom. These pumps are typically referred to as programmable pumps, and have exhibited many different types of designs. For instance, in a solenoid pump, the flow rate of medication fluid can be controlled by changing the stroke rate of the pump. In a peristaltic pump, the flow rate can be controlled by changing the roller velocity of the pump. Likewise, pumps of the constant flow type have been modified to allow for a variable and programmable flow rate. For instance, commonly owned U.S. Pat. No. 7,637,892 (“the &#39;892 patent”) teaches such a design. The &#39;892 patent, as well as related U.S. patent application Ser. Nos. 11/125,586; 11/126,101; and 11/157,437 are each incorporated herein by reference. In each case, the benefit of providing variable flow is at the forefront, so that differing levels of medication can be delivered to the patient at different times. 
         [0006]    In the &#39;892 patent, a constant flow-type pump assembly is modified to include a module that converts the constant flow pump into a programmable pump. That control module includes, inter alia, two pressure sensors, a constant flow capillary, and a valve assembly. The pressure centers are utilized to measure pressure directly from a medication chamber, and pressure just prior to entering the valve assembly. These pressure readings are utilized by a computing unit, which in turn causes a motor to operate the valve assembly to allow lesser or greater flow from the pump. The capillary preferably ensures that a maximum flow rate can only be achieved from the pump. The pump taught in the &#39;892 patent is indeed a useful programmable pump, but one which may be improved. 
         [0007]    One area in which the pump taught in the &#39;892 patent, as well as pumps taught in other prior art references, can be improved is in allowing for finer adjustment of flow rate from the pump, which is often difficult or impossible. For instance, a pump of the type taught in the &#39;892 patent may exhibit a nonlinear relationship between movement of the valve and actual flow rate from the pump, which can lead to small changes in valve position resulting in major changes in flow. Of course, a more preferable valve distance and flow relationship would be of the linear type, where the distance is gradually related to the flow rate. Another area in which prior art programmable pumps can be improved is in the sealing of certain components from the body environment in which the pump is implanted. This may be particularly important in ensuring constant operation of the pump, as well as in ensuring the safety of the patient. 
         [0008]    Therefore, there exists a need for an improved programmable implantable pump design. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    A first aspect of the present invention is a programmable pump for dispensing a fluid at varying flow rates to a patient including a constant flow module including a first chamber housing the fluid, a first opening in fluid communication with the first chamber and a second opening in fluid communication with a catheter and a hermetically sealed control module attached to the constant flow module and including a motor assembly and valve block, the valve block being in fluid communication with the first and second openings, the motor assembly having a stepper motor, a valve connected with the stepper motor, and a bellows surrounding a portion of the valve. The flow rate of the fluid dispelled from the active substance chamber is preferably affected by varying positioning of the valve. 
         [0010]    In other embodiments of the first aspect the bellows may surround the portion of the valve in all positions of the valve. The bellows may be tubular and of varying length. The valve may include a valve bushing and a valve stem extending through the valve bushing and having a tapered end. The motor assembly may further include an o-ring surrounding the valve bushing. The constant flow module may further includes a second chamber separated from the active substance chamber by a first flexible membrane. The second chamber may be filled with a propellant that acts upon the flexible membrane to push the fluid from the first chamber through first opening. During operation of the pump, fluid dispelled from the first chamber passes through the first opening, through into the valve block, into contact with the valve, out of the valve block, into the second opening and through the catheter. The control module may further include a first pressure sensor for monitoring the pressure of the fluid in the first chamber and a second pressure sensor for monitoring the pressure of the fluid in the valve block. The constant flow module may further include a fixed flow resistor. The fixed flow resistor includes a filter and a capillary, and fluid dispelled from the first chamber passes through the fixed flow resistor prior to passing through the first opening. An enclosure top may be attached to the constant flow module and covering the control module. The control module may further include a processor for determining operation of the motor. The pump may further include a circumferentially wrapped antenna extending around a perimeter of the constant flow module that is in communication with the processor. The control module may further include a positioning sensor capable of determining the positioning of the valve. The catheter may include a portion fixed to the constant flow module. A union nut may be screwed to the constant flow module and holding the control module to the constant flow module. A gasket may be held between the constant flow module and control module. The control module may further include first and second pressure sensors, first and second batteries, a circuit board, and a buzzer. The first and second pressure sensors, first and second batteries, circuit board, buzzer and stepper motor may be electrically connected to each other via a flexible conductive element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    For more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
           [0012]      FIG. 1  is a perspective view of a programmable implantable pump in accordance with one embodiment of the present invention. 
           [0013]      FIG. 2  is a top view of the programmable implantable pump shown in  FIG. 1 . 
           [0014]      FIG. 3  is a bottom view of the implantable programmable pump shown in  FIG. 1 . 
           [0015]      FIG. 4  is a right side view of the programmable implantable pump shown in  FIG. 1 . 
           [0016]      FIG. 5  is a left side view of the programmable implantable pump shown in  FIG. 1 . 
           [0017]      FIG. 6  is a rear view of the programmable implantable pump shown in  FIG. 1 . 
           [0018]      FIG. 7  is a front view of the programmable implantable pump shown in  FIG. 1 . 
           [0019]      FIG. 8  is a perspective view of the implantable programmable pump shown in  FIG. 1  with an enclosure top removed therefrom. 
           [0020]      FIG. 9  is a perspective view of a constant flow module assembly of the programmable implantable pump shown in  FIG. 1 . 
           [0021]      FIG. 10  is a top view of the constant flow module assembly shown in  FIG. 9 . 
           [0022]      FIG. 11  is cross-sectional view of the constant flow module assembly taken along line AA of  FIG. 10 . 
           [0023]      FIG. 12  is a perspective view of a control module assembly of the programmable implantable pump shown in  FIG. 1 . 
           [0024]      FIG. 13  is a top view of the control module assembly shown in  FIG. 12 . 
           [0025]      FIG. 14  is a bottom view of the control module assembly shown in  FIG. 12 . 
           [0026]      FIG. 15  is a perspective view of the control module assembly shown in  FIG. 12 , with a titanium enclosure top removed therefrom. 
           [0027]      FIG. 16  is another perspective view similar to that shown in  FIG. 15 . 
           [0028]      FIG. 17  is a top view of the control module assembly shown in  FIGS. 15 and 16 . 
           [0029]      FIG. 18  is another view of the control module assembly shown in  FIGS. 15-17 , with an additional portion removed therefrom. 
           [0030]      FIG. 19  is a top view of the control module assembly shown in  FIG. 18 , with a further additional portion removed therefrom. 
           [0031]      FIG. 20  is a top view of the control module assembly shown in  FIG. 19 , with an even further additional portion removed therefrom. 
           [0032]      FIG. 21  is a top view of a motor and valve block assembly included in the control module assembly shown in  FIG. 12 . 
           [0033]      FIG. 22  is a top view of a motor, bushing, and valve assembly included in the construct shown in  FIG. 21 . 
           [0034]      FIG. 23  is a top view of the assembly shown in  FIG. 22  with the bellows removed therefrom. 
           [0035]      FIG. 24  is a view similar to that of  FIG. 23 , with a stem bushing construct removed therefrom. 
           [0036]      FIG. 25  is a top view of the valve block depicted in  FIG. 21 . 
           [0037]      FIG. 26  is a left side view of the valve block shown in  FIG. 25 . 
           [0038]      FIG. 27  is a bottom view of the valve block shown in  FIG. 25 . 
           [0039]      FIG. 28  is a view similar to that shown in  FIG. 21 , with the valve block shown in phantom. 
           [0040]      FIG. 29  is a cross-sectional view taken along line BB of  FIG. 26 . 
           [0041]      FIG. 30  is a perspective view of union nut included in the pump shown in  FIG. 1 . 
           [0042]      FIG. 31  is a top view of an alternate embodiment constant flow module. 
           [0043]      FIG. 32  is a top perspective view of the constant flow module shown in  FIG. 31 . 
           [0044]      FIG. 33  is a side cross-sectional view of the constant flow module shown in  FIG. 31 . 
           [0045]      FIG. 34  is a top perspective view of an alternate embodiment control module assembly, with a titanium enclosure top removed therefrom. 
           [0046]      FIG. 35  is another top perspective view of the control module assembly shown in  FIG. 34 , with a titanium enclosure and circuit board removed therefrom. 
           [0047]      FIG. 36  is an exploded view of an alternate embodiment motor and valve block assembly included in the control module assembly shown in  FIG. 34 . 
           [0048]      FIG. 37  is another exploded view of the motor and valve block assembly shown in  FIG. 34 , with certain portions removed therefrom. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    In describing the preferred embodiments of the subject matter illustrated and to be described with respect to the drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to any specific terms used herein, and it is to be understood that each specific term includes all technical equivalents which operate in a similar matter to accomplish a similar purpose. 
         [0050]    Referring to the drawings, wherein like reference numerals refer to like elements, there is shown in  FIGS. 1-7  a programmable implantable pump designated generally by reference numeral  10 . As shown in those figures, pump  10  includes a constant flow module assembly  12  (shown alone in  FIGS. 9-11 ), an enclosure top  14 , and a union nut  16  (shown alone in  FIG. 30 ). Moreover, as best shown in  FIG. 8 , where enclosure top  14  has been removed, pump  10  includes a control module assembly  18  engaged with the top portion of constant flow module  12 . 
         [0051]    In constructing pump  10 , control module assembly  18  is placed on top of constant flow module assembly  12 , and union nut  16  is threaded onto a threaded portion  20  of the constant flow module (best shown in  FIGS. 9-11 ). A flange  22  formed on control module assembly  18  (best shown in  FIGS. 12 and 13 ) allows for the control module assembly to be captured by the union nut  16  and thusly fixably attached to constant flow module assembly  12 . A gasket or the like (shown as element  50  in  FIGS. 9 and 10 ) may be placed between constant flow module  12  and control module assembly  18  so as to ensure a sealed fluid connection between the various corresponding ports of those two components (discussed more fully below). Finally, enclosure top  14  is preferably snapped over the construct to form pump  10  as shown in  FIGS. 1-7 . 
         [0052]    As is also shown in  FIGS. 1-7  (as well as other figures), pump  10  also includes suture apertures  24  and a fixed catheter  26 , both on the constant flow module assembly  12 . The former are useful in fixing pump  10  within a patient&#39;s body, while the latter is preferably connectable with a longer, and in some cases more flexible, catheter that extends further within the patient&#39;s body. Fixed catheter  26  preferably includes a strain relief  28  for reducing stresses and strains at or near the connection between catheter  26  and constant flow module assembly  12 . Such strain relief can be of any design as are known in the art, and in the embodiment shown, strain relief  28  is designed to slide over catheter  26  and connect with a portion of constant flow module  12 . 
         [0053]    The constant flow module operates in much of the same fashion as in previous pumps, including those taught in the aforementioned &#39;892 patent, as well as in other commonly owned patents such as U.S. Pat. Nos. 4,969,873, 5,085,656, 5,336,194, 5,836,915, 5,722,957, 5,814,019, 5,766,150 and 6,730,060, the disclosures of which are hereby incorporated by reference herein. Essentially, and as is shown more particularly in the cross-sectional view of  FIG. 11 , constant flow module assembly  12  includes a medication chamber  30  defined by an upper portion  32  of the constant flow module and a flexible membrane  34 , and a propellant chamber  36  defined by membrane  34  and a lower portion  38  of the constant flow module. Like in other pump designs, propellant chamber  36  may in actuality be defined as a propellant pillow consisting of membrane  34  and a lower membrane  34 A (not shown). As shown in  FIG. 11 , propellant chamber  36  is preferably filled utilizing a propellant pillow  37 , such as that taught U.S. Pat. No. 5,766,150 or U.S. patent application Ser. No. 12/947,187, the disclosures of which are hereby incorporated by reference herein. As is also shown in  FIG. 11 , upper portion  32  and lower portion  38  of the constant flow module assembly  12  are preferably screwed together, thereby capturing membrane  34  (and membrane  34 A) therebetween. Of course, in other embodiments, other connection means may be employed. 
         [0054]    As best shown in  FIGS. 9 and 10 , constant flow module assembly  12  further includes a catheter access opening  40  through which a portion (e.g., a shoulder shown as a portion of below-discussed gasket  50 )  42  of catheter  26  extends, a structure  44 , an exit  46 , and an entrance/exit  48 . More particularly, opening  40  acts to both allow direct injection of fluid through catheter  26  and to accept fluid dispelled from control module assembly  18  (as will be discussed more fully below). Structure  44  preferably aids in creating a sealable connection between constant flow module assembly  12  and control module assembly  18  by creating a symmetrical upper surface of assembly  12 , thereby evenly spreading compression of a gasket (discussed below) between the two assemblies. Second exit  46  provides fluid to control module assembly  18  to be routed through a valve assembly (also discussed more fully below). Entrance/exit  48  allows for both medication to be injected into chamber  30  and a pressure reading to be taken by a pressure sensor (also discussed more fully below). Assembly  12  also includes a notch  49 . 
         [0055]      FIGS. 9 and 10  also depict component gasket  50  and circumferential antenna  52 . With regard to the former, the gasket is shown as a thin circular portion of silicone or the like which acts to seal around the various openings in flow module assembly  12 . Likewise, circumferential antenna  52  is shown as a circular component that fits over threaded portion  20  of the constant flow module and on top of a shoulder formed in the module. This shoulder is better shown in  FIG. 11 . The antenna is particularly useful in receiving signals emitted from a secondary device during operation of the pump. Circumferential antenna  52  includes a tab  53  which extends into notch  49  so as to be capable of cooperating with control module assembly  18 , as will be discussed more fully below. Finally, constant flow module  12  also includes union pins  54   a  and  54   b  for engagement with control module  18 . 
         [0056]    Turning now to  FIGS. 12-14 , a fully constructed control module assembly  18  is depicted. The module includes two titanium outer portions, namely, upper portion  56  and lower portion  58 . above-discussed flange  22  is formed on lower portion  58 . A refill aperture  60  is formed through the center of upper portion  56 . A catheter access aperture  62  is formed offset from refill aperture  60 . As best shown in  FIG. 13 , refill aperture  60  allows for a needle to pierce a central septum  64 , while catheter access aperture  62  allows for a needle to engage screen member  66 . It is to be understood that screen member  66  is designed with a plurality of apertures that are sized so as to prevent needles having a certain size from extending therethrough. This allows for larger needles to be designated for a refill procedure (through central septum  64 ), while smaller needles are provided for catheter direct access. This is an added safety measure, that is discussed in application Ser. No. 13/276,469 entitled “Mesh Protection System,” and screen member  66  is similar to the like structure formed in that application. 
         [0057]      FIG. 14  depicts a view of lower portion  58  of module  18 . As shown, lower portion  58  includes several openings, including refill opening  70 , reception opening  72 , exit opening  74  and electronic access opening  76 . An alternate embodiment antenna assembly  77  is shown removed from within electronic access opening  76 , but with wires that attach the antenna to the module depicted. It is to be understood that pump  10  can utilize either antenna assembly depicted in the present application, both antenna assemblies, or an alternate assembly not shown herein. Moreover, union pin reception openings  78   a  and  78   b  are provided for receiving union pins,  54   a  and  54   b , respectively. Refill opening  70  serves two purposes, namely, allowing for fluid injected through refill aperture  60  to pass into chamber  30  through entrance/exit opening  48 , and allowing for access (as will be discussed below) to a pressure sensor disposed within module  18 . Reception opening  72  allows for fluid dispelled from exit  46  of constant flow module  12  to be introduced into a valve assembly disposed within module  18 . Exit opening  74  overlies opening  40  and shoulder  42  of constant flow module  12  in a fully assembled state. This allows for fluid ultimately dispelled from the valve assembly included within module  18  to flow through catheter  26 , and thusly to the patient. Finally, electronic access opening  76  provides a corridor for certain internal electronic structures discussed below to communicate with tab  53  of antenna  52 . 
         [0058]      FIGS. 15-17  depict module  18  with upper portion  56  removed therefrom. As shown, within its interior, module  18  includes a circuit board  80 , a first pressure sensor  82 , a second pressure sensor  84 , a valve block  86 , a motor assembly  88 , a buzzer  90 , and a flexible conductive element  92 .  FIGS. 16 and 17  depict similar views to  FIG. 15 , albeit from different perspectives. Circuit board  80  is held to a circuit board support  94 , which is better shown in  FIG. 18  where circuit board  80  is removed. Screws  96   a - 96   d  hold circuit board  80  to circuit board support  94 . Flexible conductive element  92  preferably provides electrical interconnection among circuit board  80 , first pressure sensor  82 , second pressure sensor  84 , motor assembly  88  and buzzer  90 . Module  18  further includes a feed through  98 , which is also preferably connected with flexible conductive element  92 , and which extends through electronic access opening  76  on the bottom of module  18 . This element preferably provides the interconnection of the internals of module  18  with antenna  52 , specifically tab  53 . 
         [0059]    As noted above,  FIG. 18  depicts the internals of module  18  with circuit board  80  removed therefrom. In this view, it is shown that module  18  also includes batteries  100   a  and  100   b  for powering the pump. Also shown, is the interconnection among flexible conductive element and flexible conductive element  92  and both batteries.  FIG. 19  shows the internal structure of module  18 , this time with circuit board support  94  removed therefrom. In this figure, the configuration and interconnection among the elements and flexible conductive element  92  are further depicted. In the embodiments shown, flexible conductive element is constructed of a polymide material, but can be any other conductive element, including wires or the like. Also more clearly shown in  FIGS. 18 and 19  is the connection between motor assembly  88  and lower portion  58 . Specifically, a set screw  102  is provided at one end of the motor assembly and threaded into a portion of lower portion  58 . Moreover,  FIG. 19  shows apertures  104   a - d , which are designed to accept screws  96   a - 96   d , respectively. Thus, circuit board is held tightly not only to circuit board support  94 , but also lower portion  58 . 
         [0060]      FIG. 20  depicts module  18  in a similar view to that of  FIG. 19 , but with flexible conductive element  92  and batteries  100   a  and  100   b  being removed therefrom. In this view, a capacitor  106  is shown. This component allows for the generation of higher voltage than batteries  100   a  and  100   b  themselves. In general, capacitor  106  operates like a standard capacitor, storing charge for use in powering the pump. It is to be understood that capacitor  106  could be removed depending upon the particular batteries that are utilized. For instance, batteries that generate higher voltages and less current typically will negate the need for a capacitor. However, batteries suitable for inclusion in module  18  tend to be produced in the lower voltage range (3.2V-3.8V). Moreover, smaller capacitors could be included on circuit board  80  to achieve the same goal as capacitor  106 . 
         [0061]    FIGS.  21  and  25 - 29  focus on valve block  86 , its internal components, and its cooperation with motor assembly  88 . As shown, valve block  86  includes a pressure sensor receiving aperture  106 , as well as catheter access aperture  62 . Pressure sensor receiving aperture  106  is designed to receive second pressure sensor  84 , as well as allow for fluid to come into contact with that pressure sensor. Valve block  86  also includes a first body portion  108  and a second body portion  110 . First body portion  108  includes apertures  62  and  106 , as well as several fluid passageways and a valve receiving channel (best shown in  FIG. 28 ) for allowing fluid flow within the valve block and ultimately to the patient. Second body portion  110  is essentially a hollow cylindrical body, the interior of which is designed to receive a portion of the valve. This again is best shown in  FIG. 28 , with  FIG. 26  depicting a front view of same. It is noted that valve block  86  is depicted by itself in  FIGS. 25-27 , with  FIG. 27  depicting a bottom surface thereof. As shown in that drawing, apertures  62   a  and  106   a  cooperate with the above discussed apertures  62  and  106 , respectively. 
         [0062]    As also shown in  FIG. 21 , motor assembly  88  is connected with valve block  86  by two screws  112   a  and  112   b , which extend through apertures in a flange portion  114  of the motor assembly, and into apertures  116   a  and  116   b , respectively, of the valve block (best shown in  FIG. 26 ). This cooperation fixably connects motor assembly  88  with valve body  86 . As noted above, motor assembly  88  is also connected to module  18  via set screw  102 . Likewise, valve block  86  is connected to other portions of module  18  via pin  118 , as best shown in  FIG. 26 . That pin preferably includes a bulbous head portion that, once inserted within a hole in module  18 , acts to prevents removal of the valve block. 
         [0063]      FIG. 22  depicts motor assembly  88  without valve body  86 , and highlights the portions of the assembly that extend into the valve body. Specifically, motor assembly  88  includes a bellows  120 , valve  122 , and an o-ring  124 . Bellows  120  is preferably welded to weld ring  126 , which in turn is welded to flange  114 . Likewise, bellows  120  is preferably welded to valve at surface  128 . Referring now to  FIG. 23 , in which bellows  120  is removed, it is shown that valve  122  consists of a valve stem  130  which extends through a valve bushing  132 . It is around this valve bushing that o ring  124  is disposed. Valve stem  130  includes at a distal end a tapered portion.  FIG. 24  on the other hand depicts the assembly with a motor housing  134  removed therefrom. In this view, weld ring  126  is clearly shown. Also shown is a motor mount plug  136  which screwably connects with motor housing  134 . 
         [0064]    Motor  89  of motor assembly  88  is preferably a piezoelectric motor, as such a motor does not include a permanent magnet, which makes the motor MRI compatible. In addition, piezoelectric motors are generally of a smaller size and require less energy for operation. Still further, piezoelectric motors operate in a straight line, which is ideal in the present instance, as will be discussed below. However, it is to be understood that motor  89  could be other types of motors, including stepper motors or the like. Of course, certain of the above-mentioned benefits of the piezoelectric motor may not be met by such alternate motor designs. Operation of motor  89  imparts a force upon valve stem  130 , which moves within second body portion  110  of valve block  86 . The combination of bellows  120  and o ring  124  insures that any fluid flowing within valve block  186  cannot seep outside of that component. In other words, bellows  120  and o-ring  124  insure a sealable connection between motor assembly  88  and valve block  86 . As is shown in  FIGS. 28 and 29 , the most distal portion of valve stem  130  extends within the fluid flow path, and the conical nature of that distal portion provides that movement of the valve stem results in greater or lesser fluid flow threw valve block  86 . The inclusion of a stepper motor such as the one discussed above insures that fine adjustments of flow rate through the valve block can be realized. In fact, movement of the valve relates in a linear or near linear fashion to the flow rate. The above-discussed sealable nature of bellows  120  and o ring  24  insures hermetic sealing within the valve block, and thusly prevents fluid from flowing anywhere other than the valve block. This is particularly important given the other components of module  18 . 
         [0065]    In the embodiment shown, valve stem  130  and valve portion  132  are shown as constructed of titanium material. It is to be understood that any suitable material may be employed. Moreover, it is to be understand that valve stem  130 , at its most distal end, could include a silicon covering or the like in order to insure a full closure of the valve if desired. Likewise, while o ring  124  as shown as being constructed of a silicon material, any other suitable material may be employed. For instance, Teflon may be employed, as can a material known as PORON®. 
         [0066]    In operation, fluid dispelled from chamber  30  (under pressure provided by chamber  36 ) travels through both exits  46  and  48 . The fluid dispelled through exit  48  is preferably directed into contact with first pressure sensor  82 , so a pressure reading of the fluid within chamber  30  can be taken. The fluid dispelled through exit  46  preferably first travels through a filter and capillary construction, as are known in the art. In one example of such a structure, a filter and capillary are coiled around an underside of upper portion  32 . Fluid flows through the filter, which is designed to prevent particulates and other undesirable matter of flowing into the capillary, and thereafter flows through the capillary, which is essentially a very small tube with a small diameter that allows a maximum flow rate of fluid therethrough. That fluid then flows through aperture  106   a  and into the passages provided in valve block  86 . Second pressure sensor  84  takes a pressure reading of the fluid within the valve block. 
         [0067]    Once within valve block  86 , the fluid flows into contact with the distal end of valve stem  130 . Depending upon the positioning of the valve stem, the flow of the fluid will either be reduced or remain the same as the maximum flow rate dictated by the aforementioned capillary. Second pressure sensor  84  is positioned to take a reading of the pressure before the valve portion, and thusly the comparison of the readings taken by first pressure sensor  82  and second pressure sensor  84  can be utilized to determine the actual flow rate of the fluid after passing through the resistor and the valve. This is preferably determined by circuit board  80 , as sensors  82  and  84  are electrically connected thereto by flexible conductive element  92 . If the flow rate is not desired, motor  89  can be operated to vary the position of valve stem  130 . Subsequent to contacting the valve, fluid flows through other passages formed in valve block  86 , through aperture  62   a  and ultimately through catheter  26 . Depending upon the placement of the catheter within the patient, the fluid is delivered to the desired portion of the patient in which the catheter is directed. 
         [0068]    It is to be understood that pump  10  preferably operates with little outside interaction required. Aside from refilling chamber  30  with an active substance, a doctor or other medical professional likely only needs to interact with the pump in order to set a desired flow rate. This may be accomplished through the use of a wand or other transmitter/receiver (not shown) that interfaces with antenna  92 . Once the flow rate is set, pump  10  preferably operates on its own to maintain the flow rate. Pump  10  may also be programmed to provide different flow rates at different times of the day. For instance, patients may require lesser doses of medication while sleeping, and heavier doses of medication upon waking up. Circuit board  80  can be designed to allow for such programming. Above-noted buzzer  90  is designed to emit an audible warning upon certain conditions, including low battery, low fluid level within chamber  30 , low or high temperature conditions, and high pressure, which may indicate overfilling of chamber  30 , low pressure differential across the resistor capillary or blockage within catheter  26 . Upon recognizing the audible sound, the patient can contact his or her medical professional. 
         [0069]    Valve  122  may also include a positioning sensor (not shown) or the like associated therewith. Such a sensor may be capable of providing information relating to the positioning of the valve to circuit board  80 . Such positioning sensors can include many different designs. For example, light reflective technology can be employed to determine at any given moment the position of the valve. Likewise, valve  122  may be provided with one or more conductive elements that interact with conductive elements provided on or near valve block  86 . The completion of an electrical circuit in such a case can indicate the positioning of valve  122 . Still further, the positioning sensor can take the form of an induction coil capable of determining the positioning of the valve therein. A slide potentiometer may also be employed, as can a stack switch. 
         [0070]    During a refill procedure, pump  10  can be monitored through the use of the wand or other transmitter/receiver. A computer program associated with such device and pump  10  can indicate to the doctor whether the refill needle is correctly placed within the pump. Known problems with refilling implantable pumps are misapplications of a refill needle to the tissue of the patient (so called pocket fills) and to a bolus opening such as catheter access aperture  62 . Directly injecting a patient with a dose of medication meant for prolonged release from chamber  30  can have dire consequences. During the monitoring of the refill procedure, a quick change in pressure within chamber  30  can be recognized by the medical professional, thereby ensuring placement of the needle within refill aperture  60 . This is a significant safety feature in pump  10 . 
         [0071]    The exterior portions of pump  10  are preferably constructed of PEEK, including constant flow module assembly  12 , enclosure top  14  and union nut  16 . On the other hand, the exterior portions of control module assembly are constructed of titanium, which ensures the hermetic nature of that component. However, certain interior portions of the module are also constructed of PEEK, including circuit board support  94 . While these are indeed the materials utilized in the construction of a preferred pump  10 , other materials may be employed in other embodiments. For instance, other polymeric materials may be employed that provide for similar strength, while maintaining the low overall weight provided for by the PEEK material. Likewise, other metallic materials may be substituted for titanium, such as stainless steel or the like. The only limitation is that the materials selected should be bio-compatible to ensure such are not rejected by the patient after implantation. 
         [0072]    Several variations of above-discussed pump  10  will now be discussed. It is to be understood that all or some of these variations may be incorporated into an implantable pump according to the present invention. Where possible, like elements to those discussed above are referred with reference numerals in a different 100-series of numbers. 
         [0073]    For instance,  FIG. 31  depicts a top portion of an alternate embodiment constant flow module  312 , which includes a differently shaped gasket  350 . That gasket has been removed from  FIG. 32 . In this embodiment, a portion  342  stands alone as part of catheter  326 .  FIG. 33  depicts a side cross section of constant flow module  312 . As is seen in this view, module  312  differs from that of module  12  in that a bottom thereof is no longer contoured, but rather, exhibits a flat configuration. Constant flow module  312  has also been provided with two o-rings  313   a  and  313   b . Where ring  313   a  ensures a sealing of the propellant and medication chambers of module  312 , ring  313   b  ensures no material can leak from module  312 . Still further, module  312  includes holes  315   a - c . Hole  315   a  preferably receives a pin or the like (not shown) that acts to prevent the two housing portions included in module  312  from inadvertently disengaging by preventing unscrewing of those portions. On the other hand, holes  315   b  and  315   c  aid in connecting those portions to each other. Specifically, holes  315   b  and  315   c  are capable of interfacing with a tool for use in screwing the module portions together. Of course, other embodiments may include any number of similar holes. 
         [0074]      FIG. 34  depicts an alternate embodiment control module assembly  318  in which an element similar to the above-discussed flexible conductive element  92  has been eliminated. In this embodiment assembly  318 , a circuit board  380  acts to connect all of the electrical elements of the module.  FIG. 35  depicts the module  318  with circuit board  380  removed. 
         [0075]      FIGS. 36 and 37  depict alternate embodiment valve block  386  and motor assembly  388 , as well as the cooperation of those two elements. The major differences between this embodiment and those discussed above lies in several areas. For one, valve  422  includes a valve stem  430 , which includes an overmolded silicone valve tip  432 . This tip ensures full seating within a valve seat (not shown) located in block  386 , as well as allows for fine adjustment of flow rates therethrough. In addition, motor assembly  388  includes a solid housing  434 , and does not include a portion similar to plug  136 . Finally, motor  389  is held in place by clamp elements  389   a  and  389   b . Both elements are fitted into or onto different portions of the motor and thereafter affixed to block  386 , preferably through the use of epoxy. 
         [0076]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.