Abstract:
Disclosed is a check valve for placement near the distal end of a catheter. A continuously smooth outer surface for the catheter with check valve system assures that there is no propensity for a blood clot to form in cracks on the system&#39;s outer surface. The check valve is a formed from a low durometer, highly elastic, elastomer cylindrical tube that is shrunk into a cylindrical groove that would typically be located near the catheter&#39;s distal end. When pressurized fluid is injected through the catheter, the cylinder that is placed over one or more holes in the cylindrical groove in the catheter is forced to expand radially outward which allows the fluid to be injected into the blood vessel. When the pressure is removed, the elastomer tube retracts to its normal position which position tightly covers the holes thereby preventing any blood from entering the catheter.

Description:
FIELD OF USE 
     This invention is in the field of implantable medical devices that are used to inject medication into the vascular system of a human subject. 
     BACKGROUND OF THE INVENTION 
     There are many catheters that are used to deliver drugs into the vascular system of human subjects. Most of these catheters are open-ended which allows blood to flow into the catheter when no drug is being delivered. Although this is quite acceptable for short-term use, for catheters that remain implanted in a human subject for a time period between weeks and years, any open-ended catheter requires frequent flushing with saline solution or heparin to retain catheter patency. Although some catheters having a slit valve at their distal end to reduce this problem, there is still some opening possible between the sides of the slit where some blood can enter the catheter over long periods of time which can result in catheter blockage. 
     In U.S. Pat. No. 4,657,536, F. D. Dorman describes a check valve that can be used at the end of an indwelling catheter. However, Dorman&#39;s check valve does not have a flexible tip to minimize damage to the arterial wall during placement and for preventing damage to the wall of a blood vessel if the catheter remains implanted for several years. Furthermore, the Dorman check valve does not have a continuously smooth outer surface which lack of smoothness can cause some accumulation of blood clots that could interfere with the operation of the valve. Still further, Dorman does not teach the use of a catheter check valve in conjunction with an implantable drug port where the use of an improved, long-lived check valve would be particularly valuable. 
     SUMMARY OF THE INVENTION 
     The present invention is a check valve for placement near the distal end of a catheter. This check valve has an extraordinarily simple design so that it would operate in a highly reliable manner. The check valve design allows for a continuously smooth outer surface for the catheter with check valve system so that there is no propensity for a blood clot to form in cracks on the system&#39;s outer surface. The check valve is also designed specifically to disallow any part of the valve from separating from the catheter. This attribute prevents the creation of a foreign body that could pass downstream and cause blood flow to be stopped at some part of the vascular system. 
     The check valve is a formed from a low durometer, highly elastic, elastomer cylindrical tube that is shrunk into a cylindrical groove that would typically be located near the catheter&#39;s distal end. When pressurized fluid is injected through the catheter, the cylinder that is placed over one or more holes in the cylindrical groove in the catheter is forced to expand radially outward which allows the fluid to be injected into the blood vessel. When the pressure is removed, the elastomer tube retracts to its normal position which position tightly covers the holes thereby preventing any blood from entering the catheter. 
     The catheter can be designed to have a flexible tip and a generally hemispherical shape at its distal end so as to decrease the chance of any damage to a vessel wall during insertion or long term use of the catheter. Furthermore, the catheter with distal check valve system is ideally suited to be used with an implanted drug port for the long-term administration of drugs. Such drug administration may take place over a period of years. To retain patency for such a long-term indwelling catheter, present practice is to use a slit-valve at the end of the catheter and/or to frequently flush an open-ended catheter with heparin or at least with a saline solution. An important advantage of the present invention is that a catheter with such a check valve could retain its patency within the vascular system of a human subject for many years without ever requiring flushing of any sort and without even having a crack in the catheter&#39;s wall. Not requiring frequent flushing would save on the time and expense of medical personnel and would be less painful for the patients. The present invention, when in the form of a pass-through drug port, is ideally suited to be used in conjunction with an implanted cardiosaver system as described in U.S. patent application Ser. No. 10/051,743 by R. E. Fischell, et al. 
     Thus an object of this invention is to have a catheter that is placed for weeks to years within a blood vessel of a human subject, which catheter has a check valve with a continuously smooth outer surface to preclude any blood clot from forming on that outer surface. 
     Another object of the invention is to have a generally hemispherical distal end of the catheter that is also of a soft plastic so as to reduce the possibility of damage to the vessel wall during insertion and long-term usage. 
     Still another object of this invention is to form the check valve from a single cylindrical tube of a low durometer, highly elastic elastomer that is fixedly attached within a cylindrical groove near the catheter&#39;s distal end, which groove provides further assurance that the cylindrical tube will not inadvertently become separated from the catheter. 
     Still another object of this invention is to shape the distal and proximal ends of the cylindrical tube check valve to be angled with respect to the longitudinal axis of the catheter to create a connection between the cylindrical tube and the catheter that provides for a continuously smooth outer surface where the cylindrical tube joins the catheter. 
     Still another object of this invention is to have the catheter filled with a solution after completion of a drug injection, which solution has essentially the same osmolality as blood so as to prevent any salts or liquid within the blood from passing by osmosis through the wall of the catheter into the catheter&#39;s lumen. 
     Still another object of this invention is to have the catheter filled with a solution after completion of a drug injection, which solution includes an anti-bacterial agent to prevent bacteria from growing within the catheter. 
     Still another object of this invention is to use the check-valved catheter system with an implanted drug port for the long-term administration of fluids into a human subject. 
     These and other objects and advantages of this invention will become obvious to a person of ordinary skill in this art upon reading the detailed description of this invention including the associated drawings as presented herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an implantable drug port with attached catheter having a check valve located near the catheter&#39;s distal end. 
     FIG. 2 is a longitudinal cross section of a distal portion of the catheter with a check valve. 
     FIG. 3 is an enlarged longitudinal cross section showing details of the check valve. 
     FIG. 4 is the transverse cross section of the check valve at section  4 — 4  of FIG.  3 . 
     FIG. 5 is a longitudinal cross section of an alternative embodiment of the check valve which has an angled joint at the proximal and distal ends of the cylindrical tube which is the check valve. 
     FIG. 6A is the transverse cross section of the check valve at section  6 — 6  of FIG. 5 showing the check valve in its normal, closed position. 
     FIG. 6B is a transverse cross section of the check valve in its open position for delivering a drug into a blood vessel of a human subject. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates an implantable drug port system  10  that includes a main body  11  which has a self-sealing septum  9 . The main body  11  has a connector  13  to which a catheter  14  is attached. An example of a similar port is Product No. AP 06016 as marketed by Arrow International, Inc. The distal end of the catheter  14  has a generally hemispherical shape to minimize damage to the vessel walls where the catheter is inserted into a blood vessel of a human subject. Near the distal end of the catheter is a cylindrical tube  17  that is the check valve of the present invention. 
     FIG. 2 is a longitudinal cross section of a distal portion of the catheter  14  having an elastomer cylindrical tube check valve  17  that is placed over an opening  18 . FIG. 2 also shows a generally hemispherical, smooth distal tip of the catheter. The end portion  15  of the catheter can be formulated from a softer (lower durometer) plastic as compared to the catheter  14 . This attribute results in minimizing trauma to the vessel wall during insertion and long-term use. The tip  15  is joined to the main cylindrical portion of the catheter  14  at the junction  15 A. 
     FIG. 3 is an enlarged longitudinal cross section of the portion of the catheter  14  where the cylindrical tube check valve  17  is placed over a cylindrical groove  16  of essentially the same length as the tube  17 , which groove  16  is formed into the catheter  14 . An opening  18  having a length “L” is placed in the groove  16  directly under the check valve  17 . The length “L” of the groove  16  is typically between 5% and 95% as long as the length of the cylindrical tube check valve  17 . The length of the tube  17  should be approximately between 1 and 10 mm. An adhesive strip  19  on the side of the groove  16  opposite the opening  18  is used to fixedly attach the tube  17  into the groove  16  of the catheter  14 . The attachment of the tube  17  to the catheter  14  could also be accomplished by ultrasonic welding of the tube  17  to the catheter  14 . It is clearly seen from FIG. 3 that, even if the tube  17  is not joined to the catheter  14  by means of an adhesive or by ultrasonic welding, the edges of the cylindrical groove  16  would by themselves cause the tube  17  to remain in the position shown in FIG.  3 . To further guarantee that the tube  17  will not come out of the groove in the catheter  14 , the tube  17  would be shrunk into the cylindrical groove  16 . As is well known in the art of catheters, shrinking the tube  17  into the groove  16  can be accomplished by solvent swelling of the tube  17 , placing it over the groove and then allowing the solvent to evaporate which causes the tube  17  to shrink into the groove  16 . This effect can also be accomplished by heat shrinking of the tube  17 . In either case, the final inside diameter of the shrunk tube  17 , if unrestrained by the cylindrical groove  16 , would be smaller than the outer diameter of the groove  16 . This causes the tube  17  to be in tension which provides further assurance of a tight seal over the opening  18 . The hoop tension of the tube  17  also further guarantees that it will not come off the catheter  14  when fluid is injected into the catheter  14 . 
     FIG. 4 is a transverse cross section of the catheter  14  at section  4 — 4  of FIG. 3 showing the catheter  14 , tube  17 , opening  18  and adhesive strip  19 . The opening  18  should have a width “W” that is approximately between 10% and 95% of the inside diameter of the catheter  14 . 
     FIG. 5 is a preferred embodiment of a distal portion of a check valve and catheter system  20  which includes a catheter  21  having a central lumen  27  and a generally cylindrical groove  29 . A multiplicity of holes  24  are placed through the wall of the catheter  21  within the generally cylindrical groove  29 . Ideally there would be between one and ten of such holes, each of which could have a diameter that lies approximately between 10% and 95% of the inside diameter of the catheter  21 . The holes  24  can have a variety of distributions within the groove  29 , but an optimum distribution would have approximately three holes  24  aligned in an axial direction. The inside diameter of the catheter  21  would typically be between 0.2 and 5 mm, and the length of the groove  29  would typically be between 0.5 and 10 mm. Shrunk into the groove  29  is a generally cylindrical elastomer tube check valve  22  that can be fixedly attached to the groove  29  by means of an adhesive strip  23  (or ultrasonic bond) along a line that is diametrically opposite from the holes  24 . Because the tube  22 , if unrestrained by the groove  29 , would have an inside diameter that is smaller than the outside diameter of the groove  29 , there is formed an indentation  26  of the tube  22  into the holes  24 . Such indentations still provide a continuously smooth, crack-free outer surface for the check valve catheter system  20  so that there will be no tendency for blood clots to form on the system&#39;s outer surface. 
     An important aspect of the design of the system  20  is the angled junction  25  where the proximal and distal ends of the tube  22  join to the proximal and distal ends of the groove  29 . The angled junction  25 , when used with a tube  22  that is shrunk into the groove  29 , assures that there will be no crack formed at the junction  25  into which a blood clot could form. If formed, such a blood clot could prevent the proper functioning of the check valve. The optimum angle “A” for the angled junction  25  would be approximately between 10 and 60 degrees with respect to the longitudinal axis of the catheter  21 . 
     FIGS. 6A and 6B are transverse cross sections of the system  20  at section  6 — 6  of FIG.  5 . FIG. 6A shows the normal, unactuated position of the tube  22  and FIG. 6B shows the position of the tube  22 ′ when pressurized fluid is being delivered through the lumen  27  of the catheter  21 . FIG. 6A shows the catheter  21  having a lumen  27  and the tube  22  fixedly attached to the catheter  21  by an adhesive strip  23 . In the position of the tube  22  shown in FIGS. 5 and 6A, no blood from the vascular system of the human subject can enter into the lumen  27 . When a drug under pressure is placed through the lumen  27 , the open system  20 ′ is formed as shown in FIG.  6 B. The pressurized drug would force an opening  28  to form between the catheter  21  and the expanded tube  22 ′. Thus the drug can be delivered into the vascular system of the human subject. After the injection of drug is completed, the expanded tube  22 ′ will return to its normal diameter as shown for the tube  22  of FIGS. 5 and 6A. 
     FIGS. 1-3 and  5  clearly show an elongated cylindrical catheter  14  or  21  and check valves  17  and  22  which together have a continuously smooth outer surface that would preclude the formation of blood clots on the systems outer surface, which blood clots could interfere with the functioning of the check valves. This superior design should provide highly reliable performance within a human artery or vein for many years without requiring frequent flushing with saline or heparin. Although the catheter with check valve described herein is well suited for use with an implanted drug port, it should be understood that the catheter plus check valve can be used with any percutaneous drug delivery systems as well as any form of implanted drug delivery system. 
     Although catheters formed from a single plastic material are shown in FIGS. 2-5, it should be understood that the catheters could be formed with one plastic material on the inside of the catheter and a second plastic material coaxially extruded over the first material. Plastic materials such as (but not limited to) polyurethane, polyethylene, silicon rubber, Teflon and Nylon can be used to form the catheter or for either layer of a two layer catheter. Furthermore, any plastic material that is a low durometer, highly elastic, biocompatible elastomer can be used for the check valve. Examples of such a plastic are (but are not limited to) polyurethane, polyethylene and silicone rubber. 
     It is expected that this simple check valve, which is merely a single elastomer tube placed over one or more openings, would be simple to build and operate and therefore it would be comparatively inexpensive and highly reliable. Furthermore, it is expected that the designs described herein would have distinct advantages over slit-valve catheters which have a crack that can have a blood clot formed therein and also those catheters typically require some periodic flushing at least with saline solution. Still further, the present invention can clearly be used in conjunction with multi-lumen catheters such as central venous catheters. In this regard, one or more lumens could have a check valve and one or more other lumens could have a continuous fluid connection into the blood vessel or have a slit valve. Furthermore, although FIGS. 1 and 2 show the check valve to be located near the catheter&#39;s distal end, it should be understood that the check valve is able to be located anywhere along the length of the catheter. 
     When not injecting a drug or any other type of liquid through the catheter, it is desirable to retain a solution in the catheter that has the same osmolality as blood. This attribute would diminish any tendency for changing the nature of the liquid within the catheter because of osmosis of some component of the blood through the catheter wall. For this purpose, a normal saline solution could be used. The solution could also contain some anti-bacterial agent to prevent bacteria from forming within the catheter. 
     Various other modifications, adaptations and alternative designs are of course possible in light of the teachings as presented herein. Therefore it should be understood that, while still remaining within the scope and meaning of the appended claims, this invention could be practiced in a manner other than that which is specifically described herein.