Patent Publication Number: US-8523885-B2

Title: Implantable restriction system with load monitor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to laparoscopic implanted restriction system designed to be implanted in the body of a patient around a biological organ having a pouch or duct to regulate functioning of the organ or duct. More specifically, the present invention is directed to an implantable telemetrically powered and controlled ring suitable for use as a gastric band to treat obesity or as an artificial sphincter. 
     2. Description of the Related Art 
     Obesity refers to a body weight that exceeds the body&#39;s skeletal and physical standards. One well recognized parameter used to measure obesity is Body Mass Index (BMI), because it takes into account patient height and not just weight. BMI is calculated by dividing weight by height squared and is expressed in kg/m2. 
     Obesity is well recognized as a serious health problem, and is associated with numerous health complications, ranging from non-fatal conditions to life-threatening chronic diseases. Surgical intervention generally is the treatment of choice for patients afflicted with morbid obesity. Such intervention not only mitigates the myriad of health problems arising from being overweight, but may also reduce the risk of early death of the patient. Left untreated, morbid obesity may reduce a patient&#39;s life expectancy by ten to fifteen years. 
     Morbidly obese patients as a group are poorly adapted to attain sustainable long-term weight loss using non-surgical approaches, such as strict diets combined with exercise and behavioral modification, even though such methods are acknowledged to be the safest. For this reason, there is a continuing need for direct intervention to provide effective, long-term treatments for morbid obesity. Three main surgical procedures are currently in use: Roux-en-Y Gastric Bypass (“RYGB”), Vertical Banded Gastroplasty (“VBG”) and Adjustable Gastric Banding (“AGB”). 
     In RYGB a small stomach pouch is created and a Y-shaped section of the small intestine is attached to the pouch so that food bypasses the lower stomach, the duodenum and the first portion of the jejunum. The RYGB procedure is both restrictive, in that the small pouch limits food intake and malabsorptive, in that the bypass reduces the amount of calories and nutrients the body absorbs. 
     VBG employs a non-adjustable synthetic band and staples to create a small stomach pouch. AGB employs a constricting synthetic ring defining a gastric band that is placed around the upper end of the stomach to create an artificial stoma within the stomach. The band is filled with saline solution and is connected to a small reservoir/access-port located under the skin of the abdomen. The AGB band may be inflated, thereby reducing the size of the stoma, or deflated, thus enlarging the stoma, by puncturing the access-port with a needle and adding or removing saline solution. Both VBG and AGB are purely restrictive procedures, and have no malabsorptive effect. 
     It is sometimes necessary to re-operate, either to relieve the patient or to adjust or change the previously implanted band. In such cases, the previously implanted band must be cut and either removed or replaced. These operations are difficult to carry out, difficult for the patient to tolerate and costly. 
     Several attempts to overcome the drawbacks associated with hydraulically actuated gastric bands, are found in the prior art. For example U.S. Pat. No. 6,547,801 to Dargent et al. describes a surgically implanted gastroplasty system having a flexible tactile element that engages a motor-driven notched pulling member. The motor is powered and controlled by an inductive circuit, so that the diameter of the ring may only be changed by operation of an external remote control. 
     All of the foregoing surgical techniques involve major surgery and may give rise to severe complications. Recent developments have focused on the use of laparoscopic implantation of the gastric ring to minimize patient discomfort and recuperation time. 
     In view of the foregoing, it would be desirable to provide apparatuses and methods for regulating functioning of a body organ or duct that provides high precision in controlling the degree of constriction imposed upon the organ or duct, without the drawbacks associated with prior control mechanisms. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an apparatus for regulating the functioning of a patient&#39;s organ or duct including an elongated member having a first end and a second end. A fastener is disposed on the first end of the elongated member. The fastener is configured to engage the second end of the elongated member so that the elongated member forms a loop around the organ or duct. A tension element is disposed for movement within the elongated member. A drive element is associated with and engages the tension element for causing the tension element to control the tension applied by the elongated member against a patient&#39;s body organ or duct. A load monitor ensures that excessive pressure is not applied to a patient&#39;s body organ or duct. 
     It is also an object of the present invention to provide an apparatus wherein the load monitor includes a monitoring circuit monitoring current drawn by the drive element. 
     It is a further object of the present invention to provide an apparatus wherein drive element is motor. 
     It is another object of the present invention to provide and apparatus wherein the monitoring circuit is a closed loop feedback circuit. 
     It is also an object of the present invention to provide an apparatus wherein the monitoring circuit includes leads accessing current flowing from a power source to a motor of the drive element. 
     It is a further object of the present invention to provide an apparatus wherein the current is measured using a current sensing circuit and output current measurement is forward to a microcontroller for control of the drive element. 
     It is another object of the present invention to provide and apparatus wherein the monitoring circuit includes a Hall sensor positioned about a wire supplying a motor of the drive element with electrical power. 
     It is also an object of the present invention to provide an apparatus wherein load monitor is a strain gage. 
     It is a further object of the present invention to provide an apparatus wherein the drive element includes a motor acting upon threading of the tension element and the strain gage measures tension applied to the threading of the tension element. 
     It is another object of the present invention to provide and apparatus wherein the load monitor includes a pressure monitor associated with a fluid filled bladder forming part of the elongated member. 
     It is also an object of the present invention to provide an apparatus wherein the fluid filled bladder is formed along the interior surface of the elongated member. 
     It is a further object of the present invention to provide an apparatus wherein the fluid bladder is a separate component and may be added or fixedly attached to the elongated member prior to or during installation. 
     It is another object of the present invention to provide and apparatus wherein the fluid filled bladder is pre-filled with fluid and calibrated prior to implantation. 
     It is also an object of the present invention to provide an apparatus wherein the fluid filled bladder may be fluid calibrated post implantation. 
     It is a further object of the present invention to provide an apparatus wherein the fluid filled bladder is adjustable. 
     It is another object of the present invention to provide and apparatus wherein the fluid filled bladder is provided with a port in fluid communication with a filling tube that extends from the fluid bladder. 
     It is also an object of the present invention to provide an apparatus wherein fluid within the fluid bladder is a non-aqueous fluid or gel. 
     It is a further object of the present invention to provide an apparatus wherein load monitor includes a torque sensor measuring the motor torque. 
     Other objects and advantages of the present invention will become apparent from the following detailed description when viewed in conjunction with the accompanying drawings, which set forth certain embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a banding system in accordance with the present invention. 
         FIGS. 2A and 2B  are, respectively, a schematic diagram, partly in cross-section, of the gastric band of  FIG. 1  and a sectional view taken along line  2 B- 2 B of  FIG. 2A . 
         FIGS. 3 to 14  show various embodiments enhancing the interior surface of the ring for contact with tissue. 
         FIGS. 15A and 15B  are perspective views illustrating the degree of constriction attainable by the ring of the present invention between the fully open and fully closed positions. 
         FIGS. 16A and 16B  are cross-sectional views of the ring of the present invention along the lines  16 A- 16 A and  16 B- 16 B of  FIGS. 15A and 15B , respectively. 
         FIG. 17  is a partial perspective view of a screw thread portion of the tension element of the present invention. 
         FIG. 18  is a perspective view of an entire tension element suitable for use in the ring of the present invention. 
         FIG. 19  is a perspective view of the tension element of  FIG. 6  coupled to the rigid dorsal peripheral portion and motor housing of the ring. 
         FIG. 20  is a perspective view of the ring of  FIG. 1  straightened and inserted within a standard 18 mm trocar. 
         FIG. 21  is a cross-sectional view of an elastomeric housing of the gastric band depicting the path of the antenna wire and cavity that accepts the tension element. 
         FIG. 22  is a perspective view of the drive element housing, tension element and drive element of the present invention. 
         FIG. 23  is a perspective view of the tension element engaged with the drive element. 
         FIG. 24  is a cross-sectional view of a tension element in accordance with an alternate embodiment. 
         FIG. 25  is a cross-sectional view depicting the construction of the drive element of  FIG. 23 . 
         FIG. 26  is a cross-sectional view depicting the construction of the reference position switch. 
         FIGS. 27 to 38  show various embodiments of drive assemblies, which may be used in accordance with the present invention. 
         FIGS. 39 to 55  show various embodiments for releasing the fixed end of the tension element from its position at the second end of the ring. 
         FIGS. 56A-C  show another embodiment of implementing a balloon based back-up system in conjunction with the mechanical tension element. 
         FIGS. 57A ,  57 B and  58 A,  58 B show a couple embodiments of releasing fluid from the secondary cavity of the ring. 
         FIGS. 59 to 71  show various embodiments for releasing the tension element. 
         FIG. 72  is a schematic showing an alternate embodiment with a titanium case encasing electronic components of the invention. 
         FIGS. 73 to 76  show additional embodiments for releasing the tension element. 
         FIGS. 77 to 94  show various embodiments for releasing the free end of the tension element from engagement with the drive element in accordance with the present invention. 
         FIGS. 95 and 96  show embodiments for accessing the electronic controls of the antenna/controller pod for controlling operation of the ring in accordance with the present invention. 
         FIGS. 97A and 97B  are perspective views illustrating the clip used to close the ring into a loop. 
         FIGS. 98 and 99  show a release mechanism for a clip of the ring in accordance with an alternate embodiment of the present invention. 
         FIG. 100  is a perspective view of the antenna/controller pod of the present invention. 
         FIG. 101  is a cut-away view of the interior of the implantable antenna/controller pod of  FIG. 100 . 
         FIG. 102  is a cross-sectional view of the antenna cable of  FIG. 100 . 
         FIG. 103  is a detailed view of the signal strength indicator portion of the remote control of  FIG. 1 . 
         FIG. 104  is a schematic diagram illustrating placement of the implantable portion of the present invention within a patient. 
         FIG. 105  is a schematic view of the telemetric power and control circuitry of the present invention. 
         FIGS. 106 to 112  show various embodiments for monitoring the tension applied by the ring. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The detailed embodiments of the present invention are disclosed herein. It should be understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as a basis for teaching one skilled in the art how to make and/or use the invention. 
     Referring now to  FIG. 1 , the banding or implantable restriction system  1  of the present invention is described. The banding system  1  includes an external control  10  and implantable gastric band  21 . In the following description reference will be made, by way of illustration, to a gastric band  21  in the form of a ring  22  designed to be implanted around the stomach to selectively adjust the diameter of the opening of the stoma, and thereby control food intake. Such regulation has the effect of creating a feeling of satiety in the patient after relatively little food is consumed, and provides an effective treatment for morbid obesity. 
     It is to be understood, however, that the present invention is in no way limited to gastroplasty, but on the contrary, advantageously may be applied to regulate the functioning of other body organs or ducts, such as in the treatment of gastro-esophageal reflux disease, urinary or fecal incontinence, colostomy, ileostomy or to regulate blood flow in connection with isolated organ perfusion for treatment of cancer. When applied in the treatment of urinary continence, the implantable portion of the present banding system  1 , in particular, the elongated member in the form of a ring  22  will be implanted around the bladder or urinary tract, while in the case of fecal incontinence, the ring  22  may be implanted around a portion of the gastro-intestinal tracts, such as anal structures of the intestine. With this in mind, the present banding system  1  is MRI compatible and all elements thereof are non-ferro-magnetic. 
     As discussed above, the present invention relates to an implantable restriction system. A preferred embodiment of the implantable restriction system is disclosed herein with reference to a gastric band used in restricting the effective size of the stomach for application in bariatric procedures. As such, the implantable restriction system of the present invention is referred to as including a gastric band or ring throughout the present disclosure, although those skilled in the art will appreciate the concepts underlying the present invention may be applied in a variety of implantable restriction devices as briefly discussed above. 
     System Overview 
     With respect to  FIG. 1 , the self-contained external control  10  comprises a housing  11  having a control panel  12  and a display screen  13 . The external control  10  includes a digital signal processor and may be battery-powered or powered using an external power supply, e.g., connected to an electric wall outlet. An external antenna  14  is coupled to the external control  10  via a cable  15 . As described more fully with respect to  FIG. 105 , the external control  10  includes a controller (such as a microprocessor) that controls the emission of radiofrequency signals to the gastric band  21  to both control and power operation of the gastric band  21 . 
     The external control  10  accepts a patient microchip card  16 , which corresponds to the specific gastric band  21  implanted in the patient, and stores data, such as the implant identification number, adjustment parameters (e.g., upper and lower limits of an adjustment range, etc.) and information regarding the last adjustment position of the ring  22 . The external control  10  as shown in  FIG. 1  includes a signal strength indicator  17 , as described in more detail below with respect to  FIG. 103 , an ON/OFF button  18 , an OPEN button  19   a , a CLOSE button  19   b , a COUPLING button  19   c  and a menu options panel  20 . 
     During use of the present banding system  1 , the physician need only turn on external control  10  using the ON/OFF button  18 , position the external antenna  14  over the patient&#39;s chest above antenna/controller pod  23 , check the coupling by depressing the COUPLING button  19   c , and when the coupling is sufficient, adjust the degree of constriction using the OPEN button  19   a  or the CLOSE button  19   b  to control the effective circumference of the ring  22  in a manner discussed below in greater detail. The diameter of the gastric band  21  is continually displayed on the display screen  13  with a precision of about 0.1 mm for the entire range of diameters of the ring  22 , e.g., from 19 mm fully closed to 29 mm fully opened. 
     Still referring to  FIG. 1  and as briefly mentioned above, the gastric band  21  of the present invention includes a ring  22  coupled to an implantable antenna/controller pod  23  via an antenna cable  24 . The antenna/controller pod  23  includes a removable tag  25  that may be used to laparoscopically position the ring  22 . The ring  22  includes a first end  26  having a clip  27  that slides over and positively engages a second end  28  of the ring  22 . 
     As described in detail below, the ring  22  is configured to be straightened to pass through the lumen of a commercially available 18 mm trocar for delivery to a patient&#39;s abdomen (see  FIG. 20 ). The tag  25 , antenna/controller pod  23  and antenna cable  24  are passed through a clip  27  to form the gastric band  21  into a substantially circular ring  22  around an upper portion of the patient&#39;s stomach, thereby reducing the diameter of the opening of the stomach. In its undeformed shape, the ring  22  assumes a circular arc configuration that facilitates positioning of the ring  22  around the stomach and also in self-guiding the clipping procedure. 
     The ring  22  of the present invention comprises a flexible tubular member having a smooth, flexible and elastic membrane, thus ensuring atraumatic contact with the patient&#39;s stomach tissue that is easily tolerated. When engaged with a dorsal element  38 , the membrane  39  is stretched by an appropriate factor (i.e., 20%-40%), so that when the ring  22  is in it&#39;s fully closed position, little or no wrinkling appears on the membrane surface. The ring  22  has approximately the shape of a torus of revolution of substantially cylindrical cross-section. Alternatively, the ring  22  may have other suitable cross-sections, including rectangular. The housing  29  on the second end  28  of the ring  22 , the clip  27  on the first end  26  of the ring  22  and the dorsal peripheral portion  30  of the ring  22 , preferably are made of a biocompatible material such as silicone. An interior portion  31  of the ring  22  may be constructed in a variety of manners as discussed below in greater detail to permit engagement with the tissue without bunching or rippling, and, as discussed below in greater detail, may be covered in various manners to enhance the ring/tissue interface and protect the ring  22 . 
     Implantable Ring 
     Referring now to  FIGS. 2A and 2B , the internal structure of the ring  22  is described. In particular, and as depicted in  FIG. 2A , the ring  22  includes a flexible tension element  32  having a fixed end  33  statically mounted to the first end  26  of the ring  22  and a free end  34  that is engaged with a motor-driven drive element  35  and extends into a cavity in the housing  29 . The tension element  32  is slidingly disposed within a substantially cylindrical tube of a compressible material  36 , e.g., ePTFE, as illustrated in  FIG. 2B , so that when the tension element  32  is pulled through the drive element  35 , the compressible material  36  is compressed and the diameter of opening  37  is reduced. The compressible material  36  is preferably surrounded on its dorsal face by a dorsal element  38 . The dorsal element  38  is flexible, but sturdier than the elastomeric material of the compressible material. The dorsal element is preferably composed of silicone. Both the compressible material  36  and the silicone dorsal element  38  preferably are enclosed within a membrane  39  of elastomeric biocompatible material, as shown in  FIG. 2B , to prevent tissue in-growth between the ePTFE compressible material  36  and the silicone dorsal element  38 . The membrane  39  may be affixed to the dorsal element  38  using a biocompatible glue to prevent leakage in case of accidental puncture on the dorsal surface. 
     With reference to  FIGS. 3 to 14 , various embodiments have been developed for improving the interaction between the inner surface  112  of the ring  22  and the tissue it engages as the band  21  is constricted about the stomach of a patient. In accordance with a first embodiment as shown with reference to  FIG. 3 , a fluid bladder  114  is added to the inner surface  112  along the internal circumference of the ring  22  such that the fluid bladder  114  interfaces with the tissue. In addition, to improving the tissue band interface, the addition of a fluid bladder  114  along the inner surface  112  of the ring  22  allows for ready adjustments to the restrictive level of the ring  22 . 
     In accordance with such an embodiment, and as briefly discussed above, the fluid bladder  114  is formed along the inner surface  112  of the ring  22  for direct engagement with the tissue when the ring  22  is applied to the stomach and constricted thereabout. The fluid bladder  114  is preferably made of silicone (or other biocompatible material) and is constructed as an elongated cylindrical member  116  with a high degree of flexibility allowing it to conform to the surface of the tissue to which it is applied without adversely affecting the tissue when applied thereto for long periods of time. The cylindrical member  116  extends about substantially the entire length of the inner circumference of the ring  22 . As such, the fluid bladder  114  includes a first end  118  adjacent the first end  26  of the ring  22  and a second end  120  adjacent the second end  28  of the ring  22 . 
     The cylindrical member  116  includes a central lumen  121  shaped and dimensioned to receive a filling fluid as discussed below. The cylindrical member  116 , and ultimately the central lumen  121 , includes the closed first end  118  and the open second end  120 . The second end  120  is provided with a port  122  in fluid communication with a filling tube  124  that extends from the fluid bladder  114  to a remote fluid source  126  allowing for the controlled application of the fluid to the fluid bladder  114  for filling thereof as desired by the medical practitioner deploying and installing the present ring  22 . In accordance with such an embodiment, it is contemplated the remote source of fluid  126  could be integrated with the antenna/controller pod  23  as discussed below in greater detail. 
     The filling tube  124  is provided with a first end  128  which is secured to the port  122  of the fluid bladder  114  and a second end  130  positioned remote from the first end  128 . The second end  130  is fixedly or selectively secured to a source of fluid  126  for filling the fluid bladder  114  as one may desire in accordance with the principles of the present invention. In accordance with a preferred embodiment, the fluid source  126  is a miniature fill port which is subcutaneously implanted (for example, in conjunction with the antenna/controller pod  23 ) for access and addition of fluid as required by the needs of the patient being treated. The fill port  126  includes a flexible access septum  129  through which the medical practitioner may access the internal cavity  131  of the fill port  126  for increasing or decreasing the volume of fluid applied to the fluid bladder  114  positioned along the inner surface  112  of the ring  22  and in direct contact with the tissue of the stomach. 
     It is further contemplated that to achieve a softer tissue interface without secondary adjustability, the fluid bladder may be prefilled prior to implantation. Where such an implementation is employed, a fluid port would not be required. The fluid could be added directly through a catheter attached to the fluid bladder. Once added, the fluid would be trapped by plugging the catheter (for example, tying in a knot, adding a fluid plug, luer activated valve, etc.). 
     In the event of a mechanical or electrical adjustment feature failure the fluid bladder would allow at least minor adjustments to the band. The fluid bladder can be used as a safety feature in case the mechanical adjustment is not functioning properly, since fluid could easily be removed from the bladder un-tightening the gastric band and relieving the pressure applied to the stomach. 
     It is contemplated the fluid bladder could be prefilled with a substance or solution prior to installation. Where the fluid bladder is prefilled, the fluid within the fluid bladder is hyper-osmolar relative to the implanted physiological environment. For example, the filling fluid may be a salt solution or ionic polymer solution, sodium alginate, sodium hyaluronate, etc. The fluid may also be hypo-osmolar relative to the implanted physiological environment, such as, a non-ionic polymer solution poly(ethylene glycol). The fluid may also be a non-Newtonian fluid, such as, a polymer solution selected from the group consisting of a poly(vinylpyrrolidone), carboxymethylcellulose, poly(ethylene glycol), poly(acrylamid), sodium hyaluronate, hyaluronic acid, and alginates. The fluid may further be a non-aqueous fluid or gel, such as, a silicone oil or fluorosilicone oil. 
     In accordance with an alternate embodiment, the ring  22  is shaped and dimensioned to provide for more compliant material and/or construction by altering the cross sectional geometry of the ring  22  to reduce the spring constant of the compressible material  36  between the tension element  32  and the tissue. In addition, improved compliance and construction are achieved by altering the construction of the gastric band  21  such that a secondary, softer material is introduced into the space between the tension element  32  and the tissue, giving the gastric band  21  a reduced spring constant. Improved compliance and construction is further achieved by combining a reduced spring constant with a viscoelastic filler material to give viscoelastic (or rate dependent) deformation characteristics. 
     In accordance with this embodiment, and as show with reference to embodiments shown in  FIGS. 4 to 8 , variations in the spring constant of the gastric band  21  between the tension element  32  and the tissue is achieved through the formation of longitudinally extending space(s)  132  within the compressible material  36 . In accordance with a preferred embodiment, the space(s)  132  maintains a constant shape along the length of the compressible material  36 , although it is contemplated the shapes of the space(s)  132  may be varied along the length of the compressible material  36  and the ring  22 . In practice of the present embodiment, the spring constants may be derived or inferred from tissue interface pressures in the range of −100 mmHg to 300 mmHg gauge pressure wherein the basic relationship is determined by the formula p=F/A. However, it is also contemplated pressures outside this range may also be used. 
     The space(s)  132  may be filled with another material such as silicone rubber, a lower durometer polymer or closed-cell foam to give a reduced spring constant. The space(s)  132  within the cross section may also include viscous or viscoelastic filler materials. That is, they demonstrate rate dependent response to dynamic force conditions such as the passage of food through the esophagus. Potential viscous/viscoelastic filler materials include, but are not limited to, saline liquid or gel silicone, biogels, close cell foams, or pack granules or spears of one or more materials. 
     In addition to improving the spring constant, the incorporation of open space(s)  132  in the compressible material  36  as disclosed herein maximizes the interface between the ring  22  and the tissue thereby spreading the forces or interface pressures applied to the tissue in accordance with the present invention. 
     As discussed above, the space(s)  132  may take a variety of forms. For example, and with reference to  FIG. 4 , the space  132  takes the form of a substantially C-shaped lumen. In accordance with an alternate embodiment as shown with reference to  FIG. 5 , the space  132  takes the form of truncated triangle wherein the top section (that is, the narrow portion adjacent the tension element  32 ) of the triangle is curved and the bottom section (that is, the wide portion removed from the tension element  32 ) of the triangle includes a slightly concave base. In accordance with yet a further embodiment, and with reference to  FIG. 6 , first and second arcuate spaces  132  are provided on opposite sides of the ring  22 . Once again, and with reference to  FIG. 7 , four elongated spaces  132  are provided. The elongated spaces  132  are oriented such that when viewed across the cross section of the ring  22 , the longitudinal axis thereof extends transversely against the longitudinal axis passing through the center of the ring  22 . In accordance with yet a further embodiment, and with reference to  FIG. 8 , the spaces  132  are formed so as to extend circumferentially about the compressible material  36  of the ring  22  and take the form of arcuate members whose concave surfaces  134  faces away from the center of the ring  22  and whose convex surfaces  136  face away from the center of the ring  22 . 
     In accordance with yet another embodiment of the present invention, and with reference to  FIG. 9 , the ring  22 , and in particular, the compressible material  36 , may be provided with a fluid chamber  138  extending along the inner circumferential portion of the compressible material  36 . In contrast to the embodiment disclosed above with reference to  FIG. 3 , the fluid lumen or chamber  138  forms part of the compressible material and is preferably integrally formed with the compressible material  36 . As such, the compressible material  36  may be thought of as including a fluid lumen  138  along its inner surface, the fluid lumen  138  being shaped and dimensioned for maintaining a desired fluid therein so as to improve the stress profile being applied to the tissue. 
     In accordance with a preferred embodiment of the present invention, the fluid chamber  138  includes a cross-sectional profile, when viewed along a plane transverse to the circumferential axis running along the center of the ring  22 , that remains constant along the length of the ring  22 . The profile is elliptical defining an arcuate inner wall  140  and an arcuate outer wall  142  with the concave surfaces thereof facing each other. 
     In addition to improving the tissue to ring interface by providing greater compliance along this area, the fluid chamber  138  may also allow for expansion of the gastric band  21  in the event the mechanical adjustment system fails. In particular, the fluid lumen  138  is maintained in fluid communication with a remote fluid pressure source as discussed above with reference to  FIG. 3 . As such, and if the mechanical or electrical adjustment feature fails, fluid may be pumped into the fluid lumen  138  creating additional pressure that is transferred to the stomach about which the ring  22  is positioned. Alternatively, fluid may be removed from the fluid lumen  138  thereby relieving pressure applied to the stomach about which the ring  22  is positioned. In accordance with a preferred embodiment, it is contemplated the fluid source may be housed in and controlled by the antenna/controller pod  23  of the ring  22 . It is further contemplated, the fluid source may also be manually adjusted by a separate connection to a fluid port. 
     In accordance with still a further embodiment, the cross-sectional geometry of the gastric band  21  may be varied to cover other alternatives. As shown with reference to  FIG. 10 , the geometry is altered such that the tension element  32  is positioned off center of the compressible material  36 , that is, the cross sectional area of the ring  22  itself. By doing this, the tension element  32  takes advantage of rotational torque resulting from the off center positioning and produces mechanical advantages during the constriction of the ring  22 . 
     With reference to the embodiments shown with reference to  FIGS. 12 and 13 , a softer tissue ring interface is achieved by positioning a flexible strip  146  along the inner surface  112  of the ring  22 , and between the compressible material  36  and the membrane  39 . This strip  146  is designed to spread the forces of the tension element  32  along the entire circumference of the ring  22  and is preferably made from a polymer. With reference to  FIG. 11 , the strip  146  is placed along the inner surface  112  of the ring  22 , and not between the compressible material  36  and the membrane  39 . In accordance with a preferred embodiment, the strip  146  includes an inner surface  148  and an outer surface  150 . The inner surface  148  is substantially smooth and flat and is adapted to directly face the tissue upon constriction of the ring  22 , with the strip  146  positioned between the compressible material  36  and the membrane  39 . The outer surface  150  includes substantially flat portions  152  and a central protrusion  154  which is shaped and dimensioned to directly engage the tension element  32  upon constriction thereof. As such, and when the tension element  32  is tightened, the tension element  32  applies pressure directly to the central protrusion  154  of the flexible strip  146 . This pressure is transferred along the entire length of the flexible strip  146  such that pressure is evenly distributed along the inner surface  148  of the strip  146 . In accordance with yet another embodiment, and with reference to  FIG. 14 , the inner surface  148  of the strip  146  may take the form of a resilient tubular member  147  with additional compliance. By utilizing such a design, the interior volume  145  defined by the strip  146  may be filled with viscoelastic materials enhancing the compliance of the strip  146  and the overall tissue ring interface. 
     In accordance with one aspect of the present invention, and with reference to  FIGS. 15A ,  15 B,  16 A and  16 B, the ring  22  further comprises a layer  40  of a relatively rigid material disposed on the dorsal periphery of the ring  22 . The layer  40 , which may comprise a plastic or metal alloy, prevents the exterior diameter D of the ring  22  from changing during adjustment of the tension element  32  to reduce the internal diameter (or opening  37 ) of the ring  22 . The layer  40 , by its structural rigidity, imposes a circular arc shape for the entirety of the ring  22 . Advantageously, the layer  40  allows the tension element  32  to be adjusted following encapsulation of the ring  22  by fibrous tissue after implantation, since adjustment of the internal diameter of the ring  22  does not change the external diameter D of the ring  22 . 
     The foregoing feature is illustrated in  FIGS. 15A and 15B  where the ring  22  is shown in its fully opened and fully closed positions, respectively. As discussed above, the layer  40  forms a rigid skeleton that permits the internal diameter of the ring  22  to change while maintaining the external diameter D constant. Radial movement of the tension element  32  is transmitted to the membrane  39  by the compressible material  36 . ePTFE is particularly well-suited for use as the compressible material  36  because it can undergo a 3:1 reduction in length without experiencing a significant increase in cross-section. 
     Accordingly, and as depicted in  FIGS. 16A and 16B , increase or reduction of the effective length of the tension element  32  results in reversible radial displacement at the internal periphery of the ring  22  opposite the dorsal periphery. This in turn translates into a variation of internal diameter of the ring  22  from a fully open diameter to a fully closed diameter by expanding or controlling the ring  22  to control the tension applied by the ring  22  against a patient&#39;s body organ or duct. Preferably, the fully open internal diameter is about 35 mm, and the fully closed internal diameter is about 15 mm. More preferably, the fully open internal diameter is about 29 mm, and the fully closed internal diameter is about 19 mm. 
     Referring now to  FIG. 17 , the tension element  32  in accordance with a first embodiment is described. This tension element is disclosed in detail in U.S. Patent Application Publication No. 2005/0143766, which is incorporated herein by reference. Briefly, the tension element  32  has sufficient flexibility to permit it to be formed into the substantially circular shape of the ring  22 , while also being able to transmit the force necessary to adjust the ring diameter. The tension element  32  therefore comprises a flexible core  41 , preferably a metal alloy wire of circular cross section, on which is fixed, and wound coaxially, at least one un-joined coil spring which defines the screw thread pitch. 
     As shown in  FIG. 17 , the tension element  32  preferably comprises two un-joined coil springs that form a screw thread: a first spring  42 , wound helicoidally along the flexible core  41 , and a second spring  43  of greater exterior diameter. The second spring  43  preferably comprises coils  44  of rectangular transverse section, so as to delineate a flat external generatrix. The first spring  42  is interposed between coils  44  of the second spring  43  to define and maintain a substantially constant square screw thread pitch, even when the tension element  32  is subjected to bending. 
     As a consequence of the foregoing arrangement, the ability of the tension element  32  to maintain a substantially constant thread pitch, when subjected to bending, confers great precision on adjustments of the ring  22 . This is especially so when it is realized that as the tension element  32  is drawn through the drive element  35 , an ever-increasing curvature is imposed on the remaining portion of the tension element  32 . However, because the foregoing arrangement of un-joined coils maintains a substantially constant screw thread pitch, the energy needed to drive the drive element  35  remains low and the efficiency of energy transmission resulting from the use of a square screw thread pitch remains high. In addition, the use of a square screw thread pitch guarantees a stable adjustment position even when the drive element is unpowered. 
     Referring now to  FIG. 18 , the tension element  32  is described. The free end  34  includes a crimped cap  45 , the second spring  43  has coils with a square transverse section, and the first spring  42  (not visible in  FIG. 18 , but shown in  FIG. 17 ) is intertwined between the coils of the second spring  43 . The flexible core  41  extends through the first and second springs  42 ,  43 , and terminates close to the crimped cap  45 . In accordance with one aspect of the present invention, the tension element  32  further comprises a third spring  46  that is coupled to the flexible core  41 , and the first and second springs  42 ,  43  at junction  47 . The third spring  46  includes a loop  48  at the end opposite to junction  47 , which permits the tension element  32  to be mounted to the first end  26  of the ring  22 . 
     With respect to  FIG. 19 , the tension element  32  is shown disposed within a skeleton  50  of the ring  22 . The skeleton  50  includes a layer  51  that forms the dorsal periphery (corresponding to the layer  40  of  FIGS. 2A ,  2 B,  16 A and  16 B), an anchor  52  that accepts the loop  48  of the tension element  32 , and a drive element housing  53 . The skeleton  50  is preferably constructed from a high strength moldable plastic. As further depicted in  FIG. 19 , the skeleton  50  extends along a greater arc length than the tension element  32 . In accordance with another aspect of the present invention, the third spring  46  permits the gastric band  21  to be straightened for insertion through a standard 18 mm trocar, despite the differential elongation of the skeleton  50  and the tension element  32 . This feature is illustrated in  FIG. 20 , which depicts the ring  22  inserted through 18 mm trocar  55  so that the ring  22  is substantially straight. 
     Referring now to  FIG. 21 , the housing  29  of the free end of the ring  22  is described. The housing  29  comprises an elastomeric material, such as silicone, having a recessed portion  56 , a tension element cavity  57  and a cable lumen  58 . The recessed portion  56  is configured to accept the drive element housing  53  of the skeleton  50 , so that as the tension element  32  is drawn through the drive element  35  it extends into the tension element cavity  57 . A cable lumen  58  extends through the housing  29  so that the antenna cable  24  may be coupled to the drive element  35 . The housing  29  preferably may be grasped in area G using atraumatic laparoscopic graspers during manipulation of the gastric band  21 . 
     In  FIG. 22 , the drive element housing  53  of the skeleton  50  is shown with the drive element  35  and the tension element  32  disposed therethrough. The antenna cable  24  is coupled to a motor (not shown) disposed within the drive element housing  53 . The tension element  32  is in the fully opened (largest diameter) position, so that the crimped cap  45  contacts the printed circuit board  59  of the reference position switch, described below with respect to  FIG. 26 . 
     Because the tension element  32  must be drawn through the drive element  35  to cause tightening thereof, the tension element  32  described above necessarily requires that the tail end  34 , that is, the end nearest crimped cap  45 , of the tension element  32  extends beyond the drive element  35  with the extending portion increasing as the ring  22  is tightened, making potential interference with the viscera possible. In addition, the tension element  32  may cause localized stress to the inside surface, for example, the compressible material  36 , of the gastric band  21  as well as potentially to the viscera. 
     In accordance with an alternate embodiment and with reference to  FIG. 24 , the diameter of the ring  22  is adjusted without the need for a tension element including a tail end which is extended and retracted as the need for adjustments in the diameter of the ring  22  are desired. The tension element  32  in accordance with this embodiment is composed of an inner first strap member  440 , an outer second strap member  442  and a camming strap member  444  moveably positioned therebetween. The first strap member  440  includes an inner surface  446  and an outer surface  448 , the second strap member  442  includes an inner surface  452  and an outer surface  454 , and the camming strap member  444  includes an inner surface  456  and an outer surface  458 . The inner surface  446  of the first strap member  440  is substantially smooth and is shaped and dimensioned for facing the tissue which the ring  22  engages. The outer surface  448  of the first strap member  440  includes a plurality of recessed camming surfaces  460  shaped and dimensioned for interacting with protruding camming  462  surfaces extending from the inner surface  456  of the camming strap member  444 . Similarly, the outer surface  454  of the second strap member  442  is substantially smooth and is shaped and dimensioned for facing the tissue which the ring  22  engages. The inner surface  452  of the second strap member  442  includes a plurality of recessed camming surfaces  464  shaped and dimensioned for interacting with protruding camming surfaces  466  extending from the outer surface  454  of the camming strap member  444 . 
     As discussed above, the camming strap member  444  is shaped and dimensioned for positioning between the first strap member  440  and the second strap member  442  in manner such that the camming strap member  444  is in sliding contact with the first and second strap members  440 ,  442  but is free to move relative thereto. As such, when the camming strap member  444  moves circumferentially relative to the first and second strap members  440 ,  442 , the protruding camming surfaces  462 ,  466  of the camming strap member  444  interact with the recessed camming surfaces  460 ,  464  of the respective first and second strap members  440 ,  442 . As a result of this interaction, the first strap member  440  is caused to move inwardly or outwardly selectively decreasing or increasing the effective diameter of the ring  22 . 
     Controlled movement of the camming strap member  444  is achieved by a drive element  470  secured at the first end  472  of the camming strap member  444 . In accordance with a preferred embodiment, the drive element  470  is a conventional drive mechanism, for example, screw drive, friction belt drive, servomotor, etc. 
     It is further contemplated the recessed camming surfaces  460 ,  464  and the protruding camming surface  462 ,  466  may be adjusted in height and location along the circumference of the tension element  32  so as to adjust the ability of the tension element  32  to control adjustments in the diameter of the ring  22 . That is, the total adjustment range of the tension element  32  will depend on the configuration of the recessed and protruding camming surfaces  460 ,  462 ,  464 ,  466 , specifically, the number of camming surfaces and the height of the camming surface. In the simplest case the adjustment diameters could be described as 
     θ i =original diameter 
     h=height of wedge 
     θ f =final diameter 
     θ f =θ i +2(h) 
     This tension element  32  construction offers a variety of advantages, including: the cost of the flexible spring assembly disclosed with reference to other embodiments can be avoided and the total throw of the motor can be reduced therefore reducing the length of the tail section. Multiple camming surface configurations can be adapted to the design to achieve different adjustment ranges while a constant pressure profile on the restricted tissue can be is maintained. 
     Drive Element 
     With respect to  FIGS. 25 and 26 , the drive element  35  used in conjunction with the tension element  32  disclosed with reference to  FIGS. 22 and 23 , includes a motor  66  coupled to the antenna cable  24  that drives the nut  60  through the gears  61 . As with the various embodiments presented throughout the present disclosure, the motor may take a variety of forms including, but not limited to a stepper motor and piego motor. The nut  60  is supported by upper and lower bearings  62  to minimize energy losses due to friction. The nut  60  is self-centering, self-guiding and provides high torque-to-axial force transfer. The drive element  35  is disclosed in greater detail with reference to U.S. Patent Application Publication No. 2005/0143766, entitled “TELEMETRICALLY CONTROLLED BAND FOR REGULATING FUNCTIONING OF A BODY ORGAN OR DUCT, AND METHODS OF MAKING, IMPLANTATION AND USE”, which is incorporated herein by reference. 
     Referring now to  FIG. 26 , the reference position switch of the present banding system  1  is described. Because the drive element  35  of the present banding system  1  employs a nut  60  driven by a stepper motor  66 , there is no need for the system to include a position sensor or encoder to determine the length of the tension element  32  drawn through the drive element  35 . Instead, the diameter of the ring  22  may be directly computed as a function of the screw thread pitch and the number of rotations of the nut  60 . To ensure an accurate calculation of the degree of restriction imposed by the ring  22 , however, it is desirable to provide at least one reference point. 
     This reference datum is accomplished in the ring  22  of the present invention using a reference position switch that is activated when the ring  22  is moved to its fully open position. The crimped cap  45  on the free end of the tension element  32  serves this function by contacting electrical traces  63  on the printed circuit board  59  (and also limits elongation of the screw thread). The circuit board  59  is disposed just above the bearing  65 , which forms part of the drive element  35  (see also  FIG. 22 ). When the crimped cap  45  contacts the traces  63 , it closes a switch that signals the implantable controller that the ring  22  is in the fully open position. 
     In accordance with an alternate embodiment, and with reference to  FIG. 27 , a symmetrical drive system  170  is employed. Briefly, and in accordance with a preferred embodiment of the present invention, the drive system  170  employs two flexible members  172 ,  174  which, in accordance with a preferred embodiment of the present invention, are flexible screws simultaneously operating upon the tension element  32  using a single motor  176  with a dual actuated drive  178 ,  180 . The dual actuated drives  178 ,  180  provide directional control for loosening or tightening the flexible members  172 ,  174 . In accordance with a preferred embodiment of the present invention, the body of the tension element  32  is constructed in substantially the same manner as that described with reference to the embodiment shown in  FIGS. 17 ,  18  and  19 . However, and considering the flexible members interact with the dual actuated drives for controlled construction and expansion of the ring  22 , the body of the tension element may be constructed of various materials and may be constructed without departing from the spirit of the present invention. However, and as will be appreciated based upon the following disclosure, flexible first and second screws  172 ,  174  are secured to the opposite ends  183 ,  194  of the tension element  32  allowing for actuation in accordance with the embodiment disclosed herein. 
     By drawing the tension element  32  at both ends, and simultaneously applying pressure to the opposite ends, the applied tension is uniformly distributed along the length of the tension element  32 . 
     More particularly, a flexible first screw  172  is provided at one end of the tension element  32 . The first screw  172  includes a first end  182  and a second end  184 . The first end  182  is secured to a first end  183  of the tension element  32  and the second end  184  is fed into a first actuated drive  178  of the motor  176 . Similarly, the flexible second screw  174  includes a first end  186  and a second end  188 . The first end  186  is secured to a second end  194  of the tension element  32  and the second end  188  is fed into a second actuated drive  180  of the motor  176 . With the first and second ends  183 ,  194  of the tension element  32  respectively secured to the first end  182  of the first screw  172  and the first end  186  of the second screw  174 , and the motor  176  connecting the second ends  184 ,  188  of the first and second screws  172 ,  174 , a complete circular loop is created. The effective circumference of the circular loop is, therefore, readily adjusted by manipulating the extent to which the first and second screws  172 ,  174  are drawn into the first and second actuated drives  178 ,  180  of the motor  176 . 
     As briefly discussed above, the motor  176  is provided with first and second actuated drives  178 ,  180 . The first and second actuated drives  178 ,  180  include respective inputs  195 ,  196  that are positioned on opposites sides of the motor  176  for receiving the second ends  184 ,  188  of the respective first and second screws  172 ,  174 . As such, the second end  184  of the first screw  172  is fed into the input  195  of the first actuated drive  178  where it is engaged by a drive mechanism (for example, a screw drive in accordance with a preferred embodiment of the present invention). The second end  188  of the second screw  174  is fed into the input  196  of the second actuated drive  180  where it is engaged by a drive mechanism (for example, a screw drive in accordance with a preferred embodiment of the present invention). 
     In accordance with a preferred embodiment, the drive mechanisms of the first actuated drive  178  and the second actuated drive  180  employ nut-like features upon which a threaded surface of the first and second screws  172 ,  174  ride so as to push or pull the first and second screws  172 ,  174  through the motor body. When the motor  176  is energized, the first and second screws  172 ,  174  move in opposite directions and tighten the tension element  32  about a central axis of the ring  22 . Because both screws  172 ,  174  move at the same time, the tension element  32 , and ultimately, the gastric band  21 , can be adjusted twice as fast as a single direction screw with the same amount of work. 
     With the first screw  172  engaged by the drive mechanism of the first actuated drive  178  and the second screw  174  engaged by the drive mechanism of the second actuated drive  180 , actuation of the motor  176  is controlled to actuate the first and second actuated drives  178 ,  180  to either simultaneous draw the first and second screws  172 ,  174  into the motor  176  or the simultaneous push the first and second screws  172 ,  174  out of the motor  176  for either decreasing or increasing the effective circumference of the tension element  32 . 
     By employing the embodiment described above, symmetrical movement allows for a more uniform distribution of force on the tension element  32 . The tension element  32  is also fixedly secured to the ring  22  at an anchor point  175  diametrically opposite the motor  176 . In this way, the first and second screws  172 ,  174  connected to the tension element  32  pull the membrane  39  of the ring  22  uniformly inward or outward from the anchor point  175  diametrically opposite the motor  176  of the gastric band  21 . It should be noted that is contemplated that the anchor point is not limited to the top of the gastric band but may be located at one side or opposite the motor drive. 
     In accordance with an alternate embodiment as shown with reference to  FIGS. 28 and 29 , the drive system  170  includes a tension element  32  composed of two flexible members (referred to as springs)  202 ,  204 . The springs  202 ,  204  are linked together so as to define the tension element  32  used in increasing or decreasing the circumference of the ring. The flexible first member  202  is threaded externally like a bolt (inner spring) and the flexible second member  204  is internally threaded like a nut (outer spring). The inner spring  202  is shaped and dimensioned to seat within the outer spring  204  in a manner coupling the inner and outer springs  202 ,  204  but allowing rotation of the outer spring  204  relative to the inner spring  202  for controlled adjustment of their relative positions as discussed below in greater detail. 
     More particularly, the outer spring  204  is attached to a rotational motor  176  with the inner spring  202  threaded into the outer spring  204 . As the motor  176  turns the inner spring  202  is either drawn into or pushed farther out of the outer spring  204  to either reduce or increase the diameter of the stoma defined by the ring  22 . To prevent total restriction of the stomach, the outer spring  204  or inner spring  202  is provided with a hard stop  206  that will prevent further restriction. It will be appreciated that the inner and outer springs could also be thought of as a flexible screw and flexible nut. 
     Referring now to  FIGS. 30 and 31 , yet another embodiment is disclosed. In accordance with this embodiment, the tension element  32  mounted within the ring  22  is provided with a flexible hollow threaded shaft  208  at its first end  26  and a flexible threaded shaft  210  at its opposite second end  28 . The threaded shaft  210  is movably coupled to a drive motor  176  secured at the free end  212  of the hollow threaded shaft  208  for controlling movement of the first end  283  of the tension element  32  relative to the second end  294  of the tension element  32 . 
     More particularly, the hollow threaded shaft  208  defining the first end  283  of the tension element  32  includes a free end  212  and a coupled end  214 , while the threaded shaft  210  defining the second end  194  of the tension element  32  includes a free end  216  and a coupled end  218 . The coupled end  214  of the hollow threaded shaft  208  is secured to the coupled end  218  of the threaded shaft  210 . 
     A drive motor  176  is secured to the free end  212  of the hollow threaded shaft  208 . The drive motor  176  includes an input passageway  220  shaped and dimensioned to guide the threaded shaft  210  therethrough and into the cavity  222  defined by the hollow threaded shaft  208 . As such, and with the threaded shaft  210  engaged with the drive motor  176 , the drive motor  176  is actuated to either draw into or push threaded shaft  210  out of the hollow threaded shaft  208  to either reduce or increase the diameter of the stoma defined by the ring  22 . To prevent excessive inward or outward movement, it is contemplated the threaded shafts may be provided with a hard stop(s) (not shown). Additionally, to facilitate connection to the coupled end of the hollow shaft a tapered lead end feature may be added to the free end of the threaded shaft. Similarly, it is further contemplated the hollow threaded shaft may have a cone like feature to more readily facilitate alignment to the threaded shaft during connection. 
     In accordance with yet a further embodiment and with reference to  FIGS. 32 to 38 , a quick connect coupling  224  for use in conjunction with a screw drive mechanism  226  is employed. The quick connect coupling  224  is a snap-together feature molded into a central segment  228  of the ring  22 . 
     More particularly, the ring  22  contains the silicone sleeve that interacts with the patient&#39;s stomach to create the gastric band  21 , but the ring  22  is split at the central segment  228  to allow for controlled splitting of the ring  22  in a manner allowing for ease of deployment and ease of removal. As with the embodiments discussed above, a tension element  32  extends within the ring  22  and similarly includes a split in the central segment  228 . Accordingly, the ring  22  may be thought of as including a first segment  230  and a second segment  232 . The first segment  230  includes a first end  234  and a second end  236  and the second segment  232  includes a first end  240  and a second end  242 . The tension element  32  is similar composed of a first tension segment  244  and a second tension segment  246 . The first tension segment  244  includes a first end  248  and a second end  250  and the second tension segment  246  includes a first end  252  and second end  254 . The first end  234  of the first segment  230  and the first end  240  of the second segment  238  are linked at the motor  176  that couples the first end  248  of the first tension segment  244  to the first end  252  of the second tension segment  246 . Completing the circle defined by the ring and tension elements  230 ,  232 , the second ends  236 ,  250  of the first segment  230  and first tension segment  244  and the second ends  242 ,  254  of the second segment  232  and second tension segment  246  are linked via the quick connect coupling  224 . 
     In practice, the gastric band  21 , with the quick connect coupling  224  disconnected allows the second ends  236 ,  242  of the first and second segments  230 ,  232  of the ring  22  to move freely relative to each other. Thus, the ring  22  can be positioned adjacent the stomach and the quick connect coupling  224  is used by the surgeon to first place and attach the gastric band  21  during surgery. The first end  248  of the first tension segment  244  and the first end  252  the second tension segment  246  each terminate with a drive screw  256 . The drive screws  256  engage the drive motor  176  and are actuated thereby. The motor  176  may then be used to open and close the gastric band  21  about the stomach of the user. 
     It is contemplated the first and second tension segments  244 ,  246  could be made of braided cable, laminate polymers, or even a single wire. The body of the first and second tension segments  244 ,  246  may be substantially wider than the drive screw  256  to uniformly distribute the load. The non-braided version will be more susceptible to fatigue and failure so appropriate materials like nylon may need to be used. As discussed herein in greater detail, the first and second tension segments  244 ,  246  are housed within a center molded cavity of the gastric band  21  that allows them to slip with respect to the gastric band  21  so that as they are tightened stress does not build up in the silicone outer sleeve that would tend to wrinkle or fold the outer membrane. 
     With regard to the drive motor  176 , it is housed within a pocket in the middle of the gastric band  21  and is secured to the first end  234  of the first segment  230  of the ring  22 . The motor housing  258  is grounded and attached to the housing sleeve  260  so that when energy or power is applied; the motor shaft  262  rotates, not the motor housing  258 . The motor housing  258  is attached to a drive screw  267  that is coupled to the opposite first ends  248 ,  252  of the first and second tension segments  244 ,  246 . If one polarity is applied, the motor shaft  262  rotates in a first direction and the system is tightened drawing the first ends  248 ,  252  of the respective first and second tension segments  244 ,  246  toward one another. If the opposite polarity is applied, the motor shaft  262  rotates in a second direction opposite to the first direction and the system loosens, pushing the first ends  248 ,  252  of the respective first and second tension segments  244 ,  246  away from one another. The drive thread configuration can be changed to allow for different speed or torque ratios of the motor to the linear travel of the screws. This will also prevent back travel when the motor is not energized due to the inertia within the motor itself. Additionally, if power is always present, it is contemplated active braking could be incorporated by applying the same polarity to both poles of the motor thereby increasing its holding strength, although usage of power for braking might not be practical in certain application as it would consume power more quickly. It is further contemplated this could also be achieved passively by using a stepper motor which would inherently braking when power is removed. 
     In accordance with an alternate embodiment as shown with reference to  FIG. 34 , a tightening nut  261  is rotated around the outside of the first and second tension segments  244 ,  246  and has a worm gear  263  coupled to the motor (not shown). The worm gear  263  prevents back travel and forces cannot be passed from the tension segments  244 ,  246  back to the motor if the motor is not moving the disclosed worm gear configuration. Rotation in either direction by the motor drive shaft  265  linearly moves the screw head ends  248 ′,  252 ′ of the first and second tension segments  244 ,  246  towards each other or away from each other since the first and second tension segments  244 ,  246  are not actually rotated. It is contemplated the threading on the ends of the first and second tension segments may not be circumferential but only on one side. This would improve guidance and prevent slipping of the threads. 
     It is further contemplated the screw ends could be connected to drive cables forming the tension segments by crimping the metal thread end to the drive cable, or it could be overmolded plastic if the resulting threading was strong enough to work in conjunction with the drive. It could also be molded in the system as a hole with long fiber filler added to the plastic to improve its tension capabilities. 
     Referring to  FIG. 35 , and in accordance with another drive structure for use in accordance with the system described with reference to  FIGS. 32 and 33 , a drive  266  with an angled beveled gearing surface is connected to a motor  176  which is in turn connected to the outer portion of a gastric band  21 . In this configuration, angled racks  268 ,  270  are formed along the first ends  248 ,  252  of the first and second tension segments  244 ,  246  of the gastric band  21 . As the motor  176  rotates, both ends  248 ,  252  of the first and second tension segments  244 ,  246  of the gastric band  21  are drawn inward at the same speed if the motor  176  were to rotate in a first direction, for example, counterclockwise orientation, and the gastric band  21  is uniformly tightened. 
     With reference to  FIG. 36 , it is contemplated the beveled gearing surface of the drive  266  may be oriented at a 90° angle from the above embodiment such that the angled racks  268 ,  270  are drawn over top of one another. The angled racks  268 ,  270  in these embodiments require a track with low friction by which they can travel linearly with respect to each other. This track would also ensure that there is a solid connection to the beveled gear and that no slippage occurs. 
     In accordance with an alternate embodiment, and with reference to  FIG. 37 , the angled racks  268 ,  270  (shown above with reference to  FIGS. 35 and 36 ) are replaced by high strength cables  272 ,  273  and connected directly around a motor shaft  269  in a manner similar to a winch system. The alternative could reduce the complexity of the design as the cables would not require tight tolerances and there would be no concern that the racks could slip from the winch. 
     In accordance with yet another embodiment, and with reference to  FIG. 38 , the motor  176  is external to the gastric band  21  and has a flexible drive cable  274  that rotates any internal gears, racks, pinions, etc. (shown with reference to the drive of  FIG. 33 , although other drive systems are contemplated). The drive cable  274  is capable of providing adequate torque to the drive screw  264  in order to tighten the gastric band  21 . The flexible cable drive would be similar to that found on the Johnson &amp; Johnson Mammotome™ MR product. This flexible drive cable could be implemented into several other embodiments as well when coupled with the appropriate hardware at each of the ends. 
     While the drive element  35  of the present ring  22  is robust and not prone to failure, it may at times be necessary to release the tension element  32  in an emergency. The release of the tension element  32  would provide for immediate release of tension applied by the ring  22  to the stomach and permit removal of the ring  22  from its position about the stomach. 
     In accordance with a first embodiment of a tension element release system and with reference to  FIGS. 39 ,  40  and  41 , the tension element  32  includes a free end  34  and a fixed end  33 . The fixed end  33  is secured adjacent the first end  26  of the ring  22  via a release mechanism  312  allowing selective release of the fixed end  33  of the tension element  32  from the first end of the ring  22  for release of tension being applied by the ring  22 . The release mechanism  312  includes a jaw mechanism  314  that selectively engages the fixed end  33  of the tension element  32 . The fixed end  33  is provided with a bulbous head  316  that is selectively seated within the jaw mechanism  314  in the manner discussed below in greater detail. 
     The jaw mechanism  314  includes a fixed jaw member  318  and a movable jaw member  320 . A jaw drive element  322  is positioned between the fixed jaw member  318  and the movable jaw member  320 . The fixed jaw member  318  is substantially L-shaped and includes a first leg  324  and a second leg  326  oriented perpendicular to each other. Similarly, the movable jaw member  320  is substantially L-shaped and includes a first leg  328  and a second leg  330  oriented perpendicular to each other. The fixed jaw member  318  and the movable jaw member  320  sit facing each other in a mirror like orientation with the first legs  324 ,  328  of the respective fixed jaw member  318  and the movable jaw member  320  substantially parallel to each other and the second legs  326 ,  330  of the respective fixed jaw member  318  and the movable jaw member  320  facing each other in an aligned manner. By adopting this orientation, the fixed jaw member  318  and the movable jaw member  320  create a cavity in which the enlarged head  316  of the tension element  32  may sit while the remainder of the tension element  32  extends through the opening  332  formed between the free ends  334 ,  336  of the respective second legs  326 ,  330  of the fixed jaw member  318  and movable jaw member  320 . As will be appreciated based upon the following disclosure, a spring  321  biases the movable jaw member  320  toward the fixed jaw member  318  maintaining the free ends  334 ,  336  of the respective second legs  326 ,  330  of the fixed jaw member  318  and movable jaw member  320  in proximity to each other for holding the enlarged head  316  of the tension element  32  until it is desired to release the tension element  32 . 
     When one desires to release the tension element  32 , that is, release the enlarged head  316  of the tension element  32  from its position between the fixed jaw member  318  and the movable jaw member  320 , the jaw drive element  322  is expanded in a manner pushing the movable jaw member  320  away from the fixed jaw member  318 . As the movable jaw member  320  is pushed away from the fixed jaw member  318 , that is, as the jaw mechanism  314  is moved from its locked orientation with the fixed jaw member  318  and movable jaw member  320  in close proximity to its release orientation with the fixed jaw member  318  and movable jaw member  320  moved away from each other, the opening  332  therebetween expands until it is larger than the enlarged head  316  of the tension element  32  at which time the fixed end  33  of the tension element  32  is released from its position between the fixed jaw member  318  and the movable jaw member  320 . 
     In accordance with a preferred embodiment, the jaw drive element  322  is a balloon  338  which may be selectively expanded for engagement with the fixed jaw member  318  and the movable jaw member  320  in a manner selectively moving the fixed jaw member  318  and the movably jaw member  320  to their release orientation. While a particular jaw drive element  322  is disclosed above in accordance with a preferred embodiment of the present invention, it is contemplated other drive element mechanisms may be employed without departing from the spirit of the present invention. 
     For example, and in accordance with an alternate embodiment shown with reference to  FIGS. 42 and 43 , the jaw drive element  322  might take the form of a balloon  338  secured to the fixed jaw member  318 , which upon expansion presses against the movable jaw member  320  to place the jaw mechanism  314  in its release orientation. It is contemplated such a balloon  338  would be constructed of silicone and be supplied with fluid for expansion via a catheter  339  extending along the present apparatus. 
     Another jaw drive element  322 ′ is shown with reference to  FIGS. 44 and 45 . In accordance with this embodiment, a shape memory alloy spring  340  is positioned between the fixed jaw member  318  and the movable jaw member  320 . The spring  340  is linked to a source of electricity  342 . Upon application of the a voltage across the spring  340 , the spring  340  will change shape, for example, and in accordance with a preferred embodiment, expand, forcing the fixed jaw member  318  and movable jaw members  320  apart in a manner moving the jaw mechanism  314  to its release orientation. 
     In accordance with an alternate embodiment as shown with reference to  FIGS. 46-48 , the jaw mechanism  314  includes a first movable jaw member  320   a  and a second movable jaw member  320   b . The first movable jaw member  320   a  and the second movable jaw member  320   b  are pivotally connected with first and second spring biasing members  344   a ,  344   b  forcing them toward one another. A jaw drive element  322  is positioned between the first movable jaw member  320   a  and the second movable jaw member  320   b.    
     The first movable jaw member  320   a  is substantially L-shaped and includes a first leg  324   a  and a second leg  326   a  oriented perpendicular to each other. Similarly, the second movable jaw member  320   b  is substantially L-shaped and includes a first leg  324   b  and a second leg  326   b  oriented perpendicular to each other. Each of the first and second movable jaw members  320   a ,  320   b  include a laterally extending flange  346   a ,  346   b  through which a pivot pin  348  extends for pivotally linking the first movable jaw member  320   a  to the second movable jaw member  320   b  in a manner described above. The first movable jaw member  320   a  and the second movable jaw member  320   b  sit facing each other in a mirror like orientation with the first legs  324   a ,  324   b  of the respective first and second movable jaw members  320   a ,  320   b  substantially parallel to each other and the second legs  326   a ,  326   b  of the respective first and second movable jaw members  320   a ,  320   b  facing each other in an aligned manner. By adopting this orientation, the first and second movable jaw members  320   a ,  320   b  create a cavity in which the enlarged head  316  of the tension element  32  may sit while the remainder of the tension element  32  extends through the opening  332  formed between the free ends  334 ,  336  of the respective second legs  326   a ,  326   b  of the first and second movable jaw members  320   a ,  320   b . As will be appreciated based upon the following disclosure, the first and second movable jaw members  320   a ,  320   b  are biased toward each other maintaining the free ends  334 ,  336  of the respective second legs  326   a ,  326   b  of the first and second movable jaw member  320   a ,  320   b  in proximity to each other for holding the enlarged head  316  of the tension element  32  until it is desired to release the tension element  32 . When one desires to release the tension element  32 , that is, release the enlarged head  316  of the tension element  32  from its position between the first and second movable jaw members  320   a ,  320   b , the jaw drive element  322  is expanded in a manner pushing the first and second movable jaw members  320   a ,  320   b  away from each other. As the first and second movable jaw members  320   a ,  320   b  are pushed away from each other, that is, as the jaw mechanism  314  is moved from its locked orientation with the first and second movable jaw members  320   a ,  320   b  in close proximity, to its release orientation with the first and second movable jaw members  320   a ,  320   b  moved away from each other, the opening  332  therebetween expands until it is larger than the enlarged head  316  of the tension element  32  at which time the fixed end  33  of the tension element  32  is released from its position between the first and second movable jaw members  320   a ,  320   b.    
     As with embodiment described above, the jaw drive element  322  is a balloon  338  which may be selectively expanded for engagement with the first and second movable jaw members  320   a ,  320   b  in a manner selectively moving the first and second movable jaw members  320   a ,  320   b  to their release orientation. While a particular jaw drive element is disclosed above in accordance with a preferred embodiment of the present invention, it is contemplated other drive element mechanisms may be employed without departing from the spirit of the present invention. For example, another jaw drive element  322 ′ is shown with reference to  FIGS. 49 and 50 . In accordance with this embodiment a shape memory alloy spring  340  is positioned between the movable jaw members  320   a ,  320   b . The spring  340  is linked to a source of electricity  342 . Upon application of a voltage across the spring  340 , the spring  340  will expand forcing the movable jaw members  320   a ,  320   b  apart in a manner moving the jaw mechanism  314  to its release orientation. 
     In accordance with yet another embodiment shown in  FIGS. 51 and 52 , the fixed end  33  of the tension element  32  is secured in position for selective release via a fracture mechanism  350 . In particular, the fixed end  33  of the tension element  32  is secured to an elongated coupling element  352  extending within a shape memory alloy tube  354 , wherein upon the application of a change in temperature, for example, and in accordance with a preferred embodiment, heating, of the shape memory alloy tube  354 , the tube  354  will expand in a manner fracturing the elongated coupling element  352  and permitting release of the fixed end  33  of the tension element  32 . 
     The shape memory alloy tube  354  is substantially cylindrical and includes a proximal end  356  and a distal end  358 . The elongated coupling element  352  is shaped and dimensioned to extend within the tube  354  between the proximal end  356  and the distal end  358 . The tube  354  includes a first opening  360  at the proximal end  356  and a second opening  362  at the distal end  358 . The first opening  360  is slightly smaller than the enlarged head  316   a  of the coupling element  352  and the enlarged head  316   a  is, therefore, shaped and dimensioned to sit upon the ledge  357  defined by the first opening  360 . The second opening  362  of the tube  354  is slightly smaller than the first opening  360 . However, the second end of the coupling element  352  also includes an enlarged head  316   b  which is shaped and dimensioned to sit upon the ledge  359  defined by the second opening  362 . As such, the coupling element  352  is held between with first opening  360  of the tube  354  and the second opening  362  of the tube  354  with the enlarged heads  316   a ,  316   b  of the coupling element  352  sitting outside of the tube  354 . The coupling element  352  is provided with a reduced diameter fracture section  364  located between the enlarged head  316   a  at the first end of the coupling element  352  and the enlarged head  316   b  at the second end of the coupling element  352 . In accordance with a preferred embodiment of the present invention, the fracture section  364  is located adjacent the second end of the coupling element  352 . The fixed end  33  of the tension element  32  is secured to the coupling element  352  at the second end thereof. 
     With this construction in mind, a heating coil  366  is positioned about the shape memory alloy tube  354  for selective heating of the shape member alloy tube  354  so as to cause expansion thereof. In practice, when it is desired to release the fixed end  33  of the tension element  32 , the heating coil  366  is supplied with current causing coil  366  to heat. The heat causes expansion of the shape memory alloy tube  354 . The expansion of the shape memory alloy tube  354  results in the application of tension to the coupling element  352 . The applied tension stretches the coupling element  352  along its length as enlarged heads  316   a  and  316   b  are moved apart, which ultimately results in the fracture thereof at the weakened fracture section  364 . Once the fracture section  364  breaks, the second end of the coupling element  352  is free to fall away from the tube  354  along with the fixed end  33  of the tension element  32 . 
     It is also contemplated that cooling could be employed as a mechanism for changing the shape of the elongated tube and the tube may be cooled through the use of a Peltier-cooling element positioned thereabout. 
     In accordance with a variation of the embodiment described above with reference to  FIGS. 51 and 52 , the tension element release system is adapted to allow for fluid filling of the gastric band  21  upon the release of the tension element  32  or failure of the tension element  32 . In accordance with such an embodiment as shown with reference to  FIGS. 53 ,  54  and  55 , the ring  22  is provided with a secondary cavity  370  that is placed in fluid communication with a fluid source  374  once the tension element is released. The secondary cavity  370  extends along the circumference of the ring  22  and is adapted for filling thereof so as to apply pressure via the application of fluid pressure in manner similar to a conventional balloon based gastric band. 
     The secondary cavity  370  extends about the length of the ring  22  and the tension element  32  extends within (or adjacent to) the secondary cavity  370  such that when the tension element  32  is release as described below fluid access is provided to the secondary cavity  370  for the inflow of fluid necessary to fill the secondary cavity  370  and maintain the application of pressure by the ring  22 . 
     As with the embodiment described above with reference to  FIGS. 51 and 52 , the fixed end  33  of the tension element  32  is secured in position for selective release via a fracture mechanism. In particular, the fixed end  33  of the tension element  32  is secured to an elongated coupling element  352  extending within a shape memory alloy tube  354 , wherein upon heating of the shape memory alloy tube  354 , the tube  354  will expand in a manner fracturing the elongated coupling element  352  and permitting release of the fixed end  33  of the tension element  32 . 
     The shape memory alloy tube  354  is substantially cylindrical and includes a proximal end  356  and a distal end  358 . The elongated coupling element  352  is shaped and dimensioned to extend within the tube  354  between the proximal end  356  and the distal end  358 . The tube  354  includes a first opening  360  at the proximal end  356  and a second opening  362  at the distal end  358 . The first opening  360  is slightly smaller than the enlarged head  316   a  of the coupling element  352  and the enlarged head  316   a  is, therefore, shaped and dimensioned to sit upon the ledge  357  defined by the first opening  360 . The second opening  362  of the tube  354  is slightly smaller than the first opening  360 . However, the second end of the coupling element  352  also includes an enlarged head  316   b  which is shaped and dimensioned to sit upon the ledge  359  defined by the second opening  362 . As such, the coupling element  352  is held between the first opening  360  of the tube  354  and the second opening  362  of the tube  354  with the enlarged heads  316   a ,  316   b  of the coupling element  352  sitting outside of the tube  354 . The coupling element  352  is provided with a reduced diameter fracture section  364  located between the enlarged head  316   a  at the first end of the coupling member  352  and the enlarged head  316   b  at the second end of the coupling member  352 . In accordance with a preferred embodiment of the present invention, the fracture section  364  is located adjacent the second end of the coupling element  352 . The fixed end  33  of the tension element  32  is secured to the coupling element  352  at the second end thereof. 
     With this construction in mind, a heating coil  366  is positioned about the shape memory alloy tube  354  for selective heating of the shape member alloy tube  354  so as to cause expansion thereof. When it is desired to release the fixed end  33  of the tension element  32 , the heating coil  366  is supplied with current causing the coil  366  to heat. The heat causes expansion of the shape memory alloy tube  354 . The expansion of the shape memory alloy tube  354  results in the application of tension stretching the coupling element  352  along its length as enlarged heads  316   a  and  316   b  are moved apart which will ultimately result in the fracture thereof at the weakened fracture section  364 . Once the fracture section  364  breaks, the second end of the coupling element  352  is free to fall away from the tube  354  along with the fixed end  33  of the tension element  32 . 
     However, and in addition to the embodiment described above with reference to  FIGS. 51 and 52 , the coupling element  352  includes a central port  372  connected to a remote fluid source  374  via port  377 . The central port  372  extends from the first end of the coupling member  352  to a stop point  375  adjacent the second end of the coupling member  352 , but beyond the fracture section  364 . As such, when the fracture section  364  is broken as described above, the fluid is free to flow through the coupling element  352 , through the second opening  362  of the tube  354  and into the secondary cavity  370  for filling the secondary cavity  370  and supplying the ring  22  with a pressure source for maintaining the application of pressure against the stomach of the user. 
     Referring to  FIGS. 56A ,  56 B and  56 C, yet another embodiment of implementing a balloon based back-up system in conjunction with the mechanical tension offered by the tension element  32  is disclosed. In accordance with such an embodiment, the fixed end  33  of the tension element  32  is secured to the second end  28  of the ring  22  via a release mechanism  312  allowing selective release of the fixed end  33  of the tension element  32  from the second end  28  of the ring  22  for release of tension being applied by the ring  22 . The release mechanism  312  includes a jaw mechanism  314  that selectively engages the fixed end  33  of the tension element  32 . The fixed end  33  is provided with a bulbous head  316  that is selectively seated within the jaw mechanism  314  in the manner discussed below in greater detail. 
     The jaw mechanism  314  includes a fixed jaw member  318  and a movable jaw member  320 . A jaw drive element  322  is positioned between the fixed jaw member  318  and the movable jaw member  320 . The fixed jaw member  318  is substantially L-shaped and includes a first leg  324  and a second leg  326  oriented perpendicular to each other. Similarly, the movable jaw member  320  is substantially L-shaped and includes a first leg  328  and a second leg  330  oriented perpendicular to each other. The fixed jaw member  318  and the movable jaw member  320  sit facing each other in a mirror like orientation with the first legs  324 ,  328  of the respective fixed jaw member  318  and the movable jaw member  320  substantially parallel to each other and the second legs  326 ,  330  of the respective fixed jaw member  318  and the movable jaw member  320  facing each other in an aligned manner. By adopting this orientation, the fixed jaw member  318  and the movable jaw member  320  create a cavity in which the enlarged head  316  of the tension element  32  may sit while the remainder of the tension element  32  extends through the opening  332  formed between the free ends of the respective second legs  326 ,  330  of the fixed jaw member  318  and movable jaw member  320 . As will be appreciated based upon the following disclosure, the movable jaw member  320  is biased toward the fixed jaw member  318  maintaining the free ends forming an opening  332  between the fixed jaw member  318  and movable jaw members  320  in proximity to each other for holding the enlarged head  316  of the tension element  32  until it is desired to release the tension element  32 . 
     When one desires to release the tension element  32 , that is, release the enlarged head  316  of the tension element  32  from its position between the fixed jaw member  318  and the movable jaw member  320 , the jaw drive element  322  is expanded in a manner pushing the movable jaw member  320  away from the fixed jaw member  318 . As the movable jaw member  320  is pushed away from the fixed jaw member  318 , that is, as the jaw mechanism  314  is moved from its locked orientation with the fixed jaw member  318  and movable jaw member  320  in close proximity, to its release orientation with the fixed jaw member  318  and movable jaw members  320  moved away from each other, the opening  332  therebetween expands until it is larger than the enlarged head  316  of the tension element  32  at which time the fixed end  33  of the tension element  32  is released from its position between the fixed jaw member  318  and the movable jaw member  320 . 
     In accordance with a preferred embodiment, the jaw drive element  322  is a balloon  338  which may be selectively expanded for engagement with the jaw members  318 ,  320  in a manner selectively moving the jaw members  318 ,  320  to their release orientation. As will be appreciated with the following disclosure, the proximal end of the jaw mechanism  314  where the balloon  338  is position is in fluid communication with a fluid source  374  via a port  377  and the balloon  338  is oriented along the jaw mechanism  314  so as to block the flow of fluid until it is desired. When the balloon  338  is fully expanded for release of the fixed end  33  of the tension element  32  as described above, a needle  376  fixed relative to and extending through the movable jaw member  320  contacts the balloon  338  to rupture the balloon  338 . With the rupturing of the balloon  338 , a passageway  378  is formed between the remote fluid source  374  and the cavity formed between the fixed jaw member  318  and the movable jaw members  320 . The remote fluid source  374  is in fluid communication with the passageway  378  and fluid is free to flow through the jaw mechanism  314  and into the secondary cavity  370  (see  FIGS. 53 ,  54  and  55 ) for filling the secondary cavity  370  and supplying the ring  22  with a pressure source for maintaining the application of pressure against the stomach of the user. 
     As discussed above with regard to the embodiments in  FIGS. 53 ,  54  and  55 , a fluid source  374  is required for implementation of the embodiment. This fluid source  374  is preferably incorporated into the antenna/controller pod  23 . In order to ensure fluid pressure is not applied in an undesirable manner, the fluid source  374  is provided with a fail-safe mechanism for releasing fluid pressure in the event of a malfunction of the tension element and when desired by the operator as discussed below with regard to  FIGS. 59-67 . 
     In accordance with a variation on this embodiment, the rupture of the balloon  338  could allow for the release of fluid from the ring  22  facilitating release thereof in conjunction with the release of the tension element  32 . This would occur where the fluid source (or in this variation, the fluid reservoir)  374  is empty and the fluid is allowed to flow from a prefilled secondary cavity  370  and to the fluid reservoir  374  rather than the fluid flowing form the fluid source  374  to the secondary cavity  370 . 
     In accordance with an alternate embodiment, and with reference to  FIGS. 57A ,  57 B,  58 A and  58 B, the flow of fluid from the cavity  370  to the fluid source (or reservoir)  374  may be controlled by an electrically sensitive membrane  375  that is destroyed upon the application of the electricity. Once destroyed the passageway between the fluid reservoir  374  and the cavity  370  of the ring  22  is open allowing for the free flow of fluid. 
     In accordance with the concept of allowing for the release of fluid held in the secondary cavity  370  of the ring  22 , the fluid reservoir  374  could be an expandable reservoir that expands or contracts to control the volume of fluid (and as such the pressure applied by the ring). Expansion or contraction of the fluid reservoir  374  is controlled by a shape memory alloy actuator  377  that expands or contracts the fluid reservoir  374  based upon the application of electricity (and ultimately the generation of heat therein) thereto via electrical leads  379 . Because the fluid reservoir  374  will be in a vacuum relationship with the cavity  370 , controlled expansion and contraction of the fluid reservoir  374  will cause fluid to be drawn from or forced into the cavity  370  of the ring  22 . 
     In accordance with an embodiment shown in  FIGS. 59 ,  60  and  61 , a fluid source valve  380  is provided along the fluid path to the ring  22 . The fluid source valve  380  includes a first chamber  382  in communication with an upstream portion of the fluid source  374  via an inlet  384 . The fluid source valve  380  includes a second chamber  386  separated from the first chamber  382  by a valve release membrane  388  formed in a septum  390  separating the first chamber  382  from the second chamber  386 . The second chamber  386  includes an outlet  392  leading to a catheter  394  linking the fluid source to the ring  22 . When it is desired to allow for the flow of fluid to the ring  22 , electrical energy as applied to the valve release membrane  388  destroying the valve release membrane  388  and allowing fluid to freely flow from the inlet  384 , through the first chamber  382 , the valve release opening  389  and the second chamber  386 , and into the outlet  392  for flow though the catheter  394  and into the ring  22 . 
     In accordance with an alternate embodiment, and with reference to  FIGS. 62 ,  63  and  64 , the fluid source valve  380  includes a first chamber  382  in communication with an upstream portion of the fluid source  374  via an inlet  384 . The fluid source valve  380  includes a second chamber  386  separated from the first chamber  382  by a valve release opening  389  formed in a septum  390  separating the first chamber  382  from the second chamber  386  and in which a resilient plug  400  is positioned. The plug  400  is held in position by upper and lower resilient lips  403   a  and  403   b  respectively biasing the plug  400  with the valve release opening  389  in septum  390 . The second chamber  386  includes an outlet  392  leading to a catheter  394  linking the fluid source  374  to the ring  22 . When it is desired to allow for the flow of fluid to the ring  22 , an operator may apply pressure through the skin of a patient to access a flexible upper wall  404  of the first chamber  382  and push the plug  400  from its position within the valve release opening  389  and allow fluid to freely flow from the inlet  384 , through the first chamber  382 , the valve release opening  389  and the second chamber  386 , and into the outlet  392  for flow though the catheter  394  and into the ring  22 . 
     In accordance with yet another alternate embodiment, and with reference to  FIGS. 65 ,  66  and  67 , the fluid source valve  380  includes a first chamber  382  in communication with an upstream portion of the fluid source  374  via an inlet  384 . The fluid source valve  380  includes a second chamber  386  separated from the first chamber  382  by a valve release opening  389  formed in a wall or septum  390  separating the first chamber  382  from the second chamber  386 . A ball  406  is positioned in the second chamber  386  and held in valve release opening  389  by a spring member  402  biasing the ball  406  toward the first chamber  382  and plugging the valve release opening  389 . The second chamber  386  includes an outlet  392  leading to a catheter  394  linking the fluid source  374  to the ring  22 . When it is desired to allow for the flow of fluid to the ring  22 , an operator may apply pressure through the skin of a patient to access a flexible wall  407  of the second chamber  386  and push the spring  402  in a manner releasing the ball  406  from its position within the valve release opening  389  and allowing fluid to freely flow from the inlet  384 , through the first chamber  382 , the valve release opening  389  and the second chamber  386 , and into the outlet  392  for flow though the catheter  394  and into the ring  22 . 
     In accordance with alternate embodiments as shown with reference to  FIGS. 68 and 69 , the fixed end  33  of the tension element  32 , that is the portion of the tension element  32  secured to the ring  22  such that action of the drive element  35  causes enlargement or reduction in the effective diameter of the tension element  32 , is selectively released via a selective connection mechanism. In accordance with a first embodiment as shown with reference to  FIG. 68 , actuation of a pin  1114  (whether it be by way of shrinking or removal) allows for movement of first and second detent balls  1116 ,  1118  permitting release of a connection  1120  linking the fixed end  33  of the tension element  32  to the ring  22 . 
     In particular, the fixed end  33  of the tension element  32  is securely held in position relative to the ring  22  based upon the interference fit created between a retaining disk  1121  including a circumferential recess  1125  formed along the inner wall thereof, the first and second detent balls  1116 ,  1118 , the pin  1114  and the connection  1120 . With the various components held as shown in  FIGS. 68 and 69 , the connection  1120  is fixedly held relative to the retaining disk  1121  which is secured to the ring  22 . Once the pin  1114  is removed from its position forcing the detent balls  1116 ,  1118  into the circumferential recess  1125  and sitting within a central cavity  1127  of the connection  1120 , the detent balls  1116 ,  1118  will move centrally (as a result of the tension applied by the tension element  32 ) and the fixed end  33  of the tension element will be free to move since the interference fit will have been broken. 
     Referring to  FIG. 69 , movement of the detent balls  1116 ,  1118  is further facilitated by the provision of springs  1123  which encourage the detent balls  1116 ,  1118  to move centrally upon the removal of the pin  1114 . 
     As discussed above, removal of the pin is achieved either physically or by way of shrinking. Where it is desired to shrink the pin  1114 , the pin  1114  is preferably composed of a shape memory alloy adapted to shrink sufficiently upon the application of heat to allow for the movement of the detent balls  1116 ,  1118  from their positioned within the circumferential recess  1125 . In accordance with such and embodiment, a heater mechanism composed of a resistive wire (not shown) is coiled about the shape memory alloy pin  1114 . The heating coil uses RF energy transferred to the pin  1114  by means of an inductive coupling realized between the antenna/controller pod  23  and an external RF emitter. 
     Alternately, it is contemplated the pin may be constructed for simply sliding from its position within the central cavity of the connection. In accordance with another embodiment, the pin may be an electro activated polymer based drive element which shrinks by means of an applied voltage and/or current induced in the pin by means of an inductive coupling. 
     In accordance with a third embodiment as shown with reference to  FIGS. 70 and 71 , the fixed end  33  of the tension element  32  is selectively secured to the ring  22  by way of a retaining pin  1214 . The retaining pin  1214  is fixedly mounted within the ring  22  and engages an aperture  1213  formed in the tension element  32 . The retaining pin  1214  is actuated via a mechanically amplified retractable pin assembly  1210 . The pin assembly  1210  is secured to the ring  22  and triggered by the motion of a shape memory drive element or a piezoelectric drive element  1226 . The mechanically amplified retractable pin assembly  1210  allows the motion necessary for activating the moving retaining pin  1214  to be extremely small (for example, in the hundreds of a micrometer range). The reduced motion is achieved by means of shape memory alloy or piezoelectric based drive elements. 
     The embodiment includes a housing  1228  secured to the ring  22  and in which a spring biased retaining pin  1214  is mounted for movement between a lock positioned and a release position. The retaining pin  1214  includes an output pin  1230  shaped and dimensioned for seating within an aperture  1213  formed at the end of the tension element  32 . The retaining pin  1214  further includes a spring flange  1232  which is acted upon by a drive spring  1234  when the shape memory alloy drive element (such as nitinol)  1226  permits movement thereof. More particularly, controlled movement of the retaining pin  1214  is achieved by creating an interference fit between the retaining pin  1214  and the shape memory alloy drive element  1226  by positioning first and second detent balls  1216 ,  1218  between the pin  1214  and the drive element  1226 . The drive element  1226  includes a drive element body  1236  having an hourglass shape and moves between a first position (see  FIG. 70 ) and second position (see  FIG. 71 ). When the drive element body  1236  is in its first position, the detent balls  1216 ,  1218  are forced into an interference position preventing movement of the pin  1214  (see  FIG. 70 ). However, when the drive element  1226  is heated it breaks a coupling linking it to the base of the housing  1228  and is free to move upwardly under the bias provided by spring  1237  (see  FIG. 71 ). When the drive element  1226  moves upwardly in this manner, the detent balls  1216 ,  1218  are free to move into the narrow section of the drive element body  1236  allowing the detent balls  1216 ,  1218  to move from their position interfering with movement of the pin  1214 . Thereafter, the drive spring  1234  moves the pin  1214  to its release position disconnecting the retaining pin  1214 , in particular, the output pin  1230 , from engagement with the tension element  32 . 
     In summary, the mechanically amplified retractable pin assembly  1210  employs a shape memory alloy drive element  1226  for triggering energy release stored in a loaded compression drive spring  1234 . When in the extended position as shown with reference to  FIG. 70 , the pin  1214  is seen to be loaded by the compression drive spring  1234 . The drive spring  1234  remains firmly locked in this position due to the ball lock show in  FIG. 70 . This is mad possible by the drive element body  1236  which drives outwardly an array of detent balls  1216 ,  1218 . Once actuated however, the spring  1237  drives shape memory alloy drive element drives  1226  upwardly thereby causing the detent balls  1216 ,  1218  to roll inwardly and allowing the pin  1214  to retract under the force of the drive spring  1234 . 
     Under certain circumstances it may become necessary to release the tension element  32  for emergency removal of the ring  22  from its position around the stomach. As such, and in accordance with a first embodiment as shown with reference to  FIGS. 73 ,  74 ,  75  and  76 , the ring  22 , and in particular, the tension element  32 , is provided with a release pin  512  that allows for release of the free end  34  of the tension element  32  from its secure attachment position relative to the ring  22 . The release pin  512  transversely extends through the ring  22  at a position adjacent to the fixed end  33  of the tension element  32 . As a result, when the release pin  512  extends through the ring  22  and is in engagement with the fixed end  33  of the tension element  32 , the tension element  32  is securely held in position for contraction and expansion of the ring  22  as discussed herein. However, when the release pin  512  is pulled from its position along the ring  22  and out of engagement with the fixed end  33  of the tension element  32 , the fixed end  33  of the tension element  32  is released for free movement within the ring  22  (see  FIGS. 75 and 76 ). As such, the tension created between the free end  34  of the tension element  32  and the fixed end  33  of the tension element  32 , which ultimately allows for a reduction in the effective size of the ring  22 , is released and the ring  22  is allowed to return to its unbiased large diameter configuration. Once in this large diameter configuration, the ring  22  may be readily removed from its position about the stomach of the patient. 
     In accordance with an alternate embodiment, and with reference to  FIGS. 77 and 78 , the nut  60  of the drive element  35  is replaced with a slip nut  60  that allows for selective release of the free end  34  of the tension element  32  from its position within the drive element  35 . More particularly, the slip nut  60  allows the threaded free end  34  of the tension element  32  to slip past the drive nut  60  when necessary to allow the band restriction to be released if the motor  66  fails to operate. The slip nut  60  has the advantage of being either spring  103  loaded to release at a known pull force of the threaded screw (see  FIG. 77 ) or the slip nut  60  could be normally closed and a linkage  63  is provided that could be activated at the antenna/controller pod  23  (see  FIG. 78 ). 
     Referring now to the embodiment presented with reference to  FIG. 77 , the nut  60  is spring-loaded for release of the threaded free end  34  of the tension element  32  at a known pull force. More specifically, a slip nut  60  is a nut formed in multiple pieces which are held together via springs or other means.  FIG. 77  shows the slip nut  60  spring loaded to open at a desired pull force on the threaded free end  34  of the tension element  32 . Springs by design provide force greater than the forces generated under normal conditions when food is swallowed, but if the band is stretched circumferentially by using an esophageal dilator the force overcomes the springs and the threaded free end  34  slips through the nut  60  relaxing the restriction.  FIG. 78  shows the slip nut  60  wherein multiple pieces are held together with a linkage  63  that terminates in the antenna/controller pod  23  for disengaging the nut  60  from the threaded free end  34 . The termination of the linkage  63  could be activated by a simple toggle  516 .  FIG. 79  shows this toggle  516  and also provides a sketch of the linkage termination. The simple push pull design allows a doctor to make an incision in the skin to access the toggle  516 . A further improvement would be to provide a button, or some means of activating the linkage without cutting the skin to access the release mechanism. In implementing such an embodiment, it is contemplated the button would be spring loaded such that upon access to the button with, for example, a hypodermic needle, pushing the button releases the spring and thereby activates the linkage release mechanism. 
     With reference to the embodiment shown in  FIG. 79 , the split nut  60  is activated for release through actuation of a button  518  at the antenna/controller pod  23 . This embodiment overcomes the need for access into the patient&#39;s abdomen and could be activated without the need for incisions. If an emergency situation presented itself the patient could have a small incision made above the antenna/controller pod  23  on the sternum and the fail-safe linkage  63  could be activated directly. This would allow the device to be replaced at a later date, or troubleshoot the device and possibly replace the antenna/controller pod  23  in a subcutaneous procedure without needing to remove the entire implant. 
     Another embodiment for the release of the threaded free end  34  of the tension element  32  is shown with reference to  FIGS. 80 and 81 . This embodiment includes a nut  60  construction that improves upon the nut&#39;s ability to engage and disengage simply. The use of an elliptical nut  60  that pivots on an axis perpendicular to the axis of the threaded free end  34  of the tension element  32  allows for easy engagement and disengagement of the threaded free end  34  of the tension element  32 . This embodiment also utilizes a linkage  63  from the antenna/controller pod  23  and a switch/toggle  516  to pull the threaded free end  34  of the tension element  32  for disengagement. The nut  60  is spring loaded via spring  517  to provide positive displacement for the nut  60  to engage the threads of the threaded free end  34  of the tension element  32  when the fail-safe is not engaged.  FIG. 80  shows the elliptical nut  60  in the engaged position and  FIG. 81  shows the elliptical nut  60  in the fail-safe disengaged position. In  FIG. 81 , the linkage wire  63  that is connected to the antenna/controller pod  23  is moved to a position for fail-safe release of the threaded free end  34  of the tension element  32 , which causes the elliptical nut  60  to move and release from the threaded free end  34 . 
     In accordance with yet another embodiment as shown with reference to  FIG. 82 , an antenna/controller pod  23  that utilizes a magnetic deactivation function is disclosed. This requires a magnetic coil or magnetic emitting antenna  522  to be placed over the antenna  83  of the antenna/controller pod  23  and the oscillating electromagnetic field deactivates the device electronically. That is, the magnetic field induces a reverse polarity in the antenna/controller pod  23 , which in turn reverses the voltage sent to the motor  66 . This back drives the motor  66  without the use of the control pod in case of an electrical failure in the controller pod, but the motor was still operable. The controller pod would have a secondary circuit to allow the oscillating magnetic field coupling to generate a sufficient amount of power to drive the motor in a given direction. In this case, the desire would be to rotate the motor such that the pressure around the tissue is relieved. MRI sensitivity should not be an issue as an MRI generates a very high intensity permanent field (which will not generate a voltage in a magnetic coil or magnetic emitting antenna) and a very low intensity oscillating electromagnetic field (which will not generate a significant voltage since it is low intensity). The technical challenges of providing enough energy to the implant to reverse the voltage to the motor  66  is also challenged if the wires from the antenna/controller pod  23  becomes detached from the motor  66  or antenna/controller pod  23  itself.  FIG. 82  shows the magnet over the antenna  83  providing energy to reverse the motor  66 . 
     Referring now to other embodiments for release of the threaded free end  34  of the tension element  32 . In  FIGS. 83 ,  84  and  85 , the drive nut  60  has a split construction and is composed of four distinct elements  560   a ,  560   b ,  560   c ,  560   d  forming a central aperture  524  through which the threaded free end  34  of the tension element  32  passes for threaded driving as discussed above. A driving gear  526  is secured to the outer surface  528  of the nut  60  and drives it in a circular configuration as described above. However, the drive nut  60  is resilient and is adapted for biasing such that the threads  530  formed along the inner surface of the nut  60  disengage from threads  532  formed along the external surface  534  of the free end  34  of the tension element  32 . In particular, each of the nut elements  560   a - d  making up the nut  60  has a C-shaped cross sectional profile as shown with reference to  FIGS. 83 and 85 . The C-shaped profile includes a first plate member  536  and a second plate member  538  connected by a central connecting member  540 . The central connecting member  540  also functions as a part of the inner surface  542  of the aperture  524  through which the fixed end  33  of the tension element  32  passes. The connecting member  540  is provided with a weakened portion  544 . As such, when pressure is applied to the first plate member  536  in a direction toward the second plate member  538 , the first plate member  536  will then move downwardly toward the second plate member  538  causing the connecting member  540  to move from its normal orientation relative to the second plate member  538  and form an acute angular relationship with respect to the second plate member  538 . By applying pressure to all of the first plate members  536  of the respective nut elements  560   a - d  simultaneously, the inner threads  530  along the nut  60  are moved away from the free end  34  of the tension element  32  thereby providing for release and free movement of the tension element  32  relative to the nut  60 . 
     In accordance with a preferred embodiment, pressure is applied to the first plate member  536  of the respective nut elements  560   a - d  through the utilization of a plurality of pressure application plates  546 . Each of these pressure application plates  546  includes a resilient balloon  548  which may be expanded upon application of fluid pressure thereto. Since the pressure application plates  546  are formed so as to be positioned directly adjacent the first plate members  536  of the respective nut elements  560   a - d , when a balloon  548  is expanded, the balloon  548  will expand into contact with the first plate member  536  of the nut element  560   a - d  pushing it toward the second plate member  538  of the nut element  560   a - d  and causing the connecting member  540  to angle away from the free end  34  of the tension element  32  as described above. 
     In accordance with yet another embodiment of the present invention, and with reference to  FIGS. 86 ,  87  and  88 , the nut  60  is provided with flanges  550  upon which the internal threading  530  of the aperture  554  is positioned. These flanges  550  are secured to the nut  60  for controlled movement relative thereto. In particular, and with reference to  FIG. 86 , when the nut  60  and in particular, the flanges  550 , are intended for engagement with threading  530  formed along the outer surface  534  at the free end  34  of the tension element  32 , the flanges  550  are oriented substantially normal to the plane in which the nut  60  lies. As such, and when in this configuration, the internal threading  552  along the flanges  550  engages the threading  532  at the free end  34  of the tension element  32  and rotation of the nut  60  causes the threaded free end  34  to be moved relative to the nut  60  for drawing the tension element  32  through the nut  60 . 
     However, the rear outer surface  556  of each flange  550  is provided with a resistive heating element  558  that is connected to an electrical coil  560  secured along the back surface  562  of the outer periphery  564  of the nut  60 . As such, when electricity is applied to the coils  560 , the resistive heaters  558  are actuated heating the flanges  550 . The flanges  550  are constructed such that when they are heated, or otherwise encounter a change in temperature, they will bend away from the free end  34  of the tension element  32  forming an acute angle with the plane in which the nut  60  lies (see  FIG. 88 ). Once in this configuration, and with reference to  FIG. 88 , the free end  34  of the tension element  32  is free to move relative to the nut  60  for free movement of the tension element  32  relative thereto. 
     Referring now to  FIGS. 89 ,  90  and  91 , yet another embodiment for release of the tension element  32  is disclosed. In accordance with this embodiment, the fixed end  33  of the tension element  32  is secured to a two-bar linkage  566 . When the tension element  32  is intended for utilization in constriction of the stomach, the two-bar linkage  566  is folded so that the links  568 ,  570  nearly overlap (see  FIG. 89 ). When the band  21  needs to be released in an emergency, the two-bar linkage  566  is actuated via a pull lever  567  (see  FIG. 91 ) so as to pull the two bar linkage  566  from its folded configuration and into an extended configuration (see  FIG. 90 ). With the two bar linkage  566  in an extended configuration, the effective length of the tension element  32  is increased providing additional diameter within the ring  22  and allowing the gastric band  21  to be moved from its position along the stomach. 
     Referring now to  FIGS. 92 ,  93  and  94 , a compression, friction drive assembly  572  is utilized for pulling the tension element  32 . The friction drive assembly  572 , however, includes a release member  574  which moves the opposed rollers  576 ,  578  of the friction drive assembly  572  apart from each other allowing for free movement of the tension element  32  within the ring  22 . Controlled movement of the release member  574  is achieved via the utilization of a pull wire  580  which, when acted upon, forces the rollers  576 ,  578  of the friction drive assembly  572  apart against the bias of the spring  577  that biases them toward the tension element  32 , permitting free movement of the tension element  32 . In accordance with a preferred embodiment, and with reference to  FIG. 94 , movement of the wire  580  is controlled by a screw mechanism  579  that may be selectively acted upon with, for example, a hex wrench  581 , to loosen or tighten the wire  580 . 
     In accordance with yet another embodiment of the present invention, and with reference to  FIG. 95 , the antenna/controller pod  23  is provided with an access port  582  providing a medical practitioner with access to the control electronics of the antenna/controller pod  23  for control thereof in the event of failure. In accordance with such an embodiment a needle  584  would access the access port  582  so as to act like a contact that would either flex contacts  586 ,  588  or just bridge the contacts  586 ,  588  to run the motor  66  in the direction to open the gastric band  21  to a maximum diameter thereby relieving any pressure applied by the gastric band  21 . For such a method to work, the antenna/controller pod  23  is provided with a battery  590  having a shelf life, for example, of ten or more years, and with enough power to store energy to power the gastric band  21  for a reasonable length of time. Since there is a battery  590  provided with the antenna/controller pod  23 , telemetry could be used via wireless technology such as Bluetooth and could allow a patient to self adjust the gastric band  21  without the need for a power module. It is further contemplated rechargeable batteries may be employed and recharging may be achieved on a regular basis via a power unit at a doctor&#39;s office or while the patient is sleeping so that more benefits could come from the ability to non-invasively adjust the band. 
     In accordance with a variation on the embodiment disclosed with reference to  FIG. 96  the antenna/controller pod  23  is provided with dual access ports  582   a ,  582   b  linked to the printed circuit band  583 . As such, and when emergency situations arise under circumstances where the antenna/controller pod  23  does not have sufficient power, the two needles  584   a ,  584   b  applied to the first and second ports  582   a ,  582   b  of the antenna/controller pod  23  are charged to supply power to the antenna/controller pod  23 . In accordance with this embodiment, the first and second ports  582   a ,  582   b  are provided with self-healing elastomeric targets  592   a ,  592   b  for needle placement. 
     As briefly discussed above, the needles  584   a ,  584   b  are charged. As such, the needles  584   a ,  584   b  are connected to a power source  594  that is readily available in a hospital. When the needles  584   a ,  584   b  are contacting the conductors  586 ,  588  in the printed circuit board  583  of the antenna/controller pod  23 , the motor  66  will run in the opening direction and the diameter of the gastric band  21  is increased to eliminate any pressure applied by the gastric band  21 . 
     The gastric band  21  would then return to normal operating conditions when appropriate and can be used as designed in accordance with the principles of the present invention. The present embodiment would also function for its intended purpose in the event the printed circuit board failed provided the emergency electrical path employed in accordance with this embodiment is not part of the operating circuitry of the printed circuit board. 
     Ring Closure System 
     With respect to  FIGS. 97A and 97B , a preferred embodiment of the clip  27  for securing the gastric band  21  in the closed position is described. The clip  27  on the first end  26  of the ring  22  includes an aperture  70 , a tab  71  having a hinge  72  and a slot  73 . The aperture  70  is dimensioned to accept the second end  28  therethrough, while the slot  73  is dimensioned to accept the flange  74  disposed on the second end  28 . 
     To close the ring  22 , the clip  27  is grasped by the tab  71  and the tag  25  of the antenna/controller pod  23  (see  FIG. 1 ) is inserted through the aperture  70 . The clip  27  is then pulled toward the second end  28  so that the housing  29  passes through the aperture  70  while the housing  29  is grasped with atraumatic forceps; the conical shape of the housing  29  facilitates this action. Force is applied to the tab  71  until the slot  73  captures the flange  74 , thereby securing the ring  22  in the closed position. The physician may subsequently choose to disengage the slot  73  from the flange  74  by manipulating the tab  71  using laparoscopic forceps, for example, to reposition the ring  22 . Advantageously, however, forces inadvertently applied to the tab  71  in an opposite direction will cause the tab  71  to buckle at the hinge  72 , but will not cause the flange  74  to exit the slot  73 . Accordingly, the hinge  72  of the tab  71  prevents accidental opening of the clip  27  when the tab  71  is subjected to forces that cause the tab  71  to fold backwards away from the housing  29 , such as may arise due to movement of the patient, the organ, of or bolus of fluid passing through the organ. 
     As discussed above, it may at times become necessary to release the pressure applied by the gastric band  21 . With this in mind, and in accordance with yet another embodiment as shown with reference to  FIGS. 98 and 99 , the first and second ends  26 ,  28  of the gastric band  21  are provided with a mechanism allowing release from their locked positions via a remote latch unlock mechanism  1310 . In particular, the clip  27  holding the first and second ends  26 ,  28  of the gastric band  21  together is released via a variety of electromechanical mechanisms. For example, actuation of an emergency release button (not shown) on the antenna/controller pod  23  will cause release of the clip  27 . When the button triggers a communication, a voltage is applied on a flange actuator  1314  by the electronics of the antenna/controller pod  23 . The temperature of the actuator  1314  then increases and this triggers movement of the flange  74  toward the inside of the gastric band  21  until the band clip  27  is released (for example, via a shape memory alloy actuator or a bimetallic actuator). Such an embodiment, might allow for treatment without the patient visiting the hospital or other treatment center. The unit might be activated via modem or Internet connection by the surgeon. 
     Antenna/Controller Pod 
     With respect to  FIGS. 100 and 101 , the antenna/controller pod  23  of the present banding system is described. The antenna/controller pod  23  is disposed at the distal end of the antenna cable  24  and includes the removable tag  25  and holes  75 . The tag  25  comprises a grip structure that facilitates manipulation and placement of the antenna/controller pod  23  during implantation; after which the tag  25  is removed using a scissors cut. The tag  25  also includes hole  25   b  that allows the use of a suture thread to assist in passing the antenna/controller pod  23  behind the stomach. The holes  75  also are dimensioned to be compatible with standard suture needles from size 1-0 to 7-0 to permit the antenna/controller pod  23  to be sutured to the patient&#39;s sternum, thereby ensuring that the antenna/controller pod  23  remains accessible to the external antenna  14  and cannot migrate from a desired implantation site. 
     As shown in  FIG. 101 , the antenna/controller pod  23  encloses a printed circuit board  76  that carries the antenna  83  and microcontroller circuitry of the gastric band  21 . The antenna  83  receives energy and commands from the external control  10  (see  FIG. 1 ), and supplies those signals to the microcontroller, which in turn powers the motor  66  of the drive element  35 . The circuitry of the antenna/controller pod  23  uses the energy received from the incoming signal to power the circuit, interprets the commands received from the external control  10 , and supplies appropriate signals to the motor  66  of the drive element  35 . The circuit also retrieves information regarding operation of the motor  66  of the drive element  35  and relays that information to the external control  10  via the antenna  83 . The circuit board preferably is covered with a water-resistant polymeric covering, e.g., Parylene, to permit use in the high (up to 100%) humidity environment encountered in the body. 
     The antenna/controller pod  23  includes a mechanical closure system that is augmented by silicone glue so that the pod is fluid tight. This silicone glue also is used to protect soldered wires  79  from humidity. The antenna/controller pod  23  preferably is small, e.g., 16 mm×33 mm×4 mm, to ensure compatibility with a standard 18 mm trocar and so as to be compatible with placement on the sternum. The antenna/controller pod  23  preferably has a smooth, atraumatic shape to avoid tissue damage, has good mechanical strength to withstand handling with surgical graspers and to prevent mechanical deformation to the printed circuit board, and has good electromagnetic permeability to allow efficient energy transmission through the antenna/controller pod  23 . The antenna/controller pod  23  preferably has a relatively thin planar configuration to avoid rotation of the antenna/controller pod  23  when placed under the skin, and may include holes that permit the antenna/controller pod  23  to be sutured in position. 
     With respect to  FIG. 102 , the antenna cable  24  is shown in cross-section. The antenna cable  24  preferably is a coaxial shielded cable encapsulated in a silicone tube  77  to provide biocompatibility. The tube  77  is selected to provide leak-proof encapsulation, with sufficient strength to permit the antenna cable  24  to be manipulated with atraumatic graspers. The braided shield  78  of the antenna cable  24  prevents longitudinal deformation of the antenna cable  24 , and surrounds five helically wound insulated wires  79 . Four of the wires  79  are used to supply power to the micromotor of the drive element  35 ; the remaining wire and braided shield  78  are used to supply a signal from the reference position switch to the controller. 
     As discussed above with respect to  FIG. 1 , the gastric band  21  according to the present invention provides an integrated system for regulating food ingestion in the stomach of a patient, wherein variation of the diameter of the ring  22  may be adjusted without any invasive surgical intervention. To accomplish this, the drive element  35  is linked to the subcutaneous antenna/controller pod  23  to receive a radio frequency control and power signal. In accordance with a preferred embodiment, the motor  66  of the drive element  35  has no internal energy supply, but rather is powered by the receiving circuit of the antenna  83  through a rechargeable energy storage device, such as a capacitor. In particular, the receiving circuit converts radio frequency waves received from the external control  10  via the antenna into a motor control and power signal. In accordance with an alternate embodiment, it is contemplated the drive element may be driven via an implantable rechargeable battery. 
     Power and Control Circuitry 
     Referring to  FIG. 105 , a preferred embodiment of the circuitry employed in the external control  10  and the gastric band  21  of the present invention is described, based on the principle of passive telemetry by FM-AM absorption modulation. The external control  10  is shown on the left hand side of  FIG. 105 , and includes a microprocessor  80  coupled to the control panel  12  and the display screen  13  (see  FIG. 1 ). The external control  10  produces a signal comprising one or more data bytes to be transmitted to the implantable antenna/controller pod  23  and the drive element  35 . 
     The external control  10  includes a modulator  81  for amplitude modulation of the RF wave from the RF generator  82 , which signal is emitted by the external antenna  14 . The emitted wave is received by the antenna  83  in the antenna/controller pod  23 , where the AM demodulator  84  extracts the data bytes from the envelope of received RF signal. The data bytes then are decoded and written into an EEPROM of the microcontroller  85 . A special code is used that allows easy decoding of the data by the microcontroller  85 , but also provides maximal security against communication failure. 
     An external oscillator  86 , which is a voltage controlled oscillator (VCO), provides a clock signal to the microcontroller  85 . The external oscillator  86  may consist of, for example, a relaxation oscillator comprising an external resistor-capacitor network connected to a discharging logic circuitry already implemented in the microcontroller or a crystal oscillator comprising a resonant circuit with a crystal, capacitors and logic circuits. The former solution requires only two additional components, is suitable when the stability of the frequency is not critical, and has low current consumption; the latter solution provides a more stable frequency, but requires a greater number of additional components and consumes more power. The external oscillator  86  preferably comprises the external RC network, due to its simplicity. 
     The microcontroller  85  interprets the received instructions and produces an output that drives the motor  66  of the drive element  35 . As discussed above, the drive element  35  comprises a bi-directional stepper motor  66  that drives the nut  60  through a series of reducing gears. Preferably, the two coils of the stepper motor  66  of the drive element  35  are directly connected to the microcontroller  85 , which receives the working instructions from the demodulator  84 , interprets them and provides the voltage sequences to the motor coils. When the supply of voltage pulses to the stepper motor  66  stops, the gears are designed to remain stationary, even if a reverse torque or force is applied to the nut  60  by the tension element  32 . 
     As also described above, use of a stepper motor  66  in drive element  35  makes it is possible to obtain positional information on the nut  60  and the tension element  32  without the use of sensors or encoders, because the displacement of the tension element  32  is proportional to the number of pulses supplied to the stepper motor coils. Two signals are employed to ensure precise control, reference position signal S RP , generated by the reference position switch of  FIG. 13 , and the drive element signal S A . 
     According to one preferred embodiment, signal S A  is the voltage signal taken at one of the outputs of the microcontroller  85  that is connected to the motor coils of the drive element  35 . Alternatively, signal S A  could be derived from the current applied to a motor coil instead of the voltage, or may be an induced voltage on a secondary coil wrapped around one of the motor coils of the drive element  35 . In either case, signal S A  is a pulsating signal that contains information on the number of steps turned by the rotor and further indicates whether blockage of the mechanism has occurred. Specifically, if the rotor of the stepper motor fails to turn, the magnetic circuit is disturbed, and by induction, affects signal S A , e.g., by altering the shape of the signal. This disturbance can be detected in the external control, as described below. 
     Signals S A  and S RP  are converted into frequencies using the external oscillator  86 , so that the voltage level of signal S A  applied to the external oscillator  86  causes the oscillator to vary its frequency F osc  proportionally to the signal S A . Thus, F osc  contains all the information of signal S A . When the crimped cap  45  and the tension element  32  are in the reference position (that is, the ring  22  is fully open), the reference position switch produces reference position signal S RP . Signal S RP  is used to induce a constant shift of the frequency F osc , which shift is easily distinguishable from the variations due to signal S A . 
     If the external oscillator  86  is a relaxation oscillator, as described above, signals S A  and S RP  modify the charging current of the external resistor capacitor network. In this case, the relaxation oscillator preferably comprises an external resistor-capacitor network connected to a transistor and a logic circuit implemented in the microcontroller  85 . With S A  and S RP , the goal is to modify the charging current of the capacitor of the RC network to change the frequency of the relaxation oscillator. If the charging current is low, the voltage of the capacitor increases slowly and when the threshold of the transistor is reached, the capacitor discharges through the transistor. The frequency of the charging-discharging sequence depends on the charging current. 
     If the external oscillator  86  is a crystal oscillator, signals S A  and S RP  modify the capacitor of the resonant circuit. In this case, the crystal oscillator circuit preferably comprises a crystal in parallel with capacitors, so that the crystal and capacitors form a resonant circuit which oscillates at a fixed frequency. This frequency can be adjusted by changing the capacitors. If one of these capacitors is a Varicap (a kind of diode), it is possible to vary its capacitance value by modifying the reverse voltage applied on it, S A  and S RP  can be used to modify this voltage. 
     In either of the foregoing cases, signals S A  and S RP  are used to modify at least one parameter of a resistor-capacitor (RC) network associated with the external oscillator  86  or at least one parameter of a crystal oscillator comprising the external oscillator  86 . 
     Referring still to  FIG. 105 , signals S A  and S RP , derived from the stepper motor or from the output of the microcontroller  85 , may be used directly for frequency modulation by the external oscillator  86  without any encoding or intervention by the microcontroller  85 . By using the external oscillator  86  of the microcontroller  85  as part of the VCO for the feedback signal, no additional components are required, and operation of the microcontroller  85  is not adversely affected by the changes in the oscillator frequency F osc . The oscillating signal F osc  drives the voltage driven switch  87  for absorption modulation, such that feedback transmission is performed with passive telemetry by FM-AM absorption modulation. 
     More specifically, signal F osc  drives the switch  87  such that during the ON state of the switch  87  there is an increase in energy absorption by the RF-DC converter  88 . Accordingly, therefore the absorption rate is modulated at the frequency F osc  and thus the frequency of the amplitude modulation of the reflected wave detected by external control  10  contains the information for signal S A . As discussed below, a pickup  89  in the external control  10  separates the reflected wave where it can be decoded by FM demodulation in the demodulator  90  to obtain signal S A ′. This method therefore allows the transmission of different signals carried at different frequencies, and has the advantage that the ON state of the switch  87  can be very short and the absorption very strong without inducing an increase in average consumption. In this way, feedback transmission is less sensitive to variation in the quality of coupling between the antennas  83  and  14 . 
     In the external control  10 , the feedback signal F osc  is detected by the pickup  89  and fed to the FM demodulator  90 , which produces a voltage output V OUT  that is proportional to F osc . V OUT  is fed to the filter  91  and the level detector  92  to obtain the information corresponding to the drive element signal S A , which in turn corresponds to the pulses applied to the stepper motor coil. The microprocessor  80  counts these pulses to calculate the corresponding displacement of the tension element  32 , which is proportional to the number of pulses. 
     Signal V OUT  also is passed through the analog-to-digital converter  93  and the digital output is fed to the microprocessor  80 , where signal processing is performed to detect perturbations of the shape of the feedback signal that would indicate a blockage of the rotor of the stepper motor. The microprocessor  80  stops counting any detected motor pulses when it detects that the drive element is blocked, and outputs an indication of this status. The level detector  94  produces an output when it detects that the demodulated signal V OUT  indicates the presence of the reference position signal S RP  due to activation of the reference position switch. This output induces a reset of the position of the tension element calculated by the microprocessor  80  in the external control. In this way, a small imprecision, e.g. an offset, can be corrected. 
     As described above, the external control  10  transmits both energy and commands to the implantable controller circuitry in the antenna/controller pod  23 . The external control  10  also receives feedback information from the implantable controller that can be correlated to the position of the tension element  32  and the diameter of the ring  22 . As will be apparent to one of skill in the art, the external control  10  and the implantable controller are configured in a master-slave arrangement, in which the implantable controller is completely passive, awaiting both instructions and power from the external control  10 . 
     Pressure Measuring 
     Measuring the applied pressure via the present ring  22  is very important in ensuring that excessive pressure is not applied to the stomach. As such, the present invention incorporates the ability to measure the applied pressure in a reliable, effective and convenient manner. In accordance with a first embodiment, and with reference to  FIGS. 106 and 107 , the applied current for the motor  66  is measured and the measured current is utilized in determining the applied pressure and ultimately as a feedback system for measuring the functional state of the gastric band  21 . 
     In accordance with this embodiment, the current is monitored via a closed loop feedback system  1012  integrated into the operation of the mechanical banding system  1  of the present invention. By incorporating an electrical current measurement to measure electrical current being drawn by the motor  66  of the present banding system, the performance of the banding system may be evaluated for determination of, among other features, the applied pressure of the gastric band  21 . The current drawn by the motor  66  is directly related to the force being applied by the banding system. Any increase in the force applied by the gastric band  21  is proportionally linked to an increase in current being drawn by the motor  66  of the gastric band  21 . In practice, the current measured in accordance with the application of the present invention is correlated to the static force or pressure the ring  22  applies to the stomach tissue it encircles. 
     In addition to its use in measuring pressure, the monitoring of the applied current may also be utilized in determining any loss of performance of the banding system due to component wear down, corrosion, etc. 
     Referring to  FIG. 107 , the closed loop feedback system  1012  includes leads  1016  accessing the current flowing from the power source  1018  to the motor  66 . The current is measured using a current sensing circuit  1020  and the output current measurement  1022  is forward to the microcontroller  85  of the present drive element  35  for action in accordance with the goals of the present invention. 
     In accordance with an alternate embodiment, and with reference to  FIG. 108 , measurements of the applied current are made using a Hall sensor  1024  positioned about the wire  1026  supplying the motor  66  with electrical power. When a Hall sensor  1024  is positioned above a current carrying wire  1026 , it is capable of measuring current flow through the wire  1026  and ultimately the current being drawn for operation of the motor  66  as it constricts the ring  22  to apply pressure to the stomach which the ring  22  surrounds. In accordance with the embodiment disclosed herein, the measured current is derived from a voltage measurement across a series of resistors  1028  in line with the power source  1018  for the motor  66 . 
     Regardless of the whether a hardwired circuit is employed or a Hall sensor is employed, the voltage is calculated by utilizing Ohms Law, that is, V=IR. Assuming a fixed resistance change in current, a current is directly related to the voltage drop across the resistance of the motor  66 . A typical sensing voltage might be between 50 mV and 200 mV. 
     In accordance with an alternate embodiment, and with reference to  FIG. 109 , the tension applied by the gastric band  21 , that is the applied pressure of the gastric band  21 , is monitored by a mechanical system  1030 . In particular, the tension applied to the flexible tension element  32  is monitored utilizing a strain gauge  1032  acted on by the threading  1034  of the tension element  32 . By monitoring the force applied to the strain gauge  1032 , the operator is provided with an indication when fail-safe action is necessary. 
     The strain gage  1032  is preferably coupled to the nut  600  on the drive element housing  53 , for example, by means of a cantilevered beam  1036 . The interaction of the nut  600  with the threading  1034  of the tension element  32  provides highly accurate force measurements concerning the relationship between the nut  600  and the threading  1034  of the tension element  32 . By monitoring the force measurements, the pressure applied by the gastric band  21  is determined and operators of the gastric band  21  are readily able to determine when fail-safe action is necessary based upon a detection of excess tension in the gastric band  21 . 
     In accordance with a variation of the use of a strain gauge, the strain gauge  1032  may straddle threading on the tension element  32  so as to identify the applied force. See  FIG. 110 . To identify the applied force the strain gauge output would be connected to a circuit, such as an analog to digital converter (A/D) or microcontroller  1060 , that converts the strain into an applied force. The A/D or microcontroller  1060  would provide force data to a telemetry circuit  1062  which in turn would send the data to the external reading device  1064 . The applied force could be compared to a force threshold (either dynamic or static) either by the internal circuitry  1060  or by the external reading device  1064  which in turn would provide and indication to the state of the drive mechanism. A higher force/tension in either movement direction may indicate a mechanical failure in the drive mechanism. 
     As with the prior embodiment, and in addition to its use in measuring tension along the gastric band  21 , the monitoring of the force encountered by the strain gauge  1032  may also be utilized in determining any loss of performance of the banding system due to component wear down, corrosion, etc. As such, the strain gauge is preferably linked to a feedback system controlling operation of the drive element  35 . It is also contemplated that in addition to a strain gage, position/proximity sensors may be employed, Hall effect sensors may be employed, contact sensors may be employed or a microswitch may be employed. 
     In accordance with yet a further embodiment as shown with reference to  FIG. 111 , and where a fluid filled bladder  1038  is incorporated along the internal surface  1040  of the ring  22 , the pressure of the fluid within the bladder  1038  is measured to provide an indication as to the pressure being applied to the stomach via the present banding system  1 . 
     In accordance with this embodiment, a fluid bladder  1038  is formed along the internal surface  1040  of the mechanical gastric band  21 . The fluid bladder  1038  is formed and positioned such that it directly interfaces with tissue. In accordance with a preferred embodiment, the fluid bladder  1038  may be integrally formed with the gastric band or it may be selectively secured thereto for use in accordance with the present invention. As such, and where the fluid bladder  1038  is selectively secured to the gastric band  21 , it may be secured to the gastric band  21  prior to or during installation (implantation). A pressure sensor  1042  is linked to the fluid bladder  1038  allowing for remote monitor of the fluid pressure within the bladder  1038 . 
     By constructing the ring  22  in such a manner, not only is a softer tissue interface provided by the fluid bladder  1038 , but the inclusion of the fluid bladder  1038  allows for the ability to add a pressure sensor  1042  in the fluid path to measure the fluid pressure in the bladder  1038 . When the gastric band  21  is wrapped around the stomach tissue, the monitored pressure within the bladder  1038  relates to the pressure exerted on the tissue. This pressure reading is then used as a primary or secondary feedback to control the applied restriction employed in accordance with the gastric band  21  of the present invention. 
     In practice, and in accordance with a preferred embodiment as disclosed herein, the bladder  1038  is pre-filled with fluid and calibrated prior to implantation. While pre-implantation calibration is contemplated, it is conceived that calibration may be performed after implantation in accordance with the present invention. As such, the fluid bladder may be adjusted to ensure proper calibration. Such adjustments are achieved by connection of the fluid bladder to a filling tube via a port formed in the fluid bladder. The bladder  1038  is preferably made of silicone or another biocompatible material and is preferably filled with a non-aqueous fluid or gel, for example, silicone or fluoro-silicone oil. The pressure  1042  is preferably a piezoresistive or capacitive sensor designed for implantation in a hermetic package. The pressure  1042  is connected to a telemetry circuit  1044  allowing pressure to be read outside the body using an external reading device  1046 . 
     As with the previously discussed embodiments for measuring the applied pressure of the gastric band  21 , the pressure bladder  1038  may also serve as an indicator to the functional state of the mechanical gastric band  21 . Pressure should increase when the gastric band  21  is tightened and decrease when the gastric band  21  is loosened. If the mechanical system is not functioning correctly, there will be no change in pressure. 
     In addition to providing a fail-safe mechanism for operation of the present ring  22 , loading information garnered in the manner discussed above, may also be used to aid the surgeon in correctly setting the band&#39;s initial degree of restriction during band implantation. That is, the loading information could also be used to help ensure that the band is initially implanted with the correct degree of restrictive adjustment. In this case an indication of tension element loading would provide surgeons (especially novice ones) with an indication of whether they&#39;ve sufficiently tightened the band onto the tissue to achieve the desired constriction while also making sure that they haven&#39;t excessively tightened the band onto the tissue and/or undesirably approached the tension element&#39;s yield point. 
     The load measurements may also be used to prevent over-tightening the band during extended use. In particular, the loading information could also be used in an alternative manner if the band has auto-tightness adjustment capability. In this case the surgeon may or may not be present at the time the tension of the tension element is being adjusted. In this scenario, the load and/or strain measurements could be used to signal the control unit of the motor to either stop tightening the band if a pre-set load threshold is reached or actually reverse the direction of the motor to decrease tension element loading if the threshold has already been exceeded. One way to ensure that the loading threshold is never exceeded is to control the flow of current to the motor using commonly known techniques, such as current clipping, to ensure that the motor is never able to build up enough torque to over-tighten the tension element. Alternatively, an electrical fuse element could be used in conjunction with the current supplied to the motor such that the fuse would trip and either limit or release loads on the tension element if the current supplied to the motor ever exceeds an allowable threshold. 
     In addition to the measuring techniques discussed above, these benefits could be embodied by use of any of the load measuring techniques, such as, measuring the motor torque. In particular, the tension on the tension element may be derived from motor torque. The algorithm used in this method is well appreciated by those skilled in the art. When using a motor, measure the current drawn of the motor under load, and calculate the torque using the equation below:
 
 T =( I−I   NL ×( K   T   ×N×h )
 
     Where,
         I=Current   T=Torque   K T =Torque Constant   N=Gear Ratio (Equals 1 if there is no gearbox)   h=Gearbox Efficiency (Equals 1 if there is no gearbox)   I NL =No-Load Current       

     Please be aware this equation approximates the true load torque and does not take thermal conditions into consideration. The results are reasonably close and suitable for most purposes.” 
     The current may be determined by measuring the current across a shunt resistor in series with the motor at the power source. The microcontroller will measure the voltage across the resistor and convert the value to current using Ohm&#39;s Law (I=V/R where I=current, V=voltage and R=Resistance across the shunt resistor) in order to determine torque. 
     This value may be converted to tension since the tension element is a screw thread or cable. 
     In general, a representative conversion equation for torque to axial load (cable tension) is:
 
 T=DF  
 
     Where,
         T=Torque required   F=Desired cable tension   D=cable thread nominal diameter (major dia)       

     Since it is not generally recommended that induced stress exceed a safe fraction of the yield strength of the tension element, it may be desirable to introduce a fractional coefficient c (less than or equal to 1) in the equation:
 
 T=cDF  
 
Expressed in terms of cable tension:
 
 F=T/cD  
 
     Since this relationship is linear, however, any correlations such as those discussed below to band adjustments may be made using torque or tension. Thus, current, torque or cable tension may all be used as an adjustment parameter, much the same as the pressure measurements as described in U.S. Patent Application Publication No. 2006/0211913, entitled “NON-INVASIVE PRESSURE MEASUREMENT IN A FLUID ADJUSTABLE RESTRICTIVE DEVICE”, which is incorporated herein by reference. 
     As discussed above, the tension upon the tension element may be measured by monitoring component strain. The tension may be measured directly via a strain gauge. The strain gauge may be positioned in a number of locations such that the tension would cause a strain, i.e.,
         on the tension element  32  itself, measuring stretch of the tension element  32  (See  FIG. 110 )   between the rear hub and the nut  60  (see  FIG. 109 );   between the tension element  32  and an axially grounded portion of the hub.       

     The strain read by the strain gauge may be translated to tension element  32  tension by 
     the association:
 
σ= Eε 
 
     Where,
         σ=the cable stress=F t /A   F t =the cable tension   A=the cross sectional area of the cable   E=the elastic modulus of the material   ε=the strain in the cable       

     So,
 
 F   t   =EεA  
 
     In accordance with yet another embodiment, the strain gauge location could be used as a compressive force gage if the nut is free to translate slightly with the thread. The gauge would be positioned under the nut on the side opposite the direction of translation of the threaded shaft and the nut would impose a compressive force on to the gauge when the band is adjusted. In a manner similar to the tension measured above the force could also be measured with compression as well. Thin film load cells are commercially available and can be found in U.S. Pat. No. 6,272,936. This circuit can be made to fit a very tiny space in-between the nut  60  and the hosing plate. 
     In accordance with yet another embodiment as shown with reference to  FIG. 112 , the axial loads on the tension element  32  may be measured. In accordance with such and embodiment, the tension force between the end of the spring element (that is the tension member  32 ), and the threaded shaft at the free end  34  of the tension element  32  is measured. A small transducer  1032  is attached that measures the axial load seen by the threaded shaft as the gastric band  21  is adjusted. This could also be employed at various locations along the tension element  32 , such as those indicated by the red circles. 
     Operational Modes 
     Referring to  FIG. 103 , some of the safety features of the banding system of the present invention are described. As discussed above with respect to  FIG. 105 , both power and control signals are provided to the implantable controller from the external control  10 . Because power is delivered to the implantable controller via magnetic induction, the amount of energy delivered to the controller depends on the quality of the coupling between the external antenna  14  and the antenna circuitry contained within the antenna/controller pod  23 . 
     The quality of the coupling may be evaluated by analyzing the level of the feedback signal received by the external control  10 , and a metric corresponding to this parameter may be displayed on the signal strength indicator  17 , which includes 6 LEDs (corresponding to six levels of coupling). If the coupling between the antennas  14 ,  83  is insufficient, the motor  66  of the drive element  35  may not work properly, resulting in an inaccurate adjustment of the gastric band  21 . 
     Accordingly, in a standard mode of operation, adjustment may be made only if the coupling quality is strong enough, as indicated by having at least LED  5  or LED  6  in  FIG. 103  illuminated. If, on the other hand, poor coupling exists (e.g., one of the first four LEDs are illuminated) it is still possible to perform some adjustment of the gastric band  21 , although the adjustment may be inaccurate. 
     The design of the external control  10 , in combination with the patient microchip card  16  (see  FIG. 1 ), also ensures a high degree of efficacy and safety. First, as contemplated for use with the gastric band  21  of the present invention, the external control  10  is intended primarily for use by a physician in an office or hospital setting, and not by the patient alone. Of course, in alternative embodiments, such as to treat urinary or fecal incontinence, it would be essential to provide an external control  10  for use by the patient. The simplicity of the design of the external control  10  and ease of use would provide no impediment to use by the patient for such embodiments. 
     As discussed with respect to  FIG. 1 , patient microchip card  16  stores, among other data, a serial number identifying a corresponding gastric band  21  and the diameter of the ring  22  upon completion of the previous adjustment. When the external control  10  first transmits energy to the implantable controller of the gastric band  21 , the gastric band  21  identifies itself to the external control  10 . In the standard mode of operation, the serial number stored on the patient microchip card  16  must match that received from the gastric band  21 , otherwise no adjustment is permitted. 
     As a fail-safe, however, the physician still may adjust the gastric band  21  even if the patient has lost or misplaced his microchip card  16 . In this case, the external control  10  may be set in a “no card mode”. In this mode, the information displayed on the display screen  13  of the external control  10  corresponds only to the relative variation of the gastric band  21  during that adjustment session, and is no longer indicative of absolute diameter. When the physician activates this mode, an emergency bit is set in the memory of the implantable controller to indicate the “no card mode”. In subsequent adjustment sessions, the implantable controller will signal that the gastric band  21  was adjusted in the “no card mode” and all further adjustments will be reported on a relative basis. If the patient again locates the microchip card  16 , the emergency bit may be cleared by fully opening the gastric band  21  and thus reaching the reference contact, which re-initializes the position. Subsequent adjustments will again be managed in the standard mode of operation. 
     During adjustment of the ring  22 , a physician places the external antenna  14  in a face-to-face position on the skin of the patient relative to the antenna/controller pod  23  of the ring  22 , and to receive feedback information from which the constricted diameter of the ring  22  may be computed. In accordance with the principles of the present invention, it is possible to vary the diameter of the ring  22  without having to undertake invasive surgical intervention, and this variation may be carried out at will, because multiple control cycles may be carried out at regular or irregular intervals, solely under the control of the treating physician. 
     The banding system of the present invention is expected to be particularly reliable, relative to previously-known hydraulic bands that can be adjusted by the patient, because only the physician typically will have access to the external control box needed to adjust the ring. For a ring embodiment intended for treatment of morbid obesity, the patient therefore does not have free access to any means to adjust the diameter of the ring. 
     Moreover, because the gastric band of the present invention provides a precise readout of the current diameter of the ring in the standard mode of operation, it may not be necessary for the patient to ingest a radiographic material (e.g., barium dye) to permit radiographic visualization of the ring to confirm the adjusted size. The process of adjusting the band accordingly may be carried out in a doctor&#39;s office, without the expense associated with radiographic confirmation of such adjustments. In addition, the self-blocking configuration of the tension element and nut, in combination with the mechanical nature of the gastric band, overcome problems associated with previously-known hydraulically actuated gastric band systems. 
     Methods of Implantation and Removal 
     Referring now to  FIG. 104 , the gastric band  21  of the present invention is shown implanted in a patient. The ring  22  is disposed encircling the upper portion of the patient&#39;s stomach S while the antenna/controller pod  23  is disposed adjacent to the patients sternum ST. The antenna/controller pod  23  is located in this position beneath the patients skin SK so that it is easily accessible in the patients chest area to facilitate coupling of the antenna/controller pod  23  to the external antenna  14  of the external control  10  (see FIG.  1 ). 
     Other Features 
     In addition to the features discussed above, the present invention provides a mechanism for protecting the implanted electronics from electromagnetic interference (for example, from MRI). In particular, the electronics of the device are encased in a titanium case  1202  (see  FIG. 72 ) and the antenna  1283  is moved external to the titanium case  1202 . In this way, the electronics may be implanted deeper into the body cavity, leaving only a thin antenna near the surface of the skin. 
     In addition, time limit warning on the packaging of the device may be avoided
         where the gastric band is prefilled with fluid or gel, air would not permeate the silicone. The fluid could be incorporated during manufacturing or injected once the device is opened in the operating room. This would also improve the tissue interface of the gastric band by making it softer.   if the gastric band were shipped in fluid or instructed to place the device in a saline bath when opened, it could stay in place indefinitely.   If the silicone is coated with parylene, titanium or similar compositions to reduce permeation rates thereby increasing the open air time.   If the balloon is left unsealed. Since the band is mechanical and not hydraulic, the balloon has no functional need to be sealed.       

     As stated in the System Overview portion of the present application, the telemetrically-powered and controlled ring system of the present invention has numerous applications apart from gastric banding for the treatment of morbid obesity. For example, the ring system of the present invention may advantageously be used for the treatment of fecal incontinence, ileostomy, coleostomy, gastro-esophageal reflux disease, urinary incontinence and isolated-organ perfusion. 
     For treatment of fecal incontinence, the ring may be used with little or no modifications. In addition, because the ring adjustment procedure will be performed by the patient on at least a daily basis, a portable user-friendly external control may be used. In addition, because the ring will regularly be transitioned between the closed and fully opened position, the patient microchip card is unneeded. Instead, the fully closed position may be stored in the memory of the implantable controller, and read by the external remote at each use (subject to periodic change by the physician). 
     A similarly modified device could be used by patients who have undergone ileostomy or coleostomy, or disposed surrounding the esophageal junction, to treat gastro-esophageal reflux disease. 
     For treatment of urinary incontinence, the ring may be further modified to minimize the volume of the ring surrounding the urethra by moving the drive element motor to a location elsewhere in the lower abdomen or pelvis, and coupling the drive element to the motor via a transmission cable. 
     The present invention also may be beneficially employed to perform isolated-organ perfusion. The treatment of certain cancers requires exposure to levels of chemotherapy agents that are too high for systemic circulation. It has been suggested that one solution to this problem is perform an open surgery procedure in which blood flow to the cancerous organ is stopped and quiescent blood replaced by circulation from an external source containing a desired dose of drug. Individual or multiple rings of the present invention may be used as valves to isolate the cancerous organ and permit perfusion of the organ with high doses of drugs. Such procedures could thus be performed on a repetitive basis without surgery, thereby reducing the trauma and the risk to the patient while improving patient outcomes. 
     Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration. Further variations will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims. 
     As discussed above, it is possible to make highly accurate load measurements regarding the load applied by the ring in accordance with the present invention. This information may be used to dynamically adjust the band&#39;s degree of restriction to optimize weight loss. This may prove helpful to surgeons in making a correlation between tension on the tension element and how tightly the band is tightened on tissue. Much the same as the pressure measurements as described in U.S. Patent Application Publication No. 2006/0211913, entitled “NON-INVASIVE PRESSURE MEASUREMENT IN A FLUID ADJUSTABLE RESTRICTIVE DEVICE”, which is incorporated herein by reference; that is, the manner in which pressure magnitude and pulse counting of peristaltic waves is used as a target against which to adjust, the load or strain measurements may be used in a similar fashion as a measure of peristaltic pressure. Such systems are disclosed in U.S. Patent Application Publication No. 2006/01898888, entitled “DEVICE FOR NON-INVASIVE MEASUREMENT OF FLUID PRESSURE IN AN ADJUSTABLE RESTRICTION DEVICE”, and U.S. Patent Application Publication No. 2009/0187202, entitled “OPTIMIZING THE OPERATION OF A RESTRICTION SYSTEM”, which are also incorporated by reference. Pressure waves from esophageal peristalsis will cause tension changes in the cable which may be read and correlated to proper or improper adjustment. Pulses may be counted from this same means, along with pulse width, duration, etc. Much of the information that can be gained will be able to be derived form the present mechanism. 
     Multiple methods of storing the measured loads on the band are discloses, which include but are not limited to:
         Storing motor torque;   Storing mechanical strain;   Storing compressive and axial loads.       

     With regard to storing motor torque, the component torque, as described above, may also be stored for later analysis by a torque measuring device (torque watch). Simpler models would just record and store peak values, which may be sufficient for this application. Alternatively, a more complex model would allow for storage of continuously obtained torque information. Due to storage capacity, it is likely that the data would need to be recorded in set increments and be downloaded periodically. Alternately, if the torque was measured indirectly using a DC motor as described above, a multimeter may be used to record and store peak values and/or continuously obtain information which could then be converted to torque via the above equations. 
     As to storing mechanical strain, the component strain, as described above, may also be stored for later analysis by a strain gauge. Simpler models would just record and store peak values, which may be sufficient for this application. Alternatively, a more complex model would allow for storage of continuously obtained strain information. Due to storage capacity, it is likely that the data would need to be recorded in set increments and be downloaded periodically. 
     Compressive and axial loads may also be stored, as described above. This information is stored for later analysis by a strain gauge. A basic force gauge may be used to store compressive and axial loads. Simpler models would just record and store peak values, which may be sufficient for this application. Alternatively, a more complex model would allow for storage of continuously obtained torque information. 
     Stored information to interested parties (i.e., Surgeon, Primary Care Physician (PCP), Patient, etc.) may be relayed to other parties for use at remote locations. With regard to the relay of information to the surgeon/PCP, a surgeon or primary care physician may be interested in obtaining and using the information gathered to make determinations about the restriction provided by the band and/or complications arising from the tightness of the band. As a result, it is desirable that the information measured and stored as described above is also accessible by the surgeon or PCP. One mechanism for achieving this would be to use an external data logger which would be worn by the patient. Information stored in this device could be downloaded by the surgeon or PCP by means of a USB port. For example, see U.S. Patent Application Publication No. 2006/0199997, entitled “MONITORING OF A FOOD INTAKE RESTRICTION DEVICE” and U.S. Patent Application Publication No. 2008/0249806, entitled “DATA ANALYSIS FOR AN IMPLANTABLE RESTRICTION DEVICE AND A DATA LOGGER”, which are hereby incorporated by reference. 
     As to the relay of information to the patient, patients would be interested in obtaining some information about the status of the restriction in their band for various reasons. For example, one reason would be to indicate that there may be a problem with their implant and direct them to visit their surgeon. Since it would probably not be necessary or useful for them to receive numerical information about the torque, strain or load present in their band, a different type of relaying method would be important. One option would be an audible noise (i.e., alarm) which would indicate to them if there was a potential issue with their implant. Alternatively, if they were wearing an external data logger as described above, a visual light (i.e., flashing red or green) could indicate the status of their implant. 
     While the preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention.