Abstract:
A valve apparatus for medical applications, comprises a flexible member extending across a lumen through which a flow of materials is to be controlled. The flexible member includes a plurality of movable elements formed on opposite sides of a slit extending through the flexible member. The moveable members are biased so that when a pressure less than a predetermined threshold value is applied to the flexible member, the moveable elements are maintained in a closed position in which no flow is permitted past the flexible member and, when a pressure at least as great as the threshold value is applied to the flexible member, the moveable elements are moved to an open position separated from one another along the slit permitting flow through the lumen.

Description:
BACKGROUND INFORMATION 
     Many medical procedures require repeated and prolonged access to a patient&#39;s vascular system. For example, during dialysis treatment blood may be removed from the body for external filtering and purification, to make up for the inability of the patient&#39;s kidneys to carry out that function. In this process, the patient&#39;s venous blood is extracted, processed in a dialysis machine and returned to the patient. The dialysis machine purifies the blood by diffusing harmful compounds through membranes, and may add to the blood therapeutic agents, nutrients etc., as required before returning it to the patient&#39;s body. Typically the blood is extracted from a source vein (e.g., the vena cava) through a catheter sutured to the skin with a distal needle of the catheter penetrating the source vein. 
     It is impractical and dangerous to insert and remove the catheter for each dialysis session. Thus, the needle and catheter are generally implanted semi permanently with a distal portion of the assembly remaining within the patient in contact with the vascular system while a proximal portion of the catheter remains external to the patient&#39;s body. The proximal end is sealed after each dialysis session has been completed to prevent blood loss and infections. However, even small amounts of blood oozing into the proximal end of the catheter may be dangerous as thrombi can form therein due to coagulation which thrombi may then be introduced into the patient&#39;s vascular system when blood flows from the dialysis machine through the catheter in a later session. 
     A common method of sealing the catheter after a dialysis session is to shut the catheter with a simple clamp. This method is often unsatisfactory because the repeated application of the clamp may weaken the walls of the catheter due to the stress placed on the walls at a single point. In addition, the pinched area of the catheter may not be completely sealed allowing air to enter the catheter which may coagulate any blood present within the catheter. Alternatively, valves have been used at the opening of the catheter in an attempt to prevent leaking through the catheter when the dialysis machine is disconnected. However, the unreliability of conventional valves has rendered them unsatisfactory for extended use. 
     SUMMARY OF THE INVENTION 
     In one aspect the present invention is directed to a valve apparatus for medical applications, comprising a flexible member extending across a lumen through which a flow of materials is to be controlled. The flexible member includes a plurality of movable elements formed on opposite sides of a slit extending through the flexible member. The moveable members are biased so that when a pressure less than a predetermined threshold value is applied to the flexible member, the moveable elements are maintained in a closed position in which no flow is permitted past the flexible member and, when a pressure at least as great as the threshold value is applied to the flexible member, the moveable elements are moved to an open position separated from one another along the slit permitting flow through the lumen. 
     In a different aspect, the present invention is directed to a dialysis connector comprising a valve housing having a first end connectable to a patient line and a second end mounted to a dialysis line and a flow passage of the housing being connected to the patient line and being operatively connectable to the dialysis line in combination with a valve element mounted within the flow passage of the housing, the valve element including a flexible member extending across the flow passage, the flexible member including a plurality of movable elements formed on opposite sides of a first slit extending through the flexible member, the moveable members being biased so that, when a pressure less than a predetermined threshold value is applied to the flexible member, the moveable elements are maintained in a closed position in which no flow is permitted past the flexible member and, when a pressure at least as great as the threshold value is applied to the flexible member, the moveable elements are moved to an open position separated from one another along the first slit permitting flow through the flow passage. 
     In yet another aspect, the invention is directed to a flow shutoff device for medical applications comprising a housing attachable to a patient line and a pressure actuated valve mounted within the housing to selectively restrict flow therethrough, wherein movable elements of the valve are biased toward a closed position and are movable to an open position when a pressure applied to the valve exceeds a predetermined threshold value. Flow through the housing is prevented when the movable elements are in the closed position. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a vascular access catheter; 
         FIG. 2  is a schematic drawing of a vascular access catheter inserted in a patient&#39;s vein; 
         FIG. 3  is a top elevation view of a valve element according to an exemplary embodiment of the present invention; 
         FIG. 4  is a top elevation view of a valve element according to another embodiment of the present invention; 
         FIG. 5  is a top elevation view of a valve element with double horizontal slits according to an embodiment of the present invention; 
         FIG. 6  is a top elevation view of a valve element with Y-configured slits according to an embodiment of the present invention; and 
         FIG. 7  is a top elevation view of a valve element with a curved slit according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Semi-permanently placed catheters may be useful for a variety of medical procedures which require repeated access to a patient&#39;s vascular system in addition to the dialysis treatments mentioned above. For example, chemotherapy infusions may be repeated several times a week for extended periods of time. For safety reasons, as well as to improve the comfort of the patient, injections of these therapeutic agents may be better carried out with an implantable, semi-permanent vascular access catheter. Many other conditions that require chronic venous supply of therapeutic agents, nutrients, blood products or other fluids to the patient may also benefit from implantable access catheters, to avoid repeated insertion of a needle into the patient&#39;s blood vessels. Thus, although the following description focuses on dialysis, those skilled in the art will understand that the invention may be used in conjunction with any of a wide variety of procedures which require long term implantation of catheters within the body. 
     Examples of such implantable catheters include those manufactured by Vaxcel™, such as the Chronic Dialysis Catheter and the Implantable Vascular Access System. These devices typically are inserted under the patient&#39;s skin, and have a distal end which includes a needle used to enter a blood vessel. The devices also have a proximal end extending outside the body for connection with an outside line. These semi-permanent catheters may be sutured to the patient&#39;s skin to maintain them in place while the patient goes about his or her normal occupations. 
       FIGS. 1 and 2  show an exemplary implantable catheter for kidney dialysis. Catheter  10  has a distal end  12  that is insertable under the skin and into the patient&#39;s vein, and which remains within the patient&#39;s body for the life of the catheter  10 . For example, catheter  10  may remain implanted in the patient for two years. As shown more clearly in  FIG. 2 , distal end  12  fits within a vein  8  (e.g., the vena cava). During dialysis, blood from the patient is removed through a patient line such as catheter  10 , and is purified by a dialysis machine (not shown) which is connected to hubs  18  and  20  of catheter  10  by a dialysis line. Catheter  10  in this example includes two lumens  22  and  24  which are used respectively to remove blood from and reintroduce blood to the vessel  8 . Lumen  22  terminates at an inflow tip  14  formed at the distal end  12  of the catheter  10  while lumen  24  terminates at an outflow tip  16  formed at the distal end  12 . Inflow tip  14  and outflow tip  16  are connected to corresponding inflow and outflow hubs  18 ,  20 , which are accessible outside the body and which may be connected to external lines leading to and from the dialysis machine. 
     After the dialysis or other procedure has been completed, the catheter  10  is disconnected from the dialysis machine, and is left within the patient fluidly coupled to the patient&#39;s vascular system. When not connected to a dialysis machine, the catheter  10  is securely sealed to prevent fluids and gases from crossing into the proximal end of catheter  10  by preventing flow in and out of catheter  10  through hubs  18 ,  20 . As would be understood by those skilled in the art, this sealing prevents the risks associated with infections and thrombi which might be experienced if air or other gas or liquid and/or pathogens were to pass into the catheter  10 . 
     As indicated above, although conventional clamps or clips may be used to seal the catheter  10  between medical sessions, over time the wall of the catheter  10  may be damaged in the area to which the clamp or clip is applied. Sealing clamps or clips may also become dislodged during patient activities, increasing the risk of leaks, infections, etc. Placing a clamp on the catheter  10  also increases the bulk of the distal end of the catheter which is exposed outside the patient&#39;s body, and may adversely affect patient comfort. 
     Therefore, the catheter  10  includes one or more self sealing valves along each of the lumens  22 ,  24  to seal them when not being used during dialysis and other transfusion or infusion sessions. For example, hubs  18 ,  20  may be used to house one or more valves each of which is designed to seal the corresponding lumen  22 ,  24  under certain conditions, and to allow passage of fluids under other conditions. For example, in the case of dialysis treatment, the system of valves may seal the catheter  10  when it is not connected to an operating dialysis machine, and may allow both an outflow of non-purified blood and an inflow of purified blood to the patient when an operating dialysis machine is connected thereto. 
     Preferably, a valve system for use in such semi-permanent catheters should, when in the open position, allow a flow rate therethrough which is sufficient to allow the procedure to be completed in an acceptably short time. When in the closed position, the valve should completely seal the catheter. That is, if the valve requires excessive force to be opened, the flow rate through the catheter may be reduced to the point where the time required for the procedure is unacceptably extended. In addition, a valve system having moving parts of too great a bulk may also result in larger blockages within the catheter or the hub housing the valve thereby reducing the flow rate through the catheter. The mechanism that moves the valve into the open and closed positions may block the flow through the valve if it protrudes into the flow passage, and thus the size and bulk of the mechanism should preferably be minimized to avoid impeding flow through the open valve. 
     The portion of the valve that moves to the open position must also completely return to the closed position when the session is completed. For example, a pressure sensitive valve may be used, which opens in response to a pressure driving the flow through the catheter. In the case of a dialysis catheter, the valve or valves may open when a pressure generated by the dialysis machine exceeds a predetermined threshold to allow circulation and purification of the patient&#39;s blood. When the dialysis machine is turned off and the pressure in the dialysis line is reduced below the threshold, the valve is completely sealed to prevent further flow from and to the patient. Some pressure is also present in the patient line connecting the valve to the patient&#39;s vein as a result of the circulation in the patient&#39;s vascular system. Each of the valves must therefore be designed so that it will not respond to such pressure variations introduced by the vascular system and will not open unless a pressure above the threshold is generated externally, for example, by a dialysis machine. 
     The exemplary embodiments according to the present invention described herein obtain both a secure closure of a semi-permanent catheter implanted in a patient when the catheter is not in use and permit a flow passage that is easily opened to allow a sufficient flow rate when access to the vascular system is necessary. 
     In many applications, the pressure actuated valve system remains open for the entire length of a therapeutic session, which may last a significant amount of time. For example, in the case of a dialysis session, the valve system may remain open for up to four hours at a time, during sessions carried out up to three times a week. The exemplary embodiments of valves according to the present invention provide a seal to the catheter even after being maintained in the open position for prolonged periods of time. 
     Specific embodiments of the present invention will be described below with reference to the drawings.  FIG. 3  shows a top plan view of an exemplary embodiment of a valve element  100  used to control the flow through a medical tube such as the catheter  10  of  FIG. 1 . For example, valve element  100  may be located in a flow passage within a valve housing formed in either or both of the hubs  18 ,  20 , through which fluids flow to and from the distal end  12 . As will be apparent to those skilled in the art, the valve housing may be placed at any other location along the length of catheter  10  and may be unitary with the catheter  10 , or may be formed as a separate component. In addition, it will be apparent that a single valve housing with dual flow passages and one valve  100  within each of the flow passages may be provided instead of two separate valve housings for the hubs  18 ,  20 , respectively, to independently control fluid flow in each direction. Inflow to the patient may take place via one of the dual flow passages of the single hub, and outflow from the patient via the other flow passage. 
     In the exemplary embodiment shown in  FIG. 3 , the valve element  100  is formed as a flexible disk  110  having dimensions appropriate to the size of the flow passage within the one of the hubs  18 ,  20  into which it is to be mounted. The flexible disk  110  may be formed of any sufficiently flexible material, such as a polymeric material. More specifically, the flexible disk  110  may be formed of silicone. The flexible disk  110  may also include a peripheral portion  116  adapted to be connected to an inner surface of the flow passage to seal perimeter of the flow passage around flexible disk  110 . The valve element  100  includes a slit  112  which is extends through the entire thickness of the flexible disk  110 . The slit  112  separates two movable elements  118  from one another to form an openable portion of the disk  110  which creates a flow passage therethrough when the movable elements  118  are placed in an open position separated from one another. For example, when the edges  120  of the movable elements  118  are moved out of the plane of the flexible disk  110 , an opening through the flexible disk  110  is formed along the slit  112 . In this exemplary embodiment, the movable elements  118  are formed as resilient flaps substantially constrained in all directions except along the slit  112 . Accordingly, the elements  118  are substantially constricted and may only move along the edges  120  to form a relatively small opening. 
     In one exemplary embodiment the valve element  100  is used in conjunction with dialysis equipment, and movement of movable elements  118  to the open position is prompted by an actuating pressure of a fluid within dialysis lines  30 ,  32  which may be connected to the hubs  18 ,  20 , respectively, to connect the catheter  10  to a dialysis machine. In particular, an actuating pressure is generated by pumps in the dialysis machine to move the patient&#39;s blood between the patient and the filtration equipment. Although the movable elements  118  are formed as flexible flaps, they are formed with a predetermined amount of resilience to allow them to remain in the closed position when not acted upon by the pressure in dialysis lines  30 ,  32 . Specifically, the elements  118  are biased to remain in the closed position abutting one another along edges  120  at all times when they are not acted on by a pressure outside a range of approximately 22 to 44 mmHg. Specifically, as mentioned above, the elements  118  are formed so that the amount of resilience is sufficient to maintain them in the closed position without being forced open by fluid forces generated by natural circulation of the patient&#39;s blood. As would be understood by those skilled in the art, the amount of pressure required to open the movable elements  118  is a function of the resilience of the material forming those elements, the size and shape of the slit  112 , and the size of the flow passage containing the valve element  100 . The details of the geometry of the slit  112  and the movable elements  118  may be selected to obtain the desired characteristics of maximum flow in the open position, and to ensure that valve element  100  seals the flow passage when the pressure is removed. 
     A stiffening element  114  may be included in valve element  100 , to better control the amount of force biasing the movable elements  118  to the closed position. In particular, coupling a stiffening element to an otherwise flexible disk  110  (or forming a stiffening element integrally therewith) provides a valve element  100  including movable elements  118  more resistant to plastic deformation during sessions lasting multiple hours in which the valve element  100  is kept open. An example of a suitable stiffening member is the addition of stiffening ring  114  to the flexible disk  110 . The stiffening element  114  may, for example, be formed of a wire or embedded within the valve element  100 . Of course, those skilled in the art will understand that the stiffening element  114  may be formed of metal, plastic or any substantially rigid material. 
     In one exemplary embodiment, the stiffening ring  114  may be embedded within the material of the disk  110 , to minimize the bulk of the combination. In different embodiments, stiffening elements may be bonded to one or both sides of the valve element  100 , depending on the requirements of the use of the valve element  100 . The shape of the stiffening elements used in the valve element  100  may also be modified, depending on the desired characteristics of the force urging the movable elements  118  to the closed position. Alternatively, the stiffening elements may be integrally formed with the disk  110 . 
     As indicated above, the maximum flow that can pass through valve element  100  and the ability to close fully when the actuating pressure is removed are important design parameters for the pressure actuated valves described herein. According to embodiments of the invention, these design parameters may be controlled by properly shaping and sizing the slit or slits  112 . Selection of the dimensions of the slit  112  results in movable elements  118  having a desired shape and being constrained along selected edges. In the exemplary embodiment shown in  FIG. 3 , a linear slit having a width d of approximately 0.002 inches and a length of approximately 0.150 to 0.280 inches is provided in the center of an oval flexible disk  110  extending along a major axis of the disk. The flexible disk  110  could have a thickness of approximately 0.015 to 0.030 inches and could be manufactured from silicone, as a result its surface resistivity rating would be approximately 35 to 70 A. The movable elements  118  used in this configuration are flaps that form an opening by deflecting away from the plane of the disk  110  due to their flexibility, since they are constrained along all sides except along the slit  112 . This configuration provides satisfactory performance in a dialysis catheter application, with the catheter having conventional dimensions and providing conventional flow rates. For example, the pressure to which the valve may be subjected during dialysis may be in the range of 200 to 285 mmHg while the pressures applied to the valve by the patient&#39;s vascular system are expected to remain below 22 mmHg. Thus, the valve system will preferably be designed to remain sealed when not subjected to a pressure of at least 44 mmHg and, when subjected to the a pressure above that threshold should preferably allow a flow rate of at least 300 ml/min and more preferably at least 350 ml/min without substantially failing to meet these criteria during a life span of one or more years while being subjected to 3 or more uses of up to 4 hours each per week. 
     The performance characteristics of the valve element  100  can be further tuned by selecting an appropriate length l of the slit  112 . By altering this length l, both the maximum flow rate and the opening/closing performance of the valve element  100  will be changed. For example, increasing the length of the slit  112 , other parameters being the same, increases a maximum size of the opening through the flexible disk  110 , and makes it easier to displace the movable elements  118  to the open position as they are unconstrained along longer edges  120 . For the same reason, the movable elements  118  are subjected to a reduced force biasing them toward the closed position when the actuating pressure is removed. Both the width d and the length/of the slit  112  are selected as a tradeoff between ease/size of the opening and the biasing force closing the valve element  100  after use. 
     A different exemplary configuration of slits to define the movable elements is shown in  FIG. 4 . In this embodiment, a flexible disk  210  is provided with slits  212 ,  214  in a substantially H-shaped configuration that define movable elements  218 . The slit  212  is a substantially linear slit aligned with a major dimension of the disk  210 , and the slits  214  extend substantially perpendicular to slit  212 , disposed near terminating points thereof. This configuration of slits permits the movable elements  218  to more easily move to the open configuration, since each movable element  218  is unconstrained along both the slit  212  and the slits  214 . The pressure generated by an external pump, such as a dialysis pump, thus can more easily force the movable elements  218  to the open position. The two additional unconstrained sides of the movable elements  218  also form a larger open area of the flexible disk  210 , so that a greater flow rate can pass through the valve element  200 . 
     Additional resilient elements may also be used in the exemplary embodiment shown in  FIG. 4  to achieve desired closing characteristics of the valve element  200 . For example, a pair of resilient elements  220  may be disposed substantially parallel to the slit  212  on either side thereof. The resilient elements  220  control the deflection and provide a force biasing the movable elements  218  toward the closed position along the axis of the slit  212 . Those skilled in the art will understand that additional resilient elements  222  may be used to increase the biasing force and/or to control the deflection of the movable elements  218  along an axis parallel to the slits  214 . This exemplary combination of H-configured slits and corresponding H-configured resilient elements results in a high flow, easily opened pressure actuated valve element  200 , which is able to completely return to the closed position once the actuating pressure is removed. This configuration also resists plastic deformation that may occur when valve elements are kept in the open position for extended periods of time, and which may prevent the valve from fully closing due to retaining a “memory” of the open position. 
     Another exemplary embodiment according to the present invention is depicted in  FIG. 5 . In this embodiment, a double horizontal slit is used to define the movable elements of a valve element  250 . More specifically, a pair of substantially parallel slits  262  extends through the flexible disk  260 , substantially along a major dimension thereof. In the case of a substantially elliptical flexible disk  260 , as shown, the slits  262  are substantially parallel to a major axis of the ellipse. A movable element  264  is thus defined substantially at the center of the flexible disk  260 , and is constrained only at ends  265  thereof near termination points of the slits  262 . 
     The greater unconstrained length of the sides of the movable element  264  along the slits  262 , enables a large flow area to open as a result of an actuating pressure. For the same reason, a relatively low actuating pressure is needed to open the movable element  264 . To ensure a complete closing of valve element  250  when the actuating pressure is removed, for example, resilient elements may be added around the slits  262  to further bias the movable element  264  to the closed position. In the exemplary embodiment shown in  FIG. 5 , resilient elements  266 ,  268  are disposed in a substantially rectangular configuration surrounding the slits  262 . In this configuration the resilient elements  266 ,  268  control the deflection of the movable element  264  in directions substantially parallel and perpendicular to the slit orientation and provide a biasing force that closes the movable element  264  when the actuating pressure is removed. The resilient elements  266 ,  268  may form a complete rectangle, or may be separated at the vertices. 
       FIG. 6  shows yet another embodiment of the pressure actuated valve according to the present invention. In this exemplary embodiment, a linear slit is combined with a pair of Y-configured slits to provide a larger flow area when the valve element is placed in the open position by an actuating pressure thereagainst. As shown in the drawing, the valve element  300  is formed as a flexible disk  310  which, in this example, has a substantially elliptical shape. It will be apparent to those skilled in the art that different shapes of the flexible disk  310  may be used, depending on the shape and dimensions of the housing in which the valve element  300  is placed. A linear slit  312  is formed in the flexible disk  310 , for example along a major dimension thereof, and is complemented by two pairs of slits  314 . A first pair of the slits  314  is disposed at a first end of the slit  312  with a second one of the pairs of slits  314  being formed at the second end of the slit  312 . The slits  314  are formed at an angle with the slit  312 , so that, at each end of the slit  312 , a substantially Y-shaped configuration of slits is formed. 
     In the exemplary embodiment shown, the slits  312  and  314  do not touch one another so that the movable elements  320  are continuous with portions  322  of the flexible disk  320 . In different embodiments, the slits  312  and  314  may intersect with one another, breaking the flexible disk  320  into additional distinct moving elements. In the exemplary embodiment shown, the movable elements  320  are unconstrained along the slits  312 ,  314 , but are constrained in the region between the slits by being continuous with the portions  322  of the flexible disk  320 . The addition of the Y-configured slits permits the movable elements  320  to open to a greater extent under an actuating pressure, while retaining a biasing force sufficient to close the opening when the actuating pressure is removed. To further bias the movable elements  320  toward the closed position, resilient elements  316 ,  318  may be added. As discussed in the context of previous embodiments, the resilient elements  316 ,  318  may be disposed in a substantially rectangular pattern around the slits  312 ,  314  to control the deflection and closure of the movable elements  320  in two perpendicular directions. The resilient elements  316 ,  318  may form a completely rectangular enclosure as shown in  FIG. 6 , or may have open vertices, as shown in previous embodiments. As would be understood by those skilled in the art, the relative size and orientation of the slits  312 ,  314  may be selected to give desired flow and closing properties, for a given flexible disk  320 . 
     A further exemplary embodiment of the invention is depicted in  FIG. 7 . In this example, the valve element  350  comprises a flexible disk  360  having a slit  362  extending therethrough. The slit  362  is not a linear slit, but instead is curved about a principal axis of the flexible disk  360 . In the example shown in  FIG. 7 , the slit  362  follows a generally sinusoidal path. However other curved paths may be used with similar effect. The slit  362  defines two movable elements  364 ,  366  which are complementary to each other on opposite sides of the slit  362 . A benefit of this configuration is that, for a given length/of the slit  362 , a larger opening area of the valve element  350  may be obtained. Since the unconstrained edges of the movable elements  364 ,  366  are longer due to their curved shape, a given actuating pressure is able to displace a larger portion of the movable elements  364 ,  366  to the open position. This allows for a larger flow area through the valve element  350 . 
     As was the case in other exemplary embodiments of the invention, the resilience of the movable elements  364 ,  366  is controlled to ensure the valve fully closes once the actuating pressure is removed, and is not subject to “memory” effects after being open for extended periods of time. Accordingly, the resilience of the material forming the movable elements  364 ,  366  can be controlled, and additional resilient elements may be incorporated in the flexible disk  360 , as described above with respect to other embodiments. 
     The present invention has been described with reference to specific exemplary embodiments. Those skilled in the art will understand that changes may be made in details, particularly in matters of shape, size, material and arrangement of parts. For example, different flexible disks may be used to form the pressure sensitive valve, and may have different dimensions than those shown. Furthermore, as would be understood by those of skill in the art, any of the various features of the different embodiments described may be combined in any manner to take advantage of their various properties. Accordingly, various modifications and changes may be made to the embodiments without departing from the broadest scope of the invention as set forth in the claims that follow. The specifications and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.