Abstract:
Method and apparatus implementing and using techniques for controlling flow in a body lumen, including use of an implantable medical device. The device includes a membrane implantable in a body lumen and invertably deformable between a first position and a second position. The membrane is invertible in response to the direction of fluid flow through the lumen and can be deformable by fluid flow in the body lumen.

Description:
FIELD OF THE INVENTION 
     This invention relates to medical devices for use in a body lumen. 
     BACKGROUND 
     A venous valve functions to prevent retrograde flow of blood and allow only antegrade flow of blood to the heart. Referring to FIG. 1A, a healthy venous valve  12  is illustrated in a vessel  10 . The valve is bicuspid, with opposed cusps  14 . In the closed condition, the cusps  14  are drawn together to prevent retrograde flow (arrow  16 ) of blood. Referring to FIG. 1B, if the valve is incompetent, the cusps  14  do not seal properly and retrograde flow of blood occurs. Incompetence of a venous valve is thought to arise from at least the following two medical conditions: varicose veins and chronic venous insufficiency. 
     SUMMARY 
     This invention relates to medical devices for use with a body lumen. In one aspect, the invention features a medical device including a membrane implantable in a body lumen and invertably deformable between a first position and a second position. The membrane is invertible in response to the direction of fluid flow through the lumen and can be deformable by fluid flow in the body lumen. The membrane can be invertable relative to a radial direction of the body lumen. The membrane can be reversibly deformable between the first position and the second position. 
     Implementations can include one or more of the following. The membrane can define a portion of a cone, and can include an anchoring element adjacent a vertex of the cone. The membrane can include an anchoring element configured to embed within the body lumen, or alternatively configured to penetrate through the body lumen. The anchoring element may be, for example, a loop or a barb. The membrane can be formed of a polymer, for example, a polyurethane, polyethylene or fluoroplastic. 
     In another aspect, the invention features a medical system. The system includes multiple membranes, each membrane implantable in a body lumen and invertably deformable between a first position and a second position. Each membrane is invertible in response to the direction of fluid flow through the lumen. 
     Implementations of the system can include one or more of the following. The membranes can be symmetrically implantable in the body lumen. Each membrane can be invertable relative to a radial direction of the body lumen and can be deformable by fluid flow in the body lumen. At least one membrane can be reversibly deformable between the first position and the second position. At least one membrane can define a portion of a cone and can include an anchoring element adjacent a vertex of the cone. At least one membrane can include an anchoring element configured to embed within the body lumen or alternatively configured to penetrate through the body lumen. The anchoring element can be, for example, a loop or a barb. At least one membrane can be formed of a polymer, for example, a polyurethane, polyethylene or fluoroplastic. 
     In another aspect, the invention features a method. The method includes positioning at least one membrane in a body lumen, each membrane invertably deformable between a first position and a second position. Each membrane is invertible in response to the direction of fluid flow through the lumen. 
     Implementations of the method can include one or more of the following. The method can include positioning multiple membranes in the body lumen. The multiple membranes can be positioned symmetrically in the body lumen. The method can include penetrating an anchoring element of the at least one membrane through the body lumen or, alternatively, embedding an anchoring element of the at least one membrane into the body lumen. 
     In another aspect, the invention features a method of controlling flow in a body lumen. The method includes invertably deforming a membrane between a first position and a second position, the membrane being invertible in response to the direction of fluid flow through the lumen. Implementations can include one or more of the following. The membrane in the second position and a portion of the body lumen can define a cavity. Deformation of the membrane can be relative to a radial axis of the body lumen. The membrane can be deformable by fluid flow in the body lumen. The membrane in the first position and the membrane in the second position can be approximately mirror images of each other. The method can further include invertably deforming a plurality of membranes. 
     Embodiments may have one or more of the following advantages. One or more invertible membranes, which can function as artificial valve cusps, can be implanted at a treatment site using a catheter. As such, implantation is minimally invasive and avoids surgery and the possibility of the inherent complications. The membrane is fabricated from a polymer such as a polyurethane, polyethylene or fluoroplastic, which materials are more easily accessible than a natural tissue excised from an animal, and can be manufactured with consistency and efficiency that could be more difficult or more expensive using a natural tissue. 
     Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIGS. 1A and 1B are illustrations of a venous valve and an incompetent venous valve, respectively. 
     FIGS. 2A,  2 B, and  2 C are partial perspective views of an embodiment of a valve cusp. 
     FIG. 3 is a cross-sectional view of the valve cusp of FIG. 2A, taken along line  3 — 3 . 
     FIG. 4 is a cross-sectional view of the valve cusp of FIG. 2C, taken along line  4 — 4 . 
     FIGS. 5A,  5 B,  5 C,  5 D and  5 E are schematic views of an embodiment of a method for implanting a valve cusp. 
     FIGS. 6A and 6B are partial perspective views of an embodiment of a valve cusp. 
     FIGS. 7A and 7B are partial perspective views of an embodiment of a valve cusp. 
     FIG. 8 is a cross-sectional view of the valve cusp of FIG. 7A, taken along line  8 — 8 . 
     FIG. 9 is a cross-sectional view of the valve cusp of FIG. 7A, taken along line  9 — 9 . 
     FIG. 10 is a partial perspective view of an embodiment of an anchoring element. 
     FIG. 11 is a partial perspective view of an embodiment of an anchoring element. 
     FIG. 12 is a partial perspective view of an embodiment of a valve cusp. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 2A-2C through FIG. 4, a pair of artificial valve cusps  30  are illustrated positioned within a vessel  46 , e.g., a vein. Cusps  30  can be positioned upstream or downstream relative to an incompetent venous valve, such as the valve shown in FIG.  1 B. Each artificial valve cusp  30  includes at least one anchoring element  38  attached to an invertable portion  42 , here, an approximately triangular, flexible membrane. Anchoring element  38  is generally configured to hold invertable portion  39  at a desired location in vessel  46 . For example, anchoring element  38  can embed itself within a wall  44  of vessel  46 , or penetrate through the wall to secure cusp  30  to the vessel. Invertable portion  42  is capable of deforming between a first position and a second position, e.g., between an opened condition and a closed position, in response to flow of body fluid in vessel  46  to allow or to reduce the flow in the vessel. 
     Referring particularly to FIG.  2 A and FIG. 3, the cusps  30  are shown in a first position in which each cusp  30  forms an approximate semi-cone, such that an opening  50  is formed by the curved surfaces of the cusps  30 . The opening  50  allows antegrade flow of a fluid through the vessel in the direction indicated by arrow  48 . The membranes of invertable portions  42  are relatively thin and can conform closely to the vessel wall  44  to maximize the size of opening  50 . However, each cusp  30  is also held slightly away from the wall  44  of the vessel  46  by the anchoring element  38 , such that a gap  52  is formed between the invertable portion  42  and the wall  44 . 
     Referring particularly to FIG. 2B, retrograde flow of fluid (arrows  51 ) in the vessel can accumulate in the gap  52  and exert pressure on the invertable portion  42  of the cusp  30 . Since invertable portion  42  is flexible, it can deform under the exerted pressure and invert to form another approximate semi-cone, as shown in FIG.  2 C. That is, each cusp  30  forming a first semi-cone in the first position can invert or flip relative to a radial axis of vessel  46  to form a second semi-cone that is approximately the mirror image of the first semi-cone. As the interior  32  of the second semi-cone accumulates retrograde flowing fluid, pressure is exerted on the interior of cusp  30 , causing the cusp to move away from the wall  44  of the vessel. As a result, the space  53  between the two cusps  30  narrows, the size of opening  50  decreases, and fluid flow through the vessel and past the cusps is reduced (FIG.  4 ). 
     The cusps  30  can remain in the second position until antegrade fluid flow exerts sufficient pressure on the surface of cusps  30  opposite interior  32  and inverts the cusps to the first position. Thus, cusps  30  provide an artificial valve that automatically responds to the flow of fluid or pressure changes in vessel  46 . 
     FIGS. 5A to  5 E show one method of positioning cusps  30  at a treatment site in vessel  46  using a catheter  18  that may be delivered into the vessel  46  percutaneously. The catheter  18  is generally adapted for delivery through the vessel  46 , e.g., using a guidewire. Catheter  18  includes a long, flexible body having a central portion  21 , and a retractable sheath  22  over the central portion. Referring particularly to FIG. 5B, a cross-sectional view of FIG. 5A taken along line  5 — 5 , two grooves  25  are formed on either side of the central portion  21 , and a push rod  28  is positioned inside each of the grooves  25 . Each cusp  30  is positioned in a groove  25  in a compacted state and held in place by the retractable sheath  22  until delivery at the treatment site. 
     Catheter  18  can be delivered to the treatment site using endoprosthesis delivery techniques, e.g., by tracking an emplaced guidewire with central lumen  101 . At the treatment site, the retractable sheath  22  is retracted proximally to form an opening  26  at the end of each groove  25 . Referring particularly to FIG. 5C, push rods  28  are used to push each cusp  30  distally toward the opening  26  to push the anchoring element  38  out of the opening  26 . The cusps  30  are pushed out of the openings  26  until the anchoring elements  38  secure the cusps  30  to the wall  44  of the vessel  46 . For example, the anchoring elements  38  can embed within the wall  44  or penetrate the wall  44  and secure to the exterior of the vessel  46 . 
     After each cusp  30  is secured to the vessel  46 , the retractable sheath  22  is retracted to fully expose the cusps  30  (FIG.  5 D). The central portion  21  is then pulled proximally past the flexible (and deflectable) cusps  30  and retracted from the vessel  46  (FIG.  5 E). The cusps  30 , now secured to the wall  44 , can deform between the first and second positions, as described above. 
     Cusps  30  are preferably made of a biocompatible material capable of reversible deformation as described above. Each cusp  30  can be formed from a thin, flexible material, such as a polyurethane, polyethylene or fluoroplastic, for example, polytetrafluoroethylene (PTFE). Invertable portion  42  can be formed of one or more materials. For example, invertable portion  42  may include an edge portion that is relatively more flexible or more compliant than another portion of the invertable portion to help the edges meet and seal when the cusps  30  are in the second position. Cusps  30  can include a radiopaque material, such as a polymer including a radiopacifier, e.g., tantalum metal or bismuth oxychloride, for positioning and monitoring the cusps. 
     Similarly, anchoring element  38  is preferably biocompatible. The anchoring element  38  can be formed of a relatively rigid material, such as a polymer having suitable hardness, for example, acrylonitrile-butadiene-styrene (ABS). Other materials can be used, such as metals (e.g., tantalum, tungsten or gold), alloys (e.g., stainless steel or Nitinol), and ceramics. Anchoring elements  38  can include a radiopaque material for positioning and monitoring cusps  30 . The anchoring element can be embedded in the invertible portion or fixed to a surface of the invertible portion with, for example, adhesive. 
     Other Embodiments 
     In other embodiments, any number of cusps can be anchored to the wall  44  of the vessel  46  to function as a valve for preventing retrograde flow of blood through the blood vessel  46 . 
     Referring to FIGS. 6A and 6B, a single cusp  60  can be used. The cusp  60  can be transported to the treatment site and anchored to the wall  44  of a vessel  46  in the same manner as described above using a catheter. In a first position, the cusp  60  forms an approximate semi-cone, with the edges  63  of the semi-cone facing the wall  44  opposite from where the cusp  60  is anchored to the wall  44 . The interior of the cone forms a channel  64  allowing fluid flow past the cusp  60 . The anchoring element  65  holds the cusp  30  slightly away from the wall  44  such that a gap  66  is formed between the cusp  60  and the wall  44 . Retrograde flowing fluid can accumulate in the gap  66  and exert pressure on the cusp  60 , deforming the cusp  60  and widening the gap  66  until the pressure on the cusp  60  inverts the cusp. Referring particularly to FIG. 6B, in an inverted position the cusp  60  forms an approximate cone with the wall  44  and accumulates retrograde flowing fluid in a sack  68  formed by the interior of the cone. Accumulated fluid can exert pressure on the cusp  60 , causing the cusp  60  to move away from the wall  44 . As a result, the space  66  between the cusp  60  and the wall  44  opposite the anchoring element narrows, until the cusp  60  touches the wall  44 , in a second position as shown. In the second position, flow is reduced past the cusp  60  relative to the flow when the cusp  60  was in the first position. The cusp  60  remains in the second position until pressure exerted on the cusp  60  by the antegrade flow of fluid is sufficient to invert the cusp  60  to the first position. 
     Referring to FIGS. 7A-7B, three cusps  70   a - 70   c  can be symmetrically secured to the wall  44  of a vessel  46  in a similar manner as described above. Referring particularly to FIG. 7A, the cusps  70   a - 70   c  are shown in first position that does not substantially impede flow of a fluid through the vessel  46 . As shown in FIG. 8, the surfaces of the cusps  70   a - 70   c  conform to the wall  44  of the vessel  46 , allowing a substantial opening  72  for flow past the cusps  70   a - 70   c.  Each cusp  70   a - 70   c  is held away from the wall  44  by anchoring elements  71   a - 71   c , such that a gap  76  is formed between each cusp and the wall  44 . As described above, retrograde flowing fluid accumulates in the gap  76  and exerts pressure on the cusp  70 , causing the cusp to deform away from the wall  44 , until the cusps invert. 
     Referring particularly to FIG. 7B, in an inverted position the interior of each cusp  70   a - 70   c  accumulates retrograde flowing fluid. Exerting pressure on the cusps causes them to move toward one another, until the cusps  70   a - 70   c  meet in a second position and reduce flow past the cusps  70   a - 70   c  relative to the when the cusps  70   a - 70   c  are in the first position. Referring to FIG. 9, the opening  72  is significantly reduced, thus restricting the fluid flow. The cusps  70   a - 70   c  remain in the second position until pressure exerted on the cusps  70   a - 70   c  by antegrade flow of fluid inverts the cusps to the first position. 
     Although the embodiments above describe a device having one to three cusps, any number of cusps can be used to prevent retrograde flow through a vessel. FIG. 12 provides one example of four cusps, or membranes, used to prevent retrograde flow through a vessel. The cusps can be arranged symmetrically as shown, or can be arranged in any other configuration. Although the embodiments described above include cusps of similar size and configuration, cusps of differing sizes and configurations can be used in conjunction with each other. 
     The anchoring element can take a number of different forms that permit the end of the cusp to penetrate the wall of a blood vessel and restrain the end of the cusp from re-entering the vessel. For example, the anchoring element can be a barb element, as shown in the embodiments described above. Alternatively, the anchoring element can be a T-hook device  80  as shown in FIG. 10, wherein T-hook  80  penetrates the wall of a vessel and hooks  82  prevent the anchor from re-entering the vessel. In another embodiment, the anchoring element can define a loop  84 , as shown in FIG. 11, wherein the looped end  86  prevents the anchor from re-entering the vessel. 
     In other embodiments, a cusp can include more than one anchoring element. A cusp can have other polygonal configurations. For example, a generally rectangular cusp can be secured to a vessel using two anchoring elements adjacent to two corners of the cusp. The cusp can form a semi-cylinder. 
     Other embodiments are within the scope of the following claims.