Abstract:
A sheath is provided to protect a blade when the blade is mounted on a balloon catheter. In particular, this protection is provided while the balloon is deflated for maneuver of the catheter through the vasculature of a patient. The sheath itself is a tubular shaped member that is bifurcated into substantially symmetric halves. Further, the sheath forms a channel for protecting the blade when its halves are juxtaposed. An adhesive bonds both halves of the sheath to the surface of the balloon. When the balloon is deflated, its halves are juxtaposed to cover the blade in the protective channel. On the other hand, when the balloon is inflated, the expanded surface of the balloon pulls the opposed sheath halves that are bonded to it from each other, to thereby expose the blade.

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to interventional medical devices. More particularly, the present invention pertains to medical devices that insert cutting blades into the vasculature of a patient. The present invention is particularly, but not exclusively, useful as a sheath for protecting a cutting blade as it is being advanced or withdrawn through the vasculature. 
     BACKGROUND OF THE INVENTION 
     Through the years, many medical devices have been developed for the purpose of performing procedures wherein it is necessary to somehow cut or incise the tissue of a patient. For specific applications, interventional devices have been developed that are capable of incising tissue at predetermined locations within the vasculature of a patient. In these cases, it is necessary for the device to be maneuvered through the vasculature. Accordingly, a major consideration involves the prevention of an inadvertent or unwanted cutting or incising of tissue as the device is either being advanced into or withdrawn from the vasculature. 
     An example of an interventional medical device that has been developed for performing certain in situ procedures of the type mentioned above is disclosed in U.S. Pat. No. 5,556,405. This patent issued to Lary for an invention entitled “Universal Dilator with Reciprocal Incisor”, and is assigned to the same assignee as the present invention. As exemplified in this patent, one way to protect against the inadvertent cutting of tissue in the vasculature of a patient is to hold the cutting elements inside a protective housing as it is being moved in the vasculature. Then, while holding the protective housing stationary, an independent mechanism is used to selectively move the cutting elements out of the protective housing so they can be used for cutting. Not all interventional medical devices, however, lend themselves to such a mechanism. For instance, consider a device such as is disclosed in U.S. Pat. No. 5,797,935, which issued to Barath for an invention entitled “Balloon Activated Forced Concentrators for Incising Stenotic Segments” and which is also assigned to the same assignee as the present invention. In such devices, the mechanism that advances the cutting elements (e.g. a balloon) does so by being reconfigured (i.e. inflated). Consequently, an independent protective device that does not accommodate such a reconfiguration and, instead, remains stationary would be inoperative for such a device purpose. 
     In light of the above, it is an object of the present invention to provide a protective sheath for a blade mounted on an inflatable balloon that is opened by balloon expansion to expose the blade. Another object of the present invention is to provide a protective sheath for a blade mounted on an inflatable balloon that protects the blade from inadvertently cutting tissue as the deflated balloon is maneuvered through the vasculature of a patent. Still another object of the present invention is to provide a protective sheath for a blade mounted on an inflatable balloon that is easy to use, relatively simple to manufacture and comparatively cost effective. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a sheath is provided for protecting a blade when the blade is mounted onto the surface of an inflatable balloon. Basically, the sheath of the present invention is an elongated, tubular-shaped member that is affixed to the surface of the balloon. More specifically, this elongated member (sheath) has an outer surface, and it generally defines an axis that lies in a longitudinal plane. Further, the elongated member is bifurcated in this longitudinal plane to create two substantially symmetric halves. Between the halves, the sheath is formed with an axially aligned protective channel for receiving and protecting the blade therein when the halves are juxtaposed to each other. 
     Structurally, the sheath is bifurcated in the longitudinal plane by the protective channel and a slit that lies in the plane. In detail, the protective channel has opposed channel sides that extend from a common linear vertex in the longitudinal plane to the outer surface of the tube. Also, the slit has opposed sides that extend from the same linear vertex, in a direction away from the protective channel and toward the outer surface of the sheath. 
     For the operation of the present invention, an adhesive holds the sheath onto the surface of the balloon. Through this connection, the configuration of the sheath depends on the configuration of the balloon. Specifically, when the balloon is deflated, the opposed slit sides of the sheath are juxtaposed against each other to cover the blade inside the protective channel. On the other hand, when the balloon is inflated, and its surface is reconfigured, the opposed sheath halves are separated from each other. This then causes the slit sides to be distanced from each other to expose the blade. 
     In a preferred embodiment of the present invention the balloon will have substantially three definable portions. These are: a proximal portion; a distal portion; and a central portion that is intermediate the proximal and distal portions. More particularly, the distal and proximal portions are tapered and the intermediate central portion is substantially cylindrical. Specifically, the proximal portion of the balloon is conical shaped with a taper that has a decreasing diameter in the proximal direction. Further, for this preferred embodiment, the blade has a proximal segment that is bonded to the proximal portion of the balloon. The blade also has a distal segment that extends over the central portion of the balloon. This distal segment, however, is not bonded to the balloon. On the other hand, the sheath is bonded to both the proximal and the central portion of the balloon. Consequently, when the balloon is inflated, the sheath will separate as described above. Once exposed by the sheath, the blade becomes inclined relative to the longitudinal axis of the balloon. Specifically, this inclination happens because the proximal segment of the blade is mounted to follow the taper that is established by the proximal portion of the balloon when the balloon is inflated. On the other hand, because it is not bonded to the balloon, the distal segment of the blade will extend outwardly beyond the surface of the balloon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a perspective view of a cutting blade balloon catheter system incorporating a protective sheath in accordance with the present invention, with the balloon shown in a deflated configuration; 
         FIG. 2  is an exploded perspective view of the interaction between the protective sheath and a cutting blade; 
         FIG. 3A  is a cross-sectional view of the system for a single blade and its protective sheath as seen along the line  3 - 3  in  FIG. 1 ; 
         FIG. 3B  is a cross-sectional view of the system for a plurality of blades and their respective protective sheaths as would be seen along the line  3 - 3  in  FIG. 1 ; 
         FIG. 4  is a perspective view of the cutting blade balloon catheter system shown in  FIG. 1 , with the balloon in an inflated configuration; 
         FIG. 5  is a partial cross-sectional view of the system as seen along the line  5 - 5  in  FIG. 4 ; 
         FIG. 6  is a side elevation view of a preferred embodiment of the present invention; and 
         FIG. 7  is a side elevation view of an alternate embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A system in accordance with the present invention is shown in  FIG. 1  and is generally designated  10 . As shown, the system  10  includes a catheter  12  and has a balloon  14  that is mounted on the catheter  12 . As also shown in  FIG. 1 , the system  10  includes a sheath (elongated member)  16  that is bonded to the balloon  14  in a manner well known in the pertinent art, such as by solvent bonding. For purposes of the present invention, the sheath  16  is made of a polymer material of a type well known in the art. Further, the catheter  12  is formed with a so-called “pig tail” tip  18  that can be used to facilitate the maneuvering of the catheter  12  within the vasculature of a patient (not shown). Also, catheter  12  is shown to include a radiopaque marker  20  for locating the catheter  12  once it is in the vasculature.  FIG. 1  also indicates that an extracorporeal fluid pump  22  is connected in fluid communication with the balloon  14  to selectively inflate and deflate the balloon  14 . In detail, the structure of sheath  16  will be best appreciated by referencing  FIG. 2 . 
     In  FIG. 2  it will be seen that the sheath (elongated member)  16  is effectively bifurcated into two halves  24   a  and  24   b . Further, the sheath  16  is generally a tube shaped structure that defines a longitudinal axis  26 . Importantly, the sheath  16  is divided by a slit  28  and is formed with a protective channel  30 . As shown, both the slit  28  and the protective channel  30  extend lengthwise along the sheath  16  in a longitudinal direction. In more detail, the slit  28  extends radially from the axis  26  and lies in a longitudinal plane that is generally defined by the axis  26  and the slit  28 . Structurally, the slit  28  extends from a vertex  32  to the outer surface  34  of the sheath  16  wherein the vertex  32  is substantially parallel to the axis  26  and is in the longitudinal plane. 
     As shown in  FIG. 2 , the protective channel  30  of sheath  16  is diametrically opposed to the slit  28 . Like the slit  28 , the protective channel  30  extends from the vertex  32  to the outer surface  34 . Importantly, the dimensions of the protective channel  30  are established to conform the channel  30  to the dimensions of a blade  36 . Stated differently, the protective channel  30  is formed to receive the blade  36  therein, such as is shown for the phantom blade  36 ′ in  FIG. 2 . As envisioned for the present invention, the blade  36  will be preferably made of a stainless steel and will be approximately twenty-five millimeters in length. 
     Still referring to  FIG. 2 , it will be appreciated that the sheath  16  has a bonding area  38   a  on the half  24   a , and a similar bonding area  38   b  on the half  24   b . Both of these bonding areas  38   a  and  38   b  are located on the outer surface  34  of the sheath  16  and extend along the length of the sheath  16 . Further, these bonding areas  38   a  and  38   b  extend on the surface  34  through an arc length  40  that is approximately ninety degrees, or more. An adhesive that is placed on the bonding areas  38   a  and  38   b  bonds the sheath  16  to the balloon  14 . More specifically, this is done with the blade  36  also bonded to the balloon  14  and with the blade  36  positioned inside the protective channel  30 . Importantly, throughout the operation of the present invention, the outer surface  34  of the sheath  16  remains bonded to the balloon  14  at the bonding areas  38   a  and  38   b . Likewise, the blade  36  also remains operationally bonded to the balloon  14 . 
     By cross-referencing  FIG. 1  with  FIG. 3A  it will be noted that when the balloon  14  is deflated, the sheath  16  effectively holds and covers the blade  36  in its protective channel  30 . Further, in this configuration, the sheath  16  also helps define folds for the deflated balloon  14  that reduce the profile of balloon  14 , and thereby facilitate the maneuvering of the catheter  12  through the vasculature. As indicated by  FIG. 3B , although the disclosure here is directed toward a single sheath  16  and blade  36  combination, the present invention also contemplates the use of a plurality of such combinations. The combinations of multi-blades  36   a,b,c  and respective multi sheaths  16   a,b,c  shown in  FIG. 3B  are only exemplary. 
     As shown in  FIG. 4 , after the balloon  14  has been inflated by pump  22 , it has three definable portions. These are: a proximal portion  42 ; and intermediate portion  44 ; and a distal portion  46 . In detail, the intermediate portion  44  is substantially cylindrical shaped. On the other hand, both the proximal portion  42  and the distal portion  46  are conical shaped. Specifically, the proximal portion  42  is characterized by a taper having a decreasing diameter in the proximal direction. 
     In the operation of the system  10  of the present invention, the catheter  12  and balloon  14  are advanced into the vasculature of a patient. Accordingly, the sheath  16  and blade  36  that are respectively attached to the balloon  14  as disclosed above are also advanced into the vasculature. This is done while the balloon  14  is in its deflated configuration (see  FIG. 1 ). Once the system  10  has been advanced into the vasculature, the balloon  14  can be selectively inflated into its inflated configuration (see  FIG. 4 ). 
     The consequence of inflating balloon  14  is perhaps best appreciated by cross-referencing  FIG. 3A  (deflated configuration) with  FIG. 4  (inflated configuration). This appreciation may be further enhanced by also referencing  FIG. 5 . In overview, as the balloon  14  is inflated, the halves  24   a  and  24   b  of the sheath  16  are separated from each other. Recall, the halves  24   a  and  24   b  are individually bonded to the surface of the balloon  14 . Accordingly, because this fixed relationship between balloon  14  and the halves  24   a  and  24   b  has been previously established, and is maintained, the reconfiguration of balloon  14  (i.e. the inflation of balloon  14 ) causes the respective halves  24   a  and  24   b  to separate. In detail, when the balloon  14  is deflated ( FIG. 3A ), the sides  48   a  and  48   b  of slit  28  are juxtaposed with each other to confine and cover the blade  36  in the protective channel  30  of sheath  16 . On the other hand, when balloon  14  is inflated ( FIGS. 4 and 5 ), the slit sides  48   a  and  48   b  are separated from each other. Similarly, the sides  50   a  and  50   b  of protective channel  30  are distanced from the blade  36 . The result of all this is that the blade  36  is exposed for operational use as desired. 
     After the operational use of an exposed blade  36  has been completed, the balloon  14  may be deflated by appropriately manipulating the pump  22 . This causes the balloon  14  to return from its inflated configuration ( FIG. 4 ) to its deflated configuration ( FIGS. 1 and 3A ). As implied above, during this deflation, the interaction between the sheath  16  and the balloon  14  will cause the balloon  14  to advantageously fold along predetermined fold lines. Also, the blade  36  will again be enclosed within the protective channel  30  as the system  10  is safely withdrawn from the vasculature of a patient. 
     As contemplated by the present invention, a preferred embodiment for the system  10  provides for a tilting blade  36  (see  FIGS. 4 and 6 ). As perhaps best seen in  FIG. 6 , for this embodiment of the system  10 , although a proximal segment  52  of the blade  36  is bonded to the proximal portion  42  of the balloon  14 , a distal segment  54  of the blade  36  is not. Consequently, because the distal segment  54  of blade  36  is not bonded to the balloon  14 , the blade  36  will follow the taper of proximal portion  42 . Thus, the distal segment  54  of blade  36  will extend radially from the balloon  14 . The distal segment  54  will, however, be enclosed in the protective channel  30  and covered by sheath  16 , as disclosed above, whenever balloon  14  is deflated. In an alternate embodiment of the system  10  of the present invention, as seen in  FIG. 7 , the blade  36  and sheath  16  may be mounted directly onto the intermediate portion  44  of balloon  14 . In this case, the entire blade  36  will move through a same radial distance as the balloon  14  is inflated. 
     While the particular Balloon Blade Sheath as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.