Patent Publication Number: US-2006015136-A1

Title: Vascular filter with improved strength and flexibility

Description:
This invention relates to medical devices, such as vascular filters to be used in a body lumen, such as a blood vessel, with improved strength and flexibility. A filter according to the invention includes a proximal frame section, a distal section and a flexible thin membrane with perfusion holes of a diameter that allows blood to pass, but prevents the movement of emboli downstream.  
      Both sections can be collapsed into a small diameter delivery catheter and expanded upon release from this catheter. The membrane has a proximal entrance mouth, which can be expanded, or deployed, substantially to the same size as the body lumen. It is attached to the proximal frame section, which has the function to keep the mouth of the membrane open and prevent the passing of emboli between the body lumen wall and the edge of the filter mouth  
      In order to have a good flexibility, the membrane is made extremely thin. Normally this would create the risk that the membrane could tear easily, which could cause problems because emboli and pieces of the membrane would then be carried downstream from the filter site.  
      U.S. Pat. No. 5,885,258 discloses a retrieval basket for catching small particles, made from a slotted tube preferably made of Nitinol, a titanium nickel shape memory alloy. The pattern of the slots allows expansion of the Nitinol basket and by shape setting (heat treatment in the desired unconstrained geometry) this basket is made expandable and collapsible by means of moving it out or into a surrounding delivery tube.  
      In principle, a distal filter is made of such an expandable frame that defines the shape and enables placement and removal, plus a filter membrane or mesh that does the actual filtering work.  
      Sometimes the expandable frame and the mesh are integrated and made from a single material, for example Nitinol, as disclosed in U.S. Pat. No. 6,383,205 or U.S. Published Application No. 2002/0095173. These filters do not have a well-defined and constant size of the holes where the blood flows through, because of the relative movement of the filaments in the mesh. This is a disadvantage, because the size of emboli can be very critical, e.g. in procedures in the carotid arteries. Further the removal of such a filter, accompanied by a reduction of the diameter, may be critical because emboli can be squeezed through the mesh openings with their changing geometry.  
      A much better control of the particle size is achieved with a separate membrane or filter sheath, which has a well-defined hole pattern with for example holes of 100 microns, attached to a frame that takes care of the correct placement and removal of the filter.  
      WO 00/67668 discloses a Nitinol basket that forms the framework of the filter, and a separate polymer sheath is attached around this frame. At the proximal side, the sheath has large entrance ports for the blood and at the distal side a series of small holes filters out the emboli. This system, however, has some major disadvantages. First of all, the closed basket construction makes this filter frame rather rigid and therefore it is difficult to be used in tortuous arteries. At a curved part of an artery, it may even not fit well against the artery wall and will thus cause leakage along the outside of the filter.  
      Another disadvantage of such filters is there is a high risk of squeezing-out the caught debris upon removal, because the struts of the framework force the debris back in the proximal direction, while the volume of the basket frame decreases when the filter is collapsed. Further the construction makes it very difficult to reduce the profile upon placement of the filter. This is very critical, because these filters have to be advanced through critical areas in the artery, where angioplasty and/or stenting are necessary. Of course the catheter that holds this filter should be as small as possible then. In the just described filter miniaturization would be difficult because at a given cross section there is too much material. The metal frame is surrounded by polymer and in the center there is also a guide wire. During angioplasty and stenting, the movements of the guide wire will create further forces that influence the position and shape of the filter, which may cause problems with the proper sealing against the artery wall. This is also the case in strongly curved arteries.  
      In U.S. Pat. No. 6,348,062, a frame is placed proximal and a distal polymer filter membrane has the shape of a bag, attached to one or more frame loops, forming an entrance mouth for the distal filter bag. Here the bag is made of a very flexible polymer and the hole size is well defined. Upon removal, the frame is closed, thus closing the mouth of the bag and partly preventing the squeezing-out of debris. This is already better than for the full basket design, which was described above, where the storage capacity for debris of the collapsed basket is relatively small. The filter bag is attached to the frame at its proximal end and sometimes to a guide wire at its distal end. Attachment to the guide wire can be advantageous, because some pulling force may prevent bunching of the bag in the delivery catheter.  
      It may be clear that it is easier to pull a flexible folded bag through a small diameter hole, than to push it through. However, the deformation of the bag material should stay within certain limits.  
      If the filter is brought into a delivery sheath of small diameter, collapsing the frame and pulling the bag into the delivery sheath causes rather high forces on the connection sites of filter to frame and/or guide wire. While the metal parts of the frame slide easily through such a delivery sheath, the membrane material may have the tendency to stick and in the worst case it may even detach from the frame and tear upon placement or during use, because of too much friction, unlimited expansion, crack propagation or the like.  
      The connection of the filter bag to the frame is rather rigid, because of the method of direct attachment. Additional flexibility, combined with a high strength attachment spot would also be advantageous.  
      Methods for making kink resistant reinforced catheters by embedding wire ribbons are described in PCT/US93/01310. There, a mandrel is coated with a thin layer of encapsulating material. Then, a means (e.g. a wire) for reinforcement is deposited around the encapsulating material and eventually a next layer of encapsulating material is coated over the previous layers, including the reinforcement means. Finally the mandrel is removed from the core of the catheter.  
      Materials for encapsulating are selected from the group consisting of polyesterurethane, polyetherurethane, aliphatic polyurethane, polyimide, polyetherimide, polycarbonate, polysiloxane, hydrophilic polyurethane, polyvinyls, latex and hydroxyethylmethacrylate.  
      Materials for the reinforcement wire are stainless steel, MP35, Nitinol, tungsten, platinum, Kevlar, nylon, polyester and acrylic. Kevlar is a Dupont product, made of long molecular higly oriented chains, produced from polyparaphenylene terephalamide. It is well known for its high tensile strength and modulus of elasticity.  
      In U.S. application Ser. No. 09/537,461 the use of polyethylene with improved tensile properties is described. It is stated that high tenacity, high modulus yarns are used in medical implants and prosthetic devices. Properties and production methods for polyethylene yarns are disclosed.  
      U.S. Pat. No. 5,578,374 describes very low creep, ultra high modulus, low shrink, high tenacity polyolefin fibers having good strength retention at high temperatures, and methods to produce such fibers. In an example, the production of a poststretched braid, applied in particularly woven fabrics is described.  
      In U.S. Published Application No. 2001/0034197, oriented fibers are used for reinforcing an endless belt, comprising a woven or non-woven fabric coated with a suitable polymer of a low hardness polyurethane membrane, in this case to make an endless belt for polishing silicon wafers. Examples are mentioned of suitable yarns like meta- or para-aramids such as KEVLAR, NOMEX OR TWARON; PBO or its derivatives; polyetherimide; polyimide; polyetherketone; PEEK; gel-spun UHMW polyethylene (such as DYNEEMA or SPECTRA); or polybenzimidazole; or other yarns commonly used in high-performance fabrics such as those for making aerospace parts. Mixtures or blends of any two or more yarns may be used, as may glass fibers (preferably sized), carbon or ceramic yarns including basalt or other rock fibers, or mixtures of such mineral fibers with synthetic polymer yarns. Any of the above yarns may be blended with organic yarns such as cotton.  
      The present invention further relates to medical procedures performed in blood vessels, particularly in arteries.  
      This invention relates more specifically to systems and methods involving angioplasty and/or stenting, where protection against loose embolic material is a major concern.  
      Such procedures are performed to remove obstructions or blockages in arteries and thereby alleviate life-threatening conditions. The procedures currently employed result in a fracturing or disintegration of the obstructing material and if the resulting particles, or debris, were permitted to flow downstream within the circulatory system, they would be likely to cause blockages in smaller arteries, or their microscopic branches termed the microcirculation, downstream of the treatment site. The result can be new life-threatening conditions, including stroke.  
      Various systems and techniques have already been proposed for removing this debris from the circulatory system in order to prevent the debris from causing any harm. These techniques involve temporarily obstruction the artery, at a location downstream of the obstruction, by means of an element such as a balloon, and then suctioning debris and blood from the treatment site. While such techniques can effectively solve the problem stated above, they require that blood flow through the artery be obstructed, causing complete cessation or at least a substantial reduction in blood flow volume, during a time period which can be significant for organ survival for example, the time limit for the brain is measured in seconds and for the heart, in minutes.  
      Although filters have been used, they suffer from the limitation of either obstructing flow or allowing micro embolism due to fixed pore size. Furthermore, the collected debris can reflux out of the filter when it is closed and lead to embolism. Upon pulling back of a basket/filter with entrapped particles into a delivery catheter, debris particles may be squeezed out of the device, because the volume is strongly reduced. During this pulling back, the filter no longer covers the full cross-section of the artery, so particles that are squeezed out then can freely flow around the outer edge of the filter and move distally through the artery.  
      The invention also relates to a combined delivery/post-dilatation device for self-expanding stents.  
      Normally the delivery of self-expanding stents is done with a separate delivery sheath, which is pulled back to release the compressed stent from this sheath and allow it to deploy. If this stent does not deploy to the full size, because the reaction forces of the artery wall and lesion site are too high, it must be further expanded by an additional post-dilatation procedure. Therefore, a separate post-dilatation catheter is needed, that has to be brought into the stented lesion site and then inflated to the full size. This is an extra, time-consuming step in the procedure.  
      The present invention provides novel medical devices, such as vascular filters, with improved strength and flexibility and methods for their manufacture. These devices have a proximal frame section and a distal section, which can be collapsed into a small diameter delivery catheter and expanded upon release from this catheter. The proximal section is made as a frame of a relatively rigid material compared to the material of the distal section, for example a metal, and the distal section is provided with a flexible thin membrane, with perfusion holes in filter devices, of a diameter that allows blood to pass, but prevents the passage of emboli. The distal filter membrane has a proximal entrance mouth, which has almost the same size as the body lumen of a patient when the filter is deployed. The membrane is attached to the proximal section, which has the function to keep the mouth of the distal filter open and to prevent the passing of emboli between the body lumen wall and the edge of the filter mouth.  
      In order to have a good flexibility and a minimized crossing profile upon delivery, the membrane is made extremely thin. Tearing of the membrane is prevented by embedding in the filter membrane thin filaments of a material with high strength in the longitudinal direction, but high flexibility upon bending. Such a filter membrane with embedded filaments can have extreme flexibility and elasticity in certain directions, combined with limited deformation, high strength and prevention of crack propagation through the membrane material. Further, the filaments can be attached to the proximal frame section in such a way that the connection points act as hinges and as additional safety for the case that the membrane material might come loose from the frame.  
      The embedded filaments can include elements that help to give the membrane a desired shape after deployment.  
      The surface of the membrane filter may be coated with an additional material that improves the properties, for example the biocompatibility, drugs release or any other desired property, which the membrane itself does not offer.  
      The thus reinforced membranes can also be manufactured without holes for use for parts of catheters, inflatable parts, balloon pumps, replacement of body tissues, repair of body parts and functional parts like artificial valves and membranes, where minimal thickness and/or high strength are required.  
      Fibers are used not only as reinforcement for the membranes, but are also used as pulling fibers for the extraction the device from a delivery catheter or for retrieval, or retraction, of the device into a removal sheath. The frames can be used in temporary devices like a removable temporary stent, dilator, reamer, occlusion device for main artery or side artery, a housing for a graft, a valve, a delivery platform for drugs, radiation or gene therapy, or any other device that has to be placed and removed after some time. Applications are not restricted to arteries, but are meant for all body lumens. Placement of the devices discussed herein does not necessarily have to be done by means of a guide wire and accompanying sheath. It can also be done by any displacement member, including the surgeon&#39;s hand, stitching, tools, instruments, catheters, balloon or the like.  
      Further, the invention provides a method for producing devices such as filters by dipping on a removable mold. According to this method, thin filaments of a material with high strength in the longitudinal direction, but high flexibility upon bending, are embedded in the filter membrane. The fibers are preferably less stretchable than the membrane material. The resulting composite membrane can have extreme flexibility and elasticity in certain directions, combined with limited deformation, high strength and prevention of crack propagation through the membrane material. Another function of the embedded filaments is that they help to give the membrane a desired shape after deployment.  
      The present invention also provides improved methods and devices that prevent escape of debris from the treatment site in a blood vessel, and more specifically prevent embolism, by installing at least one appropriate filter with millipores specific to its use downstream, and possibly one such filter downstream of the treatment site in a blood vessel and manipulating those filters in a manner to assure that any debris created at the treatment site or refluxing from closure of the filters will be removed from the vascular system by physical withdrawal of the filters and/or suction.  
      For example, an embodiment of the invention may be a multistage, for example two filter, system composed of a first filter to filter the blood flow and a second filter to entrap debris from the first filter.  
      The invention further relates to a catheter system for delivery of a self-expanding stent with a combined function of delivery from a central sheath and post-dilatation, the system including a catheter having an inflatable outer section that surrounds the sheath at the distal end section of the catheter. The first step in a procedure using this system is the release of the stent by pushing it out of the sheath and pulling back of the catheter over a distance that is equal to at least the length of the stent. Then the catheter is advanced once more until the inflatable section is lined up with the stent again. For post-dilatation the inflatable section is inflated and the lesion plus stent are further expanded.  
      In one embodiment of the invention, the central lumen within the delivery sheath, where the stent has been pushed out, is reinforced to prevent it from collapsing by the hydraulic pressure of the post-dilatation balloon that surrounds it. Reinforcement of this sheath can be provided by giving the catheter a suitable rigidity at its distal end, for example by giving the catheter an increased thickness at that end. This may make the delivery sheath too rigid, which can be a disadvantage for use in tortuous arteries.  
      Therefore, the invention makes use of a more flexible delivery sheath that is prevented from collapsing by the use of a separate reinforcement. A pre-dilatation balloon can be lined up with the delivery sheath and inflated until it fills the lumen of this delivery sheath. In this way a concentric arrangement of two balloons, separately inflatable, gives a strong post-dilatation device that is extremely flexible in the deflated state.  
      A single common guide wire is used to bring the catheters to the lesion site, and the pre-dilatation catheter acts as a guiding means for the stent delivery sheath/post-dilatation balloon. By removal of the pre-dilatation catheter, leaving the inflated delivery catheter in place, a proximal occlusion system is created with a large working channel (the delivery sheath). In combination with a distal occlusion means, e.g. a distal balloon, a closed chamber is created in the artery and this can be reached with a range of instruments for inspection, treatment and flushing/suction purposes. 
    
    
       FIG. 1  is a simplified pictorial view illustrating a first component of a system according to the invention.  
       FIG. 2  is a simplified pictorial view showing the component for  FIG. 1  in an expanded state, associated with a treatment device.  
       FIG. 3  is view similar to that of  FIG. 1  showing the first component and a second component of a system according to the invention.  
       FIGS. 4A and 4B  are simplified pictorial views showing two basic embodiments of the invention.  
       FIGS. 5, 6  and  7 A are cross-sectional elevational views of various alternative embodiments of filter components of a system according to the invention.  
       FIG. 7B  is plan view of the embodiment shown in  FIG. 7A .  
       FIGS. 8, 9  and  10  are simplified pictorial views illustrating specific procedures that may be carried out with a system according to the invention.  
       FIG. 11  is an elevational view of another embodiment of a filter component of a system according to the invention.  
       FIG. 12  is a side elevational view of a component of another embodiment of a system according to the invention, including a filter in its folded state.  
       FIG. 13  is a view similar to that of  FIG. 12 , showing the filter in its expanded sate.  
       FIG. 14  is an end view of the component with the filter in the expanded state.  
       FIG. 15  is a simplified side cross-sectional view showing the other embodiment of a system in a blood vessel with two filters of the type shown in  FIGS. 12-14 .  
       FIG. 16  is a view similar to that of  FIG. 15  showing a modified form of construction of the system shown in  FIG. 15 .  
       FIGS. 17-27  are simplified pictorial views showing successive stages in an angioplasty and stenting procedure using an embodiment of a system according to the invention.  
       FIG. 17  shows a guide wire brought into an artery with a lesion.  
       FIG. 18  shows a guiding catheter with a distal protection means, brought across the lesion over the guide wire.  
       FIG. 19  shows how the distal protection means is deployed until it reaches the artery walls.  
       FIG. 20  shows a predilatation catheter, which has been advanced over the guiding catheter, in its predilatation position with inflated balloon in the lesion section. Further  FIG. 20  shows a delivery sheath with an inflatable distal section, holding a compressed stent, which is advanced over the predilatation balloon catheter.  
       FIG. 21  shows how the predilatation balloon is deflated and advanced across the lesion site, plus the semi-deployed stent after it has been delivered in the lesion area.  
      In  FIG. 22  the two balloons are lined up and brought in the stent.  
      In  FIG. 23  the predilatation balloon is inflated to create a support for the inflatable delivery sheath.  
      In  FIG. 24  the inflatable delivery sheath is inflated to perform the final angioplasty and to reach full deployment of the stent.  
      In  FIG. 25  the predilatation balloon catheter is removed from the patient&#39;s body while the inflated sheath is still in place.  
      In  FIG. 26  the chamber in the artery between distal protection means and inflated sheath is flushed to remove or catch all debris.  
      In  FIG. 27  the sheath is deflated and the distal protection means is collapsed, thus enabling removal from the artery, leaving only the stent in place.  
       FIGS. 28-31  are side elevational views showing four stages in the fabrication of an embodiment of a filter according to the present invention.  
       FIG. 32  is an elevational view showing another embodiment of a filter according to the present invention.  
       FIG. 33  is a side elevational view showing another embodiment of a filter according to the present invention in an expanded state.  
       FIG. 34  shows the filter of  FIG. 33  in a compressed state while being inserted to a desired location with a delivery sheath.  
       FIG. 35  shows the filter of  FIG. 33  being withdrawn back into the sheath.  
       FIG. 35   a  is a detail view of a portion of the embodiment of  FIGS. 33-35 .  
       FIG. 35   b  is a detail view similar to that of  FIG. 35   a,  showing a modified version of a component of the embodiment of  FIGS. 33-35 .  
       FIGS. 36   a  and  36   b  are detail views of a modified form of construction of a portion of the embodiment of  FIGS. 33-35 .  
       FIG. 37  is a side elevational view showing a modified version of the embodiment shown in  FIGS. 33-35 , and includes an inset illustrating the modification to a larger scale.  
       FIG. 38  is a side elevational view showing the filter of  FIG. 37  in a further possible operating stage.  
       FIG. 39  is a side elevational view showing another embodiment of a filter according to the present invention.  
       FIGS. 40   a  through  40   c  show a delivery system that enables a device of the present invention to be permanently placed within a body lumen.  
    
    
      The invention provides a novel method and a system to confine and remove debris from a blood vessel, thereby preventing embolism in the vascular system.  
      A first step of one embodiment of a method according to the invention includes positioning a first particle filter in the blood vessel downstream of the treatment site.  
       FIG. 1  is a cross-sectional elevational view of a first unit of a protective system according to the invention for carrying out the first step. This unit is composed of a sheath  1 , a hollow guide wire  2  and a distal particle filter  4 .  
      Filter  4  may have any shape, for example a conical shape, as shown, and is constructed to be radially expansible from a radially compressed state, shown in solid lines, to a radially expanded state, shown in broken lines at  4 ′. Preferably, at least one part of filter  4  is made of a resiliently deformable material that autonomously assumes the radially expanded state shown at  4 ′ when unconstrained. Filter  4  may be shaped using appropriate shape setting procedures to open with a flared top portion made from highly elastic material such as the memory metal nitinol.  
      Sheath  1  serves to hold filter  4  in the radially compressed state during transport of filter  4  to and from the treatment site.  
      Filter  4  has a tip, or apex, that is fixed to guide wire  2 . Guide wire  2  extends from a proximal end that will always be outside of the patient&#39;s body and accessible to the physician to a distal end that extends past the apex.  
      Guide wire  2  is preferably a hollow tube whose distal end is, according to the invention, used as a pressure sensor in communication with a pressure monitoring device  5  connected to the proximal end of guide wire  2 . Device  5  is exposed to, and senses, via the longitudinal passage, or bore, in tube  2 , the pressure adjacent to the distal end of guide wire  2 .  
      Preferably, monitoring device  5  is removably fastened to the proximal end of guide wire  2 . Device  5  would be removed, for example, when guide wire  2  is to be used to guide some other component of the device into the blood vessel after insertion of the first unit into a blood vessel, as will be described in greater detail below.  
      According to one practical embodiment of the invention, sheath  1  has an outside diameter of 1 to 1.5 mm and wire  2  has an outside diameter of 0.014-0.018 inch (approximately 0.5 mm) and is sized so that during insertion it will not disturb the obstruction that is to be removed. Filter  4  can be dimensioned to expand to an outer diameter of more than 1 mm, and preferably more than 10 mm. This dimension will be selected to be approximately as large as the diameter of the vessel to be treated.  
      Prior to insertion into a blood vessel filter  4  is arranged in sheath  1  as shown in  FIG. 1 . Then, in a conventional preliminary step, the blood vessel wall is punctured by a hollow needle, a preliminary guide wire (not shown) is introduced into the blood vessel through the needle, the needle is withdrawn, the opening in the blood vessel is dilated and a guiding catheter (not shown) is passed over the preliminary guide wire into the blood vessel to be treated. The distal, or leading, end of the guiding catheter is brought to an appropriate point ahead of an obstruction to be treated and the preliminary guide wire is withdrawn. Then, guide wire  2  and sheath  1 , with filter  4  in place, are introduced into the blood vessel in the direction of blood flow, in a conventional manner through the guiding catheter, until filter  4  is at the desired location in the vessel, usually downstream of the obstruction to be treated. Introduction through the guiding catheter facilitates accurate passage of the filter  4  and sheath  1  by preventing buckling and permitting easier positioning, as well as reducing the risk of dislodging clot particles from the obstruction, which is typically plaque. Then, the operator holds wire  2  stationary and retracts sheath  1 , which is long enough to be accessible to the operator outside the body, until sheath  1  moves clear of filter  4 , which can then expand to take on the configuration shown at  4 ′. Sheath  1  can then be fully withdrawn from the vessel. Whenever required, the proximal end of sheath  1  can be clamped shut, usually during withdrawal.  
      A second step of a method according to the invention involves performance of the desired medical treatment in the region upstream of filter  4 , which region, as shown in  FIG. 2 , is below filter  4 . Such a treatment can be for the purpose of removing an obstruction in a blood vessel  6 , and this can involve any known angioplasty procedure or any known obstruction disintegration or observation (viewing) procedure employing ultrasound, laser radiation, stent placement, etc., or any mechanical cutting procedure, etc. The device for performing this function can be guided to the site by being advanced along guide wire  2 .  
      For example, this device can be an ultrasonic device as disclosed in U.S. Pat. No. 4,870,953. This device has an output end  8  provided with a bulbous tip that applies ultrasonic vibrations to obstruction material, such as plaque or clot. Output end  8  may be guided to the site of the obstruction in any conventional manner over wire  2 , however this can be assisted by providing output end  8  with a ring, or loop,  9  that is fitted around guide wire  2  before output end  8  is introduced into blood vessel  6 .  
      After the device has been brought to the treatment site, it is operated to perform the desired treatment, in this case disintegration of plaque or clot, commonly predilation, stenting and stent dilatation. After the treatment has been performed, the treatment device is withdrawn from the blood vessel.  
      A third step of a method according to the invention includes positioning a second particle filter in the blood vessel upstream of first filter  4  and preferably upstream of the treatment site. This is accomplished by sliding guide wire  2  through an orifice in a second filter  14 , to be described below, adjacent to a guide wire  12  that carries the second filter.  
       FIG. 3  is cross-sectional elevational view of a second unit of the protective system according to the invention for carrying out the third step.  
      This second unit is composed of a second tube, or sheath,  10 , a second guide wire  12  and a proximal particle filter  14 . Sheath  10  may have a diameter of the order of 3 mm. At the time this unit is inserted into the blood vessel, filter  4  remains in place in the blood vessel, in the expanded state as shown at  4 ′ in  FIG. 1 , as does hollow guide wire  2 .  
      Proximal filter  14  has an apex provided with a ring  16  through which guide wire  2  is inserted when the second unit is still located outside of the patient&#39;s body, in order to guide the second unit into the blood vessel up to the treatment site. Second guide wire  12  is secured to ring  16 .  
      Prior to introduction into the patient&#39;s body, filter  14  is installed in sheath  10  in the manner illustrated in  FIG. 3 . The second unit is then placed over guide wire  2  and advanced into the blood vessel to the desired location.  
      After the second unit has been brought to the desired location, proximal filter  14  is held stationary by holding stationary the end of guide wire  12  that is outside of the patient&#39;s body, while retracting sheath  10 . When filter  14  is clear of the distal end of sheath  10 , filter  14  expands radially into the configuration shown at  14 ′ to engage filter  4 . This step is completed when filter  14  is fully radially expanded.  
      Because of the porous nature of filters  4  and  14 , a reasonable volume of blood flow can be maintained in the blood vessel when the filters are deployed.  
      Prior to introduction of filter  14 , any debris produced by the treatment performed in the second step will be conveyed by blood flowing to and through radially expanded filter  4 , where the debris will tend to remain. During and after introduction of filter  14  and expansion of filter  14  into the configuration shown at  14 ′, suction may be applied to the region between the filters through sheath  10 . This will help to assure that the debris remains trapped between the two filters.  
      Then, in a fourth step, debris is removed from blood vessel  6  by pulling wire  2  to move filter  4  toward, and into contact with, filter  14 , then retracting both filters into sheath  10  by pulling the guide wires  2  and  12 , thus withdrawing the assembly of filters  4  and  14  into sheath  10 . Sheath  10  with enclosed filters is then withdrawn through the guiding catheter (not shown), which is subsequently removed from the blood vessel using standard procedures. These operations are performed by pulling on guide wire  2  at its proximal end, located outside of the patient&#39;s body, while initially holding guide wire  12  stationary until filter  4 , comes to nest within filter  14 . Then both guide wires  2  and  12  are pulled in order to retract the filters into sheath  10 . Finally, both of the guide wires and sheath  10  are pulled as a unit out of the blood vessel. During any portion, or the entirety, of this step, suction may continue to be applied to filters  4  and  14  through sheath  10 .  
       FIGS. 4A and 4B  are simplified pictorial views showing two possible arrangements for a set of filters  4  and  14 . The arrangement shown in  FIG. 4A  corresponds to that shown in  FIGS. 1, 2  and  3 . The arrangement shown in  FIG. 4B  differs in that filter  4  is inverted relative to the orientation shown in  FIGS. 1, 2 ,  3  and  4 A. The arrangement of filters shown in  FIG. 4A  is applicable to short, non tortuous segments of arteries.  FIG. 4B  shows an optional filter arrangement for longer segments of arteries especially if they are tortuous.  
      When the arrangement shown in  FIG. 4B  is employed, filters  4  and  14  are positioned in the blood vessel by the first and third steps as described above. In order to withdraw the filters, guide wire  2  is pulled to bring filter  4  into a position in which its large diameter end has been introduced into the large diameter end of filter  14 . Then, as both filters are pulled into sheath  10 , filter  14  is collapsed by its contact with sheath  10  and filter  4  is collapsed by its contact with the interior of filter  14 . In this form of construction, filter  14  has an expanded diameter at least slightly greater than filter  4 .  
      The arrangement illustrated in  FIG. 4B  offers the advantages that in the first step filter  4  can be extracted from sheath  1  somewhat more easily and, after filter  4  has been expanded, any debris produced by the operation performed in the second step will tend to collect near the apex of filter  4 , away from its line of contact with the blood vessel wall.  
      One exemplary embodiment of filter  4  is shown in greater detail in  FIG. 5 . This embodiment consist of a frame, or armature, composed of a small diameter ring  22  at the apex of filter  4 , a large diameter ring  24  at the large diameter end of filter  4  and a plurality of struts  26  extending between rings  22  and  24 . The frame is preferably made in one piece of a relatively thin memory metal, which is well known in the art. One example of such a metal is nitinol. The frame is constructed to normally assume a radially expanded state, such as shown at  4 ′ in  FIG. 1 , but to be easily deformed so as to be retracted, or radially compressed, into sheath  1 .  
      The frame is covered on its outer surface with a thin sheet, or membrane,  28  of suitable filter material having pores that are sized according to principles known in the art to protect organs downstream of the treatment site. The pore dimensions are selected to allow reasonable flow of blood to organs downstream of the treatment site when the filters are in place while trapping debris particles of a size capable of causing injury to such organs. The desired filtering action will be achieved with pore sized in the range of 50 .mu.m to 300 .mu.m. This allows different millipore sizes to be used to optimize either blood flow or embolism protection. The larger pore dimensions will be used in situations where a higher blood flow rate must be maintained and the escape of small debris particles is medically acceptable.  
       FIG. 6  is a view similar to that of  FIG. 5  showing one suitable embodiment of filter  14 , which is here shown essentially in its expanded state. Like filter  4 , filter  14  includes a frame, or armature, having a small diameter ring  32  at its apex, a large diameter ring  34  at its large diameter end and a plurality of struts extending between rings  32  and  34 . Filter  14  is completed by a filter sheet, or membrane,  38  secured to the outer surfaces of struts  36 . Ring  32  provides a passage for guide wire  2 , the passage being dimensioned to allow filter  14  to move freely along guide wire  2 . Guide wire  12  is fixed to the outer surface of ring  32 .  
       FIGS. 7A and 7B  are, respectively, an elevational cross-sectional view and a plan view of another embodiment of a distal filter  44  that can be employed in place of filter  4 . This embodiment includes, like filter  4 , a small diameter ring  22 , a large diameter ring  24  and a plurality of struts  26 , with a filter sheet  28  secured to the outer surfaces of struts  26 . Here again, ring  22  has an opening for receiving guide wire  2 , which will be fixed to ring  22 .  
      Filter  44  is further provided with a second, small diameter, ring  46  and a second series of struts  48  extending between rings  24  and  46 . Ring  46  has an opening with a diameter larger then that of guide wire  2 , so that ring  46  is moveable relative to guide wire  2 .  
      All the parts of filter  44 , except for membrane  28 , like the corresponding parts of filter  4  and  14 , may be made in one piece of a memory metal that has been processed to bias the filter toward its radially expanded configuration. All of these components are sufficiently thin to allow the filter to be easily collapsed radially within its respective sheath  1  or  10 . Filter  44  will be mounted so that its apex faces in the distal direction, i.e. the cone formed by the struts  26  and filter sheet  28  have an orientation which is opposite to that of filter  4 .  
      Filter  44  is brought to its radially expanded state in essentially the same manner as filter  4 . When the filter portion is at the desired location in the blood vessel, sheath  1  will be retracted in order to allow filter  44  to expand radially. When the filters are to be withdrawn, guide wire  2  is pulled in the proximal direction until the lower part of filter  44 , composed of ring  46  and strut  48 , comes to nest either partially or fully in filter  14 . Then, both guide wires  2  and  12  can be pulled in the proximal direction in order to retract the filters into sheath  10 . During this operation, ring  46  has a certain freedom of movement relative to guide wire  2 , which will help to facilitate the radial contraction of filter  44 . Alternatively, or in addition, sheath  10  can be advanced in the distal direction to assist the retraction operation.  
      According to further alternatives, rings  22  and  46  can be dimensioned so that either guide wire  2  is fastened to ring  46  and movable longitudinally relative to ring  22 , or guide wire  2  is fixed to both rings  22  and  46 . In the latter case, radial contraction and expansion of filter  44  will still be possible in view of the flexibility and deformability of its components.  
      A system according to the invention can be used, for example, to improve the safety of bypass surgery. Referring to  FIG. 8 , an example of that surgery involves attaching vein bypass grafts to the aorta  50  starting from a point just downstream of the aortic valve  52  located between the left ventricle and aorta of the heart  54 . In such a procedure, holes  56  are cut in aorta  50  for insertion of the upstream ends of the grafts. The operation of cutting into the wat 1  of the aorta to sew on grafts can produce debris that will be carried along with blood flowing through the aorta to locations in the circulatory system where it can create an embolism in various organs, including the brain.  
      Referring to  FIG. 8 , the risk of such an occurrence can be reduced by introducing a system according to the embodiment of  FIGS. 1-3 , before holes  56  are cut, through a subclavian artery  58 , which can be accessed via the patient&#39;s arm, and the brachial artery, to bring filters  4  and  14  to a location downstream of the location where holes  56  will be cut and to expand those filters so that they extend across the blood flow path through the aorta. Then, when holes  56  are cut, any debris produced by the cutting operation will be trapped, at least initially, within filter  4 . However, while both filters are being withdrawn into tube  10 , after holes  56  have been cut and possibly after vein grafts have been sutured to the holes, some debris may be squeezed out of filter  4 , even as suction is being applied through tube  10 . If this should occur, the debris can be drawn into filter  14  so as to be safely removed from the circulatory system.  
      Another example of the use of a system according to the invention to capture debris incident to a medical procedure is illustrated in  FIG. 9 . A plaque deposit  62  is present on the wall of an internal carotid artery  64  just downstream of the junction with an associated external carotid artery  66 . A guiding catheter  68  is introduced into common carotid artery  70  and is used as a conduit for introducing all other devices required to removes plaque  62  and collect the resulting debris. Catheter  68  carries an annular blocking balloon  72  on its outer surface and is provided with a conduit (not shown) for supplying inflation fluid to balloon  72 .  
      A wire  74  carrying a Doppler flow sensor is introduced into internal artery  64  to position the flow sensor downstream of plaque  62 . Then, sheath  1  (not shown) is introduced to deploy filter  4  in external artery  66 , as described earlier herein and balloon  72  is inflated to block blood flow around catheter  68 . After filter  4  is deployed and balloon  72  is inflated, any conventional procedure, such as described above with reference to  FIG. 2 , can be carried out to disintegrate plaque  62 .  
      Then, as described with reference to  FIG. 3 , sheath  12  is advanced through catheter  68  to the location shown in  FIG. 9 , filter  14  is deployed and expanded into internal artery  66 , and suction is applied as filters  4  and  14  are retracted into sheath  10 .  
      In this procedure, starting from a time before disintegration of plaque  62 , blood flow through common carotid artery  70  is blocked by inflated balloon  72 . This results in a retrograde flow in internal artery  64  back toward common artery  70  and then antigrade flow into external artery  66 , where debris being carried by the blood flow will be trapped on filter  4 . The pressure sensing wire  74  is used to ascertain the collateral pressure, which must always exceed 40 mm Hg in the carotid. After a sufficient period of time has elapsed, filter  14  will be deployed to nest against filter  4  and both filters will be retracted into sheath  10  while suction is applied, possibly through sheath  10 . Then, balloon  72  will be deflated, sheath  10  will be withdrawn through guide catheter  68  and catheter  68  will be withdrawn.  
      In another application of the invention, the filters can be passed through a small peripheral artery into the aortic root to entrap debris generated during cardiac surgery. Such a device can be used during surgery or can be implanted for long-term use to prevent migration of blood clots to the brain under certain circumstances, such as during atrial fibrillation.  
      A further example of procedures that may be carried out with a device according to the invention is illustrated in  FIG. 10 , which shows the positioning of a device according the invention for treating an obstruction in an artery  80  or  82  emerging from the pulmonary artery  84  connected to the right ventricle  86  of a patient&#39;s heart. The right ventricle communicates with the right auricle  88  of the heart, which is supplied with blood from veins  90  and  92 . In such a procedure, sheaths  1  and  10  may be introduced through either vein  90  or  92  and then through auricle  88 , ventricle  86  and pulmonary artery  84  into either one of arteries  80  and  82  to be treated. Techniques for guiding the sheaths along the path illustrated are already well known in the art. Once positioned in the appropriate artery  80  or  82 , an obstruction removal procedure will be performed in the manner described above.  
       FIG. 11  shows another embodiment of a filter component according to the invention in the general form of a basket, or cup,  102  made of a layer  104  of a radially compressible, autonomously expandable, material, such as a memory metal, and a filter sheet  106 . Layer  104  may be fabricated by weaving memory metal wire into a mesh, or screen. Filter sheet  106  is made of a suitable plastic material, such as polyester, perforated to provide the desired filter pores, having dimensions described above. The bottom of basket  102  may be fixed to guide wire  2 , in the manner of filter  4 , described above, or may have a circular opening that is slidable along wire  2 , with a second guide wire attached to the edge of the opening, in the manner of filter  14 , as described above. Each such basket  102  will be used in the same manner as a respective one of filters  4  and  14  and will be dimensioned to extend across the blood vessel at the location where the system is to be employed.  
      The procedures described above are merely exemplary of many procedures that can be aided by utilization of the system according to the present invention and other uses will be readily apparent to medical professionals. It should further be clear that the examples shown in the drawings are illustrated in a schematic form. For example the shape of the ring  24  in  FIGS. 5, 7A  and  7 B is shown as a circle. However, for a ring that has to be collapsed to allow the filter to be pulled it into the sheath, it would be more logical to give it a slightly wavy or corrugated shape. This would make it more flexible and capable of smooth radial contraction and expansion. Another embodiment of a system having a distal protection system with a double filter according to the invention is shown in  FIGS. 12-16 .  
      In  FIG. 12-14 , a circularly cylindrical tube  150  is formed to have, at one end, which is here its distal end, a monolithic, or one-piece, distal filter that has a tubular conical shape with a pattern of slots that have been made in the surface of tube  150  by cutting, grinding, etching or any other technique. Tube  150  can be made of any material, like metal or polymer, and especially of nitinol with superelastic properties. Tube  150  may be long enough to be used as a guiding rail for catheters that are used for the angioplasty/stenting procedure.  
      At the distal end of tube  150 , the slots are cut in such a way as to form a filter that has an expansion capability of at least, for example, a factor of 4. If tube  150  is made of nitinol, the expanded shape can be programmed into the memory by a heat treatment, while the material is kept in the desired expanded shape, shown in  FIGS. 13 and 14 , by some restraining tool. This is a known technique called shape setting.  
      The slots cut at the distal end of tube  150  leave thin, circularly curved, circumferential groups of distal strips  110  and groups of intermediate strips  130 ,  131  and  132 . These strips are connected to, and interconnected by, thicker longitudinally and radially extending groups of struts  120 ,  140 ,  141  and  142  that end at the continuous, i.e., imperforate, surface of tube  150 . Upon expansion for shape setting, struts  120 ,  140 ,  141  and  142  will bend out and give the distal section of tube  150  a conical shape. The thinner strips  110 ,  130 ,  131  and  132  will deform to follow circular arcuate paths during shape setting.  
      Tube  150  may have a length sufficient to have its proximal end (not shown) extend out of the patient&#39;s body where the surgeon can manipulate it. Tube  150  can also be shorter and attached to a separate guide wire to save costs or to reduce the diameter over the majority of the length.  
      The geometry of the strips and struts is chosen so that deformation upon shape setting and during expansion/contraction stays below acceptable limits. If necessary the cutting pattern of the strips can include some solid hinges. These are preferential bending spots, created by locally reduced thickness of the material. In this way it is also possible to cause a proper folding up of the strips while the filter is forced back into the cylindrical shape after conical shape setting.  
      In  FIG. 12  the filter at the distal end of tube  150  is shown in its folded, or radially compressed, state, as it would appear when installed in sheath  1  of  FIG. 1 .  FIGS. 13 and 14  show the final shape of the filter after shape setting and then after deployment from sheath  1 . Distal strips  110  create a non-traumatic rim with a smooth series of tangential connections between the struts  120 . The series of strips  130 ,  131  and  132  connect the long struts  120 ,  140 ,  141 , and  142  together at different intermediate positions, but in principle intermediate strips  130 ,  131  and  132  could be omitted, at least if there are a sufficient number of longitudinal struts  120 ,  140 - 142  to create the desired fine mesh. However, the feasible number of struts is limited by the following parameters:  
      The initial tube diameter;  
      The minimum width of each slot, determined by the tooling;  
      The minimum required width for a stable strut; and  
      The desired expansion ratio determined by the acceptable length of each strut.  
      If the filter pores, constituted by the slots, are not fine enough, because the open area between the struts of an expanded filter becomes too large, additional circumferential groups of strips can be provided to make the mesh finer. The number of strips can be chosen freely, because they do not have an influence on the expansion ratio. For clarity only four rows of strips are shown in  FIGS. 12-14 . As can be seen, the length of the strips changes from proximal to distal. For example, strips  130  are longer than strips  131  and  132 .  
       FIG. 14  shows a top view of the expanded filter where the strips  110  have been shape set to create a smooth rim that can perfectly cover the whole cross section of an artery with a good fit.  
      The conical filter shown in  FIGS. 12-14  is meant to be used in combination with a delivery sheath, as described herein with reference to  FIG. 1 . Such a sheath can run over the surface of tube  150  and if the sheath is retracted, the filter will assume the conical shape shown in  FIGS. 13 and 14 , which is substantially the same as the shaping pattern of  FIG. 1 . When such a delivery sheath, surrounding a collapsed filter, is brought into an artery and then gently withdrawn, the filter will open up, flare out and completely obstruct the cross section of the artery. Nitinol is an excellent material for such a filter, because it can withstand high elastic strains. A nitinol filter according to this design can be deployed and collapsed elastically several times without any plastic deformation, whereas known filter materials would fail.  
      In  FIG. 15 a  pair of filters  160  and  190  each having the form shown in  FIGS. 12-14  according to the invention are used in combination in order to entrap emboli particles between them for removal from the artery.  
      During the major part of an angioplasty/stenting procedure, only the most distal filter  160  is in place. During angioplasty/stenting of the artery  170 , emboli particles  180  may be released from the lesion site and move with the blood stream until they are stopped by filter  160 . At the end of the procedure, a second filter  190  is advanced over the wire or tube  200  that is connected to filter  160 . The diameters of the distal ends of filters  160  and  190  are about the same, and filter  190  can completely be advanced over filter  160 , when it is delivered from its own delivery sheath (not shown). Filter  190  has its own tube  210 , which has a much larger inner diameter than the outer diameter of wire or tube  200  of the first filter  160 . The lumen between both tubes  200  and  210  can be used for flushing/suction. Of course this can also be performed through tube  200  as well.  
       FIG. 16  shows the system of  FIG. 15 , with the thickness dimensions of the various components illustrated more clearly, at a point in a procedure just after the second filter  190  has been brought into a position to enclose the first filter  160 , with the distal ends of both filters in contact with one another. The opening angles of both filters may be identical or, as shown, different. In case they are identical, the surfaces of both filters will mate perfectly and all debris will be trapped, like in a sandwich, between the two conical surfaces.  
      However, if the cone of the second filter  190  has a smaller opening angle than filter  160 , as shown, the situation shown in  FIG. 16  will result. The distal edges of both filters fit well together, but for the rest there is a gap between the surfaces of the two filters. This gap creates a chamber  220 , in which small particles can freely move. The advantage of this arrangement is that the particles can be removed from chamber  220  by suction through the lumen  230  between tubes  200  and  210 .  
       FIG. 16  further shows an additional filter sheet  240  that is used to capture fine particles that go through the holes in filter  160 . The holes in the filter  160  can for example have a maximum size of 250 .mu.m, while filter sheet  240  can be provided with holes, or pores, having a size of the order of only 150 .mu.m or less, dependant on the application.  
      Filter sheet  240  may be made of a fine metal sheet, a polymer, or any other flexible tissue and it can be attached to the distal strips  110  of filter  160  by means of glue, stitching or any other means. At its proximal extremity, corresponding to its center, sheet  240  may a central connection point  250  that is connected to a long wire  260  that runs completely through tube  200  to a location outside of the patient&#39;s body. With this wire  260 , filter sheet  240  can be pulled into a conical configuration before filter  160  is pulled into its delivery sheath (not shown). This makes it easier to bring filter  160  and filter  240  into a smooth collapsed state. Once filter  160  is deployed, or expanded, wire  260  may be released a little bit to enable filter sheet  240  to move away from filter  160 , thus creating additional space for entrapment of the small particles  181  that fit through the holes in filter  160 . The larger particles  182  will not go through filter  160  and will stay at the proximal side of this filter. If chamber  220  between the conical surfaces of filters  160  and  190  is large enough, and if wire  260  of filter sheet  240  is not pulled too tight, most particles can easily be suctioned out through lumen  230 . By pulling wire  260 , the particles  181  will be forced to move in the direction of the suction opening. This is another advantage of the use of a movable filter sheet  240 .  
      Finally only some very large particles will remain in chamber  220 , and they can be removed by holding them entrapped between the surfaces of the filters, while both filters are pulled back into the delivery sheath and the filters are compressed, or collapsed to their cylindrical configurations. This is done while continuous suction is applied.  
      In case the large particles are squeezed, break up and slide through the holes in filter  160 , they will again be gathered in filter sheet  240 . Eventually wire  260  can be released even more if there is a lot of material between filter  160  and filter sheet  240 . In that case, filter sheet  240  may look like a bag, filled with material, that hangs on the distal side of the completely collapsed filter  160 . This bag may not be pulled back into the delivery sheath, but will just be pulled out of the artery while it hangs at the distal tip of the sheath.  
      A major advantage of this double filter design is that upon compression of the filter cones, the emboli particles can only leave the chamber  220  through the suction lumen  230 , or they stay there to be finally entrapped mechanically between the cone surfaces or to remain in the bag.  
      The distal filter will be in place during the whole procedure of angioplasty/stenting and therefore the mesh size is very important. An additional pressure-measuring tip, distally in the blood stream may monitor perfusion. The wire that holds this tip may be integrated with wire  260  that is controlling the filter sheet  240 . Alternatively, wire  260  can have the form of guide wire  2  shown in  FIG. 1 , with a lumen connected to a pressure detector.  
      On the other hand, filter  190  is only used a very short time and therefore its mesh size may even be finer than that of filter  160 .  
      As explained above, the number of longitudinal struts is limited on the basis of the desired expansion ratio. The distance between two circumferential strips can be made rather small, but they must still be able to be bent in order to get a collapsable and expandable device. Therefore a certain gap must remain between them. Normally such a gap would be larger that 50 .mu.m, so an additional filter mesh is required in case the allowed particle size is 50 .mu.m, such as for use as a filter in a carotid artery.  
      In general, filter systems according to the invention can have many embodiments, including systems containing a distal filter with or without an additional filter mesh with a proximal filter, also with or without an additional filter sheet. Also the relative position of filter and filter sheet can be varied. The sheet can be outside of filter  160 . Further embodiments can be combinations of emboli catching devices of different geometries and/or types. Filters, balloons and sponges of all kinds can be used in multiple combinations, all based upon the principle of full entrapment of particles before the protection device is collapsed upon removal from the patient&#39;s body. Combinations of an inflatable delivery sheath according to the invention with a multi-filter arrangement, as disclosed, are also meant to be an embodiment of this invention.  
       FIGS. 17-27  illustrate the structure and successive phases in the use of another embodiment of the invention that is suitable for performing angioplasty procedures while trapping and removing debris produced by the procedures.  
       FIG. 17  shows an artery  302  with an obstruction, or lesion site,  304  that reduces the effective diameter of artery  302 . The invention can be used to treat virtually any artery throughout the body, such as for example the inner carotid artery where emboli are extremely dangerous because the particles can cause stroke in the brain.  
      A first component of this embodiment is a guide wire  306  that, in a first step of a procedure using this embodiment, is advanced through artery  302 , normally in the direction of blood flow, and past lesion site  304 . The blood pressure in artery  302  adjacent the distal end of guide wire  306  can be monitored by a pressure monitoring device that includes a miniature pressure sensor, or transducer,  310  at the distal end of guide wire  306  and a signal measuring unit at the proximal end, as represented by element  5  in  FIG. 1 . Guide wire  306  can be provided with a longitudinal lumen that can contain wires or an optical fiber to transmit electrical or optical signals from sensor  310  to the signal measuring unit and the signal measuring unit can be connected to a conventional indicator, display and/or warning device. Sensor  310  may be, for example, a distal miniature load cell, possibly of the type having a load-dependent electrical resistance. The pressure monitoring device can continuously monitor the blood pressure in artery  302  during an entire procedure.  
       FIG. 18  shows the second step in which a guiding catheter, or sheath,  312  having a longitudinal lumen carrying a distal protection means  314  is advanced over guide wire  306  until means  314  reaches a location that is distal, or downstream, of lesion site  304 . If distal protection means  314  is a filter made from a small slotted nitinol tube, it can be advanced over guide wire  306  while being retained in the lumen that extends through catheter  312 .  
      Distal protection means  314  may be a filter, as described earlier herein, or a blocking balloon, or possibly a compressible sponge element. For example, means  314  may be an expandable filter cone, or umbrella, having the form disclosed, and deployed and retracted in the manner disclosed, earlier herein with reference to  FIGS. 1-14 , and particularly  FIGS. 12-14 , held in its collapsed state within catheter  312 . If distal protection means is a balloon, it will be connected to an inflation lumen formed in or carried by catheter  312 .  
      In the next step, depicted in  FIG. 19 , the distal protection means  314  is deployed until it extends completely across the blood flow path defined by artery  302  in order to catch all emboli particles that may be released from the lesion site upon the following steps of the procedure. Protection means  314  will stay in place until the end of the procedure.  
       FIG. 20  shows the following step in which a predilatation catheter  320  is introduced over guiding catheter  312 . Predilatation catheter  320  carries, at its distal end, a predilatation balloon  322 . Predilatation catheter  320  can be advanced over guiding catheter  312  and has several purposes. First, its predilatation balloon  322  can be used to enlarge the inner diameter of lesion  304  in order to create sufficient space for positioning a post-dilatation device  326  in the form of a sheath carrying an inflatable balloon section  328 . Section  328  may, if desired, carry a stent  332  that is initially in a radially contracted, or collapsed, state. Furthermore the distal tip of the catheter  320  with balloon  322  can act as an internal support for the post-dilatation balloon  328 . The inner wall of device  326  constitutes a delivery sheath within which self-expanding stent  332  is retained prior to deployment and out of which stent  332  can by pushed by some conventional delivery means (not shown). Such a delivery means for self-expanding stents can be of any kind, for example a pusher-wire that pushes against the proximal side of the stent to push it out of the sheath.  
       FIG. 21  shows the subsequent step in which predilatation balloon  322  has been deflated and advanced in the distal, or downstream, direction. Self-expanding stent  332  has been pushed out of delivery sheath  326 . Normally, a delivery sheath only serves to bring a stent in its compressed state to the lesion site and to hold it compressed until it is to be deployed. This sheath generally has a cylindrical shape and upon delivery of the stent the sheath is pulled back, while the self-expanding stent leaves the distal tip of the delivery sheath. The sheath is then removed from the patient&#39;s body. The stent may have enough radial expansion force to fully open at the lesion site, but often this force is insufficient and the stent will stay in some intermediate semi-deployed position. A self-expanding stent can be made of several types of material, for example nitinol. Nitinol is a material with mechanical hysteresis and the force needed to collapse the stent is much higher than the radial force that the stent exerts upon deployment. This means that a nitinol self-expanding stent may be strong enough to hold an artery open, but it may need some help to reach full deployment. This help can come from post-dilatation balloon  328 .  
       FIG. 22  shows the next step in which sheath  326  is used to help deploy stent  332 . The distal end of sheath  326  with balloon section  328  can be inflated through a lumen (not shown) in the sheath wall. First the delivery sheath  326  is advanced again and the balloon area  328  is lined up with stent  332  in lesion site  304 . Inflation of balloon section  328  will now cause further expansion of stent  332 . However, the inner wall of sheath  326  that held stent  332  before delivery may collapse under the high pressure that may be needed to fully deploy stent  332 . Therefore, predilatation balloon  322  can be inflated to be used to create a stiffer inner support for sheath  326 . By lining up of both balloon sections, as shown in  FIG. 23 , a concentric double balloon segment is created, which is strong enough for post-dilatation.  
       FIG. 24  show the next step in which stent  332  is fully deployed by the combined forces of balloon  322  and post-dilatation balloon section  328 , despite the opposing forces of the artery wall at lesion site  304  that now has become a larger opening. If distal protection means  314  is a balloon and if balloon section  328  causes full proximal occlusion, a closed chamber  336  is created in artery  302  between balloon  314  and balloon section  328 .  
       FIGS. 25 and 26  show the next step in which predilatation catheter  320  has been removed, leaving inflated balloon section  328  around delivery sheath  326  in place. Although the internal support for sheath  326  has been removed, inflated balloon section  328  can easily be used for proximal occlusion means, because the pressure may be much lower than for post-dilatation of the lesion and stent deployment. Sheath  326  that held stent  332  before can now be used as a working channel, e.g. for flushing and suction. This working channel is in open connection with devices outside of the patient&#39;s body and can be used for a series of procedures in the closed chamber  336  between balloon  314  and balloon section  328 . One advantage of this closed chamber is that it can be flushed with a clear solution having a composition that can dissolve the plaque without danger for downstream body parts. Such compositions are known in the art. After flushing with a clear fluid the artery wall in the chamber region can be inspected with an endoscope or an optical fiber. This enables visual inspection under clear sight in a closed compartment of the artery including inspection of the stent surface. As long as the pressure behind the distal occlusion device is monitored, it is a safe way to work.  
      If desired, the inflatable delivery sheath/suction tube  326  can be deflated, pulled back until it is proximal of the stent section and then be re-inflated to enable additional flushing, suction and inspection, while the distal occlusion device  314  is still in place.  
      For supply of flushing fluid, a separate lumen can be made in the wall of delivery sheath  326 , running to the distal end of this sheath (not shown). Other procedures in a temporary closed chamber of an artery include ultrasonic treatment, radiation therapy and drugs delivery, among others.  
       FIG. 27  shows a final step in which post-dilatation balloon section  328  has been deflated and distal protection means  314  has been collapsed. The final step can be the removal of all devices from the patient&#39;s body, except, of course, stent  332 , which can stay there.  
       FIGS. 28-40   c  show the present invention embodied as filters that can serve as distal or proximal filters in the two-filter systems shown in  FIGS. 1-27 , where  FIGS. 28-31  particularly show a manufacturing technique that can also be used in the manufacture of the filters, as well as non-filter devices. By the present invention, filters with improved flexibility and smaller profile are described. Such a filter includes a proximal frame for expansion and contraction and a thin filter bag attached to the frame. The filter is a composite of two basic materials. In the present context, a “composite” structure is distinguished from other reinforced devices where discrete structural members are connected to or supportive of relative non-structural members without substantial integration of the two. By contrast, a composite structure includes at least a relatively non-loadbearing matrix member that surrounds (or embeds) a loadbearing reinforcement member such that the two are integrally formed to define a unitary member. With this understanding, a substantially monolithic membrane (made form, for example, a polymeric or related plastics material) merely attached to an underlying or overlying structural cage or basket (made from, for example, a metal or plastic material) is more akin to a “body-on-frame” structure rather than a “composite” structure. In the present invention, the first (matrix) material makes up the highly flexible filter membrane, where a pattern of holes in the membrane allows the flow of blood particles below a well defined size. The second (reinforcement) material is one or more fibers that possess high axial strength, but are thin enough to be flexible upon bending. The reinforcement is integrated with the membrane to create a composite structure with very flexible membrane areas where the blood is filtered, and extremely strong reinforcement fibers that take up excessive forces. The strength of the fibers prevents the membrane from tearing even in response to pulling or related moving forces, while their flexibility allows hinging at the points of attachment to the proximal frame and/or to an elongated member used for transporting the membrane to or from the location within the patient&#39;s body where the membrane is needed. The elongated member can be one of numerous conventional devices, including (but not limited to) a guide wire, a hollow tube, a tool for holding the aforementioned proximal frame, or a balloonable stent.  
      All of the fibers disclosed herein can be made from a variety of materials, including (but not limited to) Dyneema®, an extremely strong polyethylene manufactured by DSM High Performance Fibers, a subsidiary of DSM N.V. The fibers can also be combined with fibers or wires of other materials, such as Nitinol (a version of shape memory nickel-titanium alloy), to help control the expanded shape of the filter. Other viable materials for use as reinforcement fibers include those known in the fiber art, such as carbon, glass, ceramic, metals and metal alloys (including the aforementioned Nitinol), polymers (including ultra high molecular weight highly oriented polymers) or combinations thereof. Moreover, the reinforcement fibers can be made of a monofilament or multi-filament, and can be configured to have all kinds of cross sections and orientations. The fibers can be made of round, flat or different shaped monofilaments or multi-filaments. Preferably, the material making up the fibers has a modulus of elasticity that is higher than that of the surrounding membrane.  
      As part of a composite structure, the reinforcement fibers are integrated (embedded) into the membrane. The fibers can also be attached to the frame by any known technique, including the use of dipping, spraying, welding, glue, stitching, sewing, pressing, heat, light and knotting. Moreover, the fibers can be distributed over the membrane surface in a specific designed pattern or in a random pattern. In addition, the reinforcement fibers can be either continuous or discontinuous. With continuous reinforcement, the fibers are made up of one or more long strands that span the substantial entirety of the component they are reinforcing, forming a substantially rigid backbone-like structure. With discontinuous reinforcement, the fibers are shorter, typically made of numerous chopped, discrete strands that are interspersed throughout the component they are reinforcing. Even relatively short pieces of discontinuous fiber embedded into a membrane can reinforce such a membrane considerably. This is caused by the relatively short distance between adjacent fiber pieces, thus enabling distribution of applied forces to neighbor fibers. Forces can be taken up by fibers with different orientations and such fibers can either be embedded in a specific pattern or randomly distributed pattern. Combinations of long fibers and short fibers are also possible. The long fibers can for example be used for attachment to the frame and the short fibers may be used to improve the characteristics of the membrane itself Continuous reinforcement generally provides higher loadbearing capabilities and crack formation and propagation resistance, while discontinuous reinforcement generally facilitates lower cost and more complex finished composite structures. As such, the orientation and number of the reinforcement fibers is not limited and can vary with the desired application. In order to achieve a better connection between the reinforcement fibers and the membrane material, the fibers may first be coated with a material that adheres well to the membrane material, for example with the same material as the membrane.  
      The reinforcement fibers not only improve the strength of a membrane, but also can prevent stress degradation and improve the fatigue properties of heavily-loaded membranes (such as those employed in a heart valve). In addition, pulling fibers can also be used for enabling the removal of a medical device by pulling the device into a removal sheath, as will be discussed in more detail below. In this latter configuration, the pulling fibers may be embodied by either a single pulling fiber or multiple fibers. In addition, the pulling fibers can be made from the same material as the reinforcement fibers. In either case, the fiber(s) may be actuated directly by the operator, or indirectly by the guide wire through a stop as described below and in conjunction with the filter design. In addition, the fibers can be used to control the final geometry, prevent crack propagation, act as hinges at the place of attachment to the frame and prevent loss of the membrane or parts of it. Because the reinforcement enables the membrane to be made much thinner than known membranes, the crossing profile of the composite filter can be much lower than for a single polymer membrane, even if the reinforcement fibers are thicker than the membrane itself.  
      Referring next to  FIGS. 28 through 31 , a method for making a reinforced filter is carried out by first providing a paraffin mold  401  having the desired shape of the expanded, or deployed, filter bag. Paraffin is chosen because it can be removed from the filter easily at a temperature that does not cause degradation of the finished filter. In addition, with the use of a paraffin mold  401 , it is possible to make complicated or simple designs, because there is no need to remove a relatively large mandrel from the finished product after it has been made. Paraffin is of course not the only material that can be used for mold  401 ; any material that can be brought into the desired shape and can be dipped directly or after application to an intermediate layer may be used. Examples are meltable materials or materials that easily dissolve in water, including salt or sugar crystals. Other examples are fine grains in a vacuum bag or an inflated balloon which is deflated after dipping. It is also possible, for certain filter embodiments, to use a mold that can be safely removed without being melted, dissolved, or deformed. To improve the quality of the dipping process between paraffin and certain polymer (such as polyurethane), the paraffin mold  401  is first covered with a thin sheet  402  of polyvinyl alcohol (PVA). The PVA  402  is a thin sheet that can be stretched after wetting with water and pulled tight around the mold  401  and then tied together with a small clip or wire  403 . The resulting mold  401  is dipped a few times in a solution of polyurethane in tetrahydrofuran, thus building a skin (or layer) of polyurethane. By way of example, this skin can be approximately 3 microns thick. After this, mold  401  (covered with the polymer skin) is dipped in a solution of polymer and solvent until a membrane  410  is created. Referring next to  FIG. 29 , a frame  450  is then placed around the mold  401 , and reinforcement fibers  420  (which may be coated) are then mounted to the frame  450  at hinge sites  459  and laid over the surface of the mold  401 . While discontinuous fibers can be used to improve the structural properties of membrane  410 , it will be appreciated by those skilled in the art that the connection between membrane and the frame is enhanced when the hinge sites on the frame can be tied to reinforcement fibers in the composite structure. As such, a more secure connection is possible with continuous reinforcement fibers than with discontinuous fibers, as the continuous fibers can be looped around or otherwise tied to the frame&#39;s hinge sites. Additional dipping into the solution of polymer and solvent ensures full embedding of the fibers  420  into the growing polymer layer membrane  410  shown in  FIG. 30 . Finally, a perfusion hole pattern made up of holes  430  is laser drilled into the membrane  410 , as shown in  FIG. 31 . The size of the holes  430  are such that blood or related fluids can pass through, while inhibiting the passage of solid objects (such as a disdlodged emboli). Preferably, the size of the holes  430  is up approximately  100  microns in diameter, although it will be appreciated that other sizes, depending on the application, can also be employed. While the holes  430  in membrane  410  are distributed over the membrane surface in a specific designed pattern, it will be appreciated by those skilled in the art that the holes  430  could also be disposed in a random pattern, even if they cut through the reinforcement fibers  420 . After drilling of the holes  430 , the central paraffin mold  401  is removed by melting in warm water, which can be at a temperature of 50° C. The PVA  402  is easily released from the polyurethane membrane  410  and is removed. Once the membrane  410  is created, the polymer skin can be easily detached from the inside of the membrane  410  and pulled out. The surface of the membrane  410  may additionally be coated with another material, such as biocompatibility-enhancing materials or drug-release agents. While much of the discussion herein relates to a polymer-based membrane  410 , it will be appreciated that other materials could also be used to form membrane  410 , including organic tissue and tissue from human or animal origin, although the fabrication methods may be different than that depicted in  FIGS. 28-31 .  
      Referring again to  FIG. 29 , frame  450  is made of Nitinol (or similar shape memory alloy) tubing having an outer diameter of 0.8 mm by laser cutting and shape setting. At the proximal (left-hand) side, tube  455  is in its uncut state, and still 0.8 mm. in diameter. From there, tube  455  is cut to form eight longitudinal spokes  456  that end in a zigzag section with struts  457 , where the unconstrained, expanded material of frame  450  lies on a circle having an 8 mm diameter at its largest point. This frame  450  will, at any size between the maximum diameter and the collapsed size of 0.8 mm diameter, always adapt smoothly to the given geometry of the body lumen, such as an artery. Eight reinforcement fibers  420  are attached to the most distal section of frame  450  at hinge sites  429 . Fibers  420  can be attached to frame  450  by means of a knot or each fiber  420  can just be run back and forth from a distal location to hinge sites  429  and wrapped around frame  450  at that location. In the latter case, each fiber  420  will have twice the length shown. At the distal (right-hand) end of frame/filter assembly  470 , all fibers  420  converge in a guide tube  405 , where they are held in correct position for additional dipping operations.  
      Referring again to  FIGS. 30 and 31 , mold  401 , frame  450  and the surrounding fibers  420  are shown after having been dipped enough times to embed the fibers  420  into membrane  410 . By way of example, membrane  410  is 5 microns thick at places  411  where no reinforcement fibers  420  are present. Guide tube  405 , mold  401  and PVA  402  are removed after the dipping is finished and the membrane  410  has dried, as previously mentioned.  FIG. 31  shows the final filter  440 , with a pattern of laser drilled holes  430  between the reinforcement fibers  420 . Further, the fibers  420  are cut to the correct length at point  422  and attached to a central guide wire  460  via connector in the form of a nose tip  424 . The nose tip  424  can fit on top of a delivery catheter if the filter  440  is retracted into the catheter before placement into the body lumen of the patient. Note that the membrane  410  between the struts  457  at the distal end of frame  450  and the dipping line is removed, preferably by laser cutting. Filter mouth  445  is where the proximal end of filter  440  meets the distal end of frame  450 . The construction of the frame/filter assembly  470  is extremely strong and still very flexible. The 5 micron thick membrane  410  with the reinforcement fibers  420  fits easily in a delivery catheter of only 0.9 mm inner diameter and adapts to all sizes of arteries between 1 and 8 mm diameter.  
      The central guide wire  460  extends to the left from connector  424  through the membrane  410  and frame  450 , including the uncut part of tube  455 . Within connector  424 , fibers  420  are wrapped around, and secured to, guide wire  460 . To remove the filter  440  from a delivery catheter, guide wire  460  is pushed from its proximal (left-hand) end (not shown) so that a pulling force is exerted on fibers  420  due to their connection to guide wire  460  in connector  424 . Thus, all tension forces on the distal section of the filter  440  are taken up by the reinforcement fibers  420 . The membrane  410  only has to follow these fibers  420  and unfold as soon as it leaves the catheter. The filter  440  opens because of the elasticity inherent in frame  450 . In addition, the blood pressure in the artery further helps to open the filter  440  like a parachute. Upon bending of the filter  440 , there is almost no force needed at the hinge sites  459  where fibers  420  are attached to the struts  457 , so these sites (as their name implies) act as hinges. Even in highly curved arteries, the filter  440  and frame  450  still adapt well to the artery wall, resulting in almost no blood leakage between the membrane  410  and artery wall.  
      The fibers  420  are so well embedded in the membrane  410  that even if the membrane  410  were to detach from a strut  457 , the membrane  410  will still have a strong connection to the frame  450  and can be collapsed and removed from the patient safely. In case of a tear in the membrane  410 , for example starting from one of the holes  430 , the presence of the fibers  420  bridges the crack, thus stopping the tear. This crack-bridging occurs with both the shown continuous fibers, as well as with discontinuous fibers (not shown), as previously discussed. While any breach in membrane  410  is capable of liberating previously captured emboli to a downstream position in a body lumen, the composite nature of the present device not only keeps the size of the breach to a minimum (thereby minimizing such emboli liberation), but also reduces the likelihood of pieces of filter  440  breaking off and passing through the lumen.  
      After a medical procedure has been performed, the frame  450  can be collapsed to close the mouth  445  of filter  440 , and entrapping emboli and related debris therein, as the filter  440  takes on a bag-like appearance. The hinged nature of the filter/frame interface guarantees that the filled bag hangs at the distal end of the removal catheter and still can move easily through curved arteries.  
      As previously mentioned, the reinforcement fibers  420  can be used not only for their high tensile strength, but also can be combined with memory metal wires, or filaments. These can be, for example, Nitinol wires that can be shape set to almost any desired shape by heat treatment. Such wires may be embedded in or attached to the membrane  410  to guarantee a smooth folding/unfolding of the membrane  410 . An example is an embedded Nitinol wire that helps to give the mouth  445  of the filter  440  a smooth geometry that fits well to the artery wall. Such a Nitinol wire for shape control can be combined with a more flexible, but stronger, fiber, which is used to protect the membrane  410  of filter  440  against incidental overload, tear propagation or related problems that plagues non-reinforced membranes.  
      Referring next to  FIG. 32 , an alternate embodiment of the medical device of  FIG. 31  is shown, where a filter  540  is formed from a conical shaped membrane  510 . As with the embodiment depicted in  FIGS. 29-31 , the filter  540  is attached to frame  550 , although in the present case, the membrane  510  is not attached directly thereto. Instead, it is attached by a single reinforcement fiber  520  from the distal end of guide wire  560  until it reaches the struts  557  at hinge sites  559 , at which point it then wraps back to the distal tip of guide wire  560  with a reverse angle. Arrows in the drawing show how fiber  520  runs back and forth. By this method the use of knots at the fiber/frame interface is redundant and the safety is further increased, because the filter  540  can never detach from the frame  550 . As with the previous embodiment, membrane  510  can also be formed by dipping a suitably shaped mold (not shown) in a solution of polymer and solvent. Guide wire  560  is fastened to fiber  520  at least one point at the distal end of the filter  540  and extends therethrough to a proximal (left-hand) end thereof The pattern of crossing reinforcement fibers  520  gives the filter  540  different elastic properties, including improved axial elasticity. The pattern of holes  530 , preferably cut by laser, can be made in zones between the fibers  520  to avoid damage thereto. However, if the pattern of reinforcement fibers  520  is very fine, the holes  530  may be placed without regard to fiber  520  location, as there will still be enough reinforcement left even if some of fibers  520  are cut. The presence of adjacent crossings and parallel or angled uncut fibers  520  can take over some of the load-carrying capability, as can the embedding material of the membrane  510 . The conical shape of filter  540  is advantageous in that if it has a maximum expanded diameter of 8 mm, and is placed in an artery of 8 mm diameter, all holes  530  will be free from the artery wall and blood can flow through all holes  530 . As soon as debris, such as dislodged emboli, are entrapped, they will tend to collect at the most distal tip, leaving the more proximal holes open.  
      The area of the conical surface of filter  540  relates to the cross-sectional area of the artery as the length of the cone edge from base to tip relates to the radius of the artery. Preferably, the total surface area of the holes  530  should be at least equal to the cross-sectional area of the artery in order to guarantee an almost undistorted blood flow. This is the case if the ratio of the total surface area of the cone surface to the total hole surface area is smaller than the ratio of the cone surface area to the cross-sectional area of the artery, or, in other words, the total surface area of the holes  530  is at least equal to the cross-sectional area of the artery. For an artery having an inner diameter of 8 mm, a total number of 6400 holes  530  each with a 100 micron diameter is needed for the same surface area. While the type of flow through numerous small diameter holes is different from the undistorted flow through an open 8 mm artery, because the wall thickness of a reinforced membrane according to the invention can be extremely small, the length of a hole (for example only 5 microns, the thickness of the membrane) ensures a much better flow than a comparable-diameter hole in a thick membrane. The use of reinforcement fibers  520  makes it possible to reduce the thickness of membrane  510 , such that the flow resistance through the membrane wall decreases, allowing filter  540  to act as a semi-permeable membrane. A filter  540  made in conical shape will also have enough free holes  530  if used in arteries with smaller diameter. The holes  530  that touch the artery wall will not contribute to the flow, but the remaining holes  530  not in contact will have the same surface area as the actual cross section of the smaller artery.  
      Filters according to this invention are more flexible than existing filters so that they can be made longer without creating problems in highly curved body lumen. This increase in length promotes greater storage capacity for dislodged emboli. If the reinforced membrane  510  and frame  550  are mounted to each other without overlap, as in  FIG. 32 , the collapsed diameter can be made even smaller than with the embodiment shown in  FIG. 31 . Here, at a specific cross section of frame  550  near the hinge sites  559 , the frame  550 , membrane  510 , fibers  520  and central guide wire  560  cooperate to fit within the available cross section in the delivery sheath. The present construction of frame  550  has certain advantages. For example, production of frame  550  is very simple, guide wire  560  is kept in the center, and the filter  540  can be pulled out of the delivery sheath by pushing on guide wire  560  from the left to exert a pulling force on fiber  520  and membrane  510 .  
      During removal of the filter  540  from an artery, the longitudinal spokes  556  of frame  550  just have to pull the struts  557  of the zigzag section into a removal sheath. However, there may be circumstances (such as highly curved body lumen) where it is desirable to avoid having the guide wire  560  bend to the point where it interferes with or deforms the zigzag struts  557 . Similarly, there may be procedures (such as angioplasty/stenting) where axial movements of the guide wire  560  caused by the procedure can influence the position of the filter  540 . It would be better if the guide wire  560  could move freely over at least a certain axial length, as well as in radial and tangential directions, within the entire cross section of the filter  540 , without exerting any force on the expanded frame  550 .  
      Referring next to  FIGS. 33-36 , another alternate embodiment of the present invention with such a freely movable guide wire  660  is disclosed.  FIG. 33  shows a filter  640  in an expanded state such that it and frame  650  occupy a large profile. Filter  640  is constructed in such a way that it can be conveyed from a delivery sheath by pushing on guide wire  660  to exert a pulling force on filter  640 . After completion of use of the filter  640  in a medical procedure, it is removed by pulling it into a removal sheath with the aid of guide wire  660 . The pulling forces are applied in both directions by moving guide wire  660  in axial direction relative to the sheath. Guide wire  660  runs through the filter  640  and ends at guide wire distal section  662 . Fastened to guide wire  660  are stops  663  and  664  that have a larger diameter than the guide wire itself. These stops are connected tightly to the guide wire  660  by any known technique. At the distal tip of filter  640 , a ring  665  is fastened to the filter, while guide wire  660  can slide freely through ring  665  until stop  663  touches ring  665 . At the proximal side of stop  664 , a second ring  666  is mounted around guide wire  660  to allow it to slide freely therethrough. As such, both rings  665  and  666  are slide rings, and are given a smooth shape with rounded leading edges to let the guide wire  660  move easily in associated sheaths and in the artery. As can be seen in the figures, the slide rings  665 ,  666  can be connected to the filter  640  by reinforcement fibers  620 , pulling fibers  625 , membrane  610  or combinations of the above. It will be appreciated by those skilled in the art that the pulling fibers  625  may be made from the same or different amterial as the reinforcement fibers  620 , depending on the need. In the embodiment shown, pulling fibers  625  are generally configured to carry the pulling load in the proximal (leftward) direction, while reinforcement fibers  620  are generally configured to carry the pulling load in the distal (rightward) direction. In the strictest sense, while reinforcement fibers  620  also perform a pulling function (at least in the distal direction associated with insertion of the device into an appropriate body lumen), their nomenclature in this disclosure is retained to make it clear that they alone can perform the dual function of reinforcing the composite structure as well as bear a pulling load. As such, the distinction between the purely pulling capacity of pulling fibers  625  and the aforementioned dual function of reinforcement fibers  620  should be apparent from the context. Membrane  610  is connected directly to slide ring  665 , as are reinforcement fibers  620 . At the other side, reinforcement fibers  620  are connected to expandable frame  650  at hinge sites  659 , possibly together with the material of membrane  610 . Expandable frame  650  is provided with attachment points  658  at its proximal side, which are needed to pull the frame  650  back into a removal sheath  600 , shown in  FIG. 34 . Pulling fibers  625  (which, as previously discussed, may be made from the same or different material as reinforement fibers  620 ) are connected to the attachment points  658  of the proximal section of frame  650  and run to the proximal slide ring  666 , to which they are securely attached.  
      If the guide wire  660  is moved through the filter  640  in the proximal (leftward) direction, stop  664  will move freely over a distance X 1  before it touches slide ring  666 , after which fibers  625  become stretched. If the guide wire  660  is moved through the filter  640  in the distal (rightward) direction, stop  663  will move freely over a distance X 2  before it touches slide ring  665 , thereafter causing fibers  625  to hang free, as there is no axial force on slide ring  666 . This means that when the filter  640  has been placed in an artery, guide wire  660  can move freely in the cross-sectional area of the frame in both radial and tangential directions without exerting any forces on this frame. Further, the guide wire  660  can also move back and forth over a total distance X (where X=X 1 +X 2 ) in the longitudinal direction relative to the filter  640  before it influences the shape or axial position of the filter  640  in the artery. Distance X can be changed by choosing the distance between fixed stops  663  and  664 . If one of these stops is removed, distance X is maximized. The distal end section  662  of guide wire  660  must be long enough to prevent slide ring  665  from extending past distal end section  662  and becoming disengaged. With the construction of slide rings  665  and  666  on guide wire  660 , the guide wire can be rotated around its length axis without influencing the position and shape of the filter  640  and its frame  650 .  
      Further, the high degree of flexibility inherent in this design allows the length of frame  650  to be shortened and thus it makes the filter  640  more flexible and more easily usable in curvaceous arteries and arteries with limited space. In a highly curved artery, guide wire  660  may even touch the inner wall of frame  650  without exerting relevant forces on the filter  640 . Even with a highly bent guide wire  660 , the filter  640  will still maintain its full contact with the artery wall and guarantee a safe functioning of the device for a wide range of artery diameters and geometries. As can be seen from a comparison of  FIG. 33  with  FIGS. 31 and 32 , the design of  FIG. 33  gives a much smaller proximal surface of frame  650 . In  FIGS. 29-32 , spokes  456  and the proximal side of tube  455  have a certain surface area that reduces blood flow. This surface area is significantly reduced in  FIG. 33 , because only a few thin fibers  625  are interposed in the blood flow. Another advantage is that debris in the blood will less likely adhere to the thin pulling fibers  625  than to the proximal side of tube  455  and spokes  456  of  FIGS. 29-32 . An additional treatment of pulling fibers  625  to reduce the tendency of blood cells to adhere thereto is could also be employed, and is a part of this invention as well. As previously mentioned, pulling fibers  625  may be made from the same or different material as reinforcement fibers  620 . An example of such a fiber (in addition to those previously mentioned) would be a composite fiber made of a Nitinol filament core surrounded by a multifilament ultra high molecular weight highly oriented polymer. The Nitinol can be used to give some shape control to the fiber, for example to prevent adjacent fibers from becoming entangled. The polymer multifilament, besides having high strength and low strain, can have for example anti-thrombogenic or related agents embedded therein.  
      In  FIG. 34 , the filter  640  of  FIG. 33  is shown in a compressed size profile, in which it is being delivered from a delivery sheath  600 . Sheath  600  has a wall  606  and a distal end  607 . At the proximal side of the guide wire  660 , a pushing force F is applied in the distal direction, while sheath  600  is either being pulled back in the proximal direction or held in place. Stop  663  on guide wire  660  is now in direct contact with slide ring  665 , and force F is transferred by this ring to the reinforcement fibers  620  of the filter membrane  610 . By the resulting pulling force in the membrane  610  and fibers  620 , the filter  640  is stretched. Consequently, the pulling force is transferred to the collapsed frame  650  via hinge sites  659 . The frame  650  and filter  640  will easily slide out of sheath  600  by this pulling force, followed by the presently unloaded pulling fibers  625  and slide ring  666 . As can be seen, the proximal section of frame  650 , to which the fibers  625  are attached, is slightly tapered (bent inwards) to create a conical proximal side of frame  650 . In another embodiment (not shown), the proximal section of frame  650  may be cylindrical, tapered in the reverse angle (i.e., bent outward) or have any other geometry that either makes retrieval easier or serves as an anchoring to hold the filter  640  and frame  650  in place in the artery.  
       FIG. 35  shows the filter  640  in a position to be retracted into a removal sheath  600 , the latter of which has a wall  606  and a distal end  607 . At distal end  607 , the removal sheath  600  may have a flared end section  607 A, as shown in  FIG. 35   a,  a chamfered wall  607 B, as shown in  FIG. 35   b,  or a combination thereof Distal end  607  must enable the retrieval of the filter  640  into the lumen of sheath  600  by a pulling force, which is applied to the proximal end of guide wire  660  while sheath  600  is being moved in the distal direction or is being held in place. The tapered proximal section of the frame  650  also assists its insertion into removal sheath  600 . The force F 1 , applied to guide wire  660 , is transferred by stop  664  to slide ring  666 , which distributes the force to fibers  625  that are now pulling on the proximal section attachment points  658  of the proximal section of frame  650 . The ends of fibers  625  can be attached by any technique that is available, for example by putting them through respective holes in hinge sites  659  of frame  650 , and securing them by a knot  685  on the inside frame surface. The holes in attachment points  658  can have several shapes, dependant on the method of attaching the fibers  625 . The hole may be circular, like shown, oval or the like. If making a knot in pulling fiber  625  is not favorable, the fiber may be formed as a continuous loop, running back and forth to the slide ring  666 . Attachment of such a continuous loop may even be easier if there are two slots, creating hooks on both sides of the strut end of frame  650 . An example is attachment by means of a snap fit lock in the strut end. The proximal section of frame  650  have been formed in such a way that tips defining the end at the attachment points  658  are slightly curved inside with a conical top angle that is larger than the top angle of the cone defined by the stretched fibers  625 , just before the proximal section enters into removal sheath  600 . This is done to prevent the attachment points  658  of the frame proximal section from becoming stuck at the distal end  607  of the removal sheath  600 .  
      With the tapered shape of frame  650 , the tension force in fibers  625  will easily make it possible to slide the removal sheath  600  over the frame  650  until it is completely covered by this sheath  600 . Membrane  610 , eventually filled with embolic debris, does not have to be pulled into sheath  600  completely; it can instead extend from the distal end  607  while the whole device is removed from the artery.  
       FIGS. 36   a  and  36   b  are side views of an alternative embodiment frame  750 , in its expanded and collapsed shapes, respectively. This embodiment is shorter than the embodiment of  FIGS. 33-35 , and, in particular, lacks the distal end portion of the embodiment of  FIGS. 33-35 . Instead, frame  750  is composed of struts  757  configured in a zigzag-pattern. Here again the proximal section has attachment points  758  that are curved inwardly with curved tips  756  and it has attachment holes  754  for the fibers (not presently shown). The fact that the frame  750  is not subjected to a pushing force during deployment from, or retraction into, a sheath enables a further downscaling of the frame struts  757  and thus a miniaturization of the delivery profile of the device. This is also enhanced by the fact that the guide wire (not presently shown) does not influence the shape and position of the filter upon angioplasty and stenting, so the frame  750  can now also be made lighter.  
      Referring next to  FIG. 37 , another embodiment of a medical device with filter  840  frame  850  is shown. Elongated attachment parts  855  are formed at the attachment points  858  of the frame proximal section in order to bring the holes  854  for the attachment of pulling fibers  825  farther away from the expandable and collapsible unit cells of the frame  850 . This increased length helps to achieve a smoother shape upon shape setting, so that struts  857  will have the desired curvature that is needed to slide easily into the removal sheath  800  (shown in  FIG. 38 ). Placement of the attachment holes  854  at the very proximal tip of the frame struts  857  will also help to allow the frame  850  to be pulled back into the removal sheath  800  without the risk of getting stuck at the sheath entrance. The elongated struts  857  forming frame  850  can be shape set into almost any desirable angle. A part of the struts  857  may be parallel with the length axis of the filter  840 , while another part or parts may be angled inside or outside, as needed for smooth removal of the device. Outside angled tips may even help to anchor the frame  850  in the blood vessel for more axial stability.  
      Referring next to  FIG. 38 , another feature of the present embodiment is shown. The design of a filter  840  according to the invention with flexible fibers  825  makes it possible to push sheath  800  over guide wire  860  until the distal end  802  of sheath  800  reaches deep into the filter  840 . In this situation, sheath  800  may also function as a tube, where its positioning inside or beyond the frame  850  opens the possibility of flushing and/or suction through it in order to move debris either deeper into the distal end of the filter  840  or to suction debris out of filter  840 . Flushing with certain liquids can also help to make the debris smaller. An additional treatment device can also be inserted through sheath  800  disposed inside the filter  840 . This additional treatment device can be any means for inspection, measuring or all kinds of treatments like breaking up of clots by mechanical means, laser, ultrasonics, or the like. Additional retrieval devices may be brought into the filter  840  through sheath  800 . The fibers  825  will easily move with distal end  802  of sheath  800  and, dependant on the length of fibers  825 , the most distal position of sheath  800  can be chosen.  
       FIG. 39  shows another embodiment for the shape of a filter  940 , with an additional reservoir  942  for storage of debris. Normally it can be expected that the major part of the debris will collect most distally, leaving the most proximal holes  930  open for blood flow. This can be improved by providing additional reservoir  942 , which is connected to the conical section  943  of filter  940  by a portion  944 . If the diameter of reservoir  942  is half the maximum diameter of the frame  950 , the surface area that remains free for blood flow between the wall of the full reservoir and the artery wall is still 75% of the maximum surface area of the artery. The capacity of reservoir  942  can be chosen so that the closure of filter holes  930  in section  943  by abundant debris is most unlikely. Additional flushing and/or suction similar to that of the embodiment shown in  FIG. 38  may also be undertaken. Continuous monitoring of the blood flow beyond the distal end of the filter  940  can be employed to provide information regarding removal of the filter  940 . The shape and diameter of reservoir  942  will be dependent on the expected diameter and geometry of the artery that will be treated. The shape of reservoir  942  can be determined by reinforcement fibers  920 . The membrane  910  may for example be elastic, while the fibers  920  can have a limited stretchability. Dependent on the pressure inside the reservoir  942 , the diameter of the membrane  910  can be made to vary until it reaches a certain predetermined value, when the embedded fibers  920  reach their strain limit. Such fibers  920  will have a more or less tangential orientation.  
      A filter according to the invention, particularly because of the flexibility of the fibers  920 , allows an element, such as tubular sheath  800  of  FIG. 38 , to penetrate into the region enclosed by the membrane  910  to apply suction to debris contained in the filter bag either continuously or intermittently. This is particularly applicable to the distal filter of a two filter assembly. The sheath  800  can be introduced over a guide wire  960  associated with the filter  940  and can enter the filter  940  with no risk of perforating it. The safety of applying suction to the interior of the filter  940  is ensured by the nature of the material used for the membrane  910  and reinforcement fibers  920 . Such suction allows the filter  940  to be maintained relatively free of debris and helps to achieve a relative stability in blood flow through the membrane  910 . In addition, the suction element enables the filter  940  to be kept in a relatively empty condition prior to its being closed and withdrawn and prior to the use of a distal retrieval filter.  
      The frames and composite structures as shown and described herein may be used not only in relation to filters, they can also be used in numerous other medical (as well as non-medical) devices. Examples include a removable temporary stent, dilator, reamer, occlusion device for main artery or side artery, graft housing, valve, delivery platform for drugs, radiation or gene therapy, or any other device that has to be placed and removed after some time. As will be appreciated by those skilled in the art, the application of the present invention (in all of the aforementioned configurations) is not restricted to arteries, but can be used for all body lumens or in other places in the body. In addition, it will be appreciated that in certain situations, more than a single frame may be used. Similarly, membranes according to the invention can be used with or without holes. Situations calling for a non-porous membrane could include skin for grafts, stents, parts of catheters, inflatable member, balloon pumps, replacement of body tissues (such as heart valve tissues), repair of body parts and functional parts (like artificial valves and membranes), or any other part where minimal thickness and/or high strength are required. Dependent on the application, the membrane is completely closed, semipermeable or provided with holes for filtering function or improvement of cell ingrowth. Holes in the membrane can further be used to store drugs, which are slowly released from the membrane. Further holes can be used for attachment to surrounding frames or tissues. The hole pattern can be applied before, during or after the procedure of embedding the fibers. A further example is a thin but strong membrane that is held in shape by a frame with a different shape as shown in  FIGS. 33-39 . A frame does not necessarily have to be deformed before insertion, although if such deformation is desirable, it may be brought into a more suitable shape for insertion. By way of example, it can be a cylindrical expandable type, including being self-expandable. However, it may also be folded or stretched upon insertion or made deformable elastically or plastically. An example of a plastically deformable device is a surgical clip for closure of a wound or other opening. A reinforced membrane according to an embodiment of the present invention may cover such a clip to make it more leak-resistant. As previously mentioned, delivery of devices according to the invention is not restricted to the use of a guide wire in combination with a restraining sheath. Included in the invention is also delivery by any elongated member, for example a tubular catheter or a balloon catheter, a surgical tool, instrument, or even by the surgeons hands. Some of the non-filter device configurations cited above are discussed in more detail below.  
      Compliant Balloon with Expansion Limit  
      Normally balloons for angioplasty and/or stenting are made of non-compliant material, because they can be inflated to high pressures without an undesirable amount of increase of the diameter. Once the inflated state is reached, the additional increase in diameter is limited. A disadvantage of the non-compliancy is that such a balloon has a folded surface after deflation. In order to minimize the diameter of such a deflated balloon the surface has to be folded very accurately; and still the profile may be rather large. Another disadvantage of the folds is that upon inflation the folded flaps will unfold in an unsymmetrical and uneven way, so the deployment of a stent mounted on such a balloon will not occur in a smooth way.  
      With a compliant balloon, which is able to maintain a circular cross-section during all its stages of inflation and deflation, the expansion of a stenosis and/or stent will be much smoother. Since compliancy means that increase in pressure results in a concomitant increase in balloon diameter, measures need to be taken to avoid overexpansion of the balloon. This can be achieved by surrounding the balloon with a non-compliant element to limit the extent of the diameter increase. Such a non-compliant element can be simply made by applying a fiber around the balloon after it has been inflated to its desirable maximum diameter. Such a fiber can for example be dipped in glue and than wrapped around the balloon surface to reinforce this balloon surface. Alternatively, the fiber pattern is first wrapped around the surface and than the balloon plus fibers are simultaneously dipped in a polymer solution that creates a layer on the balloon surface. The fibers do not necessarily have to be applied on an existing balloon surface. They can also directly be integrated with the balloon surface when this is produced.  
      Such a layer with embedded fibers should be extremely thin and flexible, in order to be sure that upon deflation the balloon can return to its previous small diameter and still maintain a circular cross section. Therefore the use of fibers with both high axial strength and high flexibility upon bending makes such a design work well. It will be appreciated by those skilled in the art that the orientation and distribution of the fiber pattern on the balloon should be chosen so that it will give enough support to the underlying compliant balloon layer, thereby avoiding unduly large stretching in any of radial, tangential or axial directions that is not directly covered by reinforcement fibers.  
      Balloon Pumps  
      The same compliant balloon principle as described above can be used for balloon pumps, where the compliant balloon has strain limiting fibers attached to or embedded in the surface of this balloon. Balloon pumps are used for cardiac assist, where a balloon is placed in the aorta to help improve the pumping capacity. With embedded fibers, the balloon can be given a gradient in diameter upon inflation, thus causing a kind of peristaltic movement.  
      Repair of Body Parts  
      Reinforced membranes can further be used to replace or repair natural membranes. Examples are closure of holes in a natural membrane, like a hole in the wall between heart chambers, or a hole in the diaphragm. Attachment of such a reinforced membrane to the surrounding natural tissue can be easier because stitching directly with or to the embedded fibers is more reliable than to an un-reinforced membrane, which tears out sooner. Dependent on the application the reinforced membrane may have a pattern of holes, like in the described filter, be semi-permeable or be not permeable at all.  
      Heart Valve  
      In heart valves made of unreinforced polymers, problems with fatigue can occur. Often degradation of the polymer under stress causes failure. By contrast, reinforcement by fibers, according to the invention, prevents degradation and thus improves component fatigue properties. For example, the reinforced membrane of the present invention can be used as an artificial heart valve with a polymer surface and reinforcement fibers embedded therein on specific places, like the stronger and thicker sections in a natural heart valve tissue, which attach the heart valve to the surrounding tissue. In this embodiment the fibers not only reinforce the artificial membrane, but they also enable a proper attachment to the valve housing and with a proper orientation they will control the shape of the membrane and limit its elasticity.  
      Stent Grafts  
      In stent grafts, a proper pattern of reinforcement fibers can take up all high mechanical forces and improve the fatigue properties, while the membrane itself can be very thin and only serves as a matrix for these fibers. The thickness of the membrane can be minimized, which improves the expansion ratio of the stent and minimizes the crossing profile. The surface of the reinforced membrane graft may be treated with a drug eluting layer, antithrombogenic agents or any other coating which improves the biocompatibility or functionality. Such a device may also be used as a delivery platform for radiation or gene therapy. An example of an embodiment of the invention is a reinforced graft membrane, which is attached to two or more expandable frame rings similar to those discussed in conjunction with  FIGS. 33-39 . Such rings can be connected directly to the reinforcement fibers and eventually they may be made removable by means of the pulling fibers as described for the filter.  
      Occlusion Grafts  
      A stent graft, reinforced with fibers, can be used to close an aneurysm or a side artery. Basically such an occlusion device can be made of two or more expandable rings and an elongated, substantially cylindrical reinforced membrane graft in between these rings. Closure of a side artery or aneurysm is achieved by positioning one ring proximally of the section to be closed and one ring distally, with the reinforced membrane in between. The reinforcement prevents rupture of the graft wall at the location of the aneurysm or side artery. Eventually an occlusion device can also close the main artery. In such a case a device can look like the described filter with a single expandable frame, but without holes in the membrane surface. The single frame ring, which is holding the graft in place, can be placed before the critical cross section, where the closure is needed. The occlusion grafts can of course be made removable in the same way as the filter, by using a removal sheath and pull fibers to retrieve the frame plus graft into the sheath.  
      Complicated Stents  
      According to the same principle as explained above for occlusion grafts, more complicated stents can be made, for example, abdominal aortic aneurysm (AAA) stents or extremely small stents, such as those used for neurological applications. Three or more expandable frame rings, attached to a web of reinforcement fibers, which are mounted on a mandrel or mold, can be easily embedded in a polymer membrane by dipping, spraying or any available technique. After removal of the mandrel or mold an extremely flexible, but strong graft stent with high expansion ratio is the result. Again, combination with pulling fibers for placement and/or removal is an option. The thin membrane allows miniaturization of medical devices for applications like in the brain, where very thin arteries need stenting, grafting or aneurysm closure.  
      Retrieval Bag for Manipulating Matter  
      In certain surgical procedures, a membrane bag can be used to remove cut-away tissue from a mammalian body. In such bags, referred to herein as retrieval bags, the entrance is closed before pulling the device out. Reinforcement of the bag&#39;s membrane by means of embedding fibers and improvement of the attachment of the membrane by mounting the fibers directly to the expandable wire frame can reduce the risk of bag tearing or eventual detachment of the bag from the frame.  
      Temporary Devices  
      As previously discussed, the present invention also includes the use of pulling fibers connected to an expandable frame. The embodiments depicted in  FIGS. 33-39  for the filter could also be used to allow ease of collapse of a temporary device. In  FIGS. 33-39 , the temporary device is always connected to the guide wire as long as the pulling fibers remain connected to the proximal slide ring. In certain circumstances, it may be necessary to disconnect the pulling wires from the frame or the guide wire. This may be the case if the decision is made that the device has to stay in the lumen for an extended period of time, or eventually becomes permanent. Examples of temporary devices which may or may not be released according to the invention include filters, occlusion devices, stents, valves, baskets, membrane-covered clips, reamers, dilators, delivery platforms for drugs, radiation treatment or the like.  
      Such a remotely controlled detachment from the guide wire can be done in several ways. One example is that the pulling fibers are disconnected from the slide ring. This can be done by remote changing of the shape of the slide ring, thus unclamping the pulling fibers from this slide ring. Another possibility is that each pulling fiber has an eyelet at the proximal end, and all these eyelets are connected with a single long fiber, which runs through these eyelets and of which at least one end can be held or released by the operator. If one free end of this long fiber is released, it will slide through all eyelets, thus disconnecting the strut fibers from the guide wire. In another embodiment the fibers can be disconnected by cutting, melting or breaking.  
      Referring next to  FIGS. 40   a  through  40   c,  a further possibility of detaching a device from a guide wire is shown, where the fibers remain connected to a ring, but the ring itself is detached from the guide wire. Referring with particularity to  FIG. 40   a,  a simple release mechanism is made from a deformable tube  1000 , where the tube  1000  fits in ring  1066 . Tube  1000  is mounted to guide wire  1060 . Distal end  1002  of tube  1000  is provided with two stops  1002 A and  1002 B, one configured to engage a proximal side of ring  1066 , and one to engage the ring&#39;s distal side. In this configuration, the stops  1002 A,  1002 B function as a lock for the distal end of tube  1000 . Ring  1066  is connected to expandable frame  1050  by means of struts or fibers  1020 . The distal end  1002  is provided with length slots  1002 C, which enable a local diameter change of tube  1000  at its distal end  1002 . The deformation of distal end  1002  can be elastic or plastic. In addition, distal end  1002  can for example be made from nitinol and be heat treated to have a reduced diameter in its unstrained state. The guide wire  1060 , if located in distal end  1002 , keeps it in a cylindrical shape, thus pushing stops  1002 A and  1002 B outward in such a way that axial movement of tube  1000  causes movement of ring  1066 . This is clearly shown in  FIG. 40   a,  where ring  1066  is firmly attached to distal end  1002  of tube  1000 . Referring with particularity to  FIG. 40   b,  removal of guide wire  1060  relative to tube  1000  allows tube  1000  to deform to a smaller diameter, until stops  1002 A,  1002 B bend enough inward to lose contact with ring  1066 . Referring with particularity to  FIG. 40   c,  guide wire  1060  and tube  1000  are completely detached from ring  1066  and thus from fibers  1020  and frame  1050  (the latter shown in  FIG. 40   a ). An alternative for the external stops  1002 A and  1002 B can be an elastic pin (not shown) which pushes through a side hole (not shown) in the tube  1000  at the location where ring  1066  is mounted. The elastic pin only grips ring  1066  as long as the pin is pushed outward by central wire  1060 . The remainder of the apparatus works the same as described above.  
      In the situation that a device has two slide rings mounted on the same guide wire, like the filter of  FIGS. 33-39 , the release mechanism of  FIGS. 40   a - 40   c  may first be used to place the device while the end of tube  1000  is in contact with the most distal ring. After releasing this distal ring, guide wire  1060  can be pushed into distal section  1002  of tube  1000  to ensure a good grip on the proximal ring while guide wire  1060  is pulled back. If release of the proximal ring is necessary, the procedure of pulling back of guide wire  1060  is repeated. In such an approach, several stages of gripping and release are possible with a single coupling tool and a series of sliding rings.  
      It will be appreciated by those skilled in the art having regard to this disclosure that other modifications of this invention beyond these embodiments specifically described herein may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.