Abstract:
Method and apparatus for treating obesity by use of transesophageal delivery of energy to interrupt the function of vagal nerves. The energy, which may be highly focused ultrasound energy or other types of energy is delivered through the wall of the esophagus by a device placed in the esophagus. The energy delivered is sufficient to ablate a vagal nerve on the outer wall of the esophagus.

Description:
BACKGROUND OF THE INVENTION 
   Obesity has become an ever-increasing health problem. While such voluntary weight reduction programs as dieting and exercise have been helpful for some, many obese persons have required surgery to address their obesity problem. Two such surgical procedures are vertical banded gastroplasty (VBG) and the Roux-en-Y gastric bypass procedure. Both such procedures are now well known, but they are invasive in nature and involve reducing the size of the stomach. While these procedures have demonstrated a reasonable level of efficacy, there has remained a need for an obesity treatment that would not involve the patient trauma of invasive surgery and would yet be effective. 
   SUMMARY OF THE INVENTION 
   The present invention is, in general, directed to the treatment of obesity by creating an interruption of the vagal nerve, preferably in the region of the esophagus, by minimally or noninvasive means. While the present invention is not to be tied to any particular theory of operation, it appears that a hunger signal is expressed by ghrelin, a peptide primarily produced in the stomach, and transmitted to the brain through the vagal nerve. The literature e.g., “The Role of the Gastric Afferent Vagal Nerve in Ghrelin-Induced Feeding and Growth Hormone Secretion in Rats,”  Gastroenterology  2002:123:1120-1128 (October 2002) by Yukari Date et al. and “Gastroplasty for Obesity: Long-term Weight Loss Improved by Vagotomy,”  World Journal of Surgery , Vol. 17, No. 1, January/February 1993, by Kral et al., supports this theory. The Date et al. article concluded that blockade of the gastric vagal afferent abolished ghrelin-induced feeding in rats and the Kral et al. article concluded that vagotomy combined with gastroplasty was more effective in controlling weight loss than gastroplasty alone. These articles are incorporated by reference herein. 
   More specifically, a preferred embodiment of the present invention is directed to interrupting the function of the gastric vagal nerve in the region of the esophagus by using an ablating or other nerve dysfunction causing device installed in the esophagus which delivers ablating energy to one or more vagal nerve branches in a transesophageal manner. The anatomy of the vagal nerve complex varies somewhat from person to person, but, common to all is a structure comprising multiple vagal nerve branches located on the outer wall of the esophagus which run generally longitudinally along the esophagus wall. The present invention contemplates interrupting the function of one or more vagal nerve branches in a transesophageal manner by using various types of energy including radio frequency (RF) energy, high intensity ultrasound, high intensity focused ultrasound, and other types of energy as described in more detail below. 
   Typically, there are two main branches, or trunks, of the vagal nerve which are located approximately 180° from each other on the outer wall of the esophagus. Depending on patient needs, it may be sufficient to interrupt only a portion of the fibers in the nerve. In this regard, it is to be noted that, in general, myelinated vagal nerve fibers, i.e., fibers that have an outer coating, are efferent. In contrast, afferent vagal nerves are unmyelinated and have no outer covering. For some patients, it may be sufficient to interrupt the function of only the afferent vagal fibers. 
   The ultimate objective is, of course, substantial weight loss by the patient as a result of a substantial decrease in the ghrelin hunger signal transmitted through the vagal nerve branches. Thus, the success of the procedure described herein will, to some extent, be patient-dependent and, in some patients, it may be necessary to interrupt both the afferent and efferent vagal branches. 
   In practicing the present invention, the energy source may be installed in the esophagus through the throat, but nasogastric access through the nose and extracorporeal application are also contemplated. The energy may be delivered to the vagal nerve through the esophagus wall, e.g., when ultrasound is used, or by causing an energy delivery device, e.g., an electrode to be passed through the wall of the esophagus. 
   Still other energy sources can be used to interrupt the function of the vagal nerves including thermal, microwave, laser and cryogenic energy. Alternatively, the vagal nerve function can be interrupted by transesophageal delivery of a neurotoxin such as capsaicin, atropine, or botulinum toxin. Still further, mechanical means can be used to crush the vagal nerve, e.g., with a clip or pincer, or the vagal nerve can be cut transesophageally with an appropriate cutting instrument. In a preferred embodiment of the present invention, the vagal nerve will be interrupted in the vicinity of the zig-zag line, also known as the Z-line, which is genreally located in the lower esophagus between the cardiac notch of the stomach and the diaphragm. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic illustration of the general anatomy of the stomach and esophagus. 
       FIG. 2  illustrates positioning of an ablation device using a single balloon installed above the diaphragm. 
       FIG. 3  illustrates positioning the ablation device using a balloon which is inflated in the stomach. 
       FIG. 4  illustrates a positioning device using radially extending feet. 
       FIG. 5  illustrates a positioning device using a bite block. 
       FIG. 6  is a diagrammatic illustrate of the use of needles or electrodes to detect and ablate around the circumference of the outer surface of the esophagus in a manner designed to interrupt all vagal nerve branches. 
       FIG. 7  is an illustration of an ablating device which ablates a sector of the circumference of the outer wall of the esophagus. 
       FIG. 8  shows ablating at multiple levels. 
       FIG. 9  illustrates an ablation ring which can be adjusted to ablate at different angles relative to the access of the esophagus. 
       FIG. 10  illustrates the use of still another ablation device to locate and interrupt the vagal nerve. 
       FIG. 11  illustrates an endoluminal burge test which can be used to determine the extent of ablation accomplished. 
       FIG. 12  shows an ultrasound ablating device which may be used according to the present invention. 
       FIG. 13  illustrates an ultrasound device installed in the esophagus. 
       FIG. 14  illustrates an ablation device installed in the esophagus in a manner which shows the esophasgus held in its naturally relaxed configuration by a transducer device. 
       FIGS. 15 and 16  illustrate an alternative to the device shown in  FIG. 14 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Before turning to the manner in which the present invention functions, it is believed that it will be useful to briefly review the anatomy of the stomach and the esophagus. The esophagus is a muscular tube that carries food from the throat to the stomach and which passes through the diaphragm. The top end of the esophagus is the narrowest part of the entire digestive system and is encircled by a sphincter (circular muscle) that is normally closed but can open to allow the passage of food. There is a similar sphincter at the point where the esophagus enters the stomach. The walls of the esophagus consist of strong muscle fibers arranged in bundles, some circular and others longitudinal. The inner lining of the esophagus consists of smooth squamous epithelium (flattened cells). 
   As shown in  FIG. 1 , the esophagus  1  extends through the diaphragm  2  into the stomach  3 . Vagal nerve branches extend from the stomach along the outer wall of the esophagus to the brain. At the lower end of the esophagus, the juncture of the esophageal and gastric mucosa forms a zig-zag line  4 , usually referred to as the Z-line. In the area extending from the diaphragm to a point below the Z-line, there is a subhiatal fat ring which surrounds the outer wall of the esophagus. The vagal nerve branches run between the outer wall of the esophagus and the hiatal fat ring in this area. This anatomy is well understood by those skilled in the art and a more detailed description can readily be found in a standard work such as  Gray&#39;s Anatomy.    
     FIG. 2  illustrates in a diagrammatic manner an ablation device  5  which is held in place by balloon  6  which is inflated inside the upper portion of the esophagus.  FIG. 3  illustrates positioning the ablation device  5  with balloon  7  which is inflated inside stomach  3 .  FIG. 4  illustrates positioning the ablation device  5  with feet  6  which pass through the esophagus folded against the ablation device  5  and then are extended inside stomach  3 .  FIG. 5  illustrates the use of a bite block  7  to position the ablation device  5  in stomach  3 .  FIG. 6  is a diagrammatic transverse cross section of the esophagus showing, in diagrammatic form, the esophagus wall  1 , vagal nerve branches  8 , a detection/ablation device  9  having needle probes  10 . As shown, the needle probes  10  extend through the wall of the esophagus and can be used both to locate the vagus nerve and to ablate it. For detection purposes, the needle probes  10  are connected to an exterior control unit that detects and displays nerve activity in a manner well known to those skilled in the art. Once a vagal nerve is detected by a needle probe by sensing the activity of the nerve upon contact, the adjacent needle probes are energized and act in the manner of bipolar cautery probes which ablate the nerve and any other tissue between the needle probes. Preferably, the needle probes are designed in such a manner that they are held within the body of the ablation device until the device reaches its desired location. The needle probes can then be extended to penetrate the wall of the esophagus once the device has been positioned. Preferably, the needle probes are designed so that the electric current flows only at their tips so that the depth of the cautery can be focused to minimize damage to the esophagus. Cosman U.S. Pat. No. 4,565,200, Rydell U.S. Pat. No. 5,007,908, Edwards U.S. Pat. No. 5,370,675 and Edwards U.S. Pat. No. 6,129,726, each of which is incorporated by reference herein, disclose various types of electrode needle probe devices which can be used to deliver RF energy to tissue located within the body. Each of these patents discloses a device in which the needle probes are contained within the device until it has reached its desired location, at which time the needle probes are deployed to contact the tissue to which energy is to be delivered. 
   In the present invention, the needle probes can irradiate around the complete circumference of the device as shown in  FIG. 6  or from only a portion of the device as shown in  FIG. 7 . If the latter, the device can be rotated sequentially to ensure complete coverage. As further shown in  FIG. 7 , when the needle probes  13  radiate from only a portion of the circumference of the device  12 , a back balloon  11  can be used to position the device  12  in the desired location. 
     FIG. 10  illustrates an alternative sector-specific ablation device in which needle probes  13  are activated by device  12  to locate and ablate the vagal nerve in the manner described above. If a patient can obtain the desired benefit of obesity reduction by ablating the two main vagus branches  8 , the procedure is simplified and the amount of ablation necessary is reduced. On the other hand, as shown in  FIG. 8 , if multiple ablation levels  14  are found to be necessary to provide the desired benefit to the patients, more than one ablation can be performed. 
   As shown in  FIG. 9 , if the patient&#39;s anatomy makes it desirable, an ablation device  5  can be provided with an energy delivery component  15  which is adjustable such that energy can be delivered perpendicularly to the probe or at an angle to the probe. 
     FIG. 11  illustrates an endoluminal burge test which can be used to determine the extent of ablation accomplished. When a needle probe is used to deliver energy according to the present invention, the device can be provided with temperature sensors such as thermocouples which are disposed in the distal region of the needle probes. The needle probes can be formed of a variety of materials including nickel-titanium alloy. The needle probes can assume a linear or curved shape when deployed. The device may also be provided with means for cooling the treatment site with a suitable fluid such as water, air, or other liquid or gas, to control the temperature at the treatment site. Thus, the temperature sensor can either cause a cooling medium to be provided or shut off the delivery of energy through one or more needle probes. 
   In a preferred embodiment of the present invention, high intensity focused ultrasound (HIFU) is used to ablate the vagal nerve branches. The HIFU energy can be transmitted transesophageally to ablate the vagal nerves on the outer wall of the esophagus.  FIG. 12  illustrates in a diagrammatic form an ultrasound device which can be used according to the present invention. As shown, the device comprises an elongated member  16  which has an ultrasound transducer  17  mounted on its distal region. The elongated member is positioned in a housing  18  which is provided with an inflatable balloon  19 . This device may be installed by passing it through the throat and down the esophagus until it reaches its desired location with the balloon  19  deflated. The balloon  19  can then be inflated to position the device and the ultrasound transducer can be activated to transmit energy radially outwardly. Alternatively, a vacuum device can be used to position the housing. 
     FIG. 13  is a diagrammatic illustration of an ultrasound transducer installed in the esophagus. As shown in this figure, the transducer device  16  is installed in the esophagus  1  in the region of the Z-line  4 . The subhiatal fat ring  20  is also shown. When the transducer  17  is activated, ablating energy will be radiated through the wall of the esophagus to ablate the vagal nerve branches  21  which are also shown diagrammatically. 
   Although the esophagus is generally illustrated anatomically as a generally cylindrical tube, in its relaxed condition it assumes a more elliptical configuration which can be characterized as floppy. In other words, somewhat like a sock before it is put upon a foot, it does not assume a generally circular configuration unless it contains food, but otherwise has a configuration in which the opposing walls of the esophagus are closer together than they would be when in a circular configuration as shown in  FIG. 14 . In this figure, esophagus  1  with vagal nerve branches  8  on its outer wall is provided with a transducer  22  which has radially extending struts  23 . Each of these struts  23  has a rounded portion  24  at its distal end. The struts  23  and  24  serve to hold the esophagus in its relaxed generally elliptical shape and to hold the transducer  22  in the desired location as well. In an alternative embodiment illustrated in  FIGS. 15 and 16 , balloons  25  mounted on the side of the transducer-containing device  26  are implemented to hold the esophagus in a more ellipitical shape. When these types of devices are used, the transducer device  22  or  26  could be constructed to direct ultrasound energy towards the vagal nerve branches  8  in one direction or in two directions.  FIG. 15  shows the balloons  25  in the deflated state and  FIG. 16  shows the balloons in the inflated state. 
   Ultrasound heating technology, including high-intensity ultrasound and HIFU are well understood. For example, Chapter 12, entitled “Ultrasound heating technology,” of “Thermo-radiotherapy and Thermo-chemotherapy,” vol. 1, edited by Seegenschmiedt, Fessenden and Vernon, contains a thorough explanation of the use of ultrasound in thermal therapy. This chapter is incorporated by reference herein. 
   The present invention is not to be considered to be limited to the embodiments described above, but is of the full scope of the appended claims.