Abstract:
A blood flow conduit includes a first conduit portion defining a first portion of a lumen; and a second conduit portion defining a second portion of a lumen. At least one of the first or second conduit portions may include a tip portion and the other of the first or second conduit portions may include an enlarged area.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/238,391, which was filed Feb. 11, 2014 as the United States National Stage of International Patent Application No. PCT/US2012/050604, filed Aug. 13, 2012, which claims the benefit of priority of U.S. Provisional Application Ser. No. 61/522,401, filed Aug. 11, 2011. 
    
    
     BACKGROUND 
     Counterpulsation is a well-recognized form of mechanical assistance for the heart. It is used in over 100,000 patients worldwide each year and many patients with short term cardiac dysfunction can be saved. Almost all of these patients currently undergo treatment with an Intra Aortic Balloon Pump (IABP) which is composed of a balloon attached to a catheter that resides in the patient&#39;s descending aorta and which is inflated and deflated to improve the heart&#39;s performance. The balloon catheter is usually inserted in a groin artery and the catheter is connected to a console which is placed beside the patient&#39;s bed. The console shuttles a light gas, such as Helium, through the narrow catheter into and out of the balloon. The balloon is timed to empty very quickly as the heart beats, which lowers the pressure inside the aorta and makes it easy for the heart to eject blood. When the heart relaxes, the balloon fills and blood is pushed through the arteries of the heart and the rest of the body. The combination of reduced work for the heart and improved blood flow to the heart have a very salutary effect on cardiac function. 
     Unfortunately for the patient, the catheter is inserted in the groin and he or she must remain supine in bed. This condition cannot be maintained indefinitely as the patient becomes weak from immobility. Also, infection sometimes travels up the catheter and into the blood stream, causing a serious condition. 
     SUMMARY 
     According to one aspect, a blood flow conduit includes a first conduit portion defining a first portion of a lumen and a second conduit portion defining a second portion of a lumen. At least one of the first or second conduit portions may include a tip portion and the other of the first or second conduit portions may include an enlarged area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a patient with a counterpulsation system constructed according to some embodiments. 
         FIG. 2  is a perspective view illustrating a graft element of  FIG. 1  being directed toward an artery for attachment purposes. 
         FIG. 3  is a perspective view similar to  FIG. 2  and illustrating the graft element being sewn to the artery. 
         FIG. 4  is a perspective view similar to  FIGS. 2 and 3 , and further illustrating a blood flow conduit being attached to the graft element. 
         FIG. 5  is a perspective view similar to  FIGS. 2 through 4 , and further illustrating the blood flow conduit attached to the graft element. 
         FIG. 6A  is a cross-sectional view illustrating the blood flow conduit being attached to the graft element. 
         FIG. 6B  is a cross-sectional view illustrating the blood flow conduit attached to the graft element. 
         FIG. 7  is a cross-sectional view of a graft element attached to a blood flow conduit and an artery. 
         FIG. 8  is a cross-sectional view of a graft element attached to a blood flow conduit and an artery. 
         FIG. 9  is a cross-sectional view of a graft element attached to a blood flow conduit and an artery. 
         FIG. 10A  is a disassembled view, in partial cross-section, illustrating the graft element of  FIG. 9  and a blood pump. 
         FIG. 10B  is an assembled view, in partial cross-section, illustrating the graft element of  FIG. 9  and a blood pump. 
     
    
    
     DETAILED DESCRIPTION 
     An alternative form of counterpulsation is shown in  FIG. 1 . Here a pump  10  is implanted in a pacemaker pocket on the patient&#39;s right side. Blood fills the pump  10  on one side and air or other fluid fills a sac or bladder (not shown) on the other side of the pump  10 . An air drive line  12  is tunneled from the pacemaker pocket to a skin exit site  14 , so the entire pump  10  is under the skin and can remain there chronically. After the driveline  12  exits the skin, it is attached to a small air drive unit  16  that controls shuttling of pressurized air in and out of the pump  10 . A void in the pump  10  may be formed with the sac or bladder. The void fills with air as the heart beats (less cardiac work in ejecting blood) and empties to return blood into the circulation (more flow to the patient). The pump  10  is attached to the circulation with a conduit  20 . The conduit  20  shuttles blood between the patient&#39;s circulatory system and the pump  10 . This situation allows a patient to have chronic counterpulsation with full mobility. For a patient with severe and potentially non-reversible cardiac dysfunction, this is a great advantage as it is possible to live a relatively normal life—apart from the need to carry a small battery powered drive console  16 . 
     As described, the blood is shuttled in and out of the pump  10  with a conduit  20  which is connected to the circulation. There are a number of considerations related to implantation and use of this conduit  20 . First, almost every conduit has blood flowing in one direction, but this conduit  20  has blood alternating flow direction two times for each heart beat as the pump  10  fills and empties with each cardiac cycle. This creates a number of important issues which will be described. A second potential difficulty with a conduit in this situation is that it will typically be sewn to the subclavian artery  22  or axillary artery which is located beneath the clavicle and often quite deep, so it is technically difficult for a surgeon to suture the end of the conduit  20  to the artery  22 . 
     The problem of a conduit with bidirectional flow relates to the responses of blood and tissues to the interfaces with synthetic materials and the response is dependent on the direction of blood flow. Many medical devices, such as blood pumps, are connected to the patient&#39;s circulation with artificial graft material such as polyester materials like Dacron® or expanded, porous Teflon® (ePTFE) that will promote tissue or ceil ingrowth. The inside of blood pumps are generally smooth and composed of metals or plastics, When blood flows from a smooth metal or plastic blood pump into a synthetic graft (such as polyester), the interface where the pump meets the conduit (plastic or metal to synthetic graft) is a stable junction and there tends to be little problem when blood flows forward through this junction. 
     Unfortunately, experience has shown that when blood instead flows from a synthetic graft such as polyester into a smooth surfaced blood pump, a deposit of blood elements including platelets and fibrin tends to deposit at the junction of the two materials—principally on the synthetic graft and overhanging the inflow to the pump. These deposits, especially platelets, tend to attract more blood elements and large and often fragile deposits occur at this junction. These deposits can break free from the junction and enter the blood pump and be sent through the patient&#39;s circulation. These deposits can flow anywhere, but if they arrive in an artery to the brain, a stroke can result. For this reason, many successful blood pumps employ a smooth synthetic conduit (such as silicone or urethane) for blood inflow into the pump. 
     The problem with counterpulsation is that blood is flowing in an alternating bi-directional manner. One solution would be to use a smooth silicone or urethane conduit which would create a stable junction between the pump and the conduit where the blood enters into the pump. This solves the problem at the inflow to the pump. However, when a silicone material is anastomosed (sewn) to an artery, the junction develops a heavy deposit of blood material (fibrin and platelets). So merely replacing the inflow conduit with a silicone surface is not satisfactory. It is tempting to merely have a silicone conduit and add a fabric extension, but this merely moves the problem that occurs at the junction of the rough textured surface of the graft and the pump to the junction between the graft and the silicone tube or cannula. 
       FIG. 8  shows one potential solution in a cross-sectional view. The subclavian artery  22  is shown at the top of the figure. A “bubble” or enlarged area  24  of Dacron®, Teflon® or other material is sewn to the artery  22 . A silicone or other smooth material conduit portion  26  is connected to the other side of the enlarged area  24 . Rather than a direct junction, a special interface is created. The smooth silicone surface portion  26  extends with a tip portion  26   a  several millimeters inside the enlarged area  24  of fabric or other material. The walls of the silicone tip portion  26   a  do not contact the fabric or material of the enlarged area or bubble  24 . This avoids a silicone-to-fabric (or smooth-to-rough) point of contact. 
     Heart valves have been constructed with arrangements to avoid tissue ingrowth into the valve by creating an elevation—so that there is not a continuous connection between the fabric surface and the smooth surface. This elevation prevents tissue from growing over into junction point and creating a point where platelets and fibrin are deposited. The use of a small washer of material may also be of use.  FIG. 8  shows a small washer  28  around the base of the tip  26   a  that may help arrest the attachment of blood elements. 
       FIG. 9  shows that this arrangement of the “bubble” or enlarged area  24   a  of graft material is located away from the anastomosis. Specifically, enlarged area  24   a  is coupled to or includes an extension  24   b  that is anastomosed to the artery  22 . Other features may be as described previously. 
       FIGS. 10A and 10B  show a similar arrangement can be made at the junction of the pump  10 . Here, the plastic, metal or other smooth surfaced junction or tip portion  10   a  of the pump  10  is separated from the rough surface of the enlarged graft material by a bubble interface  24   a . An extension  24   b  of the graft material is sewn to the artery  22  ( FIG. 9 ) as previously described. Another extension  24   c  on the opposite end may facilitate connection to the pump interface or tip portion  10   a , along with a suitable connector  28 . The junction or interface  10   a , which serves as an inlet/outlet port that extends into, but does normally not contact, the graft material  24   a  in use. 
     These devices with bubbles or enlargements could be made In one piece. As described previously, the subclavian artery  22  is located fairly deep and the incision is small. So a surgeon who is trying to sew a graft with a bubble or enlargement on it is working in a deep hole. The bubble or enlargement on the end of a graft obscures his view of the artery. It would be useful to avoid this problem and also satisfy the need for maintaining the arrangement where the smooth and rough surfaces are not in direct linear contact. 
     Such a solution is shown in  FIGS. 2 and 3 . Here, a graft element form from material such as described above is sewn to the artery. The graft element  30  has a flange  32  at one end. The element  30  is small and easy to move around, so does not obscure the view of the surgeon.  FIG. 3  shows that it is easy to sew this element  30  around an opening  22   a  on the artery  22 . 
       FIG. 4  shows how a junction between the silicone material portion  26  of the conduit  20  and the graft element  30  is recreated when a rim or flange  34  of sewing material or graft material, for example, of the conduit portion  26  is affixed to the flange  32  on the element  30  previously anastomosed to the artery  22 . 
       FIG. 5  shows how the two flanges  32 ,  34  are sewn together. This is a very easy anastomosis to perform. 
     It will be appreciated that these flanges  32 ,  34  could be joined not just by sutures but by staples, clips, glues, clamps etc. 
       FIG. 6A  shows a side cross sectional view of the two flanges  32 ,  34  coming together. 
       FIG. 6B  shows how the bubble or enlarged connector  30  does not have to be flat—it could be beveled. Also the connector  30  does not have to be a generally spherical bubble as shown elsewhere herein. The key is only that the enlarged area keeps the silicone and graft surfaces (that is, smooth and rough flow surfaces) from direct contact at their junction during use. 
     The bubble or enlarged area  36  is quite useful as it allows the graft to move or “swivel” inside the bubble  36  and still not contact the wall of the bubble  36 . 
       FIG. 6B  also shows clips or staples  38  attaching the connector  30  to the artery  22  and attaching the flanges  32 ,  34  together. 
     The conduit portion  26  does not have to be entirely silicone. It could have any inner core that presents a compatible surface to the exposed blood. For example, the inside could be metal, have a metal spiral reinforcement, etc. It could also have graft material inside like ePTFE or other polyester. 
     The smooth surface does not have to be silicone. This is used as representative of a smooth surface. The surface could be a metal or plastic (such as in the pump connection shown in  FIGS. 10A and 10B .) 
       FIG. 7  shows a bubble or enlarged area  40  constructed by “splitting” the bubble in the middle of the hemisphere. It could be equally possible to form the junction  42  anywhere in this arrangement; the location at the hemisphere is merely an example. 
     Alternatively, a more complete bubble could be created and the silicone cannula could be slipped into a defect at the end to perform the same function. 
     It should be noted that the terms used are basically smooth (silicone, plastics, metals) and rough or textured surfaces (Dacron, Teflon, ePTFE). It is also possible to have a tightly woven or knitted material that is typically called a textile, but could function as a smooth surface. 
     Also, it is possible to create a tightly woven polyester that behaves like a smooth surface. It could be possible to bring a tightly woven sewable graft into direct contact with a silicone surface without an intervening “bubble” or step. 
     It may also be important to prevent these conduits from collapsing as they can be located below the skin and could be crushed by a patient lying on them. Reinforcement of the conduits with plastic or wire spirals or rings can be used here. In addition, extra thicknesses of polymer or plastic could be added make them stronger. 
     While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features discussed herein may be used alone or in any combination depending on the needs and preferences of the user. This has been a description of illustrative aspects and embodiments the present invention, along with the preferred methods of practicing the present invention as currently known.