Abstract:
A balloon catheter for medical treatment of a patient, including therapeutic dilatation or deployment of medical devices such as stents or grafts. The balloon catheter has an “over-the-wire configuration, including a proximal hub defining an inflation port and a guidewire port, a flexible shaft defining an inflation lumen and a guidewire lumen, a balloon near a distal end of the catheter, and a distal guidewire port. At least a portion of the shaft has an inner tubular body defining at least a portion of the guidewire lumen, surrounded by an outer tubular body defining at least a portion of the inflation lumen. A proximal portion of the inner body is reinforced by a hypotube, which provides much greater column strength and torsional stiffness. A distal end of the hypotube provides a graduated flexibility transition with a distal spiral-cut segment, in which the pitch of the spiral cut pattern decreases to provide increasing flexibility.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     1. Technical Background 
     The present invention relates generally to medical devices, and more particularly to a balloon catheter having a shaft reinforced with a hypotube. 
     2. Discussion 
     Balloon catheters are used in a variety of therapeutic applications, including intravascular catheters for procedures such as angioplasty and/or deploying medical devices such as stents. Approximately one million angioplasties are performed worldwide each year to treat vascular disease, including coronary, peripheral and neurological blood vessels partially or totally blocked or narrowed by a lesion, stenosis, thrombosis, and/or vasospasm. By way of example, the present invention will be described in relation to coronary, peripheral and neurological angioplasty treatments. However, it should be understood that the present invention relates to any balloon catheter having a shaft reinforced with a hypotube according to the present invention as recited in the following claims, and is not limited to angioplasty, or stents, or even use in blood vessels. 
     Most balloon catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens, and have an inflatable balloon attached near one end of the shaft. This end of the catheter where the balloon is located is customarily referred to as the “distal” end, while the other end is called the “proximal” end. The proximal end of the shaft is generally coupled to a hub, which defines a proximal inflation port and a proximal guidewire port. The proximal inflation port communicates with an inflation lumen defined by the shaft, which extends and is connected to the interior of the balloon, for the purpose of selectively inflating and deflating the balloon. 
     The proximal guidewire port communicates with a guidewire lumen defined by the shaft, for slidingly receiving a guidewire. The guidewire lumen extends between the proximal guidewire port in the hub at the catheter proximal end, and a distal guidewire port at the distal end of the catheter. The catheter of the present invention has an “over-the-wire” configuration in which the guidewire lumen extends essentially the full length of the catheter, between the proximal hub and the catheter distal end. 
     In general, balloon catheters according to the present invention have a shaft, of which at least a portion includes tubular inner and outer bodies, and a portion of the inner body is reinforced with a hypotube. The hypotube reinforcement has a spiral-cut segment at its distal end, to provide a smooth transition of flexibility from the hypotube-reinforced portion to a remainder of the shaft. 
     The balloon itself may define an inflatable central portion defining an inflated size, flanked by a pair of proximal and distal conical portions, flanked by a pair of proximal and distal legs or collars. The proximal and distal collars may be affixed to the shaft. 
     This disclosure of the present invention will include various possible features and embodiments. However, the present invention scope is set forth in each of the claims, and is not limited to the particular arrangements described in this disclosure. 
     An example of this type of over-the-wire balloon catheter is shown in the following patent, which is co-owned with the present invention: U.S. Pat. No. 5,370,615, entitled “Balloon Catheter For Angioplasty,” issued to Johnson on Dec. 6, 1994. 
     Common treatment methods for using such a balloon catheter include advancing a guidewire into the body of a patient, by directing the guidewire distal end percutaneously through an incision and along a body passage until it is located within or beyond the desired site. The term “desired site” refers to the location in the patient&#39;s body currently selected for treatment by a health care professional. The guidewire may be advanced before, or simultaneously with, a balloon catheter. When the guidewire is within the balloon catheter guidewire lumen, the balloon catheter may be advanced or withdrawn along a path defined by the guidewire. After the balloon is disposed within the desired site, it can be selectively inflated to press outward on the body passage at relatively high pressure to a relatively constant diameter, in the case of an inelastic or non-compliant balloon material. 
     This outward pressing of a constriction or narrowing at the desired site in a body passage is intended to partially or completely re-open or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. In the case of a blood vessel, this procedure is referred to as angioplasty. The objective of this procedure is to increase the inner diameter or cross-sectional area of the vessel passage or lumen through which blood flows, to encourage greater blood flow through the newly expanded vessel. The narrowing of the body passageway lumen is called a lesion or stenosis, and may be formed of hard plaque or viscous thrombus. 
     Some balloon catheters are used to deliver and deploy stents or other medical devices, in a manner generally known in the art. Stents, for example, are generally tubular scaffolds for holding a vessel or body passage open. 
     It is desirable to provide a balloon catheter having an optimum combination of various performance characteristics, which may be selected among: flexibility, lubricity, pushability, trackability, crossability, low profile and others. Flexibility may relate to bending stiffness of a medical device (balloon catheter and/or stent, for example) in a particular region or over its entire length, or may relate to the material hardness of the components. Lubricity may refer to reducing friction by using low-friction materials or coatings. Pushability may relate to the column strength of a device or system along a selected path. Trackability may refer to a capability of a device to successfully follow a desired path, for example without prolapse. Crossability may be clarified by understanding that physicians prefer to reach the desired site with the balloon catheter while encountering little or no friction or resistance. Profile may refer to a maximum lateral dimension of the balloon catheter, at any point along its length. 
     The balloon catheter of the present invention provides various advantages, which may include: pushability, optimized flexibility along the catheter length, torsional strength, pull strength, low profile, etc. Some embodiments of the present invention may also provide additional benefits, including smooth transitions in flexibility, lubricious guidewire lumen, etc. 
     In contrast to a distal shaft portion, the proximal portion of the shaft reinforced by the hypotube may have much greater column strength, which will tend to enhance the pushability of the balloon catheter, yet without adversely affecting flexibility in the distal portion of the shaft where flexibility is relatively more important. 
     These and various other objects, advantages and features of the present invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view of a balloon catheter; 
         FIG. 2  is a side elevation view of a balloon catheter; 
         FIG. 3  is a longitudinal cross-section view of some components of a balloon catheter; 
         FIG. 4  is a side elevation view of a tubular outer body component; 
         FIG. 5  is a side elevation view of a hypotube component; 
         FIG. 6  is a graph showing a possible pitch curve for a spiral-cut segment of a hypotube component; 
         FIG. 7  is a longitudinal cross-section view of a tubular inner body; 
         FIG. 8  is a graph showing a possible pitch curve for a braided reinforcement; and 
         FIG. 9  is a side elevation view of a balloon component. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description of the preferred embodiments of the present invention is merely illustrative in nature, and as such it does not limit in any way the present invention, its application, or uses. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention. 
     Referring to the drawings, a balloon catheter is depicted, with one of the preferred embodiments of the present invention being shown at reference number  10  in  FIG. 1 . The balloon catheter of  FIG. 1  has an inflatable balloon  12 , a relatively long and flexible tubular shaft  14 , and a hub  16 . The balloon  12  is affixed to the shaft  14  near a distal end of the shaft  14 , and the hub  16  is affixed to the proximal end of the shaft  14 . 
     The shaft defines at least two passages or lumens, one of which is an inflation lumen  18  connected to the balloon  12  for selectively inflating and deflating the balloon  12 . The inflation lumen  18  thus provides fluid communication between the interior of the balloon  12  at the distal end of the inflation lumen  18 , and a hub inflation port  20  having a coupling or luer-lock fitting at the proximal end for connecting the inflation lumen to a source of pressurized inflation fluid (not shown) in the conventional manner. 
     A second lumen defined by the catheter  10  is a guidewire lumen  26  is adapted to receive an elongated flexible guidewire  28  in a sliding fashion. The guidewire  28  and catheter  10  may thus be advanced or withdrawn independently, or the catheter  10  may be guided along a path selected with the guidewire  28 . 
     In the illustrated embodiment, shaft  14  is constructed of an inner and outer tubular body  22  and  24 . The inner body  22  defines the guidewire lumen  26 , while inflation lumen  18  is defined by an annular space between the inner and outer tubular bodies  22  and  24 . The guidewire lumen  26  extends through the inner tubular body  22  from a distal guidewire port  30  near the catheter distal end to a proximal guidewire port  32  defined by hub  16 . 
     A flexible tubular strain relief  34  surrounds shaft  14  at a transition between the shaft  14  and hub  16 . Strain relief  34  is affixed to shaft  14  and/or hub  16  in any desired manner. 
     The balloon  12  shown in  FIGS. 1 ,  2 ,  3 , and  9  has a central portion  36  defining an inflated size and a working length, flanked by a pair of tapering conical segments  38  and  40 , flanked by a pair of “legs” or collars  42  and  44 . Proximal collar  42  is affixed to outer body  24  near its distal end, and distal collar  44  is affixed to inner body  22  near its distal end. 
       FIG. 3  shows inner body  22 , outer body  24 , and balloon  12 . A pair of radiopaque markers  46  indicate the position of the central working length portion of the balloon to a physician using x-ray video. 
     A proximal portion of inner body  22  is reinforced with a hypotube  48  component. The hypotube  48  is affixed to and surrounds a portion of inner body  22 , extending from proximal hub  16  along a proximal segment of the shaft  14 . Hypotube  48  has a cylindrical segment  50  and a spiral-cut segment  52 . 
     Spiral-cut segment  52  provides a graduated transition in bending flexibility. The spiral pattern cut into hypotube may have a pitch that changes, to increase flexibility in specific areas. For example, the longitudinal distance between adjacent coils of the spiral cut path may become shorter as the spiral cut progresses from its proximal beginning to the distal end of the hypotube, as shown in  FIG. 5 . In other words, the spiral cuts are closer together at the distal end of the hypotube, and farther apart at the proximal end of the spiral cut. 
     As a result, the distal end of the hypotube is more flexible than the proximal portion of the hypotube. This transition in flexibility may be accomplished in various ways. For example, the pitch of the spiral cut may have a proximal pitch, proceeding in a linear fashion down to a smaller distal pitch. In another example, the pitch of the spiral cut may decrease from a proximal pitch A to a distal pitch B in a non-linear manner, as depicted in  FIG. 6 . In the example of  FIG. 6 , an exponential progression has been selected. Other non-linear pitch curves may be selected. 
     One particular example of an inner tubular body  22  is shown in  FIG. 7 . In this example, the inner body tube  22  has a multi-layer construction. The inner layer  54  is a lubricious polymer material, such as for example high density polyethylene (HDPE) or polytetrafluoroethylene (PTFE). The outer layer  56  is a strong polymer material, which is selected to bond well with the material(s) selected for the hub  16  and the balloon  12 . Examples of acceptable materials are nylons or polyether block amide (PEBA). In the specific example shown in  FIG. 7 , the outer layer  56  has multiple segments of differing flexibility. For example,  FIG. 7  shows a proximal, middle, and distal segment of outer layer material  58 ,  60  and  62 , arranged in order of increasing flexibility from the proximal to the distal direction. 
     In addition, the example shown in  FIG. 7  has an internal reinforcement in the form of braid  64 . The braided reinforcement is depicted in a diagrammatic manner for clarity, and may be at least a pair of wires coiled around inner body  22 , between the inner and outer layers  54  and  56 , in a criss-crossing fashion. The braid wires  64  may be a metal such as stainless steel, or another strong material such as Kevlar fibers. In the example of  FIG. 7 , the braid wires  64  are arranged with a pitch that decreases in the distal direction. In other words, the wraps of the braid wires are closer together near the distal end of inner body than at the proximal end. This decreasing pitch, measured in increasing wires per inch, may be arranged progressively along the length of the inner body, in linear or non-linear fashion, or in specific segments, illustrated in  FIG. 8 . The braid segments in  FIG. 7  may be arranged to align with the segments of different flexibility of the outer layer material, but need not be so aligned, as shown in  FIG. 7 . 
       FIG. 8  shows the number of braid wires per inch, along the length of inner body  22 . Of course, other curves and arrangements may be selected. 
     If desired, inner body may be provided with radiopaque markers, to indicate specific locations on the catheter to a physician using an x-ray video. In the example of  FIG. 7 , a pair of marker bands  66  made of a radiopaque material such as for example tungsten, platinum, etc. are provided near the distal end of the inner body. The markers may be placed on the outside of inner body, or between the inner and outer layers, as shown in  FIG. 7   
     The distal end of inner body may be arranged to form part of the distal tip of the catheter. If so, it should be optimally shaped at some point during construction of the catheter, as shown in  FIG. 7 . 
     The inner surface of tubular inner body defines at least a portion of the guidewire lumen. To enhance ease of operation, this inner surface may be of a material selected for high lubricity, which will present low frictional resistance to movement of a guidewire inserted within guidewire lumen. Some prior catheters have used an inner layer defining a guidewire lumen that is made of Teflon®, or PTFE, and it is possible to likewise use PTFE in a catheter according to the present invention. 
     Another possibility is to use a different material for the guidewire lumen. Because many guidewires have a PTFE coating, in some operating conditions, it is possible that the resulting interface between similar materials, PTFE tube on PTFE-coated guidewire, to exhibit a slight “slip stiction” effect. Accordingly, another lubricant material may be used, for example HDPE, as the inner layer of inner body. The markers may be placed around the outside of the inner body, or inside the wall of the inner body. In  FIG. 7 , marker bands  66  are placed between inner and outer layers  54  and  56  of inner body  22 . 
     The outer body  24  may be a conventional polymer tube or a more sophisticated construction. An example outer body  24  is depicted in  FIG. 4 , in which the outer body tube  24  tapers from a proximal size to a smaller distal size. In particular, outer body  24  of  FIG. 4  is a bump extrusion, in which the outer size and inner size (and therefore the wall thickness) draws down and narrows simultaneously along the length of the outer body  24 . 
     The hypotube may be made of metal which is selected to be biocompatible, such as for example stainless steel. Other acceptable metals may include nitinol, titanium, etc. 
     The inflation lumen  18  extends from the inflation port  20 , through a proximal portion of the inflation lumen  18  defined by the hypotube, through a distal portion of the inflation lumen  18  defined by the annular space between the inner and outer bodies  22  and  24 , and into the balloon. 
     The balloon catheter and stent delivery system of the present invention may be made using various methods, including extruding polymer tubes, injection-molding the proximal hub, and extruding a balloon parison and then blowing the parison into a balloon having the desired properties. It is also possible to affix polymer components to each other by heat-sealing, or by using an adhesive such as a UV-cured adhesive. 
     It should be understood that an unlimited number of configurations for the present invention could be realized. The foregoing discussion describes merely exemplary embodiments illustrating the principles of the present invention, the scope of which is recited in the following claims. Those skilled in the art will readily recognize from the description, claims, and drawings that numerous changes and modifications can be made without departing from the spirit and scope of the invention.