with reference to the number references of the above mentioned figures , the variable diameter tubular structure according to the present invention , which has been generally indicated by the reference number 1 , is made starting from an extruded tube which is properly modified and thermoformed and finally coupled to a resilient sheath assembly 2 extending through the overall length of the device body . the expansion of the tube is achieved by providing a region 3 having radially sliding walls , which are moved away as an article having a size larger than the rest diameter of the tube is caused to pass through the latter . for making the tube to a required or set contour , the following operations are performed : an extrusion of the tube with a set thickness and diameter , for example a thickness of 0 . 5 and a diameter of 6 mm ; an overlapping of the two tube open portions to a tube rest diameter , for example 5 mm , with a proper thermoforming of thus achieved contour . thus , by the above operations , a tube is achieved having an inner rest diameter corresponding to a minimum target diameter and which may be easily enlarged . a preferred configuration or embodiment of the extruded and thermoformed tube is shown in fig1 , in which the tube has a variable thickness and the two open flaps or edges thereof , indicated by the reference numbers 4 and 5 , are smugly overlapped thereby providing a precise thickness of said tube in its minimum diameter configuration . another similar solution , but with the tube having an eccentric thickness , is shown in fig2 . the tube contour may also be of the type shown in fig3 and 4 , wherein the tube is extruded to or with an even thickness , the movable flap or tube portions being overlapped , and the assembly being then thermoformed to provide a non linear contour or profile , including rough portions which may be directed either inward and / or outward depending on the thermoforming process . because the tube is extruded to a small thickness , for example 0 . 1 mm , said rough portions will be very small and generally acceptable . the material forming the variable diameter tubular structure according to the present invention is preferably polyamide , ptfe or pe . to insulate the tube inside with respect to the encompassing environment , for example with respect to arterial blood , a resilient membrane 2 is applied to the tube contour . advantageously , for facilitating the operation , said membrane 2 is extended through the overall length and profile of said tube , said membrane 2 being made of a polyurethane material and being applied to the tube in a tube rest diameter condition by a dipping coating method . if desired , said membrane 2 may also be made by extruding and gluing operating steps . a primer coating and other surface treatments may also be used . the thus made tube , accordingly , will comprise two tube layers : a stiffener layer , providing the tube duct or lumen , and a more resilient one , preventing the sliding tube portions from detaching and communications between the tube inner lumen and outer environment from occurring . the tube , on the other hand , may be easily enlarged by engaging a device having a diameter larger than that the tube rest diameter therein . a withdrawing of the inner device allowing the resilient membrane 2 to “ recover ” to their starting conditions the tube movable portions , thereby the tube will return to its rest diameter . the finished tube lubricating property may be improved by suitable lubricating or lining materials , of a type conventionally used in the medical field , thereby the tube may be easily used as a tube body for an introducer device . in such an application , a proximal part of said tube is sealed to a valve 8 holding said tube in its desirable maximum diameter condition . if the tube is used to make an introducer , then it is necessary to provide a tube tip 9 tapering to the dilatator , thereby preventing it from rubbing against the tissues traversed thereby . this result may be achieved by properly thermoforming the tip region of the tube . moreover it is preferred to provide a proper adhesion between the two tube layers , the tip being in this case made of the stiffener layer only . the inventive tube has advantageously a very small wall thickness , and may be enlarged in a “ modulable ” and adjustable manner , that is in a non permanent manner through the overall length thereof , while having a very low cost . the variable tubular structure according to the present invention may be further advantageously used to make a vascular introducer device body , as indicated by 100 in the drawing figures . in this case , the tube will have a tube end fitted to a holding valve 8 having a side arm 10 and an atraumatic blunted tip 9 , the valve being a haemostatic valve comprising a stiff fitting including a silicone diaphragm insulating the outside and inside of the vessel , but allowing medical devices to pass therethrough , said silicone diaphragm being precut , for example in the form a central star , the cuts snugly adhering to the device passing therethrough . in such a construction , the valve will be properly calibrated for allowing devices having a maximum target diameter , for example of 7 mm , to easily pass therethrough . the tube fitted to the valve , accordingly , will be opened to a target maximum diameter of 7 mm , whereas the remaining portion of the introducer body will have the target minimum diameter for example of 5 mm . the introducer , accordingly , will have , at said valve , a diameter transition conical region 11 . the vascular introducer 100 is engaged in the vessel through the patient tissue and vessel wall , by a well known seldinger &# 39 ; s procedure , in which the vessel is punctured , the guide engaged therein and then the introducer device preassembled on a dilatator being further engaged . the introducer device may be used in a like manner , by using a dilatator corresponding to the minimum target diameter , for example of 5 mm . such a dilatator is a commercially available one , as well as the other conventionally used devices . fig5 shows the guide + dilatator + introducer in an assembled condition thereof . fig6 shows the introducer device in a rest condition thereof , without any dilatator engaged therein . the introducer being then enlarged to the larger diameter , for example a maximum diameter of 7 mm , by causing a catheter to slide therethrough , said catheter having a larger diameter , as is shown in fig7 - 9 . a further advantage of the structure according to the present invention is that it does not require the use of a second dilatator . yet another advantage is that the enlargement of the introducer and , accordingly , of the tissues therethrough said introducer passes , is limited in the time and performed only as it is necessary . actually , the introduced device may have a larger diameter only at a portion of its overall length . in this case the introducer is deformed as shown in fig1 . if it is desired to achieve a channel having a larger permanent diameter , that is a diameter larger than the rest diameter , it is preferred to restrain the tube by engaging therein a second tube . since the resilient membrane may cause problems related to the introducer tip tapering and , accordingly , make the introducer making method expensive , it is possible to provide a substantially truncated introducer tip and use a dilatator having a modified tip adapted to “ protect ” the tissue against the introducer tip portion to be withdrawn owing to the introducer tube elastic feature . in this case the dilatator will have a maximum diameter either larger than or equal to the introducer rest diameter , and less than the enlarged introducer diameter , as shown in fig1 . the variable diameter tubular structure according to the present invention is susceptible to several modifications and variations , all coming within the inventive idea scope . if desired , the tube may also , not be lined by a resilient membrane , for example for a use in a dry environment , to prevent any material infiltration problems from occurring . moreover , the resilient membrane , instead of being arranged outside the tube , may be also arranged therewithin , and may also be made by an independent making process and easily sealed / glued to the tube . the membrane , in particular , may also be made by an extruding process , as a first or a second layer of the rigid tube . the membrane may also be made by subjecting the tube to a dipping method in its as extruded or it is both extruded and thermoformed condition . the tube may also be coated by hydrophilic coating material on the inner and / or outer walls thereof , to improve the sliding capability of devices engaged in the tube and / or of the tube in the patient body . the tube sliding parts may also have either a constant or variable thickness and equal to or different from that of the tube . the tube may also have either a constant or variable thickness , both in its longitudinal and in its radial direction , and may be made by extruding or molding processes . the membrane may be applied either to the overall profile of the tube or only to the sliding portion thereof , or also to the overall tube or only to a tube portion . it has been found that the invention fully achieves the intended aim and objects . in fact , the invention has provided a variable diameter tubular structure greatly improving surgical or implant procedures and greatly reducing the number of the introducer devices to perform the surgical procedure and the operating and bleeding times and the vessel or tissue traumas . the structure according to the present invention allows moreover to greatly reduce the number of operations to implant artificial different diameter channels , while facilitating a closure of the puncture place with a consequent reduction of the vessel wall trauma . in practicing the invention , the used materials , as well as the contingent size and shapes , can be any , depending on requirements .
a plastics material variable diameter tubular structure for a biomedical use has a diameter which increases as the structure is subjected to an inner force , and returns to a starting diameter in a rest condition of the structure , the tubular structure being advantageously used for making a body of a vascular introducer device .