Abstract:
The present invention provides an apparatus and method for optimizing flow in an A-V dialysis graft having a selectable constricted section. Electronic pressure and flow sensors in the arterial and venous ends of the graft are electronically coupled to a monitor to detect the arterial and venous environments and change the degree of stenosis to optimize flow. The stenosis or narrowing within the graft creates resistance for the purpose of decreasing the flow rate and pressure at the outflow end. The selectable restricted section may be provided by a balloon or a thin “slit” type valve with flexible leaves to provide the required resistance. The “slit” valve allows access to wires or catheters for the purpose of any type of graft maintenance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-in-Part Patent Application of U.S. Ser. No. 11/457,885, filed Jul. 27, 2006, now U.S. Pat. No. 7,566,317, issued Jul. 28, 2009, and entitled A-V DIALYSIS GRAFT; which is a Continuation-in-Part of U.S. Ser. No. 10/614,450, filed Jul. 7, 2003, entitled A-V DIALYSIS GRAFT CONSTRUCTION, now U.S. Pat. No. 7,108,673, issued Sep. 19, 2006; this application also includes disclosures contained in Provisional U.S. Application Ser. No. 60/829,105, filed Oct. 11, 2006, and entitled A-V DIALYSIS GRAFT; and Provisional U.S. Application Ser. No. 60/865,718, filed Nov. 14, 2006, and entitled A-V DIALYSIS GRAFT. Applicant claims the benefit under Title 35 United States Code §120 of all the above-identified applications, and incorporates them herein by reference in their entireties. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of hemo-dialysis apparatus in general and in particular to an arterial-venous graft having an intra-graft stenosis formed therein. 
     2. Description of Related Art 
     As can be seen by reference to the following U.S. Pat. Nos. 3,826,257; 4,549,879; 4,753,640; 5,713,859; 6,146,414; 6,461,321 and 6,585,762, the prior art is replete with myriad and diverse graft constructions employed for hemo-dialysis procedures. 
     While all of the aforementioned prior art constructions are more or less adequate for the basic purpose and function for which they have been specifically designed, they are uniformly deficient with respect to their failure to provide a simple, efficient, and practical means of forming an artificial intra-graft stenosis to provide increased blood flow resistance, and the associated pressure drop, during those periods when the higher blood flow rates required by hemo-dialysis are not present. 
     As virtually all physicians and health care specialists are aware, the process of hemo-dialysis requires large volumes of blood to be circulated through a filtration device. However, with prior art A-V graft designs having a uniform bore, the continued high velocity and high pressure blood flow into veins creates venous irritation and scarring leading to stenosis and eventual occlusion as well as causing increased cardiac demands. 
     Additionally, current dialysis shunts provide a continuous high flow which bypasses the patient&#39;s normal tissues and directs high pressure blood flow into the normally low pressure veins. This shunt creates what is called in medicine a “steal.” The blood flowing through the shunt bypasses tissues and then returns to the heart. This creates undue, continued stress on the heart and can invoke a situation in which the blood flow to the hand and/or arm is compromised. 
     Stanish, in U.S. Pat. No. 6,585,762 discloses a graft comprising, in the streamwise direction, a diverging portion followed by a lumen of substantially constant diameter, followed by a converging portion. Because the constant diameter lumen portion of the graft has a diameter greater than the ends, the pressure drop across the Stanish graft is minimized. 
     Buselmeier, in U.S. Pat. No. 3,826,257 discloses a converging portion followed by a lumen having a substantially constant diameter, followed by a diverging portion. The hemo-dialysis machine access tubes are located between the converging and diverging portions, in the constant diameter lumen. This arrangement, however, defeats the purpose of the flow restrictions as almost no pressure drop exists between the two ports of the access tubes. Blood will flow through the constant diameter lumen instead of, or in opposing direction to, the dialysis machine. The flow restriction must reside between the dialysis machine&#39;s access tubes to effect the needed pressure drop. 
     As a consequence of the foregoing situation, there has existed a longstanding need among medical personnel for a new and improved A-V stent graft construction having a reduced diameter portion, either of fixed diameter or variable diameter, and the provision of such a construction is the stated objective of the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, the present invention provides an apparatus and method for optimizing flow in an A-V dialysis graft having a selectable constricted section. Electronic pressure and flow sensors in the arterial and venous ends of the graft are electronically coupled to a monitor to detect the arterial and venous environments and change the degree of stenosis to optimize flow. The stenosis or narrowing within the graft creates resistance for the purpose of decreasing the flow rate and pressure at the outflow end. The selectable restricted section may be provided by a balloon or a thin “slit” type valve with flexible leaves to provide the required resistance. The “slit” valve allows access to wires or catheters for the purpose of any type of graft maintenance. The valve could either be manufactured in the graft of selectively attached post manufacturing. 
     As will be explained in greater detail, in a first preferred embodiment, the reduced diameter intermediate portion comprises a gently tapered segment having a cross sectional area that is gradually converging and gradually diverging sections, integral with the tubular member. In a second preferred embodiment, the reduced diameter portion comprises a constricted section being of selectable diameter. 
     In order to provide for a variable diameter flow restriction, a manufactured stenosis or a balloon can be disposed about the inner circumference of the lumen. When deflated, the balloon lies flat against the inner lumen wall. When inflated, the balloon restricts the flow by narrowing the diameter of the lumen. 
     In a third preferred embodiment, flow and pressure sensors, electronically coupled to a monitor, detect the arterial and venous environment and change the degree of stenosis to optimize flow. 
     A fourth embodiment uses a “slit” type valve to provide a selectable restricted section in the graft. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       These and other attributes of the invention will become more clear upon a thorough study of the following description of the best mode for carrying out the invention, particularly when reviewed in conjunction with the drawings, wherein: 
         FIG. 1  is a perspective view of the prior art uniform inside diameter A-V graft construction currently employed in hemo-dialysis procedures; 
         FIG. 2  is a representative perspective view of the A-V graft construction that forms the basis of the present invention; 
         FIG. 2A  is an enlarged detail view of the gradually constricted version of the invention; 
         FIG. 2B  is an enlarged detail view of an abruptly constricted, then gradually expanded version of the invention; 
         FIG. 2C  is an enlarged detail view of a graft using an annular stenosis balloon to provide the stenosis between the dialysis machine access needles; 
         FIG. 3A  is an enlarged detail view of the second embodiment of the invention, showing the annular stenosis balloon used to provide a variable diameter stenosis in a deflated mode; 
         FIG. 3B  is an enlarged detail view of the second embodiment of the invention, showing athe annular stenosis balloon used to provide a variable diameter stenosis in an inflated mode; 
         FIG. 4  is a perspective view of an injection reservoir for inflating and deflating the annular stenosis balloon; 
         FIG. 5  is a side elevation view of the second embodiment with the annular stenosis balloon in its inflated mode; 
         FIG. 6A  is a first view of a syringe being used to inflate the balloon; 
         FIG. 6B  is a second view of a syringe being used to inflate the balloon; 
         FIG. 6C  is a third view of a syringe being used to inflate the balloon; 
         FIG. 7  is a side elevation view of the third embodiment with pressure and flow sensors at the venous end of the graft; 
         FIG. 8  is a side elevation view of the third embodiment with pressure and flow sensors at both the arterial and venous ends of the graft; 
         FIG. 9  is a side elevation view showing a thin slit valve disposed between the arterial and venous ends of the graft; 
         FIG. 10  is a front elevational view showing a slit valve; 
         FIG. 11  is a side elevational view thereof; 
         FIG. 12  is a front elevational view of an alternative slit valve; 
         FIG. 13  is a front elevational view of another alternate slit valve; 
         FIG. 14  is a front elevational view of a valve with a single hole opening; and 
         FIG. 15  is a front elevational view of a valve of a preferred slit valve. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As can be seen by reference to the drawings, and in particular to  FIG. 2 , the improved A-V graft construction that forms the basis of the present invention is designated generally by the reference number  10 . Prior to embarking on a detailed description of the improved graft construction  10 , it would first be advisable to describe the conventional graft construction  11 , currently used as standard equipment in virtually all modern hemo-dialysis procedures. 
     As shown in  FIG. 1 , the prior art graft construction  11  includes an elongated length of hollow polymer tubing  12  having a uniform inside diameter extending from the inlet end  13  to the outlet end  14  wherein, the inlet end  13  defines the arterial anastomosis. 
     In addition, the conventional graft construction  11 , as well as the improved graft construction  10 , are commonly surgically placed within a patient&#39;s upper arm or forearm and connected via access needles  15  to a hemo-dialysis machine that withdraws blood from the arterial end  13  and removes impurities from the blood prior to re-introducing the cleansed blood through the venous end  14 . 
     As was mentioned previously, the hemo-dialysis procedure, requiring abnormally high blood flow rates through the conventional uniform internal diameter graft constructions  11 , and the presence of the conventional graft construction  11 , allows the elevated blood flow rates to continue unsubsided during those periods when the access needles  15  are not connected to the hemo-dialysis machine  100 . 
     As a direct consequence of these elevated blood flow rates, increased cardiac demands are imposed on the heart as blood is bypassed past the distal circulation. Further, the high flow rates results in venous irritation leading to stenosis and occlusion which typically occurs at the venous anastomosis. 
     As a consequence of the foregoing situation, and as shown in  FIG. 2 , the improved graft construction  10  of the present invention includes an elongated length of polymer tubing  12  having an inlet end  13 , and an outlet end  14 , and a reduced diameter intermediate portion  16  (see  FIGS. 2A-2C ) which forms the heart of this invention. 
     In the first preferred embodiment, depicted in  FIG. 2A , the intermediate portion  16  includes a gradually converging segment  16 A and a gradually diverging segment  16 B wherein, the minimum inside diameter of the intermediate portion  16  is equal to or less than ⅔ of the generally uniform inside diameter of the remainder of the length of polymer tubing  12 . The intermediate stenosis  16  necessarily resides between the hemo-dialysis machine access needles  15 . 
     Further, as depicted in  FIG. 2B , this invention also contemplates a version that includes an abruptly crimped segment  210 , selectively disposed upstream or downstream of a gradually diverging or converging segment  16 A,  16 B. 
     In  FIG. 2C , the second embodiment of the improved graft construction  10  is detailed. Here, the polymer tubing  12  is constructed to have a substantially constant diameter throughout. The stenosis  16  is provided by an annular balloon  230  disposed about the inner circumference of the polymer tubing  12 . The annular balloon  230  provides an opportunity to vary the stenosis  16 . It is to be understood that structures other than an annular balloon could be used to provide a variable stenosis. 
     The configuration of the annular stenosis balloon  230  may range from abrupt to smoothly tapering. As with the first embodiment of the improved graft construction  10 , the annular balloon  230  stenosis is positioned between both access needles  15  of the graft as clearly seen in  FIG. 5 . The design intentionally maintains high pressure on the arterial end  13  and lower pressure for the incoming returning blood from the hemo-dialysis machine  100  to the patient at the venous end  14 . 
     The design of the second embodiment of the improved dialysis graft construction  10  is shown in  FIGS. 2C-6C  and utilizes the annular stenosis balloon  230  for adjusting and maintaining the intermediate stenosis  16 . This embodiment of the improved dialysis graft construction  10  comprises four main components: the polymer tubing  12 , the annular stenosis balloon  230 , the injection reservoir  410 , and the catheter  420  connecting the reservoir  410  to the annular stenosis balloon  230 . The injection reservoir  410  and the catheter  420  are detailed in  FIG. 4 . The entire assembly, shown in  FIG. 5 , is placed surgically and remains under a patient&#39;s skin for the life of the device which is the standard of care for current, standard A-V dialysis grafts  11 . 
     As shown in FIGS.  4  and  6 A- 6 C, the injection reservoir  410  communicates with the stenosis balloon  230  by way of a small caliber catheter  420 . The reservoir  410  comprises a puncture resistant outer wall  430  and bottom (not shown), with a puncturable, self-sealing, pressure resistant top  440  as is common with many access ports used today in the healthcare field, as those of ordinary skill know. The reservoir  410  is accessed using a needle  610  and syringe  620  through the reservoir top  440 . The syringe  620  is used to inject fluid into the reservoir  410 , which then travels through the small catheter  420  and under pressure inflates the annular stenosis balloon  230 .  FIGS. 6A-6C  chronicle the inflation procedure. The amount of stenosis created is directly related to a volume of fluid injected. Once the desired stenosis is achieved, the needle  610  is removed from the reservoir top  440 , and the pressure within the reservoir  410 , catheter  420 , and annular stenosis balloon  230  remains, thus maintaining the degree of stenosis. 
     Advantages of the adjustable annular stenosis balloon graft construction  10  are many. A primary advantage is seen when attempting to maintain patency of the graft  10 . For example, if there is intimal hyperplasia (fibrous growth on the walls of the balloon  230 ) the stenosis can become more restrictive, possibly below an optimal range. This problem is evaluated using one or more of several known techniques. The stenosis can then be corrected to again be within the optional range by varying the inflation of the stenosis balloon  230 . Additionally, if an occlusion occurs within the graft  10  for any reason, the annular stenosis balloon  230  can be deflated, as shown in  FIG. 3A , thereby removing the stenosis, and the graft  10  cleared using standard medical techniques. This design feature significantly improves the ability to maintain the graft  10 . Another advantage is: many times following surgical placement of an A-V graft  10 , it is found to have too much of a steal with its associated decreased perfusion to the hand and fingers. When this is detected, the annular balloon  230  can be inflated, as shown in  FIGS. 3B and 6B , until a balance between the flow through the A-V graft  10  and to the hand and fingers is obtained. This may also be important if the patient has a change in cardiac output or blood pressure, changing the overall pressure and flow to the graft  10  and hand. 
       FIG. 7  shows a variation of the present invention where a series of pressure and flow sensors  710  are imbedded in the wall of the venous end of the dialysis graft. These are then connected to a monitor  720  that, when needed, will sense the venous environment and then adjust the balloon inflation level to optimize flow. 
       FIG. 8  shows another variation of the present invention wherein the A-V dialysis graft has flow and pressure sensors  710  at both the arterial and the venous limbs. The sensors  710  detect the variations in flow and then change the degree of stenosis optimizing flow. 
       FIGS. 9-11  show a variation of the present invention where a slit valve  810  is positioned between the arterial and venous ends of the dialysis graft. 
       FIGS. 12-15  show variations in the thin valves  820 ,  830 ,  840  and  850  suitable for creating a central stenosis. 
     Although only an exemplary embodiment of the invention has been described in detail above, those skilled in the art will readily appreciate that many modifications are possible without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. 
     Having thereby described the subject matter of the present invention, it should be apparent that many substitutions, modifications, and variations of the invention are possible in light of the above teachings. It is therefore to be understood that the invention as taught and described herein is only to be limited to the extent of the breadth and scope of the appended claims.