Abstract:
A remotely controlled gastric band system that is practically immune to external magnetic fields, such as from a Magnetic Resonance Imaging (MRI) machine, incorporates a bi-directional pump and fluid reservoir to adjust fluid volume in a gastric band. A piezoelectrically driven (e.g., rotary actuator, linear actuator) selectively compresses and expands a metal bellows hermetically sealed within a biocompatible and nonferromagnetic case such as titanium.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is related to three co-pending and commonly-owned applications filed on even date herewith, the disclosure of each being hereby incorporated by reference in their entirety, entitled respectively:  
         [0002]     “METAL BELLOWS POSITION FEED BACK FOR HYDRAULIC CONTROL OF AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Rocco Crivelli, Ser. No. ______ [Attorney Docket END5192-0519736, MP3152];  
         [0003]     “THERMODYNAMICALLY DRIVEN REVERSIBLE INFUSER PUMP FOR USE AS A REMOTELY CONTROLLED GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. ______ [Attorney Docket END5194-0519738, MP3249, MP3307];  
         [0004]     “BI-DIRECTIONAL INFUSER PUMP WITH VOLUME BRAKING FOR HYDRAULICALLY CONTROLLING AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. ______ [Attorney Docket END5196-0519740, MP3274]; 
     
    
     FIELD OF THE INVENTION  
       [0005]     The present invention relates, in general, to medically implantable reversible pumps, and more particularly, to such pumps that are suitable for long term use without fluid loss such as for hydraulically controlling an artificial sphincter.  
       BACKGROUND OF THE INVENTION  
       [0006]     Since the early 1980s, adjustable gastric bands have provided an effective alternative to gastric bypass and other irreversible surgical weight loss treatments for the morbidly obese. The gastric band is wrapped around an upper portion of the patient&#39;s stomach, forming a stoma that restricts food passing from an upper portion to a lower portion of the stomach. When the stoma is of the appropriate size, food held in the upper portion of the stomach provides a feeling of fullness that discourages overeating. However, initial maladjustment or a change in the stomach over time may lead to a stoma of an inappropriate size, warranting an adjustment of the gastric band. Otherwise, the patient may suffer vomiting attacks and discomfort when the stoma is too small to reasonably pass food. At the other extreme, the stoma may be too large and thus fail to slow food moving from the upper portion of the stomach, defeating the purpose altogether for the gastric band.  
         [0007]     In addition to a latched position to set the outer diameter of the gastric band, adjustability of gastric bands is generally achieved with an inwardly directed inflatable balloon, similar to a blood pressure cuff, into which fluid, such as saline, is injected through a fluid injection port to achieve a desired diameter. Since adjustable gastric bands may remain in the patient for long periods of time, the fluid injection port is typically installed subcutaneously to avoid infection, for instance in front of the sternum or over the fascia covering one of the oblique muscles. Adjusting the amount of fluid in the adjustable gastric band is achieved by inserting a Huber tip needle through the skin into a silicon septum of the injection port. Once the needle is removed, the septum seals against the hole by virtue of compressive load generated by the septum. A flexible catheter communicates between the injection port and the adjustable gastric band.  
         [0008]     While the injection port has been successfully used to adjust gastric bands, it would be desirable to make adjustments noninvasively. Insertion of the Huber tip syringe is typically done by a surgeon, which may be inconvenient, painful, or expensive for the patient. In addition, a skin infection may occur at the site of the insertion of the syringe. Consequently, it would be desirable to remotely control an adjustable gastric band.  
         [0009]     Infusers have been implanted in patients for controllable dispensing of a liquid drug, such as described in U.S. Pat. No. 4,581,018. A cylindrical metal bellows has a movable end that is drawn toward its nonmoving end by a lead screw that passes through the bellows into a threaded hole of the case. Thus, the volume of the metal bellows accumulator was affirmatively controlled by the number of turns made by the lead screw, avoiding inadvertent overdoses in dispensing a liquid drug.  
         [0010]     However, infuser pumps are intended to be driven in only one direction whereas adjusting constriction of the gastric band often requires that fluid be removed from the elastomeric balloon to reduce constriction as well as the reverse direction to increase constriction.  
         [0011]     In addition, it is becoming increasingly important that implanted devices in general be operable and nonresponsive to a strong magnetic field as the use of magnetic resonance imaging (MRI) becomes more common. An MRI machine produces a strong magnetic field, which may be up to 3.0 Teslas in flux density, that will impart a strong magnetic force upon any ferromagnetic material. Devices such as electrical motors may be damaged by such magnetic fields or the patient may feel discomfort. Moreover, ferromagnetic material may create artifacts in the radio frequency (RF) return that the MRI machine detects and processes by disturbing the magnetic field.  
         [0012]     In an implanted peristaltic pump, such as described in U.S. Pat. No. 6,102,678, a piezoelectric drive system is used to provide a rotary device that is lightweight, compact with very small axial volume and with the particular desirable feature of being practically unaffected by external magnetic influences. While a peristaltic pump differs substantially from a bi-directional metal bellows accumulator/pump, it would be desirable to incorporate similar features of MRI compatibility in a bi-directional infuser pump.  
         [0013]     Consequently, a significant need exists for a reversible pump suitable for medical implantation to remotely adjust a gastric band.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The present invention addresses these and other problems in the prior art, by providing a reversible pump having no ferromagnetic materials that can provide an accurately controllable volume to a second implanted device, such as a closed gastric band. In particular, a bellows accumulator may be directly collapsed or extended to positively displace fluid accumulated therein, thereby serving as both a reversible pump and reservoir, by utilizing a piezoelectric drive system that is practically immune to external magnetic fields.  
         [0015]     In one aspect of the invention, a bellow accumulator may be selectively collapsed or expanded between a larger and smaller volume as part of an implantable device in order to provide bidirectional fluid control of another implanted member. A piezoelectric drive effects this selective movement of the bellows accumulator, which being substantially nonresponsive to electromagnetic interferences means that the device may be rendered safe and operable even in proximity to an MRI machine.  
         [0016]     These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0017]     While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the same will be better understood by reference to the following description, taken in conjunction with the accompanying drawings in which:  
         [0018]      FIG. 1  is a diagrammatic view of a pump system in accordance with the present invention;  
         [0019]      FIG. 2  is a cross-sectional view of an implantable pump of the pump system taken along line A-A of  FIG. 1 ;  
         [0020]      FIG. 3  is a cross-sectional view of the implantable pump taken along line B-B of  FIG. 1 ;  
         [0021]      FIG. 4  is a front, exploded isometric view showing internal components of a first embodiment of the implantable pump of the present invention;  
         [0022]      FIG. 5  is a rear, exploded isometric view showing internal components of the first embodiment of the implantable pump of  FIG. 4 ;  
         [0023]      FIG. 6  is a schematic illustration in block diagram form of the power, telemetry, and control systems of the pump device;  
         [0024]      FIG. 7  is a diagrammatic view illustrating a pump and artificial sphincter implanted under a patient&#39;s skin and the volume of the sphincter being adjusted externally;  
         [0025]      FIG. 8  is a flow diagram illustrating the method of the present invention for adjusting an artificial sphincter via an implanted pump;  
         [0026]      FIG. 9  is a cross-sectional view of a second embodiment for the present invention in which the bellows cap is translated by a multilayered piezoelectric actuator; and  
         [0027]      FIG. 10  is a flow diagram of a second method for adjusting an artificial sphincter via an implanted pump. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Referring now to the drawings in detail, wherein like numerals indicate the same elements throughout the views,  FIG. 1  provides a diagrammatic view of an implantable pump system  20  in accordance with one embodiment of the present invention. As will be described in more detail below, pump system  20  may be implanted under a patient&#39;s skin and controlled by an active telemetry system to direct fluid flow to and from a therapeutic implant. Although the invention is described herein with specific reference to the use of the implantable pump with an artificial sphincter  21 , such as an adjustable gastric band, such description is exemplary in nature, and should not be construed in a limiting sense. The implantable pump of the present invention may also be utilized in any number of different apparatuses or systems in which it is desirable to provide bi-directional fluid flow between two interconnected subcutaneous components.  
         [0029]     As shown in  FIG. 1 , the pump system  20  includes an implantable pump device  22  having a generally cylindrical outer casing  24  extending around the sides and bottom portions of the pump device  22 , and an annular cover  26  extending across a top portion. Annular cover  26  may be of varying thickness, with the thickest portion located at the center  30  (shown in  FIG. 2 ) of the cover  26 . Casing  24  and cover  26  may be formed of titanium or another type of appropriate, non-magnetic material, as are the other parts of pump device  22  that are exposed to body tissue and fluids. The use of titanium or a similar material prevents pump device  22  from reacting to body fluids and tissues in which the pump device  22  may be implanted.  
         [0030]      FIGS. 2 and 3  are cross-sectional views showing the internal components of a first embodiment of pump device  22 , with  FIG. 3  being a 90° rotation of the  FIG. 2  view. In addition,  FIGS. 4 and 5  provide exploded isometric views from both the forward and rearward directions of pump device  22 , illustrating the relative positions of the components within the pump device  22 . As shown in  FIGS. 2-5 , thickened center portion  30  of cover  26  is molded or machined to include a duct  32 . A catheter port  34  extends laterally from duct  32  in center portion  30  to connect with an external fluid-conveying device, such as, for example, a catheter  36  as shown in  FIG. 1 . Duct  32  connects catheter port  34  with a fluid reservoir  38  in the interior of pump device  22 . Duct  32 , catheter port  34  and catheter  36  combine to provide bi-directional fluid flow between fluid reservoir  38  and a secondary implant. As shown in  FIGS. 1 and 2 , cover  26  includes a port  40  into which a hypodermic needle (not shown) may be inserted either through the patient&#39;s skin, or prior to implantation of device  22 , in order to increase or decrease the fluid volume in reservoir  38 . A septum  42  is disposed in port  40  to enable infusions by a hypodermic needle while preventing other fluid transmissions through the port  40 . Near the periphery of cover  26 , an annular lip  28  extends downwardly in overlapping contact with casing  24 . Casing  24  and cover  26  are welded together along lip  28  to form a hermetic seal.  
         [0031]     Fluid reservoir  38  comprises a collapsible bellows  44  securely attached at a top peripheral edge  46  to cover  26 . Bellows  44  are comprised of a suitable material, such as titanium, which is capable of repeated flexure at the folds of the bellows, but which is sufficiently rigid so as to be noncompliant to variations in pressure within reservoir  38 . The lower peripheral edge of bellows  44  is secured to an annular bellows cap  48 , which translates vertically within pump device  22 . The combination of cover  26 , bellows  44  and bellows cap  48  defines the volume of fluid reservoir  38 . The volume in reservoir  38  may be expanded by moving bellows cap  48  in a downward direction opposite cover  26 , thereby stretching the folds of bellows  44  and creating a vacuum to pull fluid into the reservoir. Similarly, the volume in reservoir  38  may be decreased by moving bellows cap  48  in an upward direction towards cover  26 , thereby compressing the folds of bellows  44  and forcing fluid from the reservoir into duct  32  and out through catheter port  34 .  
         [0032]     As shown in  FIGS. 2 and 3 , bellows cap  48  includes an integrally formed lead screw portion  50  extending downwardly from the center of the cap  48 . Lead screw portion  50  includes a screw thread, as indicated by numeral  51 , that operatively engages a matching thread on a cylindrical nut  52 . The mating threads  51  on lead screw portion  50  and cylindrical nut  52  enable the lead screw portion  50  to translate vertically relative to cylindrical nut  52  when the nut  52  is rotated about a longitudinal axis of the lead screw portion  50 . The outer circumference of nut  52  is securely attached to an axial bore of a rotary drive plate  54 . A cylindrical drive ring  56  is in turn mounted about an outer annular edge of rotary drive plate  54  to extend downwardly from the plate  54  on a side opposite to nut  52 . Nut  52 , drive plate  54  and drive ring  56  are all securely attached together by any suitable means, to form an assembly that rotates as a unit about the longitudinal axis formed by lead screw portion  50 .  
         [0033]     A bushing frame  58  is provided in pump device  22  and securely connected along a top edge to annular lip  28 . Bushing frame  58  includes a bottom portion  60  extending beneath bellows cap  48 , and a cylindrically-shaped side wall portion  62  spaced about the periphery of bellows  44 . A cylindrical coil bobbin  64  extends about the inner circumference of frame  58 , between the frame and bellows  44 . One or more coil windings may be wound about the circumference of bobbin  64  for providing transcutaneous signal transfer between an external power and communication source and pump device  22 . In the embodiment shown in  FIGS. 2-5 , a first coil winding  66  on bobbin  64  forms a closed loop antenna (“secondary TET coil”) that is inductively coupled to a primary transcutaneous energy transfer (TET) coil in the external interface. When the primary TET coil in the external interface is energized, an RF power signal is transmitted to the secondary TET coil  66  to provide a power supply for driving pump device  22 . A second coil winding  68  on bobbin  64  provides for control signal transfer between pump device  22  and an external programmable control interface. Coil winding  68  forms an antenna (“secondary telemetry antenna”) that is inductively coupled to a primary telemetry antenna in the external device for transmitting RF control signals between the external interface and pump  22  at a fixed frequency. A bushing  72  is press fit into bushing frame  58  to extend between frame  58  and drive plate  54 . Bushing  72  includes an axial opening for nut  52  and lead screw  50 . Bushing  72  separates bushing frame  58  and drive plate  54  to allow the drive plate and nut  52  to rotate relative to lead screw  50  without interference between the bushing frame  58  and drive plate  54 . In addition, bushing  72  prevents nut  52  from moving radially or axially toward cover  26 .  
         [0034]     As mentioned above, cylindrical nut  52 , drive plate  54  and drive ring  56  form an assembly that translates lead screw  50  of bellows cap  48  when ring  56  is rotatably driven. In the first embodiment of the present invention, drive ring  56  is rotatably driven by one or more piezoelectric harmonic motors that utilize a series of harmonic vibrations to generate rotation in the ring. In the embodiment shown in  FIGS. 2-5 , a pair of harmonic motors  74 ,  76  are placed in frictional contact with the inner circumference of drive ring  56 , so that the harmonic motion of the motors in contact with the ring produces rotation of the ring  56 . Motors  74 ,  76  may be spaced 180° apart about the inner circumference of ring  56 , beneath drive plate  54 . Motors  74 ,  76  are mounted to a support board  78 , with a tip portion  80  of each motor in frictional contact with the inner circumferential surface of drive ring  56 . When motors  74 ,  76  are energized, tips  80  vibrate against drive ring  56 , producing a “walking” motion along the inner circumference of the ring  56 , thereby rotating the ring  56 .  
         [0035]     A spring (not shown) within each motor  74 ,  76  biases motor tip portions  80  into continuous frictional contact with ring  56  to enable precise positioning of drive ring  56 , and a holding torque on the ring  56  between motor actuations to prevent position shift in the ring  56 . Drive ring  56  may be manufactured from a ceramic, or other similar material, in order to provide for the required friction with motor tip portions  80  while also limiting wear on the tip portions  80 .  
         [0036]     It should be appreciated by those skilled in the art having the benefit of the present disclosure that a piezoelectric harmonic motor, or another type of harmonic motor having no intrinsic magnetic field or external magnetic field sensitivity may be used in the present invention to enable patients with the implant to safely undergo Magnetic Resonance Imaging (MRI) procedures, or other types of diagnostic procedures that rely on the use of a magnetic field. The use of a piezoelectric harmonic motor rather than an electromagnetic servomotor in the present invention enables the device to provide the same high resolution, dynamic performance of a servomotor, yet is MRI safe. An example of a suitable piezoelectric harmonic motor for the present invention is the STM Series Piezoelectric Motor produced by Nanomotion Ltd. of Yokneam, Israel. This motor is described in detail in The STM Mechanical Assembly and the Nanomotion Product/Selection Guide, both published by Nanomotion, Ltd. Other types of harmonic motors may also be utilized in the present invention without departing from the scope of the invention. Examples of these other motors include, without limitation, the Elliptec motor by Elliptec AB of Dortmund Germany, which is described in the Elliptec Resonant Actuator Technical Manual. Version 1.2; the Miniswys motor by Creaholic of Switzerland; the PDM 130 Motor by EDO Electro-Ceramic Products of Salt Lake City, Utah which is described in the technical brochure High Speed Piezoelectric Micropositioning Motor Model PDA130.; and the Piezo LEGS motor which is manufactured by PiezoMotor Uppsala AB of Uppsala, Sweden and described in the brochure entitled Linear Piezoelectric Motors by PiezoMotor Uppsala AB. Additionally, piezoelectric inchworm motors may be utilized to drive a ceramic ring or plate, which motion is then translated into movement of a bellows. Examples of suitable piezoelectric inchworm motors include the IW-800 series INCHWORM motors produced by Burleigh EXPO America of Richardson, Tex. and the TSE-820 motor produced by Burleigh Instruments, Inc of Victor, N.Y. In addition, other types of rotary friction motors, and other types of motors which rely upon piezoelectric effects to drive a member may also be used without departing from the scope of the invention.  
         [0037]     As discussed above, each motor  74 ,  76  in the first embodiment is mounted to a board  78  using a plurality of screws or other type of secure attachment mechanism. While two motors are depicted in the figures, additional motors may be utilized provided the driving member of each motor is in frictional contact with the drive ring. In addition to supporting motors  74 ,  76 , board  78  may also include control circuitry for powering and operating the motors in accordance with signals transmitted from an external device. Alternatively, a separate circuit board could be included in pump device  22  that would include the circuitry for controlling motors  74 ,  76 . The control circuitry on board  78  is electrically connected to coil windings  66 ,  68  for receiving power to drive motors  74 ,  76 , as well as receiving and transmitting control signals for pump  22 . Board  78  is attached to a wire assembly sheath  81 , which is in turn connected by pins  83  to bushing frame  58 . The connection between board  78  and frame  58  forms a mechanical ground to prevent the board and attached motors  74 ,  76  from torquing within pump device  22  when the motors are energized. As shown in  FIGS. 3-5 , board  78  may also include one or more openings  82  for retaining plate supports  84 . Supports  84  extend between motors  74 ,  76 , from board  78  to drive plate  54 , to support the drive plate  54  and constrain the plate  54  from moving axially away from bellows  44 .  
         [0038]      FIG. 6  provides a schematic illustration of the TET power, telemetry and control systems of the present invention. As mentioned above, pump device  22  is driven by an active telemetry system in which the power required to drive the pump is transmitted to the pump device  22  from outside the patient&#39;s body using RF signals. Accordingly, pump device  22  may not require a battery or other type of internal power source, thereby eliminating the need to replace the power source and reducing the size of the implanted device. As shown in  FIG. 6 , pump device  22  is controlled by an external device  86  which includes a primary power supply and command control  88 . Control  88  generates a power signal that drives a primary TET coil  90  to generate an RF power signal  92 . Control  88  also transmits a data signal to communications antenna  94 , which generates an RF telemetry signal  96  encoded with operating data for pump device  22 . Power and communication signals  92 ,  96  are transmitted in different, fixed frequency bandwidths to pump device  22 . When antenna coils  90 ,  94  of external device  86  are placed on or near the patient&#39;s skin in the vicinity of implanted pump device  22 , power signal  92  from TET coil  90  induces a voltage in the pump internal secondary TET coil  66 . The power signal from coil  66  is transmitted to internal control circuitry  100  on board  78 . The power signal is conditioned and stepped up to a higher voltage. The signal is then used to power a motor driver  101 . Similarly, telemetry signal  96  generates a voltage signal in secondary telemetry antenna  68 . The signal generated in secondary telemetry antenna  68  is decoded by control circuitry  100 , and the control information from the signal  96  is applied to a motion control  98 . Motion control  98  interprets the control data to selectively apply power from motor driver  101  to motors  74 ,  76  to drive the motors  74 ,  76  and move bellows  44 .  
         [0039]     Motion control  98  drives motors  74 ,  76  by providing an appropriate electrical signal to each motor  74 ,  76  through a pair of electrical control lines. In the exemplary piezoelectric harmonic motor embodiment, drive ring  56  rotates in either a clockwise or counterclockwise direction depending upon which control lines are excited in the motors. Motion control  98  includes switches for directing a voltage signal amongst the different control lines. When a voltage signal is applied across a first pair of control lines, the piezoelectric element vibrates in a first mode, causing drive ring  56  to rotate in a first direction. When a voltage signal is applied to a second pair of control lines, the piezoelectric element vibrates in a second mode, causing drive ring  56  to rotate in the opposite direction. Rotation of drive ring  56  in a first direction raises bellows cap  48 , thereby decreasing the volume in fluid reservoir  38  and forcing fluid from the pump into catheter  36 . Similarly, rotation of drive ring  56  in a second, opposite direction lowers bellows cap  48 , thereby increasing the volume in reservoir  38  and causing fluid to be drawn into the reservoir through catheter  36 . By using the harmonic motors  74 ,  76  to rotate drive ring  56 , and the lead screw portion  50  acting as a transmission to transfer the rotary motion into a linear motion of bellows  44 , pump  22  provides bi-directional fluid flow in or out of the pump device  22  without the need for additional motors or gear systems to change the direction of fluid flow.  
         [0040]     Efficient power coupling of primary and secondary TET coils is described in five co-pending and co-owned patent applications filed on ______ 2004, all of which are hereby incorporated by reference in their entirety, (1) “TRANSCUTANEOUS ENERGY TRANSFER PRIMARY COIL WITH A HIGH ASPECT FERRITE CORE” to J. Giordano, Daniel F. Dlugos, Jr. &amp; William L. Hassler, Jr., Ser. No. ______; (2) “MEDICAL IMPLANT HAVING CLOSED LOOP TRANSCUTANEOUS ENERGY TRANSFER (TET) POWER TRANSFER REGULATION CIRCUITRY” to William L. Hassler, Jr., Ed Bloom, Ser. No. ______; (3) “SPATIALLY DECOUPLED TWIN SECONDARY COILS FOR OPTIMIZING TRANSCUTANEOUS ENERGY TRANSFER (TET) POWER TRANSFER CHARACTERISTICS” to Reshai Desai, William L. Hassler, Jr., Ser. No. ______; (4) “LOW FREQUENCY TRANSCUTANEOUS TELEMETRY TO IMPLANTED MEDICAL DEVICE” to William L. Hassler, Jr., Ser. No. ______; and (5) “LOW FREQUENCY TRANSCUTANEOUS ENERGY TRANSFER TO IMPLANTED MEDICAL DEVICE” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. ______.  
         [0041]      FIG. 7  illustrates an application of pumping system  20  of the present invention, in which pump device  22  is controlling fluid flow to a therapeutic device, such as an artificial sphincter  102 . An artificial sphincter, such as that indicated by  102 , could be utilized in any number of applications within a patient&#39;s body where it is desirable to vary the size of an orifice or organ. Depending upon the application, artificial sphincter  102  may take the form of a flexible, substantially non-extensible band containing an expandable section that is capable of retaining fluids. The expandable section would be capable of expanding or contracting, depending upon the volume of fluid contained therein. In the exemplary embodiment of  FIG. 7 , the expandable section of band  104  is connected to catheter  36  to enable fluid flow between the band  104  and pump device  22 . The flexible material comprising band  104  enables the band  104  to be wrapped in an encircling manner about an orifice or hollow organ inside a patient&#39;s body and the two ends of the band attached against each other. While band  104  encircles the orifice or organ, the expandable section may be fully or partially filled with a fluid through catheter  36  to narrow the diameter formed by the band, and constrict the size of the orifice or organ encircled by the band. In  FIG. 7 , the artificial sphincter  102  is an adjustable gastric banding device that is placed around a portion of a patient&#39;s gastrointestinal (GI) system in order to restrict food intake into the system. Descriptions of gastric banding devices suitable for use in the present invention are provided in one or more of the following U.S. patents: U.S. Pat. No. 4,592,339 issued on Jun. 3, 1986 to Kuzmak et al.; U.S. Pat. No. 5,226,429 issued on Jul. 13, 1993 to Kuzmak; U.S. Pat. No. 6,102,922 issued on Aug. 15, 2000 to Jakobsson et al.; and U.S. Pat. No. 5,449,368 issued on Sep. 12, 1995 to Kuzmak. Each of the above-listed patents is assigned to the assignee of the present invention and is incorporated herein by reference. As shown in  FIG. 7 , band  104  is wrapped so as to encircle an upper portion of the patient&#39;s GI tract and create a restricted opening through the tract. While band  104  encircles the GI tract, fluid may be pumped into or out of the expandable section of the band, in order to vary the diameter of the restriction in the GI tract.  FIG. 7  also illustrates an external power and control source  86  being used to control the volume of fluid in band  104 . As shown in the figure, external antennas  90 ,  94  of device  86  are positioned over the patient&#39;s skin adjacent the location of implanted pump  22 . In this position, external antennas  90 ,  94  transmit power and control signals to operate the pump and drive fluid in or out of band  104 .  
         [0042]      FIG. 8  provides a flow diagram illustrating the operation of pump system  20  in adjusting the diameter of a therapeutic device such as artificial sphincter  102 . As shown in  FIG. 8 , in an initial step (block  110 ) a sphincter adjustment is initiated by positioning external control  86  on the patient&#39;s skin adjacent to implanted pump  22 . After device  86  is in place, a medical attendant directs the device to transmit RF power signal  92  to primary TET coil  90  (block  112 ). RF power signal  92  is received by loop antenna  66  and transmitted to internal control circuitry  100  to power on pump  22 . Also during block  112 , control signal  96  is transmitted by primary telemetry antenna  94  to antenna coil  68 . Signal  96  includes data for directing motion control  98  to dispense (or infuse) a desired fluid volume from pump  22 . In block  114 , the received power and control signals are applied to motor driver  101  and motion control  98 . From the data in control signal  96 , motion control  98  determines the voltage to be applied to motors  74 ,  76 , as well as the control lines across which to apply the voltage.  
         [0043]     Motion control  98  applies a voltage signal to motors  74 ,  76  in block  116  to excite the piezoelectric element in each motor and cause the motor tips to vibrate against drive ring  56  and rotate the ring. Motion control  98  discontinues the voltage signal after drive ring  56  has rotated the instructed number of revolutions. While drive ring  56  is rotating, the rotary motion is transmitted through nut  52  and lead screw  50  of bellows cap  48  at block  118 , so that the bellows cap is translated vertically a corresponding distance to either increase or decrease the size of bellows  44 . In block  120 , fluid is directed either in or out of bellows  44  as bellows cap  48  is translated. If bellows cap  48  is translated in an upward direction, the volume in bellows  44  is decreased, thereby forcing fluid from bellows  44  and into catheter  36 . If bellows cap  48  is translated in a downward direction, the motion creates a vacuum within bellows  44  that draws fluid from catheter  36  into the fluid reservoir formed in the bellows. When motion control  98  discontinues the voltage signal across motors  74 ,  76 , revolution of drive ring  56  ceases, and the fluid volumes in bellows  44 , catheter  36  and sphincter  102  stabilize and remain fixed until motion control  98  is again instructed to excite the motors.  
         [0044]      FIG. 9  provides a cross-sectional view of a second embodiment of the present invention in which bellows cap  48  is driven by a piezoelectric actuator rather than by piezoelectric motors. In this embodiment, a mechanical lever  130  replaces the rotary drive assembly formed by drive ring  56  and drive plate  54  as well as the force transmitted through nut  52  and lead screw  50 . Lever  130  includes a beam  140  extending horizontally beneath bellows cap  48 . An extension arm  136  extends vertically from a first end  132  of beam  140  to connect the beam  140  to the underside of bellows cap  48 . A fulcrum  138  is spaced from a second end  134  of beam  140  and connects the beam  140  to control board  78 . Extension arm  136  and fulcrum  138  have a narrowed, hourglass shape and are comprised of a material that enables the arm  136  and fulcrum  138  to flex mechanically in response to an applied force on beam  140 .  
         [0045]     A piezoelectric actuator  142  extends from board  78  into direct contact with beam  140  between the second beam end  134  and fulcrum  138 . Actuator  142  is electrically connected to control circuitry on board  78 . A motion control on board  78  is connected to actuator  142  for applying an excitation voltage to drive the actuator  142 . When actuator  142  is energized, it applies a vertical force against beam  140 , pulling the beam  140  downward or pushing the beam  140  upward depending upon whether the actuator  142  is increasing or decreasing in size due to the excitation. Beam  140  pivots about fulcrum  138  in response to the actuator movement due to the flexing in fulcrum  138  and arm  136 . The pivoting of beam  140  amplifies the actuator movement to generate a linear force in arm  136  that lifts or lowers bellows cap  48 . The length of beam  140  can vary depending upon the force required to move bellows cap  48  and the beam displacement produced by actuator  142 . In this second embodiment, actuator  142  may be any type of piezoelectric actuator, such as, for example, a multi-layer piezoelectric stack actuator, a piezoelectric bimorph actuator, or a thin-layer composite-unimorph ferroelectric driver (AKA prestressed piezoelectric composite (PPC) or Thunder® actuator. Additionally, other types of piezoelectric actuators capable of moving lever  130  may also be utilized without departing from the scope of the invention.  
         [0046]      FIG. 10  provides a flow diagram for the second embodiment of the invention, in which the pump operation has been modified to utilize piezoelectric actuator  142  and mechanical lever  130  for driving bellows cap  48 . The operation of the second embodiment is the same for the initial three steps of the process. Namely, external control  86  is placed adjacent to the implant  22  (block  110 ), signal transfer is initiated to the implant using the power and telemetry antennas  90 ,  94  (block  112 ) and the received signals  92 ,  96  are applied to the motion control  98  (block  114 ). At block  150 , rather than driving motors  74 ,  76 , motion control  98  applies a voltage to actuator  142 , which moves the attached beam  140  in either an upward or a downward direction depending upon the motion of the actuator. The movement in second end  134  of beam  140  causes the beam to pivot about fulcrum  138 . Because the distance between fulcrum  138  and the first end  132  of beam  140  is greater than the distance between the fulcrum and the second end  134  of the beam  140 , the beam amplifies the motion of actuator  142  as the beam  140  pivots about the fulcrum  138 . The amplified force is transmitted linearly through arm  136  to apply a force to move bellows cap  48  at block  152 . At block  154 , the upward or downward movement of bellows cap  48  either draws fluid into bellows  44  by creating a vacuum, or forces fluid from the bellows  44  by reducing the reservoir volume in the same manner as the first embodiment.  
         [0047]     In addition to the above embodiments which couple the motor or actuator to the bellows through a mechanical amplifier transmission, bellows cap  48  may also be driven directly by a harmonic motor or harmonic actuator. In this embodiment, the harmonic motor or actuator is capable of producing sufficient actuation force and range of motion to drive the bellows cap directly from the vibrations or motions of the piezoelectric element without additional amplifying structure. The actuator is placed in direct frictional contact with the bellows cap and excited with a sufficient voltage to move the bellows cap either up or down depending upon the direction of the vibrations.  
         [0048]     In each of the above-described embodiments, an implantable pump provides bi-directional fluid flow for use in adjusting the size of an implanted therapeutic device. The pump is driven by either piezoelectric harmonic motors or a piezoelectric actuator that is powered and controlled externally through telemetry and, accordingly, does not require a battery or any type of ferro-magnetic material as is typically necessary to drive a pump motor. Accordingly, the implantable pump can be safely used in an MRI procedure, or in a similar type of procedure that utilizes a magnetic field, without torquing or heating the pump.  
         [0049]     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. In addition, it should be understood that every structure described above has a function and such structure can be referred to as a means for performing that function.  
         [0050]     For example, it will become readily apparent to those skilled in the art that the above invention has equal applicability to other types of implantable bands. For example, bands are used for the treatment of fecal incontinence. One such band is described in U.S. Pat. No. 6,461,292, which is hereby incorporated herein by reference. Bands can also be used to treat urinary incontinence. One such band is described in U.S. Patent Application 2003/0105385, which is hereby incorporated herein by reference. Bands can also be used to treat heartburn and/or acid reflux. One such band is described in U.S. Pat. No. 6,470,892, which is hereby incorporated herein by reference. Bands can also be used to treat impotence. One such band is described in U.S. Patent Application Publ. No. 2003/0114729, which is hereby incorporated herein by reference.  
         [0051]     As another example, while the long-term fluid integrity of a metal bellows accumulator has advantages in an adjustable artificial sphincter system, it should be appreciated that in some applications a bellows accumulator may comprise other materials. Moreover, a piston-like accumulator may be used with dynamic seals interposed between a ram and a cylinder rather than relying upon accordion-like sidewalls.  
         [0052]     Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.