Patent Publication Number: US-2006020164-A1

Title: Evertable insertion tube for colonoscope

Description:
RELATED APPLICATIONS  
      This application is a continuation application of PCT application PCT/IE2003/000110, filed Aug. 6, 2003 and which claimed priority to Ireland Patent Application Nos. 2002/0658 and 2002/0656 both filed Aug. 6, 2002, the contents of all which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      This invention relates to a guide device for assisting advancement of a probe through a passageway by maintaining the probe spaced from the interior walls of the passageway during advancement of the probe through the passageway. In particular this invention relates to a guide device which facilitates enhanced vision during probe advancement, especially in a tortuous passageway such as the colon.  
     BACKGROUND OF THE INVENTION  
      Conventional colonoscopy procedures involve advancing a colonoscope through the floppy sigmoid colon to the proximal end of the descending colon.  
      However, advancing a colonoscope through the sigmoid colon generally causes loops to form in the floppy sigmoid colon, and stretches the mesentery to which the sigmoid colon is attached. This results in considerable pain and discomfort for the patient.  
      It is known to use an everting tube to advance a probe through a passageway. For example, U.S. Pat. No. 4,321,915 describes such a flexible, everting tube. By applying a fluid pressure to the tube, a fibre optic tool extending through the tube is gripped and pulled along by the tube as it everts. One problem with known guide devices of this type is that because of the tube eversion action, a tool extending through the tube advances at twice the rate of the tube. Thus, the tip of the tool extends beyond the leading edge of the everting tube. U.S. Pat. No. 4,321,915 describes applying a suction to the tube when the tip of the tool has extended a distance beyond the leading edge of the tube. The suction causes the tube to disengage from the tool and allows an operator to manually retract the tool into the tube.  
      This procedure is generally inconvenient and inefficient, especially when navigating tortuous passageways such as the colon.  
      The lower gastrointestinal tract comprises the rectum, and the large intestine or colon. The colon, in a textbook arrangement of the human anatomy, extends upwards from the lower right quadrant, traverses the width of the body just below the diaphragm, travels downwards along the left side of the abdomen and then loops in an anterior retrograde manner before linking up with the rectum and the anus.  
      Even in such a textbook arrangement, the large intestine is difficult to cannulate with a colonoscope due to the flexible nature of the colonoscope and the floppy nature of the colon. This is even more difficult with the more realistic anatomies of actual people.  
      In some people, the sigmoid colon can be very long and is unfixed, except by its mesentery, and so can be extremely difficult to cannulate due to its predisposition to form loops when a colonoscope is pushed through it. Looping of the colonoscope within the sigmoid colon and transverse colon exacerbates the problems in traversing these areas.  
      Conventional colonoscopy procedures involve advancing a colonoscope through the floppy sigmoid colon to the proximal end of the descending colon. During advancement of the colonoscope through the sigmoid colon loops often form. It is difficult to then advance the colonoscope further, due to the looped nature of the sigmoid colon. Further pushing of the colonoscope simply increases the loops in the sigmoid colon without advancing the colonoscope into the descending colon.  
      The sigmoid colon is generally straightened by manipulation of the colonoscope. However advancing the colonoscope further, into the descending colon may cause the loops in the floppy sigmoid colon to reform.  
      It is known to use an overtube to prevent the reformation of loops by splinting the straightened sigmoid colon. The overtube is typically advanced over the colonoscope until the distal end of the overtube is at the proximal end of the descending colon. The overtube then maintains the sigmoid colon in the straightened configuration and prevents loops from reforming in the sigmoid colon during advancement of the colonoscope further, into the descending colon.  
      However, due to the potentially tortuous path through a colon, it is often difficult to advance an overtube over a colonoscope without kinking of the overtube occurring.  
      Furthermore, parts of the interior wall of a colon may become trapped between a colonoscope and an overtube during advancement of the overtube over the colonoscope. This may result in shearing off of the trapped part of the colon wall or puncturing of the colon wall.  
      In addition, in certain colonoscopy procedures, for example a multiple polypectomy, it is necessary to insert and remove a colonoscope several times. This requires considerable skill on the part of the colonoscopist and takes a considerable length of time.  
     SUMMARY OF THE INVENTION  
      According to the invention there is provided an evertable tube having a lumen therethrough, an inflation port for inflating the tube, and a self-closing valve at the inflation port.  
      In one embodiment of the invention, the valve comprises a sheath extending from the port along a wall of the tube.  
      The sheath may extend substantially parallel to the longitudinal axis of the tube.  
      In one case, the sheath is fixed to the wall of the tube. In one embodiment, the sheath is integral with the wall of the tube. The sheath may be of the same material as the wall of the tube.  
      In another embodiment, the tube has two or more inflation ports. The tube may be a self-closing valve at each inflation port.  
      The tube may be at least partially twisted. In one case, the tube comprises means for adjusting the twist in the tube. The tube comprises a substantially cylindrical outer sleeve section and a twisted inner sleeve section, the inner sleeve section being of the same untwisted diameter as that of the outer sleeve section.  
      At least a portion of the tube may have a non-linear shape. The tube may be biased into the non-linear shape. The tube may be sculpted or formed into the non-linear shape.  
      In another aspect, the invention provides a guide device for a probe, the device comprising: an evertable tube with a lumen therethrough, the tube being inflatable to grip a probe in the lumen such that the tube everts with advancement of the probe; and means to facilitate pulling a probe back relative to the tube to realign the probe relative to the tube.  
      In one embodiment, the device comprises means to longitudinally stiffen the tube. The stiffening means may comprise at least one bracing column located within the tube.  
      In a further aspect, the invention provides a guide device for a probe, the device comprising: an evertable tube with a lumen therethrough, the tube being inflatable to grip a probe in the lumen such that the tube everts with advancement of the probe; and at least one stiffening column to facilitate moving at least part of the tube distally relative to a probe in the lumen to align an end of the tube with an end of the probe.  
      The column may be tubular and extend co-axially around the lumen.  
      The column may comprise at least one corrugation for kink resistance and the corrugation may extend along the column in a convoluted manner.  
      The corrugation may extend around the column in a loop.  
      In another case, the column has at least one slit through the column wall extending along the column in a spiral.  
      The outer wall of the tube may be connected at each end to the inner wall of the tube to define an enclosed inflation space therebetween.  
      In one case the tube comprises an evertable tube of the invention.  
      The device may comprise stop means to selectively prevent tube eversion. The stop means may comprise a clamp engageable with the tube.  
      The invention provides in one case a guide device for a colonoscope.  
      According to another aspect of the invention, there is provided a probe assembly comprising: a probe; and a guide device for the probe, the device comprising: an evertable tube with a lumen therethrough, the tube being inflatable to grip a probe in the lumen such that the tube everts with advancement of the probe.  
      In one case, the probe comprises means to create a fluid cushion between the probe and the guide device. The probe may comprise one or more fluid openings on an outer surface of the probe for ejecting fluid therethrough to create the fluid cushion. The probe may also comprise a fluid inlet lumen in communication with the openings for passage of a fluid through the lumen and out through the openings. The probe may comprise a fluid exhaust lumen for passage of a fluid through the lumen.  
      The tube may comprise an evertable tube.  
      The device may comprise a guide device.  
      In one case the probe comprises a colonoscope.  
      In another aspect of the invention, there is provided a device for straightening a looped section of a passageway, the device comprising: an anchor for anchoring an interior wall of a passageway to the anchor; and means for advancing the anchor through a passageway.  
      In one embodiment, the anchor is movable outwardly to anchor an interior wall of a passageway to the anchor by exerting outward pressure on the interior wall of the passageway. At least part of the anchor may be inflatable.  
      The anchor may comprise an evertable tube. In one case, the tube comprises an evertable tube.  
      The anchor may comprise a guide device.  
      In one case, the means for advancing the anchor comprises a probe.  
      The device may comprise a probe assembly.  
      In one case, the device is suitable for straightening a sigmoid colon.  
      According to a further aspect, the invention provides a method of advancing a probe through a passageway, the method comprising: providing a probe; 
          providing a guide device for the probe, the guide device having a lumen therethrough;     inserting the probe through the lumen of the guide device; inflating the guide device to grip the probe; advancing the probe through the passageway with an associated eversion of the guide device; and retracting the probe relative to the guide device to align the leading end of the guide device with the leading end of the probe.        

      The guide device may be advanced over the probe by pushing the guide device over the probe.  
      The method may comprise releasing a stop means before advancing at least part of the guide device over the probe.  
      The probe may be maintained in a fixed position during the step of advancing at least part of the guide device over the probe.  
      The probe may be advanced through the passageway by pushing the probe through the passageway.  
      In a further aspect, the invention provides a method of advancing a probe through a passageway, the method comprising the steps of: providing a probe; providing a guide device for the probe, the guide device having a lumen therethrough; inserting the probe through the lumen of the guide device; inflating the guide device to grip the probe; pushing the probe to advance the probe through the passageway which causes eversion of the guide device; retracting the probe relative to the guide device to align the leading end of the guide device with the leading end of the probe.  
      In one case, at least part of the guide device is advanced over the probe to align the leading end of the guide device with the leading end of the probe.  
      The probe may be retracted through the lumen to align a leading end of the guide device with a leading end of the probe.  
      The method may comprise moving the guide device out of contact with the probe before retracting the probe relative to the guide device.  
      The invention provides, in another aspect, a method of advancing a probe through a passageway, the method comprising: providing a probe; providing a guide device for the probe, the guide device having a lumen therethrough; inserting the probe through the lumen of the guide device; inflating the guide device to grip the probe; advancing the probe through the passageway with an associated eversion of the guide device; moving the guide device out of contact with the probe; and moving at least part of the guide device distally relative to the probe to align the leading end of the guide device with the leading end of the probe.  
      In one case, the guide device is moved out of contact with the probe by deflating the guide device.  
      The guide device may be moved out of contact with the probe by creating a fluid cushion between the guide claim and the probe.  
      The method may comprise releasing a stop means before eversion of the guide device.  
      At least some of the steps may be repeated to advance the probe in an incremental manner through the passageway.  
      In one case, the method is suitable for advancing a colonoscope through a colon.  
      The invention provides, in a further aspect, a method of straightening a looped section of a passageway, the method comprising: providing an anchoring device; advancing the anchoring device through the passageway; anchoring the interior wall of the passageway to the anchoring device; and moving the anchoring device proximally to at least partially straighten the section of the passageway.  
      In one case, the anchoring device exerts outward pressure on the interior wall of the passageway to anchor the interior wall of the passageway to the anchoring device.  
      The interior wall of the passageway may be anchored to the anchoring device during advancement of the anchoring device through the passageway.  
      The anchoring device may evert during advancement through the passageway.  
      At least some of the steps may be repeated to straighten the looped section of the passageway in an incremental manner.  
      The method may be a method of straightening a sigmoid colon.  
      According to the invention, there is also provided a method of performing a colonoscopy procedure, the method comprising: inserting a colonoscope into a colon; inserting a colonic overtube into the colon; advancing the colonoscope through a floppy section of the colon; straightening the floppy section of the colon; advancing the colonic overtube over the colonoscope through the floppy section of the colon; and advancing the colonoscope distally of the straightened section of the colon.  
      In one embodiment of the invention, m the floppy section of the colon is straightened by manipulating the colonoscope and/or the colonic overtube from externally of the colon.  
      The colonic overtube may be advanced distally of the straightened section of the colon.  
      In another aspect, the invention provides a method of performing a colonoscopy procedure, the method comprising: inserting a colonoscope into a colon; inserting a colonic overtube into the colon; advancing the colonoscope through a floppy section of the colon; advancing the colonic overtube over the colonoscope through the floppy section of the colon; and advancing the colonoscope distally of the floppy section of the colon.  
      In one case, the colonic overtube is advanced distally of the floppy section of the colon.  
      The floppy section of the colon may comprise the transverse colon.  
      According to a further aspect of the invention, there is provided a method of performing a colonoscopy procedure, the method comprising: inserting a colonoscope into a colon; inserting a colonic overtube into the colon; advancing the colonoscope around a bend in the colon; advancing the colonic overtube over the colonoscope around the bend in the colon; and advancing the colonoscope distally of the bend in the colon.  
      In one embodiment, the colonic overtube remains in a fixed position during advancement of the colonoscope distally of the bend in the colon.  
      The bend may comprise the splenic flexure.  
      In another embodiment, the method comprises withdrawing the colonoscope from the colon while the colonic overtube remains in place in the colon. The method may comprise advancing a medical device through the colonic overtube to access a point in the colon distally of the colonic overtube.  
      The method may comprise mounting the colonic overtube to the colonoscope before inserting the colonoscope into the colon.  
      The colonic overtube may be advanced by extending at least part of the colonic overtube from a shortened configuration to an elongated configuration.  
      In another case the colonic overtube is advanced by pushing the colonic overtube from externally of the colon.  
      The laterally flexible nature of the colonic overtube enables the overtube to advance through a potentially tortuous path in a colon without kinking. This is particularly advantageous when the overtube is being advanced through a sharp bend in the colon, for example, when advancing the overtube through the splenic or hepatic flexures or through parts of the sigmoid colon.  
      The colonic overtube has a flexible seal at the distal end of the overtube. The seal ensures that no parts of the colon wall become trapped between the overtube and the colonoscope during advancement of the overtube over the colonoscope. This arrangement prevents shearing off of the trapped part of the colon wall or puncturing of the colon wall.  
      In some colonoscopy procedures, air or some other gas is used to insufflate the colon, for example, to blow a protruding piece of the wall of the colon laterally to clear a path for advancement of the overtube and/or the colonoscope further distally through the colon. A further advantage of the seal is that it prevents insufflation air from leaking proximally out of the colon between the colonoscope and overtube.  
      In addition, the flexible nature of the seal enables the seal to adapt to the size of the colonoscope to achieve an effective seal between the overtube and the colonoscope for a variety of differently sized colonoscopes.  
      Because the colonic overtube is of a thermally stable material, the stiffness of the overtube may be chosen to be sufficiently flexible for ease of insertion into a colon, and to remain sufficiently stiff within the colon to maintain a section of the colon, such as the sigmoid colon, in a straightened configuration.  
      The colonic overtube provides an ergonomic and easily workable means of cannulating the colon as far distally as the caecum, without requiring a long, awkward length of tubing externally of the colon.  
      The rounded tip at the distal end of the colonic overtube ensures that the overtube advances atraumatically through the colon. Any inadvertent contact between the distal end of the overtube and the interior wall of the colon will not result in damage or trauma to the colon.  
      The colonic overtube provides a bridge between the fixed rectum and the fixed descending colon over the floppy sigmoid colon, thus preventing loops from reforming in the sigmoid colon. Furthermore, the colonic overtube provides a bridge between the fixed descending colon and the fixed ascending colon over the floppy transverse colon, thus preventing loops from reforming in the transverse colon. By using the overtube of the invention, advancement of a colonoscope through a colon as far as the caecum may be achieved easier and quicker, and causes less discomfort to a patient.  
      For an overtube to successfully splint a straightened sigmoid colon, its stiffness must be above the minimum threshold of stiffness required to prevent sigmoid loops from re-forming as the colonoscope is passed through the colonoscope lumen, and advanced further into the colon.  
      However it is also desirable that the overtube is not overly stiff, as insertion of the overtube becomes more difficult due to friction as the stiffness increases. This is because a “straightened” sigmoid colon is never perfectly straight. Consequently it is almost impossible to introduce a completely rigid overtube over the colonoscope. Some degree of compliance is required by the overtube.  
      While an overtube measured at room temperature may appear stiff enough to successfully splint a straightened sigmoid colon, this may no longer be the case at body temperature. Known overtube materials show a dramatic drop in stiffness between ambient room temperature and body temperature. In order for an overtube made from such materials to splint the sigmoid colon, it will have to be made overly rigid, so that it is still above the minimum threshold of stiffness required to prevent sigmoid loops from re-forming at body temperature. This excess rigidity causes serious insertion difficulties due to friction. Alternatively, if an overtube made from such materials was made less stiff, it may be easier to insert, but may not be stiff enough at body temperature to successfully splint the straightened sigmoid colon.  
      The colonic overtube described herein is configured to be relatively thermally stable. In this way the overtube at room temperature (insertion temperature) is selected to be sufficiently compliant or floppy to be easily inserted into a colon over a colonoscope. There is then a minimal drop in stiffness between ambient room temperature and body temperature compared to other materials, so that at body temperature the overtube is above the minimum threshold of stiffness required to prevent sigmoid loops from reforming.  
      Two other features of the overtube aid the insertion process: (a) corrugations, which minimize frictional contact with the scope; and (b) extremely low friction PTFE material used in its construction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which:  
       FIG. 1  is a perspective view of a guide device according to the invention in a deflated configuration;  
       FIG. 2  is a perspective view of the guide device of  FIG. 1  in an inflated configuration;  
       FIG. 3  is a side, cross-sectional view of the guide device of  FIG. 1  in the deflated configuration;  
       FIG. 4  is a side, cross-sectional view of the guide device of  FIG. 1  in the inflated configuration;  
      FIGS.  5  to  8  are views similar to FIGS.  1  to  4  of a probe extending through a lumen of the guide device of  FIG. 1 ;  
       FIG. 9  is a side, partially cross-sectional view of a stiffening column of the guide device of  FIG. 1 ;  
       FIGS. 10 and 11  are side views of other stiffening columns;  
      FIGS.  12  to  20  are side, partially cross-sectional views illustrating advancement of the probe of FIGS.  5  to  8  through a passageway using the guide device of  FIG. 1 ;  
      FIGS.  21  to  28  are perspective views illustrating schematically advancement of the probe of FIGS.  5  to  8  through a curved passageway using the guide device of  FIG. 1 ;  
      FIGS.  29  to  33  are partially cross-sectional, side views illustrating advancement of another probe according to the invention through a passageway using the guide device of  FIG. 1 ;  
       FIGS. 34 and 35  are partially cross-sectional, side views illustrating advancement of a further probe according to the invention through a passageway using the guide device of  FIG. 1 ;  
      FIGS.  36  to  48  are schematic views illustrating straightening of a sigmoid colon using the probe of  FIGS. 34 and 35  and the guide device of  FIG. 1 ;  
       FIG. 49  is a perspective view of a vision system;  
       FIG. 50  is a perspective view of an evertable tube according to the invention;  
       FIG. 51  is a plan view of the tube of  FIG. 50 ;  
       FIGS. 52 and 53  are partially cross-sectional, side views of the tube of  FIG. 50  in use;  
       FIG. 54  is a plan view of another evertable tube according to the invention;  
       FIG. 55  is a perspective view of a colonic overtube;  
       FIG. 56  is a partially cross-sectional, side view of a distal end of the overtube of  FIG. 55 ;  
      FIGS.  57  to  61  are partially cross-sectional, side views illustrating manufacture of the overtube of  FIG. 56 ;  
       FIG. 62  is a schematic view illustrating lubrication of the overtube of  FIGS. 55 and 56 ;  
       FIGS. 63 and 64  are perspective views of a colonoscope extending through the overtube of  FIG. 55 ;  
       FIG. 65  is a schematic view of a colon;  
      FIGS.  66  to  75  are schematic views of the colonoscope and overtube of  FIGS. 63 and 64  in use in the colon of  FIG. 65 ;  
       FIG. 76  is a partially cross-sectional, side view of the colonoscope of  FIG. 63  advancing through the overtube of  FIG. 63 ;  
       FIG. 77  is an enlarged, partially cross-sectional, side view of part of the colonoscope and overtube of  FIG. 76 ;  
       FIG. 78  is a partially cross-sectional, side view of the colonoscope of  FIG. 77  advancing through another colonic overtube;  
       FIGS. 79 and 80  are partially cut-away, perspective views of other colonic overtubes;  
       FIG. 81  is a perspective view of the colonoscope and overtube of  FIG. 63  with a limiting means mounted to the overtube;  
       FIGS. 82 and 83  are partially cross-sectional, side views of the colonoscope, overtube and limiting means of  FIG. 81 ;  
       FIG. 84  is a partially cross-sectional, side view of another colonic overtube;  
      FIGS.  85  to  90  are schematic views illustrating a method of performing a colonoscopy according to the invention using another colonic overtube;  
       FIG. 91  is a schematic view illustrating another method of performing a colonoscopy according to the invention using the overtube of FIGS.  85  to  90 ; and  
       FIG. 92  is a perspective view of a distal end of a further colonic overtube. 
    
    
     DETAILED DESCRIPTION  
      Referring to the drawings there is illustrated a guide device  1  according to the invention. The guide device  1  is suitable for assisting advancement of a probe  7 , such as a colonoscope, through a passageway, such as a body cavity  11 , for example the colon.  
      The device  1  comprises an evertable tube  3  with a central lumen  8  therethrough. The tube  3  can be inflated to grip the probe  7  in the lumen  8  such that the tube  3  will evert with advancement of the probe  7 . The device  1  further comprises means to facilitate moving at least part of the probe  7  through the tube  3  in the lumen  8  to align an end of the tube  3  with an end of the probe  7 .  
      FIGS.  1  to  28  illustrate a particular embodiment of the device  1 .  
      As illustrated in  FIGS. 3 and 4 , an outer wall  2  of the evertable tube  3  is connected at each end to an inner wall  4  of the tube  3 , such that an enclosed inflation space  5  is defined between the walls  3 ,  4 .  
      In this case, the device  1  has a tubular stiffening column  6 , as illustrated in  FIG. 9 , to longitudinally stiffen the flexible tube  3 . In this way, the stiffened device  1  may be advanced over the probe  7  in the lumen  8  when the tube  3  is deflated. The stiffening column  6  is located within the inflation space  5 , and extends co-axially around the lumen  8 .  
      In use, the probe  7  is inserted through the lumen  8  of the deflated tube  3  until the leading or distal end  9  of the probe  7  is aligned with the leading or distal end  10  of the guide device  1 . The tube  3  is then inflated to grip the probe  7 , and the probe  7  and guide device  1  are now ready for insertion into the passageway  11  ( FIG. 12 ).  
      The probe  7  is advanced through the passageway  11  by pushing the probe  7  distally. Because the inflated tube  3  grips the probe  7 , the tube  3  everts as the probe  7  advances distally through the passageway  11  ( FIGS. 13 and 14 ).  
      The inflated tube  3  acts as a spacing means to prevent the probe  7  from engaging against the interior walls of the passageway  11  as the probe  7  advances through the passageway  11 . In this manner, the probe  7  advances through the passageway  11  with a frictionless rolling action of the guide device  1  and with substantially no frictional contact between the probe  7  and the passageway  11 .  
      As illustrated in FIGS.  12  to  14 , due to the everting action of the guide device  1  with the probe  7 , the leading end  9  of the probe  7  travels twice the distance of the leading end  10  of the guide device  1 . Thus, the probe leading end  9  projects distally from the guide device  1 .  
      To realign the two leading ends  9 ,  10 , the tube  3  is deflated so that the probe  7  is no longer gripped by the tube  3  ( FIG. 15 ), but there is still a central stiffening column  6  within the deflated tube  3 . This allows the probe  7  to be retracted through the lumen  8  of the tube  3  until the leading ends  9 ,  10  are aligned ( FIG. 16 ).  
      The tube  3  is re-inflated ( FIG. 17 ), and the probe  7  is further advanced through the passageway  11  by pushing the probe  7  distally ( FIG. 18 ).  
      The steps described above with reference to FIGS.  15  to  18  may be repeated as desired by the user to advance the probe  7  through the passageway  11  in an incremental manner.  
      In this way, the probe  7  advances through the passageway  11  in a “2 steps forward—1 step back” manner.  
      It will be appreciated that the guide device  1  may alternatively be advanced over the probe  7  when the tube  3  is deflated to align the leading end  10  of the guide device  1  with the leading end  9  of the probe  7 , as illustrated in  FIGS. 19 and 20 . In this case, the probe  7  is maintained in a fixed position during realignment of the leading ends  9 ,  10 .  
      Realignment of the leading ends  9 ,  10  by advancing the guide device  1  over the probe  7  has the advantage that all movement of the guide device  1  and the probe  7  is in the distal direction through the passageway  11 . This provides for a smooth advancement procedure, which can be of particular importance when the probe is being advanced through a floppy or flexible passageway, such as a colon.  
      The guide device  1  is suitable for assisting the advancement of the probe  7  through curved or tortuous passageways such as illustrated in FIGS.  21  to  28 .  
      FIGS.  21  to  28  illustrate advancement of the probe  7  through a curved passageway. The leading end  9  of the probe  7  can be aligned with the leading end  10  of the guide device  1  by retracting the probe  7  through the lumen  8  of the deflated tube  3  (FIGS.  21  to  24 ), or by advancing the deflated guide device  1  over the probe  7  (FIGS.  25  to  28 ), in a manner similar to that described previously with reference to FIGS.  12  to  20 .  
      The stiffening column  6  may be a simple tube as illustrated in  FIG. 9 . Alternatively the stiffening column  21  may comprise at least one corrugation  20  on the column  21  to resist kinking of the column  21  as the guide device  1  bends around a curve in the passageway. The corrugation  20  may extend along the column  21  in a convoluted manner, as illustrated in the column  21  of  FIG. 10 , or the corrugation may extend around the column  21  in a loop.  
      A further alternative is illustrated in  FIG. 11 , in which a stiffening column  22  has a slit  23  through the column wall, the slit extending along the column  22  in a spiral. The slit column  22  is normally flexible such that when the tube  3  is in the inflated configuration, the column  22  provides minimum resistance to eversion of the tube  3  and minimum resistance to bending of the guide device  1  through the passageway. However, when the tube  3  is deflated it has been found that the column  22  becomes much stiffer, and thus it is relatively easy to manipulate the guide device  1  and the probe  7  to align the leading ends  9 ,  10 , as described above.  
      It will be appreciated that a clamp may be provided to engage with an outer wall or an inner wall of the tube to selectively prevent tube eversion, and/or to selectively prevent advancement of the guide device over a probe in the lumen.  
      Referring to FIGS.  29  to  33  there is illustrated another probe  30  according to the invention in use with the guide device  1  described previously with reference to FIGS.  1  to  28 .  
      The probe  30  comprises a plurality of fluid openings  31  on an outer surface of the probe  30  for ejecting a fluid, such as air, through the openings  31 . A fluid inlet lumen is provided extending through the probe  30  in communication with the openings  31  to facilitate passage of air from externally of the passageway  11 , through the fluid inlet lumen and out through the openings  31 , as illustrated in  FIGS. 30 and 31 . In this manner a fluid cushion may be created between the probe  30  and the guide device  1  to move the device  1  out of contact with the probe  30  without deflating the tube  3 .  
      In use, the probe  7  is advanced through the passageway  11  with the associated eversion of the tube  3  ( FIG. 29 ), in a manner similar to that described previously with reference to FIGS.  12  to  14 .  
      To realign the two leading ends  9 ,  10 , air is passed from externally of the passageway  11 , through the fluid inlet lumen of the probe  30 , and out through the openings  31  ( FIGS. 30 and 31 ). The air exiting the openings  31  pushes the guide device  1  out of contact with the probe  30  to create a cushion of air in the central lumen  8  between the probe  30  and the device  1 .  
      Because the guide device  1  is now out of contact with the probe  30 , this enables the probe  30  to be retracted through the lumen  8  of the tube  3  until the leading ends  9 ,  10  are aligned ( FIG. 32 ).  
      The passage of air out through the openings  31  is then ceased. This causes the cushion of air between the probe  30  and the device  1  to disperse, and the tube  3  grips the probe  30  again.  
      The steps described above with reference to FIGS.  29  to  32  may be repeated as desired by the user to advance the probe  30  through the passageway  11  in an incremental manner. In this way the probe  30  advances through the passageway  11  in a “2 steps forward—1 step back” manner.  
      It will be appreciated that the guide device  1  may alternatively be advanced over the probe  30  while the air cushion is between the probe  30  and the device  1  to align the leading end  10  of the device  1  with the leading end  9  of the probe  30 . In this case the probe  30  is maintained in a fixed position during realignment of the leading ends  9 ,  10 .  
      It is not necessary for the tube  3  to be deflated to align the leading end  9  of the probe  30  with the leading end  10  of the guide device  1 .  
      Thus the inflated tube  3  maintains a grip on the wall of the passageway  11 . This may be particularly advantageous in the case where the inflated tube  3  is pulled back while gripping the wall of a colon to at least partially straighten a previously looped section of colon, such as the sigmoid colon.  
      Depending on a number of factors, such as the volume of the passageway  11 , the volumetric flow rate of the air, the duration of time for which air is passed out through the fluid openings  31 , the passageway  11  may in certain circumstances become distended or bloated as a result of the air being passed out through the fluid openings  31 , as illustrated in  FIG. 33 . In the case when the passageway  11  is a colon, this is a potentially painful and/or dangerous occurrence.  
      In  FIGS. 34 and 35  there is illustrated another probe  40  according to the invention, which is similar to the probe  30  of FIGS.  29  to  33 , and similar elements in  FIGS. 34 and 35  are assigned the same reference numerals.  
      In this case, the probe  40  comprises a fluid exhaust lumen  41  extending therethrough. In this manner the fluid exhaust lumen  41  provides a means for any excess air in the passageway  11  to escape from the passageway  11 , thereby preventing the passageway  11  from becoming distended or bloated. In particular it is not necessary for the tube  3  to be deflated, or for the cushion of air between the probe  40  and the guide device  1  to be dispersed to enable the excess air in the passageway  11  to escape.  
      Suction may be applied to the fluid exhaust lumen  41  to further assist in the removal of excess air from within the passageway  11 .  
      It will be understood that fluids other than air may alternatively be used to create the fluid cushion between the probe and the guide device. For example water could be used to create the fluid cushion.  
      FIGS.  36  to  48  illustrate the guide device  1  and the probe  40  being used to straighten a looped sigmoid colon  50 . The probe  40  may in one case be a colonoscope for advancement through a colon.  
      The probe  40  is first inserted through the lumen  8  of the deflated tube  3  until the leading end  9  of the probe  40  is aligned with the leading end  10  of the guide device  1 . The tube  3  is then inflated to grip the probe  40 , and the probe  40  and the guide device  1  are now ready for insertion into the anus  51  of the patient ( FIG. 36 ).  
      The probe  40  is advanced through the rectum  52  by pushing the probe  40 . Because the inflated tube  3  grips the probe  40 , the tube  3  everts as the probe  40  advances distally through the rectum  52  ( FIG. 37 ).  
      The inflated tube  3  also grips the interior wall of the colon, thereby anchoring the interior wall of the colon to the guide device  1 .  
      To realign the leading ends  9 ,  10 , air is passed from externally of the colon, through the fluid inlet lumen of the probe  40 , and out through the openings  31  to create the cushion of air between the probe  40  and the guide device  1 .  
      The probe  40  is then retracted through the lumen  8  of the tube  3  while maintaining the position of the guide device  1  fixed until the leading ends  9 ,  10  are aligned ( FIG. 38 ). The passage of air out through the openings  31  is ceased and the tube  3  re-grips the probe  40 .  
      The steps of advancement of the probe  40  and realignment of the leading ends  9 ,  10  may be repeated in an incremental manner ( FIGS. 39 and 40 ) to advance the probe  40  through the rectum  52  to the proximal end of the sigmoid colon  50 .  
      Next, the probe  40  and the guide device  1  are both retracted. Because the interior wall of the colon is anchored to the guide device  1 , this action causes part of the wall of the colon to be accordioned down, and thereby causes the sigmoid colon  50  to be partially straightened ( FIG. 41 ). During this straightening step there is no cushion of air between the probe  40  and the guide device  1 , and the tube  3  grips the probe  40 .  
      The steps of advancement of the probe  40  and realignment of the leading ends  9 ,  10  may be repeated in an incremental manner (FIGS.  42  to  45 ) to advance the probe  40  further through the partially straightened sigmoid colon  50 . The probe  40  and the guide device  1  are then retracted to accordion down a further part of the wall of the colon, and thereby further straighten the sigmoid colon  50  ( FIG. 46 ).  
      This process of advancement of the probe  40 , realignment of the leading ends  9 ,  10 , and straightening of the sigmoid colon  50  may be repeated in an incremental manner until the leading end  10  of the guide device  1  has reached the proximal end of the descending colon  53  and the sigmoid colon  50  has been fully straightened ( FIG. 47 ).  
      The guide device  1  and the probe  40  may be used to collapse the sigmoid colon of a patient to a reduced, straightened configuration substantially without causing stretching of the colon and the mesentery to which the colon is attached, and causing the resultant pain and discomfort to the patient.  
      It is not necessary to advance the probe  40  all the way through the sigmoid colon to the proximal end of the descending colon before beginning the reduction of the sigmoid colon using the guide device  1  and the probe  40 .  
      Because the tube  3  is not deflated upon realignment of the leading ends  9 ,  10 , this ensures that the grip exerted by the inflated tube  3  on the interior wall of the colon is maintained throughout the straightening procedure. In particular, the accordioned part of the colon wall will remain accordioned down during realignment of the leading ends  9 ,  10 .  
      The process of advancement of the probe  40 , realignment of the leading ends  9 ,  10 , and straightening of the sigmoid colon  50  involves the steps of advancement of the probe  40 , retraction of the probe  40 , retraction of the guide device  1  and passing air through the fluid inlet lumen of the probe  40  repeated in a desired sequence. This process could therefore be automated in certain cases to achieve straightening of the colon in a relatively fast, painless manner.  
      When the leading end  10  of the guide device  1  has reached the proximal end of the descending colon  53 , the tube  3  is deflated. The probe  40  may then be advanced further distally through the descending colon  53  ( FIG. 48 ) and into the transverse colon. The stiffening column  6  of the guide device  1  acts as a splint to maintain the sigmoid colon  50  in the straightened configuration. The splinting column  6  ensures that further advancement of the probe  40  through the descending colon  53  and into the transverse colon is possible by preventing loops from reforming in the sigmoid colon  50 . In this manner, the column  6  minimises the pain or discomfort experienced by the patient during this procedure.  
      In this regard the stiffening column  6  is similar to the colonic overtube described in International patent application number PCT/IE02/00029, the relevant contents of which are incorporated herein by reference.  
      Means may be provided for opening up or ripping the tube  3  to enable the user to remove the tube  3  from the colon while the stiffening column  6  remains in position splinting the straightened sigmoid colon  50 .  
      It has been found that by straightening the sigmoid colon  50  using the guide device  1  as described previously with reference to FIGS.  36  to  48 , manual steering of the probe  40  during the incremental advancement through the colon is not required. Thus, an alternative vision system  60 , as illustrated in  FIG. 49 , could be used with the guide device  1  to straighten the sigmoid colon  50 .  
      The vision system  60  comprises a head  61  containing the viewing/lighting means to facilitate visualisation of the colon, and a thin body  62 .  
      Because steering capabilities are not required for the vision system  60 , the body  62  has a particularly small diameter for ease of retraction through the lumen  8  of the tube  3  for realignment of the leading ends  9 ,  10 . In addition the body  62  may be of a low friction material for ease of retraction through the lumen  8  of the tube  3 .  
      The head  61  may be similar to a video pill.  
      Referring to FIGS.  50  to  53  there is illustrated an evertable tube  70  according to the invention, which is similar to the tube  3  of the guide device  1  of FIGS.  1  to  28 , and similar elements in FIGS.  50  to  53  are assigned the same reference numerals.  
      In this case no stiffening column is provided within the inflation space  5 .  
      The tube  70  has an inflation port  71  for inflating the tube  70  to grip a member, such as a probe, in the lumen  8 . Advancement of the member, for example through a colon, will then cause eversion of the tube  70 . In this case the inflation port  71  is provided in the form of an aperture in the outer wall  2  of the tube  70 .  
      A sheath  72  is fixedly attached to the outer wall  2  of the tube  70  by welding three sides  73 ,  74 ,  75  of the sheath  72  to the wall  2 . The sheath  72  extends from the inflation port  71  along the wall  2  of the tube  70  parallel to the longitudinal axis of the tube  70  to an open end  76  of the sheath  72 .  
      To inflate the tube  70 , air is passed, for example using a hand pump  77 , through the open end  76  of the sheath  72 , along the sheath  72  between the wall  2  of the tube  70  and the sheath  72 , through the inflation port  71  and into the inflation space  5  ( FIG. 52 ).  
      When the tube  70  has been inflated, the pump  77  is removed from the open end  76  of the sheath  72 . The air pressure A within the inflation space  5  acting on the wall  2  of the tube  70 , and the atmospheric pressure B acting on the sheath  72  combine to press the sheath  72  tightly against the wall  2  of the tube  70  ( FIG. 53 ).  
      In this manner the sheath  72  acts as a self-closing valve to prevent leakage of air from within the inflation space  5  out through the inflation port  71 .  
      In addition the low-profile sheath  4  presses tightly against the wall  2  of the tube  70  when the tube  70  is inflated, as illustrated in  FIGS. 50 and 53 . This ensures complete eversion of the tube  70  is possible.  
      It will be appreciated that the sheath  72  may be fixed to the wall  2  of the tube  70  by any suitable means, such as by adhesive bonding. The sheath  72  may alternatively be integrally formed with the wall  2 .  
      The fixing means may be reinforced in the region of the open end  76  of the sheath  72 .  
      The sheath  72  may be of the same or a different material to the wall  2  of the tube  70 .  
      More than one inflation port  71  may be provided in the wall  2 , as illustrated in the evertable tube  80  of  FIG. 54 . At each inflation port  71  a self-closing sheath valve  72  is preferably provided.  
      Because of the everting motion of the tube  80 , the inflation ports  71  move from being on the outer surface of the tube  80  into the lumen  8  along the inner surface of the tube  80 . By providing more than one inflation port  71 , this increases the possibility of a port  71  being located along the outer surface of the tube  80  when it is desired to inflate the tube  80 . In particular in certain circumstances it may be essential to inflate or deflate the tube  80  without everting or moving the tube  80 , for example when the tube  80  is in situ in a colon. In such cases the multi-inflation port configuration of the tube  80  is particularly advantageous for providing easy and fast access to an inflation port  71 .  
      It is to be understood that in another case a stiffening column may be located within the inflation space  5  of the tube  70 . In this case the tube  70  and stiffening column may be used as a guide device in a manner similar to the guide device  1  described previously.  
      It will be appreciated that the inflation port configuration described with reference to FIGS.  50  to  53  may be applied with a variety of inflatable evertable devices, such as an exsanguinator, an invaginator, an introducer device, or a hand-access device to allow surgical procedure to be converted from an open procedure into a hand-assisted laparoscopic procedure.  
      The invention is not limited to the embodiments hereinbefore described, with reference to the accompanying drawings, which may be varied in construction and detail.  
      Referring to the drawings and initially to FIGS.  55  to  77  thereof, there is illustrated a colonic overtube  101  suitable for use in a method of performing a colonoscopy according to the invention. The overtube  101  may be used to maintain a section of a colon, such as a transverse colon or a sigmoid colon, in a straightened configuration.  
      The overtube  101  has a proximal end  102  for location, in use, externally of a colon, and a distal end  103  for insertion into a colon. A typical length for the overtube  101  is 0.5 m.  
      A colonoscope lumen  104  extends through the overtube  101  to facilitate passing the overtube  101  over a colonoscope. At least a portion of the overtube  101  is laterally flexible. In this manner the overtube  101  may flex substantially without kinking during advancement of the overtube  101  through a colon. In this case and as illustrated in  FIGS. 55 and 56 , the overtube  101  defines a corrugation  105  which is convoluted, the corrugation  105  extending along the entire length of the overtube  101  from the proximal end  102  to the distal end  103 . The corrugated configuration of the overtube  101  minimises the possibility of the overtube  101  kinking as the overtube  101  is advanced over a colonoscope through a colon. As illustrated in particular in  FIG. 56 , in this case the corrugation  105  is provided on both the interior surface and the exterior surface of the overtube  101 .  
      A flexible seal is provided at the distal end  103  of the overtube  101  for sealing between the overtube  101  and a colonoscope extending through the colonoscope lumen  104 . The seal is in the form of a tubular sheath  106  of film material, in this case silicone, which is fixed to an exterior surface of the overtube  101  at the distal end  103  of the overtube  101  by means of a section of heat-shrink tubing  107 . As illustrated in  FIG. 56 , the sheath  106  extends inwardly at the distal end  103  of the overtube  101  for sealing between the overtube  101  and a colonoscope, and then distally of the distal end  103  of the overtube  101 .  
      The sealing sheath  106  can evert from this distally extending configuration to a proximally extending configuration upon movement of the colonoscope relative to the overtube  101 . This ensures a relatively large area of contact between the sheath  106  and the colonoscope which results in a secure seal between the colonoscope and the overtube  101 .  
      The sheath  106  is folded over to define an inner sealing layer  109 , and an outer sealing layer  108  around the inner sealing layer  109 . The heat-shrink tubing  107  is provided between the inner and outer layers  109 ,  108  ( FIG. 56 ).  
      The flexible nature of the seal  106  enables the seal  106  to adapt itself to the size of the colonoscope extending through the colonoscope lumen  104 . In this manner, a secure, effective seal between the overtube  101  and a colonoscope is achieved regardless of the size diameter range of the colonoscope. In addition, the film seal  106  has a very low profile which facilitates easier passage of the overtube  101  over a colonoscope through a colon, while minimising the resultant discomfort to the patient.  
      The overtube  101  comprises another section of heat-shrink tubing  110  fixed to an exterior surface of the overtube  101  at the distal end  103  of the overtube  101 . The tubing  110  extends around the distal end  103  of the overtube  101  partially into the colonoscope lumen  104  to define a rounded tip at the distal end  103  of the overtube  101 . In this manner, the rounded tip tubing  110  ensures that there are no sharp edges at the distal end  103  of the overtube  101  for atraumatic advancement of the overtube  101  through a colon. The distal end  103  of the overtube  101  may be rounded off in a variety of different ways, such as by a separately mountable tip, or during the manufacturing process.  
      The overtube  101  is of a material which is thermally stable in use in a colon. In this case the thermally stable material used for the overtube  101  is polytetrafluoroethylene (PTFE)  
      In this manner, the overtube  101  is not overly stiff so that insertion of the overtube  101  into a colon, and navigation of the overtube  101  through a colon may be achieved without undue difficulty, and without causing undue discomfort to a patient. However once inserted into the colon, the stiffness of the overtube  101  remains above the minimum threshold of stiffness required to maintain a section of colon in a straightened configuration, and to prevent sigmoid loops from reforming as a colonoscope is passed through the colonoscope lumen  104 .  
      A coating of a lubricious material such as a gel, for example a gel of silicone or polytetrafluoroethylene (PTFE) may be applied around the interior and/or exterior surfaces of the overtube  101  before use for ease of passage of the overtube  101  relative to a colonoscope and/or relative to a colon. Alternatively the coating of lubricious material may be provided as part of the overtube  101 , such as by fixing the coating to the overtube  101 , or by providing the coating integral with the overtube  101 .  
      Manufacture of the overtube  101  will be described with reference to FIGS.  57  to  61 . The overtube  101  is extruded to a typical length of 0.5 m with the convoluted corrugation  105  extending along the overtube  101  from the proximal end  102  to the distal end  103 . The section of heat-shrink tubing  110  is positioned around the distal end  103  of the overtube  101 , partially overlapping the distal end  103 , and a mandrel  111  is partially inserted into the colonoscope lumen  104  from the distal end  103  ( FIG. 57 ). Heat is applied to shrink the tubing  110  down partially onto the exterior surface of the overtube  101  and partially onto the mandrel  111 . The mandrel  111  is moved further into the colonoscope lumen  104  while rotating the mandrel  111  ( FIG. 58 ). By moving the mandrel  111  proximally, the tubing  110  is folded around the distal end  103  of the overtube  101  partially into the colonoscope lumen  104 , and by rotating the mandrel  111 , the tubing  110  is detached from the mandrel  111 . The mandrel  111  is then removed from the colonoscope lumen  104 .  
      A proximal end  112  of the tubular sheath  106  is rolled inwardly, and the sheath  106  is positioned around the distal end  103  of the overtube  101 , partially overlapping the distal end  103 . The tubular sheath  106  has a smaller diameter than the overtube  101 , so the sheath  106  is stretched to position it around the distal end  103  of the overtube  101 . The section of the heat-shrink tubing  107  is positioned around the sheath  106  distally of the rolled proximal end  112  ( FIG. 59 ), and heat is applied to shrink the tubing  107  down onto the sheath  106  to fix the sheath  106  to the exterior surface of the overtube  101  ( FIG. 60 ). The rolled proximal end  112  is then rolled out distally over the tubing  107 , off the distal end  103  of the overtube  101  to define the outer sealing layer  108  around the inner sealing layer  109  ( FIG. 61 ).  
      The assembled colonic overtube  101  is now ready for use. A biocompatible lubricant  113  is liberally applied both externally and internally to the overtube  101  ( FIG. 62 ) to ease passage of the overtube  101  relative to a colonoscope and/or relative to a colon. A colonoscope  114  is inserted into the colonoscope lumen  104  at the proximal end  102  of the overtube  101  and advanced through the lumen  104  until a distal end  115  of the colonoscope  114  emerges from the distal end  103  of the overtube  101  through the sealing sheath  106  ( FIG. 63 ).  
      The colonoscope  114  has a power/light source  116  at a proximal end  117  of the colonoscope  114 , and the overtube  101  is moved proximally over the colonoscope  114  until the proximal end  102  of the overtube  101  is adjacent the power/light source  116  ( FIG. 64 ).  
      The colonoscope  114  is now ready for insertion into the colon of a patient. A typical colon  18  is illustrated in  FIG. 65 , in which the rectum  119  leads from the anus  120  to the sigmoid colon  121 . The redundancy in the sigmoid colon  121  may be seen in  FIG. 65 . The descending colon  122  leads from the sigmoid colon  121  to the transverse colon  123 , and the hepatic flexure  125  links the transverse colon  123  with the ascending colon  126 .  
      The distal end  115  of the colonoscope  114  is inserted through the anus  120  into the rectum  119 , and the colonoscope  114  is advanced into the sigmoid colon  121  ( FIG. 66 ). As the colonoscope  114  advances through the floppy sigmoid colon  121 , a loop may form in the sigmoid colon  121 , which results in stretching of the mesentery  124  to which the sigmoid colon  121  is attached ( FIG. 67 ). When the distal end  115  of the colonoscope  114  reaches the proximal end of the descending colon  122 , the distal end  115  is anchored in the fixed descending colon  122 , and the sigmoid colon  121  is straightened by manipulating the colonoscope  114  ( FIG. 68 . When the sigmoid colon  121  has been straightened, the anchor is released ( FIG. 69 ).  
      The distal end  103  of the overtube  101  is then inserted through the anus  120  into the rectum  119 , and the overtube  101  is advanced through the straightened sigmoid colon  121  until the distal end  103  of the overtube  101  is at the proximal end of the descending colon  122  ( FIG. 70 ). In this manner, the colonoscope  114  acts as a guiding track for the overtube  101  as it advances through the colon  118 .  
      The sheath  106  effects a double-layered seal between the overtube  101  and the colonoscope  114  at the distal end  103  of the overtube  101 . This seal ensures that no parts of the interior wall of the colon  118  become trapped between the colonoscope  114  and the overtube  101  as the overtube  101  is advanced over the colonoscope  114 , and thus prevents shearing off of any parts of the colon wall, or puncturing the colon wall, or any other damage to the interior wall of the colon  118 . The sealing sheath  106  also prevents faeces or other bodily materials from leaking between the colonoscope  114  and the overtube  101  proximally out through the anus  120 .  
      With the overtube  101  extended through the straightened sigmoid colon  121 , as illustrated in  FIG. 70 , the colonoscope  114  may then be advanced further distally through the descending colon  122  and into the transverse colon  123  ( FIG. 71 ). The overtube  101  acts as a splint to maintain the sigmoid colon  121  in the straightened configuration.  
      The splinting overtube  101  ensures that further advancement of the colonoscope  114  through the descending colon  122  and into the transverse colon  123  is possible by preventing loops from reforming in the sigmoid colon  121 . In this manner, the overtube  101  minimises the pain or discomfort experienced by the patient during this procedure.  
      The overtube  101  may subsequently be further advanced through the colon  118  over the colonoscope  114  with the colonoscope  114  acting as a guiding track for the overtube  101 .  
      After the colonoscope  114  has been advanced from the descending colon  122  around the splenic flexure into the transverse colon  123 , as illustrated in  FIGS. 72 and 73 , the overtube  101  may be advanced around the splenic flexure before advancing the colonoscope  114  further through the transverse colon  123 , as illustrated in  FIGS. 74 and 75 .  
       FIG. 72  is a front view of the colon  118  and  FIG. 73  is a side view of the colon  118  with the overtube  101  in the descending colon  122 .  FIG. 74  is a front view of the colon  118  and  FIG. 75  is a side view of the colon  118  with the overtube  101  hooked around the splenic flexure.  
      It is believed that by hooking the overtube  101  around the splenic flexure before advancing the colonoscope  114  through the transverse colon  123 , the subsequent advancement of the colonoscope  114  may be achieved while minimising stretching of the splenic flexure and/or the transverse colon  123 , and also minimising the pain or discomfort experienced by the patient.  
      To more easily facilitate hooking of the overtube  101  around the relatively tight bend of the splenic flexure, the distal end  103  of the overtube  101  may be formed of a softer, more bendable material than the remainder of the overtube  101 .  
      The corrugation  105  which extends along the overtube  101  in a convoluted manner results in a discontinuous interior surface  211  of the overtube  101 , as illustrated in  FIGS. 76 and 77 . The corrugation  105  projects inwardly for contacting the colonoscope  114  in the colonoscope lumen  104 . Thus, as the colonoscope  114  is advanced through the overtube  101 , the area of contact between the colonoscope  114  and the corrugated overtube  101  is less than the area of contact that would otherwise result with a continuous interior surface  210 , as illustrated in  FIG. 78 . Because the area of contact between the colonoscope  114  and the corrugated overtube  101  is reduced, the frictional force acting between the colonoscope  114  and the corrugated overtube  101  is also reduced. In this manner, the corrugated overtube  101  enables an easier passage of the colonoscope  114  through the colonoscope lumen  104  of the overtube  101 .  
      The exterior surface  212  of the overtube  101  may be smooth, as illustrated in  FIG. 77 . This smooth surface  212  reduces the discomfort and/or pain experienced by the patient during the colonoscopy procedure while maintaining the kink-resistant and low-friction properties of the corrugation  105  on the interior surface  211 .  
      It will be understood that the discontinuous nature of the interior surface of the overtube of the invention may be achieved in any suitable manner. For example, the overtube may comprise one or more inwardly projecting elements in the form of protruding strips  220 , as illustrated in  FIG. 79 . The strips  220  may extend longitudinally along the overtube  101 , or along the overtube  101  in a convoluted manner, or may extend at least partially circumferentially around the overtube  101 . Alternatively the inwardly projecting elements may be provided in the form of a plurality of discrete protrusions  222 , as illustrated in  FIG. 80 . By contacting a colonoscope in the colonoscope lumen  104 , the inwardly projecting elements  220 ,  222  reduce the frictional force acting between the overtube  101  and the colonoscope, and thus ease passage of the overtube  101  over the colonoscope.  
      It will be appreciated that the corrugated overtube  101  may be provided in alternative forms to that described above. For example, the corrugation on the overtube  101  may extend at least partially circumferentially around the overtube  101 , and/or more than one corrugation may be provided on the overtube  101 .  
      Referring to FIGS.  81  to  83 , there is illustrated a flange  200  which may be used with the overtube  101  to prevent complete insertion of the overtube  101  into the colon  118 . The flange  200  is releasably mounted to the overtube  101 , in this case by means of a threaded arrangement  201 .  
      The threaded mounting arrangement enables the position of the flange  200  on the overtube  101  to be adjusted by a simple rotation of the flange  200  relative to the overtube  101 , as illustrated in  FIGS. 82 and 83 . Because the flange position is adjustable the colonoscopist can quickly and effectively adjust the flange  200  to suit the particular characteristics of the colon  118  undergoing treatment.  
      It will be appreciated that the flange  200  may be provided with alternative means of adjusting the position on the overtube  101 , and/or with alternative means of releasable mounting to the overtube  101 . Also the flange  200  could alternatively be provided fixed to or integral with the overtube  101  towards the proximal end  102  of the overtube  101 . Furthermore, the limiting means may be provided in an alternative form to a flange.  
       FIG. 84  illustrates another colonic overtube  230  according to the invention, which is similar to the overtube  101 , and similar elements in  FIG. 84  are assigned the same reference numerals. In this case, the overtube  230  comprises a reinforcement means, in the form of a coil  231  of metallic material embedded within the wall  232  of the overtube  230 . This composite construction enables the overtube  230  to flex laterally during advancement over a colonoscope through a potentially tortuous path in a colon substantially without kinking.  
      It will be understood that the reinforcement means may be provided in any suitable form, such as a mesh, or a braided construction. In another alternative the composite overtube may have a layered construction.  
      It is to be understood that other configurations and constructions of overtube are also possible which are laterally flexible to facilitate flexing of the overtube substantially without kinking during advancement of the overtube through a colon.  
      More than one laterally flexible portion may be provided spaced along the overtube. The positioning and/or number of the laterally flexible portions may be selected to achieve the desired kink resistance.  
      Referring to FIGS.  85  to  91 , there is illustrated another colonic overtube  700  which is suitable for use in a method of performing a colonoscopy according to the invention. The overtube  700  may be used to cannulate a colon.  
      The overtube  700  is similar to the overtube  101  of FIGS.  55  to  77 , and similar elements in FIGS.  85  to  91  are assigned the same reference numerals. The overtube  700  is extendable between a shortened configuration, as illustrated in  FIG. 85 , and an elongated configuration, as illustrated in FIGS.  86  to  91 , for cannulating at least portion of the colon  118 , in particular cannulating the colon  118  to a point distally of the descending colon  122 . In this case, a portion  701  of the overtube  700  has a concertina-type configuration in the shortened configuration ( FIG. 85 ), and an extended configuration in the elongated configuration ( FIG. 87 ). The concertinaed portion  701  is provided at the proximal end  102  of the overtube  700 .  
      In the method of performing a colonoscopy according to the invention, the overtube  700  is mounted to the colonoscope  114  with the portion  701  retracted into the concertina-like manner before insertion of the colonoscope  114  into the colon  118 . Insertion of the colonoscope  114  into the colon  118 , straightening of the sigmoid colon  121  and advancement of the overtube  700  over the colonoscope  114  are performed in a manner similar to that described previously with reference to FIGS.  66  to  71 .  
      The overtube  700  acts as a splint to maintain the naturally floppy sigmoid colon  121  in the straightened configuration. The colonoscope  114  may therefore be easily advanced through the floppy transverse colon  123  to the hepatic flexure  125  ( FIG. 85 ).  
      The floppy transverse colon  123  may now be reduced/straightened in either of two ways. The first is by manipulating the colonoscope  114  until the colon assumes the classic question mark “?” shape [ FIG. 86 ]. The concertinaed portion  701  of the overtube  700  can now be extended from the shortened configuration to the elongated configuration by pushing the overtube distally from externally of the colon over the colonoscope  114  through the descending colon  122  and the reduced/straightened transverse colon until the distal end  103  of the overtube  700  reaches the hepatic flexure  125  ( FIG. 87 ).  
      Alternatively, the concertinaed portion  701  of the overtube  700  may first be extended from the shortened configuration to the elongated configuration by pushing the overtube  700  distally from externally of the colon  118 . In this way the overtube  700  is advanced over the colonoscope  114  through the descending colon  122  and the floppy transverse colon  123  until the distal end  103  of the overtube  700  reaches the hepatic flexure  125  ( FIG. 87 ).  
      The floppy transverse colon  123  may then be straightened by manipulation of the colonscope  114  and/or the overtube  700  from externally of the colon  118  ( FIG. 88 ).  
      The overtube  700  of the present invention acts as a colonic cannula and maintains, in a stable configuration, the sections of the colon  118  that are normally floppy and mobile such as the sigmoid colon  121  and the transverse colon  123 . This gives the colon  118  the classic question mark configuration as shown in  FIG. 86 . The colonoscope  114  may therefore be advanced further into the ascending colon  126  to perform the desired colonoscopic procedure in a relatively easy, pain-free manner.  
      The colonoscope  114  may subsequently be removed through the colonoscope lumen  104  from the colon  118  leaving the overtube  700  in place in the cannulated colon  118  ( FIG. 87 ). The overtube  700  can then be used to facilitate insertion of an endoscopic instrument through the overtube  700 , for example an instrument  703  to remove polyps from the ascending colon  126  ( FIG. 90 ), or the overtube  700  can be used to facilitate reinsertion of a colonoscope.  
      When the colonoscope  114  has been removed from the overtube  700 , the overtube  700  provides a large working channel through the colon  118  through which any instrument may be quickly and easily passed to access any point in the colon  118  as far distally as the caecum. Rapid and less painful exchange of instruments and/or colonoscopes is thus facilitated by the overtube  700  because there is no contact between the instruments/colonoscopes and the inner wall of the colon  118  during insertion or withdrawal of the instruments/colonoscopes. In addition, the overtube  700  has a much larger diameter than the diameter of a typical colonoscope working channel. Thus, larger instruments may be used during a colonoscopy procedure with the overtube  700 . Larger samples may also be removed using the overtube  700 .  
      The colonoscope lumen  104  has a diameter, in this case approximately 15 mm, which results in a significantly larger cross sectional area than that of a typical colonoscope working channel.  
      If a subsequent region of interest in the colon  118  is proximally or distally of the distal end  103  of the overtube  700 , the overtube  700  may be shortened or elongated until the distal end  103  is at the desired region of interest. Alternatively the overtube  700  may be withdrawn or advanced until the distal end  103  is at the desired region of interest. While shortening or withdrawal of the overtube  700  may be achieved by simply withdrawing the overtube  700  from the colon  118 , advancement or lengthening of the overtube  700  is preferably achieved with the colonoscope  114  in situ in the colon  118 .  
      The overtube  700  is removed from the colon  118  by collapsing the elongated portion  701  to the shortened configuration and withdrawing the overtube  700  proximally out of the colon  118 . It is not necessary to reintroduce the colonoscope  114  into the colon  118  to facilitate removal of the overtube  700 . Alternatively the overtube  700  may be withdrawn from the colon  118  leaving the colonoscope  114  in place in the colon  118 . In this case, the colonoscope  114  may be subsequently withdrawn from the colon  118  thereby enabling the entire colon  118  to be examined during withdrawal of the colonoscope  114 .  
       FIG. 91  illustrates an alternative method of performing a colonoscopy according to the invention, which is similar to the method described previously with reference to FIGS.  85  to  90 . In this case, when the distal end  103  of the overtube  700  reaches the hepatic flexure  125 , the transverse colon  123  is not straightened. Instead the colonoscope  114  is advanced further into the ascending colon  126 , while the overtube  700  remains in position in the distended transverse colon  123  ( FIG. 91 ).  
      In this manner, less time is required to perform the colonoscopy procedure because no straightening of the transverse colon  123  is required. In addition the pain or discomfort caused to the patient as a result of straightening of the transverse colon  123  is avoided using this method.  
      It will be appreciated that the overtube may be extended in a number of alternative ways. For example, the overtube may comprise a plurality of overtube sections which are releasably mountable to one another to extend the overtube to the elongated configuration in a manner similar to the extension of a chimney sweeping brush. As a further possibility the overtube may comprise one or more telescopable sections.  
      In an alternative arrangement, a connecting means, such as a drawstring, may be passed distally through the colonoscope working channel out of the distal end  115  of the colonoscope  114  and attached to the distal end  103  of the overtube  700 . By maintaining the position of the colonoscope  114  fixed and pulling proximally on the connecting means from externally of the colon  118 , the distal end  103  of the overtube  700  can be advanced over the colonoscope  102  thereby extending the concertinaed portion  701  of the overtube  700 .  
      Other means of activating an actuator of the overtube from externally of the colon may also be applied to extend the overtube in situ to the elongated configuration. For example, the overtube may at least partially comprise an energy actuated polymer. By application of energy, such as a voltage difference across the overtube, a portion of the overtube may be extended.  
      The overtube  700  may have one or more laterally flexible portions spaced along the overtube  700 , similar to the corrugated arrangement of  FIG. 55 , and/or the composite arrangement of  FIG. 84 . These laterally flexible portions may assist navigation of relatively tight bends in the colon  118 , such as the splenic and hepatic flexures.  
      It is to be understood that a variety of different colonic overtubes may be employed in the method of performing a colonoscopy according to the invention, provided that the overtube may be advanced to cross the floppy transverse colon before further advancement of the colonoscope.  
       FIG. 92  illustrates another colonic overtube  710  according to the invention which is similar to the overtube  101  of FIGS.  55  to  77 . The overtube  710  comprises at least one, and in this case three, exchange lumena  705 ,  706 ,  707 , extending through the overtube  710  in addition to the colonoscope lumen  708 . The exchange lumena  705 ,  706 ,  707  are suitable for exchanging a fluid, or a medical device through the lumena  705 ,  706 ,  707 . For example, the lumen  705  may be used to provide a channel through which means for viewing the colon  118  from externally of the colon  118  can be provided, or the lumen  706  may be used to provide a channel through which means for illuminating the colon  118  can be provided.  
      It is highly advantageous to advance the overtube  710  with a visible path distally of the overtube  710  to ensure that no bowel is trapped at the distal end  103  of the overtube  710  during advancement through the colon  118 .  
      As a further alternative, the lumen  707  may be used to provide a channel for flushing or insufflating the colon  118 , for example to blow a protruding piece of the colon  118  laterally to clear a path for safe advancement of the overtube  710  through the colon  118 .  
      In the case of the overtube  710  of  FIG. 92 , the exchange lumena  705 ,  706 ,  707  are provided on an interior surface of the overtube  710  extending inwardly into the colonoscope lumen  708 . It will be appreciated that one or more of the exchange lumena may alternatively be provided on an exterior surface of the overtube  710  extending outwardly.  
      To assist with and speed up advancement of the colonic overtube into the colon  118  over the colonoscope  114  a guide device may be used, such as the guide device described in International Patent Application No. PCT/IE01/00039, the relevant contents of which are incorporated herein by reference.  
      The colonic overtube may be applied to maintain sections of the colon other than the sigmoid colon or the transverse colon in a straightened configuration. Indeed the overtube could also be applied to cannulate other body lumena, in which medical instruments are to be inserted.  
      The invention is not limited to the embodiments hereinbefore described, with reference to the accompanying drawings, which may be varied in construction and detail.