Abstract:
A graft comprises an inner interior surface defined by a relatively large radius and an outer interior surface defined by a relatively small radius for maintaining laminar flow of blood passing through the graft and thereby substantially reducing cellular proliferation and blood clotting.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part application of application Ser. No. 11/457,044 filed Jul. 12, 2006, currently pending, the entire contents of which are incorporated herein by reference. 
     
     TECHNICAL FIELD 
       [0002]    This invention relates generally to the construction of grafts, and more particularly to an improved graft construction which substantially eliminates cellular proliferation and clotting of blood flowing therethrough. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    In medicine an anastomosis is a point of surgical connection between two tubular structures. Anastomosis commonly refers to a connection made between two blood vessels. Anastomosis also defines the connection made between a blood vessel and a natural or synthetic graft. 
         [0004]      FIG. 1  illustrates a graft G connected between an artery and a vein of a patient P. Other types and kinds of graft placements are well known to those skilled in the art. Regardless of the kind of graft used or where the graft is placed, the function of the graft G is to facilitate withdrawal of blood from the patient P and return of blood to the patient P. It may be desirable to remove and return blood from a patient for any number of reasons, such as for hemodialysis. Those skilled in the art will readily understand the multiple and various reasons for removing blood from, and returning blood to, a patient. 
         [0005]    Heretofore conventional grafts have been circular in cross section. Conventional grafts tend to clog with a proliferation of cells and coagulated blood. When this occurs the graft must be surgically declotted or a new graft must be installed at a different location. Graft declotting and replacement are surgical procedures, meaning that the patient must undergo repeated surgeries simply to assure a flow of blood through the graft adequate to facilitate the specific procedure being performed. 
         [0006]    When blood flows through a conventional graft the portion thereof flowing through the outside portion of the graft flows at a different rate as compared with the flow of blood through the inside portion of the graft thereby resulting in turbulence. It is accepted by the medical community that turbulence within the graft, as documented by doppler ultrasound, predisposes the graft to failure. 
         [0007]    It is theorized that the turbulence within the graft traumatizes the inner wall of the blood vessel at the vessel-graft junction, commonly referred to as the anastamosis. The inner wall of the blood vessel is composed of endothelial cells. In response to this trauma, the endothelial cells proliferate into the lumen of the graft. Proliferation of the endothelium narrows the lumen in the vicinity of the anastamosis thereby increasing the turbulence within the graft and decreasing the blood flow rate within the graft. The increased turbulence results in additional endothelial trauma and subsequent endothelial proliferation. This cumulative process continues until the diminished blood flow within the graft renders the graft unsuitable for use. Without surgical intervention, a blood clot forms throughout the graft due to stagnant blood flow and the patient must have a new graft installed. 
         [0008]    The present invention comprises a graft which substantially reduces turbulence in blood flowing therethrough. Because turbulence is substantially eliminated, stimulation for endothelial proliferation within the graft is markedly reduced and the tendency of blood flowing through the graft of the present invention to clot is markedly reduced. This in turn substantially extends the useful life of the graft which in turn results in a significant reduction in the number of surgeries that the patient must endure during treatment. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    A more complete understanding of the present invention may be had by reference to the following Detailed Description when taken in connection with the accompanying Drawings, wherein: 
           [0010]      FIG. 1  is a diagrammatic illustration of a human arm having a graft installed thereon; 
           [0011]      FIG. 2  is a perspective view illustrating one embodiment of the graft of the present invention; 
           [0012]      FIG. 3  is a sectional view taken along the line  3 - 3  in  FIG. 2  in the direction of the arrows; 
           [0013]      FIG. 4  is a perspective view illustrating an anastomosis utilizing a conventional graft wherein blood is flowing from the graft into a blood vessel; 
           [0014]      FIG. 4A  is a sectional view taken along the line  4 A- 4 A in  FIG. 4  in the direction of the arrows; 
           [0015]      FIG. 5  is a perspective view illustrating an anastomosis utilizing the graft of the present invention wherein blood is flowing from the graft into a blood vessel; 
           [0016]      FIG. 5A  is a sectional view taken along line  5 A- 5 A in  FIG. 5  in the direction of the arrows; 
           [0017]      FIG. 6  is perspective view illustrating an anastomosis utilizing a conventional graft wherein blood is flowing from a blood vessel into the graft; 
           [0018]      FIG. 6A  is a sectional view taken along line  6 A- 6 A in  FIG. 6  in the direction of the arrows; 
           [0019]      FIG. 7  is a perspective view illustrating an anastomosis utilizing the graft of the present invention wherein blood is flowing from a blood vessel into the graft; and 
           [0020]      FIG. 7A  is a sectional view taken along the line  7 A- 7 A in  FIG. 7  in the direction of the arrows. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    An embodiment of the graft of the present invention is illustrated in  FIGS. 2 and 3 . A graft  10  comprising the invention has opposite ends  12  and  14  which are round in cross section. Between the ends  12  and  14  the graft  10  comprises a curved section  16  having the generally D-shaped cross sectional configuration illustrated in  FIG. 3 . The round cross sections comprising the ends  12  and  14  of the graft  10  transition to the generally D-shaped cross sectional configuration illustrated in  FIG. 3  in transition zones  18  and  20 . 
         [0022]    Referring specifically to  FIG. 3 , the radius R 1  defining the inside surface of the graft  10  in the curved section  16  is relatively large as compared with the radius R 2  of the outside surface of the graft  10  in the curved section  16 . The generally D-shaped cross section of the graft  10  in the curved section  16  thereof minimizes the differential in velocities as between the inner interior surface and the outer interior surface of the graft  10  in the curved section  16  thereby minimizing sheer forces and maintaining laminar flow. 
         [0023]    By maintaining laminar flow in blood flowing through the curved section  16  of the graft  10  cellular proliferation and coagulation of the blood is substantially reduced. Reduction in cellular proliferation and coagulation substantially extends the useful life of the graft  10 . This in turn substantially reduces the number of surgeries that will be required during treatment of a patient. 
         [0024]      FIG. 4  illustrates an anastomosis  21  wherein a conventional graft  22  is surgically connected to a blood vessel  23  at a vessel-graft junction  24 . The arrows represent the direction of blood flow through the graft  22  and the blood vessel  23 . In  FIG. 4 , blood is flowing through the graft  22  into the blood vessel  23 . 
         [0025]    Likewise, referring to  FIG. 6 , an anastomosis  33  is shown, wherein a conventional graft  34  is surgically connected to a blood vessel  35  at a vessel-graft junction  36 . The arrows represent the direction of blood flow through the graft  34  and the blood vessel  35 . In  FIG. 6 , blood is flowing through the blood vessel  35  into the graft 
         [0026]    Referring generally to  FIGS. 4A and 6A  in reference to  FIGS. 4 and 6 , the grafts  22  and  34  are circular in cross section. Given this circular cross sectional configuration, the grafts  22  and  34  will tend to clog with a proliferation of cells and coagulated blood. This is because when blood flows through the graft  22  into the blood vessel  23  at the vessel-graft junction  24 , or through the blood vessel  35  into the graft  34  at the vessel-graft junction  36 , the blood flowing through portions  25  and  37  of the vessel-graft junctions  24  and  36  flows at a different rate as compared with the flow of blood through portions  26  and  38  of the vessel-graft junctions  24  and  36 , thereby resulting in turbulence. 
         [0027]    It is accepted by the medical community that turbulence within a graft as documented by doppler ultrasound, predisposes a graft to failure. It is theorized that the turbulence within a graft traumatizes the inner wall of the blood vessel at the vessel-graft junction. 
         [0028]    The inner wall of the blood vessel is composed of endothelial cells. In response to this trauma, the endothelial cells proliferate into the lumen of the graft. Proliferation of the endothelium narrows the lumen in the vicinity of the vessel-graft junction thereby increasing the turbulence within the graft and decreasing the blood flow rate within the graft. The increased turbulence results in additional endothelial trauma and subsequent endothelial proliferation. This cumulative process continues until the diminished blood flow within the graft renders the graft unsuitable for use. When this occurs the graft must be surgically declotted or a new graft must be installed at a different location. Graft declotting and replacement are surgical procedures meaning that a patient must undergo repeated surgeries simply to assure the flow of blood through a graft adequate to facilitate the specific procedure being performed. Without surgical intervention, a blood clot forms throughout the graft due to stagnant blood flow and the patient must have a new graft installed. 
         [0029]    Referring now to  FIG. 5 , an anastomosis  27  is shown. A graft  28  of the present invention is surgically connected to a blood vessel  29  at a vessel-graft junction  30 . The arrows represent the direction of blood flow through the graft  28  and the blood vessel  29 . In  FIG. 5 , blood is flowing through the graft  28  into the blood vessel  29 . 
         [0030]    Likewise, referring to  FIG. 7 , an anastomosis  39  is shown, wherein a graft  41  of the present invention is surgically connected to a blood vessel  42  at a vessel-graft junction  43 . The arrows represent the direction of blood flow through the graft  41  and the blood vessel  42 . In  FIG. 7 , blood is flowing through the blood vessel  42  into the graft  41 . 
         [0031]    The grafts  28  and  41  comprising the invention have ends  46  and  47  respectively, which are round in cross section. Between the ends  46  and  47  the grafts  28  and  41  have the D-shaped cross sectional configuration illustrated in  FIGS. 5A and 7A . The round cross sections comprising the ends  46  and  47  of the grafts  28  and  41  transition to the D-shaped cross sectional configuration illustrated in  FIGS. 5A and 7A  via transition zones. 
         [0032]    Referring to  FIGS. 5A and 7A  in reference to  FIGS. 5 and 7 , the radii R 1  defining the inner interior surfaces of the grafts  28  and  41  in the D-shaped cross section are relatively large as compared with the radii R 2  of the outer interior surfaces of the grafts  28  and  41  in the D-shaped cross section. The generally D-shaped sides of grafts  28  and  41  are oriented so as to coincide with portions  32  and  45  of the vessel-graft junctions  30  and  43  respectively. The generally D-shaped cross sections of the grafts  28  and  41  minimize the differential in velocities at portions  32  and  45  of the vessel-graft junctions  30  and  43  as between portions  31  and  44  of the vessel-graft junctions  30  and  43 , thereby minimizing sheer forces and maintaining laminar flow. 
         [0033]    By maintaining laminar flow in blood flowing through the grafts  28  and  41  cellular proliferation and coagulation of the blood is substantially reduced. Reduction in cellular proliferation and coagulation substantially extends the useful life of the grafts  28  and  41 . This in turn substantially reduces the number of surgeries that will be required during treatment of the patient. 
         [0034]    Referring to  FIGS. 5 and 7 , the angular placement of the grafts  28  and  41  at the vessel-graft junctions  30  and  43  can range from 0 degrees to 180 degrees depending on the specific circumstances. Therefore, it will be necessary to optimize the exact shape of the grafts  28  and  41  at the vessel-graft junctions  30  and  43 , according to the parameters of the specific application, the generally D-shaped configuration of the grafts  28  and  41  being maintained. The graft of the present invention can be made of either natural materials, synthetic materials, or a combination thereof. 
         [0035]    Although preferred embodiments of the invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions of parts and elements without departing from the spirit of the invention.