Pressure actuated valve with improved biasing member

A valve for controlling material flow through a catheter, comprises a first flexible member including a first moveable element, wherein, when the first moveable element is in the open position, material may flow past the first flexible member through a first lumen of the catheter and, when the first moveable element is in the closed position, flow through the first lumen is prevented and a first biasing member coupled to the first flexible member for biasing the first moveable member toward the closed position.

BACKGROUND INFORMATION

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.

SUMMARY OF THE INVENTION

The present invention is directed to a valve for controlling material flow through a catheter, comprising a first flexible member including a first moveable element, wherein, when the first moveable element is in the open position, material may flow past the first flexible member through a first lumen of the catheter and, when the first moveable element is in the closed position, flow through the first lumen is prevented and a first biasing member coupled to the first flexible member for biasing the first moveable member toward the closed position.

DETAILED DESCRIPTION

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 2show an exemplary implantable catheter for kidney dialysis. Catheter10has a distal end12that is insertable under the skin and into the patient's vein, and which remains within the patient's body for the life of the catheter10. For example, catheter10may remain implanted in the patient for two years. As shown more clearly inFIG. 2, distal end12fits within a vein8(e.g., the vena cava). During dialysis, blood from the patient is removed through a patient line such as catheter10, and is purified by a dialysis machine (not shown) which is connected to hubs18and20of catheter10by a dialysis line. Catheter10in this example includes two lumens22and24which are used respectively to remove blood from and reintroduce blood to the vessel8. Lumen22terminates at an inflow tip14formed at the distal end12of the catheter10while lumen24terminates at an outflow tip16formed at the distal end12. Inflow tip14and outflow tip16are connected to corresponding inflow and outflow hubs18,20, 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 catheter10is 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 catheter10is securely sealed to prevent fluids and gases from crossing into the proximal end of catheter10by preventing flow in and out of catheter10through hubs18,20. 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 catheter10.

As indicated above, although conventional clamps or clips may be used to seal the catheter10between medical sessions, over time the wall of the catheter10may 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 catheter10also 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 catheter10includes one or more self sealing valves along each of the lumens22,24to seal them when not being used during dialysis and other transfusion or infusion sessions. For example, hubs18,20may be used to house one or more valves each of which is designed to seal the corresponding lumen22,24under 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 catheter10when 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.

Specific embodiments of the present invention will be described below with reference to the drawings.FIG. 3shows a top plan view of an exemplary embodiment of a valve element100used to control the flow through a medical tube such as the catheter10ofFIG. 1. For example, valve element100may be located in a flow passage within a valve housing formed in either or both of the hubs18,20, through which fluids flow to and from the distal end12. As will be apparent to those skilled in the art, the valve housing may be placed at any other location along the length of catheter10and may be unitary with the catheter10, 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 valve100within each of the flow passages may be provided instead of two separate valve housings for the hubs18,20, 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 inFIG. 3, the valve element100is formed as a flexible disk110having dimensions appropriate to the size of the flow passage within the one of the hubs18,20into which it is to be mounted. The flexible disk110may be formed of any sufficiently flexible material, such as a polymeric material. More specifically, the flexible disk110may be formed of silicone. The flexible disk110may also include a peripheral portion116adapted to be connected to an inner surface of the flow passage to seal perimeter of the flow passage around flexible disk110. The valve element100includes a slit112which is extends through the entire thickness of the flexible disk110. The slit112separates two movable elements118from one another to form an openable portion of the disk110which creates a flow passage therethrough when the movable elements118are placed in an open position separated from one another. For example, when the edges120of the movable elements118are moved out of the plane of the flexible disk110, an opening through the flexible disk110is formed along the slit112. In this exemplary embodiment, the movable elements118are formed as resilient flaps substantially constrained in all directions except along the slit112. Accordingly, the elements118are substantially constricted and may only move along the edges120to form a relatively small opening.

In one exemplary embodiment the valve element100is used in conjunction with dialysis equipment, and movement of movable elements118to the open position is prompted by an actuating pressure of a fluid within dialysis lines30,32which may be connected to the hubs18,20, respectively, to connect the catheter10to a dialysis machine. In particular, an actuating pressure is generated by pumps in the dialysis machine to move the patient's blood between the patient and the filtration equipment. Although the movable elements118are 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 lines30,32. Specifically, the elements118are biased to remain in the closed position abutting one another along edges120at 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 elements118are 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's blood. As would be understood by those skilled in the art, the amount of pressure required to open the movable elements118is a function of the resilience of the material forming those elements, the size and shape of the slit112, and the size of the flow passage containing the valve element100. The details of the geometry of the slit112and the movable elements118may be selected to obtain the desired characteristics of maximum flow in the open position, and to ensure that valve element100seals the flow passage when the pressure is removed.

A stiffening element114may be included in valve element100, to better control the amount of force biasing the movable elements118to the closed position. In particular, coupling a stiffening element to an otherwise flexible disk110(or forming a stiffening element integrally therewith) provides a valve element100including movable elements118more resistant to plastic deformation during sessions lasting multiple hours in which the valve element100is kept open. An example of a suitable stiffening member is the addition of stiffening ring114to the flexible disk110. The stiffening element114may, for example, be formed of a wire embedded within the valve element100. Of course, those skilled in the art will understand that the stiffening element114may be formed of metal, plastic or any substantially rigid material.

In one exemplary embodiment, the stiffening ring114may be embedded within the material of the disk110, to minimize the bulk of the combination. In different embodiments, stiffening elements may be bonded to one or both sides of the valve element100, depending on the requirements of the use of the valve element100. The shape of the stiffening elements used in the valve element100may also be modified, depending on the desired characteristics of the force urging the movable elements118to the closed position. Alternatively, the stiffening elements may be integrally formed with the disk110.

As indicated above, the maximum flow that can pass through valve element100and 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 slits112. Selection of the dimensions of the slit112results in movable elements118having a desired shape and being constrained along selected edges. In the exemplary embodiment shown inFIG. 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 disk110extending along a major axis of the disk. The flexible disk110could 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 elements118used in this configuration are flaps that form an opening by deflecting away from the plane of the disk110due to their flexibility, since they are constrained along all sides except along the slit112. 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'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 element100can be further tuned by selecting an appropriate length/of the slit112. By altering this length l, both the maximum flow rate and the opening/closing performance of the valve element100will be changed. For example, increasing the length of the slit112, other parameters being the same, increases a maximum size of the opening through the flexible disk110, and makes it easier to displace the movable elements118to the open position as they are unconstrained along longer edges120. For the same reason, the movable elements118are 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 slit112are selected as a tradeoff between ease/size of the opening and the biasing force closing the valve element100after use.

A different exemplary configuration of slits to define the movable elements is shown inFIG. 4. In this embodiment, a flexible disk210is provided with slits212,214in a substantially H-shaped configuration that define movable elements218. The slit212is a substantially linear slit aligned with a major dimension of the disk210, and the slits214extend substantially perpendicular to slit212, disposed near terminating points thereof. This configuration of slits permits the movable elements218to more easily move to the open configuration, since each movable element218is unconstrained along both the slit212and the slits214. The pressure generated by an external pump, such as a dialysis pump, thus can more easily force the movable elements218to the open position. The two additional unconstrained sides of the movable elements218also form a larger open area of flexible disk210, so that a greater flow rate can pass through the valve element200.

Additional resilient elements may also be used in the exemplary embodiment shown inFIG. 4to achieve desired closing characteristics of the valve element200. For example, a pair of resilient elements220may be disposed substantially parallel to the slit212on either side thereof. The resilient elements220control the deflection and provide a force biasing the movable elements218toward the closed position along the axis of the slit212. Those skilled in the art will understand that additional resilient elements222may be used to increase the biasing force and/or to control the deflection of the movable elements218along an axis parallel to the slits214. This exemplary combination of H-configured slits and corresponding H-configured resilient elements results in a high flow, easily opened pressure actuated valve element200, 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 inFIG. 5. In this embodiment, a double horizontal slit is used to define the movable elements of a valve element250. More specifically, a pair of substantially parallel slits262extend through the flexible disk260, substantially along a major dimension thereof. In the case of a substantially elliptical flexible disk260, as shown, the slits262are substantially parallel to a major axis of the ellipse. A movable element264is thus defined substantially at the center of the flexible disk260, and is constrained only at ends265thereof near termination points of the slits262.

The greater unconstrained length of the sides of the movable element264along the slits262, 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 element264. To ensure a complete closing of the valve element250when the actuating pressure is removed, for example, resilient elements may be added around the slits262to further bias the movable element264to the closed position. In the exemplary embodiment shown inFIG. 5, resilient elements266,268, which may comprise, for example, wires embedded within the valve element250, are disposed in a substantially rectangular configuration surrounding the slits262. In this configuration the resilient elements266,268control the deflection of the movable element264in directions substantially parallel and perpendicular to the slit orientation and provide a biasing force that closes the movable element264when the actuating pressure is removed. The resilient elements266,268may form a complete rectangle, or may be separated at the vertices.

FIG. 6shows 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 a valve element300is placed in the open position by an actuating pressure thereagainst. As shown in the drawing, the valve element300is formed as a flexible disk310which, in this example, has a substantially elliptical shape. It will be apparent to those skilled in the art that different shapes of the flexible disk310may be used, depending on the shape and dimensions of the housing within which the valve element300is to be placed. A substantially linear slit312is formed in the flexible disk310, for example along a major dimension thereof, and is complemented by two pairs of slits314. A first pair of the slits314is disposed at a first end of the slit312with a second pair of slits314being formed at the second end of the slit312. The slits314are formed at an angle with the slit312, so that, at each end of the slit312, a substantially Y-shaped configuration of slits is formed.

In the exemplary embodiment shown, the slits312and314do not touch one another so that the movable elements320are continuous with portions322of the flexible disk320. In different embodiments, the slits312and314may intersect with one another, breaking the flexible disk320into additional distinct moving elements. In the exemplary embodiment shown, the movable elements320are unconstrained along the slits312,314, but are constrained in the region between the slits by being continuous with the portions322of the flexible disk320. The addition of the Y-configured slits permits the movable elements320to open to a greater extent under an equivalent actuating pressure, while retaining a biasing force sufficient to completely close the opening when the actuating pressure is removed. To further bias the movable elements320toward the closed position, resilient elements316,318may be added. As discussed in the context of previous embodiments, the resilient elements316,318may be disposed in a substantially rectangular pattern around the slits312,314to control the deflection and closure of the movable elements320in two directions substantially perpendicular to one another. The resilient elements316,318may form a completely rectangular enclosure as shown inFIG. 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 slits312,314may be selected to give desired flow and closing properties, for a given flexible disk320.

A different exemplary embodiment according to the present invention is depicted inFIG. 7. In this example, a valve device350comprises a flexible disk360having a slit362formed therein. The slit362is not formed as a linear slit, but instead is curved about a principal axis of the flexible disk360. In the example shown inFIG. 7, the slit362follows a substantially sinusoidal path. However other curved paths may be used with similar effect. The slit362defines two movable elements364,366which are complementary to each other along the slit362. A benefit of this configuration is that for a given length l of the slit362, a larger opening area of the valve device350is obtained as compared to linear slit designs. Since the unconstrained edges of the movable elements364,366are longer due to their curved shape of the slit362, a given actuating pressure displaces a larger portion of the movable elements364,366to the open position. Thus, this design allows a larger flow area through the valve device350.

As was the case in other the exemplary embodiments of the invention, the resilience of the movable elements364,366is controlled to ensure that the valve element350fully closes once the actuating pressure is removed—even after remaining open for extended periods of time (i.e., to ensure that the valve is not subject to “memory” effects). Accordingly, the resilience of the material forming the movable elements364,366is preferably selected and additional resilient elements are incorporated into the flexible disk360, as described above with respect to other embodiments, based on the conditions to which the valve element350is to be subjected to ensure that such plastic deformation does not result in degraded performance over time.

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. 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.