Abstract:
A torque absorbing catheter having one or more torque absorbing bearings disposed at the distal end thereof. The bearings are larger than the outer diameter of any flexible region of the catheter sought to be protected from torque as the catheter is inserted through a tortuous body lumen. As the catheter is inserted through a body lumen, the bearings are rotable therein and the catheter shaft is simultaneously rotable within a bearing lumen of the bearings. This prevents transfer of torque from bearing to shaft and catheter. The invention is particularly adept at preventing torque from deforming the shape and character of a particularly flexible catheter region such as a balloon.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to catheters of any type meant for insertion through a body lumen such as vasculature. In particular, the present invention can effectively transmit torque in a desired manner along a catheter or other device for a body lumen having high profile. 
     BACKGROUND OF THE RELATED ART 
     In the last several years the field of minimally invasive surgery has grown exponentially. In particular, catheterization procedures such as angioplasty (including Percutaneous Transluminal Coronary Angioplasty) have become widely accepted norms. Even more complex procedures such as the placement of aneurysm grafts are accomplished by way of catheterization. 
     Due to the increased popularity of minimally invasive catheterization procedures, catheters have become more complex in order to accommodate additional catheter features needed for more complex procedures. Additional catheter features often result in catheters which are relatively large in diameter (i.e. high profile) and thus more susceptible to torque from a body lumen, such as vasculature, as the catheter is inserted through the body lumen. 
     One example of a complex catheter is the angioplasty catheter. Angioplasty is performed with an angioplasty catheter having an inflatable balloon at its distal end. The angioplasty catheter may be equipped with multiple lumen for inflation, deflation, guidewire access, visualization dye access, and for other purposes. The lumen will generally be located through a catheter shaft. The shaft will be of a sufficient profile to accommodate the various lumen. Such multi-lumen catheters are relatively large and stiff and therefore subject the associated flexible inflatable balloon to a considerable amount of torque upon insertion through a body lumen, in this case vasculature. 
     In order to insert a catheter such as the angioplasty catheter to a desired vessel location, the guidewire will first be inserted and steered to the site of a stenosis. Subsequently, the angioplasty catheter is inserted over the guidewire. The angioplasty catheter is steered through vasculature to the site of the stenosis with the object of placing the deflated balloon across the stenosis so that it may then be inflated to compress the stenosis against vessel walls. 
     Unfortunately, vasculature is often quite tortuous and of limited diameter. As the angioplasty catheter tightly forces its way through the vasculature, it is Subjected to vessel walls which act to wind and distort the angioplasty catheter as it makes various turns there through. The inflatable balloon, having more flexible walls than other portions of the angioplasty catheter, will distort and absorb the torque imposed by the tortuous vasculature. By the time the inflatable balloon reaches its destination it may be twisted and creased. This distortion will hamper the effectiveness of the angioplasty compression when the inflatable balloon is later inflated. 
     A similarly complex catheter procedure involves the placement of an aneurysm graft within an abdominal aneurysm. Placement of an aneurysm graft will involve an intricate delivery system, referred to here as an aneurysm graft catheter. The aneurysm graft catheter is constructed similarly to the angioplasty catheter with a balloon near its distal end. However, the aneurysm graft catheter is even larger and more complex. Proximal of the balloon, the catheter is equipped with additional obtrusive features such as a jacket guard. The jacket guard is proximal to the superior end of a capsule which houses an aneurysm graft. The balloon must be of sufficient size to aid in the deployment of the aneurysm graft from the capsule within a bifurcated aneurysm. The size of the balloon and the presence of a large diameter capsule housing an aneurysm graft increases the amount of torque which is endured by the catheter as it is forced through a tortuous vessel to the site of an aneurysm. As a result, the balloon of the aneurysm graft catheter is subjected to a significant amount of torque and again susceptible to distortion and creasing in reaching its destination. 
     As indicated in both of the above catheter procedure examples, torque control is vital to effective catheter placement and use. This is especially true where balloon or other flexible catheter features are present which are subject to torque effects. However, in addition to torque control, the catheter may display a degree of flexibility and be limited in size and stiffness in order to prevent damage to vasculature as the catheter is inserted there through. Unfortunately, more flexibility exhibited by the catheter generally equates to less torque control. Therefore what is needed is a catheter having able to overcome such torque problems and having advantages over prior art catheters. 
     SUMMARY OF THE INVENTION 
     The present invention provides a catheter. The catheter is equipped with a torque absorbing bearing disposed about a shaft of the catheter near a distal portion of a flexible region of the catheter. The catheter may be equipped with a plurality of torque absorbing bearings. The plurality includes a proximal torque absorbing bearing immediately distal of the flexible region. 
     A method of catheterization is also provided. A catheter having a torque absorbing bearing may be inserted through a tortuous body lumen. 
     A method of manufacturing a torque absorbing catheter is also provided. An embodiment is described in which a catheter shaft is molded and a torque absorbing bearing placed about the shaft. A bearing ring stop is placed adjacent the torque absorbing bearing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an overall torque absorbing catheter system of an embodiment of the present invention. 
     FIG. 2 is a front sectional view the torque absorbing bearing shown in FIG.  1 . 
     FIG. 3 is a side sectional view of the torque absorbing bearing of FIG. 2 within vasculature. 
     FIG. 4 is a view of an embodiment of the present invention in which a plurality of torque absorbing bearings are located at the distal end of a catheter. 
     FIG. 5 shows a torque absorbing catheter within tortuous vasculature and having a plurality of torque absorbing bearings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the background of the present invention is described with reference to certain balloon catheters (i.e. angioplasty and aneurysm placement catheters), the invention is applicable to any catheter meant for insertion through a tortuous lumen. This would include angiography, radiation, stent placement catheters, etc. The invention is particularly useful when the catheter involved has obtrusive catheter features having outer walls of increased flexibility, such as a balloon catheter. 
     The following description makes reference to numerous specific details in order to provide a thorough understanding of the present invention. However, each specific detail need not be employed to practice the present invention. Additionally, well-known details, such as particular materials or methods, have not been described in order to avoid obscuring the present invention. 
     With reference to FIG. 1, a torque absorbing catheter system is shown. The catheter  11  is comprised of an elongated shaft  1  having a central lumen  50  there through. Part of the central lumen may consist of a guidewire lumen  17  terminating at the distal end of the catheter  11  (i.e. an “over the wire” catheter configuration). The particular catheter  11  shown allows placement of an aneurysm graft (not shown). However, this particular type of catheter  11  is not essential. Several obtuse features are found disposed on the catheter  11  giving the catheter  11  a relatively high profile. These features include a capsule  5  meant for housing an aneurysm graft. Distal of the capsule  5  is a jacket  4  which aids in advancement of the capsule  5  through vasculature and guards the capsule  5  to help avoid unintended graft deployment. A balloon  3  is disposed distal of the jacket  4 . 
     The balloon  3  allows deployment of the aneurysm graft once the catheter  11  is advanced to the aneurysm site. That is, the balloon  3  may be inflated to secure a distal portion of the catheter  11  within vasculature. Subsequently, the jacket  4  and capsule  5  may be disengaged to allow deployment of the graft from within the capsule  5 . The balloon  3  is more flexible than the catheter shaft  1 , the jacket  4 , and the capsule  5 . Thus, the catheter  11  is not only relatively high in profile, but it also has a portion high in flexibility. This flexibility allows the balloon  3  to be inflated to the desired level but also leaves the catheter  11  potentially susceptible to torque at the location of the balloon  3 . The potential susceptibility to torque at this location is increased due to the generally high profile of the catheter  11 . However, the present invention allows such a catheter  11  to avoid the effects of torque in spite of the high profile and increased flexibility. 
     The balloon  3  terminates at a distal portion as a stem  10 . The stem  10 , is not necessarily as flexible as the remainder of the balloon  3  as its shape tapers into the shaft  1  and it need not inflate in the manner of the balloon  3 . 
     Distal of the balloon  3  is a torque absorbing bearing  2 . The bearing  2  preferably has an outer diameter  13  larger than the more flexible portions of the catheter  11 . As mentioned above, the balloon  3  is a more flexible portion of the catheter  11  of the embodiment shown. Therefore, the bearing  2  has an outer diameter  13  preferably somewhat larger than the stem  10  outer diameter  20 . This helps promote contact between vessel walls and the bearing  2  in lieu of contact between vessel walls and the balloon  3  as the catheter  11  is advanced through a tortuous vessel (not shown) with an un-inflated balloon  3 . The bearing  2  may be sized to have an outer diameter  13  larger than any feature to be shielded from vessel contact. In fact, if no significantly profiled catheter  11  body features are present other than the shaft  1  and the bearing  2 , the bearing  2  will have the effect of simply reducing torque effects upon the catheter  11  at the distal portion of the shaft  1 . However, the more proximal the feature or shaft  1 , the less shielding is available from the outer diameter  13 . Therefore, if other portions of the catheter are of concern such as additional obtuse features which have a high degree of flexibility, another bearing may be placed immediately adjacent such features as well (not shown). However, the capsule  5  and jacket  4  of the embodiment shown are not of such concern. 
     The bearing  2  shown may have an outer diameter  13  larger than features at a more proximal portion of the catheter  11  in order to aid in catheter  11  insertion. For example, the bearing  2  shown may have an outer diameter  13  larger than the capsule jacket diameter  27  so that the stress of contact between vessel walls and the jacket  4  and capsule  5  is lessened allowing easier insertion of the catheter  11 . However, if any of the obtuse features have a sufficiently high profile, the bearing  2  should not have an outer diameter  13  larger than such profile if this would subject vasculature to potential damage upon catheter  11  insertion and advancement. In such cases, sufficiently large profile features should also be relatively short in length and less flexible, thus capable of withstanding torque from vasculature without significantly distorting. This may be the case with the jacket  4  and capsule  5  of the catheter  11  shown. 
     With reference to FIGS. 2 and 3, cross sections of the bearing  2  are shown. The bearing  2  is rotable both about the shaft  1  and within the vessel lumen  30  once placed therein. The bearing  2  is comprised of stainless steel, polyethylene, or any sufficiently solid material being biocompatible, stress and moisture resistant, and having a relatively minimal coefficient of friction. In order to enhance rotability, the bearing  2  may have hydrophilic coatings in the form of an outer layer  28  and upon an inner lumen wall  34 . 
     The bearing  2  is large enough to obstruct the view of the stem  10  when viewed from the front. When placed within a vessel lumen  30 , the bearing  2  contacts the vessel wall  22  in a manner that discourages contact between the vessel wall  22  and the balloon  3 . Contact is also discouraged between the vessel wall  22  and the shaft  1  distal of the balloon  3 . The bearing  2  is shown having an outer diameter  13  larger than the stem outer diameter  20 . An orifice  12  runs through the bearing  2  forming a beating lumen  15  with inner lumen wall  34 . The shaft  1  extends through the bearing lumen  15  and provides a distal bearing ring stop  31  adjacent the bearing  2  at a more distal portion of the catheter  11 . A bearing ring stop may also be provided adjacent the bearing  2  at a more proximal portion of the catheter  11  (not shown). 
     Distal bearing ring stop  31  may be formed simultaneously with the shaft  1 . This prevents deformation of the guidewire  7  or other lumen which may occur if the distal bearing ring stop  31  is a separate structure merely molded to the shaft  1  after both have been formed. Alternatively, the stop  31  may be manufactured following molding of the shaft  1 . However, in this case, the stop  31  should be formed directly from the shaft  1  itself. This could be accomplished by heating the shaft  1  at a particular location and compressing it from a distal and a proximal end toward the heated location until the stop  31  is formed. In such a situation, the central, guidewire  7 , or any other present lumen, should be temporarily supported by a wire filler to prevent lumen deformation at the site of the heated location. 
     The distal bearing ring stop  31  is larger than the orifice  12  thereby preventing the bearing  2  from disengaging the shaft  1  by moving toward a more distal portion of the shaft  1 . The stem  10  prevents the bearing from moving toward and over the balloon  3 . The bearing  2  is free to travel along the shaft  1  between the distal bearing ring stop  31  and the stem  10 . If desirable this distance may be shortened or lengthened by altering the positioning of the distal bearing ring stop  31 . Alternatively, a proximal bearing ring stop (not shown) may be placed adjacent the bearing  2  at a more distal portion of the catheter  11  in order to define the range of bearing  2  movement over the shaft  1 . 
     As mentioned, the outer layer  28  is a hydrophilic coating. This promotes rotation of the bearing  2  within the vessel lumen  30  in spite of making forceful contact with the vessel wall  22 . Likewise, the inner lumen wall  34  of the bearing  2  has a hydrophilic coating which further enhances freedom of movement between the shaft  1  and the inner lumen wall  34 . That is, once advancement through the vessel lumen  30  proceeds the bearing  2  allows the shaft  1  to circumferentially rotate within the bearing lumen  15  and avoid the torque effects of a tortuous vessel. The bearing  2  itself avoids torque to a certain degree due to its outer layer  28  having a hydrophilic coating. The torque avoided here is torque which will not be undesirably transferred to the shaft  1  or other portions of the catheter. To the extent that torque is not avoided by rotation of the bearing  2  due to its outer layer  28  composition, it may be avoided by the ability of the shaft  1  to rotate within the bearing lumen  15  without itself twisting or causing other catheter features such as the balloon  3  to twist. The ability of the shaft  1  to rotate within the bearing lumen  15  is further enhanced by the amount of distance between the shaft  1  and the inner lumen wall  34 . The distance is large enough to prevent tight contact between the shaft  1  and the inner lumen wall  34 . The ability of the shaft  1  to rotate within the bearing lumen  15  without twisting the balloon  3  is dependent upon there being sufficient distance between the balloon  3  and vessel wall  22  as provided by the bearing  2  and its outer diameter  13  (see FIG.  1 ). 
     Referring to FIGS. 4 and 5, the distal end of the catheter  11  is shown with a plurality of bearings  2  disposed thereat. A plurality of bearings  2  may provide more stabilized vascular expansion as the catheter  11  advances through the vasculature. The bearings  2  are separated by shaft bearing gaps  25  which are of a distance adequate to allow sufficient flexure of the shaft  1  as it is advanced through tortuous vasculature. The bearings  2  must be spaced apart to avoid contact with one another. Otherwise, bending of the shaft  1  at the site of the bearings  2  will be compromised by the bearings  2  as they contact one another. In order to maintain proper bearing spacing, both a distal  31  and a proximal  40  bearing ring stop are desirable.