Patent Publication Number: US-6706055-B2

Title: Guidewire apparatus for temporary distal embolic protection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation-in-part of U.S. patent application Ser. No. 10/099,399 to Douk et al. filed Mar. 15, 2002 now pending, which is a continuation-in-part of U.S. patent application Ser. No. 09/918,441 to Douk et al. filed Jul. 27, 2001, now pending, which is a continuation-in-part of U.S. patent application Ser. No. 09/824,832 to Douk et al. filed Apr. 3, 2001 now pending, entitled “Temporary Intraluminal Filter Guidewire and Methods of Use.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to intraluminal devices for capturing particulate in the vessels of a patient. More particularly, the invention relates to a filter or an occluder for capturing emboli in a blood vessel during an interventional vascular procedure, then removing the captured emboli from the patient after completion of the procedure. Furthermore, the invention concerns a filter or an occluder mounted on a guidewire that can also be used to direct an interventional catheter to a treatment site within a patient. 
     BACKGROUND OF THE INVENTION 
     A variety of treatments exists for dilating or removing atherosclerotic plaque in blood vessels. The use of an angioplasty balloon catheter is common in the art as a minimally invasive treatment to enlarge a stenotic or diseased blood vessel. When applied to the vessels of the heart, this treatment is known as percutaneous transluminal coronary angioplasty, or PTCA. To provide radial support to the treated vessel in order to prolong the positive effects of PTCA, a stent may be implanted in conjunction with the procedure. 
     Thrombectomy is a minimally invasive technique for removal of an entire thrombus or a sufficient portion of the thrombus to enlarge the stenotic or diseased blood vessel and may be accomplished instead of a PTCA procedure. Atherectomy is another well-known minimally invasive procedure that mechanically cuts or abrades a stenosis within the diseased portion of the vessel. Alternatively, ablation therapies use laser or RF signals to superheat or vaporize a thrombus within the vessel. Emboli loosened during such procedures may be removed from the patient through the catheter. 
     During each of these procedures, there is a risk that emboli dislodged by the procedure will migrate through the circulatory system and cause ischaemic events, such as infarction or stroke. Thus, practitioners have approached prevention of escaped emboli through use of occlusion devices, filters, lysing, and aspiration techniques. For example, it is known to remove the embolic material by suction through an aspiration lumen in the treatment catheter or by capturing emboli in a filter or occlusion device positioned distal of the treatment area. 
     SUMMARY OF THE INVENTION 
     The guidewire apparatus of the invention includes a protection element comprising a filter or an occluder mounted near the distal end of a steerable guidewire, which guides a therapeutic catheter. The guidewire apparatus comprises a hollow shaft movably disposed about a core wire and, optionally, a slippery liner interfitted there between. The shaft and core wire control relative displacement of the ends of the protection element, causing transformation of the protection element between a deployed configuration and a collapsed configuration. The protection element is freely rotatable about the guidewire apparatus. A tracking member disposed adjacent the distal end of the guidewire apparatus can be used to guide the device along another guidewire. Thrust bearings may be employed to facilitate unlimited rotation of the steerable guidewire within the protection element, especially while the protection element is retained in the collapsed configuration. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where: 
     FIG. 1 is an illustration of a filter system in accordance with the invention deployed within a blood vessel. 
     FIG. 2 is an illustration of a filter system in accordance with the invention deployed within a portion of the coronary arterial anatomy; 
     FIG. 3 is an illustration of a prior art expandable mesh device, shown with the mesh in a collapsed configuration; 
     FIG. 4 is an illustration of a prior art expandable mesh device, shown with the mesh in a deployed configuration; 
     FIG. 5 is a longitudinal sectional view of a first guidewire embodiment in accordance with the invention; 
     FIG. 6 is a longitudinal sectional view of a second guidewire embodiment in accordance with the invention; 
     FIG. 7 is a cross-sectional view of the second guidewire embodiment taken along the lines  7 — 7  of FIG. 6; 
     FIG. 8 is a modified form of the cross-sectional view shown in FIG. 7; 
     FIG. 9 is another modified form of the cross-sectional view shown in FIG. 7; 
     FIG. 10 is an enlarged supplementary view of a portion of FIG. 8, which has been modified to illustrate alternative embodiments of the invention; 
     FIG. 11 is a longitudinal sectional view of a segment of a hollow shaft and liner in accordance with the invention; 
     FIG. 12 is a partially sectioned longitudinal view of a third guidewire embodiment in accordance with the invention; and 
     FIG. 13 is a partially sectioned longitudinal view of a fourth guidewire embodiment in accordance with the invention; 
     FIG. 14 is a partially sectioned longitudinal view of a fifth guidewire embodiment in accordance with the invention; 
     FIG. 15A is an enlarged view of a stop element assembly shown in FIG. 14; 
     FIG. 15B is an enlarged view of a modified form of the stop element assembly shown in FIG. 14; and 
     FIG. 16 is a partially sectioned longitudinal view of a sixth guidewire embodiment in accordance with the invention 
    
    
     The drawings are not to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a guidewire apparatus for use in minimally invasive procedures. While the following description of the invention relates to vascular interventions, it is to be understood that the invention is applicable to other procedures where the practitioner desires to capture embolic material that may be dislodged during the procedure. Intravascular procedures such as PTCA or stent deployment are often preferable to more invasive surgical techniques in the treatment of vascular narrowings, called stenoses or lesions. With reference to FIGS. 1 and 2, deployment of balloon expandable stent  5  is accomplished by threading catheter  10  through the vascular system of the patient until stent  5  is located within a stenosis at predetermined treatment site  15 . Once positioned, balloon  11  of catheter  10  is inflated to expand stent  5  against the vascular wall to maintain the opening. Stent deployment can be performed following treatments such as angioplasty, or during initial balloon dilation of the treatment site, which is referred to as primary stenting. 
     Catheter  10  is typically guided to treatment site  15  by a guidewire. In cases where the target stenosis is located in tortuous vessels that are remote from the vascular access point, such as coronary arteries  17  shown in FIG. 2, a steerable guidewire is commonly used. According to the present invention, a guidewire apparatus generally guides catheter  10  to treatment site  15  and includes a distally disposed protection element to collect embolic debris that may be generated during the procedure. Various embodiments of the invention will be described as either filter guidewires or occluder guidewires. However, it is to be understood that filters and occluders are interchangeable types of protection elements among the inventive structures disclosed. The invention is directed to embolic protection elements wherein relative movement of the ends of the protection element either causes or accompanies transformation of the element between a collapsed configuration and an expanded, or deployed configuration. Such transformation may be impelled by external mechanical means or by self-shaping memory (either self-expanding or self-collapsing) within the protection element itself. The protection element may be self-expanding, meaning that it has a mechanical memory to return to the expanded, or deployed configuration. Such mechanical memory can be imparted to the metal comprising the element by thermal treatment to achieve a spring temper in stainless steel, for example, or to set a shape memory in a susceptible metal alloy such as a nickel-titanium (nitinol) alloy. 
     Filter guidewires in accordance with the invention include distally disposed filter  25 , which may comprise a tube formed by braided filaments that define pores and have at least one proximally-facing inlet opening  66  that is substantially larger than the pores. Alternative types of filters may be used in filter  25 , such as filter assemblies that include a porous mesh mounted to expandable struts. Optionally, adding radiopaque markers to filter ends  27 ,  29 , as shown in FIG. 12, can aid in fluoroscopic observation of filter  25  during manipulation thereof. Alternatively, to enhance visualization of braided filter  25  under fluoroscopy, at least one of the filaments may be a wire having enhanced radiopacity compared to conventional non-radiopaque wires suitable for braiding filter  25 . At least the majority of braiding wires forming filter  25  should be capable of being heat set into the desired filter shape, and such wires should also have sufficient elastic properties to provide the desired self-expanding or self-collapsing features. Stainless steel and nitinol monofilaments are suitable for braiding filter  25 . A braiding wire having enhanced radiopacity may be made of, or coated with, a radiopaque metal such as gold, platinum, tungsten, alloys thereof, or other biocompatible metals that, compared with stainless steel or nitinol, have a relatively high X-ray attenuation coefficient. One or more filaments having enhanced radiopacity may be inter-woven with non-radiopaque wires, or all wires comprising filter  25  may have the same enhanced radiopacity. 
     In accordance with the invention, maintaining filter  25  in a collapsed configuration during introduction and withdrawal of filter guidewire  20  does not require a control sheath that slidingly envelops filter  25 . Thus, this type of device is sometimes termed as “sheathless.” Known types of sheathless vascular filter devices are operated by a push-pull mechanism that is also typical of other expandable braid devices, as shown in FIGS. 3 and 4. Prior art expandable mesh device  30  includes core wire  32  and hollow shaft  34  movably disposed there about. Tubular mesh, or braid  36  surrounds core wire  32  and has a braid distal end fixed to core wire distal end  40  and a braid proximal end fixed to shaft distal end  41 . To expand braid  36 , core wire  32  is pulled and shaft  34  is pushed, as shown by arrows  37  and  39  respectively in FIG.  4 . The relative displacement of core wire  32  and shaft  34  moves the ends of braid  36  towards each other, forcing the middle region of braid  36  to expand. To collapse braid  36 , core wire  32  is pushed and shaft  34  is pulled, as shown by arrows  33  and  35  respectively in FIG.  3 . This reverse manipulation draws the ends of braid  36  apart, pulling the middle region of braid  36  radially inward toward core wire  32 . 
     Referring now to FIG. 5, in a first embodiment of the invention, filter guidewire  20  includes core wire  42  and flexible tubular tip member  43 , such as a coil spring, fixed around the distal end of core wire  42 . Thin wires made from stainless steel and/or one of various alloys of platinum are commonly used to make coil springs for such use in guidewires. Core wire  42  can be made from shape memory metal such as nitinol, or a stainless steel wire, and is typically tapered at its distal end. For treating small caliber vessels such as coronary arteries, core wire  42  may measure about 0.15 mm (0.006 inch) in diameter. 
     In filter guidewire  20 , hollow shaft  44  is movably disposed around core wire  42 , and includes relatively stiff proximal portion  46  and relatively flexible distal portion  48 . Proximal portion  46  may be made from thin walled stainless steel tubing, usually referred to as hypo tubing, although other metals, such as nitinol, can be used. Various metals or polymers can be used to make relatively flexible distal portion  48 . One appropriate material for this element is thermoset polyimide (PI) tubing, available from sources such as HV Technologies, Inc., Trenton, Ga., U.S.A. The length of distal portion  48  may be selected as appropriate for the intended use of the filter guidewire. In one example, portion  48  may be designed and intended to be flexible enough to negotiate tortuous coronary arteries, in which case the length of portion  48  may be 15-35 cm (5.9-13.8 inches), or at least approximately 25 cm (9.8 inches). In comparison to treatment of coronary vessels, adaptations of the invention for treatment of renal arteries may require a relatively shorter flexible portion  48 , and neurovascular versions intended for approaching vessels in the head and neck may require a relatively longer flexible portion  48 . 
     When filter guidewire  20  is designed for use in small vessels, shaft  44  may have an outer diameter of about 0.36 mm (0.014 inch). The general uniformity of the outer diameter may be maintained by connecting proximal portion  46  and distal portion  48  with lap joint  49 . Lap joint  49 , and all other adhesive joints in the invention, may use any suitable biocompatible adhesive such as ultraviolet (UV) light curable adhesives, thermally curable adhesives or so-called “instant” cyanoacrylate adhesives from Dymax Corporation, Torrington, Conn., U.S.A or Loctite Corporation, Rocky Hill, Conn., U.S.A. Lap joint  49  can be formed by any conventional method such as reducing the wall thickness of proximal portion  46  in the region of joint  49 , or by forming a step-down in diameter at this location with negligible change in wall thickness, as by swaging. 
     Expandable tubular filter  25  is positioned generally concentrically with core wire  42 , and is sized such that when it is fully deployed, as shown in FIGS. 1 and 2, the outer perimeter of filter  25  will contact the inner surface of the vessel wall. The surface contact is maintained around the entire vessel lumen to prevent any emboli from slipping past filter  25 . Adhesive may be used to secure filter distal end  27  to tip member  43 , and to secure filter proximal end  29  near the distal end of shaft  44 . As shown in FIGS. 12 and 13, radiopaque marker bands, such as platinum rings, can be incorporated into the adhesive joints securing filter ends  27 ,  29  respectively to tip member  43  and shaft  44 . Filter  25  is deployed by advancing, or pushing shaft  44  relative to core wire  42  such that filter distal and proximal ends  27 ,  29  are drawn toward each other, forcing the middle, or central section of filter  25  to expand radially. Filter  25  is collapsed by withdrawing, or pulling shaft  44  relative to core wire  42  such that filter distal and proximal ends  27 ,  29  are drawn apart from each other, forcing the middle, or central section of filter  25  to contract radially. 
     Transition sleeve  45  is fixed about core wire  42  and is slidably located within the distal end of flexible distal portion  48  of hollow shaft  44 . Transition sleeve  45  may be made of polyimide tubing similar to that used in distal portion  48  and extends distally there from. By partially filling the annular space between core wire  42  and shaft  44 , and by contributing additional stiffness over its length, sleeve  45  supports core wire  42  and provides a gradual transition in overall stiffness of filter guidewire  20  adjacent the distal end of shaft  44 . Transition sleeve  45  is fixed to core wire  42  with a suitable adhesive, such that relative displacement between shaft  44  and core wire  42  causes corresponding relative displacement between shaft  44  and sleeve  45 . The length and mounting position of sleeve  45  are selected such that sleeve  45  spans the distal end of shaft  44  regardless of the configuration of filter  25  and the corresponding position of shaft  44  relative to core wire  42 . When constructed as described above, filter guidewire  20  provides the functions of a temporary filter combined with the performance of a steerable guidewire. 
     FIG. 6 depicts a second embodiment of the invention in which filter guidewire  120  incorporates a number of elements similar to the elements that make up filter guidewire  20 . Such similar elements will be identified with the same reference numerals throughout the description of the invention. Filter guidewire  120  includes core wire  142  and flexible tubular tip member  43  fixed around the distal end of core wire  142 , similar to the arrangement of guidewire  20 , above. Hollow shaft  144  is movably disposed around core wire  142  and is comparable, throughout its length, to relatively stiff proximal portion  46  of filter guidewire  20 . Filter  25  is positioned generally concentrically with core wire  142 . Filter distal end  27  is fixedly coupled to tip member  43 , and filter proximal end  29  is fixedly coupled near the distal end of shaft  144 . 
     Optionally, a portion of core wire  142  within the proximal end of shaft  144  has one or more bends  160  formed therein. The amplitude, or maximal transverse dimension of bends  160  is selected such that the bent portion of core wire  142  fits, with interference, within shaft  144 . The interference fit provides sufficient friction to hold core wire  142  and shaft  144  in desired axial positions relative to each other, thereby controlling the shape of filter  25 , as described above with respect to filter guidewire  20 . 
     In filter guidewire  120 , liner  145  is interfitted as a low-friction axial bearing in the annular space between core wire  142  and shaft  144 . With respect to the three coaxially arranged elements, the selected dimensions and the stack-up of dimensional tolerances will determine how liner  145  functions during the push-pull operation of core wire  142  within shaft  144 . 
     For example, FIG. 7 depicts a cross-section of filter guidewire  120  in which there is radial clearance between liner inner surface  150  and core wire  142 , and there is also radial clearance between liner outer surface  151  and the inner wall of shaft  144 . In this arrangement, liner  145  is radially free-floating in the annular space between core wire  142  and shaft  144 . The length of liner  145  is selected such that it also “floats” axially along core wire  142 . The axial movement of liner  145  along core wire  142  is limited proximally by a stop formed at the engagement of bends  160  with the inner wall of shaft  144 . Tip member  43  limits the axial distal movement of liner  145  along core wire  142 . The radial and axial flotation of liner  145  in filter guidewire  120  provides an axial bearing wherein the components with the lesser relative coefficient of friction can slide against each other. For example, if the coefficient of friction between liner inner surface  150  and core wire  142  is less than the coefficient of friction between liner outer surface  151  and the inner wall of shaft  144 , then liner  145  will remain longitudinally fixed within shaft  144 , and push-pull action will cause core wire  142  to slide within liner  145 . Conversely, if the coefficient of friction between liner inner surface  150  and core wire  142  is greater than the coefficient of friction between liner outer surface  151  and the inner wall of shaft  144 , then liner  145  will remain longitudinally fixed about core wire  142 , and push-pull action will cause shaft  144  to slide over liner  145 . The relative coefficients of friction for the movable components of the guidewire assembly may be designed-in by selection of materials and/or coatings, as will be described below. Alternatively, the degree of sliding friction may result from unplanned events, such as the formation of thrombus on one or more component surfaces or embolic debris entering the annular space(s) there between. 
     FIG. 8 depicts a modified form of the cross-sectional view shown in FIG. 7 in which liner  145 ′ is fitted against the inner wall of shaft  144 , leaving radial clearance only between liner inner surface  150 ′ and core wire  142 . FIG. 9 depicts another modified form of the cross-sectional view shown in FIG. 7 in which liner  145 ″ is fitted against core wire  142 , leaving radial clearance only between liner outer surface  151 ′ and the inner wall of shaft  144 . 
     When filter guidewire  120  is designed for use in small vessels, shaft  144  may have an outer diameter of about 0.36 mm (0.014 inch), and core wire  142  may measure about 0.15 mm (0.006 inch) in diameter. Shaft  144 , which can be made from hypo tubing, may have an inside diameter of about 0.23 mm (0.009 inch). For liner  145  to “float” in an annular space between core wire  142  and shaft  144  with such dimensions, liner outer surface  151  may measure about 0.22 mm (0.0088 inch) in diameter and liner inner surface  150  may measure about 0.18 mm (0.0069 inch) in diameter. Liner  145 ′ does not require clearance around its outside diameter, because it is fitted against the inner wall of shaft  144 . As compared to liner  145 , liner  145 ′ may have a greater wall thickness, and liner inner surface  150 ′ may have a similar inner diameter of about 0.18 mm (0.0069 inch). Liner  145 ″ does not require inside clearance because it is fitted against core wire  142 . As compared to liner  145 , liner  145 ″ may also have greater wall thickness, and liner outer surface  151 ′ may have a similar outer diameter of about 0.22 mm (0.0088 inch). 
     Liners  145 ,  145 ′ and  145 ″ may be formed of polymers selected to provide low coefficients of friction on their sliding surfaces. Typical of such polymers are polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene (FEP), high-density polyethylene (HDPE), and various polyamides (nylons). Alternatively, liners  145 ,  145 ′ and  145 ″ may be formed of a material selected for physical properties other than a low coefficient of friction, i.e. stiffness or ability to be formed with tight dimensional tolerances. For such materials, a slippery coating, such as silicone, may be applied to the sliding surface(s) in order to achieve the desired low-friction axial bearing properties. 
     Thermoset polyimide (PI) is an example of a liner material that may be selected for properties other than its coefficient of friction. PI tubing is noted for its ability to be formed with tight dimensional tolerances because it is typically formed by building up several layers of cured PI coating around a solid glass core, which is removed by chemical etching. One method of creating a slippery surface on PI tubing is to add a fluoropolymer filler, such as PTFE or FEP, to the PI coating to form one or more low-friction layers at the desired surface(s). Such polyimide/fluoropolymer composite tubing is available from MicroLumen, Inc., Tampa, Fla., U.S.A. FIG. 10 illustrates a modified form of the invention wherein the inner surface of liner  145 ′ comprises lubricious coating  150 ′. Also shown in FIG. 10 is slippery coating  155 , which may be applied to core wire  142  in conjunction with, or instead of, a slippery inner surface of liners  145  or  145 ′. Coating  155  may comprise a thin film of, for example, silicone or a fluoropolymer. 
     Another example of a liner material that may be selected for properties other than its coefficient of friction is a block copolymer thermoplastic such as polyethylene block amide (PEBA). Although a slippery coating may be applied to this material, alternatively, plasma-aided surface polymerization may be used to reduce its coefficient of friction. Plasma-aided surface functionalization to achieve high lubricity is described in U.S. Pat. No. 4,693,799 (Yanagihara et al.), and plasma surface modification is available from AST Products, Inc., Billerica, Mass., U.S.A. Plasma treated PEBA may be substituted for PTFE in liners to make use of improved physical properties, including the ability to be plastically extruded. 
     FIG. 11 depicts a variant of liner  145 ′ disposed within hollow shaft  144 . In this example, liner  145 ′ comprises a coiled filament, which may be plastic, metal, or coated or surface-treated forms of either material. The coiled variant may be applied to any of liners  145 ,  145 ′ or  145 ″, and it provides reduced contact area and concomitantly lower friction as compared to solid tubular liners. Hollow tube  144  and core wire  142  will only touch coiled liner  145 ′ on helical curvilinear portions of the outer and inner surfaces, respectively. If coiled liner  145 ′ is made with an outer diameter larger than the inner diameter of hollow tube  144 , then liner  145 ′ will generally hold itself in assembled position against the inner diameter of hollow tube  144 . Similarly, if liner  145 ″ is made as a coil with an inner diameter smaller than the diameter of core wire  142 , then liner  145 ″ will generally hold itself in assembled position around core wire  142 . 
     FIG. 12 depicts a third embodiment of the invention in which filter guidewire  220  incorporates several elements that are similar to the components of filter guidewires  20  and  120 . Core wire  242  is disposed within liner  145 , which is disposed within hollow shaft  144 . Core wire  242  is comprised of proximal section  256  and separate distal section  258 , which extends distally from shaft  144 . Sliding clearance(s) may be formed between different elongate movable components, as described above and as shown in FIGS. 7,  8  and  9 . If liner  145  is fitted against core wire  242 , as shown in FIG. 9, then liner  145  will comprise separate proximal and distal sections (not shown) corresponding to core wire proximal section  256  and core wire distal section  258 . Flexible tubular tip member  43  is fixed around the distal end of core wire distal section  258 . Transition sleeve  270  is slidably disposed about a distal portion of hollow shaft  144  and extends distally there from to a fixed coupling location on tip member  43 . Filter  25  is self-expanding and is positioned generally concentrically with the distal portion of shaft  144 . Filter distal end  27  is fixedly coupled to transition sleeve  270 , and filter proximal end  29  is fixedly coupled to shaft  144  adjacent the distal portion thereof. 
     Prior to negotiating vascular anatomy with filter guidewire  220 , filter  25  may be collapsed by advancing core wire proximal section  256  within shaft  144  and liner  145  until the distal end of proximal section  256  abuts the proximal end of distal section  258 , forming continuous core wire  242 . Continued advancement of core wire  242  through shaft  144  and liner  145  will displace tip member  43  distally away from shaft  144 . The axial translation of tip member  43  will draw sleeve  270  distally along, but not off of, the distal portion of hollow shaft  144 . The relative longitudinal movement of sleeve  270  with respect to shaft  144  causes filter distal end  27  to move away from filter proximal end  29 , transforming filter  25  from its expanded configuration to its collapsed configuration. Optionally, filter guidewire  220  may include bends  160  (not shown) in core wire proximal section  256  to provide frictional engagement between core wire  242  and the proximal end of shaft  144 . As described above regarding filter guidewire  120 , the optional friction mechanism thus created can hold core wire  242  in a selected axial position within shaft  144 , thereby retaining filter  25  in the collapsed configuration. 
     Withdrawing core wire proximal section  256  proximally through shaft  144  and liner  145  allows filter  25  to transform itself towards the expanded configuration by drawing filter ends  27 ,  29  closer together. The self-transformation of filter  25  towards the expanded configuration causes simultaneous proximal movement of sleeve  270 , tip member  43  and core wire distal section  258  relative to shaft  144 . The self-expansion of filter  25  stops when a) filter  25  reaches its pre-formed expanded configuration, or b) filter  25  encounters a radial constraint, such as apposition with a vessel wall in a patient, or c) filter  25  encounters an axial constraint, such as the proximal end of sleeve  270  contacting filter proximal end  29 , as depicted in FIG.  12 . After self-expansion of filter  25  has stopped, any further withdrawal of core wire proximal section  256  will cause it to separate from core wire distal section  258 , thereby allowing core wire distal section  258 , tip member  43 , and sleeve  270  to move freely with respect to the distal end of hollow shaft  144 . In this configuration, core wire proximal section  256  will not interfere with self-expansion or self-adjustment of filter  25  in its apposition with the vessel wall. 
     Transition sleeve  270  may be made of polyimide tubing and may be fixed to tip member  43  and to filter distal end  27  with a suitable adhesive. The length and mounting position of sleeve  270  are selected such that sleeve  270  always surrounds the distal end of shaft  144 , regardless of the configuration and length of filter  25 . Sleeve  270  can support core wire  242  across the longitudinal gap between the distal end of shaft  144  and the proximal end of tip member  43 . By contributing additional stiffness over its length, sleeve  270  also provides a transition in overall stiffness of filter guidewire  220  adjacent the distal end of shaft  144 . 
     FIG. 13 depicts a fourth embodiment of the invention in which occluder guidewire  320  incorporates several elements that are similar to the components of filter guidewires  20 ,  120 , and  220 . As distinguished from filter guidewire embodiments of the invention, occluder guidewires are typically used to temporarily obstruct fluid flow through the vessel being treated. Any embolic debris trapped upstream of the occluder element may be aspirated using a separate catheter, with or without irrigation of the area. Core wire  342  is disposed within liner  145 , which is disposed within hollow shaft  144 . Alternatively, liners  145 ′ or  145 ″ may be substituted for liner  145  such that different sliding clearance(s) may be formed between different elongate movable components, as described above and as shown in FIGS. 7,  8  and  9 . Flexible tubular tip member  43  is fixed around the distal end of core  342 . Transition sleeve  270  is slidably disposed about a distal portion of hollow shaft  144  and extends distally there from to a sliding coupling location on tip member  43 . Proximal stop  381  protrudes radially outward from the proximal end of tip member  43 , and distal stop  382  protrudes radially inward from the distal end of transition sleeve  270 . Stops  381 ,  382  interact to prevent the distal end of transition sleeve  270  from sliding proximally off of tip member  43 . Proximal stop  381  may comprise a portion of tip member  43 , such as one or more enlarged turns at the proximal end of a coil spring. Alternatively, proximal stop  381  may be created with metal or plastic elements, such as solder or polyimide bands. Distal stop  382  may comprise a portion of transition sleeve  270 , such as a rim or neck of reduced diameter formed at the distal end thereof. Alternatively, distal stop  382  may be created with metal or plastic elements, such as polyimide rings or bands. 
     Occluder  325  is self-expanding and is positioned generally concentrically with the distal portion of shaft  144 . Similar to filter  25 , occluder  325  may comprise a tubular braid, which in this embodiment is coated with an elastic material to render it non-porous. Alternatively, occluder  325  may include self-expanding struts (not shown) that support a non-porous elastic membrane, as known to those of ordinary skill in the art. A non-porous coating or membrane may be made from a variety of elastic materials, such as silicone rubber or a thermoplastic elastomer (TPE). Occluder distal end  327  is fixedly coupled to transition sleeve  270 , and occluder proximal end  329  is fixedly coupled to shaft  144  proximally adjacent the distal portion thereof. 
     In occluder guidewire  320 , occluder  325  may be collapsed by advancing core wire  342  through shaft  144  and liner  145 , causing tip member  43  to translate within transition sleeve  270  until proximal stop  381  engages distal stop  382 , as shown in FIG.  13 . Continued advancement of core wire  342  through shaft  144  and liner  145  will displace tip member  43  distally from shaft  144 , drawing sleeve  270  along, but not off of, the distal portion of hollow shaft  144 . The relative longitudinal movement of sleeve  270  with respect to shaft  144  causes occluder distal end  327  to move away from occluder proximal end  329 , which transforms occluder  325  from its expanded configuration to its collapsed configuration. Reversing the above manipulation, i.e. drawing core wire  342  proximally through shaft  144  and liner  145 , permits occluder  325  to expand itself. Self-expansion of occluder  325  will stop when one of several conditions is met, as described above with respect to self-expanding filter  25  of filter guidewire  220 . Thereafter, continued withdrawal of core wire  342  will draw tip member  43  proximally within transition sleeve  270 , creating axial separation (not shown) between stops  381 ,  382 , thereby allowing the distal end of transition sleeve  270 , with distal stop  382 , to slide freely along tip member  43 . In this configuration, core wire  342  and tip member  43  will not interfere with self-expansion or self-adjustment of occluder  325  in its apposition with the vessel wall. 
     FIG. 13 illustrates the portion of core wire  342  within hollow shaft  144  having a first proximal segment  390 , which also extends proximally from hollow shaft  144 . First proximal segment  390  is sized to fit slidingly within hollow shaft  144 , but without sufficient radial clearance for liners  145 ,  145 ′ or  145 ″. First proximal segment  390  may comprise a major length of core wire  342 , such that relatively short core wire distal segment  391  is dimensioned to receive liners  145 ,  145 ′ or  145 ″. For example, if occluder guidewire  320  is designed for use in coronary arteries, then the overall length of core wire  342  may be about 175 cm, and the length of core wire distal segment  391  may be about 15 to 25 cm. Alternatively, first proximal segment  390  may have a relatively short length such that core wire distal segment  391  and surrounding liners  145 ,  145 ′ or  145 ″ extend through a major length of hollow shaft  144 . 
     The transition in diameter between core wire distal segment  391  and first proximal segment  390  may occur as step  398 , which can limit the proximal slippage of free-floating liner  145  along core wire  342 . Optionally, occluder guidewire  320  may exclude any liner while still incorporating stepped diameter core wire  342  shown in FIG.  13 . In such an arrangement, the annular space that would otherwise be occupied by a liner can provide enlarged clearance and accompanying reduced friction between core wire  342  and hollow shaft  144 , especially when occluder guidewire  320  is curved through tortuous anatomy. Core wire  342  may also optionally include bends  160  (not shown) located distal to first proximal segment  390 . 
     In order to steer a distal protection guidewire in accordance with the invention through tortuous vasculature, tip member  43  is typically bent or curved prior to insertion of the device, which should transmit to tip member  43  substantially all of the rotation, or torque applied by the clinician at the proximal end of the device. It is most convenient for the physician to steer the device by grasping and rotating shaft  144 , and having such rotation imparted to tip member  43 , either directly or through the core wire. In distal protection guidewires of the instant invention, various design features reduce longitudinal friction between the hollow shaft and the core wire. These same friction-reducing features also reduce rotational friction between the hollow shaft and the core wire, which would otherwise be useful in transmitting rotation to steer the device. In filter guidewires  20 ,  120  and  220 , torque is transmissible from shaft  144  to tip member  43  through the braided structure of filter  25 , however this action is generally effective only when filter  25  is in the collapsed configuration. In occluder guidewire  320 , occluder distal end  327  is slidably connected to tip member  43  through transition sleeve  270  such that torque cannot be transmitted from shaft  144  to tip member  43  through occluder  325 . 
     It is therefore advantageous, as shown in occluder guidewire  320 , to include a torque-transmitting element, such as torque member  384 . Torque member  384  can comprise metal or plastic filaments that form a hollow tube of counter wound spirals or a braid. To minimize bulk and stiffness, torque member  384  may include only a single filament in each of the clockwise and counter clockwise winding directions. The proximal end of torque member  384  is bonded to the distal end of shaft  144  and extends distally there from to surround core wire  342  over a relatively short distance. The distal end of torque member  384  is bonded to the proximal end of tip member  43 , or to core wire  342  adjacent thereto. The braided, or spirally wound tubular structure of torque member  384  permits it to transmit rotation forces between shaft  144  and tip member  43 , and to do so at any length required to accommodate longitudinal displacement of shaft  144  and tip member  43  during transformation of occluder element  325  between a collapsed configuration and an expanded configuration. 
     In occluder guidewire  320 , second proximal segment  392  is located proximally of first proximal segment  390  and has an enlarged diameter approximating the outer diameter of shaft  144 . Reinforcement coil  396  surrounds first proximal segment  390  between second proximal segment  392  and the proximal end of hollow shaft  144 . Coil  396  has about the same outer diameter as shaft  144 , and helps prevent kinking of the portion of first proximal segment  390  that extends from hollow shaft  144 . Reinforcement coil  396  can vary in length to accommodate longitudinal displacement of shaft  144  and core wire  342  during transformation of occluder element  325  between a collapsed configuration and an expanded configuration. 
     Third proximal segment  394  is located proximally of second proximal segment  392  and is adapted for engagement to a guidewire extension (not shown), as is well known to those of ordinary skill in the art of guidewires. Examples of guidewire extensions usable with occluder guidewire  320  and other embodiments of the invention are shown in U.S. Pat. No. 4,827,941 (Taylor), U.S. Pat. No. 5,113,872 (Jahrmarkt et al.) and U.S. Pat. No. 5,133,364 (Palermo et al.). 
     FIG. 14 depicts a fifth embodiment of the invention in which occluder guidewire  420  incorporates several elements that are similar to the components of occluder guidewire  320 . For example, occluder guidewire  420  has core wire  442  disposed within liner  145 , which is disposed within hollow shaft  144 . Transition sleeve  270  is slidably disposed about a distal portion of hollow shaft  144  and extends distally there from. Proximal stop  481  protrudes radially outward from core wire  442 , and distal stop  482  protrudes radially inward from the distal end of transition sleeve  270 . Proximal stop  481  has a maximum transverse dimension, such as an outside diameter, that is greater than a transverse inner dimension, such as an inside diameter, of distal stop  482 . Proximal stop  481  is disposed proximal to and is capable of interacting with distal stop  482  to transmit distally directed axial force from core wire  442  to transition sleeve  270 . 
     As illustrated in FIG. 15A, proximal stop  481  may comprise a short coil fixed in the desired position around core wire  442 . To increase the strength of the attachment of proximal stop  481  to core wire  442 , at least a section of the coil may be longitudinally expanded. The resulting gaps in the coil can be permeated by a suitable bonding material, e.g., solder or adhesive, to both a larger diameter and a greater length, in comparison to unexpanded coils, as shown. 
     FIG. 15B illustrates a modified form of the stops shown on occluder guidewire  420  in FIG.  14 . Proximal stop  481 ′ may be created with metal or plastic elements, such as solder or polyimide bands, as described above regarding occluder guidewire  320 . Distal thrust bearing  483  is of the cylindrical, plain, anti-friction type and is disposed about core wire  442  between proximal stop  481 ′ and distal stop  482 . Distal thrust bearing  483  serves, as a thrust washer, to reduce rotating friction between stops  481 ′ and  482 , especially while occluder  325  is being forced into the collapsed configuration by the push-pull manipulations described above regarding occluder guidewire  320 . Reduced rotating friction facilitates turning core wire  442  within collapsed occluder  325 , thus providing enhanced steering of occluder guidewire  420  through tortuous curves and branches of a patient&#39;s vasculature. Distal thrust bearing  483  may comprise a ring of low-friction material such as a fluoropolymer, a polyamide, HDPE or polyimide/fluoropolymer composite tubing as discussed above regarding liners  145 ,  145 ′ and  145 ″. Alternatively, distal thrust bearing  483  may comprise a solid ring having a slippery coating applied thereto. Distal thrust bearing  483  may be freely situated in the described location, or it may be fixed to any of the adjacent components such as core wire  442 , proximal stop  481 ′ or distal stop  482 . 
     In occluder guidewire  420 , occluder  325  is self-expanding and is positioned generally concentrically with the distal portion of shaft  144 . Alternatively, filter  25  may be substituted for occluder  325  to create a filter guidewire in accordance with the fifth embodiment of the invention. As described above with respect to occluder guidewire  320 , occluder  325  may comprise a tubular braid that is coated with an elastic material to render it non-porous. 
     As shown in FIG. 14, occluder distal end  327  is fixedly coupled to transition sleeve  270 , and occluder proximal end  329  is rotatably coupled to shaft  144  at a location proximally adjacent the distal portion thereof. Occluder proximal end  329  may form a rotatable ring by any suitable means such as heat treatment of the braid, the use of fillers such as solder or adhesives, the addition of an internal or external ring element, or combinations of these methods. For example, FIG. 16 shows slip ring  487  located inside occluder proximal end  329 . 
     In occluder guidewire  420 , distal check element  486  protrudes radially outward from shaft  144  distal of occluder proximal end  329 . When hollow shaft  144  is drawn proximally over core wire  442 , distal check element  486  may contact occluder proximal end  329 , to which it may transmit proximally directed force from shaft  144 . Optionally, proximal check element  488  protrudes radially outward from shaft  144  proximal of occluder proximal end  329 . When hollow shaft  144  is slid distally over core wire  442 , proximal check element  488  may contact occluder proximal end  329 , to which it may transmit distally directed force from shaft  144 . Distal and proximal check elements  486 ,  488  may comprise rings, bands, coils, pins, adhesive dots, distortions in shaft  144 , or any other cooperating features that can effectively check longitudinal movement of occluder proximal end  329  while permitting rotation thereof. Thus, proximal end  329  is rotatable about shaft  144 , but may be longitudinally fixed between distal and proximal check elements  486 ,  488  respectively. Occluder  325  is free to rotate about the supporting steerable guidewire comprising, inter alia, shaft  144  and core wire  442 , because transition sleeve  270 , with occluder distal end  327  fixed thereto, is also rotatable about the steerable guidewire. Of course, the inverse description may be more clinically significant, i.e., the steerable guidewire can be rotated freely within occluder  325 , whether occluder  325  is in the deployed configuration or the collapsed configuration. 
     Occluder guidewire  420  includes tracking member  470  fixed alongside the distal end of core wire  442 . Tracking member  470  is a relatively short tube that is open at both ends and is sized to fit slidably over another guidewire. Tracking member  470  permits occluder guidewire  420  to be guided into a patient&#39;s vasculature along with, or by sliding over, another guidewire. Occluder guidewire  420  can also be exchanged easily over an indwelling guidewire. Because tracking member  470  envelopes only a short section of the other guidewire, various types of treatment catheters can be introduced over the other guidewire while occluder guidewire  420  is positioned in the patient. The clinician is thus presented with useful options of advancing therapeutic catheters over occluder guidewire  420 , or the other guidewire, or both guidewires. 
     During use of occluder guidewire  420 , occluder  325  may be collapsed by advancing core wire  442  distally through shaft  144  and transition sleeve  270  until proximal stop  481  engages distal stop  482 , as shown in FIG.  14 . Continued advancement of core wire  442  through shaft  144  will draw sleeve  270  along, but preferably not off of, the distal portion of hollow shaft  144 . The relative longitudinal movement of sleeve  270  with respect to shaft  144  causes occluder distal end  327  to separate from occluder proximal end  329 , thus transforming occluder  325  from an expanded configuration to a collapsed configuration, as shown in FIG.  14 . Reversing the above manipulation, i.e., drawing core wire  442  proximally through shaft  144 , permits occluder  325  to expand itself. Self-expansion of occluder  325  will stop when one of several conditions is met, similar to the description above with respect to self-expanding filter  25  of filter guidewire  220 . Thereafter, continued withdrawal of core wire  442  will draw its distal end proximally within transition sleeve  270 , creating axial separation (not shown) between stops  481 ,  482 , thereby allowing the distal end of transition sleeve  270 , with distal stop  482 , to slide freely along the distal end of core wire  442  between proximal stop  481  and tracking member  470 . Thus, in the deployed configuration of occluder guidewire  420 , occluder  325  can self-expand or self-adjust its apposition with the vessel wall. 
     FIG. 16 depicts a sixth embodiment of the invention in which occluder guidewire  520  incorporates several elements that are similar to the components of occluder guidewires  320  and  420 . Elements, and their positions, that are common to occluder guidewires  320  and  520  are shaft  144 , liner  145 , transition sleeve  270 , occluder  325 , core wire  342 , tip member  43 , stops  381 ,  382 , and check elements  486 ,  488 . Occluder guidewire  520  has slip ring  487  fixed within occluder proximal end  329 . Slip ring  487  is rotatably mounted about hollow shaft  144  between distal and proximal check elements  486 ,  488  respectively. The arrangement shown provides unlimited rotation of shaft  144  and core wire  342  within occluder  325 , as described above with respect to occluder guidewire  420  Proximal thrust bearing  489  is of the cylindrical, plain, anti-friction type and is disposed about shaft  144  between slip ring  487  and distal check element  486 . Proximal thrust bearing  489  serves to reduce friction between slip ring  487  or occluder proximal end  329  and distal check element  486 , thus facilitating rotation of shaft  144  within occluder  325 , especially when occluder  325  is being forced into the collapsed configuration by the push-pull manipulations described above regarding occluder guidewire  320 . Proximal thrust bearing  489  may comprise a ring of low-friction material such as a fluoropolymer, a polyamide, HDPE or polyimide/fluoropolymer composite tubing as discussed above regarding liners  145 ,  145 ′ and  145 ″. Alternatively, proximal thrust bearing  489  may comprise a solid ring having a slippery coating applied thereto. Proximal thrust bearing  489  may be freely situated in the described location, or it may be fixed to any of the adjacent components such as shaft  144 , occluder proximal end  329 , distal check element  486  or slip ring  487 . It may be especially advantageous to construct an inventive apparatus having a combination (not shown) of distal thrust bearing  483  of occluder guidewire  420  and proximal thrust bearing of occluder guidewire  520 . 
     As shown in FIG. 16, occluder guidewire  520  has tracking member  470  fixed alongside the distal end of the apparatus at the distal end of transition sleeve  270 . Since occluder guidewire  520  has both a steerable tip member  43  and tracking member  470 , a clinician can choose to insert and steer the device independently through a patient&#39;s vasculature, or the clinician can advance the same device over another guidewire. In contrast to occluder guidewire  420 , rotation of core wire  342  and tip member  43  does not attempt to revolve core wire  342  around another guidewire, if one is present within tracking member  470 . Both occluder guidewires  420  and  520  can be inserted to a desired location over another guidewire, which can then be removed, if so desired. A treatment catheter can be advanced over occluder guidewires  420  and  520  whether the other guidewire has been removed or not. 
     To adjust and maintain the relative longitudinal and/or rotational positions of core wires and the surrounding hollow shafts in the various embodiments of the invention, a removable handle device (not shown) of a type familiar to those of skill in the art may be used. Such handle devices can have telescoping shafts with collet-type clamps that grip respectively the core wires and shafts in the various embodiments of guidewire apparatuses according to the present invention. The handle device can also serve as a steering handle, or “torquer” which is useful for rotating small-diameter steerable-type guidewires that may be incorporated in the instant invention. 
     A method of using of a guidewire apparatus of the invention is described as follows. It should be noted that the example described below is unnecessarily limited to a filter guidewire embodiment. Filter guidewire  20 , having self-expanding filter  25  and hollow shaft  44  is provided, and advancing core wire  62  through shaft  44  collapses filter  25 . With filter  25  in the collapsed configuration, filter guidewire  20  is advanced into the patient&#39;s vasculature until filter  25  is beyond intended treatment site  15 . Withdrawal of core wire  62  allows filter  25  to expand. With filter  25  deployed into contact with the vessel wall, a therapeutic catheter is advanced over filter guidewire  20  to treatment site  15 , and therapy, such as balloon angioplasty, is performed. Any embolic debris generated during the therapy is captured in filter  25 . After the therapy is completed, the therapeutic catheter is prepared for withdrawal, as by deflating the balloon, if so equipped. Advancing core wire  62  through shaft  44  collapses filter  25 . Finally, filter guidewire  20  and the therapeutic catheter can be withdrawn separately or together, along with collected embolic debris contained within filter  25 . If an occluder guidewire of the invention were substituted for a filter guidewire in the above-described method, then aspiration of trapped embolic material would be performed with a separate catheter before collapsing the occluder element. 
     One benefit of the structures of filter guidewires  20 ,  120  and  220  is that guidewire tip member  43  forms a fixed length tip of the device, regardless of the configuration of filter  25 . Conversely, in occluder guidewire  320 , the tip length changes as occluder distal end  327  slides along tip member  43  during transformation of occluder  325  between expanded and collapsed configurations. The variable tip length of occluder guidewire  320  provides a short tip when occluder  325  is collapsed, but the tip needs to lengthen distally of treatment site  15 , if possible, during expansion of occluder  325 . During deployment of filter guidewires  20 ,  120  and  220 , the distal tip position of the device can remain fixed relative to treatment site  15 . This is accomplished by the user holding core wires  42 ,  142  or  242  anchored relative to the patient, while applying tension to shafts  44  or  144  in the proximal direction. Filter  25  can be maintained in a collapsed configuration by a friction mechanism including bends  160 , or by applying proximal tension to shafts  44 ,  144 , thus holding filter proximal end  29  apart from filter distal end  27 . Releasing the tension on shafts  44 ,  144 , or advancing them manually, allows filter  25  to expand by filter proximal end  29  translating distally towards filter distal end  27 . During this filter deployment, however, the distal tip does not need to move relative to filter  25  or treatment area  15 . 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made there in without departing from the spirit and scope of the invention. For example, the invention may be used in any intravascular treatment utilizing a guidewire and wherein the possibility of loosening emboli exists. Although the description herein illustrates angioplasty and stent placement procedures as significant applications, it should be understood that the present invention is in no way limited to those environments.