Abstract:
The present invention relates to balloon catheters for treating a luminal system of a patient. Specifically, the invention relates to catheters having a flexible membrane positioned at a distal portion of the catheter, the flexible membrane retained in a substantially unexposed conformation prior to deployment. Preferably the flexible membrane is capable of delivering a therapeutic agent to a localized environment when deployed to an exposed conformation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of U.S. Nonprovisional application Ser. No. 12/171,134, filed Jul. 10, 2008, this application claims priority to U.S. Provisional Application Ser. No. 60/949,736, filed Jul. 13, 2007, each of which are incorporated by reference in their entireties herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to balloon catheters for treating the luminal systems of a patient. Specifically, the invention relates to catheters having a flexible membrane positioned at a distal portion of the catheter where the flexible membrane is retained in a substantially unexposed conformation prior to deployment. Preferably the flexible membrane is capable of delivering a therapeutic agent to a localized environment when deployed to an exposed conformation. 
         [0004]    2. Description of the Related Art 
         [0005]    Heart and vascular disease are major problems in the United States and throughout the world. Conditions such as atherosclerosis result in blood vessels becoming blocked or narrowed. If this blockage or narrowing of a vessel occurs in the coronary arteries supporting the heart, which deliver oxygenated blood, this will have significant consequences, since the heart muscle must be well oxygenated in order to maintain its blood pumping action. 
         [0006]    Occluded, stenotic, or narrowed blood vessels may be treated with a number of relatively non-invasive medical procedures including percutaneous transluminal angioplasty (PTA), percutaneous transluminal coronary angioplasty (PTCA), and atherectomy. Such angioplasty techniques typically involve the use of a balloon catheter. Commonly, the balloon catheter is initially advanced over a guidewire so that the balloon is positioned adjacent a stenotic lesion. Once in place, the balloon is then inflated, and the restriction of the vessel is opened. 
         [0007]    Typically, balloon catheters are structured such that they have a balloon fastened at least at one end around the exterior of a hollow catheter shaft. The hollow interior of the balloon is in a fluid flow relation with the hollow interior of the shaft. Fluid under pressure can thereby be supplied to the interior of the balloon through the shaft in order to expand the balloon against an obstruction. 
         [0008]    Presently catheter balloon materials may be classified as compliant, semi-compliant, or non-compliant balloons. Compliance can be defined as the increase in the balloon diameter above nominal balloon pressure. Generally, non-compliant balloons have less increase in diameter, than semi-compliant balloons, which in turn have less increase in diameter than compliant balloons. 
         [0009]    Compliant balloons expand and stretch with increasing pressure within the balloon, and are made from such materials as silicone, thermoplastic elastomers (TPEs), and polyethylene or polyolefin copolymers. Non-compliant balloons, made from such materials as polyethylene terephthalate (PET) or polyamides, remain substantially at a pre-selected diameter as the internal balloon pressure increases beyond that required to fully inflate the balloon. 
         [0010]    Compliant balloon materials provide a degree of softness to the balloon which aids its passage through, and expansion within, e.g., blood vessels. Known compliant balloon materials also can display good abrasion and puncture resistance at thicknesses typically used for medical device balloons. In light of the foregoing, it is one object of the present invention to provide a balloon catheter that employs a compliant balloon. 
         [0011]    It is an object of the present invention to provide a device that is useful for recovering a balloon predictably and compactly upon deflation to facilitate in vivo movement of the balloon catheter. 
         [0012]    In addition to the above-described uses of balloon catheters in PTA, PTCA, and atherectomy, some balloon catheters are made to deliver therapeutic drugs or agents. For example, some balloon catheters deliver a systemic bolus of liquid that includes a drug to a targeted tissue location using an open catheter lumen or channel located at some length along the catheter shaft. Alternatively, the drug can be delivered by coating it on the exterior of the balloon. Unfortunately, when such delivery methods are used to deliver a controlled volume of medication to a desired tissue location, medication may be lost to systemic circulation either because of an inability of the drug to quickly penetrate local tissue, or because the drug coating has been washed away. 
         [0013]    In general, liquid formulations containing a drug or agent that are delivered to a targeted tissue location by liquid bolus may not penetrate the tissue sufficiently at the targeted tissue location to result in a significant therapeutic effect, and may be washed away by body fluids. Similarly, drug coated on the surface of a balloon can be washed away due to contact with a circulatory environment, as the circulatory environment matches the environment the drug is designed to target. Such systemic dilution substantially diminishes the effectiveness of the drugs or agents, and increases the likelihood of a greater systemic effect caused by the quantity of drug or agent washed into the bloodstream. 
         [0014]    In light of the foregoing, there is a need for an improved balloon catheter capable of delivering therapeutics in a safe and effective manner to targeted tissues within the body. The present invention includes embodiments directed toward solutions that address this unmet need. 
       SUMMARY OF THE INVENTION 
       [0015]    The purpose and advantages of the present invention will be set forth in and apparent from the description that follows, as well as will be learned by practice of the invention. Additional advantages of the invention will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings. 
         [0016]    To achieve these and other advantages and in accordance with the purpose of the invention, as embodied herein and broadly described, the invention includes a balloon catheter with an inner shaft member having a proximal end portion, a distal end portion, and a length therebetween. The balloon catheter also includes an outer shaft member that is movable relative to the inner shaft member and has a proximal end portion, a distal end portion, and a length therebetween. The balloon catheter further includes an annular flow passage disposed between the inner and outer shaft members and a flexible membrane extending between the distal end portion of the inner shaft member and the distal end portion of the outer shaft member. This flexible membrane includes both an inner surface and an outer surface and the inner surface is configured such that it is in fluid communication with the annular flow passage. The inner and outer shaft members of the balloon catheter define a chamber configured to receive the flexible membrane therein. In further accordance with the invention, the flexible membrane can include a therapeutic agent disposed thereon. 
         [0017]    In accordance with a further aspect of the invention, the sealed environment of the annular flow passage can be maintained during movement of the outer shaft relative to the inner shaft of the balloon catheter by the inclusion of a bellows component disposed at the proximal end portion of the outer shaft member, or by the inclusion of a dynamic seal disposed between the inner shaft member and the outer shaft member. 
         [0018]    In accordance with another aspect of the invention, the flexible membrane of the balloon catheter includes at least one driver segment and a delivery segment, where the driver segment defines at least a portion of a chamber configured to receive the delivery segment. In addition, the driver segment can be constructed of a material having different compliance than that of the delivery segment. Such driver segments can be constructed of materials more or less compliant than the material used to construct the delivery segment. Additionally, the driver segment or segments function to enfold the delivery segment. 
         [0019]    In accordance with a further aspect of the invention, the balloon catheter, when in a pre-deployed condition, includes a flexible membrane having spiral formations. Such spiral formations of the flexible membrane can be the result of rotational movement of the outer shaft member relative to the inner shaft member. 
         [0020]    The invention also includes a method of treating a luminal system of a patient. The method includes providing a balloon catheter as described herein, positioning the balloon catheter at a desired deployment site, introducing inflation fluid into the annular flow passage, and moving the outer shaft member relative to the inner shaft member to deploy the flexible membrane into an expanded configuration in order to treat the luminal system of the patient. In accordance with a further aspect of the invention, the method of treating a luminal system of a patient includes initial deployment of the flexible membrane to at least partially occlude the luminal system of the patient prior to full expansion of the flexible membrane. In yet another aspect of the invention, the method of treating a luminal system of a patient where the flexible membrane includes a therapeutic agent disposed thereon is provided. 
         [0021]    In accordance with a further aspect of the invention, the method of treating a luminal system of a patient includes collapsing the flexible membrane after deployment and treatment of the luminal system of the patient. Such collapse of the flexible membrane can be achieved by withdrawing inflation fluid from the annular flow passage or by movement of the outer shaft member axially or rotatably relative to the inner shaft member. 
         [0022]    In accordance with a further aspect of the invention, the method of treating a luminal system of a patient includes repositioning the flexible membrane upon collapse into a chamber configured to receive that membrane, where the chamber is defined by the outer shaft member and the inner shaft member. 
         [0023]    The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the methods and systems of the invention. Together with the description, the drawings serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    These drawings illustrate certain aspects of some of the embodiments of the present invention, and are not intended to be limiting. 
           [0025]      FIG. 1  is a schematic side view of a first representative embodiment of a balloon catheter in accordance with the present invention with a detail cross-sectional view of a flexible membrane at a distal end thereof, and  FIG. 1A  is an detail view of a dynamic seal near the proximal end of the catheter in accordance with one embodiment of the present invention. 
           [0026]      FIG. 1B  is a schematic side view of another representative embodiment of a balloon catheter of the present invention, including a bellows component disposed on the outer shaft member. 
           [0027]      FIG. 1C  is a schematic side view of another representative embodiment of a balloon catheter of the present invention, including a dynamic seal integrated into a hub disposed at the proximal end of the catheter. 
           [0028]      FIG. 2  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 1  wherein the flexible membrane is partially deployed. 
           [0029]      FIG. 3  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 1  wherein the flexible membrane is further deployed. 
           [0030]      FIG. 4  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 1  wherein the flexible membrane is fully deployed. 
           [0031]      FIG. 5  is a cross sectional view of the distal end of a balloon catheter in accordance with an alternative embodiment of the present invention wherein the flexible membrane is partially deployed. 
           [0032]      FIG. 6  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 5  wherein the flexible membrane is further deployed. 
           [0033]      FIG. 7  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 5  wherein the flexible membrane is fully deployed. 
           [0034]      FIG. 8  is a cross sectional view of the distal end of a balloon catheter prior to deployment of the flexible membrane in accordance with another embodiment of the present invention. 
           [0035]      FIG. 9  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 8  wherein the flexible membrane is partially deployed. 
           [0036]      FIG. 10  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 8  wherein the flexible membrane is fully deployed. 
           [0037]      FIG. 11  is a cross sectional view of the distal end of a balloon catheter prior to deployment of the flexible membrane in accordance with another embodiment of the present invention wherein the flexible membrane is attached in an advantageous conformation. 
           [0038]      FIG. 12  is a cross sectional view of the distal end of a balloon catheter of  FIG. 11  after deployment of the flexible membrane wherein the flexible membrane is attached in an advantageous conformation. 
           [0039]      FIG. 13A  is a cross sectional view of the distal end of a balloon catheter in accordance with another embodiment of the present invention prior to deployment of the flexible membrane. 
           [0040]      FIG. 13B  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 13A  in the process of deployment of the flexible membrane. 
           [0041]      FIG. 13C  is a cross sectional view of the distal end of a balloon catheter in accordance with the embodiment of  FIG. 13A  after deployment of the flexible membrane. 
           [0042]      FIG. 14  is a schematic side view of another representative embodiment of a balloon catheter of the present invention wherein the flexible membrane is arranged in a twisted conformation prior to deployment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. The methods and corresponding steps of the invention will be described in conjunction with the detailed description of the system. 
         [0044]    The devices and methods presented herein can be used for treating the luminal systems of a patient. The present invention is particularly suited for treatment of the cardiovascular system of a patient, such as delivery of therapeutic agents to specific locations within the patient&#39;s circulatory system. 
         [0045]    In accordance with the present invention a balloon catheter is provided with an inner shaft member having a proximal end portion, a distal end portion, and a length therebetween. The balloon catheter also includes an outer shaft member that is movable relative to the inner shaft member, and has a proximal end portion, a distal end portion, and a length therebetween. The balloon catheter further includes an annular flow passage disposed between the inner and outer shaft members and a flexible membrane extending between the distal end portion of the inner shaft member and the distal end portion of the outer shaft member. This flexible membrane includes both an inner surface and an outer surface with the inner surface configured such that it is in fluid communication with the annular flow passage. 
         [0046]    For purpose of explanation and illustration, and not limitation, exemplary embodiments of a balloon catheter for use in a cardiovascular system and other coronary indications in accordance with the invention are shown in  FIGS. 1A-4 . Additional features, aspects, and embodiments of a balloon catheter in accordance with the invention are provided in  FIGS. 5-14 , as will be described. The method of use of the representative embodiments will be described in conjunction with the device. 
         [0047]    For purposes of illustration and not limitation, as embodied herein and as depicted in  FIGS. 1A-1C , the balloon catheter  100  has an inner shaft member  10  having a proximal end portion  12 , a distal end portion  14 , and a length therebetween. The balloon catheter  100  also includes an outer shaft member  20  that is movable relative to the inner shaft member  10 , and has a proximal end portion  22 , a distal end portion  24 , and a length therebetween. 
         [0048]    The inner and outer shaft members  10 ,  20  of the balloon catheter  100  can be constructed of any suitable material including but not limited to polymer materials such as nylon, urethane, polyurethane, PEEK, PTFE, PVDF, Kyner, PE, HDPE or polyethylene of various suitable densities. As a further exemplary alternative, the inner and outer shaft members  10 ,  20  can be constructed of a composite comprising a fabrication of several different materials, such as a co-extrusion of different polymers, or a fiber-reinforced composite material such as fiber reinforced resin materials or braided materials. The inner and outer shaft members  10 ,  20  can also be constructed of alloy materials, and metallic materials such as stainless steel hypodermic tubing which is available from MicroGroup® Inc., Medway, Md. among other vendors. 
         [0049]    It is further contemplated that the inner and outer shaft members  10 ,  20  can be constructed of any bio-compatible material. As such, the inner and outer shaft members  10 ,  20  of the balloon catheter  100  can be constructed from the above-identified polymers, combinations or blends of these polymers, whether alone or in combination with other materials, or other bioabsorbable materials. 
         [0050]    The inner and outer shaft members  10 ,  20  can be manufactured using a variety of known techniques such as but not limited to: extrusion, injection molding, air-blowing, stretching, deep drawing, polymerization, cross-linking, dipping from solution, powder depositioning, sintering, electro-spinning, melt spinning, deformation under temperature, stretch blowing, chemical grafting any combination of the above with reinforcement element like metal braids, coils, glass fibers, carbon fibers and other kind of organic or inorganic fibers, liquid crystals, as well as classical machining technologies like milling, drilling, grinding, etc. In the event that metallic elements such as hypotubes, are to be incorporated, various metallic manufacturing techniques can be used, such as but not limited to, machining, tube drawing processes, drilling, milling EDM, other deformation methods, plating sputtering, electrografting, sintering, and depositioning e-polishing, among others. Additionally, the inner and outer shaft members  10 ,  20  can be constructed from polypropylene or urethane by an extrusion process using an extruder such as that available any of a number of known suppliers, such as Medical Extrusion Technologies, Inc. Murieta, Calif. U.S. Biosynthetic polymer materials can be constructed in a bioreactor according to the process disclosed in U.S. Pat. No. 6,495,152, the entirety of which is hereby incorporated by reference. The materials can be post processed in a number of ways including, for example and not by way of limitation, extrusion, molding, such as by injection or dipping, textile processing such as weaving or braiding, and forming. Forming processes that can be suitable are rolling and welding sheets of material or vacuum forming into tubular shapes, to name only a few examples. 
         [0051]    The inner and outer shaft members  10 ,  20  can be further coated with any of a variety of materials and techniques to enhance performance if desired, including a number suitable coatings and coating techniques subject to patent matters owned by Abbott Laboratories such as U.S. Pat. No. 6,541,116, U.S. Pat. No. 6,287,285, and U.S. Patent Publication No. 2002/0009535, the entireties of which are hereby incorporated by reference. For example, possible coating materials include lubricious materials such as Teflon® available from DuPont De Nemours, Wilmington, Del., U.S., and hydrophobic materials such as silicone lubricant dispersion PN 4097, available from Applied Silicone Corp., Ventura, Calif., U.S., or hydrophilic materials such as hydrogel available from Hydromer, Branchburg, N.J., U.S., or lubricious coatings such as those available from Hydro-Silk of Merritt Island, Fla., U.S. 
         [0052]    The inner and outer shaft members  10 ,  20  can have any suitable cross-sectional shape, including elliptical, polygon, or prismatic, although a circular cross-section generally is preferred. For a coronary balloon, the cross-sectional dimension generally is between about 0.01 millimeters to about 1.50 millimeters, preferably between about 0.10 millimeters and about 1.20 millimeters, most preferably between about 0.25 millimeters and about 1.00 millimeters. It will be appreciated that a balloon used for non-coronary medical applications would have different dimensions, and that this invention can be modified for use in those applications. Furthermore, in the case of a balloon catheter  100  with a “rapid exchange” (RX) guidewire design, the balloon catheter  100  can have an overall length between about 110 centimeters and 400 centimeters, preferably between about 120 centimeters and about 350 centimeters, more preferably the balloon catheter  100  has a length between about 120 centimeters and about 310 centimeters, and most preferably about 135 centimeters. In the case of a balloon catheter  100  with an “over the wire” (OTW) guidewire design, the balloon catheter  100  can have an overall length between about 110 centimeters and 400 centimeters, preferably between about 120 centimeters and about 350 centimeters, more preferably the balloon catheter  100  has a length between about 120 centimeters and about 310 centimeters, and most preferably about 300 centimeters. 
         [0053]    In general, the inner shaft member  10  of the instant invention will preferably include an inner lumen  15 . In some embodiments, the inner lumen  15  functions as a guidewire lumen. Accordingly, the balloon catheter  100  can be advanced over the guidewire  110  to the desired location. The guidewire lumen  15  can extend along essentially the entire length of the inner shaft member  10  so that the balloon catheter  100  resembles traditional “over-the-wire” catheters, as are well known in the art. Alternatively, the guidewire lumen  15  can extend along only a portion of the inner shaft member  10  so that the balloon catheter  100  resembles “single-operator-exchange” or “rapid-exchange” catheters, as are also well known in the art. Furthermore, “fixed wire” designs, as are well known in the art, may be used in connection with the instant invention as well. 
         [0054]    Referring now to  FIGS. 2-4 , there is shown a partial cross-sectional side view of the distal end portion of the balloon catheter  100 . As shown in  FIGS. 2-4 , a flexible tip  40  can extend from the distal end portion  14  of the inner shaft member  10 . A variety of distal tip configurations are known and used in the art, each generally capable of performing particular functions. In addition, the tip  40  can include a blunt tip or a tip having a pre-formed curve which functions as an atraumatic tip thereby allowing the balloon catheter  100  to be inserted within a patient&#39;s vasculature. Such a pre-formed curve ensures that the blunt tip does not pierce the vessel/artery or organ through which the balloon catheter  100  is being advanced. This and other tip designs are well known in the art. 
         [0055]    In accordance with another aspect of the invention, the outer shaft member  20  and the inner shaft member  10  define an annular flow passage  25 . In certain embodiments, the proximal end portion of the annular flow passage  25  will be either sealably connected directly to an inflation hub unit  30  as shown in  FIGS. 1B and 1C , or indirectly to an inflation hub unit  30  via an inflation lumen  14  and dynamic seal  32  as shown in  FIGS. 1 and 1A . The sealed environment of the annular flow passage  25  can be maintained during inflation of the flexible membrane and movement of the outer shaft member  20  relative to the inner shaft member  10  due to the presence of a dynamic seal  32 ,  36  disposed between the outer shaft member  20  and the inner shaft member  10 , such as shown in  FIGS. 1A and 1C . In certain embodiments this dynamic seal  32  can be located proximal to the inflation hub unit  30 , while in other embodiments it can be located distal to the inflation hub unit  30 . In accordance with alternative embodiments of the instant invention, the sealed environment of the annular flow passage  25  will be maintained by the presence of a bellows component  34  at the proximal end portion  22  of the outer shaft member  20  as shown in  FIG. 1B . 
         [0056]    As used herein, the term “flexible membrane,” refers to that portion of the balloon catheter  100  capable of undergoing deformation upon the introduction of fluid into the annular flow passage  25 . The flexible membrane, referenced in the embodiments herein for purpose of illustration by reference number  50 , can be constructed in a manner such that it exhibits noncompliant characteristics, compliant characteristics, or any combination thereof. The flexible membrane  50  can be made of any of a variety of known and suitable materials, as selected for the intended purpose of the balloon catheter  100 . Furthermore, if desired, the flexible membrane  50  can be formed of generally inflexible segments joined in a manner to facilitate a generally flexible arrangement that can be deployed as described in detail below. The flexible membrane  50  generally includes a proximal end portion, an intermediate portion, and a distal end portion. The proximal end portion and the distal end portion function as mounting portions to enable the flexible membrane  50  to be mounted to the inner or outer surface of the outer shaft member  20  and the outer surface of the inner shaft member  10  to define the annular flow passage  25  of the balloon catheter  100 . With the proximal portion and the distal portion mounted to the inner and outer shaft members  10 ,  20 , the annular flow passage  25  is in sealed fluid communication with the flexible membrane  50 . 
         [0057]    In accordance with particular embodiments of the present invention, the flexible membrane  50  is mounted to the inner and outer shaft members  10 ,  20  in a configuration that facilitates retraction of the flexible membrane  50  and/or withdrawal of the balloon catheter  100 . For example, in a preferred embodiment, the outer surface of the flexible membrane  50  can be mounted to the inner surface of the outer shaft member  20  and the outer surface of the inner shaft member  10  to introduce shoulders as illustrated in  FIGS. 11 and 12 . Alternative configurations suitable for deployment of the flexible membrane  50  also can be used. 
         [0058]    Mounting of the flexible membrane  50  to the inner and outer shaft members  10 ,  20  can be achieved through use of an adhesive, welded bond (e.g., thermal or chemical weld bond), swaging of metal rings or other known attachment methods or combinations thereof. Optionally, a band, such as a radiopaque marker band, can be utilized to attach the proximal portion and/or the distal portion of the flexible membrane  50  to the inner or outer shaft members  10 ,  20  or can be used in combination with the above processes. Additional radiopaque markers or marker bands can be secured to the outer surface of the inner or outer shaft members  10 ,  20  at any position along their length, including within the annular flow passage  25  of the balloon catheter  100 . 
         [0059]    The marker bands are preferably constructed of materials that facilitate or provide radiopacity. These materials can include, but are not limited to, platinum, alloys of platinum, gold, tungsten, tantalum, or combinations thereof, metals, alloys, plastic, polymer, synthetic material, combinations thereof, or other materials that provide an appropriate radiopaque signature. Alternatively, portions of the balloon catheter  100 , including the flexible membrane  50  and/or the inner or outer shaft members  10 ,  20  can be coated with an appropriate radiopaque material, such as, but not limited to, barium sulphate, bismuth subcarbonate, titanium dioxide, or combinations thereof, to provide radiopacity. 
         [0060]    The flexible membrane  50  can be constructed of one or more bio-compatible materials as is known, and if desired, from absorbable biomaterials. One such material is biosynthetic polyester which, advantageously, is tissue compatible and is constructed of component molecules that occur naturally in mammals. The biosynthetic polyester exhibits desirable characteristics for flexible medical devices. For instance, biosynthetic polyesters are very flexible; yet exhibit tensile strengths that are similar to ultrahigh molecular weight polyethylene. These characteristics provide for a flexible membrane  50  that can be tracked through tortuosity easily and has an acceptably high burst pressure. Illustrative biosynthetic polyesters are identified above and include 4-hydroxybutyrate and 3-hydroxybutyrate, as well as poly-L-lactide-co-glycolide, poly-dL-lactide-co-glycolide, polyester amide, chitosan, PBT, and PEG. 
         [0061]    As noted above, the balloon catheter  100  can be at least partially loaded with therapeutic agent  60  and such loading will generally occur over some portion of the flexible membrane  50 . “Therapeutic agent” as used herein, refers to any compound, mixture of compounds, or composition of matter consisting of a compound, which produces a therapeutic or useful result. The therapeutic agent  60  can be a polymer, a marker, such as a radiopaque dye or particles, or can be a drug, including pharmaceutical and therapeutic agents, or an agent including inorganic or organic drugs without limitation. The agent or drug can be in various forms such as uncharged molecules, components of molecular complexes, pharmacologically acceptable salts such as hydrochloride, hydrobromide, sulfate, laurate, palmitate, phosphate, nitrate, borate, acetate, maleate, tartrate, oleate, and salicylate. 
         [0062]    An agent or drug that is water insoluble can be used in a form that is a water-soluble derivative thereof to effectively serve as a solute, and on its release from the device, is converted by enzymes, hydrolyzed by body pH or metabolic processes to a biologically active form. Additionally, the agents or drug formulations can have various known forms such as solutions, dispersions, pastes, particles, granules, emulsions, suspensions and powders. The drug or agent may or may not be mixed with polymer or a liquid as desired. 
         [0063]    In an embodiment of the invention, at least one therapeutic agent can be selected from but not limited to anti-proliferative, anti-inflammatory, antineoplastic, antiplatelet, anti-coagulant, anti-fibrin, antithrombotic, antimitotic, antibiotic, antiallergic and antioxidant compounds. Thus, the therapeutic agent can be, again without limitation, a synthetic inorganic or organic compound, a protein, a peptide, a polysaccharides and other sugars, a lipid, DNA and RNA nucleic acid sequences, an antisense oligonucleotide, an antibodies, a receptor ligands, an enzyme, an adhesion peptide, a blood clot agent including streptokinase and tissue plasminogen activator, an antigen, a hormone, a growth factor, a ribozyme, a retroviral vector, an anti-proliferative agent including rapamycin (sirolimus), 40-O-(2-hydroxyethyl)rapamycin (everolimus), 40-O-(3-hydroxypropyl)rapamycin, 40-O-(2-hydroxyethyoxy) ethylrapamycin, 40-O-tetrazolylrapamycin (zotarolimus, ABT-578), paclitaxel, docetaxel, methotrexate, azathioprine, vincristine, vinblastine, fluorouracil, doxorubicin hydrochloride, and mitomycin, an antiplatelet compound, an anticoagulant, an antifibrin, an antithrombins including sodium heparin, a low molecular weight heparin, a heparinoid, hirudin, argatroban, forskolin, vapiprost, prostacyclin, a prostacyclin analogue, dextran, D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa platelet membrane receptor antagonist antibody, recombinant hirudin, a thrombin inhibitor including Angiomax ä, a calcium channel blocker including nifedipine, colchicine, a fibroblast growth factor (FGF) antagonist, fish oil (omega 3-fatty acid), a histamine antagonist, lovastatin, a monoclonal antibodie, nitroprusside, a phosphodiesterase inhibitor, a prostaglandin inhibitor, suramin, a serotonin blacker, a steroid, a thioprotease inhibitor, triazolopyrimidine, a nitric oxide or nitric oxide donor, a super oxide dismutase, a super oxide dismutase mimetic, estradiol, an anticancer agent, a dietary supplement including vitamins, an anti-inflammatory agent including aspirin, tacrolimus, dexamethasone and clobetasol, a cytostatic substance including angiopeptin, an angiotensin converting enzyme inhibitor including captopril, cilazapril or lisinopril, an antiallergic agent including permirolast potassium, alpha-interferon, bioactive RGD, and genetically engineered epithelial cells. Other therapeutic agents which are currently available or that can be developed in the future for use with implantable medical devices can likewise be used and all are within the scope of this invention. 
         [0064]    Examples of such antithrombotics, anticoagulants, antiplatelet agents, and thrombolytics include sodium heparin, low molecular weight heparins, heparinoids, hirudin, argatroban, forskolin, vapriprost, prostacyclin and prostacylin analogues, dextran, D-phe-pro-arg-chlorometh-ylketone (synthetic antithrombin), dipyridamole, glycoprotein IIb/IIIa (platelet membrane receptor antagonist antibody), recombinant hirudin, and thrombin inhibitors such as Angiomax™, from Biogen, Inc., Cambridge, Mass.; and thrombolytic agents, such as urokinase, e.g., Abbokinase™ from Abbott Laboratories Inc., North Chicago, Ill., recombinant urokinase and pro-urokinase from Abbott Laboratories Inc., tissue plasminogen activator (Alteplase™ from Genentech, South San Francisco, Calif. and tenecteplase (TNK-tPA). 
         [0065]    Examples of such cytostatic or antiproliferative agents include rapamycin and its analogs such as everolimus, ABT-578, i.e., 3S,6R,7E,9R,10R,12R,14S,15E,17E,19E,21S,23S,26R,27R,34aS)-9,10,12,13,14,2-1,22,23,24,25,26,27,32,33,34,34a-Hexadecahydro-9,27-dihydroxy-3-[(1R)-2-[(−1S,3R,4R)-3-methoxy-4-tetrazol-1-yl)cyclohexyl]-1-methylethyl]-10,21-dimet-hoxy-6,8,12,14,20,26-hexamethyl-23,27-epoxy-3H-pyrido[2,1-c][1,4]oxaazacyc-lohentriacontine-1,5,11,28,29(4H,6H,31H)-pentone; 23,27-Epoxy-3H pyrido[2,1-c][1,4]oxaazacyclohentria-contine-1,5,11,28,29(4H,6H,31H)-pento-ne, which is disclosed in U.S. Pat. No. 6,015,815, U.S. Pat. No. 6,329,386, U.S. Publication 2003/129215, filed on Sep. 6, 2002, and U.S. Publication 2002/123505, filed Sep. 10, 2001, the disclosures of which are each incorporated herein by reference thereto, tacrolimus and pimecrolimus, angiopeptin, angiotensin converting enzyme inhibitors such as captopril, e.g, Capoten® and Capozide® from Bristol-Myers Squibb Co., Stamford, Conn., cilazapril or lisinopril, e.g., Prinivil™ and Prinzide™ from Merck &amp; Co., Inc., Whitehouse Station, N.J.; calcium channel blockers such as nifedipine, amlodipine, cilnidipine, lercanidipine, benidipine, trifluperazine, diltiazem and verapamil, fibroblast growth factor antagonists, fish oil (omega 3-fatty acid), histamine antagonists, lovastatin, e.g. Mevacor™ from Merck &amp; Co., Inc., Whitehouse Station, N.J. In addition, topoisomerase inhibitors such as etoposide and topotecan, as well as antiestrogens such as tamoxifen can be used. 
         [0066]    Examples of such anti-inflammatories include colchicine and glucocorticoids such as betamethasone, cortisone, dexamethasone, budesonide, prednisolone, methylprednisolone and hydrocortisone. Non-steroidal anti-inflammatory agents include flurbiprofen, ibuprofen, ketoprofen, fenoprofen, naproxen, diclofenac, diflunisal, acetominophen, indomethacin, sulindac, etodolac, diclofenac, ketorolac, meclofenamic acid, piroxicam and phenylbutazone. 
         [0067]    Examples of such antineoplastics include alkylating agents such as altretamine, bendamucine, carboplatin, carmustine, cisplatin, cyclophosphamide, fotemustine, ifosfamide, lomustine, nimustine, prednimustine, and treosulfin, antimitotics such as vincristine, vinblastine, paclitaxel, e.g., TAXOL® by Bristol-Myers Squibb Co., Stamford, Conn., docetaxel, e.g., Taxotere™ from Aventis S.A., Frankfurt, Germany, antimetabolites such as methotrexate, mercaptopurine, pentostatin, trimetrexate, gemcitabine, azathioprine, and fluorouracil, and antibiotics such as doxorubicin hydrochloride, e.g., Adriamycin™ from Pharmacia &amp; Upjohn, Peapack, N.J., and mitomycin, e.g., Mutamycin™ from Bristol-Myers Squibb Co., Stamford, Conn., agents that promote endothelial cell recovery such as estradiol. 
         [0068]    Other agents and materials could conceivably be delivered into a patient anatomy in accordance with the present invention. For example, angiogenetic factors could be delivered. This includes growth factors such as isoforms of vasoendothelial growth factor (VEGF), fibroblast growth factor (FGF, e.g. beta-FGF), Del 1, hypoxia inducing factor (HIF 1-alpha), monocyte chemoattractant protein (MCP-1), nicotine, platelet derived growth factor (PDGF), insulin-like growth factor (HGF), estrogens, follistatin, proliferin, prostaglandin E1 and E2, tumor necrosis factor (TNF-alpha), interleukin 8 (Il-8), hematopoietic growth factors, erythropoietin, granulocyte-colony stimulating factors (G-CSF) and platelet-derived endothelial growth factor (PD-ECGF). In some embodiments, angiogenesis promoting factors include, but are not intended to be limited to, peptides, such as PR39, PR11 and angiogenin, small molecules, such as PHD inhibitors, or other agents, such as eNOS enhancers. 
         [0069]    While the foregoing therapeutic agents are known for their preventive and treatment properties, the substances or agents are provided by way of example and are not meant to be limiting. Further, other therapeutic agents that are currently available or may be developed are equally applicable for use with the present invention. 
         [0070]    If desired or necessary, the therapeutic agent can include a binder to carry, load, or allow sustained release of an agent, such as but not limited to a suitable polymer or similar carrier. The term “polymer” is intended to include a product of a polymerization reaction inclusive of homopolymers, copolymers, terpolymers, etc., whether natural or synthetic, including random, alternating, block, graft, branched, cross-linked, blends, compositions of blends and variations thereof. The polymer can be in true solution, saturated, or suspended as particles or supersaturated in the therapeutic agent. The polymer can be biocompatible, biosolvable, biostable, or biodegradable. 
         [0071]    For purpose of illustration and not limitation, the polymeric material can include phosphorylcholine linked macromolecules, such as a macromolecule containing pendant phosphorylcholine groups such as poly(MPCw:LMAx:HPMAy:TSMAz), where MPC is 2-methacryoyloxyethylphosphorylcholine, LMA is lauryl methacrylate, HPMA is hydroxypropyl methacrylate and TSMA is trimethoxysilylpropyl methacrylate, and w, x, y, and z are molar ratios of the monomers used in the feed. These values are typically 23, 47, 25, and 5, respectively, but they are not necessarily the ratios that exist in the finished polymer. The polymer is herein referred to generally as “PC polymer.” 
         [0072]    The therapeutic agent can include a liquid. The liquid can be any single solvent or a combination of solvents. For purpose of illustration and not limitation, examples of suitable solvents include water, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones, dimethyl sulfoxide, tetrahydrofuran, dihydrofuran, dimethylacetamide, acetates, and combinations thereof. Preferably, the solvent is ethanol. More preferably, the solvent is isobutanol. Additionally, in another aspect of the invention, multiple therapeutic agents are dissolved or dispersed in the same solvent. For purpose of illustration and not for limitation, dexamethasone, estradiol, and paclitaxel are dissolved in isobutanol. Alternatively, dexamethasone, estradiol, and paclitaxel are dissolved in ethanol. In yet another example, dexamethasone, estradiol, and ABT-578, i.e., the rapamycin analog, 3S,6R,7E,9R,10R,12R,14S,15E,17E,-19E,21S,23-S,26R,27R,34aS)9,10,12,13,14,21,22, 23,24,25,26,27,32,33,34,34a-1-Hexadecahydro-9,27-dihydroxy-3-[(1R)-2-[(1S,3R,4R)-3-methoxy-4-tetrazol-1-yl)cyclohexyl]-1-methylethyl]-10,21-dimethoxy-6,8,12,14,20,26-hexamethyl-2-3,27-epoxy-3H-pyrido[2,1-c][1,4]oxaazacyclohentriacontine-1,5,11,28, 29(4H,-6H,31H)-pentone; 23,27-Epoxy-3H-pyrido[2,1-c][1,4]oxaazacyclohentriacontin-e-1,5,11,28,29(4H,6H,31H)-pentone, are dissolved together in one solvent. Preferably, the solvent is ethanol. More preferably, the solvent is isobutanol. 
         [0073]    Additionally, the therapeutic agent includes any of the aforementioned drugs, agents, polymers, and liquids either alone or in combination. 
         [0074]    Such therapeutic agents can be applied to the flexible membrane, preferably to the outer surface of the flexible membrane using any of a variety of known techniques suitable for the intended application, thus allowing the presentation of the therapeutic agent to the external environment upon inflation. For example, a variety of techniques to apply a drug to a surface are discussed in various patent applications owned by Abbott Laboratories. The therapeutic agent is employed to induce a therapeutic effect on the tissue at the targeted location in the patient. The inclusion of the therapeutic agent creates the opportunity to provide a medical or therapeutic effect for tissue that makes contact with the flexible membrane. The therapeutic effect can be varied by the particular therapeutic agent loaded onto the balloon catheter. In addition, the therapeutic agent will transfer from the balloon catheter to the targeted tissue location of the patient upon substantive contact with the flexible membrane, and will generally remain at or on the targeted tissue location to penetrate the tissue. 
         [0075]    In addition to the therapeutic agent, the balloon catheter may be at least partially loaded with a salt or sugar compound. During expansion of the flexible membrane the salt or sugar compound can be delivered to the target tissue prior to, or concurrently with, the therapeutic agent. Upon delivery to the target tissue, the compound will recruit fluid from the tissue cells. The recruitment of fluid increases the size of the gaps that exist between cells, thereby creating channels for migration of the therapeutic agent. By making the path of the therapeutic agent easier, it will be able to penetrate the target tissue to a greater depth. In this way, a greater volume of therapeutic agent can be delivered in order to provide the intended therapeutic effect. 
         [0076]    In accordance with another aspect of the invention, the therapeutic agent will generally be formulated to coat the outer surface of the flexible membrane or be physically positioned in a manner such that an efficacious amount of the therapeutic agent does not wash away with bodily fluid passing by the balloon catheter. Techniques for making such a formulation are well known in the art and include, for example, overlaying a dissolvable film on the coating that allows for the slow release of the agent coated by such a film by including within the coating components that inhibit transfer of the therapeutic coating until heated or expanded. Alternatively, as described above, the agent can be incorporated into a hydrogel that inhibits loss of the agent due to the presence of bodily fluids prior to deployment of the flexible membrane. 
         [0077]    In accordance with alternative aspects of the invention, the therapeutic agent  60  can be physically positioned in a manner such that an efficacious amount of the therapeutic agent  60  is not lost due to the presence of bodily fluid contacting the balloon catheter  100 . Techniques for physically positioning therapeutic agents  60  on the flexible membrane  50  are well known in the art. Such techniques include, but are not limited to, the positioning of the therapeutic agent  60  within channels or pores on the flexible membrane  50  such that, when in an unexpanded configuration, the channels are inaccessible to the external environment but upon expansion the channels or pores widen and the therapeutic agent  60  is exposed to the external environment. In alternative embodiments of the present invention, the therapeutic agent  60  is contained within microcapsules attached to the flexible membrane  50  and the therapeutic agent  60  is released from the microcapsules by expansion of the flexible membrane  50 . 
         [0078]    In accordance with another aspect of the present invention, further loss of therapeutic agent  60  by the presence of bodily fluids passing by the balloon catheter  100  is inhibited by rolling the flexible membrane  50  over itself in a generally axial direction, as illustrated in  FIG. 2 . In such an embodiment, the rolled configuration will isolate the flexible membrane  50  from contact with the bloodstream during device delivery by maintaining the flexible membrane  50  within a chamber defined by the outer shaft member  20  and the inner shaft member  10 . 
         [0079]    Once the balloon catheter  100  is properly placed within a patient&#39;s vasculature, the flexible membrane  50  can be unrolled or otherwise deployed by the introduction of inflation fluid into the annular flow passage  25  and retraction of the distal end  24  of the outer shaft member  20  in a proximal direction relative to the inner shaft member  10 . Such retraction can be accomplished while maintaining the annular flow passage  25  by the presence of a dynamic seal  32  between the inner and outer shaft members  10 ,  20  as illustrated in  FIG. 1A , by the presence of a bellows component  34  disposed along the outer shaft member  20  as illustrated in  FIG. 1B , or by the presence of a dynamic seal  36  between the inner shaft member  10  and inflation hub unit  30  located at the proximal end  22  of the outer shaft member  20  as illustrated in  FIG. 1C . Upon retraction of the outer shaft member  20 , the outer surface of the flexible membrane  50  will become partially exposed to the surrounding environment. This partial exposure is illustrated in  FIG. 2 . Full retraction of the outer shaft member  20  will fully expose the outer surface of the flexible membrane  50  as illustrated in  FIG. 3 . 
         [0080]    Upon retraction, or concurrent therewith, fluid can be communicated through the annular flow passage  25  to inflate and expand the flexible membrane  50  such that the distal surface of the flexible membrane  50  comes in contact with the vessel wall. Expansion of the flexible membrane  50  in response to the introduction of fluid into the annular flow passage  25  is illustrated in  FIG. 4 . In certain embodiments, the introduction of fluid during retraction of the outer shaft member  20  will be sufficient to induce occlusion of the target vessel by a partially expanded flexible membrane  50 , after which complete expansion and treatment can occur. 
         [0081]    In an alternative embodiment, the introduction of fluid into the annular flow passage  25  is sufficient in itself to drive the retraction of the outer shaft member  20  relative to the inner shaft member  10 , and will lead to inflation of the flexible membrane  50 . Such an embodiment is illustrated in  FIGS. 5-7 , where the flexible membrane  50  preferentially expands in the unconstrained direction and the expansion will cause the flexible membrane  50  to place a proximal load on the outer shaft member  20 . As will be appreciated by one of skill in the art, a wide variety of combinations of retraction and introduction of fluid into the annular flow passage  25  fall within the scope of the instant invention and will affect retraction of the outer shaft member  20  and inflation of the flexible membrane  50 . 
         [0082]    In another embodiment, the balloon catheter  100  has a flexible membrane  50  generally contained within the annular flow passage  25  prior to deployment, such that the flexible membrane  50  is deployed distally by unraveling in a distal direction. As illustrated in  FIG. 13A , as fluid is introduced through the annular flow passage  25 , the flexible membrane  50  becomes pressurized and is driven forward within the passage. This forward progression results in an unraveling of the flexible membrane  50  as illustrated in  FIG. 13B . Once the flexible membrane  50  is fully exposed, as illustrated in  FIG. 13C , it will expand against the vessel wall. 
         [0083]    In order to prevent loss of the therapeutic agent  60  into the blood stream after deployment, it can be desirable to retrieve the flexible membrane  50  within the annular flow passage  25  defined by the inner and outer shaft members  10 ,  20 . Retrieval can be accomplished by pulling or applying a tensile load on the outer shaft member  20  as shown in  FIG. 10 . For example, in one embodiment of the instant invention, such retrieval is accomplished using the proximal end portion  12  of the inner shaft member  10  as a retrieval element. By placing a tensile load on the inner shaft member  10 , the distal end  14  of the inner shaft member  10  will cause the flexible membrane  50  to roll back into the annular flow passage  25 , where the flexible membrane  50  is protected from the flow of bodily fluid. Such a process of retrieval is illustrated in  FIG. 12 . 
         [0084]    In an alternative embodiment, if the proximal end portion  12  of the inner shaft member  10  is not accessible, it is possible to provide a retrieval element that is not integral to the inner lumen  15  of the inner shaft member  10 . For example, this can be accomplished by attaching an element that is associated with the inner shaft member  10  and which can apply a compressive load to the inner shaft member  10  over a portion of length proximal to the point of attachment. Examples of such elements include: sutures, wires, tendons, and rods, all of which can be connected at the distal end of the inner shaft member. Application of a tensile load to the element would transmit a compressive load to the inner shaft member  10 , which would thereby cause the flexible membrane  50  to retract within the annular flow passage  25 . 
         [0085]    The retraction of the flexible membrane  50  can be aided by configuring the proximal and distal ends of the flexible membrane  50  as shown in  FIG. 11 . When configured in this fashion, when the inner shaft member  10  is compressed in order to retrieve the flexible membrane  50 , the distal end of the flexible membrane  50  is curved or provided with a shape memory in a way that makes it preferentially retract into the annular flow passage  25  without becoming bunched up or folded in a way that impedes retrieval. 
         [0086]    In an alternative embodiment, loss of the therapeutic agent  60  by the presence of bodily fluids passing by the balloon catheter  100  can be inhibited by including a flexible membrane  50  having a segmented configuration. As illustrated in  FIG. 8 , such embodiments can include where the flexible membrane  50  consists of three segments: the proximal driver  52 , the distal driver  54 , and the intermediate delivery segment  56 , however, additional embodiments having fewer or more segments are also specifically contemplated as within the scope of the instant invention. In one exemplary embodiment, proximal and distal driver segments  52 ,  54  are configured such that the intermediate delivery segment  56  is protected from the surrounding environment, and only the intermediate delivery segment  56  of the flexible membrane is coated with therapeutic agent  60 . In certain embodiments it can be preferable to have the intermediate delivery segment  56  composed of a more or less flexible material than the proximal and distal driver segments  52 ,  54 . 
         [0087]    When fluid is introduced into the annular fluid passage  25 , it causes the proximal and distal driver segments  52 ,  54  to expand and forces them away from each other. This separation can be aided by the axial displacement of the inner and outer shaft members  10 ,  20  as discussed above, and can be the result of the proximal and distal driver segments  52 ,  54  and intermediate delivery segment  56  having different compliance. Such separation is illustrated in  FIG. 9 . 
         [0088]    As the proximal and distal driver segments  52 ,  54  separate, they expose the intermediate delivery segment  56  to the surrounding environment. The unconstrained intermediate delivery segment  56  is then able to expand toward the vessel wall. Upon further inflation, the proximal and distal driver segments  52 ,  54  and the intermediate delivery segment  56  become fully expanded, bringing the therapeutically coated surface of the intermediate delivery segment  56  in contact with the vessel wall. 
         [0089]    In an additional embodiment, the proximal and/or distal driver segments  52 ,  54  can be designed to preferentially expand to occlude the vessel in one or more locations, thereby preventing bodily fluids from contacting the intermediate delivery segment  56  prior to full inflation of that segment. In one such embodiment the proximal driver  52  can expand first, thereby occluding the proximal end of the vessel and preventing the flow of bodily fluid from contacting the intermediate delivery segment  56  during deployment of the device. 
         [0090]    In order to prevent loss of the therapeutic agent  60  into the blood stream after deployment of the segmented flexible membrane  50 , it may be desirable to form the proximal and distal driver segments  52 ,  54  such that they preferentially collapse only after the intermediate delivery segment  56  has collapsed and such that they return to their pre-deployment configuration. 
         [0091]    In an alternative embodiment, as shown in  FIG. 14 , loss of the therapeutic agent  60  due to the presence of bodily fluids contacting the balloon catheter  100  can be inhibited by the introduction of spiral formations  58  along the flexible membrane  50 . These spiral formations  58  can be introduced by configuring the inner and outer shaft members  10 ,  20  such that they are rotatably movable with respect to each other. As the flexible membrane  50  is associated with both the inner and outer shaft members  10 ,  20 , the rotation of the shaft members relative to each other will result in a series of spiral formations  58  in the surface of flexible membrane  50 , rendering portions of the flexible membrane  50  inaccessible to the external environment and the passing bodily fluids. As such portions are not exposed to the surrounding environment; any therapeutic agent  60  disposed therein would be protected from the blood stream. Upon proper positioning of the balloon catheter  100 , the inner and outer shaft members  10 ,  20  can be rotated in the reverse direction to remove the spiral formations  58  and the flexible membrane  50  can be inflated to effect transfer of the therapeutic agent  60  to the location to be treated. 
         [0092]    In accordance with another aspect of the instant invention, loss of the therapeutic agent  60  into the blood stream after deployment of a flexible membrane  50  that has had its spiral formations  58  removed, it would be possible to reintroduce the spiral formations  58  upon collapse of the flexible membrane  50  by rotating the inner and outer shaft members  10 ,  12  relative to each other. Such reintroduction would effectively prevent the therapeutic agent  60  disposed between the spiral formations  58  from contacting the blood stream during withdrawal or repositioning of the balloon catheter  100 . 
         [0093]    It will be appreciated, in light of the embodiments described above, that the invention describes a balloon catheter that can be used in a “universal” fashion. In particular, depending upon the length of flexible membrane deployed, the balloon catheter can be used to treat a variety of disease lengths or treatment sites. The operator can control the length of deployment through relative motion of the catheter shaft members such as previously described. Such a system is advantageous not only as it will allow users to stock a single length, but can also reduce the need for the user to swap out devices when a longer or shorter flexible membrane is needed than was initially introduced into the patient. 
         [0094]    In accordance with another aspect of the invention and as previously described in conjunction with certain aspects of the invention, a method of treating a luminal system of a patient is provided. The method includes providing a balloon catheter as described herein, positioning the balloon catheter at a desired deployment site, introducing inflation fluid into the annular flow passage and moving the outer shaft member relative to the inner shaft member to deploy the flexible membrane into an expanded configuration in order to treat the luminal system of the patient. As pointed out above, the balloon catheter can take a number of different configurations and the methods of the instant invention envision the use of any such configurations as within their scope. 
         [0095]    In accordance with additional aspects of the methods of the instant invention, the balloon catheter includes properties that facilitate its collapse and withdrawal. For example, and not by way of limitation, the methods of the instant invention include the withdrawal of inflation fluid from the annular flow passage and movement of the inner and outer shaft members relative to each other to effect the collapse of the flexible membrane. In one such embodiment, the method includes axially moving the distal end portion of the outer shaft member beyond the distal end portion of the inner shaft member such that the flexible membrane is rendered taut and less likely to catch on luminal structures as the balloon catheter is withdrawn from the patient. In an alternative embodiment, the distal end portion of the inner shaft member is moved axially relative to the outer shaft member such that the distal end portion of the inner shaft member extends beyond the distal end portion of the outer shaft member and the flexible membrane is also rendered taut and less likely to catch on luminal structures as the balloon catheter is withdrawn from the patient. In further embodiments, the methods of the present invention make use of other structures of the balloon catheter described above, such as the chamber configured to receive the flexible membrane defined by the inner and outer shaft members, to facilitate collapse of the flexible membrane and withdrawal of the balloon catheter. Methods of using such structures within the scope of the invention, such as the examples provided herein, would be readily apparent to one of skill in the art. 
         [0096]    The methods and systems of the present invention, as described above and shown in the drawings, provide for a balloon catheter with superior properties including superior therapeutic agent delivery and post-deployment catheter withdrawal capabilities. It will be apparent to those skilled in the art that various modifications and variations can be made in the device and method of the present invention without departing from the spirit or scope of the invention. For example, the instant invention can work particularly well to treat dialysis grafts. As is well known in the art, dialysis grafts are essentially sheaths connecting the arterial and venous sides of a patient&#39;s vasculature as is required when a patient is on dialysis for kidney failure. As these sheaths have a tendency for rapid and substantial restenosis, the above-described embodiments would be advantageous as an anti-restenoic agent could be delivered to the graft and the delivery would be less traumatic and more easily adjusted to fit the anatomy of the grafts. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.