Abstract:
An aortic cannula tip for reintroducing blood into the blood stream via the aorta. The tip creates a soft flame-shaped flow pattern that reduces the chances of dislodging atheromatous or adherent thromba from the inside surfaces of the aorta. A gentle tapered shape allows the tip to penetrate a small incision made in the aorta without causing undo trauma or risk of tearing. The tip includes a circumferential ridge that allows the tip to be rotated and/or pivoted while in the aorta without breaking a seal formed between the ridge and the aortal wall. A secondary port provides access to a second lumen useable to deploy an intraaortic filtration system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/673,939, filed Apr. 21, 2005, whose contents are fully incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     During surgeries where the blood stream is temporarily diverted by cardiopulmonary bypass, the patient&#39;s blood is removed from the body, heated and/or oxygenated, and returned to the body through a device known as an aortic cannula. Because the blood is under pressure, efforts are being made to provide a tip for these cannula devices that introduces the blood into the aorta in a manner that minimizes trauma while maintaining a flow rate sufficient to obtain perfusion. If the stream velocity is too high, there is a risk of dislodging atheromatous or adherent thromba from the inside surfaces of the aorta, thereby producing emboli that can lead to strokes or other complications.  
         [0003]     As the tip is to be inserted into the aorta through an incision, there is a further desire to make the tip as small as possible. However, smaller tips necessarily result in higher exit velocities that damage the blood cells.  
         [0004]     Many efforts have been made at finding an optimal compromise between tip size and exit velocity. By changing the size, shape and location of the exit openings in the tip, the exit velocities can be varied greatly. Makers of other such devices have attempted to distinguish themselves by creating signature spray patterns. However, in order to generate a spray pattern, high velocities must be used even if they are associated with small flow volumes.  
         [0005]     The continuing pursuit of the optimal configuration is indicative that a need continues to exist for an aortic cannula tip that has a small profile, yet delivers adequate quantities of blood into the aorta at a non-traumatic flow rate without damaging the blood.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The aortic cannula tip of the present invention meets the aforementioned needs by incorporating a plurality of openings that disperse the exit velocity of fluid passing therethrough. The openings are constructed and arranged to create specific relief angles that disrupt the flow pattern and soften the peak velocity force of the blood as it exits the cannula tip.  
         [0007]     The flow exits the tip through a plurality of openings that are shaped to create a flame-shaped flow pattern. The fluid flares slightly upon leaving the opening and then collapses upon itself resulting in average exit velocities that are lower than the flow velocities of the individual streams of the aforementioned prior art devices. The result of the configuration is a soft stream that is characterized by a lack of individual spray streams.  
         [0008]     In one embodiment, the flow leaves the tip through five openings, one of which includes the longitudinal axis of the device. The distally tapered tip forces the maximum volume of fluid through this center opening with excess fluid flow being forced out the remaining four side openings. Approximately one third of the fluid exiting the tip passes through the center opening. The flared streams merge together after exiting the tip to create the desired soft stream.  
         [0009]     Additionally, the aortic cannula tip of the present invention contains no exit openings on the top surface thereof. This allows the placement of a secondary component, such as a filter, on the top surface of the tip. By avoiding the placement of exit openings proximate the filter, the blood jet stream will flow away from the filter thereby preventing any emboli trapped in the filter from becoming dislodged. This configuration makes the aortic cannula tip of the present invention ideally suited for use with an intraaortic filtration system such as those shown and described in U.S. Pat. Nos. 6,592,546, 6,589,264, 6,090,097, and 6,231,544, all of which are incorporated by reference herein in their entireties. These systems are filter devices deployed via the arterial cannula to capture debris that may occur from an aortic cross clamp or manipulation of the heart during surgery. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of an embodiment of the device of the present invention;  
         [0011]      FIG. 2  is a side elevation of an embodiment of the device of the present invention;  
         [0012]      FIG. 3  is a sectional view of the device of  FIG. 1  taken along section lines  3 - 3 ;  
         [0013]      FIG. 4  is a sectional view of the device of  FIG. 2  taken along section lines  4 - 4 ;  
         [0014]      FIGS. 5-6  are perspective views of an embodiment of the device of the present invention;  
         [0015]      FIGS. 7-8  are perspective views of an embodiment of the device of the present invention creating a flame-shaped flow pattern;  
         [0016]      FIGS. 9-10  are computer representations of flow patterns exiting a prior art device and the device of the present invention, respectively;  
         [0017]      FIG. 11  illustrates an embodiment of the present invention being used with an intraaortic filtration system.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The present invention pertains to an aortic cannula tip that is attachable to a flexible cannula of a cardiopulmonary bypass circuit; a device used to supply blood back into the aorta during surgery that relies on cardiopulmonary bypass.  FIGS. 1 and 2  show that the aortic cannula tip  10  includes a distal nozzle portion  12  extending distally from a first port  14  and a second port  16 . A ridge  18  extends radially between the distal nozzle portion  12  and the ports  14  and  16 .  
         [0019]     The nozzle portion  12  includes a first lumen  20  in fluid communication with the first port  14 , which attaches to a flexible cannula of a cardiopulmonary bypass circuit (not shown).  FIG. 3  shows that the first lumen  20  is curved to follow the shape of the nozzle portion  12 , which is shaped to allow a surgeon to access the aorta at an angle relatively normal to the exterior surface of the aorta. Once an incision is made in the aorta and the very distal end of the distal nozzle portion  12  has penetrated the incision, the tip  10  is rotated along the bend of the nozzle portion  12  such that the general direction of the flow exiting from the nozzle portion  12  is relatively parallel to the normal flow path through the aorta.  
         [0020]     The nozzle portion  12  has a tapered portion  13  that tapers continually in the distal direction to the very distal tip of the nozzle portion  12 . This tapered portion  13  allows the cannula tip  10  to gently and progressively open the incision in the aorta. The tapered portion  13  thus minimizes trauma and the risk of tearing. The tapered portion  13  also causes the aorta to provide continually increasing resistance as the cannula tip  10  is advanced. The embodiment of the tip  10  depicted in the Figures has a tapered portion  13  that has a 37% reduction in tip size from a proximal side of the tapered portion  13  to the very distal tip.  
         [0021]     Similarly, the first lumen  20  is tapered distally in the nozzle portion  12 , as best shown in  FIGS. 3 and 4 . The lumen  20  carries the blood being pumped back into the aorta. The blood exits the lumen  20  through a plurality of exit openings  22 . The taper of the first lumen  20  causes the blood to accelerate gently until it reaches the openings  22 . The walls  32  of the tip  10  are of relatively constant thickness in order to facilitate a tapered exterior as well as a tapered lumen  20 . The tip  10  is constructed using a rigid material such that the tapers are preserved despite fluid pressures. In other words, the rigid material prevents the first lumen  20  from swelling or straightening when fluid under pressure is introduced into the lumen  20 . Similarly, the thickness of the walls  32  does not change when the tip  10  is subject to fluid pressure.  
         [0022]     As best seen in  FIGS. 5 and 6 , the illustrated embodiment has five exit openings  22 . One of the exit openings, opening  22   a,  wraps around the very distal end of the tip  10 . This opening  22   a  is located such that the longitudinal axis  23  of the central lumen  20  passes through the opening  22   a.  As a result, more blood passes through opening  22   a  than the other openings  22 . Preferably, approximately one third of the blood exiting the tip  10  passes through the central opening  22   a.  The other openings  22  each have longitudinal axes  24  that are roughly parallel to, but offset from, axis  23 . Preferably, the other openings have roughly parallel longitudinal axes  24  that are splayed outwardly less than two degrees from the longitudinal axis  23 . More preferably, the other openings have longitudinally axes  24  that are splayed approximately one degree from the longitudinal axis  23  of the central lumen. The angle between the longitudinal axis  23  of the central lumen and the longitudinal axis  24  of any given opening  22 , may be hereinafter referred to as a “relief angle” and is shown in  FIG. 5  as angle α.  
         [0023]     Referring back to  FIG. 3 , the second port  16  defines a second lumen  26  that leads to an auxiliary opening  28 . The opening  28  is usable for attaching a secondary component, such as a filter ( FIG. 9 ), to the tip  10 . Exemplary filter devices can be found in U.S. Pat. Nos. 6,592,546, 6,589,264, 6,090,097, and 6,231,544 and are discussed in more detail below. The exit opening  22   a  does not extend in the proximal direction as far as the other openings  22  in order to accommodate the introduction of a secondary component without interference between the secondary component and the fluid flow.  
         [0024]     The first port  14  and the second port  16  are constructed and arranged for attachment to an extracorporeal bypass pump ( FIG. 11 ). The first port  14  and second port  16  are separated from the nozzle portion  12  by a ridge  18 . The ridge  18  performs three functions. First, the ridge  18  provides feedback to the user when it contacts the arterial wall. Thus, the user feels resistance and is thus assured that the nozzle portion is fully inserted. Second, the ridge  18  forms a seal against the arterial wall to prevent leakage through the incision. Third, the ridge  18 , being rounded, allows the user to change the angle of the tip without breaking the seal between the aorta and the ridge. Preferably, the first port  14 , second port  16  and the ridge  18  are of unitary construction, as shown in  FIG. 3 . Additionally, the tip  10  has a lumen wall  32  that defines the curve of the tip  10 . In a preferred embodiment, this wall  32  is of substantially uniform thickness.  
         [0025]     In operation, the first port  14  and second port  16  are attached to a flexible cannula, which is used in the extracorporeal bypass circuit. A pump in the circuit sends oxygenated blood through the first port  14  into lumen  20 . The blood follows the curvature of the lumen in the nozzle portion  12 , where the taper of the lumen gently accelerates the blood through the openings  22 .  
         [0026]     The openings  22  are constructed and arranged to create a stream  30  that is flame-shaped when sprayed in open air ( FIGS. 7 and 8 ). The flame-shaped stream  30  is a result of the acceleration of fluid through the tapered lumen  20 , the shape of the openings  22 , and the amount of fluid passing through the central opening  22   a.  Approximately one third of all the fluid passing through the tip  10  passes through the central opening  22   a.  The accelerating fluid finds relief first at the proximal edges of the openings  22 , causing fluid to flare outwardly therefrom. However, because the openings have relief angles that are very small (less than two degrees from the longitudinal axis  23  of the central lumen), the flaring creates low pressure that draws the fluid back to the longitudinal axes  24 . Because approximately one third of the fluid is passing through the central opening  22   a  roughly along the central longitudinal axis  23 , a further strong venturi draw is created toward the center axis  23 , thereby tapering the stream  30 . The collapsing of the flared fluid back toward the central axis  23  also causes turbulence and significantly decreases the fluid velocity peak force. The result is a softer, less traumatizing stream  30 .  
         [0027]     In actual use, the stream enters the aorta, which already has blood flowing through it. Thus, the flame-shaped stream  30  does not maintain a flame-shape due to the turbulence it creates with the surrounding blood. However, the effect the stream has on the surrounding blood helps create the softer flow. Rather than producing radiating spray that impacts the walls of the aortic lumen, the stream draws the surrounding blood into it, thereby protecting the aortic walls from direct impingement. Thus, a softer introduction of blood into the aorta is provided.  
         [0028]     Comparing  FIG. 7  with  FIG. 8 , the flame-shaped flow pattern  30  includes an area  31  (shown in phantom lines) proximate the auxiliary opening  28  lacking flow due to the shape of opening  22   a.  This area allows a filtration system to be deployed without interference from the flow  30 .  
         [0029]     The design of the openings  22  ensures that the velocities of the blood streams through the openings  22  do not decrease until immediately after the fluid has left the aortic cannula tip  10 . Thus, the exit velocities through the openings are high enough to prevent clotting. The tip  10  achieves both reduced fluid velocities in the aorta and increased flow velocities through the openings, where clotting is to be avoided.  
         [0030]     Referring to  FIGS. 9 and 10 , the effect created by the small relief angles of the openings  22  is further illustrated.  FIG. 9  is a computer-generated representation of the flow pattern  50  of a tip having relief angles greater than those of the present invention. The actual tip being omitted from the Figure, the flow  50  begins as a single solid stream  52 , traveling at 36.4 inches/second, and contained within the central lumen of the device. The flow  50  then splays into individual branches  54  as it passes through openings having large relief angles, which direct the flow outwardly. Introduced into an aorta, these branches  54  would impinge on the aortic walls.  FIG. 10 , on the other hand, is a computer-generated representation of the flow pattern  60  of a tip  10  of the present invention, having relief angles of approximately one degree. Again, the tip is omitted from the Figure, which begins with a solid stream  62 , also traveling at 36.4 inches/second, passing through the central lumen of the device. The stream bulges at  64  where the flow exits the openings  22 . However, the small relief angles, and the other aforementioned fluid dynamics created thereby, prevent individual streams from forming. Rather the stream collapses upon itself and maintains the characteristics of a single, soft stream  66 . When the stream collapses upon itself, it draws native fluid inward and mixes with the introduced stream  66 .  
         [0031]      FIG. 11  illustrates the aortic tip  10  being used with an intraaortic filtration system  34 , such as the systems discussed in U.S. Pat. Nos. 6,592,546, 6,589,264, 6,090,097, and 6,231,544. In  FIG. 9 , the aortic tip  10  has been inserted into an aorta  36  in order to deploy the filtration system  34 . The rounded ridge  18  maintains an effective seal against the aorta despite being pivoted. The filtration system includes an introducer  34  and a filter assembly  40 . The introducer passes through the second port  16  into the second lumen  26  and out the auxiliary opening  28 . Due to the absence of openings  22  proximate the auxiliary opening  28 , no interference occurs between the flame-shaped flow  30  and the filter assembly  40 . Also shown is a flexible cannula  42  attached to the first port  14 .  
         [0032]     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.