Abstract:
In one embodiment, an access sheath includes a movable coil sheath that is insertable into a patient through an endoluminal or surgical approach. The sheath is inserted into a patient in a flattened configuration. A plurality of separate coils, elements, or hoops are connected by a fixed member and a control member, which are moved relative to each other to flatten the coils or hoops. Once inserted and advanced to the target surgical site, the sheath is selectively, and controllably, unflattened or expanded to a desired diameter or cross-section. A control member is affixed to one edge of the sheath and runs in the axial direction. By translating the control member in a direction parallel to the axis of the sheath, the operator causes the hoops or coils to rotate into a plane perpendicular or lateral to the axis of the sheath. A mechanical lock at the proximal end of the sheath permits the control member to be selectively constrained from translation and thus lock the sheath diameter in place.

Description:
PRIORITY INFORMATION  
       [0001]     This application claims the priority benefit under 35 U.S.C. § 119(e) of Provisional Application 60/554,334 filed Mar. 18, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to medical access devices and, in particular, to expandable medical access devices for providing minimally invasive surgical access for various surgical procedures.  
         [0004]     2. Description of the Related Art  
         [0005]     Urethroscopy is procedure commonly used by urologist to explore the upper and lower urinary tract for diagnostic and therapeutic procedures and to provide access to the bladder and ureters. Visualization is often provided by a rigid or flexible scope (e.g., a cystoscope). In these cases, a sheath is often employed to protect the urethra during cystoscope placement as well as the placement of other instrumentation. Current sheaths use a “Dotter” configuration to advance a dilatation sheath over a guide catheter designed to track a guidewire under fluoroscopic guidance.  
         [0006]     In some instances, strictures, or occlusions, are formed in the urethra because of disease or injury to the urothelium, the lining of the urethra. When a stricture occurs it can cause excessive restriction to urination, which must be relieved. A stricture may also prevent instrumented access to regions anatomically proximal to the stricture (e.g., the upper and lower urinary tract).  
         [0007]     For the male patient, strictures are often encountered in the penis or prostatic urethra. Many surgical instruments are available to “break” or “release” the stricture so the initial procedure can continue. Opening of the stricture is often necessary because of the need for endoluminal access to a point anatomically proximal to the stricture in procedures such as Ureteroscopy. In addition, instrumentation developed for treating urological pathologies is generally too large to pass beyond a stricture. Accordingly, instruments have been developed to open urethral strictures. “Bougies”, “sounds”, or “urethrotomes” are examples of such instruments. A bougie is a tapered axially elongate dilator that expands the stricture. A bougie exerts a longitudinally directed force that, because of its tapered profile, radially dilates the urethra. A urethrotome is essentially a knife that cuts the stricture in a longitudinal direction. Often a bougie will not open a stricture because the scar tissue is so tough that dilation will not open it and a urethrotome is required for the opening procedure. Both procedures tend to cause trauma, which can lead to reformation of the stricture. Given the discomfort inherent in such procedures as well as the symptomatology leading up to such procedures, patients, as a rule, would like to avoid the consequence of renewed stricture formation.  
         [0008]     Traditional cystoscopy uses cystoscopic sheaths, with effective diameters ranging from 2 to 12 mm (6 to 36 French, respectively), to gain endoluminal access to the urethra, bladder and ureters. Most procedures are performed through such sheaths. These sheaths are often oval in order to maximize the instrument carrying capability of the sheaths. The urethra is capable of easily carrying a sheath with a non-circular cross-section, as opposed to certain other body lumens such as arteries. The cystoscope sheath often includes a bulbous nose to aid in blunt expansion of the urethra during insertion. However, placing such sheaths through a urethra with a stricture often requires the use of dilators or a urethrotome as described above to open the stricture.  
         [0009]     Since strictures preferentially occur on a side of the of the urethra, the passage of sheath with a round lateral cross-section may cause a selective shearing during intmemberuction, thus damaging the urothelium. If a round instrument if forcefully advanced, the stricture may be displaced laterally, again causing a stress disruption of the urothelium. In either case, formation of a subsequent stricture or occlusion is predictable sequelae of the procedure.  
         [0010]     New devices and methods are needed to open strictures in such a way that trauma to the urethra is minimized. These devices need to provide for controllable tissue dilation once an initial tunnel is created. Such devices are particularly important for use in treating lesions of the bladder and the prostatic urethra, for example.  
       SUMMARY OF THE INVENTION  
       [0011]     There exists a general need for a ureteral dilator or temporary stent that can dilate with a more purely radially directed force and less longitudinal shear to the tissue than that exerted by traditional bougies or other dilators. There also exist a general need for an improved device for providing minimally evasive access for other surgical procedures.  
         [0012]     Accordingly, in one embodiment of the invention, an expandable surgical access device comprises a tubular assembly that a lumen that extends along a longitudinal axis. The tubular assembly comprises a plurality of structural members and a tubular sleeve. A longitudinally extending first member is coupled to the structural members by connectors that permit rotational movement of the structural members with respect to the first member about an axis substantially perpendicular to the longitudinally axis but limit longitudinal movement of the structural members with respect to the first member. A second member is coupled to at least one of the structural members. An actuator is provided for moving the second member longitudinally respect to the first member. Longitudinal movement of the second member with respect to the first member causes the lateral structural members to rotate about the axis substantially perpendicular to the longitudinal axis of the access device. The structural members rotate between a reduced profile position in which the structural members are positioned substantially within a plane that is closer to being parallel to the longitudinal axis as compared to when the structural member is in an enlarged configuration.  
         [0013]     Another embodiment of the present invention comprises a method of providing expandable surgical access. The method includes inserting a sheath into a body lumen, advancing the sheath to a target depth, expanding the sheath by rotating the ends of a structural element away from the longitudinal axis of the sheath; and removing the sheath from the body lumen.  
         [0014]     In another embodiment of the invention, the tube-like expandable sheath device comprises a movable core consisting of a spring or plurality of circular components or elements such as, but not limited to, independent coils, having round, oval or other eccentric forms. The sheath further comprises a fixed, semi-rigid connector member extending the length of the device and having flexible or rotational attachment to each circular component. The fixed connector member has the properties of substantial column strength and tensile strength but is flexible and capable of bending in the lateral direction. The sheath further comprises a control member attached, in one embodiment, 180° opposed to the fixed connector member. Movement of the control member in a longitudinal direction relative to the axis of the sheath will shift the circular components from a position 90° or perpendicular to the fixed connector member shaft to a position nearing 0° or flat so that the longitudinal axis of the sheath is in the plane of the flat circular components. The inner and outer surfaces of the sheath may be thinly coated with a biocompatible material to present a smooth surface to tissue and instrument passage while allowing the control elements to change radial configurations of the circular components. In this embodiment, movement of the control member, arm or shaft will flatten the device to reduce the overall French size and/or vertical or cross-sectional profile under operator control to negotiate channels with asymmetric size and configuration. A control mechanism or handle and locking elements located at the proximal end of the device maintains the proper tension on the control member relative to the fixed member, to the extent needed to preserve the desired final configuration.  
         [0015]     In an embodiment, the structural members have an oval cross-section, the sheath has a narrow outside diameter when the structural members are rotated into a plane parallel to the axis of the sheath. The sheath so configured would be capable of following a guidewire and allow passage through occlusions or strictures. By operating the control arm, the operator rotates the circular, or in this case oval, members into a plane perpendicular to the axis of the sheath. By rotating the circular members towards a position perpendicular to the axis of the sheath, the device outside diameter (OD) is increased and the sheath performs a radial dilation function to surrounding tissues. A corresponding increase in the inside diameter (ID) also occurs allowing the passage of a dilating balloon, optical scope or other devices such as surgical instruments and the like.  
         [0016]     Another embodiment of the invention involves a method wherein additional dilation energy may be imparted to the sheath. In this method, a dilation balloon is placed where narrowing was observed either by external fluoroscopy, MRI, internal scope or a combination of the aforementioned. Once the balloon is positioned within the internal lumen of the sheath or channel where it passes through the stricture, the balloon would be inflated using fluids such as, but not limited to, radiopaque contrast media, saline, water, gas, or the like. The radial force imparted by the balloon could be applied to gently expand the lesion as well as the sheath. The expansion maneuver may be repeated over the length of the device as required by anatomic strictures. The method of balloon expansion may be repeated if the length of the balloon is not be as long as that of the sheath. Once a fully expanded, round cross-section sheath is formed by the combination of movable elements and radial force applied by balloon expansion, the balloon is deflated and removed. With the inner lumen or channel free of devices and strictures, procedures may be performed while the sheath protects anatomic surfaces outside the lumen. It is most common for a balloon to inflate to a circular or round cross-section although other cross-sectional configurations for the balloon such as oval, pear-shaped, bell-shaped, triangular, rectangular, or trapezoidal, are also possible.  
         [0017]     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.  
         [0018]     In addition, all of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1A  is a side perspective view of an exemplary embodiment of an access sheath in a reduced cross-sectional profile configuration;  
         [0020]      FIG. 1B  is a front view of a structural member of the access sheath of  FIG. 1 ;  
         [0021]      FIG. 1C  is a side view of the structural member of  FIG. 1B ;  
         [0022]      FIG. 2A  is a side perspective view of the access sheath of  FIG. 1  in an enlarged cross-sectional profile configuration;  
         [0023]      FIG. 2B  is a cross-sectional view taken through line  2 B- 2 B of  FIG. 2A ;  
         [0024]      FIG. 2C  is a side view of an exemplary connector of the access sheath of  FIG. 1A ;  
         [0025]      FIG. 3  is a side perspective view of a modified embodiment of the access sheath of  FIG. 1  in a reduced cross-sectional profile configuration;  
         [0026]      FIG. 4  is a side perspective view the sheath of  FIG. 3  in an enlarged cross-sectional profile configuration;  
         [0027]      FIG. 5  is a lateral cross-sectional view of the sheath of  FIG. 3  and with a surgical instrument and an optical lens are inserted therethrough;  
         [0028]      FIG. 6  is a lateral cross-sectional view of the sheath of  FIG. 3  in a reduced cross-sectional profile configuration; and  
         [0029]      FIG. 7  is a side perspective view of a modified embodiment of a sheath that utilizes a dilatation balloon. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]      FIG. 1A  illustrates a perspective view of an exemplary embodiment of an expandable access device  10  in a collapsed or reduced cross-sectional profile configuration.  FIG. 2A  illustrates the access device in a expanded or enlarged cross-sectional profile configuration.  
         [0031]     In the illustrated embodiment, the access device  10  comprises a plurality of structural remembers or elements  14  an example of which is shown in  FIG. 1B . Each lateral element  14  includes an inner surface  15  which defines at least in part an opening having a cross-sectional area and outer surface  17 , which defines at least in part an outer profile. As shown in  FIG. 1C , a longitudinal or axial axis l extends through the structural member  14  in a direction generally parallel to the longitudinal axis of the access device. As the structural element is rotated about a second axis l 2 , which is generally perpendicular to the longitudinal axis l, the height of the structural member is reduced as the width stays constant. When the structural element  14  is positioned in a plane substantially normal to the longitudinal axis of the device  10 , the height is greatest. In contrast, as the structural element  14  is rotated such that it lies in a plane substantially parallel to the longitudinal axis l the height of is reduced. Accordingly, by rotating the ends  11  of the structural element  14  closer to the longitudinal axis l the profile of the structural member  14  is reduced and the access device  10  may be moved between collapsed or reduced cross-sectional profile configuration and the expanded or enlarged cross-sectional by rotating the structural elements  14  about the second axis l 2 .  
         [0032]     With reference back to  FIG. 1A , in the illustrated embodiment, the access device  10  also includes a hub  12 , a control member  16  and a static member  18 . As will be explained in more detail below, the control member  16  and static member  18  are configured for moving the structural elements  14  between the reduced cross-sectional profile configuration to the enlarged cross-sectional profile configuration. The device  10  preferably also further comprises a control knob  20  and a locking system  22  for selectively positioning the device  10  in a specific cross-sectional configuration.  
         [0033]     A sleeve  24  is coupled to the external side  17  of the structural members  14  to define, in part, an inner lumen  26 . In modified embodiments, the sleeve  24  may be coupled to the internal side  15  of the structural members  14 . In still other embodiments, the structural members  14  may be embedded within the sleeve  24 . In the figures, the sleeve  24  of the sheath  10  is rendered as transparent so that the internal components are visible. In addition, in the illustrated embodiment, the lateral elements  14  define a generally circular opening. However, as will be explained below, in other embodiments, the lateral elements  14  define openings with non-circular shapes.  
         [0034]     With continued reference to  FIG. 1A , the hub  12  serves as a point of stability and a grip for the sheath  10 . The plurality of structural elements  14  are coupled to the control member  16  which runs generally along the longitudinal axis of the sheath  10 . In the illustrated arrangement, the elements  14  are fixed, each at a point, to the control member  16 . Preferably, the control member  16  is attached to the lateral elements  14  such that the structural elements  14  are constrained in the axial direction at specific positions on the control member  16  but some rotation of the structural elements  14  relative to the control member  16  is permitted. Any of a variety of connectors such as hinging elements (e.g., loops or pins through holes) and/or flexible material may comprise the attachment between the control member  16  and the lateral elements  14  as well as between the static member  18  and the lateral elements  14 . For example,  FIG. 2C  illustrates a control member  16  or static member  18  that is attached to a structural member  14  by a connector  21  comprising a pivot shaft  23  that extend through but members  14 ,  16 .  
         [0035]     In the illustrated embodiment, the static member  18  runs generally along the longitudinal axis of the sheath  10  at a circumferential location on the lateral circular elements  14  that is preferably displaced substantially from that of the control member  16 . The static member  18  is preferably affixed to the lateral elements  14  such that longitudinal relative motion between the static member  18  and the lateral elements  14  is prohibited while rotational relative motion is permitted. With reference to  FIG. 2B , the proximal end of the static member  18  is preferably coupled to the hub  12  so that no longitudinal relative movement is permitted between the static member  18  and the hub  12 . In contrast, the proximal end of the control member  16  extends within the hub  12  and is affixed to the control knob  20  so that the control member  16  moves with the control knob  20 . The control knob  20  extends outside the hub  12  and is constrained to move within a slot  23  in the hub  12  so that longitudinal relative motion between the hub  12  and the control knob  20  is permitted within a specified range. In this configuration, the control knob  20  is fully moved to the proximal most position on the hub  12  so that the control member  16  has translated proximally and has rotated the circular lateral elements  14  about an axis perpendicular to the long axis of the sheath  10  into a collapsed configuration. The inner lumen  26  of the sheath  10  is substantially collapsed in this configuration, offering what is generally known as potential space.  
         [0036]     In the illustrated embodiment, a locking mechanism  22  is formed by the hub  12  to permit selective fixed position control over the control knob  20 . The hub  12  may include visual indicia (e.g., notches, numbers, etc.) that indicate the outside or inner diameter of the access sheath  10  as the control knob  20  is moved within the slot  23 . In addition, as mentioned above, the locking mechanism  22  may include a plurality positions in between the distal most and proximal most position. Each position may be provided with visual indicia that indicate the diameter of the access sheath when the knob  20  is positioned at a specific position in the locking mechanism  22 . Of course, those of skill in the art will recognize that other locking mechanism may be used, such as, for example, various combinations of latches, levers, locks etc. In this manner, in the illustrated embodiment, the device  10  may be selectively expanded to at least one cross-sectional profile and preferably a plurality of discrete intermediate cross-sectional profiles throughout a continuum between the largest and the smallest diameter and maintained at that size because of the locking mechanism  22 .  
         [0037]     With continued reference to  FIG. 1 , the sleeve  24  is preferably affixed at its proximal end to the hub  12 . A seal  28  is preferably provided at the proximal end of the hub  12 . The seal  28  is configured to provide an elastic seal between the hub  12  and any instrument inserted therethrough. As explained below, the seal  28  may prevent or reduce fluid loss when an instrument is inserted through the central lumen  26  of the sheath  10 .  
         [0038]     In modified embodiments, the static member  18  may also be moveable with respect to the hub  12 . In such an embodiment, relative movement between the static member  18  and the control member  16  causes the structural elements  14  to rotate.  
         [0039]     The structural elements  14 , the control member  16  and the static member  18  may be fabricated from any of a variety of materials such as, but not limited to Elgiloy, nitinol, titanium, polytetrafluoroethylene (PTFE), stainless steel, polyamide, polyester, and the like. In the illustrated embodiment, the sleeve  24  is the primary body contact surface of the sheath  10  and is intended to form a continuous wall over the open framework of the lateral hoop elements  14 . In such an embodiment, the external sleeve  24  may be fabricated from any of a variety of materials such as, but not limited to, PTFE, fluoroethylene polymer (FEP), silicone elastomer, thermoplastic elastomer (TPE), polyurethane, or the like. In certain embodiments, the external sleeve  24  may be fabric with openings or mesh grids, or it may be free from fenestrations and take the form of a continuous non-porous sheet. The external sleeve  24  may further be coated on one or both sides with anti-thrombogenic agents such as, but not limited to heparin, which is ionically, or covalently, bonded to the external sleeve  24 . The external sleeve  24  may also be coated with antimicrobial agents such as, but not limited to, silver oxide, silver azide, betadine, or the like.  
         [0040]     In still other embodiments, the external sleeve  24  may further be configured to carry electrical charge so that it can be used to deliver microwave or radio frequency (RF) energy, which can be used to cauterize or destroy cellular tissue. Metallic coatings with appropriate electrical connections leading out the proximal end of the sheath  10  may be applied to the surface of the external sleeve  24  for this purpose.  
         [0041]     In a preferred embodiment, the external sleeve  24  is a creased, flattened axially elongate structure that expands to take on the general structure of the opened lateral elements  14 . The external sleeve  24  is preferably fabricated from FEP, PTFE or expanded PTFE so that it comprises a low friction surface. Alternatively, the external sleeve  24  can be coated with materials such as, but not limited to, silicone oil, hydrophilic hydrogels, or the like to reduce friction with the tissues with which it comes in contact. In this preferred embodiment, the external sleeve  24  is not elastomeric. In a further embodiment, a plurality of longitudinally disposed structural members are arrayed around the lateral elements  14  to provide intermediate support so the containment layer  24  will not tend to cup or drape inwardly between opened lateral elements  14 . The wall thickness of the external sleeve  24  ranges between about 0.0005 inches and about 0.100 inches and is often between about 0.005 inches and about 0.040 inches. The external sleeve  24  may be extruded or formed from flat sheet and welded or bonded to form a closed axially elongate cylinder of appropriate cross-sectional shape. The external sleeve  24  may form a containment layer to prevent the passage of fluids into or out of the sheath  10 , a feature especially useful when working with malignant or carcinogenic tissue.  
         [0042]     The working length of the sheath  10  is determined by the distance between the skin surface and the target surgical site. The sheath  10  may have a working length in the range from about 1 cm to about 175 cm and more typically range between about 5 cm and about 30 cm. The working length is generally the distance between the distal most edge of the external sleeve  24  and the distal end of the hub  12 . The external sleeve  24  and the array or plurality of lateral elements  14 , as well as the control member  16  and the static member  18  project axially into the inner lumen  26  of the hub  12  but this is generally not considered useable length for cannulating a patient. The radial strength of the sheath  10  formed by the structural elements  14 , the control member  16 , the static member  18  and/or the sheath in the described configuration desirably sufficient radial to expand most soft tissue in a uniform circular fashion. This radial strength may achieved by controlling the material, thickness and configuration of these components including the configuration orientation of the lateral members  14 , which in themselves may be configured to have significant hoop strength, to create a structure that has resistance to hoop stress and point loads. In one embodiment, the distal edge of the sheath  10  is sharp in that the material of the tube is not edge treated in any way. The distal edge of the sheath  10  is, in another embodiment, atraumatic and not substantially sharp. In this embodiment, the distal edge of the sheath  10  is rendered blunt and atraumatic by attachment of a lateral member with large wall thickness and a rounded structural cross-section, or other technique known in the medical art.  
         [0043]     It will be apparent from the disclosure herein that the access sheath  10  and/or the methods described herein may also find utility in a wide variety of diagnostic or therapeutic procedures that require an artificially created access tract. For such applications, the diameter of the tubular sheath  10  in the radially collapsed configuration and its expanded or enlarged configuration will depend upon the intended surgical application. For example, depending upon the application, the collapsed diameter of the sheath  10  may lie in the range from about 1 mm to about 10 millimeters. The expanded diameter of the sheath  10  may lie in the range from about 4 mm to about 50 mm. The wide variety of diagnostic or therapeutic procedures may include but are not limited to many urological applications (e.g., the removal of ureteral strictures and stones, the delivery of drugs, RF devices and radiation for cancer treatment, etc.), gastrointestinal applications (e.g., to the removal gallstones and appendix procedures, colon therapies, esophageal treatment and the treatment of bowel obstructions), cardiovascular applications (e.g., to provide access for minimally invasive heart bypass, valve replacement or the delivery of drugs or angiogenesis agents), vascular applications (e.g., minimally invasive access to the aorta or contralateral leg arteries for the treatment of, for example, an abdominal aortic aneurysm), gynecological applications (e.g., endometrial therapies, delivery of drugs, delivery of cancer agents, sterilization procedures, etc.), orthopedic applications and breast biopsies/lumpectomies  
         [0044]     The static member  18  and the control member  16  are preferably fabricated from materials such as, but not limited, to polyester, polyamide, stainless steel, Elgiloy, nitinol, and the like. The control member  16  and the static member  18  are preferably sized so that their length extends to the distalmost structural element  14  and further extends into or to the hub  12 . The diameters of the control member  16  and the static member  18  are preferably between 0.010 inches and 0.4 inches and more preferably between 0.30 inches and 0.25 inches.  
         [0045]     The hub  12 , the control knob  20 , and the locking mechanism  22  are preferably fabricated from materials such as, but not limited to, Acrilonitrile Butadiene Styrene (ABS), polyvinyl chloride (PVC), polyethylene, polypropylene, and the like. As shown in  FIG. 1 , the control knob  16  is affixed coaxial with the hub  12 . In this embodiment, the control knob  20  passes through a slot in the hub  12 . The control knob  20  is constrained by the slot in the hub  12 , which further has a plurality of notches or other locking mechanism  22 . The control knob  20  may be spring biased to engage the notches, detents, or other locking mechanism  22 . In another embodiment, the control knob  20  is manually guided into a locked position at user discretion with no bias. Gearing or other mechanisms may be also used to transmit the energy between the control knob  20  control member  16 .  
         [0046]     The locking mechanism  22  is, in the illustrated embodiment, a positive lock that is engaged to prevent, or disengaged to allow, relative rotation between the control knob  16  and the hub  12 . In another embodiment, the lock  22  is a ratcheting mechanism that permits movement of the control knob  20  with binding or frictional click-stops. The proximal locking or ratchet mechanism  22  holds or maintains the diameter to that selected by the surgeon. The proximal lock assembly  22  is of small mass and profile to avoid interfering with surgical maneuvers. The lock  22  is further configured not require the attention of an assistant to maintain position or size. In another embodiment, an outer fixture may be placed at skin level and selectively affix to the hub  12  to assist with stabilization. The control knob  20  and the hub  12  are configured with no sharp edges or pinch points that could snare or perforate the glove of a surgeon and compromise sterility. As mentioned above, the locking mechanism  22  may also include visual indicia to indicate the diameter of the sheath  10  for a given position of the locking mechanism  22 .  
         [0047]     With reference to  FIG. 2B , in the illustrated embodiment, the seal  28  comprises a housing that is fabricated from the same materials as those used to fabricate the hub  12 . In one embodiment, the seal  28  further comprises an elastomeric membrane  31  that is suspended within the seal housing  29 . The elastomeric membrane  31  is generally configured as a washer with a central orifice  33  capable of accepting instruments therethrough and sealing to the outer surface of said instruments. The central orifice  33  of the elastomeric membrane component of the seal  28  enlarges or shrinks as necessary to accommodate a wide range of instruments. The orifice diameter of the elastomeric membrane  31 , in the unstretched state ranges from 0.1 inches to 1 inch. The elastomeric membrane  31  is fabricated from materials such as, but not limited to, silicone elastomer, thermoplastic elastomer, polyurethane, latex rubber, and the like. The elastomeric membrane  31  is preferably coated with a lubricant such as silicone oil or PTFE to minimize friction on passage of an instrument.  
         [0048]     Provision for use of the sheath  10  over a guidewire is provided either by inserting the sheath  10  over the guidewire. In this embodiment, the guidewire is inserted through the central lumen  26 f the radially collapsed sheath  10 .  
         [0049]     As mentioned above,  FIG. 2  illustrates an oblique view of an expandable sheath  10  in its fully expanded configuration in which the sheath  10  has been expanded to a diameter larger than that shown in  FIG. 1 . The sheath  10  has been expanded to the maximum diameter allowable as determined by the cross-sectional shape of the structural elements or coils  14 . The structural elements  14  may be expanded to any diameter through lumen  24  between the largest and the smallest effective diameter and maintained at that size under the influence of the locking mechanism  22 . As the structural elements  14  are rotated more completely out of a plane substantially parallel of the longitudinal axis of the sheath  10 , the cross-section of the inner lumen  26  moves from severely oval to oval with less difference between the major and minor axes to a limit condition of fully round when 90 degree rotation has been completed.  
         [0050]      FIG. 3  illustrates an oblique view of a modified embodiment of an expandable sheath  10  in its collapsed configuration. The sheath  10  of  FIG. 3  is fabricated using structural elements that have a cross-section diameter that is smaller in one direction (e.g., elliptical, pear-shaped, bell-shaped, or oval rather than circular), as are the lateral elements of the sheath in  FIGS. 1 and 2 . As mentioned above, it should be appreciated that in still other embodiments, the lateral elements may have other cross-sectional shapes (e.g., rectangular, triangular etc) the structural elements may also have one or more open sections in some embodiments.  
         [0051]     As with the embodiment of  FIGS. 1 and 2 , the expandable sheath  10  comprises a hub  12 , a plurality of elements  14 , a control member  16 , and a static member  18 . The sheath  10  further comprises a control knob  20 , a locking system  22 , and an external sleeve  24 . In this embodiment, the sheath  10  includes optional removable obturator  30 , which further comprises an optional guidewire lumen  32 .  
         [0052]     Referring to  FIG. 3 , the obturator  30  is removable through the proximal end of the sheath  10  and is inserted to aid in introduction of the sheath  10  into the patient. The obturator  30  is typically used only in the radially compressed configuration of the sheath  10 . The obturator  30  typically comprises a shaft, a distal tip and a proximal end. The shaft may be either metallic or polymeric in composition. The distal tip and the proximal end are most preferably fabricated from polymeric materials such as, but not limited to, ABS, PVC, polyurethane, PEEK, polypropylene, polyethylene, and the like. The shaft of the obturator  30  is preferably fabricated from metals or polymeric materials. The materials used for the manufacture of the obturator  30  include the same materials used for manufacture of the hub  12  and also include stainless steel, titanium, and other biocompatible metals. The obturator  30  assists in intmemberucing the sheath  10  into the lumen of the patient by helping to move tissue aside so that it is guided outward and over the exterior of the sheath  10 . The sheath  10  is generally flexible although it could also be rigid and resist lateral bending. The obturator  30  is also able to be rigid or flexible depending on the needs of the physician in instrumenting the lumen of the patient. A flexible obturator  30  may be easily fabricated using a polymeric shaft or a segmented metal or polymeric shaft. In one embodiment, the sheath  10  is flexible but the obturator is rigid so that the sheath  10  with obturator is intmemberuced in a rigid configuration but is then able to become flexible once the obturator  30  is removed. A lateral cross-section of the obturator  30  will appear extremely oval or elliptical to match the internal lumen  26  of the sheath  10  when the lateral elements  14  are rotated nearly into the plane of the longitudinal axis of the sheath  10 .  
         [0053]     In a further embodiment, the obturator  30  comprises a guidewire lumen  32  that can track or follow a guidewire placed with a Seldinger method, for example. Such an embodiment of the expandable sheath  10  is especially useful for endovascular access cases.  
         [0054]      FIG. 4  illustrates an oblique view of the expandable sheath  10  of  FIG. 3  in its fully expanded configuration in which sheath  10  has been expanded to a diameter larger than that shown in  FIG. 3 . Referring to  FIG. 1  and  FIG. 3 , the oval structural elements  14  have the benefit of generating a reduced overall profile relative to circular structural elements  14 . However, referring to  FIGS. 2 and 4 , the oval structural elements  14  are capable of generating a more useable internal lumen  26  capable of handling more than one instrument inserted through the sheath  10 .  
         [0055]      FIG. 5  illustrates a lateral cross-section of the working length of the sheath  10  of  FIGS. 3 and 4 . The sheath  10  is shown with its oval structural elements  14  rotated substantially away from the longitudinal axis of the sheath  10  to create a maximum or dilated configuration. The sheath  10  is further shown comprising an optical viewing lens or scope  40  and an instrument  42 . The oval cross-section  26  of the sheath  10  allows for simultaneous passage of both the lens  40  and the instrument  42  through the lumen  26  of the sheath  10 . The optical viewing lens or scope is typical of cystoscopes or other viewing devices and may be either rigid or flexible. Rigid scopes  40  typically have outer working length diameters in the range of 4 mm. The scope  40  and the instrument  42  are preferably passed through a seal  28  such as that shown in  FIG. 4 . The seal is an elastomeric element that prevents the escape or ingress of fluids between the instrument  42 , the lens  40  and the sheath  10 . The seal  28  of  FIG. 4  may include central hole that accepts and seals to a single axially elongate smooth instrument. In another embodiment, the seal  28  has more than one hole so that more than one instrument can be inserted therethrough and seal to the seal  28 . For example, the instrument  42  may be a set of graspers, which are inserted through a two-hole seal  28  along with a lens or scope to visualize the procedure. Such multiple instruments placed through a single sheath are an advantage of the expandable sheath  10 . The large diameter, expanded expandable sheath  10  is capable of holding two or even more instruments. In yet another embodiment, the seal  28  is omitted to allow for a more direct surgical access to the sheath  10 .  
         [0056]     In the illustrated embodiment, the external sleeve  24  generally covers the outer extent of the structural members  14  but is not physically affixed to these lateral members. Accordingly, in this embodiment, the external sleeve  24  may remain stationary longitudinally relative to the hub  12  of the sheath while the structural members  14  rotate and move axially and radially relative to the external sleeve  24 .  
         [0057]      FIG. 6  illustrates a lateral cross-section of the working length of the sheath of  FIG. 3  in a low profile configuration with its oval structural elements  14  rotated substantially toward the plane comprising the longitudinal axis of the sheath  10  thus creating a minimum or collapsed cross-sectional configuration. The sheath  10  is further shown comprising the shaft of an obturator  30  at that particular point in the cross-section. Note that the overall frontal or cross-sectional area of the working length of the sheath  10  is significantly less than that shown in  FIG. 5  where the sheath  10  is expanded. The collapsed configuration is the preferred configuration for inserting the sheath  10  into a patient. The tip of the obturator  30  is generally larger than the shaft and is preferably designed to fill the available space within the internal lumen  26 .  
         [0058]      FIG. 7  illustrates a perspective view of another embodiment of the expandable sheath  10  that include oval structural elements  14  or elements of different shapes. In this embodiment, the cross-section of the working length of the sheath  10  is similar to that shown in  FIG. 5  following rotation of the structural elements  14  into a plane normal to the longitudinal axis of the sheath  10 . The oval structural elements  14  in this embodiment may be further dilated and formed generally circular or round by way of a dilatation device  50 . The dilatation device  50  may comprise such devices such as angioplasty balloons, nitinol shape-memory elements that change shape above body temperature, and the like. In an embodiment, the oval structural elements  14  are malleable and take on a permanent round shape once dilated by the dilatation device  50 . In the embodiment shown in  FIG. 7 , the dilatation device  50  comprises an inelastic balloon  52  and a catheter shaft  54 . The catheter shaft passes through the hub  12  and the balloon  52  is positioned within the oval lateral elements  14 . The balloon is inflated to cause the malleable oval structural elements  14  to become more circular in shape. The balloon  52  shown in  FIG. 7  is located inside the distal half of the sheath  10 . In  FIG. 7 , expanding of the structural elements  14  in the proximal end of the sheath has already taken place and the balloon  52  was deflated, moved to its current location and re-inflated. Materials used to make malleable lateral elements may include stainless steel, titanium, cobalt nickel alloys, and the like. In another embodiment, the structural elements  14  are shape memory nitinol and are martensitic at body temperature. Following dilation of the structural elements  14  with the dilatation means  50 , the now expanded (e.g., rounded) lateral elements  14  may be heated using electrical resistive or Ohmic heating or even by infusion of warm fluids such as water into the sheath  10 . Such heating is used to take the temperature of the structural elements  14  above a certain austenite finish temperature, at which point, they will return to their original oval shape which lends itself to reduced sheath  10  cross-sectional area, especially when the oval structural elements  14  are rotated to the collapsed position. The austenite finish temperature appropriate for such transition is preferably between 38 degrees centigrade and 42 degrees centigrade.  
         [0059]     In certain embodiments, the sheath includes a guidewire channel, either through the sheath itself or through the center of a removable obturator. This guidewire channel provides the ability to insert the sheath, in its small diameter configuration, over a guidewire. In another embodiment, the sheath may be used as a probe under radiographic guidance (fluoroscopy, computer aided tomography (CAT), magnetic resonance imaging (MRI), or ultrasound). The sheath may further be inserted and manipulated under direct vision by including a small caliber scope to identify an anatomic path or features within a body cavity.  
         [0060]     In one embodiment of use, once an initial tissue target is identified and the appropriate location of the access confirmed, the device could, under direct, precise operator control, enlarge the access lumen by applying radial force. The surrounding tissue applies a counter pressure to that exerted by the radially dilated device, which aids in maintaining stability of the device once it is expanded. The overall diameter of the sheath can be reduced, at operator discretion, by rotating a control knob, pushing or pulling a dilating control mechanism, or other control affixed to the control member that extends axially along one edge of the sheath. A lock on the control device further allows for selectively maintaining the configuration of the sheath, once set by the user.  
         [0061]     In another embodiment, which is different than the passive mode of maintaining surgical retraction, the device can be intmemberuced via standard laparoscopic trocar and be selectively expanded to stabilize an organ or tissue with known, controlled circumvention pressure to provide the operator with a stable operative surface. Additionally, the device can be positioned to displace organs and structures to create a stable tunnel to expose a distant operative site.  
         [0062]     Another embodiment, involves a method of use wherein the device is inserted as part of a system to capture an organ. The sheath is inserted to allow safe withdrawal of another device designed to contain the amputated organ or tissue, which can then be withdrawn through the sheath to a position outside that of skin level. This method conveys the benefit of laparoscopic surgery while avoiding the challenges associated with isolated removal of a diseased organ where malignant cell isolation is of a concern.  
         [0063]     In accordance with another embodiment of use, a diseased organ or tissue mass is isolated by the surgeon by inserting the sheath to the target mass. An instrument can then be inserted through the sheath. These instruments may allow for various methods of cell or tissue destruction to be employed, with or without specimen removal. Access to the diseased organ may be accomplished under direct vision as part of a laparoscopic or percutaneous procedure. Exemplary uses of a sheath that may be selectively enlarged include applications in procedures to remove kidney stones, treat urethral strictures, perform biopsies or organ removal, perform stent implantation, and the like. The sheath is capable of being made smaller or larger in diameter to accommodate the size changes that are often required and sometimes unanticipated in a procedure. Following completion of the procedure, the sheath is removed from the patient, with or without the step of reducing the size of the sheath before removal.  
         [0064]     In yet another embodiment, it is recognized that an insulating barrier placed on the outside, or inside, of the device would confine therapeutic or diagnostic cryogenic temperatures, radio frequency (RF) waves or microwaves so that they would not reach tissues surrounding the sheath. Instead of sustaining losses along the length of the sheath, these energies may be focused substantially on the tissue or organ targeted by the device at or near its distal end. In another embodiment, a seal layer is provided that prevents migration of fluids and other materials through the wall of the sheath. An insulating exterior or interior barrier that protects displaced, healthy tissue from destructive treatments being applied to diseased tissue within the confines of the device. Electrical, thermal and radiating therapeutic devices are incorporated herein. Tissue treated in this manner could be desiccated and rendered inert and of a reduced size for more easy removal. Furthermore, healthy tissue outside the sheath is protected against contamination by pathological tissue being removed or accessed by the sheath. Such protection of healthy tissue is especially important in the case of malignant or carcinogenic tissue being removed through the sheath so that potential spread of the disease is minimized.  
         [0065]     As described above, the access sheath may comprise an axially elongate structure having a proximal end and a distal end. The axially elongate structure further has a 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 surgeon. The distal end of the device is that end is closest to the patient or 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. A direction that is defined as being anatomically proximal is closer to the heart and further from the exterior of the patient. A direction that is defined as being anatomically distal is further from the heart and closer to the exterior of the patient. Anatomically proximal and distal are often the opposite of being proximal and distal as defined relative to a surgical or endoluminal instrument and are defined as such for the purposes of this disclosure.  
         [0066]     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. For example, the sheath  10  may include instruments affixed integrally to the interior central lumen  26 , rather than being separately inserted, for performing therapeutic or diagnostic functions. 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.  
         [0067]     It also should be noted that certain objects and advantages of the invention have been described above for the purpose of describing the invention and the advantages achieved over the prior art. Of course, it is to be understood that not necessarily all such objects or 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 or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.  
         [0068]     Moreover, although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. For example, it is contemplated that various combination or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, as mentioned above, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.