as best shown in fig7 the principal components of the illustrated catheter assembly are a primary catheter tube 10 and an everting tube 12 , these being the components which actually enter the vascular system of a patient and the assembly being completed by ancilliary equipment remaining external to the patient &# 39 ; s body and including an extension tube 14 , a manifold 16 , syringes 18 and 20 for applying pressure fluid respectively to the outer annulus of the everting tube and to its internal passageway , and a pressure gauge 22 for measuring the pressure of the former fluid . in use , the primary catheter tube 10 with the everting tube 12 fully contracted therewithin is inserted into the vascular system and worked along a blood vessel in the conventional manner . then , when the leading end of the tube 10 has reached its limit of travel through the blood vessel , tube 12 is everted from within tube 10 for further advancement of the catheter along the vessel . tube 10 is a conventional form of flexible catheter tubing used for intra - vascular applications for example , a polyurethane tube of 2 . 15 mm . outside diameter , 1 . 4 mm . inside diameter and 1 meter long , the tube having its inner surface treated with a friction reducing hydromer coating . the leading end of tube 10 is tapered ( fig9 ) and the forward end of everting tube 12 is fused or welded to the outer surface of tube 10 at the leading end along with a protective cap 24 . the trailing end of tube 10 is bonded to the extension tube 14 , conveniently also of polyurethane and having an outside diameter of 3 . 8 mm ., an inside diameter of 3 . 12 mm . and a length of 0 . 6 meters . everting tube 12 is likewise extruded in polyurethane and has , for example , an outside diameter of 1 mm ., a wall thickness of 1 / 15 mm . and a length of 1 . 6 meters . this tube has its outer surface covered with a friction reducing hydromer coating , and after extrusion , is heat set to provide an indented cross - sectional profile , preferably a substantially u - shaped profile , as shown in fig2 and 3 , although other indented profiles such as a cruciform profile are also considered suitable . heat setting of tube 12 may , for example , be effected by winding the tube around a helically grooved or ridged heated drum , whereby the ridge in the drum provides the required indentation in tube 12 . as indicated , the forward end of tube 12 is opened out , turned back on itself and welded or fused to the leading end of tube 10 at point 10a under protective cap 24 , while the main body of tube 12 , the uneverted length or inner wall , is taken back through tube 10 and its rear end is bonded around the opening at the forward end of an axially moveable plastic support tube 26 . this forward end of tube 26 is also tapered and provided with a slit section 28 formed from one or more slits which serves as a valve arrangement for preventing tube 12 from being pushed back through tube 28 . the flaps so created by the slit or slits are inwardly deflected by the pressure in the annulus thus producing an obstruction to rearward motion of the secondary tube . further , the forward end of tube 26 is provided with caps 30 and 32 serving to prevent tube 12 from working back along the space between tubes 14 and 26 . the rear end of support tube 26 is attached to a sliding metal coupling arrangement 34 , to the rear of which is welded a steel tube 36 which extends back through the manifold 16 and carries a connection 38 for the syringe 20 . extension tube 14 is at its rear end attached to a metal coupling 40 connected to the manifold and the manifold has passages 42 and 44 connected respectively to syringe 18 , via a tap 46 , and pressure gauge 22 . syring 18 , thus , communicates via passage 42 , coupling 40 and extension tube 14 with the interior of primary catheter tube 10 , i . e ., with the annular space surrounding the inner wall of the everting tube 12 . with the everting tube 12 and steel tube 36 in the fully retracted condition , tube 10 is introduced into the vascular system at a suitable entry point and worked through a blood vessel in the conventional manner under fluoroscopic observation until it is advanced to its full length or until an obstruction is encountered or until friction impedes its further advance . then , steel tube 36 is advanced slightly to provide slack in the everting tube . pressure at about 1 . 7 to 2 atmospheres is applied to the annular space surrounding the inner wall of tube 12 through syringe 18 , causing eversion of tube 12 from the leading end of tube 10 until the slack in tube 12 is taken up , this process again being performed under fluoroscopic observation . the fluid used for everting tube 12 is conveniently a standard x - ray contrast media which allows the outline of tube 12 to be viewed under x - ray . tube 12 thus extends from the leading end of tube 10 , and when the slack in tube 12 is taken up , the steel tube 36 is further advanced and the process is repeated . this procedure is continued until the everting tube has reached its maximum extension , or until the target region of the blood vessel has been reached . during eversions of tube 12 , when pressure is applied through syringe 18 , the inner wall or uneverted section of tube 12 retains its indented cross - sectional profile , fig2 and 3 , while the everted outer wall is expanded to the normal substantially circular cross - section of the tube . when the maximum or required degree of eversion has been obtained , pressure in the annular space surrounding the inner wall of tube 12 can be relaxed and the inner passageway of tube 12 is then available for the application of fluid under pressure to the target region of the blood vessel via the steel tube 36 and syringe 20 . under the influence of such pressure fluid , the inner wall of tube 10 is then expanded to its normal , substantially circular cross - section , as shown in fig5 and 6 . alternatively the everting tube can be used to transport any object through the blood vessel for diagnostic or other purposes e . g ., a catheter guide wire or a small fluid sampling tube . after treatment has been terminated , the catheter can be withdrawn by releasing pressure from both syringes , retracting steel tube 36 , so that tube 12 is itself again retracted into tube 10 and then withdrawing tube 10 from the blood vessel in the normal way . it will be appreciated that a catheter assembly as herein described and its method of application , is suitable for use in effecting entry to relatively inaccessibly regions of the vascular system for either therapeutic or diagnostic purposes . where the catheter is to be used for treating stenoses by physical expansion of the vessel in the region of the stenoses , tube 12 may be provided with sections of differing diameter and in use , the apparatus can be manipulated in such a way that a diameter suited to expand a particular region of the vessel is available for use at the required location and the tube 12 being expansible under elevated pressure for this purpose . advantages of attaching the secondary tube to the distal end of the primary tube as opposed to having it originate from outside the body are two - fold : ( a ) there is less required distance for the secondary tube to be everted e . g ., 0 . 3 m as to 1 . 3 m and therefore far less friction build - up and required everting pressures , ( b ) the reduced required travel of the proximal end of the secondary tube makes practical an axial feed arrangement ( as opposed to winding the secondary tube on a drum ) which in turn enables the lumen of the secondary tube to remain open more reliably . while only a single embodiment of this invention has been described in detail , it will be appreciated that numerous modifications are envisaged within the scope of the invention as defined in the appended claims .
disclosed is a method for obtaining access to a relatively inaccessible region of a blood vessel for diagnostic or therapeutic purposes in which a primary catheter tube is inserted into the vascular system at an entry point remote from the relatively inaccessible region , the leading end of the tube is worked towards the inaccessible region in a conventional manner and then a secondary catheter tube contained within the primary tube is everted from the leading end of the primary tube to approach more closely to the required region . a catheter assembly for performing the method is also disclosed .