Abstract:
Disclosed is an expandable transluminal sheath, for introduction into the body while in a first, low cross-sectional area configuration, and subsequent expansion of at least a part of the distal end of the sheath to a second, enlarged cross-sectional configuration. The sheath is configured for use in the gastrointestinal system and has utility in the performance of endoscopic retrograde cholangiopancreatography (ERCP). The distal end of the sheath is maintained in the first, low cross-sectional configuration and expanded using a radial dilatation device. In an exemplary application, the sheath is utilized to provide access for a diagnostic or therapeutic procedure such as gallstone or pancreatic stone removal.

Description:
PRIORITY CLAIM  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/659,831, filed on Mar. 9, 2005, and U.S. Provisional Application No. 60/608,355, filed on Sep. 9, 2004, the entirety of these applications are hereby incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to medical devices and, more particularly, to methods and devices for accessing a gastrointestinal tract.  
         [0004]     2. Description of the Related Art  
         [0005]     A wide variety of diagnostic or therapeutic procedures involves the introduction of a device through a natural access pathway such as a body lumen or cavity. A general objective of access systems, which have been developed for this purpose, is to minimize the cross-sectional area of the access lumen, while maximizing the available space for the diagnostic or therapeutic instrumentation. These procedures are especially suited for the gastrointestinal (GI) tract of the human or other mammal, including the esophagus, stomach, duodenum, small intestine and organ outflow tracts such as the bile duct and pancreatic duct. Other applications include procedures in the bronchial and tracheal passages, and the lower GI tract including the colon and the anus.  
         [0006]     Endoscopic retrograde cholangiopancreatography (ERCP) is an example of one type of therapeutic or diagnostic interventional procedure that relies on natural access pathways such as the esophagus, the stomach, which is a body cavity, the duodenum, the small intestine, and the common bile and pancreatic ducts. Access to the gastrointestinal tract is gained through the nose or throat into the esophagus. During the procedure, a flexible, right-angle viewing endoscope is routed into an upper part of the small intestine, called the descending duodenum, to the sphincter of hepatopancreatic ampulla, at the entrance to the bile ducts. A guidewire and catheter are inserted through the working channel of the endoscope, through the sphincter, sometimes called the papilla or sphincter of Oddi, into the bile ducts so that radiopaque dye, generally comprising barium salts, can be injected therein to facilitate fluoroscopic and X-ray evaluation of the anatomy. ERCP is also used to route graspers into the bile and pancreatic ducts for the removal of calculi. It is also used for acquisition of biopsy samples and the placement of stents, both temporary and permanent.  
         [0007]     To perform a procedure in either the bile or pancreatic duct, an endoscope is placed into the duodenum through the esophagus, a body lumen, and the stomach, a body cavity. A guidewire, generally 0.018 to 0.038 inches in diameter but preferably 0.035 inches in diameter, is next routed, through the working channel of the endoscope and under direct visual guidance, deflected sideways, through the papilla, into the bile duct or pancreatic duct. Once guidewire control is established, a diagnostic catheter is advanced over the guidewire with the deflecting endoscope, generally a right-angle viewing endoscope, left in place. Injection of radiopaque dye allows fluoroscopic visualization of the ducts. Areas of stones or calculi show up as regions not penetrated by the dye. Calculi, largely consisting of cholesterol or, more rarely, based on calcium, are not readily visible under fluoroscopy, X-ray or computer-aided tomography (CT) so only the absence of dye can be used to see their presence using these detection systems. The calculi may be visible, however, using ultrasound or magnetic resonance imaging (MRI).  
         [0008]     Current therapeutic techniques may involve advancing a steerable, flexible, right-angle viewing, endoscope, generally as large as or larger than 15 French, to the external aspect of the papilla. Prior to performing therapeutic procedures such as stone removal, a sphincterotomy may be performed, through the endoscope, to cut the sphincter of hepatopancreatic ampulla, to gain access to the duct so that stones can be removed therethrough. Provision is generally required to deflect instrumentation through large angles coming out of the endoscope because the common bile duct and the pancreatic duct approach the duodenum at an angle between 90 degrees and 180 degrees from the direction of catheterization. The actual entrance to the common bile duct, from which the pancreatic duct is generally, but not always, a side branch, is at approximately a 90-degree to 120-degree angle to the axis of the duodenum. Once inside the common bile duct, the duct turns again through a significant angle so that it runs nearly parallel to the long axis of the duodenum. The therapeutic devices or procedures generally involve using graspers or baskets to remove stones, or catheters to deploy stents for relief of stenosis caused by tumors, for example.  
         [0009]     One of the issues that could arise during ERCP is the need to remove and replace instruments without causing undue patient discomfort or tissue damage, which could have long or short-term after effects. Some sort of external protective sheath or cannula would be useful in this capacity. Another potentially bothersome complication of the procedure is reflux (retrograde migration) of intestinal contents or material into the pancreas causing inflammation, known as pancreatitis, which can be quite severe. Such conditions are currently accepted by physicians but patient outcomes would be improved if a sphincterotomy were not required and if catheter or endoscope replacement could be more easily and gently accomplished with less tissue trauma. Gastroenterologists may be required to use sheaths or catheters with suboptimal central lumen size because they are the largest catheters that can be advanced to the distal end of the endoscope&#39;s generally 6 to 8-French working channel. Furthermore, stent placement would be facilitated if a larger working channel could be made available than the one found on most endoscopes used for this purpose. Both temporary plastic stents and permanent metallic stents may be delivered for this purpose. The stents may be either self-expanding, balloon expandable, or non-expandable, such as the case with ureteral stents.  
         [0010]     Further reading related to ERCP includes Alhalel, R, and Haber, GB, Endoscopic Therapy of Pancreatic Stones, Gastrointestinal Endoscopy Clinics of North America, Vol. 5, No. 1, 1995, pp 195-215. Data regarding complications of the procedure may be found in Christensen, M, Matzen, P, Schulze, S, and Rosenberg, J, Complications of ERCP: a Prospective Study, Gastrointestinal Endoscopy, Vol. 60, No. 5, 2004, pp 721-731. Additional information regarding ERCP can be found in-patient brochures on the subject published by the American Gastroenterological Association and is available online.  
       SUMMARY OF THE INVENTION  
       [0011]     Accordingly, one embodiment of the present invention comprises an expandable transluminal access sheath for providing minimally invasive access to a gastrointestinal tract. The sheath includes an axially elongate sheath tube comprising a proximal end, a distal end, and a through lumen extending therethrough. The sheath tube further comprises a distal region that is expandable from a collapsed configuration to an expanded configuration in response to outward pressure applied therein. A hub is coupled to the proximal end of the sheath tube. An obturator extends through the hub and sheath tube. The obturator is configured to occlude the central lumen of the sheath tube during insertion of the sheath tube into the gastrointestinal tract. The obturator comprises an obturator hub that is releasably coupled to the hub of the sheath and a guidewire lumen that extends through the obturator. The obturator further comprises a balloon dilator capable of expanding the distal region of the sheath from the collapsed configuration to the expanded configuration.  
         [0012]     Another embodiment of the present invention comprises a method of instrumenting a body lumen. In the method, an endoscope with a working channel is inserted into a patient. An exit point of the working channel is positioned beside an entrance to a branch of the body lumen. A guidewire is routed down the working channel of the endoscope and into the branch of the body. An end of the guidewire is positioned at a target location within the body lumen. The endoscope is removed from the patient leaving the guidewire in place. A sheath is inserted with a collapsed distal region and a pre-inserted dilator into the patient over the guidewire. The sheath is advanced to a treatment site within the side branch of the body lumen. The distal region of the sheath is dilated so that the distal region of the sheath is expanded. The dilator is collapsed. The dilator is removed from the sheath. The instrumentation is Inserted through the lumen of the sheath. Therapy or diagnosis is performed with the instrumentation. The sheath is removed from the patient.  
         [0013]     Another embodiment of the invention comprises an access device for insertion into a gastrointestinal tract. The device includes means for tracking over a guidewire to a target treatment site, means for diametrically collapsing at least a distal end of the sheath, means for dilating at least a portion of the distal end of the sheath, from the proximal end of the sheath, and means for removal of the sheath from the patient body lumen or cavity.  
         [0014]     Another embodiment of the invention comprises an expandable transluminal access sheath adapted for providing minimally invasive access to the gastrointestinal tract through a working channel of an endoscope. An axially elongate sheath tube is provided with a proximal end, a distal end, and a central through lumen. A distal region of the sheath is expandable, in response to outward pressure applied therein, to a diameter which is larger than that of a proximal region of the sheath. A hub is affixed to the proximal end of the sheath tube. The hub is adapted to facilitate the passage of instrumentation.  
         [0015]     A need therefore remains for improved access technology, which allows a device to be transesophageally, passed through the esophagus and stomach into the small intestine with a small introduction diameter, while accommodating the introduction of relatively large diameter instruments. It would be beneficial if a gastroenterologist did not need to inventory and use a range of catheter diameters. It would be far more useful if one catheter diameter could fit the majority of patients. Ideally, the catheter would be able to enter a vessel or body lumen with a diameter of 3 to 12 French or smaller, and be able to pass instruments through a central lumen that is 14 to 20 French. The sheath would be capable of gently dilating the papilla sphincter and of permitting the exchange of instrumentation therethrough without being removed from the body. The sheath would also be maximally visible under fluoroscopy and would be relatively inexpensive to manufacture. The sheath or catheter would be kink resistant and minimize abrasion and damage to instrumentation being passed therethrough. The sheath or catheter would further minimize the potential for injury to body lumen or cavity walls or surrounding structures.  
         [0016]     One embodiment of the present invention comprises a transluminal radially expanding access sheath. The radially expanding access sheath is used to provide selective access to the common bile duct or the pancreatic duct. In an embodiment, the sheath would have an introduction outside diameter that ranged from 3 to 12 French with a preferred range of 5 to 10 French. The diameter of the sheath would be expandable to permit instruments ranging up to 30 French to pass therethrough, with a preferred range of between 3 and 20 French. The sheath can have a working length ranging between 150-cm and 300-cm with a preferred length of 175-cm to 225-cm. The ability to pass the large traditional instruments and smaller more innovative instruments through a catheter introduced with a small outside diameter is derived from the ability to expand the distal end of the catheter to create a larger through lumen. The expandable distal end of the catheter can comprise 75% or more of the overall working length of the catheter. The proximal end of the catheter is generally larger than the distal end to provide for pushability, control, and the ability to pass large diameter instruments therethrough. In an embodiment, the sheath can be routed to its destination over or alongside one or more already placed guidewires with a diameter ranging up to 0.040 inches.  
         [0017]     Another embodiment of the invention comprises a transluminal access system for providing minimally invasive access to gastroenterological structures. The system includes an access sheath comprising an axially elongate tubular body that defines a lumen extending from the proximal end to the distal end of the sheath. At least a portion of the distal end of the elongate tubular body is expandable from a first, smaller cross-sectional profile to a second, greater cross-sectional profile. In an embodiment, the first, smaller cross-sectional profile is created by making axially oriented folds in the sheath material. These folds may be located in only one circumferential position on the sheath, or there may be a plurality of such folds or longitudinally oriented crimps in the sheath. The folds or crimps may be made permanent or semi-permanent by heat-setting the structure, once folded. In an embodiment, a releasable jacket is carried by the access sheath to restrain at least a portion of the elongate tubular structure in the first, smaller cross-sectional profile. In another embodiment, the jacket is removed prior to inserting the sheath into the patient. In an embodiment, the elongate tubular body is sufficiently pliable to allow the passage of objects having a maximum cross-sectional size larger than an inner diameter of the elongate tubular body in the second, greater cross-sectional profile. The adaptability to objects of larger dimension is accomplished by pliability or re-shaping of the cross-section to the larger dimension in one direction accompanied by a reduction in dimension in a lateral direction. The adaptability may also be generated through the use of malleable or elastomerically deformable sheath material.  
         [0018]     In another embodiment of the invention, a transluminal access sheath assembly for providing minimally invasive access comprises an elongate tubular member having a proximal end and a distal end and defining a working inner lumen. In this embodiment, the tubular member comprises a folded or creased sheath that can be expanded by a dilatation balloon. The dilatation balloon, if filled with fluids, preferably liquids and further preferably radiopaque liquids,. at appropriate pressure, can generate the force to expand the sheath. The dilatation balloon is removable to permit subsequent instrument.passage through the sheath. Longitudinal runners may be disposed within the sheath to serve as tracks for instrumentation, which further minimize friction while minimizing the risk of catching the instrument on the expandable plastic tubular member. Such longitudinal runners are preferably circumferentially affixed within the sheath so as not to shift out of alignment. In yet another embodiment, the longitudinal runners may be replaced by longitudinally oriented ridges and valleys, termed flutes. The flutes, or runners, can be oriented along the longitudinal axis of the sheath, or they can be oriented in a spiral, or rifled, fashion.  
         [0019]     In the embodiments describe above, the proximal end of the access assembly, apparatus, or device is preferably fabricated as a structure that is flexible, resistant to kinking, and further retains both column strength and torqueability. Such structures include tubes fabricated with coils or braided reinforcements and preferably comprise inner walls that prevent the reinforcing structures from protruding, poking through, or becoming exposed to the inner lumen of the access apparatus. Such proximal end configurations may be single lumen, or multi-lumen designs, with a main lumen suitable for instrument, guidewire, endoscope, or obturator passage and additional lumens being suitable for control and operational functions such as balloon inflation. Such proximal tube assemblies can be affixed to the proximal end of the distal expandable segments described heretofore. In an embodiment, the proximal end of the catheter includes an inner layer of thin polymeric material, an outer layer of polymeric material, and a central region comprising a coil, braid, stent, plurality of hoops, or other reinforcement. It is beneficial to create a bond between the outer and inner layers at a plurality of points, most preferably at the interstices or perforations in the reinforcement structure, which is generally fenestrated. Such bonding between the inner and outer layers causes a braided structure to lock in place. In another embodiment, the inner and outer layers are not fused or bonded together in at least some, or all, places. When similar materials are used for the inner and outer layers, the sheath structure can advantageously be fabricated by fusing of the inner and outer layer to create a uniform, non-layered structure surrounding the reinforcement. The polymeric materials used for the outer wall of the jacket are preferably elastomeric to maximize flexibility of the catheter. The polymeric materials used in the composite catheter inner wall may be the same materials as those used for the outer wall, or they may be different. In another embodiment, a composite tubular structure can be co-extruded by extruding a polymeric compound with a stent, braid, or coil structure embedded therein. The reinforcing structure is preferably fabricated from annealed metals, such as fully annealed stainless steel, titanium, or the like. In this embodiment, once expanded, the folds or crimps can be held open by the reinforcement structure embedded within the sheath, wherein the reinforcement structure is malleable but retains sufficient force to overcome any forces imparted by the sheath tubing.  
         [0020]     In another embodiment of the invention, it is advantageous that the sheath comprise a radiopaque marker or markers. The radiopaque markers may be affixed to the non-expandable portion or they may be affixed to the expandable portion. Markers affixed to the radially expandable portion preferably do not restrain the sheath or catheter from radial expansion or collapse. Markers affixed to the non-expandable portion, such as the catheter shaft of a balloon dilator may be simple rings that are not radially expandable. Radiopaque markers include shapes fabricated from malleable material such as gold, platinum, tantalum, platinum iridium, and the like. Radiopacity can also be increased by vapor deposition coating or plating metal parts of the catheter with metals or alloys of gold, platinum, tantalum, platinum-iridium, and the like. Expandable markers may be fabricated as undulated or wavy rings, bendable wire wound circumferentially around the sheath, or other structures such as are found commonly on stents, grafts or catheters used for endovascular access in the body. Expandable radiopaque structures may also include disconnected or incomplete surround shapes affixed to the surface of a sleeve or other expandable shape. Non-expandable structures include circular rings or other structures that completely surround the catheter circumferentially and are strong enough to resist expansion. In another embodiment, the polymeric materials of the catheter or sheath may be loaded with radiopaque filler materials such as, but not limited to, bismuth salts, or barium salts, or the like, at percentages ranging from 1% to 50% by weight in order to increase radiopacity. The radiopaque markers allow the sheath to be guided and monitored using fluoroscopy.  
         [0021]     In another embodiment of the invention, in order to enable radial or circumferential expansive translation of the reinforcement, it may be beneficial not to completely bond the inner and outer layers together, thus allowing for some motion of the reinforcement in translation as well as the normal circumferential expansion. Regions of non-bonding may be created by selective bonding between the two layers or by creating non-bonding regions using a slip layer fabricated from polymers, ceramics or metals. Radial expansion capabilities are important because the proximal end needs to transition to the distal expansive end and, to minimize manufacturing costs, the same catheter may be employed at both the proximal and distal end, with the expansive distal end undergoing secondary operations to permit radial or diametric expansion.  
         [0022]     In another embodiment, the distal end of a catheter is fabricated using an inner tubular layer, which is thin and lubricious. This inner layer is fabricated from materials such as, but not limited to, FEP, PTFE, polyamide, polyethylene, polypropylene, Pebax, Hytrel, and the like. The reinforcement layer comprises a coil, braid, stent, or plurality of expandable, foldable, or collapsible rings, which are generally malleable and maintain their shape once deformed. Preferred materials for fabricating the reinforcement layer include but are not limited to, stainless steel, tantalum, gold, platinum, platinum-iridium, titanium, nitinol, and the like. The materials are preferably fully annealed or, in the case of nitinol, fully martensitic. The outer layer is fabricated from materials such as, but not limited to, FEP, PTFE, polyamide, polyethylene, polypropylene, polyurethane, Pebax, Hytrel, and the like. The inner layer is fused or bonded to the outer layer through holes in the reinforcement layer to create a composite unitary structure. The structure is crimped radially inward to a reduced cross-sectional area. A balloon dilator is inserted into the structure before crimping or after an initial crimping and before a final sheath crimping. The balloon dilator is capable of forced expansion of the reinforcement layer, which provides sufficient strength necessary to overcome any forces imparted by the polymeric tubing.  
         [0023]     Another embodiment of the invention comprises a method of providing transluminal access. The method comprises inserting an endoscope into a patient, trans-esophageally, into the duodenum. Under direct optical visualization, fluoroscopy, MRI, or the like, a guidewire is passed through the instrument channel of the endoscope through the papilla sphincter and into the common bile duct or pancreatic duct. The guidewire is manipulated, under the visual control described above, into the bile duct or pancreatic duct through its exit into the duodenum. The guidewire is next advanced to the appropriate location within the bile duct or pancreatic duct. The eondoscope is next removed, leaving the guidewire in place. The transluminal access sheath is next advanced over the guidewire trans-esophageally so that its distal tip is now resident in the common bile duct or the pancreatic duct. The position of the guidewire is maintained carefully so that it does not come out of the ducts and fall into the duodenum. The removable dilator, which is removably affixed integrally inside the transluminal access sheath, comprises the guidewire lumen, and is used to guide, and maintain, placement of the access sheath into the urinary lumens.  
         [0024]     In another embodiment of the invention, the expandable access sheath is configured to bend, or flex, around sharp corners and be advanced into the bile duct or pancreatic duct. Provision can optionally be made to actively orient or steer the sheath through the appropriate angles. The expandable sheath also needs to be able to approach the duct from a variety of positions. Expansion of the distal end of the access sheath from a first smaller diameter cross-section to a second larger diameter cross-section is next performed, using the balloon dilator. The balloon dilator is subsequently removed from the sheath to permit passage of instruments that would not normally have been able to be inserted into the bile or pancreatic duct due to the presence of strictures, stones, or other stenoses of carcinogenic or benign origin. The method further optionally involves releasing the elongate tubular body from a constraining tubular jacket, removing the expandable member from the elongate tubular body; inserting appropriate instrumentation, and performing the therapeutic or diagnostic procedure. Once the sheath is in place, the guidewire may be removed or, preferably, it may be left in place. The sphincter of hepatopancreatic ampulla is gently dilated with radial force, preferably to a diameter of 10 mm or less, rather than being cut open by a sphincterotomy procedure or translationally dilated by a tapered dilator or obturator. In one embodiment, the use of the expandable GI sheath eliminates the need for a large diameter right-angle endoscope in the main gastrointestinal tract with resultant benefits in reduced patient discomfort.  
         [0025]     In another embodiment of the invention, further endoscopy and stone extraction may be performed with a forward-looking endoscope placed through the working channel of the expanded transluminal sheath. Endoscopes used in this embodiment can be much smaller (1 to 4 mm diameter) than standard endoscopes (generally 5 mm diameter or larger) since they do not require a working channel as that is contained within the sheath. Removed calculi or stones are fully withdrawn through the conduit of the sheath by graspers, a basket, a suction device, or the like. The stones can first be broken into smaller pieces using lasers, acoustic energy, or the like so that the pieces can be withdrawn into the sheath. The graspers may comprise jaws, basket traps, or the like. The sheath may optionally comprise a window or port in the region outside the sphincter, so that calculi, fluid, bile, irrigant, and debris can be discarded into the small intestine without the need to fully withdraw the graspers, basket, or suction device all the way out the proximal end of the sheath. The window or port can also comprise a closure that can be selectively operated to seal off the port when not in use or open the port when it is needed. The port or window can advantageously be denoted or surrounded by a radiopaque structure or marker to facilitate fluoroscopic monitoring. An advantage of the sheath of this configuration is its ability to provide a path for fluid, bile debris, blood, or other materials to be evacuated from the body lumen being accessed, whereas current systems may not offer such drainage channels. The sheath, dilator, or both can comprise multiple channels or lumens for these purposes. The sheath, in this and other embodiments, can be configured to maximize softness and resilience, especially in the area that traverses the thoracic region, since a stiff, non-resilient device may impinge, or generate pressure, on thoracic structures causing cardiopulmonary complications in the patient. The soft, compliant, resilient sheath is configured to comprise elements that provide for column strength and torqueability. In yet another embodiment, an inflatable balloon can be used to assist with tamponade or to slow or stop blood loss following therapy while coagulation occurs. In this embodiment, the balloon is affixed to the exterior of the sheath. The balloon is selectively located along the outside of the length of the sheath and can be optimally inflated to provide stability during the procedure. The balloon can also be affixed to a separate catheter slidably inserted through the sheath. Balloon inflation lumens are provided either in the catheter or as an annulus or lumen in the sheath. In another embodiment, the method comprises removal of the; sheath from the common bile duct or pancreatic duct at the end of the procedure. Finally, the procedure involves removing the elongate tubular body from the patient.  
         [0026]     In another embodiment, the side-looking endoscope is advanced to the duodenum. The expandable transluminal access sheath is advanced through the working channel of the endoscope with its dilator in place. A guidewire, preferably an atraumatic guidewire, is advanced through the working channel of the endoscope into the common bile duct. The sheath is advanced into the common bile duct or pancreatic duct, over a guidewire, while the endoscope remains in the duodenum. The sheath is next expanded by action of the dilator. The expanded region of the sheath may now be larger than that part that is resident within the working channel of the endoscope and in the embodiment where expansion is not reversible, the expanded region of the sheath cannot be retracted within the working channel. The Sphincter of hepatopancreatic ampulla is dilated, preferably in a gentle fashion and over a period of time, with or without the need for a sphincterotomy. The guidewire may or may not be removed from the sheath and instrumentation inserted therethrough to a target site. Rapid exchange guidewire apparatus, and methodology to use the apparatus, are beneficially provided in conjunction with the sheath, its dilator, or both for this and all other embodiments. The rapid exchange guidewire exchange apparatus, including guidewire access ports within 12 inches of the distal or proximal end of the sheath, are capable of handling multiple guidewires and multiple catheters being placed over said guidewires. Manipulation of each of the guidewires separately is preferably permitted by the sheath configuration. Following any therapeutic or diagnostic procedures, the sheath and side-viewing endoscope are removed from the patient, separately, or as a unit.  
         [0027]     In another embodiment, the expandable transluminal access sheath is inserted through a side-looking endoscope and advanced over a guidewire into the common bile duct or the pancreatic duct. The sheath is next dilated radially by means of an internal dilator, preferably a balloon dilator. A portion of the distal section of the sheath is then detached from its more proximal region. The balloon dilator is removed from the sheath by withdrawing proximally. In one embodiment, expansion of the dilator can be used as the mechanism to generate the detachment force on the distal end of the sheath. The endoscope, proximal sheath section, and guidewire are removed from the patient leaving the expanded sheath within the bile duct or pancreatic duct to serve as a stent. The portion of the sheath remaining within the patient following separation may project through the sphincter of hepatopancreatic ampulla or it may reside inside thus retaining sphincteric function, depending on the pathology (or lack of pathology).  
         [0028]     In one embodiment, where the transluminal access sheath is used to provide access to the biliary or pancreatic ducts, the access sheath may be used to provide access by tools adapted to perform biopsy, stone extraction, stent placement, or resection of transitional cell carcinoma and other diagnostic or therapeutic procedures. Other applications of the transluminal access sheath include a variety of diagnostic or therapeutic clinical situations, which require access to the inside of the body, through either an artificially created, percutaneous access, or through another natural body lumen.  
         [0029]     For purposes of summarizing the invention, certain aspects, advantages and novel features of the invention are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. These and other objects and advantages of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]     A general architecture that implements the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements.  
         [0031]      FIG. 1  is a front view schematic representation of the human digestive tract including the esophagus, the stomach, the duodenum, the liver, and the pancreas;  
         [0032]      FIG. 2  is a schematic cross-sectional representation of the duodenum, the common bile duct and the pancreatic duct;  
         [0033]      FIG. 3  is a schematic cross-sectional representation of the duodenum, the pancreatic duct, and the common bile duct shown with a cutaway of the wall, further with stones in the common bile duct;  
         [0034]      FIG. 4  is a cross-sectional illustration of the duodenum, the common bile duct, and the pancreatic duct with stones in the common bile duct with a side-viewing endoscope placed within the duodenum and a guidewire advanced into the common bile duct, according to an embodiment of the invention;  
         [0035]      FIG. 5  illustrates a side view of a gastric, radially expandable, collapsed, transluminal sheath, inserted into the common bile duct over the guidewire following removal of the endoscope, according to an embodiment of the invention;  
         [0036]      FIG. 6  illustrates a side view of the gastric, radially expandable transluminal sheath following expansion of its distal portion by an internal dilator, according to an embodiment of the invention;  
         [0037]      FIG. 7  is an illustration of the gastric, radially expandable transluminal sheath with the dilator having been removed, according to an embodiment of the invention;  
         [0038]      FIG. 8  illustrates a side view of the gastric, radially expandable sheath wherein and endoscope with graspers is advanced through the sheath and is removing a stone, following fragmentation, according to an embodiment of the invention;  
         [0039]      FIG. 9  illustrates a side view of a collapsed, radially expandable sheath having been inserted through the working channel of an endoscope into the common bile duct, according to an embodiment of the invention;  
         [0040]      FIG. 10  illustrates a side view of a radially expandable sheath having been inserted through the working channel of an endoscope into the common bile duct and expanded with graspers extended therethrough, according to an embodiment of the invention;  
         [0041]      FIG. 11  illustrates a side view of a radially expandable sheath having been inserted through the working channel of an endoscope into the common bile duct with the entire assembly being withdrawn into the descending duodenum to remove a stone, according to an embodiment of the invention;  
         [0042]      FIG. 12  illustrates a side view of a collapsed, radially expandable, detachable sheath having been inserted through the working channel of an endoscope into the common bile duct, according to an embodiment of the invention;  
         [0043]      FIG. 13  illustrates a side view of a radially expandable, detachable sheath having been inserted through the working channel of an endoscope into the common bile duct and then expanded by its internal dilator, according to an embodiment of the invention;  
         [0044]      FIG. 14  illustrates a side view of an expanded radially expandable, detachable sheath following removal of the deflated balloon dilator and detachment from the proximal portion of the sheath, according to an embodiment of the invention;  
         [0045]      FIG. 15  illustrates a side view of an expanded radially expandable, detachable sheath having been inserted into the common bile duct, and detached from its proximal portion, which has been removed from the patient, leaving the stent fully within the common bile duct and not projecting through the sphincter, according to an embodiment of the invention;  
         [0046]      FIG. 16  illustrates a radially expandable sheath having been inserted into the common bile duct, said sheath further comprising a window or port for disposal of debris, according to an embodiment of the invention;  
         [0047]      FIG. 17  illustrates a radially expandable sheath, wherein the sheath has an opening on one side to accommodate flow from the pancreatic duct, according to an embodiment of the invention;  
         [0048]      FIG. 18A  illustrates a side view of a collapsed, non-expanded sheath, according to an embodiment of the invention;  
         [0049]      FIG. 18B  illustrates a side view of an expanded sheath, according to an embodiment of the invention, and  
         [0050]      FIG. 18C  illustrates a side view of an expanded sheath with the dilator removed, according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0051]     The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.  
         [0052]     The disclosed embodiments, which are generally termed a catheter or a sheath, can be described as being an axially elongate hollow tubular structure having a proximal end and a distal end. Such tubular structures are generally shown as having a round or circular cross-section . However, it should be appreciated that the cross-section can have other shapes. The axially elongate structure further has a longitudinal axis and has an internal through lumen that preferably extends from the proximal end to the distal end for the passage of instruments, fluids, tissue, or other materials. The axially elongate hollow tubular structure is generally flexible and capable of bending, to a greater or lesser degree, through one or more arcs in one or more directions perpendicular to the main longitudinal axis. As is commonly used in the art of medical devices, the proximal end of the device is that end that is closest to the user, typically a gastroenterologist, surgeon, or interventionalist. The distal end of the device is that end closest to the patient or that is first inserted into the patient. A direction being described as being proximal to a certain landmark will be closer to the surgeon, along the longitudinal axis, and further from the patient than the specified landmark. The diameter of a catheter is often measured in “French Size” which can be defined as 3 times the diameter in millimeters (mm). For example, a 15 French catheter is 5 mm in diameter. The French size is designed to approximate the circumference of the catheter in mm and is often useful for catheters that have non-circular cross-sectional configurations. While the original measurement of “French” used pi (3.1415 . . . ) as the conversion factor between diameters in mm and French, the system has degraded today to where the conversion factor is exactly 3.0.  
         [0053]      FIG. 1  is a schematic frontal illustration (anterior view) of a human patient  100  comprising a pharynx  102 , a esophagus  104 , a stomach  106 , a liver  108 , a superior duodenum  110 , a descending duodenum  112 , and a pancreas  114 . In this illustration, the left anatomical side of the body of the patient  100  is toward the right of the illustration.  
         [0054]     Referring to  FIG. 1 , the pharynx  102  is a chamber in the throat of the patient  100  that is operably connected to the mouth (not shown) and nose (not shown) with further access to the trachea (not shown) and the esophagus  104 . Generally, the internal surfaces of the esophagus  104 , the stomach  106 , and the duodenum  110  and  112  comprise smooth muscle that exhibits a peristaltic motion to move food through the system.  
         [0055]      FIG. 2  is a schematic frontal illustration, looking posteriorly from the anterior side, of the descending duodenum  112 . The walls of the duodenum  112  comprise an outer longitudinal layer and an inner circular layer of smooth muscle  210  and are internally lined with submucosa  202  further comprising duodenal, or Brunner&#39;s, glands. Branching from the descending duodenum  112 , at the major duodenal papilla, also known as the ampulla of Vater,  200 , is the common bile duct  204 , and the side-branching pancreatic duct  208 . The muscular valving structure surrounding the major duodenal papilla  200  is the sphincter of hepatopancreatic ampulla, also known as the sphincter of Oddi,  206 . In this illustration, the left anatomical side of the body is toward the right of the illustration.  
         [0056]     Referring to  FIG. 2 , the sphincter of hepatopancreatic ampulla  206  permits material to exit the common bile duct  204  into the lumen of the descending duodenum  112  when digesting food is present, but prevents migration of fecal or gastric material retrograde into the common bile duct  204  or the pancreatic duct  208 . Referring to  FIGS. 1 and 2 , the common bile duct  204  serves as the main drainage channel for the gall bladder (not shown), the liver  108 , and the pancreas  114 . Any damage to the sphincter of hepatopancreatic ampulla  206  could result in infection of the aforementioned drainage source organs. The angle of the common bile duct  204  relative to the lumen of the descending duodenum  112  is shown as being approximately 120 degrees but the angle could vary between approximately 90 to 180 degrees. Furthermore, anatomical variants on the structure include circumstances where the pancreatic duct  208  and the common bile duct  204  enter the descending duodenum  112  through separate orifices in the major duodenal papilla  200 . Other configurations include those where they come together or branch just at the entrance to the major duodenal papilla  200  or where they branch a measurable distance upstream of the papilla  200 , the lafter anatomy being the one illustrated in  FIG. 2 .  
         [0057]      FIG. 3  is a frontal illustration, looking posteriorly from the anterior side, of the descending duodenum  112 . Branching from the descending duodenum  112 , at the major duodenal papilla  200 , is the common bile duct  204 , and the side-branching pancreatic duct  208 . The sphincter of hepatopancreatic ampulla  206  is also shown. Further illustrated is a cutaway view of the common bile duct  204  showing the internal lumen  300 , the wall  302 , and a stone  304  lodged therein.  
         [0058]     Referring to  FIG. 3 , the stone  304  is generally composed of cholesterol, calcium salts, or similar materials. The stone  304  forms in the common bile duct  204 , the pancreatic duct  208  or one of the other branch ducts of the common bile duct  204 . The stone  304  can migrate or lodge in the duct causing blockage, pain, infection, and the like. Such stones  304  may range in size up to 10-cm or larger and removal is often necessary. Removal of large stones through the common bile duct  204  may require dilation of the duct, dilation or surgical incision of the sphincter of hepatopancreatic ampulla  206 , or both. Removal of large stones may also entail breaking up such stones  304  using methods such as, but not limited to, high-frequency focused ultrasound, acoustic waves, radio-frequency energy, mechanical energy, light energy such as that derived from lasers, and the like.  
         [0059]      FIG. 4  is a cross-sectional illustration of the descending duodenum  112 , the sphincter of hepatopancreatic ampulla  206 , and the common bile duct  204 . A side-viewing endoscope  400  is placed within the duodenum  112  and a guidewire  402  advanced into the common bile duct  204  through the sphincter  206 . The endoscope  400  further comprises a side viewing lens  406  and a tool deflecting mechanism  408 . The endoscope  400  may further comprise internal scope deflection mechanisms to facilitate navigation of tortuous anatomy.  
         [0060]     Referring to  FIG. 4 , the endoscope  400  has on outside diameter of approximately 15 French of 5 millimeters. The endoscope  400  may further comprise a working channel (not shown), an optical telescope element (not shown), a light source channel (not shown), and an internal optional deflection mechanism (not shown). The side-viewing lens  406  is located at the distal end of the optical telescope element and may also comprise the distal end of the light source channel. The deflecting mechanism  408  may be stationary, such as an angled or curved surface, or it may be actuable from the proximal end of the end oscope  400  by way of a control rod or wire and a lever, the latter being affixed at or near the proximal end of the endoscope  400 . The deflecting mechanism  408  is located at the distal end of the working channel, which currently holds the guidewire  402  and which may ultimately also carry a catheter for therapy or diagnosis. The guidewire  402  has been advanced and turned sidewise by the deflecting mechanism  408 . Referring to  FIGS. 2 and 4 , the guidewire  402  has been inserted through the papilla  200  and into the common bile duct  204 .  
         [0061]      FIG. 5  is a cross-sectional illustration of the descending duodenum  112 , the sphincter of hepatopancreatic ampulla  206 , and the common bile duct  204 . An expandable access sheath  500  is placed over the guidewire  402 , following removal of the endoscope  400  (refer to  FIG. 4 ) and advanced into the common bile duct  204  through the sphincter of hepatopancreatic ampulla  206 . The sheath  500  further comprises a proximal non-expandable region  502 , a transition zone  512 , a distal expandable region  504 , an expansion fold  506 , a dilatation balloon  508 , a dilator shaft  510 , a sheath hub (not shown) and a dilator hub (not shown).  
         [0062]     Referring to  FIG. 5 , an expandable access sheath  500  having certain features and advantages is shown is pre-assembled with its internal dilator. An embodiment of the sheath will be described in more detail with reference to FIGS.  18 A-C The internal dilator comprises the dilatation balloon  508 , the dilator shaft  510 , and the dilator hub. The internal dilator uses multi-lumen tubing, coaxial multiple tubes, or the like to allow for guidewire  402  passage through a guidewire lumen (not shown) and for the inflation and deflation of the balloon  508 , which is located near the distal end of the dilator. The balloon  508  inflation is accomplished through a port in the dilator hub (not shown) located at the proximal end of the dilator. An inflation device such as those commercially available in the medical device business and comprising a syringe, a mechanical advantage driver, and an optional pressure gauge, is affixed to the dilator hub by way of a pressure line with a luer, or other, fitting. The deflated balloon  508  is folded to form wings and inserted inside the distal sheath expandable region  504 . The deflated balloon  508  traverses the longitudinal extents of the expandable region  504  and its position is determined by the relationship, preferably locking, between the dilator hub and the sheath hub. The expandable region  504  is folded down over the deflated balloon  508  in such a way that one or more longitudinally oriented folds  506  are created on the expandable region  504 . The expandable region  504  is now diametrically compressed. and is substantially smaller than the proximal non-expandable region  502  of the sheath  500 . The expandable region  504 , mounted over the dilator, which is slidably disposed over the guidewire  402 , can be advanced through small orifices such as the sphincter of hepatopancreatic ampulla  206 . This sheath-dilator structure  500  is very flexible and can turn sharp corners. The expandable region  504  is constructed as a composite structure with a malleable reinforcement embedded within a flexible, thin-wall polymer tube. The thin-wall polymer tube exerts insubstantial force relative to the malleable reinforcement so the configuration of the malleable reinforcement controls the configuration of the surrounding polymer. Thus, in this embodiment, the folded expandable region  504  stays folded, without the need for an outer compression jacket, until such time as the structure is expanded.  
         [0063]      FIG. 6  illustrates a side view of the radially expandable transluminal sheath  500  following expansion of its distal portion  504  by its internal dilator. The non-expandable region  502  and the transition region  512  the sheath  500  are both resident in the descending duodenum  112 . The expandable region  506  has turned through an angle and the distal end of the sheath  500  with its internal dilator are both resident in the common bile duct  204 . The balloon  508  has been expanded under pressure from a liquid-filled external inflation device (not shown) operably connected to the inflation port (not shown) on the dilator hub (not shown) at the proximal end of the dilator tubing  510 . The expandable region  504  has expanded diametrically and has dilated the sphincter of hepatopancreatic ampulla  206 . The sphincter  206  is sealed by the sheath  500  so that no intestinal material can flow retrograde back into the common bile duct  204 . The longitudinal fold  506 , shown in  FIG. 5 , is no longer visible since the fold  506  has been dilated. The distal end of the expandable region  504  is resident in the common bile duct  204  just upstream of the bifurcation where the pancreatic duct  208  joins the common bile duct  204 .  
         [0064]      FIG. 7  is an illustration of the gastric, radially expandable transluminal sheath  500  with the guidewire  402 , and the dilator, further comprising the balloon  508  and the dilator tubing  510 , all shown on  FIG. 6 , having been removed leaving only the expandable region  504  in the common bile duct  204 . The expandable region  504  continues to seal the sphincter  206 . The stone  304  is now approachable from instrumentation inserted through the central lumen  514  of the sheath  500 . In another embodiment, the sheath  500  can comprise, on its outer surface, devices for the performance of a sphincterotomy of the sphincter of Oddi  206 . The sphincterotomy devices can include electrocautery instruments, sharp blades, wires, or the like. The blades can be actuated from the proximal end of the sheath  500  and made to open up to cut radially outward into the sphincter  206 . The blades can further be sheathed or covered, the sheathing selectively withdrawn to expose the blades to the tissue so that the sphincterotomy can be performed. The wires or electrocautery elements can be electrically charged by a power supply at the proximal end of the sheath  500 . By performing a sphincterotomy prior to, during, or just after the dilation, caused by sheath expansion, the maintenance of post-procedural sphincter function and the minimization of pancreatitis can be achieved. Dilatation of the sphincter of Oddi  206  with large diameter balloons has been suggested as the cause of increased risk of post-ERCP pancreatitis. The sheath  500  is configured so that it does not dilate the sphincter of Oddi  206  to a diameter greater than 10 mm and, preferably, not greater than 6 to 8 mm diameter. By minimizing the diameter of the dilation, the muscles actuating the sphincter of Oddi are preserved, the sphincter function is preserved following the ERCP, and reflux of contaminants into the pancreatic duct and ensuing pancreatitis are minimized. In order to remove large stones, which can be as large as 20 to 40 mm in their largest dimension, it is preferable to break these stones into smaller fragments through previously described lithotripsy methodology.  
         [0065]      FIG. 8  illustrates a side view of the gastric, radially expandable sheath  500  wherein an endoscope  802 , with graspers  804  inserted through the central lumen  514 , is advanced through the sheath and is removing a stone  304 , following fragmentation of the stone  304  into smaller pieces. The pieces of stone  304  reside in the common bile duct  204 , as does the distal expandable end  504  of the sheath  500 . Note that the graspers  804  can be larger than the endoscope  802  and its instrumentation channel because the entire assembly is now passed through and protected from damaging tissue by the sheath  500 . Such a configuration, which is advantageous in removing large stones  304 , cannot be used without sheath  500 . The endoscope  802  is preferably a forward viewing endoscope with associated fiber optic bundles and light channels for illumination of the field. The endoscope can further comprise an irrigation channel or it can irrigate through the instrumentation channel.  
         [0066]      FIG. 9  illustrates a side view of a collapsed, radially expandable sheath  900  having been inserted through the working channel  902  of an endoscope  400  into the common bile duct  204 . The endoscope  400  further comprises an instrument deflector  408  and a viewing lens  406 , along with a light channel  904 . The sheath  900  further comprises a distal region  916  comprising longitudinal folds or creases  904 , a dilator balloon  910 , and a dilator shaft  912 . The sheath  900  is routed into the common bile duct  204  over the guidewire  402 . The sheath  900  further projects through the sphincter of Oddi  206 , at the entrance to the common bile duct  204 . The sphincter  206  is only slightly dilated by the sheath  900 , at this point, since the sheath is still in its compressed configuration. A plurality of calculi  304  can reside within the common bile duct  204  and impede drainage therefrom.  
         [0067]      FIG. 10  illustrates a side view of the radially expandable sheath  900  having been inserted through the working channel of the endoscope  400  into the common bile duct  206  and the distal sheath region  916  has been diametrically expanded. Referring to  FIG. 9 , the dilator balloon  910  and the dilator shaft  912  have been withdrawn from the sheath  900 . The longitudinal fold  914  has been expanded and is no longer visible in  FIG. 10 . The proximal region  918  of the sheath  900  is non-expandable and continues to reside within the endoscope  400 . A pair of graspers  804  extends beyond the distal region  916  of the sheath  900 . At this point, the distal region  916  is too large in diameter to be withdrawn into the endoscope  400  but the graspers  804  can be fully withdrawn or inserted.  
         [0068]      FIG. 11  illustrates a side view of the radially expandable sheath  900  having been inserted through the working channel of the endoscope  400  into the common bile duct  204  with the entire assembly being withdrawn into the descending duodenum  112  to remove a stone  304 . The distal end of the expandable region  916  is shown in cutaway rendition revealing the graspers  804 . The non-expandable proximal region  918  emerges from the endoscope  400 . The entire endoscope  400  and sheath  900  is being withdrawn to remove the stone  304 .  
         [0069]      FIG. 12  illustrates a collapsed, radially expandable, detachable sheath  1200  having been inserted through the working channel of an endoscope  400  into the common bile duct  204 . The proximal non-expandable region  1204  is releasably affixed to the distal expandable region  1202  by the releasable coupler  1206 . The distal expandable region  1202  comprises one or more longitudinal folds or creases  1214 . The sheath  1200  is coaxially, and slidably, connected to the dilator balloon  910 , which is affixed and operably connected to the dilator shaft  912  so that the balloon  910  can be inflated through a lumen or annulus (not shown) extending from the proximal end of the dilator (not shown). The entire assembly is slidably engaged over, and tracks, the guidewire  402 . The releasable coupler  1206  can be operably connected to an actuator (not shown) at the proximal end of the sheath  1200 .  
         [0070]      FIG. 13  illustrates the radially expandable, detachable sheath  1200  having been inserted into the common bile duct  204  and then expanded by its internal dilation balloon  910 . The balloon  910  is affixed to the dilator shaft  912 , which further comprises a central lumen for tracking over the guidewire  402 . The sheath  1200  comprises the proximal non-expandable region  1204 , the distal expandable region  1202 , and the releasable coupler  1206 . The proximal portion  1204  of the sheath  1200  extends through the working channel of the endoscope  400 .  
         [0071]      FIG. 14  illustrates the radially expandable, detachable sheath  1200  following removal of the deflated dilator balloon  910  and dilator shaft  912  and detachment of the expandable region  1202  from the proximal portion  1204  of the sheath  1200 . The guidewire  402  remains in place in the common bile duct  204 . Detachment of the expandable region  1202  from the proximal portion  1204  occurs at the coupler  1206 . The coupler  1206  can be passive and release the expandable region  1202  when the balloon  910  is inflated, or in other embodiments, can be released by pull-wires, push-wires, or actuators powered by electrical, pneumatic, hydraulic, magnetic, light, heat, microwave, radio frequency, or other similar type of power. The coupler  1206  can use releasable latches  1208 , zippers, clips, undercuts, or other mechanical interference to create the reversible coupling. In this illustration, the proximal portion  1204  is being withdrawn back into the descending duodenum  112 . Once released from the proximal portion  1204 , the expandable, releasable, distal region  1202  can reside within the anatomy and serve the function of a stent, a sphincter dilator, a sheath to facilitate further instrumentation, or a combination of the aforementioned. The guidewire  402 , shown traversing the gap between the coupler  1206  and the expandable releasable distal region  1202  is removed at the appropriate time. Situations that may require such a device include those where a carcinoma has constricted the common bile duct or pancreatic duct and where long-term palliative relief of the obstruction is indicated without the trauma of a surgical intervention.  
         [0072]      FIG. 15  illustrates a radially expandable, detachable sheath distal section  1202  having been inserted into the common bile duct  204 , and detached from its proximal portion  1204  (Reference  FIG. 14 ). The proximal portion  1204  has been removed from the patient, along with the coupler  1206 , leaving the distal sheath section  1202  fully within the common bile duct  204  and not projecting through the sphincter  206 . The distal sheath section  1202  serves the same function as a biliary stent and, in this case, is relieving a stenosis caused by a tumor  1210 , which surrounds and constricts the common bile duct  204 .  
         [0073]      FIG. 16  illustrates a radially expandable sheath  1600  having been inserted into the common bile duct  204 , said sheath  1600  further comprising a window or port  1602  for disposal of debris, such as calculi  304 . The window is an opening that operably connects the inner lumen  1610  of the sheath  1600  to the environment outside the sheath  1600 . In an embodiment, the window  1602  opens into the descending duodenum  112  through the wall of the distal expandable sheath region  1606 . The proximal non-expandable region  1604  can be withdrawn into the endoscope  400  but the distal region  1606  is too large for such withdrawal. However, the lumen  1610  of the distal region  1606  is capable of holding the graspers  804  and calculi  304  of sufficiently small size. The window or opening  1602  preferably is as wide as the diameter of the sheath  1600  in the region where the window  1602  is placed. In this configuration, the sheath expandable region  1606  dilates and protects the sphincter  206  from damage and allows for instrument passage therethrough. The window or opening  1602  can comprise radiopaque markers  1608  to facilitate location and to denote the location and extents of the window  1602  during fluoroscopic monitoring.  
         [0074]      FIG. 17  illustrates a radially expandable sheath  1700 , wherein the sheath  1700  comprises an expandable, releasable distal region  1702 , a non-expandable proximal region  1704 , a releasable coupler  1706 , and a flow window  1710  to accommodate flow from the pancreatic duct  208 . The distal region  1702  is shown expanded, and it resides in the common bile duct  204 . The sheath  1700  is placed over a guidewire  402  and through the working channel of an endoscope  400 , which is located in the descending duodenum  112 . The sheath distal region  1702  extends through the sphincter of hepatopancreatic ampulla  206  and holds the sphincter open, in this embodiment. The distal region  1702  further comprises asymmetric radiopaque markers  1712  to provide rotational and longitudinal orientation information. The radiopaque markings  1712  are advantageously asymmetric and capable of providing rotational position information when their image or shadow is projected onto a two-dimensional plane. The radiopaque markings  1712  are fabricated from tantalum, platinum, iridium, gold, barium or bismuth salts, or the like. They can be triangular, for example, or they can be of other asymmetrical shape and further enhanced in their delineation of orientation by having multiple markers that change the projected pattern as a function of rotational orientation. The opening  1710 , in an embodiment, further comprises one or more radiopaque marker  1714  denoting the extents of the opening  1710  to allow for positioning under fluoroscopy, further aided by the asymmetric marker  1712 . The guidewire  402  is shown traversing the gap between the coupler  1706  and the expandable, releasable distal region  1702 .  
         [0075]     FIGS.  18 A-C illustrate in more detail an expandable access sheath according to one embodiment of the invention. Additional details and further embodiments can be found in U.S. patent application Ser. No. 11/199,566, filed Aug. 8, 2005, the entirety of which is hereby incorporated by reference herein.  FIG. 18A  illustrates a radially expandable sheath  1800 , wherein the sheath  1800  is in its collapsed, small diameter configuration. The sheath  1800  is configured for use in the gastrointestinal tract of the human or other animal. The proximal end of the sheath  1800  comprises the inner dilator shaft  1818 , the outer dilator shaft  1824 , and the dilator hub  1816 . The dilator hub  1816  is integrally molded with, welded to, or is bonded thereto, to the guidewire port  1832 . The dilator, or catheter, hub  1816  allows for gripping the dilator and it allows for expansion of the dilatation balloon  1820  by pressurizing an annulus between the inner dilator shaft  1818  and the outer dilator shaft  1824 , said annulus having openings into the interior of the balloon  1820 . The balloon  1820  is bonded, at its distal end, either adhesively or by fusion, using heat or ultrasonics, to the inner dilator shaft  1818 . The proximal end of the balloon  1820  is bonded or welded to the outer dilator shaft  1824 . In another embodiment, pressurization of the balloon  1820  can be accomplished by injecting fluid, under pressure, into a separate lumen in the inner or outer catheter shafts  1818  or  1824 , respectively, said lumen being operably connected to the interior of the balloon  1820  by openings or scythes in the dilator tubing. Such construction can be created by extruding a multi-lumen tube, rather than by nesting multiple concentric tubes. The distal end  1804  generally comprises the distal sheath tube  1822  which is folded into one or more creases  1828  running along the longitudinal axis and which permit the area so folded to be smaller in diameter than the sheath tube  1806 . The inner dilator shaft  1818  comprises a guidewire lumen  1834  that may be accessed from the proximal end of the dilator hub  1816  and passes completely through to the distal tip of the dilator shaft  1818 . The guidewire lumen  1834  is able to slidably receive guidewires up to and including 0.038-inch diameter devices. The distal sheath tube  1804 , in its collapsed configuration, can accept a removable shroud (not shown) that protects the distal sheath tube  1804  during shipping and handling and helps to maintain compression of the collapsed distal section  1804  prior to insertion in to the patient. The shroud is removed prior to inserting the sheath  1800  into a patient and will not pass over a guidewire without first removing the shroud to reveal the guidewire lumen  1834  on the dilator.  
         [0076]     The distal end  1804  further comprises the dilator shaft  1818  and the dilatation balloon  1820 . The dilator hub  1816  may removably lock onto the sheath hub  1808  to provide increased integrity to the system and maintain longitudinal relative position between the dilator shaft  1818  and the sheath tubing  1822  and  1806 . The dilator hub  1816  is releasably affixed to the sheath hub  1808  by a snap, latch, bayonet mount, thread mount, or other quick-connect arrangement. The dilator hub  1816  is mated to the sheath hub  1808  so that it is held radially along its entire circumference or at a minimum of three points constraining against lateral relative axial movement in both directions orthogonal to the long axis of the sheath  1800 . It is advantageous that the dilator hub  1816  be rotationally constrained within the sheath hub  1808  when they are mated so the operator cannot rotate the dilator hub and its attached balloon  1820  relative to the sheath hub  1808  and its attached distal sheath tube  1806 . The dilator hub  1816  can be constrained to the sheath hub  1808  by a key arrangement with slots or dimples (not shown) in one component and protrusions (not shown) in the other component that are slidably received in the axial direction. When the sheath hub  1808  and the dilator hub  1816  are axially pulled apart, the rotational constraint is thereby disengaged.  
         [0077]     The dilator shaft  1818  and the balloon  1820  are slidably received within the proximal sheath tube  1806 . The dilator shaft  1818  and balloon  1820  are slidably received within the distal sheath tube  1822  when the distal sheath tube  1822  is radially expanded but are frictionally locked within the distal sheath tube  1822  when the tube  1822  is radially collapsed. The outside diameter of the distal sheath tube  1822  ranges from 4 French to 16 French in the radially collapsed configuration with a preferred size range of 5 French to 10 French. The outside diameter is critical for introduction of the device. Once expanded, the distal sheath tube  1822  has an inside diameter ranging from 8 French to 20 French. The inside diameter is more critical than the outside diameter once the device has been expanded. The wall thickness of the sheath tubes  306  and  322  ranges from 0.002 to 0.030 inches with a preferred thickness range of 0.005 to 0.020 inches.  
         [0078]      FIG. 18B  illustrates a cross-sectional view of the sheath  1800  of  FIG. 18A  wherein the balloon  1820  has been inflated causing the sheath tube  1822  at the distal end  1804  to expand and unfold the longitudinal creases or folds  1828 . The distal sheath tube  1822  has the properties of being able to bend or yield, especially at crease lines, and maintain its configuration once the forces causing the bending or yielding are removed. The proximal sheath tube  1806  is affixed to the sheath hub  1808  by insert molding, bonding with adhesives, welding, or the like. The balloon  1820  has been inflated by pressurizing the annulus between the inner tubing  1818  and the outer tubing  1824  by application of an inflation device at the inflation port  1830  which is integral to, bonded to, or welded to the catheter hub  1816 . The pressurization annulus is operably connect to the balloon  1820  at the distal end of the outer tubing  1824 . Exemplary materials for use in fabrication of the distal sheath tube  1822  include, but are not limited to, polytetrafluoroethylene (PTFE), fluorinated ethylene polymer (FEP), polyethylene, polypropylene, polyethylene terephthalate (PET), and the like. A wall thickness of 0.008 to 0.012 inches is generally suitable for a device with a 16 French OD while a wall thickness of 0.019 inches is appropriate for a device in the range of 36 French OD. The resulting through lumen of the sheath  1800  is generally constant in French size going from the proximal end  1802  to the distal end  1804 . The balloon  1820  is fabricated by techniques such as stretch blow molding from materials such as polyester, polyamide, irradiated polyethylene, and the like. In other embodiments, the inner lumen of the sheath  1800  within the distal end  1804  is greater than or less than the inner lumen of the sheath  1800  at the proximal end  1802 .  
         [0079]      FIG. 18C  illustrates a side view of the sheath  1800  of  FIG. 18B  wherein the dilator shaft  1818 , the balloon  1820 , and the dilator hub  1816  have been withdrawn and removed leaving the proximal end  1802  and the distal end  1804  with a large central lumen capable of holding instrumentation. The shape of the distal sheath tube  1822  may not be entirely circular in cross-section, following expansion, but it is capable of carrying instrumentation the same size as the round proximal tube  1806 . Because it is somewhat flexible and further is able to deform circumferentially, the sheath  1800  can hold noncircular objects where one dimension is even larger than the round inner diameter of the sheath  1800 . The balloon  1820  is preferably deflated prior to removing the dilator shaft  1818 , balloon  1820  and the dilator hub  1816  from the sheath  1800 . The transition zone  1836  is shown in an exemplary embodiment wherein the proximal sheath tube  1806  is feathered into the distal sheath tube  1804  to provide a smooth transition in properties. The edges of the tubing at the transition zone  1836  appear, in an embodiment, as serrations. The serrations are preferably triangular in shape and between 0.1 and 5 cm long. The number of serrations can range between 1 and 20.  
         [0080]     Referring to  FIGS. 18A and 18B , the distal tubing  1804  further may comprise longitudinal runners or flutes separated by longitudinal slots or depressions. The folded distal sheath tube  1804  is constructed from materials that are plastically deformable, or malleable, such that the circumference is irreversibly increased by expansion of the dilator balloon  1820  and the outward forces created thereby. The wall thickness of the folded sheath tube  1804  is generally constant as the folded sheath tube  1804  is dilated. The folded sheath tube  1804 , once dilated, will generally provide sufficient hoop strength against collapse that it keeps surrounding tissues open. The optional longitudinal runners or flutes separated by the slits or depressions provide a reduced friction track for the passage of instrumentation within the folded sheath tube  1804 . The runners or flutes can be fabricated from materials such as, but not limited to, PTFE, FEP, PET, stainless steel, cobalt nickel alloys, nitinol, titanium, polyamide, polyethylene, polypropylene, and the like. The runners or flutes may further provide column strength against collapse or buckling of the folded sheath tube  1804  when materials such as calcific or cholesterol-based stones or other debris is withdrawn proximally through the sheath  1800 . The runners or flutes may be free and unattached, they may be integral to the ID material, or they may be affixed to the interior of the folded sheath tube  1804  using adhesives, welding, or the like. In the case of flutes, the structure can be integrally formed with the folded sheath tube  1804 , such forming generally occurring at the time of extrusion or performed later as a secondary operation. Such secondary operation may include compressing the folded sheath tube  1804  over a fluted mandrel under heat and pressure. The flutes may advantageously extend not only in the distal region  1804  but also in the interior of the proximal part of the sheath tubing  1806 , and/or, but not necessarily the hub  1808 .  
         [0081]     The guidewire port  1832  is generally configured as a Luer lock connector or other threaded or bayonet mount. The guidewire is inserted therethrough into the guidewire lumen  1834  of the dilator tubing  1818  to which the guidewire port  1832  is operably connected. The guidewire port  1832  is preferably integrally fabricated with the dilator hub  1816  but may be a separately fabricated item that is affixed to the dilator hub  1816 . A Tuohy Borst or other valved fitting is easily attached to such connectors to provide for protection against loss of fluids, even when the guidewire is inserted.  
         [0082]     Referring to  FIG. 18C , the proximal sheath tube  1806  further comprises a proximal reinforcing layer, an inner layer and an outer layer. The distal sheath tube  1804  further comprises a longitudinal fold  1828 , a distal reinforcing layer, an outer layer, and an inner layer. The proximal reinforcing layer is embedded within the proximal sheath tube  1806 , which is a composite structure, preferably formed from an inner and outer layer. The proximal reinforcing layer can be a coil, braid, or other structure that provides hoop strength and pushability to the proximal sheath tube  1806 . The proximal reinforcing layer can be fabricated from metals such as, but not limited to, stainless steel, titanium, nitinol, cobalt nickel alloys, gold, tantalum, platinum, platinum iridium, and the like. The proximal reinforcing layer can also be fabricated from polymers such as, but not limited to, polyamide, polyester, and the like. Exemplary polymers include polyethylene naphthalate, polyethylene terephthalate, Kevlar, and the like. The proximal reinforcing layer, if it comprises metal, preferably uses metal that has been spring hardened and has a spring temper.  
         [0083]     Further referring to  FIG. 18C , the distal sheath tube  1804  is constructed from a composite construction similar to that of the proximal sheath tube  1806 . The distal reinforcing structure, however, is not elastomeric but is malleable. The distal reinforcing structure is preferably a coil of flat wire embedded between the inner layer and the outer layer. The crease or fold  1828 , shown in  FIG. 18A , runs longitudinally the length of the distal sheath tube  1804  and is the structure that permits the distal sheath tube  18 O 4  to be compacted to a smaller diameter than its fully expanded configuration. There may be one fold  1828 , or a plurality of folds  1828 . The number of folds  1828  can range between 1 and 20, and preferably between 1 and 8, with the sheath tubing  1804  bendability and diameter having an influence on the optimal number of folds  1828 .  
         [0084]     The construction of the distal sheath tube  1804  can comprise a coil of wire with a wire diameter of 0.001 to 0.040 inches in diameter and preferably between 0.002 and 0.010 inches in diameter. The coil can also use a flat wire that is 0.001 to 0.010 inches in one dimension and 0.004 to 0.040 inches in the other dimension. Preferably, the flat wire is 0.001 to 0.005 inches in the small dimension, generally oriented in the radial direction of the coil, and 0.005 to 0.020 inches in width, oriented perpendicular to the radial direction of the coil. The outer layer has a wall thickness of 0.001 to 0.020 inches and the inner layer has a wall thickness of between 0.001 and 0.010 inches. The wire used to fabricate the coil can be fabricated from annealed materials such as, but not limited to, gold, stainless steel, titanium, tantalum, nickel-titanium alloy, cobalt nickel alloy, and the like. The wire is preferably fully annealed. The wires can also comprise polymers or non-metallic materials such as, but not limited to, PET, PEN, polyamide, polycarbonate, glass-filled polycarbonate, carbon fibers, or the like. The wires of the coil reinforcement can be advantageously coated with materials that have increased radiopacity to allow for improved visibility under fluoroscopy or X-ray visualization. The radiopaque coatings for the coil reinforcement may comprise gold, platinum, tantalum, platinum iridium, and the like. The mechanical properties of the coil are such that it is able to control the configuration of the fused inner layer and the outer layer. When the reinforcing layer is folded to form a small diameter, the polymeric layers, which can have some memory, do not generate significant or substantial springback. The sheath wall is preferably thin so that it any forces it imparts to the tubular structure are exceeded by those forces exerted by the malleable distal reinforcing layer. Thus, a peel away or protective sleeve is useful but not necessary to maintain the collapsed sheath configuration.  
         [0085]     The inner layer and the outer layer preferably comprise some elasticity or malleability to maximize flexibility by stretching between the coil segments. Note that the pitch of the winding in the distal reinforcing layer does not have to be the same as that for the winding in the proximal reinforcing layer because they have different functionality in the sheath  1800 .  
         [0086]     Referring to  FIGS. 18A, 18B , and  18 C, due to stress hardening of the reinforcing layer and residual stress in the folded inner layer and outer layer, some remnant of the fold  1828  may still exist in the distal tube  1804 . The expansion of the sheath  1800  in this configuration can be accomplished using a balloon  1820  with an internal pressure ranging between 3 atmospheres and 25 atmospheres. Not only does the balloon  1820  need to impart forces to expand the distal sheath tube  1804  against the strength of the reinforcing layer but it also needs to overcome any inward radially directed forces created by the surrounding tissue. In an exemplary configuration, a sheath  1800  uses a flat wire coil-reinforcing layer fabricated from fully annealed stainless steel  304 V and having dimensions of 0.0025 inches by 0.010 inches. The coil has a pitch of 0.024 inches and allows the sheath to fully expand, at a 37-degree Centigrade body temperature, to a diameter of 16 French with between 4 and 7 atmospheres pressurization. The inner layer is polyethylene with a wall thickness of 0.003 to 0.005 inches and the outer layer is polyethylene with a wall thickness of 0.005 to 0.008 inches. The sheath  1800  is now able to form a path of substantially uniform internal size all the way from the proximal end to the distal end and to the exterior environment of the sheath at both ends. Through this path, instrumentation may be passed, material withdrawn from a patient, or both. A sheath of this construction is capable of bending through an inside radius of 1.5 cm or smaller without kinking or becoming substantially oval in cross-section.  
         [0087]     The distal edge of the distal part of the sheath  1800  can comprise a fairing to smooth the transition between the small diameter dilator balloon  1820  of  FIG. 18A  and the folded sheath tubing  1804 . The transition at the distal end of the folded sheath tubing  1804  can be sharp and require a fairing, which can be a cone of material, elastomeric or rigid, or it can be a bolus of material under the balloon  1820 .  
         [0088]     The expandable sheath  1800  can be fabricated in a small size and could include an integral (or separately introduced) small endoscope with a diameter of 1 to 2 mm with preferably forward-viewing capability and associated illumination channels operably connected to a light source operably connected to the proximal end of the endoscope. Such a combination could be maneuvered through the esophagus, stomach and duodenum. Optional steerable componentry including a flexion point proximal to the distal end of the sheath and pull wires and deflection mechanisms can facilitate the procedure. The sheath can be stabilized by a collar or balloon device so the forward looking scope could be stabilized and directed to access the sphincter either directly or with guidewire control. This would allow the endoscope operator to evaluate the nature of a stricture, for example, a stone blocking a duct could be assessed for size and position. Current use of fluoroscopy only denies the operator this visual assessment. Similarly, in the case of strictures, tissue could be assessed for pathology and visually directed biopsy could be accomplished by directly selecting the site of tissue sampling, with fluoroscopic guidance as an adjunctive, rather than a primary guiding methodology. Current methods of biopsy sampling are only 40% to 50% effective and this efficacy rate could be improved with the invention. Such an access system could incorporate sphincterotomy and balloon dilatation to permit the sheath to pass beyond obstacles.  
         [0089]     The sheath can comprise an inflatable balloon to stabilize a small endoscope in a small sheath. The scope and/or sheath can accommodate a 0.035-inch, or larger, diameter guidewire through one of its lumens. The instrument channel or lumen in the endoscope can also accommodate baskets, graspers, or balloons, all of which can be operated within the view of the endoscope. A major consequence of pursuing gastrointestinal endoscopic diagnosis and therapy in this manner is the elimination of a 15 to 20 mm diameter endoscope to access, position, and visualize the duodenal wall to a point where the ampulla of Vater, the sphincter of Oddi, etc. can be identified. Once so positioned, much smaller devices are maneuvered through the sphincter of Oddi by scope rotation, followed by lateral deflection of guidewires and catheters followed by advancement through the sphincter. The patient is heavily sedated during this time to permit the unnatural esophageal occlusion that occurs during scope placement. The majority of cardiopulmonary complications occur as a result of the sedation required to accommodate the large scope passage and not the therapeutic gastrointestinal procedure itself.  
         [0090]     Referring to  FIGS. 18A  and  FIG. 2 , in another embodiment, the sheath  1800  comprises an implant (not shown), which is detached and left within the sphincter of Oddi  206 , said implant being either a one-way valve or a plug. The implant is beneficial because a surgical procedure of endoscopic origin dilates or cuts the sphincter of Oddi such that it, in some cases, no longer serves to prevent retrograde flow into the common bile duct  204  or the pancreatic duct  208 . Dilation, or overdilation, can cause the sphincter of Oddi  206  muscle to become dysfunctional, or temporarily incontinent, for a short period of time such as one or more days, sufficient to cause pancreatitis and other complications. The plug, in an embodiment, can be fabricated from resorbable materials such as polylactic acid, polyglycolic acid, or other sugar or carbohydrate that ultimately dissolves. The valve can be a simple duck-bill valve that permits flow from the common bile duct  204  and pancreatic duct  208  into the descending duodenum  112 . The valve can be. fabricated from silicone elastomer, C-Flex, or the like and have a seat that is fabricated from bioresorbable materials similar to those specified for the plug. The seat of the valve will dissolve over time and cause the valve to dislodge into the duodenum  112  from which it will eventually pass along with other fecal material. The valve seat or the plug can have antibiotics or other pharmacologic agents embedded or formed therein to minimize the chance of infection, for example. These agents can be encapsulated within microcapsules or microspheres to permit release over time or after a specified period of time. In another embodiment, the valve or plug are affixed to the exterior of the sheath  1800  so that when the sheath  1800  is removed, the valve or plug remain behind within the sphincter of Oddi  206 .  
         [0091]     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the sheath may include instruments affixed integrally to the interior central lumen of the mesh, rather than being separately inserted, for performing therapeutic or diagnostic functions. The hub may comprise tie downs or configuration changes to permit attaching the hub to the mouth, nose, or face of the patient. The dilatation means may be a balloon dilator as described in detail herein, it may rely on axial compression of a braid to expand its diameter, or it may be a translation dilator wherein an inner tube is advanced longitudinally to expand an elastomeric small diameter tube. Dilation may also occur as a result of unfurling a thin-film wrapped tube or by rotation of a series of hoops so that their alignment is at right angles to the long axis of the sheath. The embodiments described herein further are suitable for fabricating very small diameter catheters, microcatheters, or sheaths suitable for cardiovascular or neurovascular access. These devices may have collapsed diameters less than 3 French (1 mm) and expanded diameters of 4 to 8 French. Larger devices with collapsed diameters of 16 French and expanded diameters of 60 French or larger are also possible. Such large devices may have airway or lower gastrointestinal tract applications, for example, the latter being accessed via laparoscopy, oral, or a rectal approach, for example. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is therefore indicated by the appended claims rather than the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.