Abstract:
A tubing assembly and method of manufacture for a catheter having an inner tubular member defining a lumen, an outer tubular member surrounding said inner member, and a braid mounted between the tubular members to provide rigidity to the flexible catheter. The braid preferably has different braid densities in selected regions along the length of the catheter. In addition, the outer tubular member preferably includes a number of segments each having different mechanical properties. In this configuration, both the polymer characteristics and the braid density may be independently varied along the length of the catheter to maximize catheter performance.

Description:
CROSS REFERENCES TO CO-PENDING APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 08/936,983 filed Sep. 25, 1997, entitled “Catheter Having a High Tensile Strength Braid Wire Constraint and Method of Manufacture”, which is a continuation-in-part of U.S. patent application Ser. No. 08/800,926 filed Feb. 13, 1997, entitled “Catheter Having an Adhesive Braid Wire Constraint and Method of Manufacture”, which is a continuation-in-part of U.S. Pat. No. 5,603,705 filed Aug. 15, 1995, entitled “Catheter Joint with Restraining Device”, which is a continuation of U.S. patent application Ser. No. 08/171,925, filed Dec. 22, 1993, entitled “Catheter Joint with Restraining Device”, both of which are related to U.S. patent application Ser. No. 08/108,973, filed Aug. 18, 1993, entitled “Improved Thin-Walled Catheter”, all assigned to the assignee of the present invention, which disclosures are all incorporated herein by reference. This application is also related to U.S. patent application Ser. No. 08/800,927 filed Feb. 13, 1997, entitled “Guide Catheter Having Selected Flexural Modulus Segrnents”, which is a continuation-in-part of U.S. patent application Ser. No. 08/703,635, filed Aug. 27, 1996, entitled “Guide Catheter Having a Plurality of Filled Distal Grooves”, which is a continuation-in-part of U.S. patent application Ser. No. 08/195,222, filed Feb. 14, 1994, entitled “Elastic Guide Catheter Transition Element” now issued as U.S. Pat. No. 5,569,218, all assigned to the assignee of the present invention, the disclosures of which are all incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to the field of medical devices, and more particularly, to the field of catheters such as guide catheters used for the placement of medicines and medical devices within the body and diagnostic catheters used to inject radiopaque fluids within the body for treatment and diagnosis of vascular diseases. Specifically, the invention is directed to a catheter tube, particularly useful in intravascular guide catheters, incorporating regions of different braid density and/or material characteristics, and methods of manufacture therefor. 
     BACKGROUND OF THE INVENTION 
     The use of intravascular catheters for treatment of the body is well known in the field of medicine. The need for a choice of catheter sizes and types has grown rapidly as the techniques for their use have been greatly improved and the types of medical uses have expanded quickly. One such catheter is a guide catheter which includes a tubular member having a lumen therethrough. Guide catheters are commonly used in diagnostic and treatment techniques related to vascular disease such as angioplasty. 
     A guide catheter is typically inserted into the femoral artery and routed to a location near a treatment or diagnostic site through the aorta over the aortic arch to the ostium of a target vessel. The guide catheter provides a conduit so that fluid or another medical device can be delivered easily to the proximate location of treatment via the lumen of the guide catheter. Prior art catheters often include a tubular member including a pair of congruent tubes, the inner one defining the lumen. A hub is connected at the proximal end of the tubes, which in addition to providing access to the lumen for fluids and the like, is often used to input torque and other necessary pressures to the tubes during their placement within the body. A tip of a selected design is placed at the distal end of the tubes. 
     In order for the physician to place the catheter at the correct location in the vessel, the physician must apply longitudinal and rotational forces. The catheter must be rigid enough to transmit sufficient force from the proximal end to the distal end, yet flexible enough to navigate the bends in the blood vessel. Further, the catheter must be torsionally rigid to transmit the applied torque and radially rigid to resist kinking. One way to accomplish a balance between longitudinal rigidity and flexibility, while insuring sufficient torque and radial strength, is to provide a support member in the catheter shaft. Typically, the support member is provided between an inner tube and an outer tube to form the catheter shaft. 
     The support member is often a braid of metal wires or the like. The performance criteria of a catheter can be affected by altering the density (i.e., pic count) of the braid. Specific performance criteria which can be altered include shaft stiffness, curve support, and kink resistance. Altering the braid pic count can affect shaft stiffness by changing the amount of polymer in the catheter shaft and the degree of interstial bonding between the polymer and the inner tube. Altering the braid can also affect curve support in a similar manner. Polymer in the shaft forming the curve provides support and shape memory. In addition, an optimal degree of braid density is required in the curve to provide a degree of flexibility so that the catheter shaft can align coaxially to the engaged artery. Finally, altering the braid pic affects kink resistance. Increasing braid pic will normalize the braid angle to the catheter surface and increase the amount of reinforcing wire in the shaft. 
     It is possible to construct a device that is very rigid to obtain the correct amount of shaft stiffness and curve support. However, the resulting device may track poorly, be traumatic to the patient&#39;s arteries and kink easily due to its rigidity. Similarly, it is possible to construct a very flexible device to increase trackability, limit the trauma the device imparts to the blood vessels and limit kinkability. However, the device then may become too flexible to provide sufficient shaft stiffness and curve support. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes many of the disadvantages associated with the prior art by varying the braid density in specific regions of the catheter, thereby optimizing shaft stiffness, curve support and kink resistance. Further, the present invention contemplates placing a number of segments, each having selected mechanical characteristics, at desired locations along the length of the catheter. Accordingly, the present invention may allow both the mechanical characteristics and the braid density to be independently varied along the length of the catheter to help reduce catheter back-out and maximize catheter performance. 
     In one illustrative embodiment of the present invention, a catheter shaft having a first region and a second region is provided. A support member extends along at least a portion of the catheter shaft including along the first region and the second region. The support member has a first portion that corresponds to the first region of the catheter shaft and a second portion that corresponds to the second region of the catheter shaft. The density of the support member is changed by changing the diameter of the support member in the first portion relative to the second portion. Thus, the first portion of the support member may provide different torsional rigidity, flexibility, and radial strength to the catheter shaft relative to the second portion. 
     Preferably, the support member is braid that is disposed between an inner layer and outer layer of the catheter shaft. To increase the diameter of the braid, it is contemplated that the inner layer may have an increased diameter in the first region relative to the second region. This may be accomplished in any number of ways, including providing an annulus or short tubular segment of material around the inner layer adjacent the first region, or using a sleeve to selectively increase the density of the braid in the first region, as more fully described below. 
     It is also contemplated that the outer layer of the catheter shaft may include two or more segments, wherein at least one of the segments includes a material that has different mechanical characteristics than another one of the segments. For example, the catheter may include a first tubular section and a second tubular section, wherein the first tubular section includes a plastic material that has one or more different mechanical properties than the plastic material of the second tubular section. As more fully described in U.S. patent application Ser. No. 08/800,927 filed Feb. 13, 1997, entitled “Guide Catheter Having Selected Flexural Modulus Segments”, selected polymers having different characteristics may be used for various regions of the catheter. This may allow the rigidity of the catheter to be increased in discrete segments, thereby increasing the curve resistance while maintaining the flexibility of the catheter. Accordingly, the present invention may allow both the polymer characteristics and the braid density to be independently varied along the length of the catheter for optimal catheter performance. 
     The present invention also contemplates a number of methods for forming a catheter having a support member with various braid densities along its length. One illustrative method for forming a catheter having an inner tube and a support member includes the steps of: providing the support member over the inner tube; causing a first region of the support member to have a first diameter, wherein the first region has a proximal end and a distal end; securing the support member relative to the inner tube proximate the distal end of the first region; causing a second region of the support member to have a second diameter, wherein the first diameter is different from the second diameter, and wherein the second region overlaps at least a portion of the first region; and securing the support member relative to the inner tube proximate the distal end of the second region. The support member may be secured to the inner tube using any number of techniques including using a suitable adhesive or an annulus of heat shrink tubing. 
     More specifically, the above method for forming a catheter having an inner tube and a support member may includes the steps of: sliding the support member distally over the outer surface of the inner tube; sliding a first sleeve having a distal end over at least a portion of the support member until the distal end of the first sleeve reaches a first location, the first location being distal of the proximal end of the inner tube; securing the support member relative to the inner tube proximate the first location; removing the first sleeve; sliding a second sleeve having an inner diameter that is less than the inner diameter of the first sleeve over the support member until a distal end of the second sleeve reaches a second location, wherein the second location is proximal of the first location; and securing the support member relative to the inner tube proximate the second location. 
     Another illustrative method of the present invention for forming a catheter having an inner tube and a support member includes the steps of: forming an inner tube having a first region and a second region, wherein the first region has a first outer diameter and the second region has a second outer diameter; sliding the support member distally over at least a portion of the inner tube including over the first region and the second region; tensioning the support member against the first region and the second region; and providing an outer layer over the support member. Preferably the first region of the inner tube has an increased outer diameter relative to the second region, and is formed by providing an annulus or tubular segment of material around the inner tube over the length of the first region. 
     These and other various advantages and features of novelty which characterize the present invention are pointed out with particularity in the claims annexed hereto and forming a part hereof However, for a better understanding of the invention, its advantages and the objects obtained by its use, reference should be made to the drawings which form a further part hereof and to the accompanying descriptive matter, in which there are illustrated and described preferred embodiments of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, in which like reference numerals indicate corresponding parts or elements of preferred embodiments of the present invention throughout the several views: 
     FIG. 1 is a partial cut-away side view of an illustrative catheter in accordance with the present invention; 
     FIG. 2 shows a partial cross-sectional side view of a mandrel having an inner layer provided thereon; 
     FIG. 3 shows a braid provided over the inner layer of FIG. 2; 
     FIG. 4 shows a first diameter sleeve provided over part of the braid of FIG. 3; 
     FIG. 5 shows the first diameter sleeve of FIG. 4 in a distal position, exposing only the distal end of the braid; 
     FIG. 6 shows the exposed distal portion of FIG. 5 secured to the inner layer; 
     FIG. 7 shows the first diameter sleeve of FIG. 6 partially removed from the braid; 
     FIG. 8 shows the first diameter sleeve of FIG. 7 completely removed from the braid; 
     FIG. 9 shows a second diameter sleeve provided over part of the braid of FIG. 8, and the exposed portion of the braid just distal of the second diameter sleeve secured to the inner layer; 
     FIG. 9A shows an exaggerated view of an area of interest of FIG. 9; 
     FIG. 9B shows another view similar to FIG. 9A except that it shows different means of securing the braid to the inner tubular member; 
     FIG. 10 shows the second diameter sleeve of FIG. 9 partially removed from the braid; 
     FIG. 11 shows the second diameter sleeve of FIG. 10 completely removed from the braid; 
     FIG. 11A shows an exaggerated view of an area of interest of FIG. 11; 
     FIG. 12 shows a first outer tube, a second outer tube and a plug tube positioned over the braid of FIG. 11; 
     FIG. 13 shows a heat shrink sleeve positioned over the first outer tube, the second outer tube and the plug tube of FIG. 12; 
     FIG. 14 shows the catheter of FIG. 13, with the heat shrink sleeve removed; 
     FIG. 15 shows the catheter of FIG. 14 with the proximal and distal ends trimmed; 
     FIG. 16 shows a partial cross-sectional side view of a mandrel having an inner layer provided thereon, with the two rings provided around the inner layer; 
     FIG. 17 shows a braid provided over the inner layer and the two rings of FIG. 16; 
     FIG. 18 shows a perspective view of a grab washer for tensioning the braid of FIG. 17; 
     FIG. 19 shows the grab washer of FIG. 18 tensioning the braid of FIG. 17; and 
     FIG. 20 shows the braid fully tensioned over the inner layer and the two ring layers. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein. However, it should be understood that the disclosed embodiments are merely exemplary of the present invention which may be embodied in various systems. The discussion with respect to FIG. 1 is directed to a catheter in accordance with an illustrative embodiment of the present invention. The discussion with respect to FIGS. 2-15 is directed to a first method for forming a catheter in accordance with the present invention. The discussion with respect to FIGS. 16-20 is directed to a second method for forming a catheter in accordance with the present invention. It should be recognized, however, that elements of each embodiment and method may be incorporated in a catheter construction in combinations as would be well understood by one skilled in the art. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to variously practice the present invention. 
     FIG. 1 shows a guide catheter  10 , which may be a thin-walled catheter. Catheter  10  includes an outer tubular member which surrounds and is coaxial with an inner tubular member. The outer tubular member and the inner tubular member are described in more detail below. A support member is positioned between the inner tubular member and the outer tubular member. 
     The support member may be a braid of metal wire, and may have a first braid density in a first region  20 , a second braid density in a second region  22  and a third braid density in a third region  24 . While three regions are shown in FIG. 1, it is contemplated that the any number of regions may be used, and the number of regions may be selected based on the desired application of the catheter. 
     The distal end of the braid  26  is preferably secured to the inner tubular member using an adhesive as disclosed in U.S. patent application Ser. No. 08/936,983 filed Sep. 25, 1997, entitled “Catheter Having a High Tensile Strength Braid Wire Constraint and Method of Manufacture”, or via a short sleeve of a heat shrink material such as FEP. The adhesive preferably is a UV cure urethane or epoxy, such as is available from Dymax Corporation in Torrington, Conn. 
     The braid may also be secured to the inner tubular member at a location  30  between the first region  20  and the second region  22 , and at a location  32  between the second region  22  and the third region  24 . Preferably, the density of the braid is different in the first region  20 , the second region  22  and the third region  24 . As more fully described below, the density of the braid may be changed by altering the inner and/or outer diameter of the braid in each of the respective regions. By selecting the appropriate number of regions and the placement of the regions, the flexibility of the catheter may be optimized to reduce the tendency for catheter back-out. 
     It is also contemplated that the outer tubular member may include a number of segments, each positioned at a desired location along the length of the catheter. Each of the segments may be formed from a material that has different mechanical characteristics relative to the other segments. In the embodiment shown, the outer tubular member includes a first segment  38  and a second segment  40 . The first segment is shown joining the second segment at line  42 . The material used for the first segment  38  may have one or more properties that differ from the properties of the material used to form the second segment  40 . For example, the first segment  38  may be formed from a material that has less flexibility than the material used for the second segment  40 . This allows the rigidity of the catheter to be increased at discrete segments. Accordingly, the present invention may allow both the material characteristics of the outer tubular member and the braid density to be independently varied along the length of the catheter to help reduce catheter back-out and maximize catheter performance. 
     The inner tubular member is preferably formed from polytetrafluroethelene (PTFE), and the outer tubular member is preferably formed from PEBAX. The outer surface of the PTFE inner tubular member is preferably chemical etched so that the braid can more readily be adhered thereto. The chemical etch may also aid the PEBAX outer tubular member to more readily adhere to the inner tubular member when urged through the interstitial spaces of the braid during processing, as more fully described below. 
     FIGS. 2-15 illustrate a first method for forming a catheter in accordance with the present invention. FIG. 2 shows a mandrel  50  having an inner tubular member  52  provided thereon. The mandrel  50  is preferably made from a stainless steel, and the inner tubular member  52  is preferably made from PTFE. FIG. 3 shows a braid  54  provided over the inner tubular member  52 . As shown, the braid  54  is not yet tensioned and therefore has a non-uniform outer diameter. The proximal end of the braid is preferably twisted to anchor the proximal end of the braid relative to the inner tubular member  54 , as more clearly shown in FIG.  4 . 
     FIG. 4 also shows a first sleeve  56  having a first inner diameter provided over part of the braid  54 . Preferably, the first sleeve  56  is formed from PTFE. As the first sleeve  56  is slid over the braid  54 , the braid  54  assumes a constant outer diameter defined by the inner diameter of the first sleeve  56 . The diameter of the braid  54  then defines the density of the braid in that region. It has been found for each 0.001″ decrease in the outer diameter of the braid  54 , the braid density may change by as much as 7 pic. 
     FIG. 5 shows the first sleeve  56  slid distally over the braid  54  to a distal position, wherein only the distal end  60  of the braid  54  is exposed. In this position, nearly the entire braid  54  has a constant braid density defined by the inner diameter of the first sleeve  56 . With the first sleeve  56  in place, the exposed distal portion  60  of the braid  54  is secured to the inner tubular member  52 , as shown in FIG.  6 . The distal portion  60  of the braid  54  is preferably secured using a UV cure adhesive or epoxy  62 , as disclosed in U.S. patent application Ser. No. 08/936,983 filed Sep. 25, 1997, entitled “Catheter Having a High Tensile Strength Braid Wire Constraint and Method of Manufacture”. It is also contemplated that the distal portion  60  of the braid  54  may be secured relative to the inner tubular member  52  using a ring of heat shrink material such as FEP. 
     Once the distal portion  60  of the braid  54  is secured relative to the inner tubular member  52 , the first sleeve  56  is removed. FIG. 7 shows the first sleeve  56  partially removed, and FIG. 8 shows the first sleeve  56  completely removed. 
     FIG. 9 shows a second sleeve  64  provided over a first region  68  of the braid  54 . Like the first sleeve  56 , the second sleeve  64  is preferably formed from PTFE. However, the second sleeve  64  preferably has a reduced inner diameter relative to the first sleeve  56 . In this configuration, as the second sleeve  64  is slid over the braid  54 , the braid  54  assumes a reduced outer diameter in a first region  68 . This produces a lower braid density in the first region  68 . By reducing the diameter and thus the braid count of the braid in the first region  68 , the additional braid is pushed into a second region  70 . This increases the braid density in the second region  70 . As indicated above, it has been found that it is possible to obtain a change of approximately 7 pic for each 0.001″ decrease in the outer diameter of the braid  54 . 
     With the second sleeve  64  in place, an intermediate portion  72  of the braid  54  is secured to the inner tubular member  52 . The intermediate portion  72  of the braid  54  is secured to the inner tubular member  52  using a UV cure adhesive or epoxy  66 , as disclosed in U.S. patent application Ser. No. 08/936,983 filed Sep. 25, 1997, entitled “Catheter Having a High Tensile Strength Braid Wire Constraint and Method of Manufacture”. It is also contemplated that the intermediate portion  72  of the braid  54  may be secured relative to the inner tubular member  52  using a ring of heat shrink material such as FEP. 
     FIG. 9A shows a magnified and exaggerated view of a mandrel  50  covered by an inner tubular member  52  with braid  54  partially covered by second sleeve  64 . The braid  54  has a first region  68  and a second region  70  separated by the second sleeve  64 , as well as an intermediate portion  72 . The braid  54  has a reduced outer diameter  55   a  in the first region  68 , and a greater outer diameter  55   b  in the second region  70 . Part of the braid  54  in the intermediate portion  72  has been secured to the inner tubular member  52  using a UV cure adhesive or epoxy  66 . It is contemplated that, rather than a UV cure adhesive or epoxy  66 , a ring of heat shrink material  67  may be used to secure the braid  54  in the intermediate portion  72  to the inner tubular member  52 , as shown in FIG.  9 B. 
     Once the intermediate portion  72  of the braid  54  is secured relative to the inner tubular member  56 , the second sleeve  64  is removed. FIG. 10 shows the second sleeve  64  partially removed, and FIG. 11 shows the second sleeve  64  completely removed. At this point, the braid  54  may be secured to the inner tubular member  52  n ear the proximal en d of the inner tubular member  52 , as shown at  80 . The portion of the braid that is proximal to the inner tubular member  52  may then be removed. FIG. 1A shows a magnified and exaggerate d view similar to that of FIG. 11, wherein the braid  54  is shown having a lesser diameter  55   a  in a first region  68  and a greater diameter  55   b  in a second region  70 . 
     FIG. 12 shows a first outer tube  90 , a second outer tube  92  and a plug tube  94  positioned over the braid  54  of FIG.  11 . The first outer tube  90  and second outer tube  92  preferably have different mechanical characteristics or properties. For example, the first outer tube  90  may be less flexible than the second outer tube  92 . Referring to FIG. 13, the first outer tube  90 , the second outer tube  92  and the plug tube  94  are maneuvered to abut one another, and a heat shrink sleeve  100  is provided thereover. Sufficient heat is applied to cause the first outer tube  90 , the second outer tube  92  and the plug tube  94  to become softened. The heat also causes the heat shrink sleeve  100  to contract. The axial and longitudinal forces of the contracting heat shrink sleeve  100  cause the first outer tube  90 , the second outer tube  92  and the plug tube  94  to bond to one another. The catheter is then cooled, and the heat shrink sleeve  100  is removed. The plug tube  94  is also removed, preferably by cutting, as shown in FIG.  14 . Thereafter, the mandrel  50  is removed, as shown in FIG.  15 . 
     FIGS. 16-20 illustrate another method for forming a catheter in accordance with the present invention. In this method, the inner diameter of the braid is changed to provide one or more regions that have different braid densities. Referring specifically to FIG. 16, a mandrel  110  is shown having an inner tubular layer  112  provided thereon. The mandrel  110  is preferably made from a stainless steel, and the inner tubular member  112  is preferably made from PTFE. To increase the inner diameter of the braid, one or more rings of material may be provided circumferentially around selected regions of the inner tubular member  112 . For example, a first ring or annulus  114  is provided around a first region  117  of the inner tubular member  110 . Likewise, a second ring or annulus  116  is provided around a second region  118  of the inner tubular member  110 . In a preferred embodiment, annulus  114  and annulus  116  are formed from PEBAX, and the outer surface of the PTFE inner tubular member  112  is chemically etched to allow improved bonding between the PTFE inner tubular member  112  and annulus  114  and annulus  116 . 
     FIG. 17 shows a braid  120  provided over the inner tubular layer  112 , annulus  114  and annulus  116 . As shown, the braid  120  is not yet tensioned and therefore has a non-uniform outer diameter. The proximal end of the braid may be twisted to anchor the proximal end of the braid relative to the inner tubular member  112 , as described above. The distal end  122  of the braid is then secured to the inner tubular member  112  using an adhesive  124  or a ring of heat shrink tubing, as described above. 
     FIG. 18 shows a perspective view of a grab washer  130  for tensioning the braid  120  of FIG.  17 . The grab washer  130  preferably includes a bore  132  therethrough with a number of slits  134  extending outward from the bore  132 . Between each of the slits is a flap  136 . The slits  134  allow the diameter of the bore  132  to change by pushing the flaps  136  laterally from the plane of the grab washer  130 . 
     The bore  132  of the grab washer  130  receives the distal end  128  of the catheter. The grab washer  130  is then slid proximally over the catheter such that the flaps  136  engage the braid  120 , as shown in FIG.  19 . The flaps tension the braid about the outer surface of the catheter. When the grab washer  130  passes over annulus  114  or annulus  116 , the inner diameter of the braid increases. It has been found that it is possible to obtain a change of approximately 7 pic for each 0.001″ increase in the inner diameter of the braid  54 . FIG. 20 shows the braid  120  fully tensioned over the inner tubular member  112  and the two annulus rings  114  and  116 . 
     An outer layer having a number of regions each having different mechanical properties may be provided over the braid  120 . This may be done in accordance with the discussion of FIGS. 12-15 above. It is contemplated that the wall thickness of the outer layer segments may be adjusted in the regions of annulus  114  and annulus  116  so that the outer diameter of the catheter is consistent. 
     Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate the other useful embodiments within the scope of the attached claims.