Patent Publication Number: US-2013253410-A1

Title: Resistive Anti-Obesity Devices

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/850,185, filed Aug. 4, 2010, which is a divisional of U.S. application Ser. No. 11/330,705, filed Jan. 11, 2006, now U.S. Pat. No. 7,771,382, which claims the benefit of U.S. Provisional Application No. 60/662,570, filed on Mar. 17, 2005 and U.S. Provisional Application No. 60/645,296, filed on Jan. 19, 2005. 
     The entire teachings of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     According to the Center for Disease Control (CDC), over sixty percent of the United States population is overweight, and almost twenty percent are obese. This translates into 38.8 million adults in the United States with a Body Mass Index (BMI) of 30 or above. The BMI is defined as a person&#39;s weight (in kilograms) divided by height (in meters), squared. To be considered clinically, morbidly obese, one must meet one of three criteria: BMI over 35, 100 pounds overweight, or 100% above ideal body weight. There is also a category for the super-obese for those weighing over 350 pounds. 
     Obesity is an overwhelming health problem. Because of the enormous strain associated with carrying this excess weight, organs are affected, as are the nervous and circulatory systems. In 2000, the National Institute of Diabetes, Digestive, and Kidney Diseases (NIDDK) estimated that there were 280,000 deaths directly related to obesity. The NIDDK further estimated that the direct cost of healthcare in the U.S. associated with obesity is $51 billion. In addition, Americans spend $33 billion per year on weight loss products. In spite of this economic cost and consumer commitment, the prevalence of obesity continues to rise at alarming rates. From 1991 to 2000, obesity in the U.S. grew by 61%. Not exclusively a U.S. problem, worldwide obesity ranges are also increasing dramatically. 
     One of the principle costs to the healthcare system stems from the co-morbidities associated with obesity. Type-2 diabetes has climbed to 7.3% of the population. Of those persons with Type-2 diabetes, almost half are clinically obese, and two thirds are approaching obese. Other co-morbidities include hypertension, coronary artery disease, hypercholesteremia, sleep apnea and pulmonary hypertension. 
     Although the physiology and psychology of obesity are complex, the medical consensus is that the cause is quite simple—an over intake of calories combined with a reduction in energy expenditures seen in modern society. While the treatment seems quite intuitive, the institution of a cure is a complex issue that has so far vexed the best efforts of medical science. Dieting is not an adequate long-term solution for most people. Once an individual has slipped past the BMI of 30, significant changes in lifestyle are the only solution. 
     There have been many attempts in the past to surgically modify patients&#39; anatomies to attack the consumption problem by reducing the desire to eat. Stomach staplings, or gastroplasties, to reduce the volumetric size of the stomach, thereby achieving faster satiety, were performed in the 1980&#39;s and early 1990&#39;s. Although able to achieve early weight loss, sustained reduction was not obtained. The reasons are not all known, but are believed related to several factors. One of which is that the stomach stretches over time increasing volume while psychological drivers motivate patients to find creative approaches to literally eat around the smaller pouch. 
     Surgeries can generally be separated into restrictive procedures, malabsorptive procedures and combinations thereof. At least two surgical procedures that successfully produce long-term weight loss are the Roux-en-Y gastric bypass, and the biliopancreatic diversion with duodenal switch (BPD). Both procedures reduce the size of the stomach plus shorten the effective-length of intestine available for nutrient absorption. Reduction of the stomach size reduces stomach capacity and the ability of the patient to take in food. Bypassing the duodenum makes it more difficult to digest fats, high sugar and carbohydrate rich foods. 
     The Laparoscopic Adjustable Gastric Band is a device that is placed around the top of the stomach to create a restriction. This forces the patient to eat smaller meals as the food must pass from the small pouch into the rest of the stomach before he/she can eat again. This device however does require surgery for its placement and is difficult to remove. 
     These procedures carry a heavy toll. The morbidity rate for bariatric surgical procedures is alarmingly high with 11% requiring surgical intervention for correction. Early small bowel obstruction occurs at a rate of between 2-6% in these surgeries and mortality rates are reported to be approximately 0.5-1.5%. While surgery is effective, the current invasive procedures are not acceptable with these complication rates. Laparoscopic techniques applied to these surgeries result in fewer surgical complications but continue to expose these very ill patients to high operative risk in addition to requiring an enormous level of skill by the surgeon. Devices to reduce absorption in the small intestines have been proposed (see U.S. Pat. No. 5,820,584 (Crabb), U.S. Pat. No. 5,306,300 (Berry) and U.S. Pat. Nu. 4,315,509 (Smit)). However, these devices have not been successfully implemented. Restrictive devices include Laparoscopic Adjustable Gastric Banding (LABG) (see for example U.S. Pat. No. 5,226,429 (Kuzmak)) and gastric balloons (see for example U.S. Pat. No. 4,823,808 (Clegg et al.) and U.S. Pat. No. 6,755,869 (Geitz)). 
     SUMMARY OF THE INVENTION 
     The present invention relates to methods, devices and systems that provide an increased sense of satiety to a person by increasing the resistance to the outflow of food from the stomach. Gastric emptying can be slowed using devices that slow the passage of chyme through the intestines. Slowing gastric emptying may induce satiety for a longer period and may therefore reduce food consumption. Although many of these concepts include intestinal liners, they need not. The resistor concept may be applied to a simple anchor and resistor without a long liner. 
     Restrictive devices have been previously described but most commonly are described to reside within the stomach. Anchoring devices in the stomach is difficult as the stomach is a particularly active region of the anatomy tending to tear out devices implanted therein. The devices described herein are more typically anchored in the intestines. 
     Devices which include liners can be implanted within the intestine to prevent the contact of partially-digested food (i.e., chyme) with the intestine thereby reducing one or more of hormone triggers, digestion and absorption of nutrients. By adding a resistive feature to these devices passage of chyme through the device can be slowed. By reducing the flow below a rate at which chyme flows in an unrestricted intestine, the chyme can build up along a proximal end of the device. The chyme build-up slows the gastric emptying process, as there will be less volume available within the intestine to accommodate additional chyme from the stomach, or the pressure required to pass the chyme from the stomach to the intestine is higher than normal. 
     It is believed that slowing emptying of the stomach may ultimately reduce the amount of food a patient consumes. Alternatively or in addition, an intestinal implant device creating a resistance within the intestine requires the bowel to exert more energy to propel the chyme than would otherwise be necessary without the resistance. Such a restriction can slow gastric emptying, cause higher energy expenditure, and lead to weight loss. 
     Methods are provided for inducing weight loss within a patient by treating a region of the intestine below the pyloric sphincter and slowing gastric emptying responsive to the treated region, resulting in a prolonged feeling of satiety by the patient. The treatment can include implanting at least a portion of a device below the pyloric sphincter. Preferably, the implanted device reduces the flow of chyme into the proximal intestine. For example, the device provides an artificial stricture through which the chyme passes. The artificial stricture can include a diaphragm narrowing the intestinal lumen. The diaphragm can include a membrane defining a reduced aperture. Alternatively or in addition, the artificial stricture can include a liner defining a central lumen through which chyme passes, the artificial stricture being coupled to the liner. 
     In some embodiments, the artificial stricture is adjustable. For example, the stricture can be formed using an adjustable member coupled to adjust the diameter of the interior lumen of a liner. The adjustable member can be combined with a securing feature adapted for adjustably securing the adjustable member in place once a desired restriction is achieved. In other embodiments, the adjustable member includes a balloon that can be adjusted by inflation and deflation. 
     In other embodiments, the restrictive element is elastomeric and passively controls the outlet pressure of the stomach by varying in diameter depending on the inlet pressure. 
     In other embodiments, the implanted device includes a dampening liner adapted to reduce peristaltic efficiency. The dampening liner can be a semi-rigid liner. In yet another embodiment, the implanted device occupies a non-negligible volume within the intestine, thereby reducing the available intestinal volume and limiting the amount of chyme that can be accommodated. 
     Alternatively or in addition, the present invention relates to a gastrointestinal implant including a resistive feature adapted to be secured within the intestine and distal to the pyloric sphincter. When implanted, the resistive feature impedes gastric emptying. An anchor can be coupled to the resistive feature for attaching the resistive feature to the gastrointestinal tract. In some embodiments, the resistive feature includes a sleeve or liner defining a central lumen through which chyme can pass. The liner itself can define a central lumen having a constricted region of a reduced diameter. 
     In another embodiment the gastrointestinal implant includes a resistive coating provided on an interior surface of the liner. For example, the resistive coating can include artificial cilia aligned to impede the passage of chyme. In yet other embodiments, the resistive feature includes a bent wire, such as a contorted wire formed from a resilient wire, such as Nitinol wire. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1A  is a schematic diagram illustrating a side view of the embodiment of the invention including an artificial stricture; 
         FIG. 1B  is a schematic diagram of an end view of the embodiment of  FIG. 1A ; 
         FIG. 2  is a graph illustrating the pressure drop of an exemplary fluid through an orifice of varying size; 
         FIG. 3  is a side view of an embodiment of the invention including a liner having one or more restrictive members; 
         FIGS. 4A-4D  are end views showing alternative types of restrictive members used in the embodiment of the invention shown in  FIG. 3 ; 
         FIG. 5  is a schematic diagram illustrating an embodiment of the invention including a liner having a narrowed region; 
         FIG. 6  is a schematic diagram illustrating an alternative embodiment of the invention including a tapered segment and a narrowed region; 
         FIG. 7  is a schematic diagram illustrating an embodiment of the invention including a tapered liner; 
         FIG. 8A  is a schematic diagram illustrating an embodiment of a tapered anchor; 
         FIG. 8B  is a schematic diagram illustrating an exemplary mandrel used to form the tapered anchor of  FIG. 8A ; 
         FIGS. 9A and 9C  are schematic diagrams illustrating side views of an embodiment of the invention including a drawstring restrictor shown in the open and partially-closed positions, respectively; 
         FIGS. 9B and 9D  are schematic diagrams illustrating end views of the embodiment of the invention shown in  FIGS. 9A and 9C , respectively in the open and partially-closed positions; 
         FIG. 10A  is a schematic diagram illustrating a side view of an embodiment of a ball-and-cleat locking mechanism for locking the drawstring of  FIGS. 9A-9D ; 
         FIG. 10B  is a schematic diagram illustrating a side view of an embodiment of a hook-and-eyelet locking mechanism for locking the drawstring of  FIGS. 9A-9D ; 
         FIG. 10C  is a schematic diagram illustrating a side view of an embodiment of a crimp-type locking mechanism for locking the drawstring of  FIGS. 9A-9D ; 
         FIG. 10D  is a schematic diagram illustrating a cross-sectional side view of an embodiment of a friction locking mechanism for locking the drawstring of  FIGS. 9A-9D ; 
         FIG. 10E  is a schematic diagram illustrating an axial cross section of the embodiment shown in  FIG. 10D ; 
         FIG. 11A  is a schematic diagram illustrating a side view of an embodiment of the invention including an inflatable restrictive member; 
         FIG. 11B  is a schematic diagram illustrating an end view of the inflatable restrictive member shown in  FIG. 11A ; 
         FIG. 12  is a partially-cut-away schematic diagram illustrating an embodiment of the invention providing a thick-walled liner; and 
         FIG. 13  is a partially-cut-away schematic diagram illustrating an embodiment of the invention providing an internal resistive surface; 
         FIG. 14A  is a schematic diagram illustrating a side view of an embodiment of the invention including a solid mass within the intestine; 
         FIG. 14B  is a schematic diagram illustrating an end view of the embodiment including a solid-mass shown in  FIG. 14A ; 
         FIG. 15  is a schematic diagram illustrating a cross-sectional view of an embodiment of the invention using a filter; and 
         FIG. 16A  is a schematic diagram illustrating the artificial structure of  FIG. 1A  implanted within the proximal duodenum; and 
         FIG. 16B  is a schematic diagram illustrating a repositioning device engaging the artificial stricture of  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of preferred embodiments of the invention follows. 
     This general concept relates to providing an increased sense of satiety by slowing gastric emptying by providing resistance to the outflow of food from the stomach and through the intestines. An increased sense of satiety is obtained by slowing emptying of an animal&#39;s stomach. Gastric emptying can be slowed by providing resistance to the outflow of food, or chyme, from the stomach. In general, an animal perceives a sensation of satiety when the stomach fills. It is believed that by slowing gastric emptying into the duodenum, an animal can maintain a feeling of satiety for a longer period of time. Consequently, an animal no longer feeling hungry will tend to eat less. 
     There are several approaches that can be used to increase resistance to flow of the chyme. For example, a device having features adapted to resist the flow of chyme can be implanted within the gastrointestinal tract distal to the stomach. At least one approach is simply placing a sleeve or liner within the intestine. The mere presence of the liner can add some resistance to the flow of chyme therethrough. 
     Alternatively or in addition, an implant can include at least one resistive feature, such as a reduced-diameter aperture, or stricture, that artificially narrows a region of the gastrointestinal tract. A resistive implant is preferably placed at a predetermined location within the body and adapted to remain there throughout a course of treatment. To maintain the implant in place, at least a portion of the device is secured to the surrounding anatomy. Securing of an implant can be accomplished using an anchor coupled to the device. Anchoring within the gastrointestinal tract, however, poses numerous challenges due at least in part to the physiology of the anatomical region, its high degree of motility, and pressures resulting from digestive forces. 
     One region of the gastrointestinal tract that is particularly well suited for anchoring the resistive implant is the proximal duodenum. Compared to the stomach, the pylorus, and even distal regions of the small intestine, the proximal duodenum is relatively immotile. Additionally, the proximal duodenum defines a slightly enlarged cavity just distal to the pyloric sphincter referred to as the duodenal bulb. An anchor of the type shown in  FIG. 1A  that expands to conform to the lumen is particularly well suited for positioning within the bulbous duodenum. The shape of the cavity and its relatively low motility will enhance performance of the anchoring device. 
     An exemplary artificial stricture  100  adapted for gastrointestinal applications is illustrated in  FIG. 1 . The device  100  includes an anchoring element  105  coupled to an artificial stricture. The artificial stricture retards the flow of chyme therethrough. The anchor  105  is adapted to anchor the device  100  within the gastrointestinal tract. When placed at or below the pylorus, the stricture operates to slow gastric emptying. The anchor is adapted to hold the device securely in place under gastrointestinal forces and pressures. 
     The anchor can be a radial spring defining an opening therethrough for the passage of chyme and adapted to engage the surrounding tissue of the hollow organ within which it is implanted. Thus, the anchor  105  can provide an interference fit to the surrounding tissue. In some embodiments, the perimeter of the anchor is in sealable communication with the surrounding tissue of the lumen to prevent leakage of chyme and fluids beyond the artificial stricture. 
     The artificial stricture can be formed from a blocking material  110  coupled to the anchor  105 , the blocking material defining an aperture  115  therein. For example, the blocking material can include the same materials described in more detail below in reference to intestinal liners. The blocking material is dimensioned to at least cover the cross-sectional area of the lumen within which it is implanted. For an implant adapted for use in the proximal duodenum of an adult male, the diameter of the impermeable material would be at least about 25 millimeters. 
     The stricture is created by forming an aperture  115  having a reduced cross-sectional area, or diameter within the blocking material  110 . The aperture can be formed, for example, by simply cutting or punching a hole of the appropriate dimensions into the blocking material  110 . For example, the hole can be less than about 10 millimeters in diameter for the exemplary 25 millimeter implant. In some embodiments, the aperture is about 5 millimeters in diameter or less. It is unlikely, however, that an orifice of less than about 2 millimeters would be used in a human application as food particle passing through the pylorus are typically about 1-2 millimeters or less in size. 
     Fluid mechanics can be used to determine the size orifice needed to provide a restriction within the duodenum. For example, the Bernoulli equation can be applied to the flow of a Newtonian fluid through an orifice as provided in equation 1. In this equation, ΔP represents the pressure drop across the orifice, p corresponds to the fluid density, Q corresponds to the volume flow (determined as the product of the fluid velocity and the flow area), D is the diameter of the unobstructed opening (e.g., about 25 mm in the example of  FIG. 2 ), and d is the diameter of the orifice in millimeters. In the example of  FIG. 2 , the diameter of the orifice is varied between about 2 and 10 mm. 
       Δ P =(8 pQ   2 )/(π 2   D   4 )*[( D/d ) 4 −1]  (1)
 
     An exemplary graph of the pressure drop through an orifice of varying size is provided in  FIG. 2 . The graph was determined by applying equation 1 using an assumed velocity of about 2 cm/sec, which corresponds to the mean flow rate of chyme through the intestines. Considering peristaltic pressures on the order of 20-40 inches of water (an exemplary range of pressures corresponding to an adult human) the orifice size should be less than about 5 mm in diameter to provide flow resistance. More preferably, the orifice size is less than 5 mm. For example, an orifice of about 3 mm provides increased flow resistance under nominal anticipated peristaltic pressures. 
     In some embodiments, the aperture is adjustable. For example, an aperture can be increased by stretching it until the blocking material defining the aperture plastically deforms to a new, larger diameter. Stretching can be accomplished using a balloon inserted into the aperture, the balloon being inflated after insertion. The pressure of the inflated balloon will stretch a suitable blocking material to a larger size. When the balloon is removed, the material will retain the enlarged aperture. In other embodiments, the blocking material is elastomeric such that the aperture is permitted to temporarily expand above certain pressures to prevent blockage of the aperture for food particles larger than the minimum dimension the aperture returning to its reduced diameter thereafter. 
     Referring again to  FIG. 1 , the anchor  105  generally defines a central lumen through which chyme flows. The anchor, which can be at or distal to the pylorus, can include a stent, such as the stents described in U.S. patent application Ser. No. 10/339,786 filed on Jan. 9, 2003 (now U.S. Pat. No. 7,025,791), incorporated herein by reference in its entirety. Alternatively or in addition, the anchor can include a radial spring, such as the wave anchor illustrated and described in more detail in U.S. patent application Ser. No. 10/858,851 filed on Jun. 1, 2004 (now U.S. Pat. No. 7,476,256) and incorporated herein by reference in its entirety. 
     The anchor  100  can attach to the intestine using a frictional or interference fit. Thus, the anchor can have a relaxed diameter that is greater than the maximum anticipated diameter of the intestine, such that the anchor will provide an outward force against the adjacent anatomy acting to keep the anchor in place. Alternatively or in addition, the anchor  105  can include one or more external barbs  125  further securing the implant device in the presence of peristalsis. Preferably, the barbs  125  are sized and positioned to engage muscular tissue. Exemplary barbs are described in more detail in U.S. patent application Ser. No. 10/339,786 filed on Jan. 9, 2003 (now U.S. Pat. No. 7,025,791), and U.S. patent application Ser. No. 10/858,852 filed on Jun. 1, 2004 (now U.S. Pat. No. 7,476,256), incorporated herein by reference in its entirety. 
     The anchor  100  can also include one or more repositioning features. As shown the device includes a drawstring  127  at its proximal end. The drawstring  127  is threaded through the open end of the anchor  100  such that it can be grasped and used to facilitate repositioning of the anchor  100  within the body or removal of the anchor  100  from the body. Removal methods and devices using a drawstring are described in U.S. Application Attorney Docket No. 3588.1008-001, entitled “Removal and Repositioning Device” filed on Dec. 22, 2005 and incorporated herein by reference in its entirety. 
     In some embodiments, an anchor is attached to a material similar to the blocking material. For example, the anchor can be encapsulated between overlapping layers of a tubular segment of blocking material. The blocking material  110  defining the aperture  115  can then be formed in the same blocking material that is attached to the anchor  105 . Alternatively, a different blocking material can be used. 
     The blocking material  110  can first be formed into a suitable pattern, such as the circle shown and then attached to the anchor and/or to material covering the anchor  105 . When the anchor  105  is also attached to the blocking material, the different segments of blocking material can be sealably attached together using any suitable means. For example, the blocking material  110  can be attached to the anchor covering by suturing. Alternatively or in addition, the blocking material  110  can be attached to the anchor covering by a chemical fastener, such as an adhesive, and/or by thermal bonding. Formed in this manner, the attached blocking material  110  may extend for some distance L from the distal end of the anchor  105  when in the presence of a proximal pressure (e.g., the material bulges out in an elongated or domed fashion). In some embodiments, the blocking material  110  is attached in a relatively taught manner, similar to the skin of a drum to limit any axial extent L of the blocking material  110  beyond the distal end of the anchor  105 . 
     In some embodiments, the resistive implant includes a liner. As shown in  FIG. 3 , an implant device  200  includes an elongated liner  210  adapted for placement within a hollow organ, such as the intestine. In some embodiments, the implant  200  includes an anchor  205  coupled to the liner  210 , with the anchor  205  adapted to secure at least a portion of the liner  210  within the lumen of the intestine. For example, a hollow anchor similar to those anchors described above can be attached to the proximal end of the liner  210  to secure the proximal end of the liner  210  to the surrounding tissue of the intestine. Once implanted, the liner  210  is extended distally from the anchor along the intestine. 
     Preferably, any of the implantable devices described herein can be configured to be removable. Thus, any permanence of a resistive device only applies during the period in which the device is implanted within the patient. Thus, a resistive device can be removed should the need arise. Alternatively or in addition, a different or even the same resistive device can be re-implanted within the same patient. 
     The liner  210  can be formed from a thin yet durable biocompatible material and is generally unsupported and tending to collapse upon itself when empty. For example, the liner  210  can be formed from a fluoropolymer, such as expanded polytetrafluoroethylene (ePTFE). In some embodiments, the liner material is formed using a combination of different materials, such as ePTFE with a different fluoropolymer such as fluorinated ethylene propylene (FEP). The combination of ePTFE and FEP provides a low coefficient of friction, while also being substantially non-permeable. Alternatively or in addition, the liner is formed using polyolefin (e.g., LPDE, HPDE, polypropylene) films. Gastrointestinal liners are described in more detail in U.S. patent application Ser. No. 10/339,786 filed on Jan. 9, 2003 (now U.S. Pat. No. 7,025,791), incorporated herein by reference in its entirety. 
     The liner  210  can have a diameter corresponding to the nominal expanded diameter of the lumen within which it is implanted. Current liners being used in porcine testing include diameters of about 25 millimeters, believed to be close to the diameter of the bowel. A liner having a similar diameter is also believed to be suitable for use within the proximal portion of the small intestine of an adult human. The length of the liner can vary from centimeters to a meter or more depending upon the particular application. 
     The liner  210  provides the added feature of preventing contact between the intestinal walls and any chyme contained therein. The liner can also delay the mixing of chyme with digestive enzymes secreted within the intestine. 
     In some embodiments, the liner implant includes an eversion-resistance zone adapted to reduce the likelihood of eversion of the liner in a proximal direction (i.e., toward the stomach). Without precautions, a negative pressures or reverse peristalsis within the intestine (e.g., when vomiting) will tend to push the liner back through the anchor. The eversion resistance zone can be provided by reinforcing a region of the liner, just distal to the anchor. Liners having eversion resistant features are described in U.S. patent application Ser. No. 11/147984, filed on Jun. 8, 2005 claiming priority to Provisional Application No. 60/645,296 filed on Jan. 19, 2005 incorporated herein by reference in their entireties. 
     The liner  210  can include one or more restrictive elements  215   a,    215   b  (generally  215 ) positioned therein to partially block the intestinal lumen thereby impeding the flow of chyme and subsequently delaying emptying of the stomach. The restrictive elements  215  can include diaphragms that provide a partial blockage within the liner. For example, the diaphragm can be formed from an impermeable membrane defining an aperture or orifice that is smaller than the diameter of the liner  210 . The diaphragms can have different orientations and configurations adapted to produce a desirable resistance to the flow of chyme within the liner  210 . 
     The anchored liner  210  provides a framework for positioning and securing the diaphragms  215 . As illustrated, a first diaphragm  215   a  is attached to the liner at a first distance L 1  measured distally from the proximal end of the liner. A second diaphragm  215   b  can optionally be attached to the liner  210  at a second distance L 2  measured distally from the first diaphragm  215   a.  The distal end of the liner  210  can terminate at the location of the last diaphragm  215  or optionally may extend further as illustrated. 
     Exemplary diaphragms  215  are described below and can be attached to the liner using any suitable method of attachment. For example, the diaphragms  215  can be attached using chemical fastening means, such as adhesives or thermal bonding. Alternatively or in addition, the diaphragms  215  can be attached using mechanical fastening means, such as sutures, staples, and clips. 
     The diaphragm  215  can take on any conceivable shape. Exemplary diaphragms are shown in  FIGS. 4A through 4D . A diaphragm  300  defining a single aperture or orifice  305  is shown in  FIG. 4A . The orifice  305  is defined within a diaphragm providing a closed surface  300 . The orifice  305  provides a reduced-diameter stricture. 
     An alternative embodiment is a partial-block diaphragm  310  is shown in  FIG. 4B . The partial-block diaphragm  310  is shaped and positioned to block a portion of the intestinal lumen. As shown, the partial-block diaphragm  310  can include a planar surface bounded between a chord  312  and the perimeter of the adjacent liner  314 . Selection of the chord controls the surface area of the bounded diaphragm  310  and subsequently controls the percent blockage provided. For example, selection of a chord  312  corresponding to a diameter of the circular arc will result in a 50% blockage. More generally, the shape of the partial-block diaphragm  310  can take on other forms and need not be limited to the exemplary shape described herein. 
     In another embodiment shown in  FIG. 4C , the diaphragm  320  includes more than one smaller orifices  325 . The number and size of the orifices  325  can be used to control the percent blockage of the lumen resulting in resistance to the flow of chyme. Additionally, the diameter of the orifices  325  themselves can be used to provide further resistance by limiting the size of solids allowed to pass. For example, multiple circular orifices  325  can be distributed in a regular or irregular pattern across the surface of the diaphragm  320 . 
     In some embodiments, the diameter of the diaphragm is about 25 mm, corresponding to the internal diameter of the liner  210 , with each orifice  325  having a respective smaller diameter (e.g., about 3 millimeters or less). Alternatively or in addition, the size of the aperture can be increased by removing one or more portions of the diaphragm between groups of orifices  325 . Such alterations can be accomplished prior to implantation of the device, or in situ using an endoscope. The material can be removed or the aperture otherwise enlarged by selectively cutting the material between different apertures. In some embodiments, perforations  326  are provided between different orifices  325  and along the diaphragm itself to facilitate alterations. 
     In yet other embodiments, the diaphragm  330  includes a screen or sieve as illustrated in  FIG. 4D . A screen or sieve  335  can be coupled to a frame  330  to facilitation attachment to the diaphragm  330  to the liner  210   
     Alternatively or in addition, an artificial stricture can be created within the liner itself. An exemplary liner-based stricture device  400  is shown in  FIG. 5 . The device  400  includes an elongated liner  410  having an internal diameter and defining a reduced diameter over at least a portion of the liner length. In some embodiments, the device  400  includes an anchor  405  coupled to the proximal end of the elongated liner  410  to retain the device within the gastrointestinal tract when implanted therein as described above. The liner  410  contains an axial region  412  having a reduced diameter to provide a permanent restrictor  415 . For instance, the liner  410  could be reduced in diameter forming the hourglass configuration shown. Thus, the elongated liner&#39;s diameter measured along its axis transitions from a first diameter D 1  (e.g., 25 millimeters), at a proximal end and for a predetermined length L along the liner, to a lesser diameter D 2  (e.g., about 3 to 10 millimeters). The reduced diameter persists at least briefly, and then may or may not transition back again to a larger diameter (e.g., back to D 1 ). 
     In some embodiments the lesser diameter (e.g., D 2 ) persists for only a short distance resulting in the hourglass configuration; whereas, in other embodiments the reduced diameter may extend for a predetermined length along the axis. The resulting reduced diameter provides a permanent stricture, or narrowed orifice, tending to slow gastric emptying by reducing the rate at which chyme flows through the orifice and consequently through any portion of the intestine proximal to the orifice. 
     In another embodiment, not shown, substantially the entire length of the liner can be sized having a diameter smaller than would otherwise be provided by the intestine alone. For example, a liner defining a central lumen with a diameter less than 25 millimeters (e.g., between about 5 and 20 millimeters) would also impede the flow of chyme by increasing its flow resistance. 
     In an alternative embodiment shown in  FIG. 6 , an implantable device  500  includes a restrictor formed by a liner  510  coupled at its proximal end to an anchor  505  adapted to anchor the liner with the gastrointestinal tract. In particular, the device  500  includes an aperture  515  having a reduced diameter D 2 , similar to that describe above in relation to  FIG. 5 . Additionally, however, the device  500  includes a tapered liner segment  520  between the anchor and the aperture  515 . The tapered segment  520  transitions a first diameter D 1  to a lesser diameter by “necking down” a proximal portion of the device. The tapered segment  520  can be accomplished in a reinforced region of the liner just distal to the anchor  505  (e.g., the eversion-resistant feature). Such a restrictor provides a permanent orifice, of a diameter less than the natural lumen, thereby slowing gastric emptying. It is believed that the tapered region  520  will reduce the loss of water from the chyme suspension that might otherwise occur in a more abrupt transition. 
     Alternatively or in addition, the length of the liner can slow gastric emptying. Some test observations indicate that animals having longer liner implants (e.g., 4 ft, or about 1.2 meters) appear to eat less, or at least less quickly, than do animals with similar, but shorter liners (e.g., 2 ft, or about 0.6 meters). At least one reason that the length of the liner matters is that the longer the liner, the slower the propagation of chyme through it. An animal may have a greater sense of fullness as the chyme winds through the intestines more slowly. Also, the intestines may need to work harder to pass the chyme. Thus, the liner length can affect energy expenditure directly. 
     Abrupt restrictions, such as those provided by the hourglass taper ( FIG. 5 ) and the diaphragm ( FIGS. 3 and 4 ) are focal restrictions in that they transition from a larger diameter to a smaller diameter over a relatively short distance. One disadvantage of such focal restrictions is that they may lead to an abrupt and unwanted separation of water from the chyme suspension at the orifice, making the chyme thicker and more difficult to pass. One means of avoiding this unwanted removal of water is to provide a liner that is tapered gradually over its length. 
     As shown in  FIG. 7 , an implantable device  600  includes a liner  610  coupled at its proximal end to an anchor  605 , which is adapted to anchor the device  600  within the gastrointestinal tract. The liner provides a first diameter D 1  at its proximal end closer to the stomach and a second diameter D 2  that is less than the first diameter at its distal end, further from the stomach. Thus, the diameter of the liner varies or tapers between the first and second diameters along a length L. The particular profile of the taper is selectable and can be chosen, for example, at the time the liner is formed. Thus, the diameter of the liner can change along its length in a linear fashion, as shown. Alternatively or in addition, the diameter can change along the length of the liner according to one or more other mathematical functions including polynomial, exponential, and/or logarithmic functions. Preferably, the chyme would remain well hydrated through the liner until the distal end where a larger restriction would lie. 
     Illustrated in  FIG. 8A  is a schematic diagram of an embodiment of the invention including a tapered anchor  705 . The anchor  705  can be formed providing a proximal opening  710  having a first diameter D 1  and a distal opening  715  having a second diameter D 2  that is less than the first. The anchor  705  can be formed from rigid or semi-rigid material. For example, the anchor can be formed from an alloy, such as stainless steel or Nitinol. In some embodiments, at least the distal region of the anchor is resilient, temporarily expanding to pass material sized larger than the second diameter therethrough, then returning to its reduced diameter. For example, the distal opening  715  can flex outward, temporarily opening to a larger diameter D 2 ′ when subjected to an expanding force  716  due to elevated internal pressure above about 75 inH 2 O. This would permit the anchor to open if it became obstructed with a large food particle and relieve the obstruction as the stomach forces chyme through at elevated pressure. Tapered anchors  705  can be combined with any of the other features described herein including a liner and one or more diaphragms. When combined with a liner, sufficient excess liner material is provided to allow expansion of the anchor&#39;s distal end. 
     Wire anchors, such as the wave-type anchors described above can be formed by forming a wire about a mandrel. An exemplary mandrel  750  that can be used to form a tapered anchor is shown in  FIG. 8B . The mandrel  750  is shaped according to a desired taper profile having a first diameter D 1  at its proximal end  755  and a tapered region leading to a reduced diameter D 2  at its distal end  760 . The mandrel  750  may contain other features to facilitate forming the anchor thereon. For example, the mandrel  750  shown provides a number of posts  765  about which a wire is bent to form a tapered anchor. 
     In some embodiments, the artificial stricture provides an adjustable orifice. For example, the adjustable orifice can be provided within a gastrointestinal liner. Thus, the diameter of the orifice can be adjusted to selectably increase and/or decrease its diameter. Varying the diameter of the orifice similarly affects the resistance offered by the device to the flow of chyme therethrough and can be advantageous for tailoring performance of the device during a particular course of treatment. For example, if a patient outfitted with an adjustable device is not losing weight sufficiently, the diameter of the orifice can be altered to vary the performance (i.e., the orifice can be narrowed to provide more restriction, ideally leading to greater weight loss). Preferably, adjustments to the orifice can be accomplished remotely or using an endoscopic procedure and without the need for surgery. Alternatively or in addition, adjustment can be accomplished through a remote, subcutaneous route. 
     An exemplary embodiment of an artificial stricture having an adjustable orifice is illustrated in  FIGS. 9A through 9D . An intestinal implant  800  includes an anchor  805  coupled to a length of liner  810 . At least a portion of the liner is altered to form an adjustable orifice or restriction. As shown, the liner  810  can be altered using a drawstring  820 . For example, the implant  800  includes a collapsible lumen and a drawstring. The collapsible lumen is operable by adjusting the drawstring  820  to selectively change the size of a constriction within the lumen. Thus, the drawstring can be used to alter the size of the orifice between an unconstrained diameter D 1  ( FIG. 9A ) and a reduced diameter D 2  ( FIG. 9C ). In some embodiments, the drawstring  820  is provided at a distal end of a relatively short gastrointestinal liner  810 , as shown. Alternatively, the liner  810  may extend for a predetermined length and the drawstring  820  positioned at any preferred location along the length of the liner  810 . 
     The drawstring  820  can be sewn into the liner  810  in a purse string fashion, as shown. That is, the drawstring can be laced through holes or eyelets  825  formed in the liner material and extending about the perimeter of the liner  810  ( FIG. 9B ). Alternatively or in addition, the drawstring can be inserted into a hem or a casing, provided within the liner  810  (not shown). Usually, when using a hem or a casing at least one access port will be necessary through which the drawstring can be grasped for adjustment. 
     In some embodiments, the drawstring includes at least one feature adapted for grasping. For example, the drawstring can include at least one loop  822  that may extend within the interior lumen of the liner. The loop  822  can be grasped by a device and manipulated to alter the diameter of the liner. As shown in  FIG. 9D , pulling the loop  822  results in a reduction of the diameter of the liner  810 . 
     In yet other embodiments, the drawstring  820  can be used to adjust the diameter of the anchor  805  itself. For example, the drawstring  820  can be woven through the distal end portion of an anchor  805  (not shown), such that an adjustment of the drawstring  820  changes the diameter of the distal end of the anchor  805 . 
     Once implanted, the drawstring  820  can be accessed remotely (e.g., endoscopically). An instrument, such as a hook, or pinchers can be used to grasp an exposed portion of the drawstring. Once grasped, the drawstring  820  can be adjusted to create a smaller or larger opening. For example, the drawstring  820  can be pulled away from a wall of the liner  810  (e.g., radially inward), in a proximal or distal direction along the length of the liner  810  (e.g., axially), or in a combination of both radial and axial directions. 
     The drawstring  820 , once adjusted, can include a feature, such as a locking means, to retain the drawstring  820  in the adjusted position. It should be noted that locking the drawstring holds it in place to prohibit any further unintentional adjustment (e.g., expansion) of the orifice. Preferably, the locking means is reversible such that it can be locked, unlocked, and then locked again for re-adjustment. For example the drawstring can include a mechanical clip, or more simply a knot, suitably placed to limit further adjustment. In some embodiments a knot can be provided in the drawstring to prohibit expansion of the device beyond a maximum diameter as set by placement of the knot. 
     Shown in  FIG. 10A  is a cross-sectional view of an embodiment of a liner having a ball-and-cleat locking means adapted to lock a drawstring  920 , once adjusted. A portion of the drawstring  920  is wrapped around a segment of the liner  910 , such that the drawstring  920  can be used to narrow the interior of the liner  910 . For example, one end of the drawstring  921  can be secured with respect to the liner  910 . The free end of the drawstring  920  can then be wrapped about the exterior of the liner  910 , forming a loop thereabout. The free end can be further threaded through an opening  922  into the interior of the liner  910 . By adjusting, or pulling the free end of the drawstring  920  with respect to the secured end  921 , the diameter of the loop is reduced, thereby reducing the interior diameter of the liner. 
     A number of balls  930 , or knots, are provided along a portion of the drawstring  920  (e.g., a suture). As the drawstring  920  is adjusted, a portion of the drawstring  920  containing the ball  930  is coupled to a cleat  935  to restrict further adjustment of the drawstring. The cleat  935  can be coupled to the liner  910  or more preferably to a portion of the anchor  905 . 
     In another embodiment (not shown), at least a proximal portion of the drawstring can be replaced by a sturdy tape with an integrated gear rack, or notched belt. A ratchet including an opening can be attached to the liner or anchor. The ratchet includes a pawl that selectively engages teeth along the belt as a free end of the belt is threaded through the ratchet. Thus, similar to a cable tie-wrap device, the drawstring can be adjusted in one direction by simply pulling the free end of the belt. Adjustment in an opposite direction is generally prohibited by the pawl. 
       FIG. 10B  is a cross-sectional view of an alternative embodiment of an adjustable implant device  940  using a hook-and-eyelet locking means for locking a drawstring  920 ′. Thus, one or more hooks  950  are provided along a portion of the liner. A loop  955  or eyelets formed in the drawstring  920 ′ are adapted to engage at least one of the hooks  950 . A portion of the drawstring  920 ′ is wrapped around a segment of the liner  910 , such that the drawstring  920 ′ can be adjusted to narrow the interior of the liner  910 . The hooks  950  are configured to selectably engage a loop or eyelets  955  to secure the drawstring  920 ′ once adjusted. For example, a linear array of hooks  945  can be attached to the anchor  905  and/or to the liner  910 . The drawstring  920 ′ is adjusted, as described above, and a portion of the drawstring  920 ′ is position to engage a selected one of the array of hooks  945  corresponding to a preferred diameter of the liner  910 . 
     Alternatively or in addition, a crimp-type locking means can be used to crimp a portion of the drawstring thereby restricting further adjustment. One embodiment of a crimp-type locking means is shown in  FIG. 10C . Thus, a graspable feature  965  of a drawstring  960  is pulled through one or more crimpable elements  970 . When the drawstring  960  is positioned to produce a desired aperture, at least one of the crimpable elements  970  is crimped about the drawstring  960 . If further adjustment is necessary, the crimpable element  970  securing the drawstring  960  can be breached to free the drawstring  960 . After further adjustment, the drawstring  960  can be secured again by crimping another one of the crimpable elements  970  to again secure the drawstring  960 . 
     Yet another embodiment of a friction-type locking means is shown in  FIG. 10D . A portion of the drawstring  960  is drawn through a resilient channel  980  that is biased in a “pinched” or closed position. Thus, referring to the cross-sectional diagram of  FIG. 10E , the walls of the resilient channel  980  pinch a portion of the drawstring  960  without application of an external force, thereby maintaining the drawstring  960  in fixed position. Subsequent adjustment of the drawstring is possible by applying an external force that flexes the compliant channel (e.g., forces  981 ′,  981 ″ directed along the arrows of  FIG. 10E ) thereby counteracting its biasing force. When flexed in this manner, the resilient channel  980  conforms to an open configuration as indicated in phantom, thereby releasing its grip on the drawstring  960 . Thus, the resilient channel  980  is opened (i.e., the pinch is removed), which allows the portion of the drawstring contained therein to be further adjusted. Once readjustment is completed, the external force is removed from the resilient channel  980  allowing it to revert to its biased configuration to pinch the drawstring, once again holding it fixed. In some embodiments, the resilient channel  980  includes internal features, such as teeth  985 , adapted to enhance the securing force provided to the entrapped portion of the drawstring  960 . 
     In some embodiments, as shown in  FIGS. 11A and 11B , an implant  1000  includes an adjustable orifice provided by an inflatable device, such as a balloon. For example, the interior aperture  1015  of a toroidal balloon  1012  defines a central orifice having a diameter D 2 . The adjustable orifice (e.g., balloon  1012 ) can be coupled to either an anchor  1005  or a liner  1010  coupled at its proximal end to the anchor  1005 . As illustrated, a balloon  1012  is attached to a proximal portion of the liner  1010 . In some embodiments in which the balloon  1012  is attached to the anchor  1005 , without a liner  1010 . The balloon  1012  can be attached to either the liner  1010  or the anchor  1005  using any suitable means of attachment including mechanical fasteners, such as sutures or clips, or chemical fasteners, such as adhesives or bonding. 
     To adjust the internal diameter of the toroidal balloon  1012 , once implanted, an endoscope (not shown) can be inserted into the patient and directed to an area near the balloon  1012 . A needle can then be passed through the endoscope to the balloon  1012 . The balloon  1012  can include a septum through which the needle can access the balloon  1012 . A fluid, preferably such as water, or even a gas, can be injected into or removed from the balloon  1012  selectively inflate or deflate the size of the balloon  1012 , thereby adjusting the size of the orifice  1015  between different-sized apertures  1017 ′,  1017 ″ as shown in  FIG. 11B . 
     In some balloon embodiments, the implant  1000  includes a small inflation/deflation tube  1025  coupled between the balloon  1012  and a remote location  1030 . The tube  1025  can be used to inflate and/or deflate the balloon  1012  by allowing a fluid or gas to be transferred into or out of the balloon  1012  from the remote location  1030 . In some embodiments, the small tube  1025  passes from the balloon  1012  proximally into the stomach, and through a wall of the stomach into a subcutaneous reservoir. Alternatively, the small tube  1025  passes from the balloon  1012  to an injection port  1020 . Preferably, the injection port  1020  is located just below the skin  1021 . Thus, a needle can be used to pierce the skin  1021  for accessing the injection port  1020 . Once accessed, the needle is again used to transfer a fluid or gas between to or from the balloon  1012 , thereby adjusting the size of the balloon  1012 . In other embodiments, one end of the tube  1025  exits the patient. Again, fluid could be injected into or removed from the balloon through this tube  1025  to adjust the size of the opening. 
     In addition to simply providing a narrower channel through which chyme will flow, the liner can reduce the efficiency of natural peristalsis. Peristalsis refers to the forces exerted by the intestine to mix and pass chyme distally through the intestine. In the presence of a liner, peristaltic forces provided by the intestine must operate upon the chyme through the liner material. Preferably, the liner is adapted to channel most if not all of the chyme through its central lumen. 
     In some embodiments, the efficiency of peristalsis can be reduced by using a dampening liner. A dampening liner includes preferred material properties adapted to absorb and/or resist at least some of the peristaltic force provided by the intestine. Thus, liners that are thicker and/or more rigid will tend to dampen the peristaltic forces more so than thinner liners formed from the same material. 
     Such a dampening liner can be configured for implantation within the digestive tract to reduce efficiency of peristalsis. A partially-cut-away of an embodiment of a dampening liner  1100  is shown in  FIG. 12 . A thick-walled liner  1110  is coupled at its proximal end to an anchor  1105  adapted for implantation within the gastrointestinal tract. The stiffer the material of the liner  1110 , the less effective peristalsis will function since the forces that the intestine exerts to pass chyme F 1  must work through the liner material  1110 . Thus the resulting forces acting upon chyme within the liner  1110  are represented by a second force F 2  that is less than F 1  due at least in part to the damping features of the liner  1110 . 
     In some embodiments, it may be desirable to have a relatively flexible liner near the bile and pancreatic ducts so as not to block the ampulla of vater, but a stiffer material more distal, to increase resistance to flow. Thus, the properties of the liner material can be varied along the liner. For example, the same material can be provided with various thicknesses to control variations in the damping performance of the liner along its axis. Alternatively or in addition, different materials can be combined to provide the desired damping values. Configurations can include overlapping portions of the same and/or different materials and/or adjacent regions formed from different materials. 
     Alternatively or in addition, the device can include an interior surface adapted to impede the flow of chyme. For example, as shown in the partially-cut-away schematic diagram of  FIG. 13 , a textured liner device  1200  includes a liner  1210  coupled at its proximal end to an anchor  1205 . The interior surface of the liner  1210  wall includes surface features designed to interfere with the flow of chyme, thus acting to retard the flow against natural peristaltic forces. The surface features can include multiple artificial cilia  1215 . Preferably, the artificial cilia  1215  are oriented in a proximal direction to maximize their effectiveness. The artificial cilia  1215  can be created by brushing or abrading the interior surface of the liner  1210  in a direction against the flow of chyme. This can raise a nap in the surface of the material biased to the direction of the abrasion. 
     Gastric emptying can also be slowed by implanting a mass having a non-negligible volume within the intestine. A blocking mass takes up room within the intestine causing a restriction of sorts within the intestine at least along the length of the mass. Consequently, progression of chyme through the intestine is slowed. The mass provides a smaller volume within the intestine within which to hold chyme as well as a smaller lumen cross-sectional area for the chyme to pass. 
     In an exemplary embodiment, an implantable mass  1300  shown  FIG. 14A  can be implanted within the duodenum to slow the progression of chyme within a portion of the intestinal lumen. In some embodiments, the mass  1300  can be implanted at least partially in other parts of the intestine that may be distal to the duodenum. The mass  1310  can include a solid material, such as a rod. The rod can be solid, braided, or have any other suitable linear construct capable of being attached to the anchoring means  1305  and extended into the intestine. 
     The elongated, or rod-type blocking mass  1310  is implanted axially along the duodenum, such that the available area of a cross section of the intestine is reduced by the cross-sectional area of the blocking mass, as shown in  FIG. 14B . The implanted mass  1310  can also slow gastric emptying by simply occupying a portion of the available volume within the intestinal lumen. Thus, both the length and diameter of the blocking mass can be adjusted to occupy a selectable volume. 
     Still further, the implanted mass  1300  can reduce the efficiency of peristalsis by absorbing or blocking at least a portion of the peristaltic force applied to chyme in the vicinity of the implanted mass  1300 . Thus, the density and/or compliance of the blocking mass  1300  can also be selected to suitably reduce peristaltic efficiency. 
     As illustrated, the blocking mass  1310  can be anchored in the intestine using a gastrointestinal anchor  1305 , such as any of the anchoring devices described above. For example an anchor  1305  is attached to the proximal end of the blocking mass  1310  using any suitable attaching means. Alternatively or in addition, the blocking mass  1310  can be attached to the intestine without an attached anchor  1305 . For example, the blocking mass  1310  can be attached using mechanical fasteners, such as barbs, clips, sutures, staples, etc. As suturing to an intestine can be difficult, the sutures can extend from the implant within the intestinal lumen, through the intestine wall, and to another portion of the anatomy located outside of the intestine. Preferably, the mechanical fasteners couple to muscular tissue to securely anchor the device  1300 . Alternatively or in addition, the blocking mass  1310  can be attached using other attaching means, such as chemical fasteners (e.g., surgical adhesives). 
     In yet another embodiment, an aperture can be formed from one or more contorted elongated elements, such as bent wires. An exemplary embodiment is shown in the axial cross section of  FIG. 15 . One or more elongated members  1425  (i.e., wires) can be twisted in an irregular, convoluted manner to produce resistance to the passage of chyme. The resistance is due at least in part to reduced apertures or screen formed by overlapping portions of the convoluted wire  1425 . In some embodiments the wire is a metal wire, such as a metal alloy. In a preferred embodiment, the wire is a Nickel-Titanium alloy referred to as a Nitinol. The wire can be anchored within the intestine using any suitable anchoring means  1430 , such as mechanical fasteners, barbs, sutures, etc. In some embodiments, the implanted wire provides sufficient force for an interference fit keeping it in place. Anchoring can be enhanced with any of the above anchoring means by locating the anchor  1420  in a proximal portion of the duodenum  1400 , just distal to the pyloric sphincter  1420  and proximal to the ampulla of vater  1422 , referred to as the duodenal bulb  1420 . 
     A cross section of a proximal duodenum  1400  is illustrated in  FIG. 16A  including an artificial stricture  100  ( FIG. 1A ) implanted therein. The stricture is positioned distal to the pylorus  1410  and proximal to the ampulla of vater  1422 , in the duodenal bulb  1420 . The stricture  100  includes barbs  125  that are sized to engage muscular tissue of the intestine. The radial expansive force of the anchor maintains the proximal end of the stricture  100  sealably engaged with the interior walls of the duodenal bulb  1420 . The radial force is also sufficient to keep the barbs  125  firmly implanted within the surrounding tissue. Chyme emptying into the duodenum  1400  through the pylorus  1420  encounters the artificial stricture  100 . The reduced aperture of the stricture decreases the rate at which chyme passes into the distal duodenum  1400 . As chyme continues to empty from the stomach, the chyme builds up along a proximal side of the stricture  100 . Thus, the stomach empties at a slower rate than would otherwise occur without the stricture due to its reduced aperture of the stricture  100 . Exemplary fluid flow rates can be 2 cm/sec through a 25 mm diameter opening. 
     The stricture material  100  may be constructed of a compliant or non-compliant polymer. If non-compliant, such as 0.0005″ thick ePTFE and FEP, then the hole size remains fixed and also can be dilated with a balloon as it will plastically deform. If compliant, such as with 0.015″ thick, 40-60A durometer silicone, the hole may enlarge in response to elevated pressures that result when the hole gets obstructed by large food particles. 
     Another means to provide a self-clearing restriction is if a compliant band is placed around the liner or outlet. One such concept would be made if the drawstring  820  of  FIG. 9C  were replaced with a loop about 3 mm in diameter formed using a thin elastomeric band. If the orifice becomes obstructed, stomach pressure would rise and the elastomeric band may increase in diameter and relieve the obstruction. 
     As described above, the artificial stricture  100  can include a drawstring  125  to assist in the repositioning or removal of the device  100 . As shown in  FIG. 16B , a repositioning device  1500  having a grasping element  1505  can be inserted into the body to grasp a portion of the device  100 . For example, the repositioning device  1500  can be inserted endoscopically through the stomach and at least partially through the pylorus  1420  to a region near the proximal end of the implanted device  100 . The grasping element  1505  can then be manipulated to engage the drawstring  125  of the device  100  for repositioning or removal. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. It should also be appreciated that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, implantation locations, types of anchors, etc. have been described for use with the disclosed embodiments, others besides those disclosed may be utilized without extending the scope of the invention, including implantation locations in or above the pylorus.