Abstract:
The present invention is primarily directed to a rapid exchange catheter that permits axial movement of an inner conduit within an outer conduit comprising: • an outer conduit; • an inner conduit, suitable for total or partial passage over a guide wire, wherein said inner conduit is movably disposed within the lumen of said outer conduit, wherein the proximal end of said inner conduit is angled such that it pierces the wall of said outer conduit; • means for permitting axial movement of said inner conduit within said outer conduit, such that said movement is not hindered by the passage of the angled proximal part of the inner conduit through said outer conduit; and • means, situated at the proximal end of the outer conduit, for causing axial pushing-pulling movements of said inner conduit.

Description:
This application is the U.S. national phase of International Application No. PCT/IB2006/002955, filed 13 Oct. 2006, which designated the U.S., and claims priority to U.S. Provisional Patent Application No. 60/726,160, filed 14 Oct. 2005, and is a continuation application of U.S. Utility patent application Ser. No. 11/477,812, filed 30 Jun. 2006, the entire contents of each of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to balloon catheters. More particularly, the invention relates to a rapid exchange balloon catheter system, wherein the length and shape of the inflated balloon may be adjusted in situ. 
     BACKGROUND OF THE INVENTION 
     Rapid exchange (“monorail”) catheters typically comprise a relatively short guide wire lumen provided at a distal end section thereof, and a proximal guide wire exit port located between the catheter&#39;s distal and proximal ends. This arrangement allows exchange of the catheter over a relatively short guide wire, in a manner which is simple to perform and which can be carried out by a single physician. Rapid exchange catheters have been extensively described in the art, for example, U.S. Pat. No. 4,762,129 (to Bonzel), U.S. Pat. No. 4,748,982 (to Horzewski) and EP0380873 (to Enger). 
     Rapid exchange catheters are commonly used in Percutaneous Transluminal Coronary Angioplasty (PTCA) procedures, in which obstructed blood vessels are typically dilated by a distal balloon mounted on the catheter&#39;s distal end. A stent is often placed at the vessel&#39;s dilation zone to prevent reoccurrences of obstruction therein. The dilation balloon is typically inflated via an inflation lumen which extends longitudinally inside the catheter&#39;s shaft between the dilation balloon and the catheter&#39;s proximal end. 
     The guide wire lumen passes within a smaller section of the catheter&#39;s shaft length and it is accessed via a lateral port situated on the catheter&#39;s shaft. This arrangement, wherein the inner tube is affixed to the catheter&#39;s shaft at the location of its lateral port, usually prevents designers from developing new rapid exchange catheter implementations which require manipulating the inner shaft. For example, extending or shortening the catheter&#39;s length during procedures may be advantageously exploited by physicians to distally extend the length of the catheter into a new site after or during its placement in the patient&#39;s artery, for example in order to assist with the passage of tortuous vessels or small diameter stenoses, or to allow in-situ manipulation of an inflated balloon at the distal end of the catheter. 
     The rapid exchange catheters of the prior art are therefore usually designed for carrying out a particular procedure and their implementations are relatively restricted as a consequence of the need for at least one catheter shaft to exit the catheter system laterally, between the proximal and distal ends of said system. Consequently, a need exists for a rapid exchange catheter that could overcome the above mentioned restriction and which would allow expansion of the range of applications of such catheters. 
     It is therefore an object of the present invention to provide a rapid exchange catheter having an adjustable balloon length and shape which may be modified during a procedure. 
     It is another object of the present invention to provide a rapid exchange balloon catheter wherein the shape and/or volume of a standard inflated balloon may be adjusted during a procedure. 
     It is a further object of the present invention to provide a rapid exchange balloon catheter capable of collecting samples and/or debris from the body treated site and reducing the risk of distal embolization of any material that may be dislodged during inflation of the balloon at the treated site. 
     Other objects and advantages of the invention will become apparent as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The present invention provides rapid exchange (RX) catheter systems in which the length of a distal section of the catheter and the shape and/or volume of its distal balloon may be manipulated during procedures carried out therewith. Such implementations are ideally suited for use in debris collection applications, as will be described in detail hereinbelow. However, the RX configurations of the present invention may also be used in any other RX applications wherein it is necessary to alter the length of a distally-placed balloon element. 
     Consequently, the present invention is primarily directed to a rapid exchange catheter that permits axial movement of an inner conduit within an outer conduit comprising:
         a) an outer conduit;   b) an inner conduit, suitable for total or partial passage over a guide wire, wherein said inner conduit is disposed within the lumen of said outer conduit such that the longitudinal axes of said inner and outer conduits are substantially parallel, wherein said inner conduit is capable of being moved along its longitudinal axis in relation to said outer conduit and wherein the proximal end of said inner conduit is angled such that it pierces the wall of said outer conduit;   c) means for permitting said axial movement of said inner conduit within said outer conduit, such that said movement is not hindered by the passage of the angled proximal part of the inner conduit through said outer conduit; and   d) means, situated at the proximal end of the outer conduit, for causing axial pushing-pulling movements of said inner conduit.       

     In one preferred embodiment of the above-defined rapid exchange catheter, the means for permitting unhindered axial movement of the inner conduit is provided by a sealing sleeve that is slidably fitted around the external conduit, such that the angled proximal portion of said inner conduit passes firstly through an elongated aperture in the wall of the external conduit, and secondly through a tightly sealed aperture in said sealing sleeve, such that upon axial movement of the inner conduit, said sealing sleeve is capable of preventing the transfer of fluid through said elongated aperture. The sealing sleeve is constructed such that it can provide a sealing effect under fluid pressure conditions appropriate for the balloon that is being inflated. Thus, in one non-limiting preferred embodiment, the sealing sleeve is capable of preventing fluid transfer through the elongated aperture at balloon inflation pressures of up to 16 atmospheres. 
     In another preferred embodiment, the above means for permitting unhindered axial movement of the inner conduit is provided by a two-part inner conduit construction, whereby the first, proximal part of said construction is non-movable, and wherein the second, distal part is slidably disposed within said proximal part. 
     In a further preferred embodiment, the abovementioned means for permitting unhindered axial movement of the inner conduit is provided by a two-part inner conduit construction, whereby the first, proximal part of said construction is non-movable, and wherein the second, distal part is slidably disposed over said proximal part. 
     In a still further preferred embodiment, the aforementioned means for permitting unhindered axial movement of the inner conduit is provided by a three-part inner conduit construction, whereby the first, proximal part of said construction is non-movable, and wherein the second, intermediate part is disposed within said proximal part, and wherein the third, distal part is slidably disposed within said intermediate part. 
     In another preferred embodiment of the rapid exchange catheter of the present invention, the means for causing axial movements of the inner conduit mentioned hereinabove comprise one or more wires, the distal end(s) thereof being attached to the inner conduit, and the proximal end(s) thereof extending beyond the proximal end of the outer conduit. 
     In another aspect, the present invention also provides a rapid exchange balloon catheter system comprising:
         a) an outer conduit;   b) an inner conduit, suitable for total or partial passage over a guide wire, wherein said inner conduit is disposed within the lumen of said outer conduit such that the longitudinal axes of said inner and outer conduits are substantially parallel, wherein said inner conduit is capable of being moved along its longitudinal axis in relation to said outer conduit, wherein the proximal end of said inner conduit is angled such that it pierces the wall of said outer conduit, and wherein the distal tip of said inner conduit extends beyond the distal tip of said outer conduit;   c) an angioplastic balloon whose proximal margin is attached to the outer surface of the distal tip of said outer conduit, and whose distal margin is attached to the outer surface of the portion of the inner conduit that extends beyond the distal tip of said outer conduit, and wherein the distal and/or proximal end portion(s) of said balloon are capable of intussusception upon proximal movement of said inner conduit in relation to said outer conduit;   d) means, situated at the proximal end of the outer conduit, for causing axial pushing-pulling movements of said inner conduit;   e) means for the introduction of an expansion fluid into the annular space formed between the inner surface of the outer conduit and the outer surface of the inner conduit and therefrom into the lumen of said balloon, and for the removal thereof;   f) means for minimizing or preventing pressure changes within said annular space upon axial movement of said inner conduit in relation to said outer conduit; and   g) means for permitting axial movement of said inner conduit within said outer conduit, such that said movement is not hindered by the passage of the angled proximal part of the inner conduit through said outer conduit.       

     In one preferred embodiment of the rapid exchange balloon catheter system defined hereinabove, said system is constructed such that the distal portion of the balloon is capable of intussusception upon proximal movement of the inner tube in relation to the outer tube. 
     In one preferred embodiment of this aspect of the invention, the means for causing axial movements of the inner conduit comprise one or tore wires, the distal end(s) thereof being attached to the inner conduit, and the proximal end(s) thereof extending beyond the proximal end of the outer conduit. 
     In another preferred embodiment of this aspect of the invention, the means for preventing pressure changes comprises a plunger slidably disposed within the proximal end of the outer conduit, wherein said plunger is connected to the axial pushing-pulling means, such that upon operation of said pushing-pulling means, said plunger is caused to slide either distally or proximally, thereby changing the volume of the outer conduit. 
     Any suitable means may be employed for permitting unhindered axial movement of the inner conduit in the above-defined rapid exchange balloon catheter system. Preferably, however, these means are as defined in any one of the preferred embodiments disclosed hereinabove and claimed hereinafter. 
     In one preferred embodiment of the rapid exchange balloon catheter system of the present invention, the inner and outer conduits are characterized by their ability to withstand axially directed forces in the range of between 2 and 20 Newton without undergoing significant deformation. In the context of the present invention, the term “significant deformation” refers to changes in conduit length in excess of 5% of the total length of said conduit. While these conduits may be constructed of any suitable material capable of withstanding the aforementioned forces, in a preferred embodiment, the inner and outer conduits are constructed either from a biocompatible polymer (which in a preferred embodiment is selected from the group consisting of braided nylon thread and nylon thread that has undergone orientation treatment) or from flexible stainless steel tube. 
     In one preferred embodiment of the rapid exchange balloon catheter system of the present invention, the balloon is, characterized by having, in its inflated state, a pre-folding profile, i.e. it has shape which is capable of assisting and guiding the intussusception of the distal portion thereof upon proximal movement of the inner conduit in relation to the outer conduit. 
     In one particularly preferred embodiment of the catheter system, the aforementioned balloon pre-folding profile is achieved by manufacturing the balloon such that it has (in its inflated state) a tapered shape with a rounded distal extremity. 
     Preferably, the balloon is constructed from Nylon 12, Pebax or mixtures thereof. It is to be recognized, however, that the balloon may also be constructed of any other suitable materials as are well known in the art, without deviating from the scope of the present invention as defined in the claims. 
     It should be noted that in each of the embodiments of the catheter systems of the present invention disclosed and described hereinabove, a lubricant (such as silicone oil or mineral oil) may be present in order to facilitate the mutual sliding of the various conduits. 
     In another aspect, the present invention also provides a method for collecting debris from an internal passage of a mammalian subject comprising the steps of: 
     a) inserting a rapid exchange balloon catheter system as defined hereinabove into said internal passage, and advancing said catheter until the distal tip thereof has reached the site, at which it is desired to collect debris; 
     b) inflating the balloon with expansion fluid; 
     c) pulling the inner conduit of said balloon catheter in a proximal direction, such that the distal and/or proximal end(s) of said balloon intussuscept(s); 
     d) deflating the balloon, thereby forming a cavity into which debris is collected and entrapped; and 
     e) removing the balloon catheter from the internal passage of the subject, together with the entrapped debris. 
     In one preferred embodiment of the presently-disclosed method, the aforementioned internal passage is a vein or artery. 
     All the above and other characteristics and advantages of the present invention will be further understood from the following illustrative and non-limitative examples of preferred embodiments thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example in the accompanying drawings, in which similar references consistently indicate similar elements: 
         FIGS. 1A to 1C  show longitudinal section views of a rapid exchange catheter according to one preferred embodiment of the invention wherein the distal section of the inner tube comprises an internal slidable tube; 
         FIGS. 1D and 1E  demonstrate the use of different balloons for different manipulations thereof; 
         FIG. 1F  demonstrates a piston-like construction for preventing pressure accumulation within the catheter during retraction; 
         FIGS. 2A to 2C  show longitudinal section views of a rapid exchange catheter according to a second preferred embodiment of the invention wherein the diameter of the distal section of the inner tube is adapted to receive an internal slidable tube; 
         FIG. 3  shows a longitudinal section view of a rapid exchange catheter according to a third preferred embodiment of the invention wherein the distal section of the inner tube comprises an external slidable tube; 
         FIG. 4  shows a longitudinal section view of a rapid exchange catheter according to a fourth preferred embodiment of the invention wherein the diameter of the distal section of the inner tube is adapted to be received in an external slidable tube; 
         FIG. 5  shows a longitudinal section view of a rapid exchange catheter according to a fifth preferred embodiment of the invention wherein the distal section of the inner tube comprises a fixed inner tube (on which an external slidable tube is mounted; 
         FIGS. 6A to 6C  show longitudinal section views of a rapid exchange catheter according to a sixth preferred embodiment of the invention wherein the inner tube of the catheter is encompassed by a slidable intermediate tube; 
         FIGS. 7A to 7C  show longitudinal section views of a rapid exchange catheter according to a seventh preferred embodiment of the invention comprising a movable inner tube affixed to a slidable sealing sleeve; 
         FIG. 8  schematically illustrates the four balloon designs that were analyzed and compared in the finite element analysis study: a. Standard 20° tapering; b. 20° tapering with smooth round ending; c. Round ending; d. Round ending with initial retracting; 
         FIG. 9  graphically depicts the displacement vs. retracting force for the four balloon shapes, compared at an inflation pressure of 6 atmospheres; and 
         FIG. 10  graphically depicts the maximum force generated in the catheter tubes following balloon folding, measured for different balloon inflation pressures. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention aims to provide rapid exchange catheter implementations in which the length of a distal section of the catheter and the shape and/or volume of its distal balloon may be manipulated during procedures carried out therewith. 
     In general, the rapid exchange catheter of the invention comprises an outer catheter shaft and an inner tube provided therein, wherein the lumen of said inner tube may be accessed via a lateral port provided on the catheter&#39;s shaft. In some of the preferred embodiments of the present invention described herein the inner tube of the catheter is affixed to the catheter&#39;s outer shaft and the catheter&#39;s length and its balloon are manipulated by a unique construction of the inner tube. In these constructions the catheter&#39;s inner tube may comprise a slidable distal tube that may be moved by the operator, distally or proximally relative to the catheter&#39;s outer shaft, via a displacement rod attached thereto. Alternatively, the inner tube may be disposed within the lumen of a slidable intermediate tube which may be moved by the operator distally or proximally relative to the catheter&#39;s shaft. 
     In further embodiments of the invention a unique catheter construction is developed in order to provide a movable inner tube affixed to a slidable sealing sleeve which allows the operator to move the inner tube distally or proximally relative to the catheter&#39;s outer shaft and thereby manipulate its length and balloon. 
       FIG. 1  shows longitudinal section views of a first embodiment of the rapid exchange catheter  10  of the invention wherein the distal end of the catheter&#39;s inner tube  14  comprises a slidable internal tube  13 . Catheter  10  comprises a hollow outer shaft  6  comprising inner tube  14  installed therein, and a slidable internal tube  13  placed in inner tube  14  such that it protrudes distally via a distal opening thereof. In this construction the inner lumens of inner tube  14  and slidable internal tube  13  are linked, thereby providing a continuous inner lumen ending at a distal opening of slidable internal tube  13 . Proximal end of balloon  11   a  is attached to hollow outer shaft  6  at proximal attachment points  2   b  provided around the outer surface of a distal section thereof, and the distal end of said balloon is attached to the slidable internal tube  13  at distal attachment points  2   a  provided around the outer surface of a distal section of said slidable internal tube. 
     The lumen of inner tube  14  may be accessed via a lateral port  12  provided on hollow outer shaft  6 , between the distal and proximal ends thereof. Guide wire  5  (or other suitable accessories) may be inserted via lateral port  12 , advanced along the inner lumens of inner tube  14  and slidable internal tube  13 , and exit the inner lumen of slidable internal tube  13  through a distal opening thereof. 
     Slidable concentric member  13  is adapted to fit into inner tube  14  and its diameter is preferably smaller than the diameter of inner tube  14  such that it seals its distal opening while comfortably permitting distal or proximal sliding of slidable internal tube  13  therethrough. Distal end portion of displacement rod  18  is attached to slidable internal tube  13  thereby allowing the operator to move slidable internal tube  13  distally or proximally relative to the catheter&#39;s outer shaft by pushing or pulling the proximal tip of displacement rod  18 . 
     Further sealing of the distal opening of inner tube  14  may be achieved by an annular gasket  4  attached to the surface of distal tip of inner tube  14  such that a distal portion thereof is pressed against an annular portion of the outer surface of slidable internal tube  13 . 
     The proximal portion of hollow shaft  6  comprises a fluid port  17  used for inflating or deflating balloon  11   a  by an inflation fluid pressurized therethrough, an optional discharge valve  16  installed in discharge valve outlet  15 , and rod aperture  19  for moving displacement rod  18  distally or proximally therethrough. 
     During a typical procedure catheter  10  is inserted into a body treatment site in which balloon  11   a  may be inflated by an inflation fluid (designated by arrows  7   a  in  FIG. 1A ) pressurized through inflation fluid port  17 , for effecting dilation or other procedures in said treatment site and/or for anchoring said balloon therein. The pressurized fluids pass via the hollow interior of hollow shaft  6  and reach the interior of balloon  11   a  via a distal opening of said shaft. In its inflated state, shown in  FIG. 1B , the hollow interior of hollow shaft  6  and the internal space of balloon  11   a  are filled with pressurized inflation fluid. The distal opening of inner tube  14  is sealed by slidable internal tube  13  and (optionally) by gasket  4 , thereby preventing leakage of pressurized inflation fluid thereinto. The pressure of the inflation fluid inside the system presses the gasket and improves the sealing provided by gasket  4 . On the other hand, when the pressure of the inflation fluid is reduced the gasket&#39;s grip on the outer surface of inner tube  14  is diminished which makes it easier for the gasket to slide over it. 
     The requisite procedure is typically carried out in the inflated state of the balloon. By using the catheter of the invention for such procedures the operator may manipulate the catheter length and the shape and volume of balloon  11   a  by pulling displacement rod  18   b , thereby moving slidable internal tube  13  proximally further into inner tube  14 , as demonstrated by arrows  8   a . As a result, the distal end of balloon  11   a  collapses and folds internally, as shown in  FIG. 1C , which increases the pressure of the inflation fluid. Whenever the pressure of the inflation fluid inside the hollow interior of hollow outer shaft  6  and in balloon  11   a  is above a predetermined threshold value a slender passage of discharge valve  16  is expanded to allow portions of inflation fluid to exit via discharge valve outlet  15  and thereby reduce the pressure of inflation fluid below said threshold value. 
     It should be noted that the use of pressure discharge elements  15  and  16  constitutes merely one possible, exemplary means of pressure reduction. 
     Hollow outer shaft  6  is preferably made from a polymer or metal material, such as stainless 316, nitinol, or nylon, and it may be manufactured utilizing conventional methods, such as extrusion and laser cutting. The diameter of the hollow interior of hollow shaft  6  is generally in the range of 1-2 mm (millimeters), preferably about 1.2 mm, and the diameter of inflation fluid port  17  is generally in the range of 2-6 mm, preferably about 3 mm. The diameter of discharge valve outlet  15  is generally in the range of 2-6 mm, preferably about 3 mm, and the entire length of hollow shaft  6  is generally in the range of 500-2000 mm, preferably about 1200 mm. 
     Inner tube  14  is preferably made from a flexible polymer or metal material, such as pebax, nylon, stainless or nitinol and it may be manufactured utilizing conventional methods, such as extrusion and laser cutting. The diameter of inner lumen of inner tube  14  is generally in the range of 0.3-1 mm, preferably about 0.8 mm, and its entire length is generally in the range of 100-300 mm, preferably about 120 mm. Slidable internal tube  13  is preferably made from a flexible polymer or metal type of material, such as pebax, nylon, stainless or nitinol, and it may be manufactured utilizing conventional methods, such as pebax, nylon, stainless or nitinol. The diameter of inner lumen of slidable internal tube  13  is generally in the range of 0.3-1 mm, preferably about 0.5 mm, and its entire length is generally in the range of 30-150 mm, preferably about 70 mm. 
     In view of the axially-directed stretching and buckling forces exerted on the inner and outer tubes during elongation and shortening of the balloon, said tubes need to be constructed such that they are able to withstand axially-directed forces in the range of between 2 and 20 Newton without undergoing deformation. In order to achieve this aim, the conduits may be constructed of a braided material or of materials having a defined molecular orientation. The approximate maximum forces that the inner and outer tubes need to withstand (for two difference size ranges of balloon) are as follows:
         2.5-4 mm balloons: the tubing should withstand up to 500 g; polymer tubing made of nylon or pebax reinforced during the manufacturing process can be used.   4-5 mm (or larger) balloons: the tubing should withstand forces up to 2 kg. In this case it will be necessary to use a braided tube (polymer tube with metal mesh reinforcement).       

     Results for a representative study of the forces generated during balloon folding are presented in Example 2, hereinbelow. 
     Balloon  11   a  is preferably a type of non-compliant or semi-compliant or low-compliant balloon such as manufactured by Interface Associates (USA). It may be manufactured utilizing conventional methods known in the balloon catheter industry from a biocompatible polymer type of material such as nylon 12 PET. Its length is generally in the range of 5-50 mm, preferably about 20 mm, and its diameter is generally in the range of 2 to 12 mm, preferably about 3 to 5 mm. The proximal and distal edges of balloon  11   a  are preferably adhered to the outer surfaces of hollow shaft  6  and slidable internal tube  13 , at circumferential attachment points  2   b  and  2   a  respectively, by utilizing a low profile type of adhesion such as thermo bonding, UV adhesives or acrylic manufactured by Locktight. Preferably, the balloon should have a burst pressure within the range of 12-20 atmospheres. 
     The shape of balloon  11   a  has been found by the present inventors to be critical in order for said balloon to fulfill its intended functions in the presently-disclosed and claimed catheter system, namely:
         i. to facilitate folding in such a way that the desired annular space is formed at the distal end of the intussuscepted balloon, by the application of the lowest possible retracting force;   ii. to create a cavity inside the balloon during and after deflation; and   iii. to present a low profile that will facilitate introduction and withdrawal of the deflated balloon into and out of the catheter system and body passage.       

     The materials and design of the balloon, especially the shape of the distal taper and the relationship between the distal and the proximal taper, thus allow the balloon to fold smoothly and with relatively low pulling forces. This also insures that the balloon will fold only its distal side. 
     It appears, from modeling studies performed by the inventors, that a tapered balloon with a smooth round ending folds best and has a relatively low retracting force, when compared to standard tapered balloon or a balloon with a round ending. In a particularly preferred embodiment, the balloon has a proximal taper cone shaped with a 15-17 degree angle, and a 15 degree round cone distal taper, having a radius of about 0.5 mm at the junction of the taper and the neck. The results of the aforementioned modeling studies are presented in Example 1, hereinbelow. 
     Displacement rod  18  may be manufactured from a metal wire or tube, such as Stainless steel, Nitinol (Nickel Titanium) and/or from a polymer, having a diameter generally in the range of 0.2-2 mm, preferably about 0.5 mm, and length generally in the range of 50-150 mm, preferably about 100 mm. Distal portion of displacement rod  18  may be adhered to the distal section of slidable internal tube  13 . Most preferably, distal portion of displacement rod  18  may be combined into the wall of internal tube  13  thereby enhancing its rigidity and the grip provided therewith. Rod aperture  19  is adapted to allow conveniently moving displacement rod  18  therethrough while providing suitable sealing of the hollow interior of hollow shaft  6 , thereby preventing leakage of inflation fluid therefrom. 
     The inflation fluid is preferably a saline or a saline mixed with radio-opaque solution in different ratios. A syringe pump, or other suitable inflation pumps, as commonly used in the field, may be used for introducing the inflation fluid into the system. The pressure in the system in its various states is typically in the range of 0 to 25 atmospheres. 
     While different discharge valves may be employed, discharge valve  16  is preferably implemented by an annular element having an axial slender passage passing therein. In such implementation discharge valve  16  is manufactured from an elastomer type of material, such as PVC by an injection molding process. Its outer diameter is generally in the range of 2-6 mm, preferably about 4 mm, and its slender passage is designed to expand whenever a pressure gradient of about 4 bar evolves between its ends. 
     Optionally, a proximal part  18   c  of rod  18  is made to be wide enough to occupy a volume of space within a proximal portion  6   b  of hollow shaft  6 , as shown in  FIG. 1F . This piston-like construction  18   c  allows for a syringe like action of rod  18  when retracted proximally, causing it to evacuate enough space in the proximal portion  6   b  of the lumen of hollow shaft  6 . This extra space will then be filled by inflation fluid, thereby preventing pressure accumulation within the catheter during retraction of the rod  18 . 
     As shown in  FIG. 1C  in its folded state distal cavity  3   a  is obtained by the inwardly folded distal sections of balloon  11   a . The volume encompassed by cavity  3   a  may be enlarged by (partially or entirely) deflating the balloon in this folded state, thereby filling the enlarged cavity with samples and/or debris from the treatment site. Different distal balloons may be designed to provide various balloon manipulations as exemplified in  FIGS. 1D and 1E . 
     For example, in balloon  11   b  shown in  FIG. 1E  a proximal section of the balloon collapses and folds inwardly in response to movement of slidable internal tube  13  proximally, thereby forming a proximal cavity  3   b . Such a result may be achieved by using a balloon which has higher resistance to folding at its proximal tapered end relative to its distal tapered end This can be achieved by using a balloon having different angles at its distal and proximal tapers, wherein a steeper taper facilitates its folding. 
     As another example, in balloon  11   ab  shown in  FIG. 1D  both, proximal and distal, sections of the balloon are folded in response to movement of slidable internal tube  13  proximally, thereby forming a proximal cavity  3   b  and a distal cavity  3   a . This result may be obtained for example by using a balloon  11   ab  with a symmetric shape—namely, the balloon having the same taper at its distal and proximal sides. 
     The procedure for using the balloon catheter of the present invention may be briefly described as follows:
         1) Insertion of catheter into the body via peripheral blood vessel by use of standard rapid exchange methods, as are well known in the art;   2) Inflation of the balloon by injecting inflation fluids via fluid port  17  and the inner lumen of outer shaft  6 , as demonstrated by fluid inflation arrows  7   a  in  FIG. 1A ; the pressure inside balloon  11  may be in general about 1-25 Atmospheres, preferably about 6 Atmospheres.   3) In this state, with the balloon catheter  10  firmly anchored at the treatment site, the inner lumens of inner tube  14  and of slidable internal tube  13  may now be utilized for operating at the treated site with different interventional tools (not shown), as may be required.   4) If required, a sample or other liquid or solid matter (for example fluids, secretions, and/or debris) may be collected from the treatment site, by pulling proximally displacement rod  18  thereby releasing retracting slidable internal tube  13  proximally, as demonstrated by arrow  8   a  in  FIG. 1B . During retraction of slidable internal tube  13  by the operator the distal tip of balloon  11  collapses and its outer surface portions are folded inwardly over the distal tip of slidable internal tube  13  and thereafter over itself as further portions of the balloon collapse, as illustrated in  FIG. 1C .   5) Retraction of slidable internal tube  13  and the resulting inward folding of balloon  11  shorten the overall length of inflated balloon  11  which actually reduces the volume of inflated balloon  11 . Consequently, the pressure exerted by the inflating fluids increases, resulting in a considerable pressure increase in balloon  11  and inner lumen of outer shaft  6 . Whenever the pressure in balloon  11  and inner lumen of outer shaft  6  reaches a certain set-point (e.g., 5-20 atmospheres) inflation fluids can be discharged via discharge valve  16 , as shown by arrows  7   b  in  FIG. 1B , such that the pressure in balloon  11  and inner lumen of outer shaft  6  remains within a predetermined pressure range (e.g., 5-20 atmospheres). Another exemplary option for discharging pressure is by widening the proximal section  18   c  of rod  18  so it can act similar to a syringe action, as shown in  FIG. 1F . During this step the operator can determine via a graduated scale (not shown) provided on rod  18  the amount of length of inner tube  14  that has been retracted and in this way determine when to stop the retraction of inner tube  14 .   6) Subsequently, balloon  11  is deflated by retracting inflation fluids via fluid port  17 . As a result, the pressure inside balloon  11  and inner lumen of outer tube  6  is substantially decreased, and balloon  11  is deflated. The reduction in the volume of balloon  11  results in enlargement of distal cavity  3   a.          

     The operator then retracts balloon catheter  10  proximally such that portion of fluid/secretion and debris confined within proximal cavity  3   a  are withdrawn with the balloon catheter  10  (not shown in the figures). The debris, objects or samples collected may be easily collected when the entire length of balloon catheter  10  is ejected from the body of the treated subject, by pushing the inner tube  14  distally and unfolding the folded portions of balloon  11 , thus restoring the deflated state of balloon  11  (shown in  FIG. 1A ). 
       FIGS. 2A to 2C  show longitudinal section views of a rapid exchange catheter  20  according to a second preferred embodiment of the invention wherein the diameter of a distal section  24   b  of the inner tube  24   a  is adapted to receive internal slidable tube  13 . In this preferred embodiment the diameter of distal section  24   b  of inner tube  24   a  is made relatively greater than the diameter of the proximal section thereof. Internal slidable tube  13  is designed to tightly fit into proximal section  24   b  and thereby seal its distal opening and prevent leakage of inflation fluid thereinto. Alternatively or additionally, sealing may be achieved by gasket  4  attached to the distal section  24   b  of inner tube  24   a  such that a distal portion thereof is pressed against an annular portion of the outer surface of slidable internal tube  13 . Internal slidable tube  13  and the proximal section of inner tube  24   a  may be manufactured to have the same inner diameter, thereby forming a substantially homogenous inner lumen therebetween, particularly when internal slidable tube  13  is advanced all the way into distal section  24   b.    
     The structure and geometrical dimensions of elements of catheter  20  are much the same as those elements designated by the same numerals which were described above with reference to  FIGS. 1A to 1C . In addition, the construction of the catheter tubes such that they are able to withstand the axially-directed stretching and buckling forces in this, and in all subsequent embodiments, are as described hereinabove, in connection with the first-described embodiment. Similarly, balloon  11   a  may be inflated by inflation fluid ( 7   a ) pressurized via inflation fluid port  17 , and catheter&#39;s  20  length and the shape and volume of balloon  11   a  may be manipulated by moving displacement rod  18  distally or proximally, as exemplified in  FIGS. 2A to 2C . Different balloons may be designed to provide various balloon folding configurations as exemplified in  FIGS. 1D and 1E . The optimal balloon shape for use with this, and with all subsequently described embodiments is as described hereinabove, with reference to the first described embodiment. 
     Inner tube  24   a  may be manufactured by an extrusion and laser cutting process from a plastomeric or metallic type of material, preferably from nylon, PET or stainless steel. The diameter of the distal section of inner tube  24   a  is generally in the range of 0.3-2 mm, preferably about 0.5 mm, and the diameter of slidable internal tube  13  is adapted to provide tight fitting and the necessary sealing of distal opening of inner tube  24   a  when said internal tube is inserted thereinside. 
       FIG. 3  shows a longitudinal section view of catheter  30  according to a third preferred embodiment of the invention wherein the distal section of the inner tube  14  comprises an external slidable tube  13   a . In this preferred embodiment the distal end of balloon  11   a  is attached to the slidable external tube  13   a  at distal attachment points  2   a  provided around the outer surface of a distal section of said slidable external tube. The diameter of external slidable tube  13   a  is made relatively greater than the diameter of inner tube  14 . External slidable tube  13   a  is designed to tightly fit over the outer surface of the proximal section of inner tube  14  and to thereby seal its distal opening and prevent leakage of inflation fluid thereinto. Alternatively or additionally, sealing may be achieved by gasket  4  attached to the proximal end portion of external slidable tube  13   a  such that a proximal portion thereof is pressed against an annular portion of the outer surface of inner tube  14 . 
     Using such external slidable tube  13   a  in catheter  30  permits the attachment of a relatively short displacement rod  18   a  to the proximal section of said slidable tube  13   a . Alternatively or additionally, the distal portion of displacement rod  18   a  may be combined into the wall of external slidable tube  13   a  along its longitudinal length, thereby enhancing its rigidity and the grip provided therewith. 
     The structure, geometrical dimensions of elements of catheter  30  designated by the same numerals, and the method of manipulating its length and balloon volume and shape, are much the same as those elements and manipulating method which were previously described hereinabove and therefore, for the sake of brevity, said elements will not be further discussed at this point. External slidable tube  13   a  may be manufactured by an extrusion and laser cutting process from a plastomeric or metallic type of material, preferably from nylon or stainless steel. The diameter of external slidable tube  13   a  is adapted to provide tight fitting and the necessary sealing of distal opening of inner tube  14  when said external slidable tube is mounted thereover. For example, the diameter of external slidable tube  13   a  may be in the range of 0.3-2 mm, preferably about 0.8 mm. 
     A fourth preferred embodiment ( 40 ) of the invention is demonstrated in the longitudinal section view shown in  FIG. 4 , wherein the diameter of the distal section  44   b  of inner tube  44   a  is adapted to be received in an external slidable tube  13   a . In this preferred embodiment the distal end of balloon  11   a  is attached to the slidable external tube  13   a  at distal attachment points  2   a  provided around the outer surface of a distal section of said slidable external tube. The diameter of distal section  44   b  of inner tube  44   a  is made relatively smaller than the diameter of the proximal section thereof. External slidable tube  13   a  is designed to tightly fit over proximal section  44   b  and thereby seal its distal opening and prevent leakage of inflation fluid thereinto. Alternatively or additionally, sealing may be achieved by gasket  4  attached to the proximal end of External slidable tube  13   a  such that a proximal portion thereof is pressed against an annular portion of the distal section  44   b  of inner tube  44   a.    
     The external slidable tube  13   a  of catheter  40  allows attachment of a relatively short displacement rod  18   a  to the proximal section of said slidable tube  13   a . Alternatively or additionally, the distal portion of displacement rod  18   a  may be combined into the wall of external slidable tube  13   a  along its longitudinal length, thereby enhancing its rigidity and the grip provided therewith. 
     The structure, geometrical dimensions of elements of catheter  40  designated by the same numerals, and the method of manipulating of its length and balloon&#39;s volume and shape, are much the same as those elements and the manipulating method which were previously described hereinabove and therefore will not be further discussed here. Inner tube  44   a  may be manufactured by an extrusion and laser cutting process from a plastomeric or metallic type of material, preferably from nylon or stainless steel. The diameter of the distal section  44   b  of inner tube  44   a  is generally in the range of 0.3-2 mm, preferably about 0.5 mm, and the diameter of external slidable tube  13   a  is adapted to provide tight fitting and the necessary sealing of distal opening of inner tube  44   a  when said external tube is mounted thereover. 
     In a fifth preferred embodiment of the invention, illustrated in the longitudinal section view shown in  FIG. 5 , an external slidable tube  13   a  is mounted over an inner tube  54   b  protruding distally through a distal opening of fixed inner tube  54   a  of catheter  50 . In this preferred embodiment the distal end of balloon  11   a  is attached to the slidable external tube  13   a  at distal attachment points  2   a  provided around the outer surface of a distal section of said slidable external tube. A proximal end portion of inner tube  54   b  is fitted into a distal opening of fixed inner tube  54   a , such that it seals said distal opening and most of its longitudinal length protrudes distally therefrom into the hollow interior of hollow shaft  6 . The diameter of external slidable tube  13   a  is adapted to tightly fit over the external surface of inner tube  54   b , thereby sealing its distal opening while allowing it to be easily moved distally or proximally thereon by the operator. 
     Sealant  4   c  may be applied to the proximal end of inner tube  54   b  in order to provide enhanced sealing of the distal opening of fixed inner tube  54   a . Sealing of the distal opening of inner tube  54   b  may be achieved by an annular gasket  4  attached to the proximal tip of external slidable tube  13   a  such that a proximal portion thereof is pressed against an annular portion of the outer surface of inner tube  54   b.    
     Gaskets  4  can be made of a flexible material such as silicone or polyurethane. Alternatively, gaskets  4  may be implemented by an added lubricant such as mineral oil or silicone oil which improves the sliding between the tubes. The sealing may be further increased by increasing the pressure in the balloon. 
     It should be noted that tubes  13   a  and  54   a  may be fixed tubes such that tube  54   a  is fixed to the shaft  6  and tube  13   a  is fixed to the distal neck of balloon  11   a , such that tube  54   b  can slide into both tubes. 
     The structure, geometrical dimensions of elements of catheter  50  designated by the same numerals, and the method of manipulating of its length and balloon&#39;s volume and shape, are much the same to those elements and manipulating method which were previously described hereinabove and therefore will not be discussed here, for the sake of brevity. Fixed inner tube  54   a  and external slidable tube  13   a  may be manufactured by an extrusion and laser cutting process from a plastomeric or metallic type of material, preferably from nylon or flexible metal. Their diameters are adapted to provide tight fitting and the necessary sealing of distal openings of fixed inner tube  54   a  and of inner tube  54   b.    
       FIGS. 6A to 6C  show longitudinal section views of a sixth preferred embodiment of the invention in which the inner tube  64  of catheter  60  is encompassed in a slidable intermediate tube  33   b . In this preferred embodiment the distal end of balloon  11   a  is attached to the slidable intermediate tube  33   b  at distal attachment points  2   a  provided around the outer surface of a distal section of said slidable intermediate tube. Horizontal opening  38  is provided on an upper side of slidable intermediate tube  33   b . Inner tube  64  protrudes upwardly through horizontal opening  38  towards the upper side of hollow shaft  6  at the location in which it is affixed thereto and provide an access to its lumen via lateral port  12 . 
     During a procedure balloon  11   a  may be inflated by pressurized fluid (designated by arrows  7   a  in  FIG. 6A ) provided via inflation fluid port  17 . As illustrated in  FIG. 6B , pressurized fluid passes through the hollow interior of hollow shaft  63  into the internal space of balloon  11   a . The catheter and its balloon in the inflated state are illustrated in  FIG. 6B . The proximal section of intermediate tube  33   b  between horizontal opening  38  and the proximal end of intermediate tube  33   b  may be sealed by a sealant  66  in order to prevent entry of inflation fluids thereinto. Whenever the pressure in balloon  11   a  and hollow interior of hollow shaft  63  is greater than a predetermined threshold value, a portion of the inflation fluids is discharged via discharge valve  16  installed in discharge valve outlet  15 . 
     The proximal section of intermediate tube  33   b  protrudes proximally via proximal opening  65  provided at the proximal end of shaft  63 . Proximal opening  65  is designed to conveniently allow the sliding of intermediate tube  33   b  therethrough while providing suitable sealing thereof and preventing leakage of inflation fluid therefrom. Manipulation of the catheter length and its balloon shape and volume are performed by sliding the intermediate tube  33   b  proximally or distally relative to the catheter shaft. 
     For example, after inflating balloon  11   a  the operator may pull the proximal section of intermediate tube  33   b  (shown by arrow  8   a  in  FIG. 6B ) thereby causing distal section of balloon  11   a  to collapse and fold inwardly and deform cavity  3   a , as illustrated in  FIG. 6C . Horizontal opening  38  is adjusted to allow sliding intermediate tube  33   b  proximally into a state in which attachment point  2   a  reaches the distal end of shaft  63 , and on the other hand, to allow sufficient distal sliding of intermediate tube  33   b  in order to enable stretching the full length of balloon  11   a.    
     Intermediate tube  33   b  may be manufactured by extrusion or laser cutting processes, from a plastomer or metallic type of material such as nylon, Teflon, or flexible stainless steel. The diameters of inner tube  64  and of intermediate tube  33   b  are adapted to allow insertion of inner tube into the lumen of intermediate tube  33   b  while providing suitable sealing thereof and preventing leakage of inflation fluids thereinto. For example intermediate tube  33   b  may have an inner diameter of about 0.8 mm and the outer diameter of inner tube  64  may be of about 0.78 mm. 
     Intermediate tube  33   b  can be manufactured by an extrusion process in which the ID (internal diameter) has an appropriate tolerance to fit over the outer diameter of inner tube  64 . Inner tube  64  and intermediate tube  33   b  are assembled together such that lateral port  12  is located in the horizontal opening  38  of intermediate tube  33   b . Thereafter the tubes  64  and  33   b  are inserted into the hollow shaft  63  and lateral port  12  can be attached to hollow shaft  63 . 
     It should be noted that intermediate tube  33   b  is not necessarily a complete tube. While the distal portion of intermediate tube  33   b  should be of a tubular shape, its proximal portion may have other cross-sectional shapes such as a semilunar shape. Alternatively, the proximal portion of intermediate tube  33   b  may be implemented by a wire attached to its distal portion and exiting catheter  60  via proximal opening  65 . 
       FIGS. 7A to 7C  show longitudinal section views of a catheter  70  according to a seventh preferred embodiment of the invention wherein the inner tube  74  is made movable by affixing it to a slidable sealing sleeve  79 . In this preferred embodiment the distal end of balloon  11   a  is attached to the inner tube  74  at distal attachment points  2   a  provided around the outer surface of a distal section of said inner tube. 
     The structure, geometrical dimensions of elements of catheter  70  designated by the same numerals, and the method of manipulating its length and balloon&#39;s volume and shape, are much the same as those elements and manipulating method which were previously described hereinabove and therefore will not be further discussed herein, for the sake of brevity. 
     As with previous embodiments of the invention the inner tube  74  is disposed in the hollow interior of the catheter&#39;s hollow outer shaft  76  and a curved section  37  thereof comprising lateral port  12  protrudes outwardly therefrom. A lateral opening  9  is provided on hollow outer shaft  76  from which said curved section  37  of inner tube  74  is protruding outwardly from hollow shaft  76 . Lateral opening  9  is sealed by sealing sleeve  79  mounted over an outer surface of hollow outer shaft  76 . Sealing sleeve  79  is designed to tightly fit over the outer surface of hollow outer shaft  76 , and to seal lateral opening  9  and the attachment area between sealing sleeve  79  and the curved section  37  of inner tube  74  protruding therefrom. Moreover, sealing sleeve is also made slidable to allow its movement distally or proximally within the limits imposed by lateral opening  9 . 
     In this way a movable inner tube  74  is obtained. The operator may inflate (designated by arrows  7   a  in  FIG. 7A ) balloon  11   a  and move inner tube distally or proximally by sliding sealing sleeve  79  over hollow shaft  76 . Additionally or alternatively, a displacement rod  48  may be employed for this purpose. Displacement rod  48  may be attached to a proximal section of inner tube  74  and a proximal section thereof can be made available to the operator via a proximal opening  75  provided at the proximal end of hollow shaft  76 . Proximal opening  75  is designed to allow conveniently sliding displacement rod  48  therethrough while providing suitable sealing thereof and preventing leakage of inflation fluid therefrom. 
     Lateral opening  9  is adjusted to allow moving inner tube  74  proximally into a state in which attachment point  2   a  reaches the distal end of hollow shaft  76 , and on the other hand, to allow sufficient distal movement of inner tube  74  in order to enable stretching of balloon  11   a  to its fullest length. 
     Sealing sleeve  79  can be manufactured by an extrusion and laser cutting process from a plastomer or metallic type of material, preferably from nylon or flexible stainless steel. The sealing and attachment of sealing sleeve  79  and the curved section  37  of inner tube  74  is preferably obtained by bonding these parts together by thermo-bonding or any other adhesive method such that they can: slide together. The diameter of sealing sleeve  79  is adjusted according to the geometrical dimensions of hollow shaft  76 . For example, if the diameter of hollow shaft is about OD (outer diameter) 1.2 mm then the diameter of sealing sleeve is made about ID 1.22 mm. 
       FIG. 7C  demonstrates an implementation of catheter  70   a , similar to catheter  70 , wherein an inner sealing sleeve  77  is adapted to be installed in the hollow interior of hollow shaft  76 . In this implementation inner sealing sleeve  77  is adapted to be pressed against the inner wall of hollow shaft  76  about the area of lateral opening  9  and thereby to provide suitable sealing thereof. As in catheter  70  illustrated in  FIG. 7A , an essentially vertical section of inner tube  74  protrudes outwardly via inner sealing sleeve  77  and may be accessed by the operator via lateral port  12 . The sealing and attachment of inner sealing sleeve  77  and vertical section of inner tube  74  may be obtained using the same means described above with reference to catheter  70 . 
     Inner sealing sleeve  77  can be manufactured by an extrusion and laser cutting: process from a plastomeric or metallic type of material, preferably from nylon or flexible stainless steel. The sealing and attachment of inner sealing sleeve  77  and the vertical section of inner tube  74  is preferably obtained in a similar manner as was explained hereinabove. The diameter of sealing sleeve  77  is adjusted according to the geometrical dimensions of hollow shaft  76 . For example, if the diameter of hollow shaft is about ID 1 mm then the diameter of inner sealing sleeve is made about OD 0.98 mm. 
     All of the abovementioned parameters are given by way of example only, and may be changed in accordance with the differing requirements of the various embodiments of the present invention. Thus, the abovementioned parameters should not be construed as limiting the scope of the present invention in any way. In addition, it is to be appreciated that the different tubes, balloons, shafts, and other members, described hereinabove may be constructed in different shapes (e.g. having oval, square etc. form in plan view) and sizes from those exemplified in the preceding description. 
     It should be noted that the different balloon catheter embodiments of the invention which were described hereinabove may be implemented with different types of balloon enabling folding of the proximal section of the balloon, the distal section of the balloon, or both proximal and distal sections of the balloon, as was exemplified hereinabove with reference to  FIGS. 1D and 1E . 
     Furthermore, it should be noted that the different balloon catheter embodiments of the invention which were described hereinabove may be used for delivering a stent mounted on the balloon, and placing said stent in the treatment site as commonly performed in standard stent procedures. 
     EXAMPLES 
     Example 1 
     Finite Element Analysis (FEA) of a Debris-Collecting Balloon for Use in the Present Invention 
     FEA is a computerized tool which was used to optimize the balloon design in order to improve its ability to fold in the desired way. The FE model describes an inflated balloon which edge is retracted, resulting in folding of the balloon. The simulation was performed on different balloon designs and at varied inflation pressures, taking into account the mechanical properties of the balloon material, which was chosen to be nylon 12 or pebax. 
     Assumptions: 
     i. The balloon is made of a homogenous and isotropic material. 
     ii. The balloon&#39;s shape is symmetrical around its longitudinal axis. 
     iii. The balloon&#39;s shape is symmetrical around its mid transverse axis. 
     iv. The folding results in flexural stresses in the balloon material. Thus the mechanical properties (Modulus and Poisson Ratio) of the substance when flexed are taken into account in the FE analyses. 
     Methods: 
     a) The analyses were performed using a nonlinear Finite Elements Analysis (FEA) program MSC.MARC. This software allows assessment of the structural integrity and performance of parts undergoing large deformations as a result of thermal or structural load (www.mscsoftware.com).
 
b) The analyses were nonlinear, assuming large displacements and taking into account stiffness change due to geometry update and sequential forces.
 
c) The model was 2D axisymmetric.
 
d) The model consisted of about 1000 nodes and 1000 2D solid elements.
 
e) Constant pressure was applied from within the balloon on its walls, reflecting the inflation pressure. Simultaneously, gradually increased axial force was exerted to the edge of the balloon, resulting in its folding. The displacement of the balloon wall in the horizontal (longitudinal) axis was measured versus the applied force.
 
f) The longitudinal axis of the balloon was kept fixed, while the balloon walls were free to move/fold as a result of the axial load.
 
g) The balloon&#39;s specifications are listed in the following table:
 
                                                 Balloon Specifications               Balloon length [mm]   20           Balloon Outer Diameter [mm]   3           Tube Outer Diameter [mm]   0.4           Balloon Body Wall Thickness [μm]   10           Neck Wall Thickness [μm]   50           Tube Wall Thickness [μm]   100           Tapering   varying           Material   PET (Polyethylene               Terephthalate)           Mechanical Properties           Flexural Modulus [Kg/mm 2 ]   100           Flexural Yield Strength [Kg/mm 2 ]   8.15           Poisson Ratio   0.4                        
h) Four balloon designs were analyzed, wherein the differences reside in the design of their tapering (see  FIG. 8 ):
         Standard 20° tapering   20° tapering with smooth round ending   Round ending   Round ending with initial retracting
 
i) The simulations were performed at five different inflation pressures: 1, 3, 6, 9 and 12 atmospheres.
 
Results:
       

       FIG. 9  shows the displacement vs. retracting force for the four balloon shapes at an inflation pressure of 6 atmospheres. Considering the maximal force required for collapse of the balloon, the Tapered-Round Ending Balloon required the lowest force, whereas the Round Ending Balloons need the greatest force to collapse. The Tapered Ending Balloon is somewhere between them. The slope of the Tapered Ending Balloon in the initial phase seems to be relatively moderate compared to the other balloon configurations. The moderate slope indicates higher stiffness. In other words, higher force is required to induce a given displacement. The slope of the Tapered-Round Ending Balloon is the steepest one, and suggests relatively high compliance to folding. 
     The balloon retracted shape vs. the original shape, at different inflation pressures was also studied (results not shown). The results demonstrated that the Tapered Ending Balloon is barely retracted, compared to the Round Ending Balloons which are retracted in a more smooth and continuous fashion. This is in spite of the higher force required to fold them. 
     Conclusion: 
     From the above analyses it was concluded that the inflation pressure and the balloon geometry have an important role in determining of the required folding force and the folding style. It appears that a tapered balloon with a smooth round ending folds best and has a relatively low retracting force, when compared to standard tapered balloon or a balloon with a round ending. 
     Example 2 
     Determination of the Force that is Required in Order to Fold the Balloon at Different Inflation Pressure 
     Equipment and Materials: 
     3.0 mm Nylon 12 Vestamid L2101F Balloon (Interface Associates 316079-1) 
     Glass tube with inner diameter of 3 mm. 
     Guidant HI-TORQUE CROSS-IT 200XT 0.014″ Guidewire. 
     Hounsfield Test Equipment Model TX0927, 50-N load cell. This computer controlled testing machine enables determining tension, compression, shear, flexure and other mechanical and physical properties of materials. The machine provides selection of test speeds and direction of travel. It can measure the force and displacement values and can also graphically display the test.
 
Assouline Compressor type 1.5 HP.
 
Fluid dispensing system Model 1500XL.
 
Procedure:
 
     The balloon was inserted into a 3-mm glass tube, at straight position or inclined to 45°. A guidewire was inserted into the inner tube in order to stabilize the folding motion. The balloon was inflated using a compressor and the inflation pressure was controlled by a dispenser. The procedure was performed at pressures ranging between 3-7 atm, with increments of 1 atm. The balloon was folded using the Hounsfield Test machine, by pulling the inner tube at speed of 100 mm/min up to 20 mm, and then pushing back at the same speed until the balloon was completely unfolded. 
     Four tests were conducted at each pressure, to confirm that the results could be replicated. 
     Results: 
     The maximal force required for folding the balloon at each pressure is presented in  FIG. 10 . The maximal force increases with the inflation pressure for both positions (straight and inclined) and ranges between 2-3.5 N (200-350 gr) with increments vary between 0.2-0.4 N (20-40 gr) per step of 1 atm in pressure. Higher inflation pressure requires greater force to fold the balloon. The relationship is approximately linear (R 2 =0.98). The maximal forces are slightly lower for the inclined position; however, repeated tests at the straight position revealed that the lesser forces result from the material fatigue. To support this assumption, visual examination of the balloon after 40 repeats showed that the balloon material lost its flexibility and looked crumpled. 
     The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.