Abstract:
A medical device for treating esophageal tissue comprises a catheter, a balloon, placeable within the esophagus of the patient, and a refrigerant. The refrigerant is deliverable into the interior of the balloon so to place the balloon into an expanded, cooled state so that the balloon can press against and cool esophageal tissue. In other examples the medical device may include means for limiting radial expansion of the balloon.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional patent application No. 60/805,965 filed 27 Jun. 2006 and having the same title, attorney docket number WILL 1001-1. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    Barrett&#39;s Esophagus is a pre-cancerous condition of the esophagus typically often associated with gastric reflux disease (GERD). Although GERD can be medically controlled, Barrett&#39;s Esophagus does not spontaneous resolve once the GERD has abated. However, it has been shown that if Barrett&#39;s Esophagus is ablated, the normal esophagus lining can be restored and therefore lowering the risk of developing esophageal cancer. 
         [0003]    A variety of techniques have been evaluated for ablation of this condition. These techniques include photodynamic therapy, endoscopic resection of the lining of the esophagus, and ablation using a variety of energy sources such as argon plasma coagulation (APC), radio-frequency (RF) and cryogenic via a direct spray of liquid nitrogen. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    An example of a medical device for treating atypical esophageal tissue comprises a placement catheter, an expandable balloon and a supply of refrigerant. The placement catheter comprises a distal portion and a lumen. The expandable balloon is mounted to the distal portion of the placement catheter to create a catheter assembly. The balloon has an interior coupled to the lumen. The balloon is placeable within the esophagus of the patient. The supply of a refrigerant is deliverable through the lumen and into the interior of the balloon so to place the balloon into an expanded, cooled state so that the balloon can press against and cool esophageal tissue. In other examples the medical device may include means for limiting expansion of the balloon. Such expansion means may include (a) a radial expansion-limiting tubular braid surrounding the balloon and having a first end fixed to the catheter assembly and a second end movable along the placement catheter, and (b) means for fixing the second end at a chosen position relative to the placement catheter so to limit radial expansion of the tubular braid thereby preventing overexpansion of the balloon. 
         [0005]    An example of a method for treating atypical esophageal tissue is carried out as follows. A catheter assembly is selected. The catheter assembly includes a placement catheter comprising a distal portion, a lumen and an expandable balloon mounted to the distal portion, the balloon having an interior coupled to the lumen. The balloon is placed within the esophagus of a patient. The balloon is positioned at a target site having atypical esophageal tissue. A refrigerant is delivered through the lumen and into the interior of the balloon thereby (a) expanding the balloon to a chosen size, and (b) cooling the balloon so that the balloon presses against and cools the atypical esophageal tissue. In other examples a radial expansion limiting step may comprise the following steps. The balloon may be surrounded with a radial expansion-limiting tubular braid and having a first end fixed to the catheter assembly and a second end movable along the placement catheter. The second end may be fixed to the catheter assembly at a chosen position thereby (a) limiting radial expansion of the tubular braid, and (b) preventing overexpansion of the balloon. Other examples may also comprise cooling only a portion of the esophageal tissue in contact with the expanded balloon. 
         [0006]    Other features, aspects and advantages of the present invention can be seen on review the figures, the detailed description, and the claims which follow. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a simplified overall view of one example of a medical device made according to the invention with elements of other examples shown in dashed lines; 
           [0008]      FIG. 2  is an enlarged, simplified cross-sectional view of the distal portion of the medical device of  FIG. 1 ; 
           [0009]      FIG. 3  illustrates the balloon of  FIG. 1  in a collapsed state with a braided structure covering the balloon and a distal portion of the placement catheter; 
           [0010]      FIG. 4  illustrates the structure of  FIG. 3  with the balloon in a radially expanded state and showing how the braided structure shortens longitudinally as the balloon expands; 
           [0011]      FIG. 5  is a simplified cross-sectional view of another example in which two balloons are inflated generally equal amounts within an esophagus; 
           [0012]      FIG. 6  is a schematic side illustration the balloon structure of  FIG. 5 ; and 
           [0013]      FIG. 7  is a view similar to that of  FIG. 5  but with only one balloon inflated. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The following description of the invention will typically be with reference to specific structural embodiments and methods. It is to be understood that there is no intention to limit the invention to the specifically disclosed embodiments and methods but that the invention may be practiced using other features, elements, methods and embodiments. Preferred embodiments are described to illustrate the present invention, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows. 
         [0015]    All of the techniques listed above suffer from ‘usability’ drawbacks. Photodynamic therapy renders the patient susceptible to sunlight for several months following treatment and has a high procedural complication rate. Mechanical resection is training intensive and may not achieve 100% removal of the condition. Ablation techniques such as APC only treat a small area at a time and controlling the depth of ablation is difficult. Current RF ablation techniques require precise sizing of the treatment catheter and require another console for the physician to operate. The direct spray of liquid nitrogen can be training intensive and is very operator dependent; this system also requires an additional console and a constant supply of liquid nitrogen. 
         [0016]    The present invention addresses many of the limitations of the current technologies. Embodiments of the invention typically include a self sizing treatment catheter connected to a refrigerant delivery handle. The invention is particularly useful for treating Barrett&#39;s esophagus but may also be useful for treating other esophageal tissues, typically by cryogenic ablation of the atypical tissue. 
         [0017]    According to some embodiments of the invention, see  FIGS. 1 and 2 , the medical device  10  comprises a catheter assembly  12  and a refrigerant supply  14 . The catheter assembly  12  comprises a balloon  16 , preferably an elastomeric material such as polyurethane or silicone, mounted to a placement catheter or shaft  18 . In one embodiment the balloon  16  will be capable of producing an inflated diameter of between 15-45 mm. In another embodiment, multiple balloon sizes may be required to cover the desired range of esophagus sizes; in this embodiment, it is desirable to have individual balloon diameters that are variable by at least 2 mm. For example, 6 different sizes could be developed to cover the complete range of 15-45 mm in which case each size covers a 5 mm range. The balloon length may be 10-100 mm. The shaft  18  may comprise a plastic such as polyurethane such that the balloon may be appropriately bonded to the shaft; other appropriate, biocompatible materials such as PEBAX and polyethylene may also be used. The shaft  18  will be less than 8-Fr in order to be compatible with a conventional diagnostic endoscope, which typically has an accessory channel size of 2.8 mm. However, larger shaft sizes up to 11-Fr may be utilized for catheters designed for conventional therapeutic endoscopes. Shaft  18  may include a delivery lumen  20 , which may be used for delivery of the refrigerant, running through, and which may be concentric with, the shaft  18  and may have an inner diameter of, for example, 0.004-0.025″ (0.10-0.71 mm). In some embodiments, as disclosed in  FIG. 2 , the delivery lumen  20  may comprise a separate delivery tube  22  passing through the interior of the shaft  18 ; all or part of delivery tube  22  could also pass along the exterior of shaft  18 . This delivery tube  22  may comprise a high-strength material such as polyimide. In other embodiments, the shaft itself will define at least a portion of the refrigerant delivery lumen. 
         [0018]    A fluid saturated liquid/gas refrigerant  24 , indicated by arrows  24  in  FIG. 2 , such as nitrous oxide or a hydrofluorocarbon, is provided from the refrigerant supply  14  through a manifold  26  at the proximal end  28  of the shaft  18 , through the delivery lumen  20  and into the interior  30  of the balloon. As shown in  FIG. 1 , one example of a refrigerant supply  14  of medical device  10  comprises a flow control device  32  which may be hand-held, coupled to a disposable cylinder  34  of refrigerant. The size of the cylinder  34  may be between 10 to 50 cubic centimeters in volume. The refrigerant supply  14  may be integral to the catheter assembly  12  or stand-alone. The refrigerant  24  will typically be continuously injected, at room temperature or warmer, into the delivery lumen  20  and in some embodiments will exit into the interior  30  of the balloon  16 . The refrigerant will then undergo a phase change from liquid to gas, simultaneously expanding the balloon and rapidly drawing energy from the surrounding esophageal tissue and causing the tissue to be cooled. The gas may then exhaust though shaft  18  and exit out of the manifold  26  though a port  27 . In some other embodiments, the refrigerant supply may require external heating to maintain the desired delivery pressure. The balloon  16  will then expand until contact with the tissue of the esophagus  36  has been made. 
         [0019]    The placement of the balloon  16  at the target site and expansion of the balloon is preferably monitored by conventional techniques, such as direct endoscopic visualization. Other endoscopic spectroscopy techniques such as Fluorescence, Raman, or Light Scattering may be useful for identification of atypical esophageal tissue. In order to lower the risk of injury to the esophagus the balloon pressure should be minimized and may be less than 10-psig. Balloon pressure is primarily dependent on the refrigerant flow rate and can be controlled by manipulating the sizes of shaft  18  and/or lumen  20 . Pressure can also be controlled though a back-pressure regulator  29 , shown in dashed lines in  FIG. 1 , attached to port  27 . Cooling of the esophagus, in particular the atypical esophageal tissue, is typically achieved by evaporation of liquid refrigerant in the balloon  16  which will draw heat away from the esophageal tissue at the target site. In order to ablate or otherwise alter the atypical tissue, it is desirable to cool this tissue until it has frozen. Typically, intracellular ice formation is required for substantial necrosis of the atypical tissue. The target temperature to achieve sufficient intracellular ice formation in the atypical esophageal tissue may be between −25 and −100 C. As undesirable side effects of the cryoablation treatment such as esophageal perforation or stricture may occur if necrosis occurs deeper than the mucosa, the depth of ablation may be controlled by regulating the time that the cooling is applied to the esophagus. Based on typical mucosal thickness of 0.5-2 mm, the required time for ablation may be less than 60 seconds. 
         [0020]    It may be desirable to limit the expansion of the balloon so as to prevent damage to the esophagus. In such cases, a braided structure, see  FIGS. 3 and 4 , may be used over the outside of the balloon  16 . A distal portion  42  of the braided structure may be fixed to the distal end of the catheter assembly  12 , that is to the shaft  18  and/or to the balloon  16 , and a proximal portion  44  of the braided structure  40 , lying proximal to the balloon  16 , may be secured to an expansion control rod  46  through a sleeve  50 . The proximal end  51  of the control rod  46  may be secured to and may be movable axially with a control element  52 , which may be lockable or securable, so that the expansion control rod  46  may move parallel to the placement catheter  18 . During use the balloon  16  will be initially inflated to make contact with the esophageal wall  48 . This will cause the braided structure  40  to foreshorten which will pull the expansion control rod  46  towards the balloon  16 . Once the balloon  16  has reached a desired diameter, the expansion control rod  46  may be secured relative the placement catheter using control element  52 ; this will prevent additional radial expansion of the braided structure  40  and, in turn, prevent additional dilation of the balloon  16 . The use of a radial expansion-limiting tubular braid decreases the compliance of balloon  16 . Other techniques for limiting the radial expansion of the balloon  16 , such as a coil wrapped around the balloon that when unwound will allow for a progressively larger expansion, may also be used. 
         [0021]    One desirable feature of a balloon-based esophageal tissue treatment system is that the full circumference of the esophagus  36  may be treated simultaneously. However, it may be possible that the desired tissue treatment site extends around only part of the circumference of the esophagus. In this case, it may be desirable to protect portions of the esophagus from the cryoablation. One embodiment of the invention for doing so is illustrated in  FIGS. 5-7 . In this embodiment, a second balloon  54  may be located adjacent to a first, refrigerant-inflatable balloon  16 , balloon  16  acting as a cryoballoon  16 . The second balloon  54  may act as an insulating balloon  54 . The second, insulating balloon  54  may be constructed of either a compliant material, such as polyurethane or silicone, or non-compliant material, such as PET or nylon, and would typically be manually inflated with an insulating fluid such as air. As shown in broken lines in  FIG. 1 , a non-refrigerant compressed fluid supply  56 , similar to refrigerant supply  14 , can be used. Supply  56  may include a nonrefrigerant source  58 , such as a compressed air cylinder, and a flow control device  60 . Supply  56  may be coupled to second balloon  54  in the same manner as refrigerant supply  14  is coupled to balloon  16 . Leaving the second, insulating balloon  54  uninflated may permit the refrigerant-inflatable balloon to expand over substantially the entire circumference. See  FIG. 7 . Also, a refrigerant may be used in both balloons to provide full circumferential coverage. During operation, the insulating balloon  54  could be inflated in such a way to protect from, for example, 0 to 75% of the circumference of the esophagus. Additional flexibility or control, or both, may be achieved using more than two balloons with the individual balloons being inflatable with the refrigerant and/or with a non-refrigerant. Instead of using separate balloons, a single balloon may include two or more inflatable regions for selective inflation using a refrigerant or a nonrefrigerant. In addition, balloons may be provided or segmented to permit control of cooling of the tissue in a longitudinal or axial direction. 
         [0022]    The above descriptions may have used terms such as above, below, top, bottom, over, under, et cetera. These terms are used to aid understanding of the invention are not used in a limiting sense. 
         [0023]    While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims. 
         [0024]    Any and all patents, patent applications and printed publications referred to above are incorporated by reference.