Abstract:
A prosthetic venous valve having a two-piece housing which includes upstream and downstream sections. The upstream section contains a circular seat against which an occluder comes in sealing contact when the valve is in its closed position. The downstream housing section is shaped so as to prevent escape of the occluder downstream and to halt the reciprocating motion of the occluder in the open position where there is an open pathway past the occluder. A plurality of fins on the interior of the downstream housing section or on the surface of the occluder assure there is a blood flow path downstream past the occluder in the open position. The two-piece construction allows the housing sections to be axially spaced apart so that blood comes in contact with the interior surface of the patient&#39;s vein immediately downstream of the upstream section of the housing. Such arrangement is biologically advantageous and permits momentary deflections of either of the housing sections from its normal coaxial orientation without harm to the valve or disruption of its functioning.

Description:
FIELD OF THE INVENTION 
     The present invention relates to prosthetic valves for replacement use in patients and more particularly to replacement venous valves that can take the place of a malfunctioning valve in a blood vessel of a patient. 
     BACKGROUND OF THE INVENTION 
     The distribution and transportation of blood between different parts of the body is regulated by many physical factors, and the lack of knowledge with respect to venous flow and the behavior of venous valves has often made current treatment of venous disorders ineffective. In the last decade, a fair amount of attention has been given to difficulties that occur in circulation in humans that result from nonoperative or malfunctioning venous valves. Apparatus and medical procedures have been developed for excising such malfunctioning valves. 
     Venous valves act to assist the return of venous blood to the heart as part of the physiological pumping system known as the “venous pump” or “muscle pump”. Venous valves are one-way valves arranged so that the direction of blood flow can only be towards the heart. Every time the legs are moved, or muscles tensed, a bolus of blood is propelled towards the heart. This bolus, moving towards the heart, opens and crosses a venous valve. Reverse flow is then prevented by the closing action of the venous valve. In the next movement or contraction, the venous blood bolus is lifted through the next venous valve and so forth until it has returned to the heart from the lower extremities via the venous or muscle pump. This venous pump is independent of the contraction of the heart. 
     Venous return from an extremity of the body is not actually dependent upon properly functioning valves when a patient is in the supine position because the existing pressure gradient to the heart may be sufficient to assure normal return. However, proper functioning of venous valves in the lower extremities can be of critical importance in minimizing pressure build up when the body is not in the supine position. Unfortunately, diagnosis of a problem with one or more venous valves has not been sufficient because there are currently no known commercially available prosthetic valves that can function satisfactorily as a replacement for a malfunctioning native valve. 
     Some relatively simple, experimental venous valves have been developed, such as those shown in U.S. Pat. Nos. 5,358,518, 5,500,014, and 5,607,465, and one somewhat more complicated venous valve implant is shown in U.S. Pat. No. 5,824,061. Moreover, a double-ball check valve and intraluminal graft is shown in U.S. Pat. No. 5,697,968, and a self-expanding poppet valve that can be inserted through a catheter while confined in a tubular sheath is shown in U.S. Pat. No. 5,397,351. 
     The potential for thrombosis at replacement venous valves is a very important consideration for, because of its very nature, the valve is always in contact with blood; thus, such must be given the utmost attention. As one alternative, devices have also been designed to simply bypass venous valves by holding them open, such as that shown in U.S. Pat. No. 5,843,171. In addition, devices have been constructed to test the operation of both artificial and natural venous valves, such as that shown in U.S. Pat. No. 5,272,909. However, despite the considerable work that has gone into this area, satisfactory solutions have not yet been achieved; thus, the search for more satisfactory prosthetic venous valves has continued. 
     SUMMARY OF THE INVENTION 
     Improved prosthetic venous valves have now been developed which have a two-piece housing arrangement. The two housing pieces are separated from each other but are so associated with the vein of a patient as to confine an occluder or poppet in an operative location. In one preferred embodiment, a generally tubular two-piece housing is made of rigid material and designed to be positioned within the vein in a spaced-apart relationship, separated from each other by a short section of the interior of the vein itself. A first or upstream section of the housing is formed with a seat which is shaped so as to provide a seal when in contact with the occluder or poppet, which has a suitable shape, e.g. that of a sphere; the occluder is confined within the valve housing so it can shift between the interiors of the upstream section and the downstream section of the housing. The downstream section should have an interior surface that cooperates with the occluder so as to prevent the occluder&#39;s escape downstream and position it within the interior of the two-piece valve housing in a way to provide an open discharge pathway for blood to flow through the venous valve in response to pumping. Occluders of several different shapes may be used. 
     The invention also envisions a housing having a more elongated upstream section that confines and generally guides an elongated occluder and that allows a downstream section to be installed exterior of the vein. The invention also envisions the incorporation of a surrounding retainer, such as a wire harness arrangement or a perforated tube or the like that spaces the separate sections of the housing a desired distance apart, which harness arrangement could additionally include detents or splines that would engage the interior surface of the vein and immobilize the prosthetic venous valve at the desired location within the vein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view through a prosthetic venous valve embodying various features of the present invention, showing the ball occluder in closed position in contact with the upstream seat. 
     FIG. 2 is a view similar to FIG. 1 showing the ball occluder in open position. 
     FIG. 3 is a plan view of the valve of FIGS. 1 and 2 with the section line  2 — 2  showing the plane along which FIGS. 1 and 2 are sectioned. 
     FIG. 4 is a view similar to FIGS. 1 and 2 showing the valve installed in the vein of a patient with the occluder at an intermediate location between the closed and fully open positions, depicted in FIGS. 1 and 2, respectively. 
     FIGS. 5 and 6 are sectional views, similar to FIGS. 1 and 2, of an alternative embodiment of a prosthetic venous valve embodying various features of the invention. 
     FIG. 7 is a view similar to FIG. 4 of a slightly modified version of the valve of FIGS. 5 and 6 with the occluder shown in an intermediate position between the closed and fully open position. 
     FIG. 8 is a view similar to FIG. 4 of another prosthetic venous valve embodying various features of the invention, with the body shown in cross-section and the occluder shown in elevation in closed position. 
     FIG. 9 is an elevational view of the occluder shown in FIG. 8 rotated 90° from the orientation therein. 
     FIG. 9A is a perspective view of the valve of FIG. 8 shown in its open position. 
     FIG. 10 is an elevational view of yet another prosthetic venous valve embodying various features of the invention. 
     FIG. 11 is a bottom view of the valve shown in FIG.  10 . 
     FIG. 12 is a fragmentary top view of the valve shown in FIG.  10 . 
     FIG. 13 is a sectional view taken generally along line  13 — 13  shown in FIG. 12 with the occluder shown in the open position and in elevation. 
     FIG. 14 is a view similar to FIG. 13 showing the occluder in section and in the closed position. 
     FIG. 15 is an elevational view of an occluder, enlarged in size, that might be alternatively used in the valve body of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Illustrated in FIG. 1 is a prosthetic venous valve  11  which embodies various features of the present invention. The valve includes separate upstream and downstream housing sections  13 ,  15  and an occluder  17  which is designed to travel back and forth within the interior confines of the separate housing sections. 
     The upstream section  13  is generally tubular in shape, being of circular cross-section and having an entrance end  19  of reduced diameter relative to a main body portion  21 , which provides an interior central region  23  of greater diameter than the occluder  17 . The transition surface between the entrance end portion  19  and the sloping interior wall surface of the central region  23  forms a seat  25  for the ball occluder  17 . When the occluder  17  is in contact with the seat  25 , upstream liquid flow vertically downward (in the orientation shown in FIG. 1) is positively prevented. 
     The downstream housing section  15  is also generally tubular in shape having an interior surface  27  which is generally the shape of a right circular cylinder except for one or more, preferably three, radially extending detents  29 . The diameter of the interior surface  27  is larger than the diameter of the occluder  17  so that blood can always flow freely through the downstream section  15  regardless of the position of the occluder  17 . The detent or detents  29  may generally have the shape of a triangular fin which is thicker at its base than at the tip; they preferably have upstream walls which guide the ball occluder to a central location where it abuts the three detents when there is blood flow in a downstream direction through the valve  11 . As best seen in FIG. 3, the detents  29  extend radially into the interior of the central region of the downstream section of the housing to a sufficient extent to block the passage of the occluder  17  therethrough. As best seen in FIG. 2, when the venous valve  11  is in the open position with downstream flow occurring, which in this instance is radially upward through the valve  11 , the occluder  17  is centered within the central region by contact with the three detents  29  leaving three large open regions between the fins  29  (which are aligned at 120° intervals) through which blood can freely flow. With less than three detents, the occluder might not be centered but will still provide the desired downstream flow passageway. 
     To secure the valve  11  in place within a patient&#39;s vein, a pair of circular ridges  33  are provided on the exterior surface of the downstream section of the housing  15 , one generally adjacent each end, and a similar circular ridge  35  is provided on the exterior surface of the reduced diameter upstream end  19  of the upstream housing section  13 . FIG. 4 depicts the valve  11  in place in the vein of a patient. 
     To install the valve  11 , the surgeon may slit the vein to excise the native valve using a venous valve cutter such as that shown in U.S. Pat. No. 5,601,580. Once the malfunctioning valve has been excised, the prosthetic venous valve  11  can be installed requiring only a minimal slit in the sidewall of the vein because of the two-piece construction. For example, a slit might be made downstream of the defective valve, and after excising it, the upstream section  13  of the housing could first be installed and then secured in place using a surgical tie  39  in the region between the ridge  35  and the outwardly expanding surface of the main body portion  21 , as shown in FIG.  4 . Thereafter, the downstream section  15  which may carry the ball occluder  17 , as generally shown in FIG. 2, would be installed so as to be positioned at the appropriate spaced-apart distance from the upstream section. It is secured in place by two ties  39  positioned inboard of the ridges  33 . 
     The distance between the adjacent central ends of the two housing sections is preferably between about 20 and 35% of the diameter of the spherical occluder  17 . This spacing is preferred for a prosthetic valve  11  wherein the diameter of the interior surface  27  is between about 120% and about 140% of the diameter of the occluder; more preferably, the interior diameter of the downstream section is between about 125% and about 135% of the diameter of the occluder. With such a relationship, the two-piece construction has particular advantages. In addition to facilitating manufacture of the venous valve  11 , the implanted arrangement reduces the amount of contact between blood and the foreign material from which the housing is constructed by providing a short section of natural vein within the interior of the valve itself, thus reducing the pathway created from foreign material into two shorter sections separated by a section of natural vein. Even more importantly, there is provided a certain flexibility which allows some displacement between the two sections of the housing in a direction transverse to the axis through the valve  11 , and this can be an important feature for a venous valve that may be located near the surface of the patient&#39;s leg or the like where flexure to coaxial alignment will likely occur during exercise and/or as a result of other contact with objects outside the body. The three converging upstream walls  31  of the fins  29  always center the ball occluder at the axis in the full open position, and the sloping walls of the interior of the central region  23  of the upstream section likewise smoothly guide the ball to the seat  25 . It can be seen from FIG. 4 that this relationship of the occluder  17  with each of the housing sections  13 ,  15  is independent of the other, and thus the valve will continue to operate even if there should be deflection of one of the housing sections in a transverse direction so that both are momentarily no longer coaxial. 
     The housing sections  13 ,  15  and the occluder  17  can be made of any suitable non-thrombogenic biocompatible material, e.g. titanium, titanium-nickel alloys, dense molded polymeric materials and the like; however, the preferred materials for construction of the valve housing and the occluder are pyrolytic carbon (pyrocarbon) and pyrocarbon-coated graphite. Most preferred is material made from a graphite substrate coated with On-X™ pyrocarbon, which is available from Medical Carbon Research Institute, LLC, of Austin, Tex. and which is described in detail in U.S. Pat. No. 5,514,410, issued May 7, 1996. Because there will not be a large pressure gradient driving the flow of blood through a venous valve when the body is in a supine position, it may be desirable to utilize an occluder  17  which has a density close to the density of human blood. Such an occluder will tend to incur more movement during times of low pressure gradients, minimizing the potential for stasis and possible thrombus formation. 
     Depicted in FIGS. 5 and 6 is an alternative embodiment of a venous valve  43  embodying various features of the invention which it will be recognized as having similarity to the venous valve  11 . The valve  43  has an upstream housing section  45 , a downstream housing section  47  and a ball occluder  49 . The upstream housing section  45  has essentially the same construction as the section  13  depicted in FIG.  1 . It includes an entrance portion  51  of reduced diameter and a main body portion  53  wherein there is a seat  55  for the ball occluder  49 . 
     The downstream housing section  47  has an axial length about twice that of the section  15  with a downstream exit portion  57  of reduced diameter. The downstream housing section functions the same as the downstream section  15 , having a central region  58  with an interior surface  59  from which three triangular fins  61  having diagonally oriented guide edges  63  protrude radially inward and provide three open flow passageways  65 . The extended downstream end  57  of the housing section  47  facilitates securing the venous valve within the vein, and its exterior surface contains a similar circular ridge  67 . A similar circular ridge  69  is provided on the exterior surface of the upstream housing section  45 . The axially extended downstream housing section  47  facilitates smooth interconnection with the vein and smooth flow downstream from the prosthetic valve  43 . 
     Depicted in FIG. 7 is a valve  71  which is the same as the valve  43  except for the inclusion of two additional circular ridges  67   a  and  69   a , and accordingly the other elements are referred to using the same reference numerals as in the valve  43 . The valve  71  incorporates a surrounding retainer which may be in the form of a wire cage  73  that includes a plurality of longitudinally extending strands  75  of radioopaque wire, which extend from end to end, and a plurality of coils  77  at each end, where the wire is wrapped about the reduced diameter entrance and exit ends of the valve in the regions respectively between the circular ridges  67  and  67   a  and  69  and  69   a . Thus, these strands  75  bridge the center gap between the two spaced-apart housing sections  45 ,  47 , uniting the two spaced-apart sections. Other equivalent surrounding retainer structures may alternatively be used. 
     The valve  71 , with the two spaced-apart housing sections  45 ,  47  appropriately assembled and spaced apart from each other within the wire cage  73  provides a device which, for example, might be installed through a thin-walled catheter inserted into the vein from which the malfunctioning valve has been excised. As an option, the wire cage  73  may be formed with a plurality of barbs  79  of spring-like character that can be positioned to lie against the exterior of the housing but, upon release, will extend outwardly to the orientation shown in FIG.  7  and engage the interior surface of the vein. As shown therein, barbs  79  associated with the upstream section  45  extend diagonally downstream and vice-versa. Accordingly, the valve  71  with the illustrated wire cage  73  would reasonably be installed within a thin sheath when transported, as for example within a catheter, to the desired location in the vein of the patient. When the valve is correctly positioned, the sheath is withdrawn, and the barbs  79  spring radially outward and affix the valve  71  within the vein. The wire and the barbs or other surrounding retainer can be made of tantalum, titanium or an appropriate alloy thereof which is biocompatible and preferably radioopaque so that it will be prominently displayed on any x-ray radiograph. Generally, the structure, e.g. wire, should have sufficient thickness or size to resist inadvertent bending so as to maintain desired spacing invivo within a patient. 
     Illustrated in FIG. 8 is another alternative two-piece venous valve  81  which is shown in place in the vein  83  of a patient. The valve  81  differs from those previously described in that its upstream housing section  85  is elongated and its downstream housing section is disposed exterior, rather than interior, of the vein  83 . The elongated upstream section  85  complements an elongated occluder  89 , and the downstream section is in the form of a split collar  87 . The elongated occluder  89  has a generally hemi-spheroidal upstream end  91  and is smoothly reduced in cross-sectional area along its length toward the downstream end; it has a length at least about twice that of its diameter. Its contour is such to create three valleys  92  located between three generally axially extending fins  93 , that are regularly spaced apart from one another at about 120° intervals. Although two or four or more fins might be used, three are preferred. 
     The upstream housing section  85  has an entrance end  95  of reduced diameter and a central cylindrical section having an interior surface  97  of greater diameter than the hemi-spheroidal end  91  of the occluder  89 . The transition surface between the larger diameter interior surface  97  and the reduced diameter entrance end  95  provides a seat  99  against which the hemi-spheroidal upstream end  91  of the occluder is in sealing contact when the valve is in the closed position, as shown in FIG.  8 . The fins  93  may be straight and axially aligned; however, as best seen in FIG. 9, they are preferably curved, e.g. helically oriented, or otherwise oblique to the central axis. The fins  93  have base sections  100  which are of generally constant thickness in order to provide valleys  92  therebetween of relatively large dimension to serve as blood flow passageways, but at their upper ends, the fins are formed with enlarged pad sections  101  of wider dimension for a purpose explained hereinafter. 
     As previously indicated, the downstream section  87  of the housing is of split collar construction and is installed in surrounding relationship to the exterior of the vein. It may be of rigid material, such as a curved split sleeve of pyrocarbon, or it may be of a polymeric material, such as Gortex, that is shaped as desired. In either event, it may be directly sutured in place and/or wrapped about its exterior with gauze and then sutured in place. The collar may be located a desired distance downstream from the upstream section  85  of the valve after it has been secured in location using an appropriate tie  103  or the like, as previously maintained with respect to the valve  11 . 
     In operation, when the patient is standing still, the valve  81  is in the position shown in FIG. 8 with the occluder  89  forced against the seat  99  in the upstream housing section of the valve, thus closing the valve and preventing blood from pooling up in the lower leg and generating excessive pressure. As the leg muscles are moved or tensed, a natural venous pump is activated which pumps toward the heart. The enlarged pad sections  101  near the downstream ends of the three fins  93  contact the interior surface of the vein and halt the occluder at this location, with the blood flowing through the valleys  92  between the three equally spaced-apart fins  93  as depicted in FIG.  9 A. As previously indicated, the fins  93  are preferably obliquely oriented, as best seen in FIG. 9, or helically curved, so that the occluder  89  will have a tendency to rotate slightly about its axis each time it reciprocates between the open and closed position. As a result, the pad sections  101  near the ends of the fins  93  will not hit the exact same locations on the interior surface of the vein located within the upstream end region of the collar  87  each time it opens, but instead there will be essentially uniform contact with the vein surface about the 360° of this collar region over a multitude of valve openings. The materials for construction of the valve  81  may be the same as previously mentioned for the valve  11 . 
     Depicted in FIGS. 10-14 is another alternative embodiment of a venous valve  105  embodying various features of the invention which is slightly elongated in shape as compared to the valve  11 . It includes an upstream housing section  107 , a downstream housing section  109  and an occluder  111 . The upstream housing section  107  has a construction similar to that of the housing section  13  being slightly more elongated in its central section  113  and formed with a similar seat  115 . The downstream housing section  109  can be a duplicate of the upstream section  107  having a similar seat  117 . The occluder  111  is elongated having the overall shape of a right circular cylinder with hemispherical ends from which three diagonal slices have been removed, positioned at 120° intervals. More specifically, the occluder has a hemispherical upstream end  119  that is sized to seal against the seat  115 . The downstream end of the occluder  111  has a partial hemispherical surface in the form of three smooth ridges  121  (as best seen in FIG.  12 ). The three slices that are removed from the theoretical shape provide three planar surfaces  123  that create flow passageways or valleys between the three ridges  121 . 
     In response to pressure gradients, the elongated occluder  111  moves between a closed position illustrated in FIG. 14 where the hemispherical upstream end  119  is in sealing contact with the seat  115  and an open position illustrated in FIG.  13 . In the open position, the three ridges  121  contact the seat  117  at approximate 120° intervals with the blood flowing downstream through the flow passageways provided by the flat surfaces  123 . 
     Illustrated in FIG. 15 is an alternative embodiment of an occluder  125  that might be used in a valve having a pair of upstream and downstream housing sections generally similar to the sections  107 ,  109  wherein the downstream section  109  is slightly elongated. The occluder  125  has a generally torpedo-shaped body  127  with a hemispherical upstream end  129 , with the downstream portion of the body being generally ovoid. The occluder includes three fins  131  which extend radially outward from the ovoid body. The fins  131  have straight, radially outer, guide surfaces  133  with obliquely oriented flat or curved lateral surfaces  135 , and they are arranged at equal intervals about the occluder. The straight surfaces  133  guide and slide against the interior surface of the downstream housing section  109  as the occluder  125  moves between its open and closed positions. The oblique orientation of the fins  131  causes the occluder to rotate about its axis. 
     Although the invention has been described with certain preferred embodiments, which include what is presently considered to be the best modes of carrying out the invention, it should be understood that various changes and modifications that would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention which is defined by the claims appended hereto. For example, although some of the housing sections are shown as generally being secured within the vein by ties that are looped around the vein, it should be understood that other methods as known in this art, for example suturing, could be alternatively employed. Although three fins or detents are generally illustrated, more or less could alternatively be used in any of the valves illustrated. Although there are advantages in having the upstream and downstream sections of the housing spaced apart in its operative environment, it should be recognized that the facing ends of the housing sections could be easily shaped so as to interengage so as to create a continuous valve body in which the occluder would be confined. Instead of the wire cage  73 , an alternative form of a surrounding retainer may be used, e.g. a perforated tube. The disclosures of all U.S. patents mentioned herein are expressly incorporated herein by reference. 
     Particular features of the invention are emphasized in the claims which follow.