Abstract:
A vascular reinforcement device and method reduces increased vascular pressure of a vein in the presence of forces applied externally to the vein. The device is arranged to continuously overlie of a vein and has a longitudinal dimension and a cross-sectional dimension. The longitudinal dimension is greater than the cross-sectional dimension and is flexible while the cross-sectional dimension of the device is resistant to change. The device is deployed so as to overlie a wall of the vein. The device and method find particular advantageous application for treating preeclampsia or hypertension associated with obesity.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention generally relates to a device and method for reinforcing a vein when exposed to external forces. The present invention more particularly relates to a device and method for reinforcing a renal vein for treating hypertension associated with, for example, obesity or treating preeclampsia.  
           [0002]    Preeclampsia is defined as pregnancy induced hypertension associated with either proteinuria (an excess of serum proteins in the urine) and/or edema. It occurs in five to ten percent of pregnancies, typically after the twentieth week of gestation. Risk factors include multiple gestation pregnancies and first time pregnancies.  
           [0003]    Preeclampsia can progress to eclampsia, with cerebral symptoms leading to convulsions. The condition is associated with systemic vasospasm wherein arteries throughout the body narrow. This can lead to multi-organ system dysfunction wherein many organs of the body, including the kidneys, brain, eyes, liver, etc., are unable to function normally because of altered blood flow and increased blood pressure.  
           [0004]    The cause of preeclampsia is still being debated. However, a new and different cause than that proposed thus far is contemplated by the present invention.  
           [0005]    In the human anatomy, the left renal vein, which conducts blood from the left kidney to the inferior vena cava and back to the heart, passes over and is immediately adjacent to the aorta. The aorta is an artery and thus is at high pressure and has a rigid structure when compared to the compliant vascular structure of a relatively low pressure in the left renal vein. The weight and expansion of the abdomen of obese persons or of the pregnant uterus due to the growing fetus in a confined space causes compressive forces to develop within the abdominal area. These forces can compress the compliant left renal vein against the rigid aorta.  
           [0006]    Flow through a vein is equal to the pressure drop from one end of the vein to the other divided by the vascular resistance. In a vein, vascular resistance is very sensitive to the diameter of the vein. In fact, vascular resistance in a vein increases in inverse relation to the fourth power of radial decrease. For example, if the radius is halved, the vein pressure increases by a factor of sixteen in order to maintain constant flow. As a further example, and to illustrate how small vein diameter changes can effect vascular pressure, if a vein is normally 6 mm in diameter and the diameter is decreased by 1 mm, the vascular pressure from end to end will double for constant flow.  
           [0007]    The kidney among many things tries to maintain homeostasis of body fluid. It is sensitive to fluid pressure and can adjust its vascular resistance over a wide range to maintain relatively constant renal blood flow and filtration rate. As noted above, even a small decrease in the left renal vein diameter can thus result in a tremendous increase in left renal vein vascular pressure as the kidney attempts to maintain a constant blood flow. Hence, the expanding uterus, due to growth of a fetus, can exert external pressure on the left renal vein against the relatively rigid aorta to cause left renal vein diameter decrease and the concomitant extreme increase in left renal vein pressure.  
           [0008]    The left kidney will see the increased and higher than normal renal vein pressure. Sensors in the kidney respond to the higher than normal renal vein pressure. In an attempt to increase diuresis the kidney produces a higher volume of renin. Increased renin production leads to increased angiotension II production. Angiotension II causes the blood vessels to constrict, leading to systemic (whole body) vasospasm and increased blood pressure. This in turn leads to aldosterone production which causes water retention in the kidneys. This still in turn causes decreased kidney perfusion due to vasospasm and the vicious cycle continues, known in pregnancy as preeclampsia.  
           [0009]    The foregoing events can be triggered by circumstances other than pregnancy. For example, obesity in either men or women can cause external forces to be exerted on the left renal vein against the aorta, leading to a higher than normal renal vein pressure resulting in hypertension and preeclampsia symptoms. Hence, an effective treatment for preeclampsia and hypertension resulting from increased renal vein pressure is urgently needed and desirable. The present invention provides a device and method for such treatment.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides a method of treating preeclampsia. The method includes the steps of providing a vascular reinforcement device, and placing the vascular reinforcing device adjacent to a wall of the left renal vein in a position which overlies the aorta. The placing step may include the step of implanting the vascular reinforcement device within the left renal vein.  
           [0011]    The present invention provides also a method of treating hypertension associated with obesity. The method includes the steps of providing a vascular reinforcement device, and placing the vascular reinforcing device adjacent to a wall of the left renal vein in a position which overlies the aorta. The placing step may include the step of implanting the vascular reinforcement device within the left renal vein.  
           [0012]    The present invention further provides a method of reducing increased vascular pressure of a renal vein by forces applied external to the renal vein. The method includes the steps of providing a reinforcement device arranged to continuously overlie, in adjacent relation to, an inner wall of the renal vein, the device having a flexible longitudinal dimension and a relatively rigid cross-sectional dimension resistant to reduction in the presence of applied external forces to the renal vein, and overlying the wall of the renal vein with the reinforcement device.  
           [0013]    The present invention still further provides a method of reducing increased vascular pressure of a vein in the presence of forces applied external to the vein. The method includes the steps of providing a reinforcement structure arranged to continuously overlie, in adjacent relation to, a wall of a vein, the reinforcement structure having a longitudinal dimension and a cross-sectional dimension, the longitudinal dimension being greater than the cross-sectional dimension, the reinforcement structure being longitudinally flexible and cross-sectionally resistant to area change and overlying the wall of the vein with the reinforcement structure.  
           [0014]    The present invention further provides a vein reinforcement device including reinforcement structure means for lining and reinforcing a wall of the vein, the reinforcement structure means having a longitudinal dimension and a cross-sectional dimension, the longitudinal dimension being greater than the cross-sectional dimension, the longitudinal dimension being flexible and the cross-sectional dimension being resistant to change in the presence of external forces applied to the vein.  
           [0015]    The present invention further provides a renal vein reinforcement device comprising a reinforcement structure of substantially cylindrical configuration. The reinforcement structure is arranged to continuously overlie, in adjacent relation to, an inner wall of a renal vein, has a flexible longitudinal dimension and a cross-sectional dimension resistant to reduction in the presence of applied external forces to the renal vein to reduce increased vascular resistance.  
           [0016]    The present invention further provides a vein reinforcement device to reduce increased vascular resistance of a vein when exposed to externally applied forces. The device includes a reinforcement structure arranged to continuously overlie, in adjacent relation to, a wall of a vein. The reinforcement structure has a longitudinal dimension and a cross-sectional dimension defining an area, the longitudinal dimension being greater than the cross-sectional dimension, is longitudinally flexible and is cross-sectionally resistant to area change.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify identical elements, and wherein:  
         [0018]    [0018]FIG. 1 is a simplified diagram of the human abdominal cavity illustrating the kidneys, the aorta, the inferior vena cava, the renal veins, and a device embodying the present invention implanted in the left renal vein;  
         [0019]    [0019]FIG. 2 is a side view of a vein reinforcement device embodying the present invention;  
         [0020]    [0020]FIG. 3 is a simplified view of a device embodying the present invention being deployed in the left renal vein in accordance with one embodiment of the present invention;  
         [0021]    [0021]FIG. 4 shows a device embodying the present invention being deployed in the left renal vein prior to expansion of the device in accordance with another embodiment of the present invention;  
         [0022]    [0022]FIG. 5 is a view, similar to FIG. 4, showing the device after being expanded for deployment in the left renal vein;  
         [0023]    [0023]FIG. 6 is a side view of another vascular reinforcement device embodying the present invention;  
         [0024]    [0024]FIG. 7 is an end view of the reinforcement vascular device of FIG. 6; and  
         [0025]    [0025]FIG. 8 is a side view of a further vein reinforcement device embodying the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Referring now to FIG. 1, it illustrates an abdominal cavity  10 . As illustrated in FIG. 1, the abdominal cavity  10  includes the right kidney  12 , a left kidney  14 , the inferior vena cava  16 , and the aorta  18 . Also illustrated in FIG. 1 are the right renal vein  20 , the left renal vein  22 , and a vascular reinforcement device  24  embodying the present invention. The device  24  is implanted within the left renal vein  22  to reduce increased vascular pressure of the left renal vein when the left renal vein is exposed to external pressure or force.  
         [0027]    As previously described, and as may be noted in FIG. 1, the left renal vein  22  is connected between the left kidney  14  and the inferior vena cava  16  to support blood flow from the left kidney  14  to the heart through the inferior vena cava  16 . As will also be noted, the left renal vein  22  passes over and adjacent to the aorta  18 . The aorta  18  is relatively rigid. Hence, external forces applied to the left renal vein  22  cause the relatively compliant renal vein to deform when pressed against the aorta. This causes a decrease in the left renal vein cross-sectional area or diameter. In an attempt by the left kidney  14  to maintain ample blood flow, the pressure within the left renal vein to the left of the aorta increases. As previously described, the pressure increase can be pronounced for even small decreases in left renal vein size. The increased pressure is sensed by the kidney  14  and causes the kidney to increase the production of renin leading to the previously described cascading effects towards preeclampsia or hypertension.  
         [0028]    To reduce such increases in left renal vein pressure, a vascular reinforcement device  24  is implanted within the left renal vein. The device has a cross-sectional area which is resistant to change by the external forces. This allows the device  24  to reinforce the left renal vein against externally applied forces. The result is that the left renal vein pressure increases are reduced in the presence of applied external forces. Excessive renin production is precluded and preeclampsia or hypertension is avoided.  
         [0029]    A vascular reinforcement device  26  embodying the present invention is shown in FIG. 2. The device includes a reinforcement structure  28  which may be a laser cut tube of Nitinol, as known in the art, or may be a wire structure formed of Nitinol, for example. Other structures may also be employed such as tubular structures formed of resilient material such as, silicon rubber, for example. The reinforcement structure has a longitudinal dimension  30  at least sufficient for spanning the entire diameter of the aorta and may be long enough to essentially span the entire length of the left renal vein  22 . The reinforcement structure  28  also has a cross-sectional area. The cross-sectional area is preferably circular but may have other configurations. The cross-sectional area, in accordance with this embodiment, is defined by a diameter  32 .  
         [0030]    The device  24  is thus configured to continuously overlie a wall of a vein, such as a left renal vein  22 , in close adjacent relation thereto. The device may be dimensioned for overlying an outer wall of the vein. Preferably, the device is dimensioned to overlie an inner wall of a vein as, for example, the device  24  of FIG. 1. To that end, the device may have a diameter on the order of 6 mm for use in the left renal vein, for example. However, as one skilled in the art will appreciate, veins may be of various sizes and hence the device diameter may vary to accommodate different sized veins  
         [0031]    In accordance with the present invention, the device may take advantage of the compliant nature of veins by actually being slightly greater in diameter than the vein in which it is deployed. This provides further assurance that ample vein size will be preserved in the presence of applied external forces.  
         [0032]    While the device  26  must be relatively rigid in cross-section in the sense of resisting diameter reduction in the presence of applied external forces, it is still preferably formed of resilient material to be able to return to its original shape should an intense force be applied to it. This avoids the device from being permanently collapsed or crimped by such intense forces to enable the device to remain effective. Hence, to that end, Nitinol is a preferred material. However, other resilient materials known in the art may also be used. In those applications where resilience is of less importance, less resilient materials may be used, such as stainless steel, for example.  
         [0033]    Since vascular pressure is generally less than arterial pressure, the device need only resist diameter reduction to external forces of up to about 50 mm of mercury. As used herein the term “resist diameter reduction” is meant to define the ability of the vascular reinforcement device to maintain sufficient cross-sectional area to support blood flow under substantially normal vascular pressure. At the same time, the device must be flexible and compressible to outside forces in excess of 100 mm of mercury, for example. Outside forces may push the vein against arteries near to it and the vein should compress before the artery adjacent to it. Hence, if the device is too resistant to cross-sectional reduction in the presence of external applied forces, it is possible that an underlying artery may be distorted as a result of excessive pressure being exerted against the vein in which the device is employed. Hence, the resilience of the device precludes such distortion of adjacent arteries and thus prevents constriction of adjacent arteries. However, since the device is resilient, once the excessive force subsides, the device will return to its original shape to maintain a low vascular pressure within the vein in which it is deployed.  
         [0034]    As illustrated in FIG. 2, the longitudinal dimension  30  is greater than the cross-sectional dimension defined by the diameter  32 . The device  26  is longitudinally flexible. This permits the device to comply to the shape of adjacent rigid body structures such as the aorta or other arteries.  
         [0035]    [0035]FIG. 3 shows another vascular reinforcement device  40  embodying the present invention being implanted in the left renal vein  22 . As shown in FIG. 3, the device is implanted by first advancing a catheter  42  up a vein of the leg, such as the femoral vein, (not shown) into the inferior vena cava  16 . The catheter is advances into the left renal vein  22  as illustrated. The device  40 , which is expandable, is then advanced through the catheter  42  in a collapsed state by a push tube  44 . When the device  40  reaches the left renal vein where it crosses the aorta  18 , the device is released by further advancement, whereupon it expands to continuously line an inner wall  23  of the left renal vein  22 . After the device  40  is thus deployed, the advancement tube  44  and catheter  42  are removed.  
         [0036]    [0036]FIG. 4 shows another vascular reinforcement device  50  embodying the present invention being employed in accordance with a further embodiment. Here, the device  50  is balloon expandable by a balloon  52 .  
         [0037]    The device  50  is implanted by first advancing a catheter  54  into the inferior vena cava  16  and into the left renal vein  22  as illustrated. Next, the device  50  and balloon  52  are advanced by a flow tube  56  through the catheter  54  and into the left renal vein  22  where the left renal vein  22  crosses the aorta  18 . Then, a pressure device  58  having a pressure meter  60  is used to inflate the balloon  52 .  
         [0038]    As best seen in FIG. 5, the inflated balloon  52  has expanded the device  50  to continuously line the inner wall  23  of the left renal vein  22 . Once the device is fully expanded, the balloon is deflated. The deflated balloon  52 , flow tube  56 , and catheter  54  are then removed leaving the device  50  in place to reinforce the left renal vein and reduce increased vascular pressure within the left renal vein notwithstanding applied external forces to the left renal vein.  
         [0039]    [0039]FIGS. 6 and 7 show another vascular reinforcement device  70  embodying the present invention. The device  70  is generally cylindrical in configuration having a longitudinal dimension  72  and a cross-sectional dimension defined by a diameter  74 . As may best be seen in FIG. 7, the device  70  includes the reinforcement structure  28  previously illustrated in FIG. 2. Here, however, the reinforcement structure  28  is coated or covered with an external coating  76 . The external coating may be formed of silicon rubber, Teflon, or polyurethane. The coating  72  is made thin enough for flexibility so as to enable the device  70  to retain all of the structure benefits of the reinforcement structure  28  as previously described.  
         [0040]    A further vascular reinforcement device  80  embodying the present invention is shown in FIG. 8. The device includes a reinforcement structure  82  which again may be a wire structure formed of Nitinol, for example, or a laser cut Nitinol tube. The reinforcement structure has a longitudinal dimension  84  at least sufficient for spanning the entire diameter of the aorta and may be long enough to essentially span the entire length of the left renal vein  22 . The reinforcement structure  82  also has a cross-sectional area. The cross-sectional area is preferably circular but may have other configurations. The cross-sectional area, in accordance with this embodiment, is defined by a diameter  86 .  
         [0041]    In addition to the structural features of the vein reinforcement devices previously described, the device  80  offers a further feature. Here it may be noted that the midsection  88  of the device  80  is formed of wire which is heavier stock than the wire forming end sections  90  and  92 . Preferably, the wire stock gradually decreases in diameter from the midsection  88  to the end sections  90  and  92 . When the device  80  is formed by laser cutting a Nitinol tube, the midsection  88  may have supports which are wider than the supports in the end sections  90  and  92 . This allows the device  88  to become gradually soft out from the device midsection to provide a transition zone. This may prevent trauma to the vein when external forces are present. More particularly, the potential for the vein to shear at the end of the device when exposed to external forces is reduced while the midsection still provides reduced increases in vascular pressure. Hence, the device offers less change in cross-sectional area from the midsection  88  to the end sections  90  and  92  while the midsection  88  offers sufficient resistance to cross-sectional change to permit the device to sufficiently reduce increases in vascular pressure.  
         [0042]    While particular embodiments of the present invention have been shown and described, modifications may be made, and it is therefore intended in the impended claims to cover all such changes and modifications which fall within the true spirit and scope of the invention.