Abstract:
The invention emulates the operation of a healthy urethra by providing a valve with a large differential between the opening pressure and the closing pressure. The differential is achieved by using a snap action created by the action of the urine flow on a force that drops off rapidly with displacement. A preferred way to achieve such as force is by using permanent magnets. The valve is installed simply by insertion into the urethra and can easily be removed. No surgical procedure is involved.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention is in the medical field, and specifically for the prevention of urinary incontinence in men and women. 
       BACKGROUND OF THE INVENTION  
       [0002]    Incontinence is a well known medical problem becoming more common as people age. The majority of incontinence occurs in women, accelerated by anatomical changes following childbirth. Prior art treats incontinence by anatomical corrections done via minor surgery and by artificial urethral valves, restoring the ability of the urethra to act as a valve. In a healthy person the urethral muscles, acting together with the muscles contracting the bladder, are effective in achieving free flow when emptying the bladder and achieving a good seal against leakage at all other times. An ideal prosthetic urethral valve needs to open at a pre-determined point and provide as little obstruction to flow as possible. It should remain fully open as pressure drops, until bladder is completely emptied and pressure drops to a very low value. At this point valve should close and not open until original opening pressure was reached again. The problem is made more difficult by the low pressures involved. Typical opening pressure in a female should be about 20 cm of water and closing pressure should be a few cm, preferable less than 3 cm of water. Such low pressures can only supply very low forces inside the valve (a few grams) making the design of a reliable valve quite difficult. For this reason almost all prior art relies on the user to manually open and close the valve. Some prior art relies on automatic timers. The methods used by prior art to control the valve are: magnetic (bringing a strong magnet to the vicinity of the urethra to open valve), hydraulic (using a manually activated balloon or pump to inflate or deflate a cuff), electronic (wireless transmission of a control signal) and even a simple plug removed by the user in order to empty bladder. U.S. Pat. Nos. 4,457,299; 4,553,533; 4,822,333; 5,888,188; 6,183,520; 6,027,442 and 6,652,448 disclose a self acting valves however this valve do not have a sufficient difference between the opening pressure and the closing pressure, therefore starts to close before the bladder is fully voided. A more detailed explanation of the difference between a simple spring activated valve and the present invention is given in the detailed description of the invention. The fluid filled implementation disclosed in the &#39;299 patent has even less desirable characteristics than a spring as the compression force required to collapse a sealed fluid filled enclosure goes up faster than linear. U.S. Pat. No. 5,112,306 addresses the need to prevent early closure of the valve by adding a closure delay. U.S. Pat. Nos. 5,088,980; 5,437,604; 5,722,932 and 6,213,936 use the Bernoulli effect, a liquid filled bag or a compound valve system to create some differential between the opening pressure and the closing pressure but fail to meet the requirement for very large differential and unrestricted flow, as they create the differential by severely restricting the flow. Clearly when urine pressure drops below 10 cm of water the voiding of the bladder will take a long time if the flow is very restricted, as flow rate drops with pressure. In a healthy person urination proceeds at an almost constant flow and then stops abruptly. Only a valve having a very sharp closing point set at a very low pressure (as low as a few cm of water) and minimal obstructions will emulate the operation of a healthy urethra. The prior art uses magnets for externally switching the valve between two states; the invention uses magnetic forces inside valve to achieve a self-acting valve having only two states: fully open or fully closed. It is an object of the invention to provide a simple automatic valve not requiring any external activation and having full flow as the pressure decreases during the voiding of the bladder. Another object is to provide a valve closely emulating the natural action of a healthy urethra. A further object is to provide a valve that is easy to insert and remove without need of any surgery. 
       SUMMARY OF THE INVENTION  
       [0003]    The invention emulates the operation of a healthy urethra by providing a valve having only two states, fully open or fully closed, with a large differential between the opening pressure and the closing pressure. The differential is achieved by using a snap action created by the action of the urine flow on a force that drops off rapidly with displacement. A preferred way to achieve such as force is by using permanent magnets. The valve is installed simply by insertion into the urethra and can easily be removed. No surgical procedure is involved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0004]      FIG. 1  shows a cross section of the female bladder and urethra with the valve installed in the urethra. 
           [0005]      FIG. 2  shows a graph of the flow vs. pressure of a conventional valve and of the valve according to the invention. 
           [0006]      FIG. 3  shows a cross section of the valve as installed in the urethra. 
           [0007]      FIG. 4  shows a cross section of an alternate embodiment. 
           [0008]      FIG. 5  shows a version of the valve for installation on the outside of the urethra. 
           [0009]      FIG. 6  shows the method of installing and removing the valve. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]    Referring to  FIG. 1 , valve  4  controls the flow of urine  2  from bladder  1  through urethra  3 . A female anatomy is depicted but the invention is beneficial to both men and women. 
         [0011]    In order to emulate a correctly functioning urethra the valve needs to fully open at a set pressure and stay fully open, with as little flow restriction as possible, till bladder is empty and pressure drops to a small fraction of opening pressure. The pressure difference between the opening and closing pressure is also known as hysteresis. A simple spring loaded valve does not have the desired property. A spring provides little hysteresis, as can be seen in  FIG. 2 , showing flow as a function of bladder pressure. A spring loaded valve  4 A will typically have a graph  5 . When pressure reaches the opening point the valve opens slightly, and increased pressure increases the amount of valve opening and flow. 
         [0012]    When pressure is reduced the graph generally traces back the increasing pressure graph. The desirable characteristic is shown in graph  6 . Up to the opening pressure P 2  there is no flow. At P 2  the valve opens and full flow is achieved. The reason the flow keeps increasing with pressure above point P 2  is because any orifice will have increased flow with increased pressure. When pressure is reduced, graph  6  resembles a graph of a simple orifice until the shut-off pressure P 1  is reached. At that point the valve shuts off completely and there is no leakage. Clearly P 2  needs to be significantly larger than P 1  to avoid frequent urination. Valve  4  achieves the desired characteristics by the use of a magnet. 
         [0013]    Referring now to  FIG. 3 , valve  4  is inserted into urethra  3  and in held in place by one or more grooves and ridges  11 . The body of valve  4  is made of metal, ceramic or a polymeric material such as silicone rubber or polyurethane. A magnetic ring  7  is embedded inside valve  4  and a corrosion resistant ball made of ferromagnetic material such as type 400 stainless steel forms a valve when attracted by magnet  7  to valve body  4 . 
         [0014]    Ball  8  can be plated for increased corrosion protection. Suitable plating materials are metals such as gold or platinum or ceramic coatings. Shapes other than a solid sphere can be used for size and weight reduction. A lighter weight of ball  8  is sometimes desirable to prevent activation by inertial forces when doing vigorous exercise. Ridges  9  prevent the ball  8  from falling out but it can easily pushed in or out past ridges  9  if needed, due to the elasticity of the housing. This is desirable in case a catheter needs to be inserted into the bladder without removal of the valve from the urethra. 
         [0015]    It is well known that the attractive force of a magnet falls off rapidly as a function of distance. The exact relationship can vary from the inverse second power of distance to as much as the seventh power, depending on the exact geometry. The ball  8  is held securely in place in housing  4  and forms a good seal, particularly with an elastomeric housing, until urine pressure separates it slightly from its seat. As soon as it separates, the magnetic force drops significantly causing the ball to be pushed by urine flow to ridges  9  and providing a large flow cross section. When urine flow stops or drops to a very low level, ball  8  is attracted back by magnet  7  and seals the valve. Since ball  8  is ferromagnetic, valve can always be activated by placing a strong magnet outside the body in the vicinity of the urethra. This will allow emptying the bladder even before full pressure was reached. 
         [0016]    By the way of example a valve was tested with the following parameters: 
         [0017]    Dimensions: Outside diameter 7 mm, length 10 mm, hole diameter of ball seat 4.5 mm, diameter of section housing the ball 6 mm, material is hard polyurethane (durometer of 80 Shore A). 
         [0018]    Ball: Series 400 stainless steel ball with a diameter of 5 mm. 
         [0019]    Magnet: Magnet ring is made of rare earth magnet with a cross section of 0.×1 mm and diameter of 6 mm. Spacing between edge of ring and ball was adjusted experimentally for opening pressure of 20 cm water. Spacing was about 0.5 mm. Magnetization was along the axis of the ring. 
         [0020]    It was found out that the valve fully opened at 20 cm water and stayed fully open until pressure dropped to about 2 cm of water. Opening pressure could be adjusted from 10 cm water to 60 cm water by slightly changing the distance between ring and ball. These adjustments had little effect on closing pressure. 
         [0021]    In order to prevent possible infection in the contact area between the valve and the urethra, the valve can by coated by a drug eluting coating, similar to the practice with coronary stents. A material with anti-microbial properties, such as silver, can also be used. 
         [0022]    By the way of example, grooves  11  can have a thin silver rings at the bottom of each groove. In the alternative the complete valve can be fabricated from an anti microbial material or the polymer used to make the valve can be mixed with a material having both microbicide and fungicide properties such as zinc pyrithione or titanium dioxide. It should be understood that a suitable valve would have to be chosen for each user, based on the diameter of the urethra and the optimal opening pressure. The desired opening pressure can be established by an urodynamic test. 
         [0023]    An alternate form of the valve is shown in  FIG. 4 . An elastomeric tube  13  is bonded at both ends to valve body  4 . A magnet  7  is placed on the outside of one wall and a ferromagnetic material (or another magnet)  12  is placed on the opposing wall. When urine pressure overcomes the magnetic attraction between parts  7  and  12 , the elastomeric tube snaps to position  13 A. When urine pressure drops to near zero, tube snaps back to original position  13  because of the magnetic attraction between parts  7  and  12 . The advantage of this configuration compared to the configuration of  FIG. 3  is that it allows access to the bladder, if needed, without removing the valve. It was found out that this configuration gave less accurate set points than the one of  FIG. 3 . In order to reduce the required sealing pressure between the two walls of part  13 , one or more fine ridges  21  can be added in the direction perpendicular to the flow. Such ridges can accommodate small particles without affecting the sealing of the valve. 
         [0024]    A third embodiment is similar to  FIG. 4  but does not use magnets. Elastomeric insert  13  is molded in a manner having two stable shapes, shown by  13  and  13 A. With no pressure it snaps to shape  13 , but when expanded it snaps to shape  13 A until pressure drops back. 
         [0025]    Such a snap action is well known in mechanical engineering and is used, for example, by most keyboards. It is sometimes referred to as “negative K spring”. The advantage of eliminating the metallic parts is better compatibility with MRI scanners; however, the set points were not as repeatable as the configuration of  FIG. 3 . Clearly elastic snap action can also be achieved by adding a separate snap action spring to the outside of tube  13 . Still another configuration is shown in  FIG. 5 . This places the snap action outside the urethra, eliminating the risk of infection but requiring minor surgery. The principle of operation is similar to  FIG. 3  and  FIG. 4 : a magnet  7  embedded in polymeric clip  4  is pinching-off urethra  3  by being attracted to ferromagnetic insert (or another magnet)  12  embedded in opposing part of clip  4 . As in previous examples, the magnets can be replaced by a snap action spring mechanism. 
         [0026]      FIG. 6  shows, by the way of example, a tool  14  that can be used to insert and remove valve  4 . The tool has a disc-shaped tip  17  that fits into valve  4 . When button  16  is pressed, tip  17  expands into the shape shown in  17 A and grips valve  4 . Ridges  9  prevent the valve from sliding off the expanded tool. Handle  15  is used to hold the tool similar to holding a syringe. The expansion of tip  17  is achieved by placing a longitudinal cut  18  in the tool and having the distal tip of shaft  19  elastically spread the two halves of tip  17  apart when pushed in. 
         [0027]    The configuration of  FIG. 4  allows access to the bladder without removing the valve. In the configuration shown in  FIG. 3  the ball needs to be removed when access to the bladder is desired without removal of the valve. This is performed by a tool similar to tool  14  except tip  17  is shaped as to have curved fingers  20  when inserted into valve  4  fingers  20  will grip ball  8  and pull it past ridges  9 . After access is no longer needed ball  8  is replaced using same tool. Expanding fingers  20  by pressing on  19  will release the ball.