CROSS-REFERENCE TO PRIOR APPLICATIONS
This application is a continuation of, and claims priority to, copending U.S. application Ser. No. 10/630,885, filed on Jul. 30, 2003.
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Many medical procedures require repeated and prolonged access to a patient'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's kidneys to carry out that function. In this process, the patient'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'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'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'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.
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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
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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\'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 V-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.
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Semi-permanently placed catheters may be useful for a variety of medical procedures which require repeated access to a patient\'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\'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\'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\'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\'s vein, and which remains within the patient\'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\'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\'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\'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\'s vein as a result of the circulation in the patient\'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.