Abstract:
An access port comprises a housing with a first opening formed therein and a septum mounted within the housing sealing the first opening, the septum including an outer surface covering the first opening and self-sealing after penetration by a needle and an attachment portion for securing the septum to the housing, the attachment portion including a chamfer which, when the septum is mounted within the housing is subject to a force oriented substantially perpendicularly with respect to a plane of the outer surface, the chamfered portion redirecting a portion of the force to compress the outer surface. A septum for an access port comprises an attachment portion adapted to abut a septum seat of the access port and an operative surface adapted to permit penetration by a needle and resealing itself after removal of the needle in combination with a chamfered portion providing a transition between the attachment portion and the operative surface, the chamfered portion re-directing a component of a force applied to the chamfered portion to compress the operative surface.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Medical procedures for the treatment of chronic diseases often require repeated and prolonged access to a patient&#39;s vascular system to inject therapeutic compounds and/or to sample or treat the patient&#39;s blood. Certain procedures are repeated often enough that it is impractical and dangerous to insert and remove the catheter and the needle from the patient&#39;s vein at every session. Many patients are thus fitted with a semi permanent catheter to permit repeated access to the patient&#39;s vascular system.  
         [0002]     Semi-permanently implanted catheters are generally designed to be as small and thin as possible, to simplify the insertion procedure and to reduce discomfort to the patient. Access to such a catheter is typically provided by one or more ports, which are in fluid connection with the catheter and thus with the patient&#39;s vascular system. The port or ports generally have a very thin profile, so they may be implanted in the patient with a minimum of discomfort. In most cases, such a port is implanted subcutaneously, in a pocket formed surgically in the patient&#39;s chest or arm so that it lies just under the skin, in a location that is easily accessible to medical personnel. More specifically, a septum of the port is positioned just under the skin so that therapeutic agents may be injected into the port through the skin and through the surface of the septum.  
         [0003]     Insertion of therapeutic agents into the catheter is typically carried out by injecting the fluid through the septum of the port, using the needle of a syringe or a similar device. The septum includes at least one surface that is capable of resisting damage cause by multiple piercings from the needle, while re-sealing itself after the needle is withdrawn. The service life of such ports is therefore limited by the durability of the septum. After a certain number of punctures, the septum becomes damaged and is no longer able to re-seal itself. Fluids flowing in the catheter, such as blood, can then leak from the septum necessitating replacement of the port and possibly of the entire catheter. This procedure involves surgically opening the subcutaneous pocket, removing the damaged port from the catheter, and reinserting a new port with an undamaged septum. Replacing the port adds considerable expense, inconvenience and discomfort to the procedure and increases the risk of infections and other complications.  
       SUMMARY OF THE INVENTION  
       [0004]     In one aspect, the present invention is directed to an access port comprising a housing with a first opening formed therein and a septum mounted within the housing sealing the first opening, the septum including an outer surface covering the first opening and self-sealing after penetration by a needle and an attachment portion for securing the septum to the housing, the attachment portion including a chamfer which, when the septum is mounted within the housing is subject to a force oriented substantially perpendicularly with respect to a plane of the outer surface, the chamfered portion redirecting a portion of the force to compress the outer surface.  
         [0005]     The present invention is further directed to a septum for an access port comprises an attachment portion adapted to abut a septum seat of the access port and an operative surface adapted to permit penetration by a needle and resealing itself after removal of the needle in combination with a chamfered portion providing a transition between the attachment portion and the operative surface, the chamfered portion re-directing a component of a force applied to the chamfered portion to compress the operative surface.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a diagram showing a perspective view of a injection access port having a septum according to an embodiment of the present invention;  
         [0007]      FIG. 2  is a diagram showing an exploded view of the injection access port shown in  FIG. 1 ;  
         [0008]      FIG. 3  is a side elevation view of the septum according to an exemplary embodiment of the invention;  
         [0009]      FIG. 4  is a side elevation view of the septum according to another embodiment of the invention;  
         [0010]      FIG. 5  is a side elevation view of the septum according to a third embodiment of the invention;  
         [0011]      FIG. 6  is a side elevation view of the septum according to a fourth embodiment of the invention; and  
         [0012]      FIG. 7  is a side elevation view of the septum according to a fifth embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]     The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The invention is related to medical devices used to introduce fluids into a venous catheter. Specifically, the devices according to the invention are used to increase the useful life of venous ports that may be implanted in a patient to interface with an implanted venous catheter. However, those skilled in the art will understand that the present invention is equally applicable to a wide range of applications in which a port with puncturing a self-sealing septum is implanted in the body. For example, although the invention is described for use with a port for the injection of fluids, the port may just as well be used to withdraw fluids with no change in structure.  
         [0014]     As described above, catheters are often semi-permanently implanted to facilitate repeated access to a patient&#39;s vascular system. Such catheters may comprise a flexible elongated portion that extends through tissue to enter a blood vessel or other organ. The proximal end of the catheter may be connected to a port placed subcutaneously (e.g., in the chest or the arm) to provide access to the catheter.  
         [0015]     The port allows fluids (e.g., chemotherapy agents, blood products, nutrients, therapeutic agents etc.) to be introduced into the patient&#39;s vascular system via a syringe or other similar device. The port is a thin element generally connected directly to the catheter through an outlet and having an inlet opening positioned so as to remain substantially flush with the patient&#39;s skin after implantation. When not in use, the inlet opening is sealed to prevent blood and other fluids from leaking from the catheter, and at the same time to prevent contaminants from entering into the catheter. To that end, septa have been used to cover and seal the inlet openings of such ports. Such a septum generally comprises a flexible membrane that overlies the inlet opening and seals it with the material forming the septum being selected for its ability to continue sealing the port even after repeated punctures by a needle. For example, silicone or other elastomeric materials have been used to form such septa.  
         [0016]     In normal use, the septum is punctured with a needle whenever it is necessary to inject a fluid into the port. Over time, the cumulative damage degrades the material forming the septum so that, after being punctured a sufficient number of times, the septum is unable to re-seal itself after withdrawal of the needle. When the septum is still new, the elastic properties of the membrane tend to “bunch up” or push together the edges of the hole left in the membrane by the puncture. As the membrane is used and the number of holes formed therein increases, the amount of elastic membrane material present around new punctures to close the edges thereof decreases until new holes can no longer be fully closed. At this point, leakage through the operative membrane of the septum begins.  
         [0017]     The undesirable result described above is exacerbated if the membrane of the septum is placed under tension as the openings left by punctures are stretched when the membrane is under tension. In addition, tension may tear the membrane around the holes, so that over time the puncture openings become larger and may tear through the membrane. The number of punctures that a septum may withstand depends on the size of the port, the material used, and the size of needles used to inject fluids therethrough. As would be expected, larger needles cause more damage while a larger surface area septum provides more room to spread out the punctures. High quality ports may withstand around 10,000 punctures before replacement is necessitated.  
         [0018]     Exemplary embodiments of a septum according to the present invention improve the durability of the corresponding venous port by reducing degradation of the septum due to large numbers of punctures. As will be described in greater detail, an increase in puncture damage resistance is obtained by applying a compressive force to the septum membrane. The compressive force pushes together the edges of individual puncture holes and assists the elastic properties of the membrane in sealing such holes. According to the present invention, the improvement to the membrane forming the operative surface of the septum allows an increase in the number of punctures that can be withstood by the septum before excessive leakage requires replacement. Thus, the incidence of surgical procedures required to replace the port or the entire catheter is reduced.  
         [0019]      FIGS. 1 and 2  show, respectively, a perspective view and an exploded view of a venous port having a septum according to an embodiment of the present invention. According to the exemplary embodiment, the port  100  is designed to fit subcutaneously in a pocket surgically created in the patient&#39;s chest, arm or other suitable location with a needle piercing membrane facing outward. In this embodiment, the housing of the port  100  is formed of two parts, a base  104  and a cover  102 . For example, the base  104  and the cover  102  may be secured together frictionally or with a mechanical interlocking connection, to prevent separation of the two components after they have been placed within the patient&#39;s body. As would be understood by those skilled in the art, the exact shape of the base  104  and the cover  102  may vary depending on the specific requirements of the port design. Accordingly, the following description is exemplary only and different configurations may be used to achieve the same results as described below.  
         [0020]     The base  104  is designed to form a well  200  into injected into which fluid injected into the port  100  is temporarily collected. The well  200  is in fluid communication with an outlet opening  108  of the port  100 , which in turn leads to a connection with a catheter (not shown). In one exemplary embodiment, a valve  110  may be placed at the opening of the outlet  108  to prevent undesired flow into or out of the catheter. In this exemplary embodiment, the cover  102  comprises a shroud portion  118  designed to form an outer surface of the port  100 , and a top portion  120  defining an inlet opening  202 . The top portion  120  is intended to be flush under the patient&#39;s skin when the device is implanted, so that a needle can enter the opening  202  after piercing the patient&#39;s skin and a septum  106  closing the opening  202 . The shroud portion  118  may be shaped to interlock with the outlet portion  108  of the base  104 , and may have a cutout portion around the outlet opening  108  and the inlet opening  202  is sized to substantially match the size of a septum  106 , so that when the device is assembled, the inlet opening  202  is sealed by the septum  106 .  
         [0021]     The septum  106  comprises a top membrane  112  that acts as the operative surface of the port  100 , through which the therapeutic compounds are injected. The septum  106  may also include an attachment portion  114  to secure the septum  106  in place within the port  100 . In the exemplary embodiment, the attachment portion  114  is an annular element that surrounds a periphery of the top membrane  112  extending outward substantially perpendicularly therefrom. According to the present invention, a chamfer portion  208  provides a transition between the operative surface of the membrane  112 , and the attachment portion  114 . The purpose of the chamfer portion  208  is to apply a compressive force to membrane  112 . In the exemplary embodiment, this force is provided by the compression of the septum  106  between the base  104  and the cover  102  when the port  100  is assembled. The shape and orientation of the chamfer portion  208  re-directs the force applied by the assembled components of the port  100  to the septum  106 , so that a component of that force acts radially inward along the membrane  112 .  
         [0022]     More specifically, the chamfer portion  208  of the septum  106  comprises an annular surface  210  formed on an underside of the septum  106  facing the base  104 . The annular surface  210  is adapted to overlie and abut a septum seat  204  of the base  104 , when the port  100  is assembled. In this manner the septum seat  204  provides an inner support to the chamfer portion  208 . When the port  100  is assembled by securing the cover  102  to the base  104 , the septum  106  is squeezed between those two components. A bottom bearing surface  206  of the cover  102  presses down on the chamfer portion  208 , squeezing it against the septum seat  204 . The inner bearing surface  201  of the cover  102  also applies a force radially inward against the chamfer portion  208 . The shape of the chamfer portion  208  causes a component of the downward force applied thereto by the inner bearing surface to be re-directed radially inward along the surface of the membrane  112  around the periphery thereof, so that a compressive force is applied to the operative surface of the septum  106 . Thus, the chamfer portion  208  gives to the septum a shape similar to that of a top hat.  
         [0023]     As shown in  FIG. 3 , and more clearly illustrated in the enlarged view of the chamfer portion  208 , a force F is applied to the chamfer portion  208  when the base  104  and the cover  102  are assembled, with the septum  106  sandwiched therebetween. Since the surface  116  of the chamfer portion  208  is angled with respect to a direction of the force F, a force component F 1  acting perpendicular to the surface  116  results. The force F 1  can be further divided into horizontal and vertical components to illustrate radially inward component F 2  of the force F 1 . As the force F is applied around the periphery of the surface of the membrane  112 , the force component F 2  is directed radially inwardly around the circumference of the membrane  112  compressing the membrane  112 . As described above, this compressive force acting radially inward on the membrane  112  increases the tolerance of the membrane  112  to puncture damage. In one exemplary embodiment, the chamfer portion  208  comprises a separate angled surface  116  disposed at an angle of approximately 45 degrees to the plane of the operative surface of the membrane  112  and, consequently, to the direction of the force F applied by assembly of the port  100 . (Please provide a range for this angle) Those of skill in the art will understand that different angular orientations may be used to optimize the septum  106  for various applications.  
         [0024]     The combination of a properly shaped chamfer portion of a septum, and of a venous port housing shaped to hold the septum in place thus provides an increased resistance to damage due to punctures through the septum. Although the present exemplary embodiment describes a port housing formed of two separate components, other housing configurations may be successfully used. According to the invention, when a force is applied to the septum by the components of the assembled venous port, the chamfer portion of the septum may be designed to convert a component of that applied force into a compressive force acting radially inward along the operative surface. Different configurations of the port&#39;s housing may thus be devised to apply the proper force to the septum when the port is assembled.  
         [0025]     As will be understood by those of skill in the art, additional shapes of the septum&#39;s chamfer portion may be used. For example,  FIG. 4  shows a septum  400  according to a second embodiment of the invention, where the chamfer portion  408  comprises an angled surface  416  extending directly from a top membrane  412  to an upper surface  418  of an attachment portion  414 . The angle at which the surface  416  is oriented may be selected to produce desired characteristics of the septum. When the upper surface  418  and the lower surface  420  are squeezed between a base and a cover of the corresponding venous port, the angled surface  416  causes a component of the vertical force to be applied radially inward to compress the upper membrane  412 . As described above, the result is an improved ability of the membrane  412  to re-seal puncture holes therethrough after a needle is withdrawn.  
         [0026]     A third exemplary embodiment according to the invention is shown in  FIG. 5 . Here, the transition between an upper membrane  512  of the operative surface and an attachment portion  514  is carried out by a step  516 . The precise characteristics of the step  516  may be developed to obtain a desired compression in the membrane  512 , and to facilitate the assembly of the corresponding venous port. For example, the step  516  may be substantially rectangular, with surfaces at right angles to the top membrane  512 , and to the sides of an attachment portion  514 . In an alternative embodiment, the surfaces of the step  516  may be oriented at different angles, and may not be perpendicular and parallel, respectively, to the top and side surfaces of the septum  500 .  
         [0027]      FIG. 6  shows a side elevation view of a fourth embodiment of a top hat-shaped chamfered septum  600  according to the present invention. In this embodiment, the chamfer portion  608  comprises a curved fillet  616  extending between the top membrane  612  of the operative surface and a surface of the attachment portion  614 . In the exemplary embodiment, the curvature of the fillet  616  has a substantially constant radius, however alternative designs may include variable radii to offer more complex curves. The curved fillet  616  is preferably convex, to facilitate transferring to the top surface  612  a compressive component of the force applied during assembly of the septum  600  in the corresponding port. A curved fillet  616  may offer advantages in durability over chamfer portions having more angular features, since fewer angles and edges which concentrate stresses are present in the design.  
         [0028]     Additional benefits with respect to the useful life of the septum may be obtained by using an oversized septum, in relation to the inlet opening of the venous port. For example, as illustrated in  FIG. 7 , a septum  700  may include an operative surface comprising a top membrane  716 , which has a larger diameter than the underlying inlet opening of the port. As shown in the diagram, the inlet opening of the corresponding venous port may have a diameter “d” which is smaller than the diameter of the top membrane  716 . Thus, when the operative surface of the septum  700  is squeezed into the inlet opening of the port, the side surfaces of the inlet opening of the port will apply a compressive force to the septum  700 . To maximize the useful life of the port, the oversized septum may be fitted with any of the chamfer portions described above, so that a compressive force is applied to the top membrane  716 .  
         [0029]     According to the present invention, the assembly details of the venous port being assembled may dictate some of the design features of the septum. For example, the angle taken by the surfaces of the chamfer portion may vary to match the corresponding surfaces of the port. The various dimensions and orientations of the septum&#39;s surfaces also may vary, in accordance with the size and shape of the port in which the septum is used. Accordingly, great latitude may be used within the general shape of the top hat-shaped septum, according to the present invention, to fit the device in an appropriate venous port. As described above, many shapes of chamfer portions may be used to apply a compressive force to the operative surface of the septum, by re-directing a component of the force applied during port assembly. The materials used in forming the septum, as well as cost and ease of assembly considerations may determine which specific design is selected.  
         [0030]     The present invention has been described with reference to specific embodiments, and more specifically to a septum used in a venous catheter port. However, other embodiments may be devised that are applicable to other medical devices, without departing from the scope of the invention. Accordingly, various modifications and changes may be made to the embodiments, without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive illustrative rather than restrictive sense.