Patent Document

FIELD OF THE INVENTION  
         [0001]    The present invention pertains to a resilient, flexible, compressible, biocompatible prosthesis insertable into the stomach to effect weight loss over a controlled period.  
         BACKGROUND OF THE INVENTION  
         [0002]    The incidence of obesity and its associated health-related problems have reached epidemic proportions in the United States. See, for example, P. C. Mun et al., “Current Status of Medical and Surgical Therapy for Obesity”  Gastroenterology  120:669-681 (2001). Recent investigations suggest that the causes of obesity involve a complex interplay of genetic, environmental, psycho-behavioral, endocrine, metabolic, cultural, and socioeconomic factors. Severe obesity is frequently associated with significant comorbid medical conditions, including coronary artery disease, hypertension, type II diabetes mellitus, gallstones, nonalcoholic steatohepatitis, pulmonary hypertension, and sleep apnea.  
           [0003]    Estimates of the incidence of morbid obesity are approximately 2% of the U.S. population and 0.5% worldwide. Current treatments range from diet, exercise, behavioral modification, and pharmacotherapy to various types of surgery, with varying risks and efficacy. In general, nonsurgical modalities, although less invasive, achieve only relatively short-term and limited weight loss in most patients. Surgical treatments include gastroplasty to restrict the capacity of the stomach to hold large amounts of food, such as by stapling or “gastric banding.” Other surgical procedures include gastric bypass and gastric “balloons” which, when deflated, may be inserted into the stomach and then are distended by filling with saline solution.  
           [0004]    The need exists for cost effective, less invasive interventions for the treatment of morbid obesity.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a novel system for treatment of morbid obesity by use of a bioabsorbable gastric prosthesis placed in the stomach through a minimally invasive procedure. The prosthesis takes up space in the stomach so that the stomach can hold a limited amount of food, and preferably exerts pressure on the upper fundus to create a sensation of being full. The material of the prosthesis can be selected to degrade over a predetermined period and pass out of the patient without additional intervention.  
           [0006]    In the preferred embodiment, the prosthesis is a porous weave of bioabsorbable filaments having an open mesh configuration. The prosthesis can be formed from a cylindrical stent, such as by reverting the ends of the cylinder and joining them at the center. The filaments preferably have memory characteristics tending to maintain an oblate shape with sufficient resiliency and softness so as not to unduly interfere with normal flexing of the stomach or cause abrasion of the mucus coat constituting the inner lining of the stomach. The prosthesis may be free floating in the stomach, but is shaped so as to be biased against the upper fundus, or it may be tacked in position adjacent to the fundus by bioabsorbable sutures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 is a somewhat diagrammatic elevation of a stomach and adjacent parts of the alimentary canal, with the wall adjacent to the viewer partially broken away to reveal an intragastric prosthesis in accordance with the present invention;  
         [0009]    [0009]FIG. 2 is a side elevation of a cylindrical stent from which a prosthesis in accordance with the present invention may be formed;  
         [0010]    [0010]FIG. 3 is a side elevation of a prosthesis in accordance with the present invention, formed from the stent of FIG. 2; and  
         [0011]    [0011]FIG. 4 is a diagrammatic elevation corresponding to FIG. 1, illustrating insertion of a prosthesis in accordance with the present invention through the esophagus and into the stomach. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]    The present invention provides a volume-filling prosthesis insertable into the stomach for treatment of morbid obesity by taking up space in the stomach to reduce its capacity and by exerting pressure to create a sensation of being full, particularly on the upper fundus.  
         [0013]    [0013]FIG. 1 illustrates a central portion of the alimentary canal including the distal segment of the esophagus  10 , the stomach  12 , and the duodenum  14  (proximate segment of the small intestine). The esophagus  10  opens into the stomach  12  toward the top of the lesser curvature  16  adjacent to the fundus  18 . The pyloric part  20  of the stomach leads to the duodenum by way of the gastric outlet or pylorus  22  which forms the distal aperture of the stomach and has an enclosing circular layer of muscle which is normally contracted to close the aperture but which relaxes to provide an open but restricted passage. Although subject to substantial variation in different individuals, representative dimensions for the stomach are approximately 8 cm long (fundus to pylorus) by 5 cm wide (greatest distance between lesser and greater curvatures), with the esophageal opening being approximately 2 cm in diameter and the pylorus having a maximum open diameter of about 2 cm.  
         [0014]    In accordance with the present invention, an oblate, volume-filling prosthesis  24  is held within the stomach, sized for reception in the proximate portion adjacent to the opening of the esophagus and fundus. Such prosthesis preferably is a porous body formed of a loose weave of thin polymer filaments  26 , having large spaces between filaments for an open area of at least about 80%, preferably more than 90%, so as not to impede the flow of gastric juices or other functioning in the stomach. The filaments  26  have substantial memory characteristics for maintaining the desired oblate shape and size. However, the filaments preferably are sufficiently soft and flexible to avoid abrasion of the mucus coat forming the inner lining of the stomach and to enable normal flexing and shape changes. The size of the prosthesis  24  is substantially greater than the opening of the esophagus, at least about 3 cm in the narrowest dimension, preferably at least about 4 cm. The longer dimension of the oblate prosthesis is greater than 4 cm, preferably at least about 5 cm to prevent the prosthesis from free movement within the stomach. The size and shape of the prosthesis tend to maintain it in the position indicated in FIG. 1, adjacent to the fundus  18  and remote from the pyloric part  20 . Thus, while the prosthesis occupies a substantial portion of the volume of the stomach, preferably approximately one-half the volume, the prosthesis does not interfere with normal digestion of food, such as by gastric juices (hydrochloric acid and digestive enzymes) nor with passage of food through the pyloric part  20  and its opening  22  to the duodenum  14 .  
         [0015]    With reference to FIG. 2, the prosthesis can be formed from a substantially cylindrical stent  28  having the desired porous weave and large open area. The filaments  26  and weave pattern are selected to achieve memory characteristics biasing the prosthesis to the cylindrical condition shown. In the preferred embodiment, the opposite ends  30  of the stent are reverted, the end portions are rolled inward, and the ends are secured together such as by suturing. Alternatively, a disk of the same pattern and material can be used in securing the reverted ends together. The resiliency of the filaments tends to bulge the resulting prosthesis  26  outward to the desired oblate shape.  
         [0016]    Prior to reversion of the ends, stent  28  in the condition shown in FIG. 2 can be approximately 2-3 cm in diameter and approximately 8-10 cm long, in a representative embodiment. The filaments can have a diameter of about 0.010 inch to about 0.25 inch. The filaments may be coated or impregnated with other treating agents, such as appetite suppressants, or agents to decrease the likelihood of gastric problems, such as ulcers, due to the presence of a foreign object. However, such problems are unlikely due to the biocompatible nature and the resilient flexibility of the prosthesis.  
         [0017]    It is preferred that the filaments  26  be formed of a bioabsorbable polymer such as a polyglycolic acid polymer or polylactic acid polymer. Similar materials are used for some bioabsorbable sutures having “forgiving” memory characteristics and sufficient “softness” that tissue abrasion is inhibited. The absorption characteristics of the filaments  26  can be selected to achieve disintegration of the prosthesis  26  within the range of three months to two years, depending on the severity of obesity. In the preferred embodiment, the prosthesis will absorb and pass naturally from the stomach approximately 6 months after deployment.  
         [0018]    Nonbioabsorbable materials may be used, such as Nitinol, which exhibit the desired springiness but which would require that the prosthesis be retrieved. An advantage of the preferred, bioabsorbable embodiment of the invention is that delivery can be through the esophagus, with no additional intervention being required.  
         [0019]    With reference to FIG. 4, preferably from the condition shown in FIG. 3, the prosthesis  26  can be compressed to a generally cylindrical shape having a diameter of no more than about 2 cm such that the compressed prosthesis can be carried in a short (approximately 5 cm to 6 cm long) loading tube  32 . The loading tube can be advanced along the esophagus by a central tube  34  of smaller diameter, under the visualization allowed by a conventional endoscope  36 . The tube  34  can enclose a core wire  38  to actuate a pusher mechanism  40  for ejecting the prosthesis  26  when the opening of the esophagus into the stomach has been reached. The endoscope and deployment mechanism can then be retracted.  
         [0020]    While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. For example, while it is preferred that the prosthesis be sized for self-retention in the desired position in the stomach, it also may be secured in position by a few sutures applied endoscopically, preferably in or adjacent to the fundus area of the stomach.

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