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 for hydraulic control of a gastric band. A piezoelectric driver (e.g., rotary actuator, linear actuator) selectively compresses and expands a metal bellows hermetically sealed within a biocompatible and nonferromagnetic enclosure or case such as titanium. Directly sensing a position of the metal bellows yields an accurate reading of volume contained therein, allowing for closed-loop control of the gastric band.

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: 
        “PIEZO ELECTRICALLY DRIVEN BELLOWS INFUSER FOR HYDRAULICALLY CONTROLLING AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Ser. No. ______;     “THERMODYNAMICALLY DRIVEN REVERSIBLE INFUSER PUMP FOR USE AS A REMOTELY CONTROLLED GASTRIC BAND” to William L. Hassler, Jr., Daniel F. Dlugos, Jr., Ser. No. ______; and     “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. ______.       
 
     
    
     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]     An artificial sphincter may 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 sphincters 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. One particular example of an artificial sphincter is an adjustable gastric banding device, such as described in U.S. Pat. Nos. 4,592,339, 5,226,429, 6,102,922, and 5,449,368, the disclosure of each being hereby incorporated by reference. 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.  
         [0007]     The gastric band is wrapped around an upper portion of the patient&#39;s stomach just inferior to the esophago-gastric junction, 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. Thus, different degrees of constriction are desired, and adjustment is required over time as the patient&#39;s body adapts to the constriction.  
         [0008]     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.  
         [0009]     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.  
         [0010]     In an afore-mentioned co-pending application entitled “PIEZO ELECTRICALLY DRIVEN BELLOWS INFUSER FOR HYDRAULICALLY CONTROLLING AN ADJUSTABLE GASTRIC BAND” to William L. Hassler, Jr., Ser. No. ______, an advantageous infuser containing no ferromagnetic materials provides an accurately bi-directionally controllable volume of fluid to a closed gastric band. The infuser has a titanium bellows accumulator, which may be collapsed or extended to positively displace fluid accumulated therein, thereby serving as both a reversible pump and reservoir. Thereby a bi-directional pump that is practically immune to external magnetic fields is achieved, unlike previously known implants that contained a metal bellows for controllable dispensing of a liquid drug, such as described in U.S. Pat. No. 4,581,018. Thereby, such an implanted device may undergo Magnetic Resonance Imaging (MRI) without damage to the device or patient.  
         [0011]     Accurate delivery of fluid from a bellows accumulator benefits from a feedback control system and as a means for determining bellows position relative to its housing. In the U.S. Pat. No. 4,581,018 patent, position feedback was provided by a rotary encoder connected to the output shaft of an electrical motor used to rotate the cylindrical metal bellows. In this instance, the rotations of the motor are determined by counting incremental marks on an optical disk of the encoder for the purpose of dispensing at a uniform rate.  
         [0012]     However, in creating a device that may be required to pump in both directions with long intervals therebetween, it is believed that counting rotations of a rotary actuator in some instances may inaccurately reflect the volume in the bellows accumulator. For example, the current volume of the reservoir is not directly sensed, and thus integrating a rate of dispensing to calculate a change in volume still suffers if the starting point is not known or if fluid is transferred inadvertently due to leakage or other factors.  
         [0013]     In other infuser devices, sensing fluid pressure within the bellows accumulator has been used as an indirect measurement of volume, relying upon a fixed relationship in pressure and volume since the bellows accumulator is collapsed based on a gauge pressure exerted thereon by a propellant within an infuser device housing. However, such pressure sensing assumes that the fluid pressure is not varied by pressure external to the infuser device, such as would be expected in a closed artificial sphincter system. Specifically, the amount of back pressure would vary somewhat unpredictability. Examples of such pressure-based sensing include U.S. Pat. No. 5,507,737 (pressure gauge), U.S. Pat. No. 5,974,873 (strain gauge), and U.S. Pat. No. 6,315,769 (spring and pressure sensitive resistor).  
         [0014]     Recently, it has been recognized as desirable to sense remaining fluid volume in a drug dispensing infuser device in order to determine when refilling is necessary. To that end, U.S. Pat. No. 6,542,350 discloses forming a variable capacitance between the bellows accumulator and the infuser device housing to sense volume. Similarly, U.S. Pat. No. 6,482,177 discloses forming a variable inductance between the bellows accumulator and the infuser device housing to sense volume. In both instances, using the sensed volume for such purposes was not suggested other than relaying a value by telemetry for display to a human operator. This is understandable in that these drug dispensing applications meter small amounts of a drug without significant variations in external backpressure to the infuser. Continuous volume sensing was not addressed. Power consumption for volume sensing would create an undesirable increase in battery size. In addition, accuracy of the variable capacitors or inductors may have been insufficient for these purposes, especially as the portions of the variable capacitor or inductor move away from one another in the presence of electromagnetic interference.  
         [0015]     Consequently, a significant need exists for sensing a position of an implanted bellows accumulator representing a fluid volume for closed loop control of an implanted artificial sphincter.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     The present invention addresses these and other problems in the prior art by providing volume sensing of a bellows accumulator so that accurate, closed-loop motion control of the bellows accumulator may be achieved.  
         [0017]     In one aspect of the invention, a method for hydraulically controlling an implantable artificial sphincter includes a programmer that sends a position signal to an external telemetry coil. The signal is transmitted to an implanted telemetry coil receiver, which delivers it to an implanted microprocessor. The positive control signal then enters a feedback loop-summing junction, which also receives an error signal. The net signal flows to the bellows actuator, which is powered by the secondary transcutaneous energy transfer (TET) coil. A bellows position sensor determines the prior bellows position and an electronic position signal is provided to a control algorithm, which in turn provides the error signal to the summing junction to tell the actuator to move to a new position. Thereby, accurate bi-directional hydraulic control of the artificial sphincter is achieved, even if the rate of fluid dispensing varies due to circumstances such as changing actuation performance or unpredictable back pressure to the infuser device.  
         [0018]     In another aspect of the invention, a bi-directional infuser device for an artificial sphincter system incorporates volume sensing for closed-loop adjustment control by control circuitry incorporated into the infuser device. In response to an external programmer command to adjust volume, the control circuitry performs closed loop control of an actuation mechanism with reference to volume sensing until the commanded volume is achieved.  
         [0019]     In another aspect of the invention, the bi-directional infuser device is part of an implantable artificial sphincter system that is remotely powered and telemetrically controlled by an external assembly including a primary TET and telemetry coil or coils that advantageously allow noninvasive adjustment of an artificial sphincter, such as a gastric band. Thereby, the need to insert a syringe to adjust volume is avoided, along with the accompanying inconvenience, discomfort and increased likelihood of infection.  
         [0020]     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  
       [0021]     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:  
         [0022]      FIG. 1  is a perspective environmental view of an adjustable artificial sphincter system being closed-loop remotely controlled based upon volume sensing.  
         [0023]      FIG. 2  is a top plan view of a bi-directional infuser device of the adjustable artificial sphincter system of  FIG. 1 .  
         [0024]      FIG. 3  is a sectioned side elevation view of the infuser device of  FIG. 2 , taken along section line  3 - 3 , showing a version of a bellows accumulator position sensor based on variable inductance, and showing a bellows in an extended position.  
         [0025]      FIG. 4  is a sectioned side elevation view of the infuser device of  FIG. 2 , similar to  FIG. 2 , but showing a bellows in a collapsed position.  
         [0026]      FIG. 5  is a sectioned side elevation view of the infuser device of  FIG. 2 , taken along section line  3 - 3 , showing a second version of a bellows accumulator position sensor based on optical sensing based on reflectance from a lead screw varying with distance, and showing a bellows in a collapsed position.  
         [0027]      FIG. 6  is a sectioned side elevation view of the housing of  FIG. 1 , taken along section line  2 - 2 , showing a third version of a bellows accumulator position sensor based upon absolute optical angular encoding, and showing a bellows in a collapsed position.  
         [0028]      FIG. 7  is a sectioned bottom plan view of  FIG. 6 , taken along section line  7 - 7 , showing an encoding ring on the underside of the driven disk and a single scanner to read absolute angular displacement therefrom.  
         [0029]      FIG. 8  is a sectioned side elevation view of the housing of  FIG. 2 , taken along section line  2 - 2 , showing a fourth version of a bellows accumulator position sensor based upon a potentiometer, and showing a bellows in a collapsed position.  
         [0030]      FIG. 9  is a block diagram of closed loop control of an artificial sphincter system for collapsing and extending the bellows accumulator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     Turning to the Drawings wherein like numerals denote like components throughout the several views, in  FIG. 1 , an artificial sphincter system  10  regulates the amount of fluid maintained in an implantable artificial sphincter assembly  12  powered by transcutaneous energy transfer (TET) and under telemetry control of an external assembly  13 . In the illustrative version, the artificial sphincter system  10  is used for weight reduction therapy. A stoma is formed between an upper portion  14  and lower portion  15  of a patient&#39;s stomach  16  to slow the passage of food and to provide a sense of fullness. The implantable artificial sphincter assembly  12  includes an expandable gastric band  18  that encircles the stomach  16  to form the stoma. An infuser device  20  is anchored subcutaneously on a layer of muscular fascia within the patient or in another convenient location. A flexible catheter  22  provides fluid communication between the gastric band  18  and the infuser device  20 .  
         [0032]     It should be appreciated that the gastric band  18  includes an inwardly directed bladder to expandably receive a fluid, such as saline solution, from the catheter  22  to allow adjustment of the size of the stoma formed therein without having to adjust the attachment of the gastric band  18 . The infuser device  20  advantageously prevents fluid moving in either direction between adjustments so that long-term implantation is realized.  
         [0033]     As an advantageous approach to reducing the necessary size of the infuser device  20  is to utilize TET for powering actuation and control circuitry from the external portion  13 . Telemetry relays the amount of fluid in the infuser device  20  to the external assembly  13  for display, and in some applications for closing the loop on volume adjustment. To that end, the external system  13  may include a primary coil  24  positioned outside of the patient proximally placed to the infuser device  20  that is inside of the patient to inductively couple with a secondary coil (not shown) located within the infuser device  20 . A programmer  26 , which is connected via electrical cabling  28  to the primary coil  24 , activates and monitors the primary coil  24 .  
         [0034]     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 James 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 Resha H. 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. ______.  
         [0035]     With reference to  FIGS. 2-4 , an implantable infuser device  30  incorporates inductive volume sensing. Infuser device  30  includes a fluid discharge head  32  and a cylindrical outer casing  34  sealed hermetically thereto, such as by welding. Discharge head  32  has a discharge conduit  36  sealably attached thereto and in fluid communication with a cylindrical bellows fluid accumulator (“bellows”)  38 . Bellows  38  has an open (fixed) end  40  welded to an inner surface of discharge head  32 . Bellows  38  also has a closed (moving) end  42  fixedly attached to a lead screw  44  centered at the longitudinal axis of bellows  38  and extending away from bellows  38 . Lead screw  44  has fine male threads such as ¼″- 32  thereon.  
         [0036]     Connected to and extending from discharge head  32  surrounding the circumference of bellows  38  is a cylindrical member  46  having a rigid bottom surface  48  and a clearance hole  50  centered therein through which lead screw  44  passes. Press-fit inside cylindrical member  46  and outside the perimeter of bellows  38  is a cylindrical bobbin  52  for housing spaced-apart secondary telemetry and transcutaneous energy transfer wire coils (not shown) in annular coil cavities  53 ,  54  formed with the cylindrical member  46 , for receiving an actuation signal and induced power respectively from outside the patient&#39;s body to operate the infuser device  30 .  
         [0037]     Cylindrical outer casing  34  has a base  56  substantially parallel to the inner surface  57  of discharge head  32 . Fixedly attached to this base  56  is control circuitry, depicted as a circuit board  58 , which contains a microprocessor and other electronic devices for operating the infuser device  30 . Attached to circuit board  58  are two piezoelectric motors  60  symmetrically spaced about lead screw  44 , having drive mechanisms frictionally contacting an inner rim  62  of a disk  64  centered about lead screw  44 . Disk  64  has an internally threaded boss  66  extending therefrom toward bellows  38 . Threaded boss  66  has matching ¼″- 32  threads, which accurately mate with threads of lead screw  44  to form a nut which when rotated with disk  64  by motors  60  about lead screw  44 , drive lead screw  44  and bellows  38  axially to expand or collapse the bellows  38 . Motors  60  and TET/telemetry coils (not shown) are electrically connected to circuit board  58 , all contained within outer casing  34 .  
         [0038]     It is desirable to sense the extended or collapsed position of bellows  38  to closed-loop control that position in order to accurately transfer a desired volume of fluid to and from the bellows  38 . To that end, a pancake inductance coil  68  is placed in fixed position parallel to and axially aligned with closed end  42  of bellows  38 . Coil  68  is preferably attached to a rigid bottom surface  70  of cylindrical member  46 , for example, to minimize the distance between the coil  68  and the closed end  42  of the bellows  38 . A parallel tuned tank circuit on circuit board  58 , commonly known in the electronic controls art, oscillates at a frequency of resonance depending on the number and diameter of turns in inductance coil  68 , the electrical capacitance in parallel with coil  68 , and the closeness of closed end  42  to coil  68 , forming an inductive position sensor  80 . In the illustrative version, inductance coil  68  is a spiral shaped coil of about 200 turns made of 40 gauge copper wire. A microprocessor on the circuit board  58  measures the frequency of oscillation and compares it to a table of frequencies in order to provide an error signal to indicate how close the actual bellows position is to the command position desired. Piezoelectric motors  60 , combined with driven disk  64  and threaded boss  66 , actuate the bellows  38  via lead screw  44 , forming a bellows actuators  90 .  
         [0039]     It should be appreciated that a position sensor that is not dependent upon the presence and/or rotation of a lead screw such as the afore-described inductive position sensor may have application in an infuser device that is thermodynamically actuated, such as described in the afore-mentioned cross-referenced applications.  
         [0040]     In  FIG. 5 , an infuser device  130  has identical components to the infuser device  30  of  FIGS. 2-4  with the exception of using optical position sensing of the bellows  38 . In particular, instead of an inductance coil, position sensing, and thus volume sensing, is alternatively accomplished by an optical sensor  168 . A light emitting diode (LED)  182  is shown mounted to a circuit board  138  beside a photodiode  184 , also mounted to the circuit board  138 . Both LED  182  and photodiode  184  are positioned near the axis of a lead screw  134  so that LED  182  emits light that is reflected by a distal end  186  of lead screw  144  toward photodiode  184 . Since the LED  182  emits noncolumnated light, the distance of the distal end of the lead screw  144  from the photodiode  184  is inversely related to the amount of light from the LED  182  reflected from the lead screw  144  that is collected by the photodiode  184 . A distal end  186  of the lead screw  144  may include surface treatment or shaping to provide a monotonic amount of reflected light as a function of distance, accommodating for instance an offset from the axis of the lead screw  144  of the LED  182  and/or the photodiode  184 . The LED  182  and photodiode  184  and distal end  186  of lead screw  134  form position sensor  180 . Photodiode  184  and LED  182  components are ubiquitous in many forms and performance. Many different ones and combinations of them can be successfully utilized in this application by one skilled in the control art.  
         [0041]     In  FIGS. 6 and 7 , an infuser device  230  has identical components as infuser device  30  but incorporates an angular optical position sensor, depicted as an optical encoder  280 . In particular, instead of LED  182  and photodiode  184  aimed at the lead screw  144 , a LED  282  and photodiode  284  are mounted to a circuit board  238  and are located near an inner rim  242  of a rotatable disk  244 . On the side of disk  264  facing circuit board  238  is printed a circular pattern of radial lines  286  having high contrast with their background. LED  282  and photodiode  284  form a scanner  288 , which senses the position of the circular pattern of radial lines  286 . When disk  264  rotates to move a lead screw  234 , scanner  288  signals an encoder portion of circuit board  238  a count of lines  286  which have passed by. The count of lines  286  is directly proportional to movement of lead screw  244  and therefore of the bellows  38 .  
         [0042]     In another version of the scanner and lines embodiment of angular optical position sensor  280 , a second scanner, not shown, is placed at 90 degrees out of phase with respect to the encoding pattern  286  and to scanner  288  to form a quadrature form of encoding, commonly known in the control art, which enables the encoder  280  to sense both position and direction of disk rotation. In yet another version, a gray scale, not shown but commonly known in the encoding art, replaces the simple radial line pattern. The gray scale establishes absolute position of the rotatable disk  264  because each position of the gray scale provides a unique signature.  
         [0043]     In  FIG. 8 , an infuser device  330  has identical components as infuser device  30  but incorporates angular resistance position sensor  380  instead of an inductive, linear optical, or angular optical position sensor  80 ,  180 ,  280 . Instead of LED and photodiode reflectance or scanners, and instead of an inductance coil, position sensing is achieved by a potentiometer  382 . A rotatable disk  364  has a boss extension  388  that is fixedly connected to a shaft  390  of the potentiometer  382  whose body is mounted to a circuit board  338 . When disk  364  is rotated to drive a lead screw  344 , shaft  390  of the potentiometer  382  is rotated. Such rotation is directly proportional to the movement of lead screw  344  and therefore of the bellows  38 . Thus, bellows position control is achieved in this alternative by measuring the resistance within the potentiometer  382  and comparing that resistance with a table of resistances in the microprocessor of the circuit board  338 . The table of resistances in the microprocessor is part of the control algorithm  54 . Potentiometer components are ubiquitous in very many forms, and performance. Many different ones and combinations of them can be successfully utilized in this application by one skilled in the control art.  
         [0044]     In  FIG. 9 , a control system  400  performs closed-loop volume feedback in order to accurately adjust and maintain hydraulic volume in the adjustable gastric band  18  of  FIG. 1 . In the illustrative version, this control system  400  includes an inner control loop  402  performed by the infuser device  30 ,  130 ,  230 ,  330  (not shown in  FIG. 9 ) to accurately adjust to a desired volume. In the illustrative version, the infuser device  30 ,  130 ,  230 ,  330  is TET powered as well as receiving telemetry commands from an outer control loop  404 . It should be appreciated that the inner control loop  402  may be closed outside of the infuser device  30 ,  130 ,  230 ,  330 , as depicted by the smaller box  406 , as described above. In the illustrative version, however, the infuser device  30 ,  130 ,  230 ,  330  closes the inner control loop  402 , as depicted by box  407  utilizing position sensing (block  408 ) that is responsive to bellows movement. A control algorithm  410  converts the sensed position value into a calculated error signal.  
         [0045]     An external portion of the control system  400  is provided by an external programmer  412  that selects a volume for adjusting the artificial sphincter and transmits this position command from an external (primary) telemetry circuit  414  to an internal (secondary) telemetry circuit  416  that is converted to a command position value  418 . Differential summing of the command position value  420  and the error signal results in bellows actuator drive command  422  that results in a bellows movement that is sensed as part of the iterative, closed-loop control of volume adjustment.  
         [0046]     In the version with an inductive position sensor  80 , the table of frequencies in the microprocessor is part of the control algorithm  410 . In the linear optical position sensor  180 , bellows position control is achieved by measuring the amount of reflected light at the photodiode  184  and comparing that with a table of light levels in the microprocessor. The table of light levels in the microprocessor is part of the control algorithm  410 . The control algorithm  410  modifies the error signal in order to eliminate the difference between the actual bellows position and the command bellows position  418 . This error signal modification can be as simple as using a Proportional, Integral, and Differential (PID) control law. This control law, commonly known in the control art, takes the original error signal and multiplies it by a fixed proportional gain constant, and then adds it to the integration of the original error signal with respect to time multiplied by an integral gain constant, and then this sum is added to the time derivative of the original error signal multiplied by a deferential gain constant to form the final error signal to be summed with the command signal. By adjusting or tuning these three different gain constants, the position error signal can be optimized for smoothest and quickest response over the bellows range of travel.  
         [0047]     In a version with an angular optical sensor  280 , bellows position is sensed in this alternative by measuring the count of lines passing the scanner and comparing that count with a table of line counts in the microprocessor of circuit board  238  to establish an error signal in the control system illustrated in  FIG. 9 . The table of line counts in the microprocessor is the control algorithm  410 . The scanner  288  and lines  286  form position sensor  280 . Scanning components are ubiquitous in very many forms, and performance. Many different ones and combinations of them can be successfully utilized in this application by one skilled in the control art.  
         [0048]     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.  
         [0049]     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.  
         [0050]     For another example, while microprocessor closed-loop control with position conversion lookup tables is described, various other forms of computational circuitry may be used to perform closed-loop control, such as operational amplifier filter circuits, a state machine, a neural network, lumped component analog control circuitry, etc.  
         [0051]     For an additional example, while a cylindrical titanium bellows accumulator with accordion-like sides is illustrated herein, it should be appreciated that other shapes of accumulators and other materials may be used consistent with aspects of the invention. For example, forming a sidewall of a resilient material may advantageously achieve greater displaceable volume, allowing further reduction in the size of an implant.  
         [0052]     Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.