Abstract:
A venous valve device provides antegrade blood flow in venous vessels of the body having dysfunctional valves; it is formed in situ from autologous vein conduit not having a valve present locally. An overlap region is formed by attaching two opposing walls of the vein together in a generally axial direction forming two tubular regions. One region provides antegrade blood flow and the other region provides a sinus cavity that is filled during the initiation of retrograde blood flow. A valve cusp is formed by attaching vessel wall together forming a commissure that extends between the two overlap regions. A single valve cusp moves toward the sinus cavity to allow antegrade blood flow and moves away from the sinus cavity to block retrograde blood flow. The venous valve can also be formed from biological tissue from an autologous, heterologous, or other tissue source and implanted interpositionally at the site of valvular incompetancy.

Description:
This is a continuation of U.S. application Ser. No. 09/814,265, filed Mar. 21, 2001 now U.S. Pat. No. 6,562,068, which is a continuation of U.S. application Ser. No. 09/328,835, filed Jun. 8, 1999 now U.S. Pat. No. 6,241,763. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a device and method for a vascular valve for the vascular system and more specifically for the venous vascular system of the human body and a method for forming the venous valve and more specifically for forming the venous valve from a native vein that may have been enlarged diametrically within the patient causing the naturally occurring venous valve to become incompetant. 
   2. Description of Prior Art 
   Venous valves are found within native venous vessels and are used to assist in returning blood back to the heart in an antegrade direction from all parts of the body. The venous system of the leg for example includes the deep venous system and the superficial venous system, both of which are provided with venous valves which are intended to direct blood toward the heart and prevent backflow or retrograde flow which can lead to blood pooling or stasis in the leg. Incompetent valves can also lead to reflux of blood from the deep venous system to the superficial venous system and the formation of vericose veins. Superficial veins which include the greater and lesser saphenous veins have perforating branches in the femoral and popliteal regions of the leg that direct blood flow toward the deep venous system and generally have a venous valve located near the junction with the deep system. Deep veins of the leg include the anterior and posterior tibial veins, popliteal veins, and femoral veins. Deep veins are surrounded in part by musculature tissue that assist in generating flow due to muscle contraction during normal walking or exercising. Veins in the lower leg have a static pressure while standing of approximately 80-90 mm Hg and this pressure can be reduced during exercise to 60-70 mm Hg. Despite exposure to such pressures, the valves of the leg are very flexible and can close with a pressure drop of less than one mm Hg. Due to the endothelial covering on the venous valves, they are able to remain patent and resist thrombosis with blood flow rates of less than 50 ml/min found typically in some of the smaller veins of the lower leg. Although the present invention has direct application to the treatment of venous valvular dysfunction of the leg, it is understood that the invention is not limited to this application and can be applied equally well to the treatment of veins throughout the human body as well as other tubular elements of the body requiring a valve. 
   Veins typically in the leg can become distended from prolonged exposure to excessive pressure and due to weaknesses found in the vessel wall causing the natural venous valves to become incompetent leading to retrograde blood flow in the veins. Such veins no longer function to help pump or direct the blood back to the heart during normal walking or use of the leg muscles. As a result, blood tends to pool in the lower leg and can lead to leg swelling and the formation of deep venous thrombosis and phlebitis. The formation of thrombus in the veins can further impair venous valvular function by causing valvular adherence to the venous wall with possible irreversible loss of venous function. Continued exposure of the venous system to blood pooling and swelling of the surrounding tissue can lead to post phlebitic syndrome with a propensity for open sores, infection, leading to possible limb amputation. 
   Repair and replacement of venous valves presents a formidable problem due to the low blood flow rate found in native veins, the very thin wall structure of the venous wall and the venous valve, and the ease and frequency of which venous blood flow can be impeded or totally blocked for a period of time. Surgical reconstruction techniques used to address venous valve incompetence involve venous valve bypass using a segment of vein with a competent valve, venous transposition to bypass venous blood flow through a neighboring competent valve, and valvuloplasty to repair the valve cusps. These surgical approaches are described in medical journals and in standard surgical text books. These surgical techniques are highly technique dependent and difficult to perform by a highly trained vascular surgeon. 
   The presence of a low or intermittent blood flow rates found in the veins of the lower leg requires that any suitable venous valve replacement contain an endothelial covering to protect the vessel against thrombosis. Blood stoppage for a period of time in contact with most foreign material can result in thrombus formation, and ensuing failure of any venous valve constructed of a polymeric material or some biomaterials. 
   Quijano describes in U.S. Pat. No. 5,500,014 the use of a biological valvular prosthesis that is obtained from the jugular vein of an animal. The valve is chemically fixed to give it strength. The fixing process tends to cause such valves to be stiff and calcification has been known to occur at flexation sites. Another problem with valves of this type is their lack of forming a stable endothelium with the resulting formation of thrombus when blood flow is impeded or temporarily blocked. Others have tried constructing venous valves out of a biological tissue material obtained from another species or the same species. Some tissues that have been used include pericardium and venous tissue treated with a crosslinking treatment. These devices have suffered problems associated with calcification, tissue degradation, tissue rejection, acute thrombosis, long term thrombosis, and valvular failure due to mechanical dysfunction. 
   Another vascular prosthesis that is constructed out of polymeric or metallic components is described by Camilli is U.S. Pat. No. 5,358,518. He describes a movable rigid or semi-rigid plate that pivots and allows unidirectional blood flow through the venous tube. The biomaterials used in the device of Camilli will not form a stable endothelium on the blood flow surface; due to the low blood flow and often times interrupted blood flow found within the venous system, this device will be prone to thrombosis and failure. 
   Laufer (U.S. Pat. No. 5,810,847) describes an appliance that is constructed out of a biomaterial that is attached to the cusps of an existing venous valve. Such a polymeric appliance will have a propensity to thrombosis in the low blood flow conditions found in the venous system. Also, many patients with venous problems do not have suitable valves onto which the appliance described by Laufer can be attached. 
   Lane describes in U.S. Pat. Nos. 5,147,389 and 4,904,254 and Shifrin describes in U.S. Pat. No. 5,476,471 devices that are intended to surround the outer surface of incompetent or insufficient venous valves. These devices are intended to reduce the diameter of the vessel in the region of the incompetent valve allowing the natural cusps to approximate each other leaving the valve commissures intact. For these devices to work properly, the valves of the vein must not be adherent to the vessel wall, this adherent condition is often found when the vessel is exposed to deep venous thrombosis. This significantly limits the patient population that can benefit from a device of this type. 
   A treatment for venous valvular dysfunction in patients that have had their vein wall distended and their valves irreversibly damaged is needed. The treatment should involve autologous tissue such that an endothelial layer is present in blood contact and thrombosis due to low flow is not of concern. The treatment should be easily performed so that patients with tissue edema and ulcers can tolerate the intervention and heal the area being accessed. The treatment should be applicable to those patients who have had deep venous thrombosis, phlebitis, or other vascular trauma and have irreversibly lost venous valvular function. 
   SUMMARY OF THE INVENTION 
   The present device and method for forming a venous valve overcomes the disadvantages of prior art prosthetic venous valves constructed out of crosslinked biological tissue, polymeric, or other biomaterials and it also overcomes problems associated with the surgical repair of venous valves. The venous valve of the present invention is constructed directly from the distended vein of a patient and it does not require the presence of an existing venous valve. Since the valve of the present invention is being constructed from autologous vein tissue with the natural endothelium of the vein in immediate contact with the blood, thrombosis such as that associated with biologic, polymeric, or other biomaterial constructed prosthesis is not a major concern. The venous valve of the present invention is configured from a segment of distended vein forming a new venous valve within the distended vein. Problems associated with irreversible valvular destruction or adhesion to the vessel wall due to deep venous thrombosis, phlebitis, or other vascular trauma will not influence the formation of the valve of the present invention within a distended vein. The method of forming the venous valve of the present invention is intended to be much simpler than venous valve bypass, valvular transposition, or valvuloplasty as performed by the peripheral vascular surgeon. The present method of forming the venous valve is intended to require only a minimally invasive surgery involving an easier and direct surgical procedure that can be applied to almost any distended vein. 
   The venous valve of the present invention involves identifying a segment of cylindrical tubular shaped distended vein and forming it into a venous conduit with a working valve in it. The venous valve has an overlap region that contains a through-flow member to allow antegrade blood flow through the venous valve and a sinus member which provides a cavity that is filled during the initiation of retrograde flow. A single valve cusp is located between the overlap through-flow member and the overlap sinus member. The valve cusp is capable of moving toward the sinus member to allow antegrade flow and moving to block the through-flow portion during the initiation of retrograde or back flow. The venous valve can also have an inlet transition region and it can have an outlet transition region. The transition regions are intended to provide a gradual tapering of the blood flow path from the distended vein to the smaller diameter of the overlap region. The blood flow surface of the through-flow and sinus portions of the overlap region, the transition regions, and the valve cusp are all endothelialized with the natural endothelium found in the native distended vein. 
   The structure of the venous valve is most easily and clearly described using cylindrical coordinates to describe the native distended vein and its relationship to various aspects of the venous valve that is formed from it. A cross section taken through the distended vein on the inlet side of the venous valve and facing downstream can be assigned a zero degree radian that intersects with the vein wall at a zero degree wall. Similarly one can identify a 90, 180, 270, or another degree wall along the vein wall at the inlet end of the overlap region. A zero degree line can be identified as that portion of the distended vein wall that extends axially and passes through the zero degree wall. The zero degree line describes venous wall material that may be sewn, sutured, stapled, bonded by adhesive, or attached in another way to another portion of venous wall material. The zero degree line can include the inner or outer surface of the vessel wall or it can include the entire vessel wall. Similarly, 90, 180, and 270 degree lines can also be identified. A first quadrant can be identified as the venous vessel wall that extends from the zero degree line to the 90 degree line. Similarly, a second, third, and fourth quadrant can also be identified. 
   For ease of describing the present invention, the vessel wall has been divided into quadrants, however it is understood that the vessel could be divided into a much greater number of sectors, each sector describing a smaller angle than 90 degrees and a smaller wall surface area than is occupied by a quadrant. Also, for ease of understanding, a wall line has been defined for the purposes of the drawings as extending approximately parallel to the centerline or axis of a tubular vessel. It is understood that for the venous valve of the present invention that a wall line is only required to have a component in the axial direction. 
   The venous valve of the present invention is intended to direct blood flow in a single antegrade direction from upstream to downstream, from its inlet to its outlet, toward the heart. The overlap region of this invention has an inlet and outlet end and an axial overlap length. In one embodiment of the present invention a segment of distended vein with an axial overlap length is identified. The zero degree line of the vein is brought into contact with the 180 degree line and the vein walls are attached using an attachment means which includes suturing or sewing, staples, adhesives or other bonding agents, thermal or other forms of welding, or other physical or chemical attachment mechanisms. It is understood that reference to the zero degree line, 180 degree line or other degree lines, points, or quadrants are approximate references and deviations from these lines, points, or quadrants are allowed within the framework of the present invention. For ease of understanding the invention is being described such that a wall line extending approximately parallel to the axis and extending throughout the overlap region is attached to another parallel wall line. It is understood that the wall lines need not be parallel to the axis and they need not extend throughout the overlap region to describe the present invention. To describe the present invention only a portion of such a wall line need be attached to a portion of another wall line. The 90 and 270 degree lines are brought into contact and the walls are attached using attachment means. At the inlet end of the overlap region, the first, second, and fourth quadrants are attached using attachment means. At the outlet end of the overlap region, the first and fourth quadrants are attached together. 
   The overlap region has a through-flow member defined by the third and fourth quadrant. At the outlet end of the overlap region is an opening between the first and second quadrant that provides entry into the sinus member of the overlap region. The first and fourth quadrant which are attached at the outlet end of the overlap region serve as the valve cusp. This attachment is not required to occur at the outlet end of the overlap region. It is understood that a portion of the first and fourth quadrants are attached together to form a member of the valve cusp. The cusp moves into approximation with the second quadrant during antegrade flow, and moves into approximation with the third quadrant during the initiation of retrograde or back flow allowing the sinus cavity or member to fill with blood. During antegrade blood flow through the venous valve, blood is directed through the through-flow member from the inlet to the outlet of the overlap region. This occurs for example in the legs during muscular contraction associated with walking or running or when the leg is in a reclined position and the pulsing of the heart moves the blood throughout the body including blood return from the legs. During the period of time that blood is not moving in an antegrade direction such as during standing or between periods of muscle contraction, blood is prevented from moving in a retrograde direction or from backflow or reflux by the venous valve. At the outlet end of the overlap region some backflow will go into the sinus member of the venous valve causing the sinus member to fill. This occurs as retrograde blood flow through the through-flow member generates fluid shear stresses upon the valve cusp causing it to move in the direction of flow. Due to geometrical constraints of the valve cusp with the inner and outer walls of the overlap region, the valve cusp also moves away from the second quadrant and allows blood to enter the sinus member of the overlap region. A small pressure difference between the blood at the inlet end of the sinus member and the outlet end of the sinus member which is dead ended and will not allow further retrograde blood flow, provides the driving force for blood entry into the sinus member. The valve cusp will move toward the third quadrant causing the through-flow member to close and stop further backflow or retrograde flow. 
   The four quadrants of the overlap region can be supported either within the walls or on the surface of the walls to resist possible stretching. A suture, thread, ribbon or other supportive means can be sewn, sutured, bonded, or placed along the third quadrant of the through-flow member at the inlet end to ensure that the entrance to the overlap region does not enlarge with continued exposure to pressure. Similarly, a supportive means can be attached to or placed along the second quadrant of the sinus member or the third quadrant of the through-flow member at the outlet end to ensure that further venous distension does not prevent the valve cusp from providing closure to the through-flow member. Additionally, further supportive means can be placed throughout any of the four quadrants to support both the through-flow member and sinus member. 
   The venous valve of the present invention can have an inlet transition region to connect the inlet end of the overlap region to the cylindrically shaped distended vein and an outlet transition region to connect the outlet end of the overlap region to the cylindrically shaped distended vein. These transition regions provide a tapered shape for blood to follow from the large distended vein to the smaller diameter for the through-flow member of the overlap region and back to the large diameter of the distended vein. Several possible ways of forming the transition regions are possible and are provided in the present invention in various embodiments to the invention. 
   The inlet transition region will be described at a location adjacent to the inlet end of the overlap region and at a location approximately half way between the inlet end of the overlap region and the cylindrically shaped native distended vein. Near the inlet end of the overlap region, the transition region has its zero degree wall in approximation to the 180 degree wall, and the 90 degree wall is in contact with and attached to the 270 degree wall. At the location halfway between the overlap region and the cylindrically shaped vein, approximately the 45 degree wall is attached to the 315 degree wall. This provides approximately a linear tapering of the diameter of the inlet transition region from the overlap region to the cylindrically shaped vein. It is understood that attachments can be made continuously along the transition region, not just at the two points that have been identified. Any excess material from the first and fourth quadrant that extends into the lumen of the transition region or extends out from the lumen of the transition region can be trimmed off or removed, provided that a leak tight attachment has been made along the transition region. The outlet transition region can be constructed in a manner similar to that of the inlet transition region. 
   An alternate method of constructing the inlet transition region again can be examined at two locations with interpolation or extrapolation of the results to other locations along the transition region. At the junction of the inlet transition region with the inlet end of the overlap region the zero degree point is in contact with and attached to the 180 degree point and the first quadrant can be attached to the second quadrant. At a location approximately half way between the inlet end of the overlap region and the cylindrically shaped distended vein, the 45 degree point is in contact with and attached to the 135 degree point. It is anticipated that a continuum of points are attached along the transition region such that a generally tapered shape for the transition region is formed from the overlap region to the cylindrically shaped vein. 
   In another embodiment for forming the overlap region, a segment of cylindrically shaped distended vein is placed into a flattened conformation and the first and fourth quadrants are attached together along the inlet end of the overlap region and cut at the inlet end of the overlap region through the first and fourth quadrant. Similarly, the distended vein is attached together along the outlet end of the overlap region and cut through the first and fourth quadrants of the outlet end of the overlap region. The zero degree line is placed into contact with and attached to the 180 degree line from the inlet end to the outlet end of the overlap region. This is accomplished by inverting the first and fourth quadrants into the second and third quadrants. This forms two separate tubes in the overlap region one for through flow of blood between the third and fourth quadrant and one to serve as the sinus member of the overlap region between the first and second quadrant. At the inlet end of the overlap region the first and second quadrants are attached together. This is necessary to prevent antegrade blood flow from entering into the sinus member of the overlap region. The 90 and 270 degree lines are attached together from the inlet end to the outlet end of the overlap region to hold the sinus member into immediate contact with the through-flow member of the overlap region. This provides a single lumen between the third and fourth quadrant for through flow through this member of the overlap region. At the outlet end of the overlap region is located the leading edge of the single valve cusp that is made up of the first and fourth quadrants of the overlap region. The valve cusp is completely endothelialized along with all blood contact surfaces of the venous valve. The inverted nature of the leading edge provides this embodiment with a particularly good resistance to thrombosis. The walls of the valve can be supported as described earlier with the other embodiments. 
   The inlet transition regions for the embodiment just discussed can be formed by attaching the first and fourth quadrants together on a line that extends from a point of attachment of the 90 and 270 degree walls at the inlet end of the overlap region along a beveled pathway to a zero degree wall on the cylindrically shaped distended vein. The beveled or tapered pathway provides a smooth blood flow transition from the distended vein to the overlap region. Any excess venous tissue that extends from the beveled attachment line to the zero degree line in the transition region can be trimmed off or removed. The outlet transition region can be similarly constructed. 
   It is noted that the construction of the venous valve of this invention requires some means for attachment between various quadrants of the venous wall. In forming the attachment of the zero degree line with the 180 degree line of the first embodiment, or attaching one quadrant to another along an inlet or outlet end of the overlap region, or for forming many other of the wall attachments or wall cuts, the distended vessel can be placed in a flattened position to allow the attachments to be made easier. The venous valve of this invention lends itself well to a mechanism that will assist the surgeon in making the attachments and cuts and allow the formation of this venous valve to be made quickly and consistently. 
   It is understood that the inlet and outlet transitions region embodiments can be interchanged with each other when possible. It is understood that other possible variations of the overlap region or transition regions may exist that are not shown by the drawings but are indeed taught by this patent application and should be considered as part of the teachings of this disclosure. The teachings of this patent application are not limited to the drawings and embodiments included herein. 
   It is further understood that the venous valve of the present invention can be constructed out of biological tissue such as venous tissue from animal sources, autologous tissue such as pericardium or venous tissue from another part of the body, or polymeric materials such as those used in vascular grafts. A venous valve of the present invention can be constructed as per the methods taught in the present disclosure and the resultant venous valve can be implanted interpositionally into a vein of a person at the venous site that requires a functioning venous valve. An embodiment such as this provides the advantage of simplicity of design and ease of formation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
       FIG. 1  is an isometric view of distended vein segment; 
       FIG. 2  is an isometric view of a first embodiment of the venous valve of this invention; 
       FIG. 3A  is an isometric view of an overlap region in an early stage of formation; 
       FIG. 3B  is an isometric view of an overlap region from an inlet end; 
       FIG. 3C  is an isometric view of an overlap region from an outlet end; 
       FIG. 4  is an isometric view of an overlap region with wall support; 
       FIG. 5A  is a partially sectioned view of the first embodiment of the venous valve of this invention in a flattened state; 
       FIG. 5B  is a sectional view of the inlet or outlet distended vein in a flattened state; 
       FIG. 5C  is a partially sectioned view of the first embodiment of the venous valve of this invention conformed for blood flow; 
       FIG. 5D  is a sectional view of the inlet or outlet distended vein conformed for blood flow; 
       FIG. 6A  is a sectional view of the inlet end of the overlap region in a flattened state; 
       FIG. 6B  is a sectional view of the inlet end of the overlap region during antegrade blood flow; 
       FIG. 7A  is a sectional view of the outlet end of the overlap region during venous valve formation; 
       FIG. 7B  is a sectional view of the outlet end of the overlap region during antegrade blood flow; 
       FIG. 7C  is a sectional view of the outlet end of the overlap region during retrograde blood flow; 
       FIG. 8A  is a sectional view of one inlet transition region embodiment near the overlap region during venous valve formation; 
       FIG. 8B  is a sectional view of one inlet transition region embodiment near the inlet distended vein during venous valve formation; 
       FIG. 8C  is a sectional view of one inlet transition region embodiment near the overlap region during antegrade blood flow; 
       FIG. 8D  is a sectional view of one inlet transition region embodiment near the inlet distended vein during antegrade blood flow; 
       FIG. 9A  is a sectional view of one outlet transition region embodiment near the overlap region during venous valve formation; 
       FIG. 9B  is a sectional view of one outlet transition region embodiment near the inlet distended vein during venous valve formation; 
       FIG. 9C  is a sectional view of one outlet transition region embodiment near the overlap region during antegrade blood flow; 
       FIG. 9D  is a sectional view of one outlet transition region embodiment near the inlet distended vein during antegrade blood flow; 
       FIG. 10A  is a sectional view of a second inlet transition region embodiment near the overlap region during venous valve formation; 
       FIG. 10B  is a sectional view of a second inlet transition region embodiment near the outlet distended vein during venous valve formation; 
       FIG. 10C  is a sectional view of a second inlet transition region embodiment near the overlap region during antegrade blood flow; 
       FIG. 10D  is a sectional view of a second inlet transition region embodiment near the outlet distended vein during antegrade blood flow; 
       FIG. 11A  is a partially sectioned view of an alternate embodiment of the venous valve of this invention in an early stage of formation with early attachment lines; 
       FIG. 11B  is a sectional view of the inlet end of the overlap region during an early stage or formation; 
       FIG. 11C  is a partially sectioned view of an alternate embodiment of the venous valve of this invention in an early stage of formation with overlap region and transition region cuts; 
       FIG. 11D  is a partially sectioned view of an alternate embodiment of the venous valve of this invention in an early stage of formation with an inverted fold; 
       FIG. 11E  is a partially sectioned view of an alternate embodiment of the venous valve of this invention; 
       FIG. 12  is a sectional view of an inlet end of an overlap region of an alternate embodiment of the venous valve of this invention with antegrade blood flow; 
       FIG. 13A  is a sectional view of an outlet end of an overlap region of an alternate embodiment of the venous valve of this invention with antegrade blood flow; 
       FIG. 13B  is a sectional view of an outlet end of an overlap region of an alternate embodiment of the venous valve of this invention with retrograde blood flow into an overlap sinus member; 
       FIG. 14A  is a sectional view of an alternate inlet transition region embodiment near the overlap region with antegrade blood flow; 
       FIG. 14B  is a sectional view of an alternate inlet transition region embodiment near the inlet distended vein with antegrade blood flow; 
       FIG. 15A  is a sectional view of an alternate outlet transition region embodiment near the overlap region with antegrade blood flow; 
       FIG. 15B  is a sectional view of an alternate outlet transition region embodiment near the outlet distended vein with antegrade blood flow; 
       FIG. 16  is an isometric view of an alternate embodiment of the venous valve of this invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the venous valve of the present invention is formed from an approximately cylindrically shaped segment of distended native vein and the formation occurs with the vein in place in its naturally occurring in situ position. Once the venous valve has been formed, it can be contiguous with or it can be attached to native vein tissue both upstream and downstream from the venous valve. The structure of the venous valve and the methods for its construction are most easily and accurately described by referring to a cylindrical coordinate system to describe various properties or characteristics of the native vein and apply these characteristics to the formation of the venous valve of the present invention. 
   A venous valve of an embodiment of the present invention could also be formed from a segment of vein or other tissue taken from any suitable location within the same patient that requires the venous valve. The segment of vein containing the valve formed by the methods of the present invention could then be transsected from its natural venous location or other location and interposed into the autologous vein that requires the venous valve. Autologous tissue such as pericardium or other tissue conduits could also be used to form the venous valve of the present invention. Pericardial tissue could be formed into an approximate cylindrical shape or tubular shape and formed into the vein of the present invention as described by the present disclosure. Such a formed venous valve would be implanted by standard interpositional surgical procedure into the vein of a patient requiring a venous valve by simply transsecting a portion of the patients vein and interposing a segment of tissue containing a valve formed by the present invention into its place using standard surgical technique or other less invasive technique. A venous valve of the one described in the present invention could also be formed out of biological tissue obtained from an animal venous conduit, a venous conduit from another human, other suitable conduit, pericardial tissue, or other suitable tissue. Such tissue could be treated using a crosslinking agent such as glutaraldehyde or other crosslinking or strengthening agent to enhance strength and reduce the antigenic character of the tissue. The biological tissue or tissue conduit could then be formed into a venous valve using the methods described in the present invention. The formed venous valve of the present invention could then be interposed into the vein of a patient requiring a venous valve. The venous valve of the present invention could also be formed out of polymeric or a composite material including polymers, metals, ceramics, or other biologically compatible materials. Such polymeric or composite materials could be formed into an approximately tubular shape and further formed into the venous valve of the present invention using the methods taught in this disclosure. Such tubular means from which the venous valve of the present invention can be constructed therefore include autologous vein, autologous tissue formed into a tubular shape of approximately round or other cross sectional shape, non-autologous biological conduit, non-autologous biological tissue, polymeric conduit, polymeric fabric, polymeric sheeting, or polymeric material formed into a conduit, or a composite material conduit. 
     FIG. 1  is an isometric view of a distended vein segment  5  or other tubular conduit that can be formed into the venous valve of this invention with an inner surface  10 , an outer surface  15 , a vein wall  20 , a wall area  21 , and a distended vein segment diameter  22 . The distended vein segment  5  can be formed into the venous valve of the present invention. The distended vein segment  5  can also be transsected and replaced by a venous valve of the present invention formed from another suitable biocompatibe material formed into a tube and being described by similar nomenclature. The distended vein segment  5  is shown extending from an inlet vein-transition junction  25  to the outlet vein-transition junction  30 . The distended vein segment  5  is a portion of the autologous vein that requires a venous valve. At or near the inlet vein-transition junction  25  is found a zero degree radian  35  extending from a centerline  40  through an inner surface zero degree point  45  to an outer surface zero degree point  50 . A cut-away view is shown in  FIG. 1  to provide an easier understanding of the structure of the vein or other tubular structure and to establish a terminology that will be used later to describe the present invention. An inner surface zero degree line  55  is a line that passes along the inner surface  10  of the vein and travels generally parallel to the centerline  40  in an axial direction passing through the inner surface zero degree point  45 . Similarly, an outer surface zero degree line  65  is a line generally parallel to the centerline  40  and passes along the outer surface  15  through the outer surface zero degree point  50 . The vein wall along the zero degree radian  35  extending from the inner surface zero degree point  45  to the outer surface zero degree point  50  is referred to as zero degree wall  70 . A zero degree wall line  75  is defined as the zero degree wall  70  that follows the wall of the vein along a line generally in a direction parallel to the centerline  40  and passing through the zero degree wall  70 . The zero degree wall  70  and zero degree wall line  75  are defined to allow an alternate description of attachment between two vein walls to be made. The zero degree wall line includes the inner  55  and outer  60  surface zero degree lines plus the wall in between. Attachment between a zero degree wall line  75  and a vein wall  20 , for example, is understood to mean that either the inner surface  10 , the outer surface  15 , or the venous tissues between the inner  10  and outer  15  surfaces of the venous wall  20 , or the vein wall  20  including both surfaces along the zero degree wall line  75  can be attached to another vein wall  20 . In a similar manner a 90 degree wall  80  can be identified for the distended vein segment  5  at a location of intersection between a 90 degree radian  85  and the vessel wall  20 . The 90 degree radian  85  is rotated clockwise  90  about the centerline  40 , an angle  95  of 90 degrees from the zero degree radian  35  and with respect to an antegrade flow direction  100 . A 90 degree wall line  105  can then be identified in a manner similar to that described for the zero degree wall line  75  and the vein wall  20  that extends between the zero 75 and 90 ( 105 ) degree wall lines is considered the first quadrant  110 . Similarly, a 180 ( 115 ) and  270  ( 120 ) degree wall, a  180  ( 125 ) and  270  ( 130 ) degree wall line, and a second  135 , third  140 , and fourth  145  quadrant can be identified. In a manner similar to that discussed earlier, an inner surface  90  ( 150 ),  180  ( 155 ), and  270  ( 160 ) degree point and an outer surface  90  ( 165 ),  180  ( 170 ), and 270 ( 175 ) degree point can be defined. Similarly, an inner surface  90  ( 180 ),  180  ( 185 ), and  270  ( 190 ) degree line and an outer surface  90  ( 195 ),  180  ( 200 ), and  270  ( 190 ) degree line can be identified. 
   It is understood that the zero, 90, 180, and 270 degree lines for the inner surface, outer surface, and wall as they are discussed in this disclosure are not required to be exact but are used only for ease of understanding. Actual attachment lines for the valve of the present invention can vary from what is described in this disclosure by approximately 90 degrees or more depending upon the condition of the native distended vein, the accuracy of the procedure, and the ability of the present venous valve formation methods to allow for considerable modification without changing the overall teachings and function of the valve. The description provided in  FIG. 1  is intended to provide a simplified system to describe the device and method of formation of the present venous valve in an understandable way. The distended vein segment  5  was divided into quadrants for ease of description although it is understood that the vein segment could be divided into more numerous sectors (not shown), each sector having less than 90 degrees and having a wall surface area less than a quadrant. Although the quadrants used in this disclosure are positioned in a clockwise  90  manner, it is understood that the location of the first quadrant  110  was arbitrarily chosen. Individual sectors which could have been used to describe the venous valve of the present invention can be assigned arbitrarily about the distended vein segment  5  to describe the line and wall attachments of the present invention. It is further within the understanding of the present invention that a portion of an inner  10  or outer  15  surface or wall area  21  of a quadrant or a sector could be attached to a portion of an inner  10  or outer  15  surface or wall area  21  of another quadrant over a specific area without changing the function of the venous valve. Such a surface attachment or a wall area attachment is understood to be included within the teachings of the present invention. It is also understood that an attachment of an inner or outer surface line or a wall line to another surface or wall line involves more of the vein wall than simply a line. It is assumed that a portion of the vein wall  20  on each side of such a line attachment is involved in the attachment in order to provide strength to the attachment. A surface line attachment or a wall line attachment therefore is understood to involve a wall area  21  in forming the attachment. 
     FIG. 2  is an isometric view of a first embodiment of the venous valve  210  of the present invention. The venous valve of this embodiment is made up of three separate regions, the inlet transition region  215 , the overlap region  220 , and the outlet transition region  225 . The venous valve  210  of one embodiment is joined contiguously to the inlet distended vein  230  at the inlet vein-transition junction  25  and to the outlet distended vein  235  at the outlet transition-vein junction  30 . The overlap transverse dimension  240  is smaller than the inlet distended vein diameter  245  or the outlet distended vein diameter  250 . The inlet transition region  215  provides a smooth blood flow transition in an antegrade flow direction  100  from the larger inlet distended vein diameter  245  to the smaller overlap transverse dimension  240  at the overlap inlet end  255 . The outlet transition region  225  provides a smooth blood flow transition in the antegrade flow direction  100  from the overlap outlet end  255  to the outlet transition-vein junction  30 . In the overlap region  220 , the inner surface zero degree line  55  is shown in contact with the inner surface 180 degree line  185 , and having an inner surface zero and 180 degree line attachment  265 . This inner surface zero and 180 degree line attachment  265  can involve a surface attachment method such as a thermal or laser weld, a biological glue or adhesive, or other surface attachment means. Additionally, the inner surface zero and 180 degree line attachment  265  in the overlap region  220  can involve the entire vessel wall, by attaching the zero ( 75 ) and 180 ( 125 ) degree wall lines with sutures, staples, or any other wall attachment means including laser, thermal, or other fusion methods that will attach the zero degree wall line  75  and the 180 degree wall line  125  together in the overlap region  220 . An example of such means  268  is shown in  FIG. 2  extending in the overlap region  220 . This inner surface zero and 180 degree line attachment  265  is shown to extend from the overlap inlet end to outlet end but it is understood that it can extend over only a portion of this overlap region  220  without affecting the function of the valve of the present invention. The outer surface zero  65  and 180 ( 200 ) degree lines are also shown. An outer surface  90  and 270 degree line attachment  270  is also present in the overlap region  220 . This outer surface  90  and 270 degree line attachment  270  can be made by attaching the outer surfaces together using thermal or laser bonding methods or with biological glues or adhesives. Outer surface  90  and 270 degree line attachment  270  can also be made using sutures, staples, fusion methods, or other attachment means to attach the 90 degree wall line  105  to the 270 degree wall line  130  with attachment extending through a portion of or through the entire vessel wall  20 . This outer surface  90  and 280 degree line attachment  270  can be intermittant and can extend over only a portion of the length of the overlap region  220  without affecting the function of the venous valve of the present invention. 
     FIG. 3A  is an isometric view of the overlap region  220  of one embodiment of the venous valve of the present invention in an early stage of formation. The vein wall  20  that is to form the overlap region  220  between the overlap inlet  255  and outlet  260  end has been partially flattened by allowing the first  110  and fourth  145  quadrant to be positioned above the second  135  and third  140  quadrant, respectively. This allows the zero degree wall line  75  to lie directly upon the 180 degree wall line  125  and allow ease of surface or wall attachment means to hold the inner surface zero degree line  55  against the inner surface 180 degree line  185 . The outer surface zero 65 and 180 ( 200 ) degree line and the antegrade flow direction  100  are shown. It is understood that the overlap region  220  may be flattened to a greater extent than is shown in  FIG. 3A  prior to forming the inner surface zero and 180 degree line attachment  265 . 
     FIG. 3B  is an isometric view of the overlap region  220  showing the overlap inlet end  255  of the venous valve  210  of this invention. The inner surface zero and 180 degree line attachment  265  extends from the overlap inlet end  255  to the overlap outlet end  260 ; this divisional attachment divides the overlap region into two tubular members, one member between the first  110  and second  135  quadrants, and another member between the third  140  and fourth  145  quadrants. The two tubular members provide two separate lumens or compartments without leakage of blood across the divisional attachment. Such a divisional attachment could be formed by attachment of two sectors together instead of quadrants as shown in the drawings for ease of description. An overlap inlet end first and second quadrant attachment  275  at the overlap inlet end forms a closure attachment that prevents blood flow in an antegrade flow direction  100  from entering between the first  110  and second  135  quadrant. This overlap inlet end first and second quadrant attachment  275  can be made by attaching the inner surface  10  of the first  110  and second  135  quadrant using surface attachment means such as bonding agents or welding methods as described earlier or attachment can be made through the vein wall  20  of the first  110  and second  135  quadrants using sutures, staples, fibers, or other wall attachment means. An example of such surface or wall attachment means  278  is shown in  FIG. 3B , and can be formed of a suture or other material. An overlap inlet end first and fourth quadrant attachment  280  is also found at the overlap inlet end  255 ; this attachment  280  prevents antegrade blood flow from entering between the first  110  and fourth  145  quadrants. This overlap inlet end first and fourth quadrant attachment  280  forms a portion of the valve cusp attachment that is required to hold the walls of the first  110  and fourth  145  quadrants together over at least a portion of the wall. This overlap inlet end first and fourth quadrant attachment  280  can be made by attaching the outer surfaces  15  of the first  110  and fourth  145  quadrants from the 270 ( 120 ) and 90 ( 80 ) degree wall to the zero degree wall  70  using surface attachment means on the outside surfaces of the first  110  and fourth  145  quadrants or using wall attachment means that attach the vein wall of the first  110  and fourth  145  quadrants together at the overlap inlet end  255 . The first  110 , second  135 , and fourth  145  quadrants can all be attached together at the overlap inlet end  255  using a single surface or wall attachment means, an example of which is shown by reference numeral  278 . Attachment of the outer surface  90  ( 195 ) and  270  ( 205 ) degree lines from the overlap inlet end  255  to the overlap outlet end  260  holds the outer surfaces  15  of the first  110  and fourth  145  quadrants into approximation with each other throughout the overlap region  220  and forms an approximation attachment. The 90 degree wall line  105  can be attached to the 270 degree wall line of the overlap region  220  using attachment means including sutures, staples, or fusion methods. An example of such attachment means  278  is shown in  FIG. 3B , and can be formed of suture or other material. 
   The overlap inlet end  255  is shown as a transverse section that extends in a direction perpendicular to the antegrade flow direction  100 . It is understood that the overlap inlet end can be positioned on a bevel or at an angle with respect to the direction of flow in an antegrade direction  100 . Additionally, the overlap inlet end first and second quadrant attachment  275  is not required to be located in immediate apposition to the overlap inlet end first and fourth quadrant attachment  280 . All reference numerals correspond to those elements previously or otherwise described. 
     FIG. 3C  is an isometric view of the overlap region  220  showing the overlap outlet end  260  of the venous valve  210  of the present invention. At the overlap outlet end  260 , an overlap outlet end first and fourth quadrant attachment  285  is formed to attach the inner surfaces  10  (see  FIG. 1 ) of the first  110  and fourth  145  quadrants along the overlap outlet end  260 . This overlap outlet end first and fourth quadrant attachment  285  can be made using bonding agents, biological glues, or other adhesives, or it can be formed from a thermal, laser, or fusion process, or other surface method that bonds tissue surfaces or tissue walls together. The overlap outlet end first and fourth quadrant attachment  285  can also be formed by sewing or suturing the vein walls together along the overlap outlet end or by using staples or other wall attachment means. An example of such surface or wall attachment means  278  is shown in  FIG. 3C , and can be formed of suture, staples, metallic or polymeric fibers, or other material. Laser fusion, thermal fusion, and other fusion methods can also be considered wall attachment means since they can extend into the central tissue found in the vein wall to achieve their attachment. The overlap outlet end first and fourth quadrant attachment  285  along with the overlap inlet end first and fourth quadrant attachment  280  (see  FIG. 3B ) form a valve cusp attachment that identifies one way of attaching the first  110  and fourth  145  quadrants together. Such a valve cusp attachment can be formed using attachment means to hold a portion of the inner surfaces  10  of the first  110  and fourth  145  quadrants together or hold a portion of the walls of the first  110  and fourth  145  quadrants together such that they are attached and can function as a valve cusp  290 . All reference numerals correspond to those elements previously or otherwise described. 
   The outer surface  90  and 270 degree line attachment  270  is shown holding the outer surface 90 degree line  195  in contact with the outer surface 270 degree line  205  from the overlap inlet end  255  to the overlap outlet end  260 . This outer surface  90  and 270 degree line attachment  270  is an approximation attachment and is not required in this embodiment to be continuous and can have intermittent attachments as long as the outer surfaces  15  of the first  110  and fourth  145  quadrants are held in apposition with each other in the overlap region  220 . The inner surface zero and 180 degree line attachment  265  is shown in  FIG. 3C  to extend from the overlap inlet end  255  to the overlap outlet end  260  and this divisional attachment could involve only a portion of the overlap region  220  as long as it forms two tubular members as shown in  FIG. 3C  within the overlap region  220  that do not leak substantial blood flow across this attachment  265 . An overlap through-flow member  295  is formed by the third  140  and fourth  145  quadrants of the overlap region  220  providing a passage for blood flow in an antegrade flow direction  100 . An overlap sinus member  300  is formed by the first  110  and second  135  quadrants of the overlap region  220 . The second  135  and fourth  145  quadrants which are attached at the overlap outlet end first and fourth quadrant attachment  285 , form the valve cusp  290  with a commissure  305  or leading edge of the valve cusp  290  located at the overlap outlet end first and fourth quadrant attachment  285 . During blood flow in an antegrade direction  100 , the valve cusp  290  is displaced toward the second  135  quadrant and the inner surface  10  (see  FIG. 1 ) of the first quadrant  110  can come into contact with the inner surface  10  of the second quadrant  135 . Movement of the valve cusp  290  during blood flow in an antegrade direction  100  provides a large overlap through-flow member diameter  310  and the least resistance to blood flow. Antegrade blood flow can occur in the veins of the leg during leg muscle contraction and with the legs in a reclined position. Initiaition of blood flow in a retrograde flow direction  315  in the overlap through-flow member  295  can initiate in the veins of the leg during leg muscle relaxation or during periods of standing. Retrograde flow of blood in a direction opposite to the antegrade flow direction  100  can create shear stresses on the inside surface of the fourth quadrant  145  causing the commissure  305  of the valve cusp  290  to move toward the third quadrant  140  with possibly some displacement toward the overlap inlet end  255  and away from the inner surface  10  of the second quadrant  135 . Blood flow enters the overlap sinus member  300  due to a small pressure driving force that can be approximately 0.1 to 1 mm Mercury (Hg) from the overlap outlet end  260  to overlap inlet end  255  of the overlap sinus member  300 . As blood fills the overlap sinus member  300  which is dead ended at the overlap inlet end  255 , the valve cusp  290  is moved toward the third quadrant  140  of the overlap region  220 . The valve commissure  305  comes into contact with or adjacent to the inner surface  10  of the third  140  quadrant of the overlap region  220  and stops any further blood flow in a retrograde direction  100  from occurring in the overlap through-flow member  295 . For the valve commissure  305  to reach from the inner surface of the third quadrant  140  during antegrade flow, to the inner surface of the second quadrant during initiation of retrograde flow, the valve cusp length  320  should be at least approximately one half the overlap through-flow member diameter  310  (see FIG.  3 B). The overlap region length  325  can be approximately the same length as the valve cusp length  320 . Due to the formation methods for the overlap region  220  of the present venous valve embodiment, the overlap through-flow member diameter  310  can be approximately one half of the distended vein segment diameter  22  from which it has been formed, and the overlap region length  325  can be approximately at least one quarter of the distended vein segment diameter  22  from which it has been formed. The overlap region length  325  could be longer than one quarter of the distended vein segment diameter  22  and could be as large or larger than the distended vein diameter  22 . An excessively long overlap region length  325  extending more than approximately ten times the through-flow member diameter  310  could have the disadvantage that the overlap sinus member  300  could have a tendency toward thrombosis due to blood stasis in that member. All reference numerals correspond to those elements previously or otherwise described. 
   It is understood that the venous valve  210  of the present invention is not required to be formed from a distended vein, and other materials of construction can also be used. It is further understood that the overlap region length  325  used in the previous discussion is used to provide an easily understandable estimate of a valve cusp length  320 . The valve cusp  290  can be formed with a beveled outlet end (not shown), and is not required to have a valve cusp length  320  equal to the overlap region length  325 . 
     FIG. 4  is an isometric view of the overlap region  220  showing external wall support  330  such as suture, metal wire, polymeric fiber, ribbon, or other wall support means being placed around the outside surface  15  of the second  135  and third  140  quadrants at the overlap inlet end  255 . Internal wall support  335  such as suture, metal wire, polymeric fiber, polymeric ribbon, or other support means can also be placed within, sutured within, or placed through the vein wall as shown within the second  135  and third  140  quadrants at the overlap outlet end  260  or elsewhere throughout all or a portion of the venous valve of the present invention. Such internal  335  or external  330  wall support can help to resist distension of the overlap inlet  255  or outlet  260  end and ensure long term function of the venous valve of this invention. It is understood that internal  335  or external  330  wall support can be used at either or both the overlap inlet or outlet end. Internal  335  or external  330  wall support can also be used to support all four quadrant walls of the overlap region  220  throughout the entire overlap region  220  between the overlap inlet  255  and outlet  260  ends. Such internal  335  or external  330  wall support can extend within a transverse section of the overlap region  220  as shown in  FIG. 4 , it can extend axially  60  (see  FIG. 1 ) in the antegrade flow direction  100 , or it can have components in both directions. All reference numerals correspond to those elements previously or otherwise described. 
     FIG. 5A  is a partially sectioned view of an embodiment of the venous valve  210  of the present invention in a flattened condition as could be found during the formation of the venous valve.  FIG. 5C  is a partially sectioned view of an embodiment of the venous valve of the present invention with antegrade blood flow passing through it. Sectional views of the inlet  230  or outlet  235  distended vein are shown in a flattened conformation as can be found during venous valve formation in FIG.  5 B and in a round conformation providing blood flow in FIG.  5 D.  FIGS. 5A-5D  will be discussed collectively. The zero degree wall line  75  is attached to the 180 degree wall line  125  in the overlap region  220  forming an overlap zero and 180 degree wall line attachment  340  or divisional attachment. The 90 degree wall line  105  is attached to the 270 degree wall line  130  in the overlap region  220  forming an overlap  90  and 270 degree wall line attachment  345  or approximation attachment. The venous valve  210  of the present invention is shown to have an overlap region  220  which is contiguous with the inlet  215  and outlet  225  transition regions. These regions do not have to be contiguous; they can be attached together or portions of the vein wall  20  can be cut and removed as found in a later embodiment. The venous valve  210  of the present invention is only required to have an overlap region  220 . The inlet  215  and outlet  225  transition regions provide smooth blood transition from inlet distended vein  230  to the overlap region  220  and from the overlap region  220  to the outlet distended vein  235 , but are not required in the venous valve  210  of the present invention. The inlet transition region  215  can be contiguous with the inlet distended vein  230  if it is formed in situ from an existing native vein. Similarly, the outlet transition region  225  can be contiguous with the outlet distended vein  235 . Alternately, an embodiment of the venous valve of the present invention extending from the inlet vein-transition junction  25  to the outlet transition-vein junction  30 , or another embodiment extending only from the overlap inlet end  255  to the overlap outlet end  260  can be interposed surgically into a vein that requires a venous valve. The venous valve  210  of the present invention can also be constructed of biological tissue, polymeric material, or autologous tissue taken from another part of the anatomy and formed into the venous valve. All reference numerals correspond to those elements previously or otherwise described. 
     FIG. 6A  is a sectional view of the overlap inlet end  255  during the formation of the valve of the present invention. The first  110  and second  135  quadrants are attached by the overlap inlet end first and second quadrant attachment  275 . The first  110  and fourth  145  quadrants are attached by the overlap inlet end first and fourth quadrant attachment  280 . The third  140  and fourth  145  quadrants form the overlap through-flow member  295 . The zero degree wall  70  is attached to the 180 degree wall  115  with an overlap inlet end zero and 180 degree wall attachment  350 . The overlap inlet end zero and 180 degree wall attachment  350  extends from the overlap inlet  255  to outlet  260  end forming an overlap zero and 180 degree wall line attachment  340  (see FIG.  5 A). The 90 degree wall  80  is attached to the 270 degree wall  120  with an overlap inlet end  90  and 270 degree wall attachment  355 . The overlap inlet end  90  and 270 degree wall attachment  355  extends from the overlap inlet  255  to outlet  260  end forming an overlap  90  and 270 degree line attachment  345  (see FIG.  5 A). The attachment  275 ,  280 ,  350 , or  355  can be a wall or surface attachment formed using sutures, staples, adhesives, laser welding, or other attachment means or methods described earlier. 
     FIG. 6B  is a sectional view of the overlap inlet end  255  during blood flow in an antegrade flow direction  100  (see  FIG. 5C ) through the overlap through-flow member  295 . The overlap through-flow member diameter  310  can be approximately one half of the inlet or outlet distended vein segment diameter  22  from which it may be formed. Other configurations can similarly be used to form the overlap inlet end of the present invention. Other reference numerals are the same as those found in FIG.  6 A. 
     FIG. 7A  is a sectional view of the overlap outlet end  260  during formation. The first  110  and fourth  145  quadrants are attached by the overlap outlet end first and fourth quadrant attachment  285 . The 90 degree wall  80  and the 270 degree wall  120  are attached by the overlap outlet end  90  and 270 degree wall attachment  360 . The zero degree wall  70  is attached to the 180 degree wall  115  at the overlap outlet end  260  by an overlap outlet end zero and 180 degree wall attachment  365 . The first  110  and fourth  145  quadrants are attached by the overlap outlet end first and fourth quadrant attachment  285 . The first quadrant  110  is not attached to the second quadrant  135  and the third quadrant  140  is not attached to the fourth quadrant  145  at the overlap outlet end. Surface or wall attachments are formed using materials and methods as described earlier. 
     FIG. 7B  is a sectional view of the overlap outlet end with blood flow in an antegrade flow direction  100  (see  FIG. 5C ) showing the overlap through-flow member  295  with an overlap through-flow member diameter  310 . All reference numerals are the same as found in FIG.  7 A. 
     FIG. 7C  is a sectional view of the overlap outlet end with retrograde filling of the overlap sinus member  300 . Retrograde filling of the overlap sinus member  300  causes retrograde flow through the through-flow member  295  to reduce significantly or cease. All other reference numerals are the same as in FIG.  7 A. 
   As seen in  FIGS. 5A and 5C , the venous valve  210  of the present invention can have an inlet  215  or an outlet  225  transition region to provide a smooth transition of blood flow from the inlet distended vein  230  or the outlet distended vein  235  to the overlap region  220 . The inlet  215  or outlet  225  transition region can be contiguous with the overlap region  220  or the transition regions can be contiguous with the inlet  230  or outlet  235  distended veins; or the inlet  215  or outlet  225  transition regions can be attached to the overlap region  220 , or the transition regions can be attached to the inlet  230  or outlet  235  distended veins using sutures or other attachment means. 
     FIGS. 8A and 8B  are sectioned views of the inlet transition region  215  without blood flow and in a state of being formed. The zero degree wall  70  and the 180 degree wall  115  are shown for reference. As shown in  FIG. 8A  approximately a 45 degree wall  370  can be attached to approximately the 315 degree wall  373  at an inlet transition  45  and 315 degree wall attachment  382 . As shown in  FIG. 8B  approximately the 20 degree wall  384  can be attached to approximately a 340 degree wall  386  at an inlet transition  20  and 340 degree wall attachment  388 . Additional inlet transition attachments are made in a similar manner to form a line of inlet transition wall attachments between the first  110  and fourth  145  quadrants that form a tapered line of attachments in the inlet transition region  215  from the overlap region  220  to the inlet distended vein  230  (see FIGS.  5 A and  5 B). This tapered line of attachment forms a beveled attachment that extends from the overlap region to the distended vein with either a straight or curved bevel that directs the blood flow smoothly from the inlet distended vein  230  to the overlap region  220 . All reference numerals correspond to those elements previously or otherwise described. 
     FIGS. 8C and 8D  are similar to  FIGS. 8A and 8B  except that the inlet transition region  215  is shown as though blood flow in an antegrade flow direction  100  were present in an inlet transition flow lumen  392 . An inlet transition diameter  394  for the inlet transition flow lumen  392  of  FIG. 8C  is smaller than an inlet transition diameter  396  for an inlet transition flow lumen  402  of FIG.  8 D. Inlet transition excess tissue  406  is shown extending into the inlet transition flow lumen  392  of FIG.  8 C. The inlet transition excess tissue can be attached to the first or fourth quadrant wall or it can be trimmed off and removed. All reference numerals correspond to those elements previously or otherwise described. 
   One embodiment for forming the outlet transition region  225  is shown in  FIGS. 9A and 9B .  FIGS. 9A and 9B  are sectioned views of the outlet transition region  225  without blood flow and in a state of being formed. The zero degree wall  70  and the 180 degree wall  115  are shown for reference. As shown in  FIG. 9A  approximately the 45 degree wall  370  can be attached to approximately the 315 degree wall  373  at an outlet transition  45  and 315 degree wall attachment  411 . As shown in  FIG. 9B  approximately the 20 degree wall  384  can be attached to approximately the 340 degree wall  386  at the outlet transition  20  and 340 degree wall attachment  416 . Additional outlet transition attachments are made in a manner similar to that described for the inlet transition region  215  to form a continuous line of outlet transition wall attachments that form a tapered transition from the overlap region  220  to the outlet distended vein  235 . This tapered line of attachment forms a beveled attachment that extends from the overlap region to the distended vein with either a straight or curved bevel that directs the blood flow smoothly from the overlap region  220  to the outlet distended vein  230 . Wall and surface attachments are formed using materials and methods as discussed earlier. 
     FIGS. 9C and 9D  are similar to  FIGS. 9A and 9B  except that the outlet transition region  225  is shown as though blood flow in an antegrade flow direction  100  were present in an outlet transition flow lumen  421 . An outlet transition diameter  426  for the outlet transition flow lumen  421  of  FIG. 9C  is smaller that an outlet transition diameter  432  for an outlet transition flow lumen  437  of FIG.  9 D. Outlet transition excess tissue  442  is shown extending into the outlet transition flow lumen  421  of FIG.  9 C. The outlet transition excess tissue  442  can be attached to the first  110  or fourth  145  quadrant wall or it can be trimmed off and removed. All reference numerals correspond to those elements previously or otherwise described. 
   One embodiment for forming the inlet transition region  215  is shown in sectional views in  FIGS. 10A and 10B .  FIG. 10A  represents a position along the inlet transition region similar to that of FIG.  8 A and  FIG. 10B  represents a position similar to that of FIG.  8 B. In  FIGS. 10A and 10B  it is understood that the inlet transition region  215  is shown in a flat conformation such that it may not have blood flow going through it such as during the formation of the venous valve  210  of the present invention.  FIGS. 10A and 10B  show the first  110 , second  135 , third  140 , and fourth  145  quadrants in a similar conformation to that found in the overlap region  220  for ease of understanding the formation of the transition region of this embodiment of the present invention. In  FIGS. 10A and 10B  the zero degree wall  70  and the 180 degree wall  115  are not attached, and the 90 degree wall  80  and the 270 degree wall  120  are not attached. In  FIG. 10A  attachment of the first quadrant  110  to the second quadrant  135  can occur approximately from a 45 degree wall  370  to a 135 degree wall  447  forming an inlet transition  45  and 135 degree wall attachment  452 . An example of an attachment means  278  is shown in  FIG. 10A , and can include sutures or other materials or attachment methods or attachment means as described earlier. In  FIG. 10B  attachment of the first quadrant  110  to the second quadrant  135  can occur approximately from a 70 degree wall  457  to a 110 degree wall  462  forming an inlet transition  70  and 110 degree wall attachment  468 .  FIGS. 10A and 10B  represent two sections along the inlet transition region  215 ; the locations for attachment of portions of the first  110  and second  135  quadrants are approximate and correspond to positions along the axial length of the transition region similar to those found in  FIGS. 8A and 8B , respectively. A continuous or intermittent line of attachments is intended to form a tapered transition for blood flow from the inlet distended vein  230  to the overlap inlet end  255  to direct blood flow from the inlet distended vein  230  into the overlap inlet end  255 . It is understood that additional attachments are made along the entire inlet transition region  215  extending from the overlap region  220  to the inlet distended vein  230 . Inlet transition excess tissue  472  can be trimmed off or removed provided that the attachments made from the first  110  to the second  135  quadrants form a continuous beveled line from the overlap region  220  to the inlet distended vein  230  that can withstand venous blood pressure without leakage. All reference numerals correspond to those elements previously or otherwise described. 
     FIGS. 10C and 10D  are similar to those of  FIGS. 10A and 10B  respectively except that the inlet transition region  215  is shown as though blood flow with an antegrade flow direction  100  (see  FIG. 5C ) were passing through an inlet transition flow lumen  478  of FIG.  10 C. The inlet transition flow lumen  478  shown in  FIG. 10C  has an inlet transition diameter  482  that is smaller than the inlet transition diameter  488  of the inlet transition flow lumen  492  shown in FIG.  10 D. The inlet transition diameter of the inlet transition flow lumen gets progressively smaller as it extends from the inlet distended vein  230  to the overlap region  220 . The inlet transition excess tissue  472  does not extend into the inlet transition lumen of this embodiment and can be cut off without affecting the function of the present invention. All other reference numerals are the same as those in  FIGS. 10A and 10B . 
     FIGS. 11A-D  describe an alternate embodiment of the present invention.  FIGS. 11A and 11B  show a distended vein segment  5  lying flat with the fourth  145  quadrant and third  140  quadrant lying adjacent to the first  110  and second  135  quadrant, respectively. The overlap region  220  extends from the overlap inlet end  255  to the overlap outlet end  260 . The inlet transition region  215  can be contiguous with or it can be attached to the overlap inlet end  255  and the outlet transition region  225  can be contiguous with or it can be attached to the overlap outlet end  260 . The inlet distended vein  230  can be contiguous with or it can be attached to the inlet transition region  215  and the outlet distended vein  235  can be contiguous with or it can be attached to the outlet transition region  225 . The outer surface zero degree line  65  and zero degree wall  70  and the inner surface zero degree line  55  are shown near the top of FIGS.  11 A and  11 B, and the outer surface 180 degree line  200  and 180 degree wall and inner surface 180 degree line  185  are shown near the bottom of  FIGS. 11A and 11B . An overlap inlet end first and fourth quadrant attachment  280  is formed to attach the first quadrant  110  to the fourth quadrant  145  at the overlap inlet end  255 . This overlap inlet end first and fourth quadrant attachment  280  can be made using suture, staples, adhesives, tissue bonding agents, fusion methods, metallic fiber, polymeric fiber, or other surface or wall attachment means. An example of such wall or surface attachment means is shown by reference numeral  278  in  FIG. 11B , it can be formed of suture or other material as described earlier for previous embodiments. An overlap outlet end first and fourth quadrant attachment  285  is formed to attach the first quadrant  110  to the fourth quadrant  145  at the overlap outlet end  260  using surface or wall attachment means. The overlap inlet end and outlet end first and fourth quadrant attachments  280  and  285  form the valve cusp attachment. It is understood that such valve cusp attachment requires only that a portion of the first  110  and fourth  145  quadrant walls area  21  be attached together. 
   The vein walls  20  of the first  110  and fourth  145  quadrants are cut adjacent to the overlap inlet end first and fourth quadrant attachment  280  at an overlap inlet cut  505  as shown in FIG.  11 C. Similarly, the vein walls  20  of the first  110  and fourth  145  quadrants are cut adjacent to the overlap outlet end first and fourth quadrant attachment  285  at an overlap outlet cut  510  as shown in FIG.  11 C. 
   The first  110  and fourth  145  quadrants of the overlap region  220  undergo an inverted fold  515  to bring the inner surface zero degree line  55  into direct contact with the inner surface 180 degree line  185  in the overlap region  220  as shown in FIG.  11 D. The zero degree wall line  75  is attached to the 180 degree wall line  125  at the overlap zero and 180 degree wall line attachment  340  forming a divisional attachment in the overlap region  220  using sutures, staples, bonding agents, fusion methods or other surface or wall attachment means. This divisional attachment forms two separate lumens or spaces that do not have significant leakage between them. It is understood that the overlap zero and 180 degree wall line attachment  340  need not be attached from the overlap inlet  255  to outlet  260  end as long as two tubular members are formed by a divisional attachment, a divisional attachment being a surface or wall attachment that can form two separate flow channels that do not allow substantial blood flow to pass across the attachment. 
   At the overlap inlet end  255 , the first  110  and second  135  quadrants are attached forming an overlap inlet end first and second quadrant attachment  275  or closure attachment as shown in  FIG. 11D and 11E . The closure attachment does not allow antegrade blood flow to enter between the first  110  and second  135  quadrants. In the overlap region  220  the outer surface 90 degree line  195  is attached to the outer surface 270 degree line  205  forming the outer surface  90  and 270 degree line attachment  270  or approximation attachment; this attachment can be found along only a portion of the outer surface  90  and 270 degree line attachment  270  without affecting the function of the vein valve  210  of the present invention. The approximation attachment serves to hold the  90  and 270 degree lines in approximation with each other at least intermittently. The 90 degree wall line  105  and the 270 degree wall line  130  are attached in the overlap region  220  to form the overlap  90  and 270 degree wall line attachment  345 . At this stage of formation, the overlap region  220  has been formed into one embodiment of the venous valve  210  of this invention. An inlet  215  or outlet  225  transition region can be contiguous with or attached to the overlap region  220 . The overlap region  220  could also be interpositionally attached between an inlet  230  or outlet  235  distended vein. The overlap outlet end first and fourth quadrant attachment  285  forms a valve cusp free edge or commissure as described in other previous embodiments of the invention. The inverted fold  515  of the first  110  and fourth  145  quadrants provides the valve cusp free edge of this embodiment that has the endothelialized surface folded over such that it approximates the other endothelialized surface. The endothelialized surface of the commissure is similar to the inner surface of the distended vein. The venous valve of  FIG. 11E  is shown in a conformation that would provide for antegrade or retrograde blood flow. All reference numerals correspond to those elements previously or otherwise described. 
     FIG. 12  is a sectional view at the overlap inlet end  255  showing the overlap inlet end first and fourth quadrant attachment  280  and the overlap inlet end first and second quadrant attachment  275 . The overlap inlet end first and second quadrant attachment  275  forms a closure attachment that will prevent blood flow in an antegrade direction  100  (see  FIG. 11E ) from entering between the first  110  and second  135  quadrants. The overlap through-flow member  295  formed by the third  140  and fourth  145  quadrants provides space for antegrade blood flow through the overlap region  220  (FIG.  11 E). 
     FIGS. 13A and 13B  are sectional views of the overlap outlet end showing the overlap outlet end first and fourth quadrant attachment  285 . In  FIG. 13A  the overlap through-flow member  295  provides space for blood flow in an antegrade direction  100 ; the valve cusp  290  which is formed from the first  110  and fourth  145  quadrants, is in contact with the second quadrant  135 . During the initiation of retrograde flow, the valve cusp  290  moves into contact with the third quadrant  140  as shown in FIG.  13 B. Blood will flow into the overlap sinus member  300  causing the valve cusp  290  to prevent continued blood flow in a retrograde direction  315  (see  FIG. 11E ) in the overlap through-flow member  295  as the valve cusp remains in contact with the third quadrant  140 . It is understood that the valve cusp  290  is formed by an attachment of a portion of the first quadrant  110  to a portion of the fourth quadrant  145  along a wall line attachment. This attachment could be formed by attaching a portion of a wall area  21  of the first quadrant  110  to a portion of a wall area  21  of the fourth quadrant  145 . Such a valve cusp  290  could similarly be formed by attachment of two sectors together forming a wall line attachment or a wall area attachment. 
   The inlet  215  and outlet  225  transition regions can be formed contiguously with the overlap region  220  or they can be attached using surface or wall attachment means. One method for forming the inlet  215  and outlet  225  transition regions contiguously with the overlap region  220  is shown in  FIGS. 11A-11E .  FIG. 11A  shows an inlet transition beveled attachment  520  that attaches the first  110  and fourth  145  quadrants together in the inlet transition region  215 . The inlet transition beveled attachment  520  extends from the overlap inlet end first and fourth quadrant attachment  280  along a beveled angle to the outer surface zero degree line  65 . Similarly, an outlet transition beveled attachment  525  is made extending from the overlap outlet end first and fourth quadrant attachment  285  along a beveled angle to the outer surface zero degree line  65 . These inlet  520  and outlet  525  beveled attachments can be made using surface or wall attachment means as described earlier and can be a curved line attachment; beveled line attachments are not required to be a straight line. 
   An inlet transition beveled cut  530  is made through the first  110  and fourth  145  quadrants adjacent to the inlet transition beveled attachment  520  on the side of the attachment nearest to the outer surface zero degree line  65  as shown in FIG.  11 C. Similarly, an outlet transition beveled cut  535  is made through the first  110  and fourth  145  quadrants adjacent to the outlet transition beveled attachment  520 . The inlet  540  and outlet  545  transition excess tissue can be removed. The inlet  215  and outlet  225  transition regions provide a smooth contiguous transition from the overlap region  220  to the inlet  230  and outlet  235  distended vein as shown in FIG.  11 E. 
     FIGS. 14A and 14B  are sectional views of the inlet transition region  215 . The 180 degree wall  115  is shown for reference. As shown in  FIG. 14A  approximately the 45 degree wall  370  can be attached to approximately the 315 degree wall  373  at an inlet transition  45  and 315 degree wall attachment  382 . As shown in  FIG. 14B  approximately the 20 degree wall  384  can be attached to approximately the 340 degree wall  386  at the inlet transition  20  and 340 degree wall attachment  388 . Additional inlet transition attachments are made in a manner to form the inlet transition beveled attachment  520  shown in FIG.  11 A. An inlet transition diameter  550  for the inlet transition flow lumen  555  of  FIG. 14A  is smaller that an inlet transition diameter  560  for an inlet transition flow lumen  565  of FIG.  14 B. The inlet transition excess tissue  540  (see  FIG. 11C ) that was attached to the first  110  or fourth  145  quadrant wall has been trimmed off and removed. 
     FIGS. 15A and 15B  are sectional views of the outlet transition region  225 . As shown in  FIG. 15A  approximately the 45 degree wall  370  can be attached to approximately the 315 degree wall  373  at an outlet transition  45  and 315 degree wall attachment  411 . As shown in  FIG. 15B  approximately the 20 degree wall  384  can be attached to approximately the 340 degree wall  386  at the outlet transition  20  and 340 degree wall attachment  416 . Additional outlet transition attachments are made in a manner to form the outlet transition beveled attachment  525  shown in FIG.  11 A. An outlet transition diameter  570  for the outlet transition flow lumen  575  of  FIG. 15A  is smaller than an outlet transition diameter  580  for an outlet transition flow lumen  585  of FIG.  15 B. The outlet transition excess tissue  545  (see  FIG. 11C ) that was attached to the first  110  or fourth  145  quadrant wall has been trimmed off and removed. 
     FIGS. 16  shows an isometric view of one embodiment of the venous valve  210  of the present invention. The overlap region  220  is contiguously joined to the inlet  215  and outlet  225  transition regions which are contiguously joined to the inlet  230  and outlet  235  distended veins, respectively. The inlet  215  and outlet  225  transition regions have inlet  520  and outlet  525  transition bevel attachments, respectively. The overlap region  220  has an outer surface  90  and 270 degree line attachment  270  extending from the overlap inlet end  255  to the overlap outlet end  260 . 
   The inner and outer surface line attachments and wall attachments presented in this disclosure describe  FIGS. 1-16  in a clear manner. It is understood that in forming the venous valve  210  of the present invention the attachments made from one quadrant or sector to another are not required to be the surface line or wall line attachments as they are presented in  FIGS. 1-16  and their descriptions. A wall line attachment for example could occur over only a portion of the overlap region  220  and it is not required to extend parallel to the centerline  40 ; a surface or wall line attachment is only required to have a directional component in the direction of the centerline  40  or axial direction  60 . Surface line attachments and wall line attachments can be beveled or formed at an angle with respect to the centerline  40 . Wall line attachments made at the overlap inlet or outlet end can be beveled or formed at an angle with respect to the centerline  40 . A portion of a wall area  21  from one quadrant or sector can be attached to the wall area  21  of another quadrant or sector; this surface or wall attachment can be used to form a portion of the valve cusp or form the attachments found on other aspects of the venous valve described in this disclosure. 
   It is understood that the overlap region of one embodiment can be combined with an inlet or outlet transition region of another embodiment. The method of forming the venous valve of this invention can also involve combinations describing the formation of the overlap region or transition region from any of the embodiments presented in this disclosure. Furthermore, it is understood that the valve of this invention can be formed from a combination of autologous tissue used for either the overlap region or a transition region combined with heterogeneous biological tissue or synthetic material used for another portion of the venous valve.