Abstract:
The invention provides, in various embodiments, devices and methods relating to ex-vivo organ care. In certain embodiments, the invention relates to aortic cannulas for use in perfusion systems to return perfusate to the heart or delivering perfusate from the heart while the organ is sustained ex vivo at physiologic or near-physiologic conditions.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to Application Ser. No. 62/215,825, titled “Aortic Cannula for Ex Vivo Organ Care System,” filed Sep. 9, 2015, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to medical devices and, in particular, aortic cannulas for use in ex vivo organ care systems. Specifically the invention relates to aortic cannulas used to return perfusate to the heart or delivering perfusate from the heart while the organ is sustained ex vivo at physiologic or near-physiologic conditions. 
       BACKGROUND 
       [0003]    Current organ preservation techniques typically involve hypothermic storage of the organ in a chemical perfusate solution on ice. However, uses of conventional approaches results in injuries that increase as a function of the length of time an organ is maintained ex-vivo. These time restrictions limit the number of recipients who can be reached from a given donor site, thereby restricting the recipient pool for a harvested heart. Even within the few hour time limit, the heart may nevertheless be significantly damaged. 
         [0004]    Effective preservation of an ex-vivo organ would also provide numerous other benefits. For instance, prolonged ex-vivo preservation would permit more careful monitoring and functional testing of the harvested organ. This would in turn allow earlier detection and potential repair of defects in the harvested organ, further reducing the likelihood of transplantation failure. The ability to perform simple repairs on the organ would also allow many organs with minor defects to be saved, whereas current transplantation techniques require them to be discarded. In addition, more effective matching between the organ and a particular recipient may be achieved, further reducing the likelihood of eventual organ rejection. 
         [0005]    Improved ex-vivo organ care has been achieved through the use of an ex-vivo organ care system which maintains organs at physiologic or near-physiologic conditions. Not only does the system maintain the organ at physiologic temperatures, but in the case of the heart, the system maintains perfusate flow through the organ. In addition the system measures and monitors electric stimulation in the heart. The ex vivo organ care system where the heart sustained ex vivo at physiologic or near-physiologic conditions are described in application Ser. No. 11/822495 entitled “Systems for monitoring and applying electrical currents in an organ perfusion system,” U.S. Pat. No. 8,304,181 entitled “Method for ex-vivo organ care and for using lactate as an indication of donor organ status,” and U.S. Pat. No. 8,409,846 entitled “Compositions, methods and devices for maintaining an organ,” which are incorporated herein by reference. 
         [0006]    To maintain physiologic or near-physiologic perfusate flow through the heart, the organ must interface with the system via the aorta. This interface is achieved via an aortic cannula. Current aortic cannula designs lead to organ slippage, difficulties in maintaining a liquid tight seal, and damage to the aorta. Often these designs rely solely upon a cable tie in contact with the aorta to tighten the aorta to the aortic cannula. Depending on the size of the aorta and the size of the aortic cannula, there is a risk of laceration due to the cable ties exerting too much tension on aortic tissue, or the risk of leakage if they do not exert sufficient tension. Thus, there exists a need for an aortic cannula that is easy for health care workers to deploy, creates a tight seal with the aorta, reduces aortic slipping, and causes minimal damage to the aorta. 
         [0007]    In view of the foregoing, improved devices for attaching the aorta to the system and methods of use in ex vivo organ care systems are needed. 
       SUMMARY 
       [0008]    In one embodiment the invention includes an aortic cannula for use with an ex vivo organ care system and methods of using the same. One aspect of the invention includes an aortic cannula comprising, a cannula body which further comprises, a fitting adapted to connect to an organ care system, an aorta interface to contact an aorta, and a pivot arm strap operably connected to a pivot mount, wherein the pivot mount allows the pivot arm strap to uniformly contact the aorta to hold the aorta on the aorta interface. In one embodiment, the aortic cannula further comprises a pivot arm connected to the pivot arm strap and to the pivot mount, such that when the pivot arm is moved toward the cannula body by rotation around the pivot mount the pivot arm strap moves away from the cannula body. In another embodiment of the aortic cannula the pivot arm and the pivot arm strap are parts of a single piece. In another embodiment, the aortic cannula comprises a spring which applies pressure to the pivot arm strap to hold the aorta on the aorta interface. In another embodiment of the aortic cannula a dowel pin communicates with the spring to allow the pivot arm to rotate around the dowel pin. In another embodiment of the aortic cannula the pivot arm further comprises a grip pad used to depress the top of the pivot arm. In another embodiment of the aortic cannula the grip pad is textured. In another embodiment of the aortic cannula the grip pad is removable. In another embodiment of the aortic cannula the pivot arm straps further comprise a loop and guide which retain a cable tie around the pivot aim strap. In another embodiment, the aortic cannula further comprises windows sized to normalize the compression exerted on the aorta by the cable tie such that the same amount of pressure will be exerted on the aorta regardless of the size of the pivot arm strap for a given cable tie tension. In another embodiment, the aortic cannula further comprises a connector used to reversibly secure the aortic cannula to an organ chamber. In another embodiment of the aortic cannula the connector is a threaded locking nut. In another embodiment of the aortic cannula the aorta interface is textured. 
         [0009]    One aspect of the invention includes a method of using an aortic cannula to place a heart in fluid communication with an organ care system the method comprising, selecting an aortic cannula sized to fit the aorta of the heart the aortic cannula comprising, a cannula body further comprising, a fitting adapted to connect to an organ care system, an aorta interface to contact an aorta, and a pivot arm strap operably connected to a pivot mount, wherein the pivot mount allows the pivot arm strap to uniformly contact the aorta to hold the aorta on the aorta interface, depressing the pivot arm such that it rotates around the dowel pin and the pivot arm strap moves away from the cannula body, placing the cannula in the aorta, releasing the pivot arm, tightening a cable tie around the pivot arm strap to hold the aorta in place, and inserting the tapered fitting into an organ care system. In one embodiment, the method further comprises the step of suturing surgical felt pledgets on the aorta before placing the aorta on the aortic cannula. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0010]    The following figures depict illustrative embodiments of the invention. 
           [0011]      FIG. 1  illustrates a diagram depicting an aortic cannula in one embodiment. 
           [0012]      FIG. 2 a    illustrates a side view of a cannula body in one embodiment. 
           [0013]      FIG. 2 b    illustrates a side view of a cannula body and a spring pocket according to one embodiment. 
           [0014]      FIG. 2 c    illustrates a side view of a cannula body in one embodiment. 
           [0015]      FIG. 3 a    illustrates one embodiment of a pivot arm. 
           [0016]      FIG. 3 b    illustrates a side view of a pivot arm and strap according to one embodiment. 
           [0017]      FIG. 3 c    illustrates another view of a pivot arm and strap according to one embodiment. 
           [0018]      FIG. 3 d    illustrates another view of a pivot arm and strap according to one embodiment. 
           [0019]      FIG. 3 e    illustrates a top view of a pivot arm and strap according to one embodiment. 
           [0020]      FIG. 4  illustrates a diagram showing the shape of a cannula body texture in one embodiment. 
           [0021]      FIG. 5  illustrates a top view of a pivot mount according to one embodiment. 
           [0022]      FIG. 6  illustrates a tip holder according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Cannula Body 
         [0024]      FIG. 1  is a diagram depicting the aortic cannula  100  in one embodiment. The aortic cannula device  100  comprises a cannula body  114 , a locking nut  102 , and a pivot arm  140 . The cannula body  114  may contain three sub-sections, a tapered fitting  108 , a tapered midsection  130  and an aorta interface  132 . These subsections can be seen in  FIG. 1  as well as in various side views of the cannula body  114  depicted in  FIGS. 2 a -2 b   . In one embodiment, the cannula body  114  is made from injection molded clear polycarbonate. However, one of skill in the art would understand that the cannula body can be made from other types of plastic or any other suitable material. 
         [0025]    One of skill in the art would recognize that the while the shape of the cannula body  114  should be generally cylindrical, the opening need not be perfectly circular. The three sub-sections, tapered fitting  108 , tapered midsection  130 , and aorta interface  132 , may be of different lengths relative to one another. In addition the different subsections may be made from one piece and they may have the same diameter. One of skill in the art would also recognize that the taper angle in the sub-sections, tapered fitting  108 , tapered midsection  130 , and aorta interface  132 , may vary so long as the aorta interface reaches a diameter within the typical range of the diameter of an human aorta. 
         [0026]    One end of the aortic cannula  100  forms tapered fitting  108 . The tapered fitting is sized to couple to a female connector on an organ chamber (not shown) to create a seal. A threaded locking nut  102 , pictured in  FIG. 1 , is used to reversibly secure the aortic cannula  100  to the organ chamber (not shown). In one embodiment, the locking nut  102  has four wings  104  extending from its outer surface that are used for gripping and turning the locking nut  102  in one embodiment the wings  104  are rectangular. One of skill in the art would understand that the wings  104  could be any shape or omitted. The locking nut  102  may have a lip protruding inward from its bottom edge that snaps over locking ridge  110  and into the locking groove  112  on the cannula body  114 . The locking groove  112  and the locking ridge  110  can be seen in  FIG. 1  and  FIGS. 2 a -2 b   . Alternatively, the locking nut  102  may be secured to the cannula body  114  using other mechanisms known to one skilled in the art. Once the locking nut  102  is seated in the locking groove  112 , the aortic cannula  100  is securely fastened to the organ chamber (not shown) by turning the locking nut  102 . Perfusate can be perfused through the cannula into the heart without leaking. One of skill in the art would understand that other designs can be used to attach the aortic cannula  100  to the organ chamber to prevent leakage. 
         [0027]    One of skill in the art would understand that the aortic cannula  100  can be connected to an organ care system or any other tube, device, or path of flow. In addition, one of skill in the art would appreciate that the locking nut  102  may be omitted in embodiments where the male-female connection between the aortic cannula  100  and the organ care system (not shown) is tight enough to prevent leakage. One of skill in the art would also recognize that the locking nut  102  could be replaced with other types of connectors generally used in the art to create a flow path between two tubes. 
         [0028]    The tapered midsection  130  extends from the bottom edge of the tapered fitting  108  to the top edge of the aorta interface  132 . The tapered midsection  130  reaches a final diameter the size of the aorta interface  132 . The tapered midsection  130  helps to ensure smooth fluid flow from the aorta interface  132  to the tapered fitting  108 . The tapered midsection  130  also helps minimize air trap and hemolysis and improve hemodynamics due to the smooth transition in flow path. The tapered midsection  130  has a pivot mount  122  and a spring pocket  106 . The pivot mount  122  and the spring pocket  106  may be integrated with the tapered midsection  130 . In one embodiment, the tapered midsection  130  has two pivot mounts  122  and two spring pockets  106 , shown in  FIGS. 1 and 2   b . The pivot mounts  122  are located on each side of the cannula body  114 . One of ordinary skill in the art would understand that one or more pivot mounts  122  and spring pockets  106  could be used. As shown in  FIG. 5 , in one embodiment the pivot mount  122  has a circular center hole  138  sized to receive a dowel pin  120 . The spring pocket  106  is located on the cannula body  114  and provides a space for a torsional spring (not shown). The dowel pin  120  fits through one side of the center hole  138  on the integrated pivot mount  122 , through the center of the torsional spring in the spring pocket  106 , and through the other side of the center hole  138  on the integrated pivot mount  122 . The torsional spring is oriented in spring pocket  106  such that depressing the pivot arm compresses the spring. One end of the torsional spring rests in the spring end pocket  134  on the thumb pad  116  seen in  FIG. 3 a   . One of ordinary skill in the art would understand that there are various ways to attach the pivot mount  122  to the cannula body  114  that allows the pivot mount  122  to pivot or move so that the aorta can be fit onto the cannula body  114  in operation. In one embodiment, the pivot mount  122  is made from injection molded polycarbonate, acetyl, or any suitable material. 
         [0029]    One of skill in the art would also recognize that the torsional spring could be replaced with other types of spring loading mechanisms or omitted completely. The torsional spring could also be replaced by a molded leaf spring on the pivot arm or on the grip pad. With the use of a molded leaf spring the dowel pin would be omitted and cylindrical bosses on the cannula body  114  or a similar structure could be used to perform the same function. 
         [0030]    The aorta interface  132  is located adjacent the tapered midsection  130 . The aorta interface  132  may be of a constant diameter and sized to fit within the aorta. The diameter of the aorta interface  132  can be between 0.5 and 2 inches. In some embodiments the diameter of the aorta interface  132  can be between 0.75 and 1.125 inches. Preferably, in some embodiments the diameter of the aorta interface is 0.75 inches, 0.875 inches, 1 inch, or 1.125 inches. The aorta interface  132  may be smooth or textured.  FIG. 1  illustrates a texture  128  on the aorta interface  132  to help prevent the aorta from slipping off of the cannula body  114 . In the embodiment shown in  FIG. 1 , the aortic cannula  100  is placed in the aorta so that the aorta does not rise above the end of the texture  128 .  FIG. 4  is a cross sectional view of one embodiment of the texture  128 . The texture  128  may be of any shape. In one embodiment the texture  128  comprises concentric ridges extending around the aorta interface  132  that are sloped at a 45 degree angle on their lower side and are perpendicular to the cannula body  114  on their upper face. This design allows the aorta to slide onto the aorta interface  132  easily, but prevents the aorta from sliding off the aorta interface  132 . Preferably the ridges are about 0.005 inches tall. However, one of skill in the art would understand that the texture features could be of any shape and size to allow the aorta to be situated around the aorta interface  132  and to help hold the aorta in place while minimizing damage to the tissue. In one embodiment, the radial edge of the aortic interface  132  does not have a ridge to minimize trauma to the tissue. Alternatively, one of skill in the art would recognize that a ridge could be designed to minimize tissue trauma and to hold the aorta in place. 
         [0031]    Pivot Arm 
         [0032]    A pivot arm  140  is coupled to the pivot mount  122 .  FIGS. 3 a - e    illustrate different views of a pivot arm and pivot arm strap (discussed below) in one embodiment. The pivot arm  140  allows the device  100  to adjust and grip aortas of different thicknesses. In one embodiment the cannula body  114  includes two pivot arms  140  coupled to two pivot mounts  122  on the cannula body. One of ordinary skill would understand that the number of pivot arms  140  corresponds to the number of pivot mounts  122 . The pivot arm  140  comprises a grip pad  116 , a sliding pivot window  118 , and a strap  124 . The sliding pivot window  118  allows the strap  124  to maintain uniform contact with the aorta through a range of motion. The grip pad  116  can be smooth, or contain features such as molded ridges or other texture to stop the user&#39;s fingers from slipping. The grip pad can be any shape, preferably round. In some embodiments the grip pad  116  may be detachable. In other embodiments a reusable tool that attaches to the pivot arms  140  could be used in place of the grip pads  116 . The dowel pin  120  allows the pivot arm  140  to rotate around the dowel pin  120  when it is actuated. The pivot arm  140  is made from injection molded acetyl or any material with similar properties. One of skill in the art would recognize that while the sliding pivot provides certain advantages over a fixed pivot point, a fixed pivot point could also be used. Some embodiments may include a locking mechanism to hold the pivot arm  140  in an open position. 
         [0033]    Pivot Arm Strap 
         [0034]    The pivot arm strap  124  is coupled to the pivot arm  140 . The pivot arm strap is best seen in  FIGS. 1 and 3 . As shown in  FIG. 1 , in one embodiment the cannula body  114  includes two pivot arm straps  124  coupled to two pivot arms  140 . One of ordinary skill would understand that the number of pivot straps  124  corresponds to the number of pivot arms  140 . The pivot arm strap  124  and the sliding pivot window  118  allow the cannula body  114  to uniformly grip the aorta. The pivot arm strap  124  is designed to be stiff enough to hold the aorta, while maintaining enough flexibility to conform to the aorta and minimize tissue damage. The pivot arm straps  124  are curved. The pivot arm strap  124  optionally has a loop  136  and a guide  142  to retain a cable tie (not shown) around the pivot arm strap  124 . The cable tie is made from a flexible nylon material or material with similar properties. Once the cable tie has been threaded through the loop  136  and slotted in the guide  142 , it is tightened to the desired tension. The amount that the cable tie is tightened is the same for all sizes of cannulas. Windows  126  in the pivot arm strap  124  normalize the pressure exerted on the aorta by altering the surface area of the strap in contact with the aorta. Accordingly, the size of the windows  126  vary depending on the size of the aorta. The size of the windows  126  are calculated so that when the cable tie is tightened, it exerts the same compression on the aorta for every size device  100 . Thus, the compression exerted on the aorta holds it in place without damaging the tissue. One of ordinary skill would understand that alternatively, the cable tie may be tightened to a specific tension for each size of the device  100 . In addition, other mechanisms of clamping to hold the aorta in place could be used in place of the cable tie, for example a hose clamp or a tension strap. Additionally, the pivot arm strap  124  and the windows  126  could be of different shapes and sizes. Alternatively, the windows could be omitted. One of skill in the art would also understand that the pivot arm  140  and the pivot arm strap  124  could be sections of a single piece. In addition, one of skill in the art would understand that the inner surface of the pivot arm strap  124  could be smooth, or textured for additional traction. 
         [0035]    In one embodiment, the aorta is secured to the cannula body. The grip pad  116  is depressed by the user causing the pivot arm  140  to move around the sliding pivot window  118  and to compress torsional spring. The pivot arm  140  rotates around the dowel pin  120  in the sliding pivot window  118  and the pivot arm straps  124  move away from the cannula body  114 , which makes room to place the cannula in the aorta in a preferred manner than if the pivot point were fixed. When the grip pad  116  is released the torsional spring (not shown) exerts pressure on the pivot arm strap  124  and temporarily holds the aorta in place. The straps closes on the aorta and the sliding pivot window  118  allows the pivot point to change in order to compensate for variations in tissue thickness and maintain alignment and concentricity of pivot arm  140  to cannula body  114  through the full range of rotation. This allows the strap  124  to seat uniformly on the aorta. Then, the cable tie is threaded through the loop  136  and between the guide  142 . The cable tie is tightened to a predetermined tension. One of skill in the art would understand that the cable tie could be replaced with other mechanisms for securing the pivot arm straps  124 . In some embodiments the cable tie can come preassembled in the loops  136 . 
         [0036]    Pledgets 
         [0037]    In sonic embodiments, the user may suture surgical felt pledgets on the aorta. The pledgets serve as an additional measure to retain the aorta on the cannula body  114  because the pledgets provide a barrier that does not slide between the pivot arm strap  124  and the cannula body  114 . Four sets of two (one inside, one outside) pledgets are equally spaced around the aorta and sutured. One of skill in the art will recognize that more or fewer pledgets may be used. In one embodiment, the aorta is positioned onto the cannula body  114  so that the pledgets are not directly above a space between the pivot arms  140  to prevent the pledgets from sliding through the space between the two sides of the pivot arm straps  124 . It will be recognized by one of skill in the art that the pledgets may be placed anywhere on the aorta and end up in any orientation with respect to the pivot arm straps. The pledgets may be standard, surgical felt pledgets. Alternatively, they may be injected molded, rigid, elastomeric pledgets made of a high Durometer material, such as silicone, or a similar material. One of skill in the art would understand that the pledgets could be replaced with other materials that attach to the tissue, and that provide an anchor to prevent the device from sliding between the strap and the cannula body or damaging the tissue. Examples of these materials include, but are not limited to, a continuous ring of material that attaches to the tissue or a staple. 
         [0038]    Tip Holder 
         [0039]      FIG. 6  depicts a tip holder  601 . The tip holder  601  is generally cylindrical, though it may have other shapes. The tip holder has a handle  603 . The handle may take any shape that allows a user to hold the tip holder  601 . The tip holder  601  can also have threads  602 . The locking nut  102  can be screwed onto the threads  602 . The tip holder  601  can also have a stopper  604  which protrudes from the tip holder  601  and serves as a stopping point for the locking nut  102 . One of skill in the art would understand that other designs can be used to attach the locking nut to the tip holder. Alternatively, the tip holder may be secured to the aortic cannula  100  using other mechanisms known to one skilled in the art. Once secured, the tip holder can be used to hold the aortic cannula  100  with or without a heart positioned on the aortic cannula  100 . 
       EXAMPLE 1 
       [0040]    The aortic cannula  100  may be used to connect a heart to an organ chamber (not shown). The aortic cannula  100  holds the aorta open and in place and allows perfusate to be perfused through the heart so the heart can be maintained in near physiologic conditions. In one embodiment, to deploy the aortic cannula, the user first selects an aortic cannula  100  that is sized to fit the heart. In one embodiment the aortic cannula  100  may be selected by measuring the aorta. The user depresses the thumb pads  116  on the spring-loaded pivot arms. When the user depresses the grip pads  116 , the pivot arms  140  rotate around the dowel pin  120  within the sliding pivot window  118  and the pivot arm straps  124  move away from the cannula body  114  making room to place the cannula in the aorta. The user can place the cannula in the aorta. Then the user releases the thumb pads allowing the pivot arms  140  to close on the aorta. The pivot arms  140  may be operated at the same time or individually. The pressure created by the torsional springs temporarily holds the aorta in place. The user may adjust the aorta position, if necessary, such that aorta is fully engaged on the cannula body  114 . Next the user places a cable tie through the loops  136  and guides  142  in the pivot arm straps  124 . The user then tightens the cable tie to hold the aorta in place. In some embodiments the cable tie may be tightened using a tool which tightens the cable tie to a predetermined force. The user inserts the tapered fitting  108  into the organ chamber (not shown). Then the user tightens the locking nut  102 . One of skill in the art will recognize that in some embodiments the aortic cannula  100  could first be seated in the organ chamber and then the aorta could be secured to the aortic cannula  100 .