MXPA00006880A - Vascular access port with elongated septum - Google Patents

Abstract

An elongated access port (18) has a needle-impenetrable housing (40) that includes a base (44) with an upstanding encircling sidewall (70) and a cap (42) with a depending encircling skirt (46) for receiving the sidewall (70). An access aperture (130) encircled by a continuous rim (138) of elongated shape extending through the cap (42) may be elliptical, oval, polygonal, or parabolic-ended. A needle-penetrable septum (91, 168, 170, 172, 178, 180, 182, 187, 202, 232) is installed in the access aperture (130) with the periphery (138, 188, 204) of the septum (91, 168, 170, 172, 178, 180, 182, 187, 202, 232) in sealing engagement with the rim (128) of the access aperture (130). Prior to installation, periphery (138, 188, 204) is geometrically proportional to and larger than the access aperture (130). The relative sizes and shapes of the rim (128) and the periphery (138, 188, 204) produce substantially uniform hydrostatic pressure in regions of the installed septum (91, 168, 170, 172, 178, 180, 182, 187, 202, 232) subjectable to needle penetration. Opposite faces (140, 142) of the septum (91, 168, 170, 172, 178, 180, 182, 187, 202, 232) at the periphery (138, 188, 204) are urged together between the cap (42) and the top (120) of the sidewall (70) of the base (44).

Description

PORT OF VASCULAR ACCESS WITH WALL ALARGED DIVIDER DESCRIPTION OF THE INVENTION The present invention relates to vascular access systems and, more specifically, to ports of implantable vascular access for use in such systems. Implantable vascular access systems are used extensively in the medical field to facilitate the performance of recurrent therapeutic tasks within a patient's body. Such a vascular access system generally includes an implantable vascular access port attached to the proximal end of a vascular catheter. A typical vascular access port has an impenetrable needle housing that encloses a fluid reservoir that is accessible from the outside of the access port through a needle-penetrable elastomeric partition wall. The vascular access port also includes an outlet rod which projects from the housing and encloses a fluid passage communicating with the fluid reservoir. The distal end of the catheter is mechanically coupled to the vascular access port in fluid-tight communication with the fluid reservoir used by the outlet rod. The entire system, both the vascular access port and the catheter attached thereto, is implanted in the body of a patient. The distal tip of the catheter is placed in a predetermined location where the therapeutic activity is going to take place. The distal tip of the catheter is either open ended or is provided with a pressure sensitive valve that allows the flow of uni or bidirectional fluid therethrough during the use of the system by medical personnel. Once the vascular access system is implanted, the tip of a hypodermic needle can be used selectively and respectively to access the fluid reservoir of the access port by penetrating the skin at the implantation site for the access port and then advancing through the dividing wall of the access port itself. The syringe associated with the hypodermic needle that is capable of delivering a medication or other fluids within the fluid reservoir. This flow through the exit stem and the vascular access port and through the catheter attached thereto, so that it becomes infused into the patient's body at the distal tip of the catheter. Alternatively, the syringe is capable of sucking the bodily fluids from the vicinity of the distal tip of the catheter by removing such fluids along the catheter, through the outlet shank and the fluid reservoir of the vascular access port, finally to the hypodermic needle inside the syringe.

For the use of an implanted vascular access port to be successful in the long term, the dividing wall of the vascular access port must have specific properties. For example, when the tip of a hypodermic needle penetrates the dividing wall, the material of the dividing wall around the axis of the hypodermic needle should form an effective seal around the outside of that needle. Otherwise, the fluid will escape from the fluid reservoir to the outside of the vascular access port along the exterior of the hypodermic needle axis. This needle sealing feature of the dividing wall of a vascular access port is influenced by several factors, some of which will be explored subsequently. The dividing wall must also impose a predetermined amount of needle retention force on the axis of any hypodermic needle that has penetrated through it. The needle retention force refers to the tendency of a dividing wall to resist the removal from the shaft of any hypodermic needle. Improper needle retention force can allow the tip of the shaft of a hypodermic needle to be inadvertently removed from the dividing wall, even after the tip of the hypodermic needle shaft has penetrated the dividing wall to the fluid reservoir in the vascular access port. This is very painful for the patient and interrupts the therapeutic process. If the removal of the hypodermic syringe is detected, the attention of the medical staff will be necessary, at least to redirect the penetration of the tip of the hypodermic needle through the dividing wall of the vascular access port. If the inadvertent removal of the tip of the hypodermic needle shaft from the dividing wall is not detected, however, the fluids in the syringe associated with the hypodermic needle will not enter the fluid reservoir of the vascular access port when the infusion is made of those fluids. Instead, the fluids will be injected subcutaneously into the bag in which the vascular access port is implanted. The necrosis of the tissue surrounding the implantation bag will occur as a result, complicating the therapeutic activities and requiring frequent removal and reimplantation elsewhere in the complete vascular access system. A fundamental aspect of the needle retention force imposed on the axis of a hypodermic needle through any given partition wall is the degree of force required to cause the tip of that hypodermic needle to advance through the partition wall from the surface. outside to the inside surface of it. This is referred to as the needle penetration force. The needle retention force and the needle penetration force for a given dividing wall are generally identical, although directed in the opposite direction. It is desirable that the amount of needle penetration force that is within a range that facilitates the work of medical personnel. First, the penetration force of the needle for a given partition wall can not be substantial, or the process of access to the fluid reservoir of the vascular access port associated with the tip of the shaft of a hypodermic needle will be difficult for medical personnel and dangerous for the patient. On the other hand, the needle penetration force for a given partition wall must be clearly different and usually greater than the force required to advance the tip of the axis of a hypodermic needle through the patient's tissue at the implantation site for the port. of vascular access. If that is the case, medical personnel who use a hypodermic needle to access the fluid reservoir at a vascular access port will be informed by touch when the tip of the hypodermic needle has actually been found and advanced through the vessel. dividing wall. Such tactile feedback has been reported to be particularly useful.

The sealing effectiveness, the needle retention force and the penetration force of the needle for a given dividing wall are each related in part to the amount and types of forces applied to the dividing wall by the vascular access port housing. in which the dividing wall is installed. While the torsional forces and stresses are occasionally applied to the dividing wall by accommodating the vascular access port on which the dividing wall is installed, it is more common for the forces applied to it by a housing to be directed inwardly. towards the body of the dividing wall. In general, the greater the forces directed inward that are applied to the dividing wall, the greater the sealing effectiveness of the dividing wall around the axis of the hypodermic needle. Likewise, the needle retention force and the needle penetration force imposed on the axis of that hypodermic needle by the dividing wall will be greater. Inwardly directed forces imposed on a partition wall installed by the housing of a vascular access port must, however, not be so large that the penetration of the dividing wall with the tip of a hypodermic needle results in the hollowing of the dividing wall ,. When the tip of the hypodermic needle advances through the dividing wall, cupping occurs if any portion of the dividing wall material is forced into the axis of the hypodermic needle through the opening in the tip of the hypodermic needle. That portion of the dividing wall material forced into a hypodermic needle in this process is effectively removed from the rest of the body of the dividing wall material. The hollowing of the dividing wall produces small particles separated from the dividing wall that likewise enter the fluid that is infused by the vascular access system implanted within the vascular system of the patient. These particles can block the flow of fluid through the exit port of the vascular access port, or if they escape through the exit port of the vascular access port, they can be trapped in the patient's cardiovascular system. In addition, the hollowing of the dividing wall produces small passages through the body of the dividing wall. Occasionally these passages extend completely through the dividing wall, from the outside of it to the fluid reservoir within the vascular access port. The inwardly directed forces imposed on the partition wall installed by the housing of a vascular access port must initially propel the body material of the dividing wall inwardly upon itself to close those passages after the axis of the hypodermic needle is withdrawn from it. However, the continued cupping eventually leads to several forms of failure of the dividing wall which can not be overcome by inwardly directed forces. The continuity of the material of the dividing wall is increasingly compromised, resulting in disintegrated areas of the partition wall matrix. Eventually, spillage of the fluid can be expected through the partition wall from the fluid reservoir in the vascular access port. Once such fluid escapes to the outside of the vascular access port, necrosis of the tissue surrounding the subcutaneous pocket in which the vascular access port was implanted will occur, causing the aforementioned consequences. • Subcutaneous placement of a vascular access port is difficult to accurately predict the cross-sectional location of the dividing wall of that vascular access port that will be penetrated by a hypodermic needle at any given time. The partition wall installed in the vascular access port must therefore exhibit substantially uniform needle seal characteristics, needle retention and needle penetration through the entire area of the dividing wall exposed to needle penetration. In this way, the quality of the interaction between a dividing wall and the axis of a hypodermic penetrating needle will be substantially independent of the location at which the tip of the hypodermic needle actually enters the dividing wall. The desire to produce uniform characteristics of needle sealing, needle retention and needle penetration in a dividing wall have historically indicated that the dividing walls are circular in cross section. Uniform tension may occur in the material of a circular partition wall by an installation of the partition wall - in a circular access opening having an internal diameter that is smaller than the outer periphery of the partition wall. The rim of the access opening then forces the periphery of the dividing wall inwardly in the plane of the partition wall in a shape that is radially uniform around the entire periphery thereof. The use of a round dividing wall produces uniform properties in the installed partition wall however, it has disadvantages. For example, it is desirable for a partition wall to be so installed in the housing of a vascular access port to present at least a minimum amount of exposed needle target area toward the exterior of the vascular access port. This facilitates the location of the dividing wall by palpating the patient's skin at the implant site of the vascular access port. It also reduces the chances that any probe given by the tip of the shaft of a hypodermic needle through the patient's tissue at the site of implantation will completely lose the dividing wall. The loss of the needle target area of the dividing wall of the vascular access port is a painful event for the patient. It is an event that also presents more important risks. If the loss is not detected by the medical staff, the fluids in the associated hypodermic syringe could be injected subcutaneously into the bag in which the vascular access port is implanted, producing consequences already discussed above. A large needle target area in the dividing wall of a vascular access port also decreases the likelihood that the desirable repeated selective penetration of the dividing wall by the tip of a hypodermic needle will inadvertently become concentrated over time in any small region of the dividing wall. The dispersion of the puncture sites over a large needle target area slows down the destructive effects of needle penetration, such as the dividing wall hollowing and therefore contributes to the longevity of the dividing wall. Circular divider walls that exhibit a desired minimum amount of needle target area need vascular access ports that are correspondingly large in each direction parallel to the plane of the dividing wall. Vascular access ports of such a proportion can be implanted only in large areas of tissue correspondingly in the body of a patient, such as in tissue areas in the hip or chest. Occasionally in robust adults, implantation in the upper arm is also possible. The implantation of a vascular access port in those locations is not, however, completely convenient for repeated ongoing therapy. In these locations, reaching the vascular access port with the tip of a hypodermic needle requires that the patient at least be partially undressed and remain that way throughout, the vascular access port being involved in the therapeutic activity. The implantation of vascular access ports in easily accessible portions of the human anatomy such as in the extremities of an adult patient would be preferable. There, a vascular access port easy to locate by palpation and easy to access with the tip of the. shaft of a hypodermic needle. The relatively large dimensions of a vascular access port using a round dividing wall also prevent the use of the vascular access port with small children or infants, since there simply are no large areas of tissue in the bodies of such potential patients. The configuration of a vascular access port to accommodate a round dividing wall also has consequences in relation to the way in which the implantation of the vascular access port should occur. The vascular access ports with round dividing walls are correspondingly relatively wide in each parallel direction of the dividing wall. As a result, relatively large incisions should be made in a patient's skin when the subcutaneous pouch is formed in which the vascular access port will be implanted. The larger the incision, the longer the healing process must be at the implantation site before therapy can begin using the vascular access port. Correspondingly, the potential for infection or other potential is greater. complications Accordingly, it is an object of the present invention to provide an improved vascular access system and to do so in particular by providing an improved vascular access port for use in such systems. Another object of the present invention is to provide a vascular access port having a conventional fluid capacity, although it is capable of insertion through a small incision into a subcutaneous pocket in a patient's body. A further object of the present invention is to provide a vascular access port as described above and can be implanted in minor tissue areas in the body of an adult patient and the particular in the extremities thereof. A related object of the present invention is to provide a vascular access port as described above that can be used with infants and toddlers. On the other hand, it is an object of the present invention to provide a vascular access port as described above in which the hollowing of the dividing wall is reduced to a minimum and in which an acceptably large needle target area is maintained. Still another object of the present invention is to provide a vascular access port that is not limited to the use of a circular dividing wall in order to produce in the installed partition wall the desired characteristics of needle sealing, needle retention and needle penetration. . Still another object of the present invention is to provide vascular access ports of the types described above in which features, such as needle sealing, needle penetration and needle retention in the installed partition wall are uniform through the entire cross section of the dividing wall. The additional objects and advantages of the invention will be set forth in the following description, and in part will be obvious from the description or can be learned by practicing the invention. The objects and advantages of the invention can be realized and obtained by means of the instruments and combinations particularly indicated in the appended claims. In order to achieve the above objects, and in accordance with the invention as presently and extensively described herein, an implantable vascular access port is provided in which an elastomeric, elongated, needle-penetrable partition wall is installed in an impenetrable housing by needle. The housing is formed of a base and a lid interacting cooperatively. The base of the housing has a floor with a continuous circular side wall that rises from it. The side wall ends away from the floor in a dividing wall support wall. The interior space of the base corresponds to the fluid deposit of the access port. The cover of the housing has an upper wall with a skirt that hangs from it. The skirt of the lid is configured to receive the end of the side wall of the base that carries the support wall of the dividing wall. Formed through the upper wall of the lid is an access opening that communicates with the fluid reservoir of the access port, when the side wall of the base is received in the lid. The access opening has an elongated outer periphery defined by a ring circling continuously. By way of example but not limitation, the ring may have an elliptical, oval, polygonal or parabolic termination. There is a dividing wall retaining flange extending radially into the access opening from the rim side of the access opening adjacent the exterior of the vascular access port. The dividing wall retaining flange assumes a parallel, spaced relation towards the dividing wall support shoulder, when the side wall of the base is received in the housing cover. A vascular access port according to the teachings of the present invention also includes a dividing wall that is elongated in a cross section taken in the plane thereof. Therefore, a dividing wall according to the teachings of the present invention may have a periphery in the plane thereof, i.e., by way of example and not limitation, substantially elliptical, substantially oval, substantially polygonal or provided with ends endings that are substantially parabolic.

The natural configuration of a dividing wall will be used to refer to the condition of the dividing wall when the dividing wall is free of forces that are eventually imposed on the dividing wall by the housing within which the dividing wall is to be installed. The cross section of the natural configuration of the dividing wall in the plane thereof is generally more expansive than the access opening into which the dividing wall is to be installed. For optimum characteristics in the installed dividing wall, however, the periphery of the dividing wall in the natural configuration thereof is geometrically proportional substantially to the rim of the access opening. Once the dividing wall is installed in the access opening of a housing of a vascular access port, the periphery of the dividing wall is in a continuous sealed coupling with the rim of the access opening. This is the installed configuration of the dividing wall. In the installed configuration of the dividing wall, the periphery of the dividing wall is displaced radially inwardly in the plane of the dividing wall with respect to the natural configuration thereof by forces imposed on the periphery of the dividing wall by the rim of the dividing wall. the access opening. The periphery of the dividing wall in the natural configuration thereof has a thickness that is greater than the distance between the dividing wall support shoulder and the dividing wall retaining flange, when the side wall of the base is received in the partition wall. housing cover. The dividing wall is placed in the access opening with the periphery of the dividing wall placed between the retaining flange of the dividing wall on the lid and the supporting wall of the dividing wall on the base of the housing. The opposite faces of the periphery of the dividing wall are, as a result, urged towards one another by the retaining flange of the dividing wall and the dividing wall support shoulder when the housing is assembled. Those axial forces on the periphery of the installed dividing wall, in combination with the radially inwardly directed forces imposed by the access opening side, produce a substantially uniform hydrostatic pressure in the region of the installed partition wall that is accessible to the Needle penetration during the use of the implanted access port. This in turn results in needle sealing characteristics, needle retention and needle penetration substantially uniform in the installed configuration of the partition wall. A dividing wall according to the teachings of the present invention includes an external face on the side of the partition wall that faces the outside of the vascular access port housing in the installed condition of the dividing wall and an internal face on the partition wall. side of the opposite dividing wall of the external face. In another aspect of the present invention, the support means are integrally formed with the dividing wall "to prevent folding of the dividing wall in the installed configuration thereof By way of example and not limitation, such support means may understand a target needle dome on the outer face of the dividing wall The objective dome may be smaller in extent than the outer face of the dividing wall Commonly, the objective dome is placed outside the housing of the access port by means of forces imposed on the periphery of the dividing wall in the installed condition thereof An alternative or complementary form of support means -according to the teachings of the present invention may comprise a reinforcement plunger on the inner face of the dividing wall The reinforcement plunger may be smaller in extension than the inner face of the dividing wall., the reinforcing plunger is moved towards the interior of the vascular access port housing by forces imposed on the periphery of the dividing wall in the installed condition thereof. A pair of orthogonal axes can be associated with the dividing wall in the plane of the same. For convenience, these are the longitudinal axes of the dividing wall, which are coincident with the maximum extent of the dividing wall in the plane thereof, and the lateral axis of the dividing wall which coincides with the maximum extension of the dividing wall. the dividing wall in the plane thereof measured perpendicular to the longitudinal axis of the dividing wall. The longitudinal axis of the dividing wall intersects the periphery of the dividing wall at the respective longitudinal ends of the dividing wall and these longitudinal ends of the dividing wall are displaced inwardly from the natural configuration of the dividing wall within the installed configuration of the dividing wall. dividing wall through the first displacements substantially equal to non-zero, which are directed along the longitudinal axis of the dividing wall. Correspondingly, the longitudinal axis of the dividing wall intersects the periphery of the dividing wall at respective medial ends thereof. The medial ends of the partition wall are displaced inwardly from the natural configuration of the partition wall within the installed configuration thereof by second displacements substantially equal to non-zero which are directed along the lateral axis of the partition wall. The periphery of the dividing wall and the rim of the access opening in which the dividing wall is installed are configured such that the combination ratio of the first displacements in the distance between the longitudinal ends of the dividing wall in the natural configuration of the dividing wall is equal to the ratio of the combination of the second displacements to the distance between the middle ends of the dividing wall in the natural configuration of the dividing wall The relation of the combination of the first displacements to the distance between the longitudinal ends of the dividing wall in the natural configuration thereof is, however, equal to the stress imposed along the longitudinal access of the dividing wall in the installed configuration of the dividing wall. the combination of the second displacements to the distance between the medial ends of the dividing wall in the natural configuration thereof it is equal to the tension along the middle axis of the dividing wall in the installed configuration of the dividing wall. Therefore, the installation of a dividing wall in an access opening according to the teachings of the present invention, the tension along the longitudinal axis of the dividing wall is preferably equal to the tension along the lateral axis of the dividing wall. the dividing wall. Alternatively, the distance between a first pair of points on the periphery of the dividing wall that are placed on the longitudinal axis of the barreara are reduced in the installed configuration of the dividing wall relative to the natural configuration of the barreara by a first distance Of compression. Correspondingly, the distance between a second pair of points on the periphery of the dividing wall placed on the lateral axis thereof is reduced in the installed configuration relative to the natural configuration of a second compression distance. • In accordance with the teachings of the present invention, the ratio of the first compression distance to the distance between the first pairs of points in the natural condition of the dividing wall is equal to the ratio of the second compression distance to the distance between the second pair of points in the natural condition of the dividing wall.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the manner in which the above citations and other advantages and objects of the invention are obtained, a more particular description of the invention briefly described above will be converted by reference to a specific embodiment thereof. which is illustrated in the attached drawings. Understanding that those drawings illustrate only a typical embodiment of the invention and are therefore not considered as limiting their scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: Figure 1 is a perspective view of an implantable vascular access system including a vascular access port incorporating the teachings of the present invention attached to a vascular catheter and implanted in the body of a patient; Figure 2 is an enlarged perspective view of the vascular access port of Figure 1 and the portion of the catheter immediately attached thereto; Figure 3 is an exploded perspective view of the components of the vascular access port of Figure 2 with the catheter disassembled therefrom; . Figure 4 is a cross-section elevation view of the lid of Figure 3 taken along section line 4-4 shown herein; Figure 5 is a cross-sectional elevation view of the base of Figure 3 taken along section line 5-5 shown therein; Figure 6 is an elevation view in cross section of the base of Figure 5 received in the lid of Figure 4; "Figure 7 is a cross-section elevation view of the natural configuration of the non-installed partition wall of Figure 3 taken along the section line 7-7 shown therein, which coincides with the longitudinal axis of the dividing wall, Figure 8 is a cross-sectional elevation view of the assembled vascular access port of Figure 2 taken along section line 8-8 shown therein, Figure 9 is a diagram containing views in comparative plan superimposed on a common coordinate axis of a dividing wall incorporating the teachings of the present invention, first in a natural condition thereof free of forces imposed externally and shown in shading, and secondly in a condition not installed thereof shown in solid line with the outer periphery displaced radially inwardly, as when disposed in the vascular access port in Figures 2 and 8; Figure 10 is a perspective view of a quadrant of a virtual dividing wall incorporating the teachings of the present invention in the natural configuration of the mass superimposed by a finite element mesh; Figure 11 is a perspective view of the quadrant of the virtual partition wall and the associated finite element mesh of Figure 10 showing gradients of hydrostatic pressure produced therein by application along the longitudinal and lateral axes of the virtual dividing wall of a radially inwardly directed tension of 6.4 percent; Figure 12 is a perspective view of a quadrant diagram of the virtual partition wall and the associated finite element mesh of Figure 10 showing gradients of hydrostatic pressure produced therein by application along the longitudinal axes and side of the virtual partition wall of a radially inwardly directed tension of 6.4 percent in addition to the application to the periphery of a virtual partition wall of an 8 percent axial compression; Figure 13 is a diagram containing comparative elevation profile views superimposed on a common axis of symmetry of the dividing wall of Figure 3 in the natural configuration thereof shown in shading and in the installed configuration thereof shown in FIG. solid line; Figure 14 is a comparative plan view of a first elliptical divider wall family of identical length incorporating the teachings of the present invention and exhibiting different configurations; Figure 15 is a comparative plan view of a second family of elliptical divider walls of identical width incorporating the teachings of the present invention and exhibiting different configurations; Figure 16 is a comparative plan view of a completely elliptical dividing wall in dotted line superimposed on the plan view of an oval partition wall incorporating the teachings and deriving the benefits of the present invention; Figure 17 is a comparative plan view of a completely elliptical dividing wall in dotted line superimposed on the plan view of a solid dividing wall having parabolic ends that incorporate the teachings and obtain the benefits of the present invention; and Figure 18 is a comparative plan view of a completely elliptical partition wall in dotted lines superimposed on the plan view of a solid line dividing wall having a polygonal periphery incorporating the teachings and deriving the benefits of the present invention.

In Figure 1, a patient 10 is shown to have a chest 12, a right arm 14 and a forearm 15 associated therewith. A vein 16 extends from the forearm 15 through the arm 14 and into the chest 12. Implanted subcutaneously on the forearm 15 of the patient 10 is a modality of a vascular access port 18 that incorporates the teachings of the present invention. Also implanted with the vascular access port 18 is an elongate foldable vascular catheter 20 which is coupled at a proximal end 22 thereof to the vascular access port 18. The catheter 20 enters the vein 16 in the vicinity of the vascular access port. 18 and extends into the vein 16 from the forearm 15 through the arm 14 and into the chest 12 of the patient 10. The distal end 24 of the catheter 20 has advanced through the vein 16 to a desired location within the chest 12 of patient 10 near the heart of it. The distal end 24 and the catheter 20 is open, or is provided with a pressure sensitive valve to allow fluid flow in one or two directions therethrough according to the intended use of the vascular access port 18 and the catheter 20. The combination of vascular access port 18 and catheter 20 is therefore capable of functioning as a vascular access system. By virtue of the configuration of the vascular access port 18, however, that component of the vascular access system is susceptible to implantation in small areas of tissue in the body of the patient 10 such as in the forearm 15 thereof. This capacity of the vascular access port 18 is related not to a reduction in the overall volume occupied by the vascular access port 18, but rather to the configuration of that volume in a vascular access port in accordance with the teachings of the present invention This configuration in the vascular access port is a primary consequence of the space of the elastomeric partition wall installed therein For the same reasons, the vascular access port 18 can be used as a component of a vascular access system that It will benefit young children and infants A needle 26 of a hypodermic syringe 28 is used to deliver the drug transcutaneously into the fluid reservoir at the vascular access port 18. The medicament flows through the catheter 20 and is discharged into the body of patient 10 at a distal end 24 of catheter 20. Alternatively, once the tip of needle 26 is received In the fluid reservoir of the vascular access port 18, the hypodermic syringe 28 can be used to aspirate the body fluid samples from the vicinity of the distal end 24 of the catheter 20. Those body fluids are withdrawn into and out of the catheter 20 toward the fluid reservoir in the access port 18 and from there through the needle 26 inside the hypodermic syringe 28. As illustrated in Figure 2, the vascular access port 18 includes an impenetrable needle housing 40 enclosing a fluid reservoir not visible in Figure 2. A partition wall penetrable by elastomeric needle 91 allows repeated selective access to the fluid reservoir in the housing 40 when it is penetrated by the needle tip of a hypodermic syringe such as the hypodermic syringe 28 shown in Figure 1. The portion of the dividing wall 91 exposed to the outside-of the vascular access port 18 is referred to as the target area of needle of dividing wall 91. As shown in Figure 2, the objective needle area of dividing wall 91 has a maximum extension, or length Lt, or a width t measured perpendicular to the length Lt thereof. The target area of the needle of the dividing wall 91, therefore has a generally elongated configuration. As used herein in relation to any structure, the term "elongated" is intended to refer to that corresponding structure having the general dimensions, measured in orthogonal directions that are not equal.

For example, as shown in Figure 2, the vascular access port 18 has a maximum extension or length LA, between a proximal end 30 and an opposite distant end 32 to which the proximal end 22 of the catheter 20 is attached. The length LA of the vascular access port 18 between the proximal end 30 and the distal end 32 thereof is greater than the width WA of the vascular access port 18 measured perpendicular to the length LA thereof. Accordingly, the access port 18 is also elongated within the meaning of that term intended herein. The degree of elongation in different structures can be compared using several normalization parameters that are derivable for a given structure from the length and width thereof. A first parameter is the aspect ratio. The aspect ratio of a structure is the ratio of the length of the structure divided by the width of the structure. A structure that lacks elongation has a width equal to the length of it. Therefore, the aspect ratio of a structure that lacks elongation is equal to 1.00, and all elongated structures have aspect ratios that are greater than 1.00. The higher aspect ratios reflect more extreme degrees of elongation.

A second parameter of elongation is the eccentricity. The eccentricity E of an elongated structure of length L and width is determined from the following equation: a structure that lacks elongation has a width equal to the length L thereof. Therefore, the eccentricity of a structure that lacks elongation is equal to zero. All elongated structures have eccentricities that are greater than zero and less than 1.00. The larger eccentricities reflect more extreme degrees of elongation. A better appreciation of the internal structure of the vascular access port 18 can be obtained by reference to Figure 3 which is an exploded perspective view of the elements thereof. As illustrated herein, the housing 40 includes an elongated lid 42 and a corresponding elongate base 44. The lid 42 is a cup-like structure comprising an upper wall 56 and a skirt 46 that depends therefrom and that terminates in the interior. a suture rim 54. As illustrated in Figure 3, the skirt 46 continuously surrounds the top wall 56 of the lid 42. However, the appropriate discontinuous non-surrounding structures attached to or depending on the top wall 56 could be in a configuration complementary to the base 44 function with the same efficiency as the skirt 46 in the vascular access port 18. The outer surface 48 and the inner surface 58 of the cover 42 are joined in a suture rim 54. The inner surface 58 of the lid 42 forms the dividing wall of a receiving chamber 60 shown for greater advantage in Figure 4. The receiving chamber 60 is adapted to fit closely into the base 44, the other c omponent of the housing 40 in the manner illustrated in Figure 6. The receiving chamber 60 opens outwardly for that purpose to the outside of the lid 42 at a box assembly inlet 61 which is also shown for best advantage in Figure 4. The assembly inlet 61 is substantially surrounded by the suture rim 54. An elongated lens aperture 59 is formed through the top wall 56 of the cap 42 towards the receiving chamber 60. The cap 42 has a proximal end 50 and an opposite distant end 52 in which a U-shaped rod groove 62 is formed through the suture rim 54 and the skirt 46. A plurality of circumferentially spaced suture channels 64 on the outer surface 48 of the lid 42 are extends from the upper wall 56 towards the suture rim 54. There, the suture rim 54, is provided in each case with a respective suture hole 66. The suture holes 66 are used to secure the port of vascular access 18 in a subcutaneous implant bag. The base 44 of the housing 40 includes a floor 68 and a continuous surrounding side wall 70 that rises therefrom. As will be understood more clearly by reference to Figure 5, the interior surface 76 of the housing 44 includes the floor and walls of a fluid reservoir 78 of the vascular access port 18 that is formed inside the base 44. The base 44 has a proximal end 72 and a distal end 74 from from which is projected a rod housing 80 of U-shaped cross-section. As best seen in Figure 5, a passage 82 extends longitudinally through the rod housing 80 to the fluid reservoir 78. rod 80 is received in the rod groove 62 of the lid 42, when the side wall 70 of the base 44 is engaged in the receiving chamber 60 of the lid 42 in the manner shown in Figure 6. The vascular access port 18 it also includes a substantially cylindrical outlet rod 84 shown in perspective in Figure 3 including a proximal end 86 that is configured to be received within the passage 82 in the rod housing 80. The distal end 88 d the outlet rod 84 is used to couple the vascular access port 18 with the catheter 20. It is possible in contrast to fabricate the base 44 of the housing 40 with an outlet rod, such as the output rod 84 which is integrally formed with the same. A passage 90 extends longitudinally through the exit rod 84 from the proximal end 86 to the distal end 88 thereof. As a result, the passage 90 communicates with the fluid reservoir 78 when the proximal end 86 of the output rod 84 is received in the passage 82 of the rod housing 80. Such a view of the structures described can be better derived from the Figure 8. The receiving chamber 60 in the cover 42 is configured to surround the end of the side wall 70 of the base 44 away from the floor 68 thereof. By assembling the cover 42 and the base 44 in this manner, the base 44 enters the receiving chamber through the assembly inlet 61 and advances into the mass up to the suture rim 54 on the cover 42 is rinsed with the outer surface 69 of base floor 68. The stem housing 80 is received in the rod groove 62, so that the outlet rod 84 projects outwardly from the assembly. The objective aperture 59 then allows communication between the exterior of the housing 40 and the fluid reservoir 78 therein.

The lid 42, the base 44 and the outlet rod 84 can each be made from a medical grade plastic. In the alternative, each can be fabricated from other impenetrable needle materials, such as metals to ceramics or composites. The cover 42, the base 44 and the rod 84 can be individually made from different materials if desired. Figure 3 also illustrates the final component of the vascular access port 18, a partition wall penetrable by an elastomeric needle. As illustrated in Figure 3, the partition wall 91 is a substantially long structure with an outer periphery 138. In a cross section of the partition wall 91 taken in the plane P thereof, the periphery 138 of the partition wall 91 is substantially elliptical. However, other configurations for the periphery of an elongated partition wall such as partition wall 91 are within the scope of the present invention and will be described with reference to subsequent figures. The partition wall 91 has a central axis Ac that is perpendicular to the plane P and passes through the center 164 of the upper surface of the partition wall 91. When installed in a vascular access port 18, the partition wall 91 is placed between the base 44 and the cover 42. As a result, the partition wall 91 seals the objective aperture 59, although the partition wall 91 nevertheless permits repeated selective access to the fluid reservoir 78 via the shaft tip of a hypodermic needle that it is advanced penetratingly through the partition wall 91. The partition wall 91 is made of a medical grade silicone or other comparable materials having a Shore "A" durometer on a scale from about 28 to about 85. More preferably the Shore durometer "A" of the material of the partition wall 91 is on a scale from about 35 to about 75 and more preferably on a scale from about 45 to about 65. The internal characteristics of housing components 44 will be discussed in more detail below. As illustrated in Figure 4, the skirt 46 of the lid 42 has an inner surface 92 that extends between an upper end 94 and a lower end 96 thereof. Except in the rod groove 62 formed therethrough, the skirt 46 surrounds the receiving chamber 60. Shaped at the lower end 96 of the skirt 46 is an alignment groove 106. The alignment groove 106 is substantially continuous in the illustrated embodiment , being interrupted in the rod groove 62, but the alignment groove 106 can be configured in another way, provided that the corresponding structures on the base 44 are appropriately modified in a complementary manner. Projecting radially inwardly from the inner surface 92 at the upper end 94 thereof, is a continuous dividing wall retaining flange 98. The dividing wall retaining flange 98 terminates in a free internal surface 100 that surrounds the objective aperture. 59 in a continuous way. Extending between the inner surface 92 of the skirt 46 and the inner surface 100 of the dividing wall retaining flange 98 is a bng surface 102 that is continuous in the illustrated embodiment. A first clamping flange 104 projects from the bng surface 102 normal thereto at a location adjacent to the internal surface 100 of the retaining flange of the partition wall 98. The first clamping flange .104 is continuous in the embodiment of vascular access port 18 illustrated. As illustrated in Figure 5, the side wall 70 of the base 44 has an outer surface 118 and an inner surface 116 surrounding the fluid reservoir 78. Extending radially outwardly from the outer surface 118 of the side wall 70 in the floor 68 is an alignment shoulder 124 that is substantially continuous in the illustrated embodiment, which is interrupted by the rod housing 80. The alignment shoulder 124 may be configured in another manner, provided that the corresponding structures on the lid 42 are suitably modified in a complementary manner. The side wall 70 of the base 44 extends from the floor 68 to a free dividing wall support shoulder 120 that is continuous in the illustrated embodiment. Irrigating from the dividing wall support shoulder 120 adjacent the inner surface 116 of the side wall is a second holding flange 122 which is also continuous in the illustrated embodiment. • Figure 6 illustrates the relationship between the structures of the lid 42 and the base 44, when the base 44 is received in the lid 42. The side wall 70 of the base 44 is configured to tightly fit within the receiving chamber 60 the cover 42 with the alignment shoulder 124 on the base 44 which fits in the alignment slot 106 on the cover 42. The support surface 102 of the partition wall retaining flange 98 is, as a result, placed in spaced parallel relation to the shoulder of dividing wall support 120, separated therefrom by a distance D. The portion of the receiving chamber 60 not so filled by the base 44 and not intended to function as part of the fluid reservoir 78 then functions as an opening dividing wall receiver 126. The portion of the inner surface 92 of the skirt 46 of the lid 42 on the dividing wall support shoulder 120 functions correspondingly as a continuous ring 128 of the dividing wall receiving aperture 126. The rim 128 of the dividing wall receiving aperture 126 is elongated in shape and in the illustrated embodiment is in harmony with the transverse section of the periphery 138 of the partition wall 91 which is substantially elliptical . However, other configurations of the ring 128 of the dividing wall receiving aperture 126 are within the scope of the present invention. By way of example and not limitation, the ring 128 can therefore be finished in elliptical, oval, polygonal or parabolic form. With the base 44 assembled in the cover 42, the objective aperture 59 communicates between the exterior of the housing 40 and one side of the dividing wall receiving chamber 126. The opposite side of the dividing wall receiving chamber 12 communicates with the storage tank. fluid 78. Therefore, the lens aperture 59 and the partition wall receiving aperture 126 function together as an access aperture 130 through which the fluid reservoir 78 communicates with the exterior of the housing 40. In general, the periphery of an elongated partition wall, such as the partition wall 91, is geometrically proportional to, although larger than, the shape of the rim of the access opening of the vascular access port in which the partition wall is not installed. The ramifications of this feature of the partition wall 91 on the interactions of the elements of the housing 40 with the partition wall 91 are contemplated in substantial detail in the proper course. A cross-sectional elevation view of the partition wall 91 in the natural configuration thereof, free of external forces is shown in Figure 7. There, the partition wall 91 can be seen to include a partition wall body 136 having a partition wall. external face 140 on the side of the partition wall 91 which faces the outside of the housing 40 when the partition wall 91 is installed therein. Correspondingly, the partition wall body 136 has an internal face 142 on the opposite side of the partition wall 91 from the outer face 140 thereof. On the periphery 138, the dividing wall body 136 assumes a minimum thickness TP between the outer face 140 and the inner face 142. Around the central axis Ac of the partition wall 91, however, the central thickness Tc of the partition wall body 136 is a maximum, greater than the peripheral thickness TP of it. The increase in thickness of the dividing wall body 136 towards the center 164 of the partition wall 91 is a result of the formation of structures on the external face 140 and the inner face 142 respectively. Radially inward from the periphery 138 of the dividing wall 91, the outer face 140 of the partition wall body 136 warps laterally outward from the partition wall body 136 to form a needle objective dome 144. Accordingly, the dome of needle target 144 is smaller in extension than what is outer face 140 of dividing wall body 136. As best seen in Figure 3, needle target dome 144 is enclosed within a limit 145 that is elongated . When the partition wall 91 is assembled in the housing 40 in the form of Figure 2, it is the portion of the outer face 140 of the partition wall body 136 within the boundary 145 of the needle target dome 144 that is exposed to the outside of the access port 18 through the objective aperture 59. Thus, in the embodiment of the vascular access port 18 illustrated, the surface of the needle objective dome 144 is substantially coincident with the needle target area of the dividing wall 91. In most cases it can be anticipated that the limit 145 of the needle target dome L44 will substantially coincide with the internal surface 100 of the dividing wall retaining rim 98. However, within the scope of the teachings of the present invention , this relationship does not necessarily have to always exist. In addition, while the limit 145 of the needle target dome 144 may appear in Figure 3 to be similar in shape to the periphery 138 of the partition wall 91, this relationship also need not be maintained in accordance with the teachings of the present invention. . Radially inwardly from the periphery 138 of the partition wall 91, the inner face 142 of the partition wall body 136 warps laterally outward from the partition wall body 136 to form a reinforcing plug 146. Accordingly, the reinforcing plug 146 is smaller in extension than what is the inner face 142 of the dividing wall body 136. As will be better appreciated in Figure 7, the reinforcing plug 146 is enclosed within a boundary 147 that is elongated very similar to the limit 145 of needle target dome 144. When the partition wall 91 is assembled in the housing 40, it is the portion of the inner face 142 within the boundary 147 of the reinforcing plug 146 that is exposed to the fluid reservoir 78 over the interior of the port. of vascular access 18.

In most cases it would be desirable for the boundary 147 of the reinforcing plug 146 to engage the inner surface 116 of the side wall 70 of the base 44. Under these circumstances, the boundary 147 of the reinforcing plug 146 will assume substantially the same shape as the cross section of the fluid reservoir 78 taken in a plane parallel to the floor 68 of the base 44. However, within the scope of the teachings of the present invention, this relationship need not necessarily always exist. Further, while the boundary 147 of the reinforcing plug 146 may be similar in shape to the periphery 138 of the partition wall 91, this relationship also need not necessarily be maintained in accordance with the teachings of the present invention. In Figure 7, the limit 145 of the needle target dome 144 overlies precisely the limit 147 of the reinforcing plug 146. This is a result of the structural relationships that exist between the needle impenetrable elements of the housing 40. First , as best illustrated in Figure 6, the inner surface 100 of the dividing wall retaining rim 98 on the lid 42 is the same size and shape as the inner surface 116 of the side wall 70 of the base 44. Therefore, the lens aperture 59, which is limited by the internal surface 100 of the retention flange of the partition wall 98, corresponds in size and shape to the cross section of the fluid reservoir 78 which is limited by the inner surface 116 of the side wall 70 of the base 44. Secondly, when the base 44 is received in the lid 42, in the manner illustrated in Figure 6, the inner surface 100 of the dividing wall retaining flange 98 is arranged in precise alignment with and on the inner surface 116 of the side wall 70 of the base 44. Thus, the objective aperture 59 is superimposed on the fluid reservoir 78 when the components of the housing 40 have been assembled. Although those relationships between the housing elements 40 of the vascular access port 18 have proven effective, those relationships need not necessarily be reproduced in an accurate manner in an access port presenting the teachings of the present invention. The access port 18 is assembled by the initial placement of the partition wall 91 within the cover 42 so that the needle objective dome 144 is received within the objective aperture 59. The portion of the external face 140 of the body of dividing wall 136 which is radially outside the limit 145 of the needle target dome 144 as a result rests against the abutment surface 102 on the partition wall retaining flange 98. The base 44 is then inserted into the cover 42, interspersing the dividing wall 91 between them. The dividing wall support shoulder 120 is urged against the inner face portion 142 of the partition wall body 136 which is radially outside the boundary 147 of the reinforcing plug 146. This seals the access to the fluid reservoir 78 through the lens aperture 59. The result is shown in cross-section in Figure 8, which illustrates the installed configuration of the partition wall 91. The cover 42 is secured to the base 44 by ultrasonic welding of the alignment shoulder 124 of the base 44 in the alignment notch 106 of the cover 42. In the alternative, various medical grade adhesives or conventional mechanical connections can be used to secure the cover 42 and the base 44. Ultrasonic welding or a medical grade adhesive is also used for securing the proximal end 86 of the rod 84 in the passage 82 of the rod housing 80. The housing 40 interacts with the installed configuration of the pair elongate partition 91 to produce a substantially uniform tension in the partition wall 91 in the plane P thereof. The substantially uniform tension of this type in the installed configuration of the partition wall 91 results in a uniform needle seal, needle penetration and needle retention characteristics across the entire cross section of the partition wall 91. The cupping The needle in the dividing wall 91 is minimized by adjusting within acceptable limits the uniform stress degree of this type produced in the installed configuration of the dividing wall 91. Those effects of the interaction of the housing 40 on the dividing wall 91 they will be explored in detail in the proper course. The catheter 20 is coupled to the rod 84 by the proximal sliding end 22 of the catheter 20 on the free distal end 88 of the rod 84. A cylindrical locking sleeve 148 is then advanced along the catheter 20 toward and in engagement against the port of the catheter. vascular access 18. To implant the vascular access port 18, a subcutaneous pocket is first created in which the vascular access port 18 is received. For this purpose an incision is made in the skin of patient 10 at the implant site intended for , and a bag is elongated through it under the skin. The vascular access port 18 is inserted through the incision into the subcutaneous pocket and secured thereto as desired using suture holes 66. The exit rod 84, which is positioned at the distal end 74 of the base 44 in alignment with the longitudinal axis of the housing 40, enters the subcutaneous pocket at the end, following the balance of the vascular access port 18. In doing so, the vascular access port 18 can be secured in the subcutaneous pocket before the medical staff is required to attend the vascular catheter 20 implant. The catheter 20 can be coupled to the exit rod 84 of the vascular access port 18 after the access port 18 has been introduced and secured within the subcutaneous implant pocket. The positioning of the exit rod 84 on an end end of the housing 40 allows the incision to be made in the skin of the patient 10 so that it is only so long that it will accommodate the width A, instead of the length LA, of the vascular access port. 18. The elongation of the vascular access port 18 therefore reduces the length of the incision required for the implant thereof. The elongation in the vascular access port 18 is facilitated to a greater extent by the elongation of the dividing wall 91 that is installed therein. In one aspect of the present invention, the access means is provided in the housing 40 to allow communication of selected fluid through the partition wall 91 with the fluid reservoir 78 via the needle tip of a hypodermic syringe and to produce a substantially uniform tension in the partition wall 91 in the installed configuration thereof. By way of example and not limitation, one embodiment of such access means according to the teachings of the present invention includes access opening 130 shown for best advantage in Figure 6. With dividing wall 91 positioned in the opening of access 130 as in Figure 8, the fluid communication selected can be performed at will with the fluid reservoir 78 only by passing through the partition wall 91 the needle tip of a hypodermic syringe, such as the hypodermic syringe 28 shown in FIG. Figure 1. The interaction between the access opening 130 and the dividable wall 91 also produces a substantially uniform hydrostatic pressure in the portion of the partition wall 91 accessible for probing by the needle 26 in the installed configuration of the partition wall 91. This in turn results in a needle penetration force and a substantially uniform needle retention force in that portion of the wall div. isoria Accordingly, in one aspect of the access means according to the teachings of the present invention, the restriction means is provided to move the periphery 138 of the partition wall 91 radially inward in the plane P of the partition wall 91. By way of example and not limitation, one embodiment of such constraining means comprises a ring, such as ring 128 of access opening 130, which has a shape in the plane thereof that is geometrically proportional to, although smaller that the cross section of the wall of the periphery 138 of the dividing wall 91 in the plane P thereof. When the dividing wall 91 is positioned in an access opening configured in this manner, the ring 128 radially inwardly displaces the periphery 138 of the partition wall 91 in the plane thereof in such a way that as has been found to produce a pressure substantially uniform hydrostatic in the portion of the partition wall 91 accessible for needle penetration. The diagram in Figure 9 will be used to illustrate the relative configuration of access opening 130 and dividing wall 91 used towards that end. In Figure 9, a natural configuration periphery 154 of the dividing wall 91 is shown in shading, which corresponds to the profile of the periphery of a partition wall 91 before being placed in the access opening 130 of the housing 40. of comparison, is also shown in Figure 9, although in solid line, there is an installed configuration periphery 156 of the dividing wall 91 which illustrates the size of the periphery of the dividing wall 91 once the dividing wall 91 is placed within the access opening 130 of the housing 40. Superimposed on a periphery of natural configuration 154 and the installed configuration periphery 156 in Figure 9 is a coordinate axis. For convenience, the origin of the coordinate axis coincides with the center 164 of the partition wall 91 both in the natural configuration and in the installed configuration thereof. The first of the axes of the coordinate axis is an X axis that coincides with the maximum extension of the dividing wall 91 and therefore with the longitudinal axis 158 thereof both in the natural configuration and in the installed configuration. The second axis of the coordinate axis is a Y axis that coincides with the maximum extent of the partition wall 91 measured perpendicular to the longitudinal axis 158. Therefore, the Y axis of the coordinate axes in Figure 9 is coincident with the lateral axis 159 of the dividing wall 91 in the natural configuration and in the installed configuration thereof.

As illustrated in Figure 9, the natural configuration of the partition wall 91 has a natural configuration periphery 154 with a maximum extension or length Li which is reduced in the installed configuration of the partition wall 91 to an installed configuration periphery 156 which has a maximum length or length L2. In an orthogonal direction, the partition wall 91 in the natural configuration thereof has a natural configuration periphery 154 with a maximum extent measured perpendicular to the longitudinal axis 158 which is equal to the width i. This partition wall dimension 91 decreases in the installed configuration thereof to produce an installed configuration periphery 156 having a corresponding width W2. A point P _ (x_ ,, yi) on the natural configuration periphery 154 of the dividing wall 91 is illustrated only by way of example, in the first quadrant of the superimposed coordinate axis shown. The partition wall 91 is positioned in the access opening 130 configured to produce a substantially uniform hydrostatic pressure in the portion of the partition wall 91 subjected to needle penetration. Upon assuming this condition is installed in the access opening 130, the ring 128 of the access opening 130 imposes on each point on the periphery of natural configuration 154 of the partition wall 91 a force that is directed radially inwardly. The force FP shown in Figure 9 represents the force of this type applied by the ring 128 of the access opening 130 to the point Pi on the periphery of natural configuration 154. As a result of the imposition of said forces, each point on the The natural configuration periphery 154 of the dividing wall 91 is displaced radially inwardly. With the center 164 of the dividing wall 91 remaining fixed at the origin of the superimposed coordinate axis shown, under the influence of the force Fp, the point Pi on the periphery of natural configuration 154 of the dividing wall 91 assumes the new location on the installed configuration periphery 156 at the point P2 (x2r y2) - The point P2 (x2, y2) on the installed configuration periphery 156 of the partition wall 91 also has effect on the rim 128 of the access opening 130. This it is due to the sealed coupling effected by the installed configuration periphery 156 of the partition wall 91 with the rim 128 of the access opening 130. It is intended in accordance with the teachings of the present invention to configure the rim 128 of the access opening 130 and the periphery 138 of the dividing wall 91 so that the installed configuration of the partition wall 91, a compressive stress ex occurs in the partition wall 91 along the longitudinal axis. udinal 158 of the dividing wall 91 which is equal to a compressive tension e and produced in the partition wall 91 along the lateral axis 159 thereof. Therefore, in the installed configuration of the dividing wall: [2] ex = ey Using the terms illustrated in Figure 9, the change in length of the natural configuration of the partition wall 91 along the longitudinal axis 158 thereof in the assumption of the installed configuration of the dividing wall 91 is a first compression distance Cx calculated as follows: [3] Cx = L2 - Li. Similarly, the change in the width of the natural configuration of the partition wall 91 along the lateral axis 159 upon assuming the installed configuration of the partition wall 91 is equal to a second compression distance Cy calculated as follows: The tension imposed on an article is equal to the ratio of the change in length or width of that article to the original length or width respectively thereof. Therefore, the ratio of the first compression distance Cx to the maximum extension or length Li of the partition wall 91 in the natural configuration thereof is equal to the ratio of the second compression distance Cy to the width i of the wall Divide 91 in the natural configuration of it. Substituting Equation Nos. 3 and 4 above in Equation No. 2, the following relationship occurs: Li - L2 W - W2 [5] = Li Wi Alternatively, with the center 164 of the dividing wall 91 remaining fixed at the origin of the superimposed coordinate axis shown, the longitudinal ends of the dividing wall 91 are each displaced from the natural configuration thereof in the installed configuration thereof by means of first displacements substantially equal to zero along the longitudinal axis along the longitudinal axis 158 of the partition wall 91. Correspondingly, the middle ends of the partition wall 91 are displaced inwardly from the natural configuration thereof in the installed configuration thereof by second substantially nonzero shifts directed along the lateral axis 159 of the partition wall 91. In those terms, Equation No. 2 and Equation No. 5 stipulate that the ratio of the combination of the first displacements at the distance between the longitudinal ends of the dividing wall 91 in the configuration The natural ratio of the same is equal to the ratio of the combination of the second displacements to the distance between the middle ends of the dividing wall 91 in the natural configuration thereof. One approach to achieving the condition stated in Equation No. 2 along the longitudinal axis and the lateral axis of the dividing wall 91 is to configure the rim 128 of the access opening 130 to be smaller than the natural configuration of the dividing wall 91 and geometrically proportional to the periphery 138 thereof. The effectiveness of this design relationship has been verified through empirical studies. One embodiment of a partition wall, such as the partition wall 91 and a corresponding access opening 130 with a ring 128 that conforms to the above teachings each have elliptical configurations and the following dimensions identified by the corresponding reference characters in the Figure 9. Divided wall: Ll = 0.68 inches Wl = 0.47 inches Aspect ratio = = 1.45 Access Opening: Ll = 0.64 inches Wl = 0.44 inches 2 Aspect ratio 1.45 According to the dividing wall 91 and the access opening 130 were elliptical and had equivalent aspect ratios and eccentricities, the dividing wall 91 and the access opening 130 were geometrically proportional. However, it should be noted that the opening 130 is not simply smaller in each measurement direction than the partition wall 91 by some fixed increment, this is more readily apparent when the difference in size between the partition wall 91 and the access opening 130 is compared along the orthogonal directions of measurement taken respectively parallel to the longitudinal axis 158 of the partition wall 91 and the lateral axis 159 of the partition wall 91. Along the longitudinal axis 158, the difference in size between the partition wall 91 and access opening 130 was as follows: Li - L2 = 0.040 inches On the other hand, the difference in size between the dividing wall 91 and the access opening 130 along the lateral axis 159 was as follows: Wi - W2 = 0.030 inches The computer modeling of the installation of according to the teachings of the present invention a dividing wall, such as the dividing wall 91 sized as indicated above, in an access opening, such as the access opening 130 dimensioned as indicated above, has the provisions provided in relation to to the internal tensions developed in an installed configuration of such dividing wall. Of primary interest was to quantify a fixed parameter at each location through the needle penetration region of the installed configuration that would be correlated in some way with the needle penetration force and the needle retention force at that location. The force of needle penetration in a given case depends on the number of properties of the needle that is used and the material of the dividing wall that is penetrated. For example, the resistance to needle penetration is proportional to the size of the needle, the internal cohesion of the dividing wall material that resists the separation at the tip of an advancing needle and the drag forces that arise between the outside of the needle and the dividing wall material along the trajectory of the penetration of the needle. These frictional drag forces naturally increase as the trajectory of the needle penetration is lengthened during the advance of a needle from the outside of a dividing wall through the dividing wall body through the dividing wall body to the fluid reservoir inside. of the housing in which the dividing wall is installed. However, these factors are in a relative sense substantially unchanged for any given needle and any given dividing wall, changing very little as a result of the forces imposed on the dividing wall by the housing in which the dividing wall is installed. Therefore, these factors only marginally support the stability of the partition wall installed in a housing, on the ability of the material of the dividing wall to seal around the outside of a penetrating needle during the presence of the needle axis in the path of the needle. penetration of the same, or on the effectiveness of the material of the dividing wall to seal the trajectory of the penetration of needle once the axis of the needle has been removed.

The medical-grade silicone is, for practical purposes, a material similar to incompressible fluid that responds to forces imposed externally by free distortion, balancing the internal pressure and sharing the stresses produced by those forces and the resulting deformation. Therefore, the state of internal tension of an installed silicone partition wall is characterized by a physical parameter referred to as hydrostatic pressure. In the study of the distribution of hydrostatic pressure in the installed configuration of the dividing wall 91, finite element analysis techniques were used. The first stage in that process involved the development in computer software of a virtual partition wall of the size and shape of the partition wall 91. The virtual partition wall was mathematically subdivided into a large plurality of very small splice block elements, each defined by six (6) flat faces intersecting eight (8) linear edges that each end between a pair of eight (8) corners. The block elements provided the best relationship between numerical accuracy and computational efficiency by conducting a finite element analysis of the behavior of the general structure of the virtual dividing wall under externally imposed forces. Care should be taken in the planning of the block elements to avoid the creation of extremely irregular shapes. This approach to the conducted study is illustrated in Figure 10. There, a quadrant of a virtual dividing wall 149 is illustrated superimposed by a finite element mesh screen that resulted from the mathematical subdivision of the virtual partition wall 149 into one. plurality of block elements 150. A subset 151 of the adjacent block elements 150 is shown offset out of the finite element screen mesh, on the outer face 140 of the partition wall body 136 of the virtual partition wall 149 near the limit 145 of the needle target dome 144. Additionally an individual block structure 150a is shown displaced laterally from the position thereof in the sub-assembly 151. For ease, the dividing virtual partition wall 149 did not include the reinforcement plug 146 of the type illustrated in Figure 7. Therefore, while the outer face 140 of the partition wall body 136 of the virtual partition wall 149 is molds closely into shape and size to the outer face 140 of the partition wall 91, the inner face 142a of the virtual partition wall 149 is flat within the periphery 138.

The response parameters of the silicone material of the dividing wall 91 were given empirically and adjusted by a non-linear regression process to an adequate mathematical representation. This mathematical representation of the response parameters of the partition wall material 91 was added to the software illustrating the virtual partition wall 149. A condition of the behavior of the non-compressible material was imposed on the material of the virtual partition wall 149 by the software of calculation. Next, the surfaces of the rigid virtual housing representing the surfaces of the cover 42 and the base 44 defining the access opening 130 were also programmed into the computer software. Such virtual box surfaces included the abutment surface 102 and the inner surface 92 of the cap 46, as well as the dividing wall support shoulder 120 on the base 44. For ease, the first fastening flange 104 on the support surface 102 and the second clamping flange 122 on the dividing wall support shoulder 120 were omitted. The analysis procedure in a two-stage form is illustrated in the order of implementation first in Figure 11 and then in Figure 12. The first bearing surface 102 and the dividing wall shoulder 120 were imposed against the outer face 140 and the internal face 142a respectively of the partition wall 149 around the entire periphery 138 thereof. Then, the inner surface 92 was placed in contact with the periphery 138 of the virtual partition wall 149 and moved radially inward, imposing forces on the periphery 138 of the virtual partition wall 149 as those imposed on the partition wall 91 in the configuration installed by the inner surface 92 of the skirt 46 of the lid 42. In this manner, a radially inwardly directed tension of 6.4 percent in the plane of the partition wall 91 was imposed on the virtual partition wall 149 by computer software and it was presented later in visual form. The results are shown in Figure 11. The contour lines hydrostatic pressure 152 illustrating the conditions of hydrostatic pressure in the virtual partition wall 149 is charted on the outside of the virtual partition 149. The hydrostatic pressure ranges between each of the hydrostatic pressure contour lines 152 were also labeled in Figure 11. The deformation in the virtual partition wall 149 produced by the application of the radially inwardly directed tension is more evident in Figure 11 along the inner side 142a near the periphery 138. The inner face 142a can be seen to warp axially outward from the planar configuration of the inner face 142a illustrated in the natural configuration of the virtual partition wall 149 in Figure 10. Significantly, in the degree of stress directed radially inward, the hydrostatic pressure in the needle penetration region of the Virtual partition wall 149 is relatively uniform, ranging from about 10 pounds per square inch to about 26 pounds per square inch. The pressure gradient patterns of the type shown in Figure 11 correspond to relatively uniform internal stress conditions across the entire needle penetration region of an installed partition wall. Consequently, the retention force needle exerted on the tip of a needle, such as needle 26 of the syringe and hypodermic 28, which penetrates the partition wall 91 substantially the same for any point in the cross section of the partition wall 91 in the one that penetrates. Correspondingly, the needle penetrating force that resists penetration of the partition wall 91 by the tip of a needle, such as the needle 26 of the hypodermic syringe 28, it is also the same for any point of the cross section of the transversal section of the dividing wall 91 in which the penetration is attempted. This is the most effective consequence, and one that was not previously obtained in any systematic way in an installed partition wall that was not circular. A second aspect of the interaction of partition wall 91 and housing 40 also contributes to the development of idealized uniform voltage conditions in the installed configuration of partition wall 91. In yet another aspect of the access means according to teachings of the present invention, the fastening means are provided to drive the outer face 140 and the inner face 142 of the partition wall body 136 toward each other at the periphery 138 thereof. As seen in Figure 6, the distance D between the bearing surface 102 on the retaining lips 98 and the support shoulder 120 is smaller than the peripheral thickness TP shown in Figure 7 between the inner face 142 and the outer face 140 of the dividing wall body 136 at the periphery 138 of the partition wall 91. Accordingly, when the partition wall 91 is placed in the access opening 130 in the housing 40, the periphery 138 of the partition wall 91 tapers axially between the partition wall retaining lip 98 and the dividing wall support shoulder 120. Corresponding to the structural aspects of the access port 18, the finite element analysis of the virtual partition wall 149 extended beyond that illustrated in the Figure 11 to reflect the force of the clamping periphery 138 of the partition wall 91 against the dividing wall support shoulder 120 with the first bearing surface 102. To do so in this way a, the internal surface 92 remained fixed at a location that produced the radially inwardly directed tension of 6.4 percent illustrated in Figure 11. the bearing surface 102 remained fixed, and the dividing wall shoulder 120 was advanced axially until such a degree that it imposed an axial tension of 8.0 percent on the virtual partition wall 149 around the periphery 138 thereof. The results are shown in Figure 12. The hydrostatic pressure contour lines 152 illustrate the hydrostatic pressure conditions in the virtual partition wall 149 and are plotted on the outside of the virtual partition wall 149. The hydrostatic pressure scales between each of the hydrostatic pressure contour lines 152 are also labeled in Figure 13. The accentuated deformation of the virtual partition wall 149 in relation to that observed in Figure 11, is seen in Figure 12 resulting from the application of the axial tension. This distortion is more evident in Figure 12 along the inner face 142a near the periphery 138. Significantly, the combination of this degree of axial tension with the radially inwardly directed tension imposed on the virtual partition wall 149 illustrated in Figure 12 it produced the relatively uniform hydrostatic pressure in the needle penetration region of the virtual partition wall 149. The hydrostatic pressure in the needle penetration region of the virtual partition wall 149 as illustrated in Figure 12 is largely measure a desirable scale from about 18 pounds per square inch to about 30 pounds per square inch. It would also be acceptable for the hydrostatic pressure to be on the scale from about 10 pounds per square inch to a scale of about 46 pounds per square inch. Finally, a scale from about 5 pounds per square inch to about 56 pounds per square inch is also appropriate. Those hydrostatic pressure scales have been given to produce an average needle retention force equal to approximately 1.1 ± 0.1 pounds. This level of needle retention force is considered to be optimally desirable for medical personnel and is on the scale where the risks of cupping of the dividing wall are relatively minimal. Although somehow less desirable, the needle retention force on a scale from about 0.5 pounds to about 1.5 pounds is also acceptable. The Needle retention force on a scale from about 0.35 pounds to about 2.5 is somewhat less desirable, although the needle retention force on a scale from about 0.2 pounds to about 3.5 pounds will be sufficient in many circumstances. Figure 13 illustrates the effect of the partition wall profile 91 of this axial deformation in a combination with the radially inwardly directed movement of the periphery 138 of the partition wall 91 produced by the housing 40 when the partition wall 91 is installed in the opening 130. In Figure 13, a natural configuration profile 160 of the partition wall 91 in the natural configuration thereof is illustrated in shading. This illustration corresponds to the profile of the dividing wall 91 shown in Figure 7. Superposed on the natural configuration profile 160 is an installed configuration profile 162 in solid line of the dividing wall 91 in the installed configuration thereof. This illustration corresponds to the profile of the dividing wall 91 shown in Figure 8. The natural configuration profile 160 and the installed configuration profile 162 are superposed on a common central axis Ac of the dividing wall 91 previously introduced in Figure 3. A From Figure 8, it can be seen that the periphery 138 of the installed configuration of the partition wall 91 is surrounded on three (3) sides, respectively, by the side 128, the partition wall retaining ring 98 and a support shoulder of dividing wall 120. As a result, several forces illustrated in Figure 13 are imposed on partition wall 91. A force F? 2a radially directed inwardly is imposed on the periphery 138 of partition wall 91 in plane P thereof. . The force Fi28 is produced by the ring 128 of the access opening 130. Simultaneously, the axially directed forces are imposed in opposite directions, respectively, on the outer face 140 and the inner face 142 of the partition wall body 136 in the periphery 138 of the dividing wall 91. A first of these axially directed forces Fgg which is imposed on the outer face 140 of the partition wall body 136 at the periphery 138 of the partition wall 91 by the partition wall retaining lip 98. The other of the axially directed opposing forces is the force F? 20, which is imposed in a direction opposite to that of the force F98 on the inner face 142 of the partition wall body 136 at the periphery 138 of the dividing wall 91 by the dividing wall support shoulder 120. Accordingly, according to the dividing wall 91 is driven within the installed configuration thereof, the material thereof in the pe rim 138 is displaced radially and axially inwardly. This inward displacement of the material results collectively in turn in the axially outward displacement of the needle target dome 144 indicated by the arrows X. In addition, the reinforcing plug 146 is displaced outwardly from the dividing wall body 136 as shown in FIG. indicated by the arrows Y. This effect on the material of the dividing wall 91 caused by the axial directed force Fgg and the axially directed force F120 improves the sealing effectiveness of the partition wall 91 in the access opening 130. It also improves the uniformity of the hydrostatic pressure in the portions of the dividing wall 91 accessible to the penetration of the needle produced by the greater part by the directed force Fi28 inwards. The general levels of hydrostatic pressure within the partition wall material 91 should be on a wide scale from about 5 pounds per square inch to about 50 pounds per square inch. Nevertheless, most preferably the hydrostatic pressure in the partition wall 91 in the installed condition thereof must be on a scale from about 10 pounds per square inch to about 40 pounds per square inch. A scale from about 15 pounds per square inch to about 30 pounds per square inch is most preferred. The fastening means according to the teachings of the present invention may optionally include the first fastening flange 104 on the cover 42 of the housing 40 and the second fastening flange 122 on the base 44 of the housing 40. Although the first flange of clamping 104 and the second clamping flange 122 move axially towards each other the outer face 140 and the inner face 142 of the periphery 138 of the partition wall 91, the volume of the partition wall material pushed inward is relatively smaller when it is compared with that resulting from the force F? 28 applied by the ring 128 of the access opening 130. The force F98 applied by the dividing wall retaining lip 98 and the force F? 20 applied by the shoulder of dividing wall support 120. The first fastening flange 104 and the second fastening flange 122 function primarily to retain the periphery 138 of the partition wall 91 securely in the access opening 130 in the installed configuration thereof. Doing so significantly avoids the folding or movement of the partition wall 91 in the access opening 130 in reaction to the forces illustrated in Figure 13. The design of an acceptable elongate vascular access port, such as a vascular access port 18, allows a wide variation in and between the parameters of the dividing wall used with them. Those partition wall parameters may be altered substantially at will for the purpose of producing - in an elongated access port - one or more optimum characteristics in the installed configuration of the dividing wall. For example, as the central thickness Tc of the partition wall 91 increases, features such as needle sealing, needle penetration and needle retention in the partition wall 91 increase correspondingly. On the other hand, it may be desirable to minimize the size or thickness of the dividing wall in order to reduce the overall size of the vascular access port in which the dividing wall 91 is installed. Therefore, compromise is required between the objectives of the optimum partition wall characteristics in the installed partition wall and the size of a vascular access port, even if constructed in accordance with the teachings of the present invention. Such relationships are common in the design of a vascular access port suitable for a specific specialized use. Another example can provide more illustration. If the central thickness Tc of the dividing wall 91 decreases, and if it is desired to maintain some predetermined level of features of the dividing wall in the installed partition wall, then the radially inwardly directed force F? 2a imposed on the periphery 138 of the wall Divide 91 in the configuration installed by ring 128 can be increased. If the partition wall 91 is extremely thin, the radially inwardly directed force F? 2s is necessary to maintain the predetermined partition wall characteristics may also be greater to prevent the placement of the partition wall 91 in the access opening 130 manually during the vascular access port assembly 18. The additional manufacturing cost of doing so by machine may exceed the advantage of a very thin dividing wall in the intended application. Further, as the central thickness Tc of the partition wall 91 is decreased and the radially inwardly directed force F? 28 imposed compensatively on the periphery 138 thereof is increased, the opportunity of folding, crushing or narrowing in the installed configuration of the partition wall 91 is also increased. These consequences represent undesirable examples of the loss of structural stability in the installed configuration of the partition wall 91. Any loss of structural stability in the The installed configuration of partition wall 91 endangers the maintenance of desirable partition wall characteristics. Therefore, folding, constriction or crushing in an installed partition wall are always objectionable, regardless of the nature of the partition wall characteristics obtained. If structural stability does not exist in an installed partition wall, the desirable partition wall characteristics may correspondingly not be stably maintained. Accordingly, in yet another aspect of the present invention, a partition wall, such as partition wall 91, is provided with support means to prevent folding in the installed configuration of the partition wall. By way of example and not limitation, the needle target dome 144 is formed integrally with the partition wall 91 on the external face 140 of the partition wall body 136.

Alternatively, or in addition to, the reinforcing plug 146 is formed integrally with the partition wall 91 on the inner face 142 of the partition wall body 136. Each of the needle target dome and the reinforcing plug 146 respectively, increase the thickness of the dividing wall body 136 in the vicinity of the center 164 of the dividing wall 91. This in turn prevents folding or narrowing in the partition wall 91, but not without increasing the peripheral thickness Tp of the partition wall 91. The arrangement allows the effective thickness of the dividing wall 91 to be improved without correspondingly increasing the size of the vascular access port 18. The thickness and configuration of the needle target dome 144 and the reinforcement dome 146 can be varied to different specific applications. The design of those structures interact closely on arrival at any desired objective with the overall size of the dividing wall 91 of the plane P thereof and the amount of force directed radially inwards F? 2s intended to be applied in the installation of the dividing wall 91. An additional parameter that can be adjusted to vary the degree of hydrostatic pressure in the installed configuration of partition wall 91 is the degree of axial displacement directed in mutually opposite manner effected on outer face 140 and inner face 142 in the periphery 138 of the dividing wall body 136. By increasing the axial displacements at the periphery 138 of the partition wall body 136, the central thickness Tc of the dividing wall 91 or the radially inwardly directed force F? 28 imposed on the dividing wall 91 may even be decreased in a compensatory manner to a degree The present invention contemplates that vascular access ports can be designed in which the characteristics of the dividing wall installed therein is achieved at will by varying independently or in combination with the thickness of the dividing wall, the degree of radially inwardly directed forces imposed on the dividing wall, or the degree of axial compression of the periphery of the dividing wall effected to achieve installation. It is contemplated, for example, that the restoration can be made to such ends for the use of a dividing wall retaining lip 98 and a dividing wall support shoulder 120 having a non-uniform distance D therebetween. This can be achieved by altering the spacing between the retaining lip of the dividing wall 98 and the dividing wall support shoulder 120 in selected regions around the access opening 130. The desirable patterns of uniform hydrostatic pressure in the installed configuration of a wall Dividers can be produced in a variety of elongated divider wall configurations. For example, illustrated in Figure 14 in plan view is a first group of elliptical divider walls, 168, 170 and 172 that are superimposed on an individual coordinate axis. Like the coordinate axis illustrated in Figure 9, that of Figure 14 includes an axis X that is coincident with the common longitudinal axis 174 of the first group of divider walls and a Y axis that is coincident with the common lateral axis 176 of the first group of dividing walls. The origin of the coordinate axis is located in the common center 164 of the first group of dividing walls. The partition walls 168, 170 and 172 share a common width B measured along the lateral axis 176, although it varies between each in length as measured along the common longitudinal axis 174 thereof. The dividing wall 172 with the longer length A3 has an aspect ratio and an eccentricity that are greater than those of the dividing wall 168 or the dividing wall 170. Correspondingly, the dividing wall 168 with the smallest length Ai has a relation of aspect and an eccentricity that are less than those of partition wall 170 or dividing wall 172.

However, in each case, using the principles described above, it is possible to design an appropriate corresponding housing and the access opening in which any group of dividing walls 168, 170 or 172 is installed while producing uniform hydrostatic pressure characteristics. in the installed configuration of each one. A second group of elliptical divider walls 178, 180 and 182 is illustrated in Figure 15. There, as in Figure 14, the second group of divider walls has been superimposed on a coordinate axis having the origin thereof placed in a common center 164 of the second group of dividing walls. The coordinate axis of Figure 15 includes an axis X that is coincident with the common longitudinal axis 183 of the second group of dividing walls and a Y axis that is coincident with the common lateral axis 184 of the second group of dividing walls. The partition walls 178, 180 and 182 share a common maximum extension, or length A, measured along the common longitudinal axis 183, although the width of each respective partition wall measured along the lateral axis 184 varies throughout the Second group of dividing walls. As the partition wall 182 has the greatest width B3, the partition wall 182 has an aspect ratio and an eccentricity that are less than those associated with the partition wall 180 or the partition wall 178. Correspondingly, since the partition wall 178 has the smaller width Bi, the partition wall 178 has an aspect ratio and an eccentricity that are greater than those associated with the dividing wall 180 or the dividing wall. However, in each case, using the principles described above, it is possible to design a corresponding housing and the access opening in which any of the second group of partition walls 178, 180 and 182 is installed, while producing stress characteristics. uniform in the installed configuration of each one. The partition walls 172, 170 and 168 in Figure 14 and the partition walls 178, 180 and 182 in Figure 15 are examples of a very particular category of elongated divider walls that embody the teachings of the present invention. The divider walls illustrated in Figures 14 and 15 are referred to as "truly elliptical". A truly elliptical dividing wall has an outer periphery that is defined by the following individual continuous mathematical relationship: [6] x ^ + ¿= 1, where a2 b2 2a = the length of the ellipse along the longitudinal axes of it; and 2b = the width of the ellipse taken perpendicular to the length The eccentricity E of a dividing wall that is truly elliptical is, as a result, given by the following equation, which is similar to Equation No. 1: the elongated divider walls within the scope of the present invention include many different divider wall types of the divider walls that are truly elliptical. For example, illustrated in Figure 16 in dotted line is a truly elliptical partition wall 186 on which an oval partition wall 187 having a periphery 188 that is in several locations almost congruent with the periphery of the truly elliptical partition wall has been superimposed. 186. The periphery 188 of the partition wall 187, comprises respective semicircular end ends 189 tangentially interconnected by a pair of straight sides 190. While the partition wall 187 and the completely elliptical partition wall 186 have equal lengths A, the width B? 87 of the oval partition wall 187 is smaller than the Bise width of completely elliptical partition wall 186. This results in a greater aspect and eccentricity in the completely elliptical partition wall than in the oval partition wall 187. However, it should be noted that by the appropriate increase in the radius of curvature of the semicircular ends 189 of an oval partition wall l, the partition wall 187 is capable of producing an alternative oval partition wall having a length A and a width equal to the width B? 86 of the completely elliptical partition wall 186. This will result in equal aspect ratios and eccentricities in the dividing wall completely elliptical 186 and the alternative oval, although the alttive oval partition wall would have a larger target area than would the fully elliptical partition wall 186. Those comparative features of each of the partition walls illustrated in Figure 16 should be illustrated advantageously in the design of a port of elongated vascular access for a specific intended use. However, both divider walls illustrated in Figure 16 are elongated within the scope of the present invention, and the partition wall 187, while not completely elliptical, is in several aspects of the substantially elliptical design. In a similar manner, illustrated in Figure 17 in dotted line is a truly elliptical partition wall 200 superimposed on an elongated partition wall 202 having, mathematically, a relatively complex periphery 204. For convenience of analysis, the fully elliptical partition wall 200 and the elongated dividing wall 202 have been superimposed in turn on an axis of coordinates that have their origin in the common center 164 of the divider walls illustrated. The coordinate axis of Figure 17 includes an axis X that coincides with the longitudinal axis 206 of the completely elliptical partition wall 200 and the partition wall 202 and a Y axis that coincides with the common lateral axis 208 of each. The longitudinal axis 206 intersects the periphery 204 of the elongated partition wall 202 at a first end end portion 210 and a second end end portion 212. The first end end portion 210 and the second end end portion 212 are symmetrical about the common longitudinal axis. 206. In the illustrated embodiment, the first end end portion 210 and the second end end portion 212 are also mirror images of one another. The first end end portion 210 intersects the second end end portion 212 non-tangentially at the first vertex 218 and a second vertex 220, each of which is positioned on a common lateral axis 208. The periphery of the first end portion 210 and of the second end portion 212 are substantially parabolic. Accordingly, the point at which the periphery of the first end end portion 210 intersects the longitudinal axis 206 is referred to as the apex of the first end end portion 210. Similarly, the point at which the second end end portion 212 intersects the longitudinal axis 206 is referred to as the apex of the second end end portion 212. Likewise, the periphery of the first end end portion 210 and the periphery of the second end end portion 212 each have a corresponding associated focal point that is positioned intlly. the periphery 204 of the elongate partition wall 202. These are focal points 214 corresponding to the first end end portion 210 and the focal point 216 corresponding to the second end end portion 212. A parabolic end portion of a partition wall has a periphery extl that is defined by the following mathematical relationship: [8] Y2 = 2ax, where • a = distance between vertex and focal point of the parabolic curve In view of the mathematical form other than the final end portion 210 and the end end portion 212, the partition wall 202 will be referred to hereinafter as the "parabolic termination" partition wall 202. It should be noted that the dividing wall with parabolic termination 202 and the completely elliptical dividing wall 200 each have * lengths A and widths B identical. Therefore, the aspect ratio and eccentricity of each are the same respectively. It has been given by experimentation that the ability to produce the characteristics of uniform hydrostatic pressure in a dividing wall, such as the finished dividing wall in a parabolic shape 202, is improved in relation to the ability to do so in relation to other wall types. elongated dividers, including completely elliptical divider walls such as elliptical divider wall 200. However, the parabolic termination dividing wall 202 has a surface area slightly smaller than that of the completely elliptical partition wall 200 and would accordingly have a smaller needle target area than that of the fully elliptical partition wall 200, despite the length A and the identical width B of each one. Those comparative characteristics of each of the divider walls illustrated in Figure 17 can be advantageously used in the design of an elongated vascular access port for specific intended use. However, both divider walls illustrated in Figure 17 are elongated within the scope of the present invention and the partition wall with parabolic termination 202 while not being completely elliptical, is in several aspects of substantially elliptical design. Figure 18 presents another comparison. There, a completely elliptical dividing wall 230 is shown in dotted line superimposed on an elongated partition wall fc 232 with a periphery including a plurality of straight sides 23.6 intersecting each other at the vertices 238. The straight sides 236 do not need to be equal in length. length or in any way placed symmetrically, although the latter feature is evident in the elongated partition wall 232. It is also not necessary for the straight sides 236 to be tangential to the completely elliptical partition wall, since the fully elliptical partition wall 230, as is the case for the straight sides 236 shown in Figure 18. The alternative polygonal configurations use less or more straight sides than the eight (8) sides illustrated in Figure 18 would also be appropriate. In view of the shape of the periphery of the elongated partition wall 232, the elongated partition wall 232 will be referred to below as a "polygonal" partition wall 232. It should be noted that the fully elliptical partition wall 230 and the polygonal partition wall 232 have each lengths A and widths B identical. Therefore, the aspect ratio and eccentricity of each are the same respectively. The polygonal partition wall 232 has a surface area slightly larger than that of the fully elliptical partition wall 230 and accordingly it should be expected to have a larger needle target area than the fully elliptical partition wall 230 despite the length A and the identical B width of each. Those comparative characteristics of each of the divider walls illustrated in Figure 18 should be advantageously used in the design of an elongate vascular access port for the specific intended use. However both divider walls illustrated in Figure 18 are elongated within the scope of the present invention, and the polygonal partition wall 232, while not being completely elliptical, is in several aspects of substantially elliptical design. The polygonal partition wall 232 is presented in order to demonstrate that the teachings of the present invention contemplate the use of elongated divider walls in a wide range of ways. These shapes can be considered substantially elliptical, although if they are not considered so, the dividing walls of these shapes can be installed in the housing of a vascular access port if the access opening in the housing thereof is designed in accordance with the teachings of the present invention to produce uniform stress characteristics in the? Installed configuration of the dividing wall. By doing so in this way, numerous vascular access ports can be provided which are elongated and aligned in shape and therefore amenable to successful implantation in areas of small tissue, such as in the extremities of an adult patient or in the body of an infant or a small baby. Such elongated vascular access ports do not however need to undergo any reduction in the needle target area in the dividing wall used therewith or to exhibit undesirable irregularities in the characteristics of needle sealing, needle retention or needle penetration. The divider pads with needle objective domes with eccentricities of 0.81, 0.90 or greater may be incorporated into access devices. Forecasts and previously described discoveries independent of the design of future vascular access ports from the limitations and disadvantages derived from an exclusive trust in dividing walls that are round in cross section. 20 The invention can be presented in other specific forms without departing from its spirit or essential characteristics. The described modalities are considered in all aspects only as illustrative and not as restrictive. The scope of the invention is therefore indicated by the appended claims instead of the foregoing description. All changes that fall within the meaning and scope of equivalence of the claims will be encompassed within its scope.

Claims (94)

1. CLAIMS 1. An implantable vascular access port comprising: (a) an impenetrable needle housing enclosing a fluid reservoir, the housing having an access opening formed therethrough, communicating between the fluid reservoir and the exterior of the housing, the rim of the access opening assumes a generally elongated shape; and (b) a generally planar, needle-penetrable, elastomeric dividing wall, the partition wall has a periphery in a cross section of the partition wall taken in the plane thereof that is geometrically proportional to and larger than the rim of the partition opening. access, the dividing wall is placed in the access opening with the periphery of the dividing wall in sealed engagement with the rim of the access opening, whereby by placing the dividing wall in the access opening the periphery of the dividing wall it is displaced inwardly in a direction parallel to the plane of the dividing wall by the rim of the access opening. An access port according to claim 1, characterized in that the housing comprises: (a) a base comprising a floor and a continuous surrounding side wall that rises therefrom, the interior of the base corresponds to the tank of fluid of the housing; and (b) a cover comprising an upper wall and a skirt that hangs therefrom, the cover is configured to receive the end of the side wall of the base remote from the floor of the same in the skirt thereof, and the access opening is formed through the top wall of the lid at a location communicating with the fluid reservoir of the housing when the side wall of the base is received in the lid skirt. An access port according to claim 2, characterized in that the skirt of the cover is an individual continuous structure surrounding the side wall of the base when the side wall of the base is received in the skirt of the cover. An access port according to claim 2, characterized in that: (a) the side wall of the base ends remote from the floor thereof in a continuous dividing wall support shoulder placed in a plane parallel to the floor of the base; and (b) the cap comprises a dividing wall retaining flange projecting radially inward toward the access opening from the rim side thereof adjacent to the exterior of the upper partition wall of the cap, the retaining flange of the cap. The dividing wall has a generally flat resting surface on the side of the dividing wall retaining rim opposite the exterior of the upper wall of the lid, the abutting surface of the dividing wall retaining ridge being in spaced apart relation parallel to the supporting shoulder of dividing wall when the side wall of the base is received in the skirt of the lid. An access port according to claim 4, characterized in that the periphery of the dividing wall is thicker than the distance between the dividing wall support shoulder and the abutment surface of the retaining flange of the dividing wall, when the side wall of the base is received in the skirt of the lid, whereby the periphery of the dividing wall is axially compressed between the dividing wall support shoulder and the bearing surface of the retaining flange of the dividing wall when the The side wall of the base is received in the skirt of the lid with the dividing wall placed in the access opening. An access port according to claim 4, characterized in that the edge of the retaining flange of the dividing wall remote from the rim of the access opening is geometrically proportional to and smaller than the shape of the rim of the access opening. An access port according to claim 6, characterized in that the edge of the retention flange of the dividing wall is congruent with the cross section of the fluid reservoir taken in a plane parallel to the floor of the base of the housing. An access opening according to claim 4, characterized in that it further comprises: (a) a first dividing wall fastening flange projecting from and normal to the supporting wall of the dividing wall; and (b) a second dividing wall fastening shoulder projecting from and normal to the bearing surface of the retaining lip of the dividing wall. An access port according to claim 8, characterized in that (a) the first dividing wall fastening flange is positioned along the edge of the dividing wall support shoulder adjacent to the fluid reservoir; Y (b) the second dividing wall fastening flange is positioned along the edge of the abutment surface of the dividing wall retaining flange remote from the rim of the access opening. 10. An access port according to claim 1, characterized in that the access opening has a longitudinal axis coincident with the maximum extension of the access opening and the longitudinal axis of the access opening intersects the ring thereof at respective end ends of the access opening, and the access opening further comprises an outlet rod projecting from the housing in a location adjacent to one of the end ends of the access opening, the outlet rod enclosing a longitudinal fluid passageway that it extends from the end of the outlet rod remote from the housing through the housing to the fluid reservoir. An access port according to claim 2, characterized in that the access opening has a longitudinal axis coinciding with the maximum extension of the access opening and the longitudinal axis of the access opening intersects the ring thereof at both ends end of the access opening, and the access opening further comprises an outlet rod projecting from the housing at a location adjacent to one of the end ends of the access opening, the outlet rod enclosing a longitudinal fluid passage extending from the end of the outlet rod remote from the housing through the housing to the fluid reservoir. An access port according to claim 11, characterized in that the exit rod is carried by the base of the housing and projects through the skirt of the housing cover when the side wall of the base is received in the skirt from the top. An implantable vascular access port comprising: (a) an impenetrable needle housing enclosing a fluid reservoir, the housing having an access opening formed therethrough communicating between the fluid reservoir and the exterior of the housing , the access opening is defined by a continuous elongated surrounding ring; and (b) a generally planar, needle-penetrable, elastomeric dividing wall, the partition wall is positioned in and sealing the access opening in an installed configuration of the dividing wall with the periphery of the partition wall in continuous engagement with the rim of the partition wall. access opening, the dividing wall when free from imposed external forces is able to assume a natural configuration where the periphery of the cross section of the dividing wall taken in the plane thereof is geometrically proportional to and greater than the rim of the partition wall. access opening, by assuming the installed configuration the periphery of the dividing wall is displaced inwardly in the plane of the dividing wall with respect to the natural configuration thereof by forces imposed on the periphery of the dividing wall by the rim of the access opening. An access port according to claim 13, characterized in that the periphery of the dividing wall in the cross section thereof is substantially elliptical. An access port according to claim 13, characterized in that: (a) the dividing wall has a longitudinal axis coinciding with the maximum extension of the dividing wall in the plane thereof, the longitudinal axis of the dividing wall intersects the periphery of the dividing wall at the respective longitudinal ends of the dividing wall, the longitudinal ends of the dividing wall are displaced inward from the natural configuration thereof to the installed configuration thereof substantially by first parallel displacements different from zero directed towards the longitudinal axis of the dividing wall; (b) the dividing wall has a lateral axis coinciding with the maximum extension of the dividing wall in the plane thereof measured perpendicular to the longitudinal axis of the dividing wall, the lateral axis of the dividing wall intersecting the periphery of the dividing wall in respective middle ends thereof, the middle ends of the dividing wall are displaced inward from the natural configuration thereof in the installed configuration thereof by second substantially non-zero second displacements directed parallel to the lateral axis of the dividing wall; and (c) the ratio of the combination of the first displacements to the distance between the longitudinal ends of the dividing wall in the natural configuration thereof is equal to the ratio of the combination of the second displacements to the distance between the middle ends of the dividing wall in the natural configuration of it. An access port according to claim 13, characterized in that: (a) the dividing wall has a longitudinal axis coinciding with the maximum extension of the dividing wall in the plane thereof, and a lateral axis coinciding with the extension maximum of the dividing wall in the plane thereof measured perpendicular to the longitudinal axis of the dividing wall; (b) the distance between a first pair of points on the periphery of the dividing wall placed on the longitudinal axis thereof is reduced in the installed configuration relative to the natural configuration by a first compression distance; (c) the distance between a second pair of points on the periphery of the dividing wall placed on the lateral axis is reduced in the installed configuration relative to the natural configuration by a second compression distance; and (d) the ratio of the first compression distance to the distance between the first pair of points between the natural configuration of the dividing wall is equal to the ratio of the second compression distance to the distance between the second pair of points in the natural configuration of the dividing wall. An access port according to claim 13, characterized in that the dividing wall comprises: (a) an external face on the side of the dividing wall facing the outside of the housing in the installed configuration of the dividing wall; (b) an inner face on the side of the dividing wall opposite the outer face; and (c) support means formed integrally with the dividing wall to prevent folding of the dividing wall in the installed configuration thereof. 18. An access port according to claim 17, characterized in that the support means comprises a needle objective dome on the outer face of the dividing wall. 19. An access port according to claim 18, characterized in that the needle target dome is smaller in extension than the external face of the dividing wall. An access port according to claim 18, characterized in that in the installed configuration of the dividing wall, the needle target dome is displaced towards the outside of the housing by forces imposed on the periphery of the dividing wall by the rim of the access opening. 21. An access port according to claim 17, characterized in that the support means comprises a reinforcing plug on the inner face of the dividing wall. 22. An access port according to claim 21, characterized in that the reinforcing plug is smaller in extension than the internal face of the dividing wall. 23. An access port according to claim 21, characterized in that in the installed configuration of the dividing wall, the reinforcing plug is moved towards the interior of the housing by forces imposed on the periphery of the dividing wall by the rim of the opening of the partition. access. An access port according to claim 13, characterized in that the forces imposed on the periphery of the dividing wall by the rim of the access opening in the installed configuration of the dividing wall produce substantially uniform hydrostatic pressure in the portion of the dividing wall. the dividing wall accessible for the penetration of the needle into the installed configuration of the dividing wall. 25. An access port according to claim 24, characterized in that the substantially uniform hydrostatic pressure in the portion of the dividing wall is in the range of about 0.35 kilograms per square centimeter to about 3.94 kilograms per square centimeter. 26. An access port according to claim 24, characterized in that the substantially uniform hydrostatic pressure in the portion of the dividing wall is in the range of about 0.70 kilograms per square centimeter to about 3.24 kilograms per square centimeter. 27. An access port according to claim 24, characterized in that the substantially uniform hydrostatic pressure in the portion of the dividing wall is in the range of about 1.27 kilograms per square centimeter to about 2.11 kilograms per square centimeter. An implantable vascular access port comprising: (a) a generally planar, needle-penetrable, elastomeric dividing wall having an elongated periphery in a cross-section of the dividing wall taken in the plane thereof; and (b) an impenetrable needle housing defining: (i) a fluid reservoir enclosed within the housing; (ii) a lens aperture formed on the exterior of the housing; and (iii) a dividing wall receiving aperture communicating between the objective aperture and the fluid reservoir, the dividing wall receiving aperture has a generally elongated ring, the aperture of the dividing wall receiving aperture is geometrically proportional to and smaller that the periphery of the dividing wall, the dividing wall is placed in the dividing wall receiving opening with the rim of the dividing wall receiving opening by inwardly displacing the periphery of the dividing wall. 29. An access port according to claim 28, characterized in that the housing comprises a dividing wall retaining flange projecting radially inward toward the dividing wall receiving opening from the rim of the dividing wall receiving opening in the side thereof adjacent to the outer surface of the housing, the edge of the dividing wall retaining rim remote from the rim of the dividing wall receiving aperture defines the periphery of the objective aperture. 30. An access port according to claim 29, characterized in that the edge of the dividing wall retaining rim remote from the rim of the access opening is substantially elliptical. 31. The access port according to claim 29, characterized in that the housing comprises a dividing wall support shoulder projecting radially inwardly from the rim of the dividing wall receiving opening on the side thereof opposite the rim of the wall. retaining dividing wall, the edge of the dividing wall support shoulder away from the rim of the dividing wall receiving aperture is coincident with the periphery of the fluid reservoir. 32. An access port according to claim 31, characterized in that the edge of the dividing wall support shoulder away from the rim of the opening is substantially elliptical. An access port according to claim 31, characterized in that the periphery of the dividing wall is compressed between the dividing wall retaining lip and the dividing wall support shoulder when the dividing wall is placed in the receiving opening of the partition wall. dividing wall. 34. An access port according to claim 28, characterized in that the cross section of the dividing wall taken in the plane thereof is substantially elliptical. 35. An access port according to claim 28, characterized in that the objective aperture is substantially elliptical in the plane thereof. 36. An access port according to claim 28, characterized in that the dividing wall is comprised of a material having a Shore hardness "A" on a scale of about 25 to about 85. 37. An access port according to claim 28, characterized in that the dividing wall is comprised of a material having a Shore hardness "A" on a scale of about 35 to about 75. 38. An access port according to the claim 28, characterized in that the dividing wall is comprised of a material having a Shore hardness "A" on a scale of about 45 to about 65. 39. An access port according to claim 28, characterized in that the dividing wall comprises: (a) an external face on the side of the dividing wall facing outwardly of a housing in the installed configuration of the dividing wall; (b) an inner face on the side of the dividing wall opposite the outer face; and (c) support means formed integrally with the dividing wall to prevent folding of the dividing wall in the installed configuration thereof. 40. An implantable vascular access port comprising: (a) an impenetrable needle housing enclosing a fluid reservoir, the housing comprising: (i) a base comprising a floor and a continuous surrounding side wall that rises from the the side wall ends in a continuous dividing wall support shoulder remote from the floor, the interior space of the side wall of the base corresponds to the fluid reservoir of the housing; and (ii) a cover configured to receive the dividing wall support shoulder and the side wall of the base, the cover has an access opening formed therethrough which communicates with the fluid reservoir of the housing when the rear wall dividing wall support and side wall of the base are received in the cover, the access opening has an elongated ring comprising a continuous surrounding surface oriented perpendicular to the plane of the access opening; (b) a generally planar, needle-penetrable, elastomeric dividing wall, the partition wall is positioned in and sealing the access opening in an installed configuration of the dividing wall with the periphery of the partition wall in continuous engagement with the rim of the partition wall. access opening and with the periphery of the dividing wall secured against the dividing wall support shoulder of the side wall of the base by the lid, the partition wall when free of imposed external forces is able to assume a natural configuration where the periphery of the dividing wall in a cross section taken in the plane thereof is geometrically proportional to and larger than the rim of the access opening, whereby upon assuming the installed configuration, the periphery of the dividing wall is displaced inwardly in the plane of the dividing wall in relation to the natural configuration of the same by forces imposed on the periphery of the dividing wall by the rim of the access opening; (c) an outlet rod projecting from the housing and enclosing a longitudinal fluid passage communicating between the end of the outlet rod remote from the housing through the housing to the fluid reservoir. 41. An access port according to claim 40, characterized in that: (a) the dividing wall has a longitudinal axis coinciding with the maximum extension of the dividing wall in the plane thereof, the longitudinal axis of the dividing wall intersects the periphery of the dividing wall at respective longitudinal ends of the dividing wall, the longitudinal ends of the dividing wall are displaced inward from the natural configuration thereof to the installed configuration thereof by first non-zero displacements directed parallel to the axis longitudinal of the dividing wall; (b) the dividing wall has a lateral axis coinciding with the maximum extension of the dividing wall in the plane thereof measured perpendicular to the longitudinal axis of the dividing wall, the lateral axis of the dividing wall intersecting the periphery of the dividing wall in respective middle ends of the dividing wall, the middle ends of the dividing wall are displaced inward from the natural configuration thereof to the installed configuration thereof by second substantially deferential displacements of zero directed parallel to the lateral axis of the dividing wall; and (c) the ratio of the combination of the first displacements to the distance between the longitudinal ends of the dividing wall in the natural configuration thereof is equal to the ratio of the combination of the second displacements to the distance between the middle ends of the dividing wall in the natural configuration of it. 42. An access port according to claim 40, characterized in that the cross section of the dividing wall taken in the plane thereof is substantially elliptical. 43. An access port according to claim 40, characterized in that the dividing wall comprises: (a) a substantially flat dividing wall body having an external face on one side of the dividing wall facing the outside of the housing in the installed configuration of the dividing wall and an internal face on the side of the dividing wall opposite the external face; (b) a needle target dome on the outer face of the dividing wall body; and (c) a reinforcing dome on the inner face of the dividing wall body. 44. An access port according to claim 40, characterized in that the base and the cover are comprised of plastic. 45. An access port according to claim 40, characterized in that the base and the cover are comprised of metal. 46. An access port according to claim 40, characterized in that the dividing wall is comprised of silicone. 47. An implantable vascular access port comprising: (a) an impenetrable needle housing enclosing a fluid reservoir, the housing having an elongated access opening formed therethrough that communicates between the fluid reservoir and the exterior of the reservoir. accommodation; and (b) an elongate, generally planar penetrable, elastomeric needle-shaped partition wall having a periphery in a cross-section of the partition wall taken in the plane thereof enclosing an area greater than the cross-sectional area of the partition opening. access, the dividing wall is positioned in the access opening in an installed configuration thereof wherein forces exerted on the partition wall by the access opening move the periphery of the partition wall inward and produce substantially uniform hydrostatic pressure in the wall. portion of the dividing wall accessible for the penetration of the needle into the installed configuration of the dividing wall. 48. An access port according to claim 47, characterized in that the housing comprises: (a) a base comprising a floor and a continuous surrounding side wall that rises therefrom, the interior of the side wall of the base corresponds to the fluid reservoir of the housing; and (b) a cover comprising an upper wall and a skirt that hangs therefrom, the cover is configured to receive in the skirt thereof the end of the side wall of the base remote from the floor thereof, and the Access opening is formed through the top wall of the lid at a location communicating with the fluid reservoir of the housing when the side wall of the base is received in the lid skirt. 49. An access port according to claim 47, characterized in that the dividing wall comprises: (a) an external face on the side of the dividing wall facing the outside of the housing when the dividing wall is placed in the access opening; (b) an inner face on the side of the dividing wall opposite the outer face; and (c) a needle objective dome on the outer face of the dividing wall. 50. An access port according to claim 49, characterized in that the needle target dome has an eccentricity on a scale greater than 0.72. 51. An access port according to claim 49, characterized in that the needle target dome has an eccentricity in a scale greater than 0.81. 52. An access port according to claim 49, chaerized in that the needle objective dome has an eccentricity on a scale greater than 0.90. 53. An access port according to claim 49, chaerized in that the needle objective dome is smaller in extension than the external face of said dividing wall. 54. An access port according to claim 47, chaerized in that the cross section of the dividing wall taken in the plane thereof has an eccentricity on a scale greater than about 0.72. 55. An access port according to claim 47, chaerized in that the cross section of the dividing wall taken in the plane thereof has an eccentricity on a scale greater than about 0.81. 56. An access port according to claim 47, chaerized in that the cross section of the dividing wall taken in the plane thereof has an eccentricity on a scale greater than about 0.90. 57. An access port according to claim 47, chaerized in that the access opening has an eccentricity on a scale greater than 0.72. 58. An access port according to claim 47, chaerized in that the access opening has an eccentricity on a scale greater than 0.81. 59. An access port according to claim 47, characterized in that the access opening has an eccentricity on a scale greater than 0.90. 60. An access port according to claim 47, characterized in that: (a) the dividing wall has a longitudinal axis coinciding with the maximum extension of the dividing wall in the plane thereof, and a lateral axis coinciding with the extension maximum of the dividing wall in the plane thereof measured perpendicular to the longitudinal axis of the dividing wall; (b) the distance between a first pair of points on the periphery of the dividing wall placed on the longitudinal axis thereof is reduced in the installed configuration relative to the natural configuration at a first compression distance; (c) the distance between a second pair of points on the periphery of the dividing wall placed on the lateral axis is reduced in the installed configuration relative to the natural configuration at a second compression distance; and (d) the ratio of the first compression distance to the distance between the first pair of points in the natural configuration of the dividing wall is equal to the ratio of the second compression distance to the distance between the second pair of points in the natural configuration of the dividing wall. 61. An access port according to claim 47, characterized in that the cross section of the dividing wall taken in the plane thereof is substantially elliptical. 62. An access port according to claim 47, characterized in that the cross section of the dividing wall taken in the plane thereof is substantially oval. 63. An access port according to claim 47, characterized in that the dividing wall has a longitudinal axis coinciding with the maximum extension of the periphery of the dividing wall in the cross section thereof taken in the plane thereof, the The longitudinal axis of the partition wall intersects the periphery thereof at respective end end portions of the partition wall, and the periphery of each of the end end portions of the partition wall is substantially parabolic. 64. An implantable vascular access port comprising: (a) an impenetrable needle housing enclosing a fluid reservoir; (b) a generally planar, needle-penetrable, elastomeric dividing wall having an elongated periphery in a cross-section of the partition wall taken in the plane thereof; and (c) access means formed in the housing between the fluid reservoir and the exterior of the housing to receive the partition wall and to produce a substantially uniform hydrostatic pressure in the portion of the partition wall accessible for needle penetration when the wall Divide is received in the means of access. 65. An access port according to claim 64, characterized in that the access means comprise an access opening communicating between the fluid reservoir and the exterior of the housing, the rim of the access opening is substantially geometrically proportional and less than the periphery of the dividing wall, whereby the rim of the access opening radially displaces the periphery of the dividing wall inward when the dividing wall is received in the access opening. 66. An access port according to claim 64, characterized in that the access means comprise: (a) an access opening communicating between the fluid reservoir and the exterior of the housing and having a surrounding continuous elongated ring; (b) a dividing wall retaining flange projecting radially inward toward the access opening from the rim side thereof adjacent the exterior of the housing; and (c) a dividing wall support shoulder projecting radially inwardly from the rim of the access opening on the side thereof opposite the dividing wall retaining rim., the periphery of the dividing wall is compressed between the dividing wall retaining rim and the dividing wall support shoulder, when the dividing wall is received in the access opening. 67. An access port according to claim 64, characterized in that the access means comprise: (a) restraining means for moving the periphery of the dividing wall radially inward in the plane of the dividing wall; and (b) fastening means for driving against opposite sides of the dividing wall at the periphery thereof. 68. An access port according to claim 67, characterized in that the restriction means comprises an access opening communicating between the fluid reservoir and the exterior of the housing, the rim of the access opening is in a substantially geometrically proportional way and smaller than the periphery of the dividing wall. 69. An access port according to claim 68, characterized in that the fastening means comprise: (a) a dividing wall retaining flange projecting radially inward toward the access opening from the rim side of the same adjacent to the exterior of the housing; and (b) a dividing wall support shoulder projecting radially inward toward the access opening from the side of the rim opposite the dividing wall retaining rim, the distance between the dividing wall retaining rim and the shoulder wall. The dividing wall support is smaller than the thickness of the dividing wall between the opposite faces thereof at the periphery thereof. 70. An access port according to claim 69, characterized in that it further comprises a first dividing wall fastening flange projecting from and normal to the dividing wall support shoulder.71. An access port according to claim 69, characterized in that it further comprises a second dividing wall fastening flange that is # project from the side of the wall retaining flange 5 divider opposite the dividing wall support shoulder. 72. An access port according to claim 69, characterized in that the dividing wall support shoulder comprises a continuous surrounding flat surface. 10 73. An access port according to claim 69, characterized in that the side of the dividing wall retaining flange opposite the dividing wall support shoulder comprises a flat, continuous surrounding surface. 74. An access port according to claim 64, characterized in that the periphery of the dividing wall is substantially elliptical. 75. An implantable vascular access port comprising: (a) an impenetrable needle housing enclosing a fluid reservoir communicating with the exterior of the housing through an access opening, the rim of the access opening is substantially elliptical; and (b) a generally flat dividing wall, 25 penetrable by needle, elastomer having a periphery in a cross section of the dividing wall taken in the plane thereof which is substantially elliptical and which is larger than the rim of the access opening, the dividing wall is placed in the aperture of access with the periphery of the dividing wall in sealed engagement with the rim of the access opening, whereby upon placing the partition wall in the access opening, the periphery of the partition wall is displaced radially inwardly by the rim of the partition wall. access opening in a direction parallel to the plane of the dividing wall. 76. An access port according to claim 75, characterized in that the dividing wall exhibits substantially uniform hydrostatic pressure in the portion of the partition wall accessible for needle penetration, when the dividing wall is placed in the access opening. 77. An access port according to claim 76, characterized in that the substantially uniform hydrostatic pressure in the portion of the partition wall accessible for needle penetration is on a scale from about 0.70 kilograms per square centimeter to about 1.83 kilograms per square centimeter. . 78. An access port according to claim 75, characterized in that the periphery of the dividing wall is oval in shape. 79. An access port according to claim 75, characterized in that the periphery of the dividing wall comprises an elongated polygon. 80. An access port according to claim 79, characterized in that the polygon has at least eight sides. 81. An access port according to claim 79, characterized in that the polygon has at most eight sides. 82. An access port according to claim 75, characterized in that the dividing wall has a longitudinal axis coinciding with the maximum extension of the periphery of the dividing wall in the cross section thereof taken in the plane thereof, the The longitudinal axis of the partition wall intersects the periphery thereof at respective end end portions of the partition wall, and the periphery of each of the end end portions of the partition wall is substantially parabolic. 83. An access port according to claim 75, characterized in that the periphery of the dividing wall is a complete ellipse. 84. An access port according to claim 75, characterized in that the periphery of the dividing wall is a continuous curve definable by a simple mathematical equation. 85. An access port according to claim 75, characterized in that the dividing wall is comprised of a material having a Shore hardness "A" on a scale of about 45 to about 65. 86. An access port in accordance with Claim 75, characterized in that when the partition wall is positioned in the access opening, the partition wall exhibits a substantially uniform needle retention force on a scale of approximately 90.8 grams to approximately 1589 grams. 87. An access port according to claim 75, characterized in that when the dividing wall is placed in the access opening, the partition wall exhibits a substantially uniform needle retention force on a scale of approximately 158.90 grams to approximately 1135 grams. . 88. An access port according to claim 75, characterized in that when the dividing wall is placed in the access opening, the partition wall exhibits a substantially uniform needle retention force in the range of approximately 227 grams to approximately 681 grams. . 89. A needle-permeable, elastomeric partition wall for installation in a radially inwardly compressed condition 5 that seals an access opening that communicates through the housing of an implantable vascular access port with a fluid reservoir therein, the wall dividing characterized in that it comprises: (a) an elongated dividing wall body ^ 10 generally penetrable by needle having a longitudinal axis coinciding with the maximum extension of the dividing wall body in the plane thereof; and (b) a periphery of surrounding sides placed generally perpendicular to the plane of the wall body 15 partition, the longitudinal axis of the dividing wall body intersects the periphery of the dividing wall body in ^ first and second respective end end portions thereof, and the periphery of the first end end portion of the partition wall body in the plane of the wall body The dividing line assumes a first substantially parabolic shape. 90. A dividing wall according to claim 89, characterized in that the periphery of the second end end portion of the dividing wall body in the plane of the dividing wall body assumes a second 25 substantially parabolic form. 91. A dividing wall according to claim 89, characterized in that the first parabolic shape has a focal point located on the longitudinal axis of the dividing wall body. 92. A dividing wall according to claim 90, characterized in that the periphery of the first end end portion of the dividing wall body intersects the periphery of the second end end portion of the partition wall body non-tangentially at a first vertex and a second vertex. 93. A partition wall according to claim 90, characterized in that the periphery of the second end end portion of the partition wall body is a mirror image of said periphery of the first end end portion of the partition wall body. 94. A partition wall according to claim 90, characterized in that the first end end portion of the partition wall body and the second end end portion of the partition wall body are each symmetrical with respect to the longitudinal axis of the partition wall body.