Abstract:
An elongated, tubular-shaped balloon for a balloon catheter includes three regions along its length, in sequence: a proximal region, an intermediate region, and a distal region. The intermediate region is defined by a curved outer surface that is established by a radius of curvature r 1 . Similarly, a curved inner surface for the intermediate region is established by a radius of curvature r 2 , wherein r 1 ≧r 2 . Balloon thickness at the center of the intermediate region is t c , while balloon thickness in both the proximal and distal regions is t (t&gt;t c ). The stretchability and bendability of the balloon material is directly proportional to the thickness of the balloon, to thereby shape the balloon as a prolate spheroid when inflated.

Description:
[0001]    This application is a continuation-in-part of application Ser. No. 14/201,495, filed Mar. 7, 2014, which is currently pending. The contents of application Ser. No. 14/201,495 are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains generally to catheters having an inflatable balloon that can be used to position the distal end of the catheter at a target site in the vasculature of a patient. More particularly, the present invention pertains to a balloon for a balloon catheter that provides minimal radial forces between the balloon and a vessel wall when inflated to decrease the incidence of vessel dissection and perforation. The present invention is particularly, but not exclusively, useful as a balloon that can adapt to different vessel diameters to minimize the need for multiple balloon catheters. 
       BACKGROUND OF THE INVENTION 
       [0003]    Inflatable balloons are often used to dilate a blockage in an artery with minimal radial forces on the arterial wall. This is done to cause less vascular injury such as dissection and perforation. Also, balloons can be employed for placing stents in the vasculature of a patient. In another application, balloons can be used to anchor a portion of a catheter at a target site in the vasculature of a patient. Typically, for this purpose, an inflatable balloon is mounted at the distal end of the catheter. The distal end of the catheter is then inserted into the patient and advanced within the patient&#39;s vasculature to a treatment site. There, at the treatment site, the balloon is inflated until it contacts the wall of the vessel. Once positioned, the catheter can be used, for example, to perform diagnostic imaging, infusion of a medicament, the placement of a stent, or to anchor the catheter as required by a particular protocol, 
         [0004]    Generally, for these procedures, balloons are made of a compliant material. In more detail, balloons made of a compliant material continue to expand as the internal pressure in the balloon is increased. This is to be contrasted with a non-compliant balloon which expands to a predetermined size and shape as the internal pressure in the balloon is increased. In one application, a non-compliant balloon can be used to exert force on a vessel wall, for example, to expand a constricted artery. 
         [0005]    Heretofore, compliant balloons have been used which, when inflated, establish a substantially tubular, ‘hot dog’ shape within a vessel. With increasing inflation, the hot dog shaped balloons elongate, increasing the contact area between the balloon and the internal wall of the vessel. This results in a substantial contact area between the balloon and internal vessel wall. In some cases, however, a substantial contact area between the balloon and internal vessel wall is undesirable. Moreover, it may be undesirable to have a balloon/vessel wall contact area that varies with inflation pressure. 
         [0006]    In light of the above, it is an object of the present invention to provide a balloon for a catheter that can operationally adapt to different vessel diameters and tolerate high-pressure inflation within the vasculature of a patient. Another object of the present invention is to provide a balloon for a catheter that maintains a substantially constant inter-contact surface area between the balloon and a vessel wall over a range of inflation pressures. Yet another object of the present invention is to provide a prolate spheroid-shaped balloon that is easy to use, is simple to implement and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with the present invention, a balloon system for positioning a distal end of a catheter at a treatment site includes an elongated catheter shaft that is formed with a lumen. For the balloon system, the shaft defines a longitudinal axis, extends from a proximal end to a distal end, and has an outer diameter d o . 
         [0008]    In addition to the shaft, the system includes a tubular shaped balloon membrane that is made of a compliant material such as urethane. Typically, the balloon membrane has a length L between its proximal end and its distal end. In any event, the actual value for the length L is discretionary and will depend on the particular application. For the system, the proximal and distal ends of the balloon membrane are affixed to an outer surface of the shaft to establish an inflation chamber between the balloon membrane and the outer surface of the shaft. 
         [0009]    For the present invention, the balloon membrane can have a non-uniform thickness between the proximal and distal ends of the membrane to establish a selected membrane shape when the balloon is inflated. For example, the selected membrane shape can be a prolate spheroid. 
         [0010]    In one embodiment of the balloon system, the balloon membrane can be thicker at the ends (i.e. the proximal and distal ends) than a region midway between the ends. With this arrangement, a relatively short and a relatively flat inter-contact surface in the midway region of the membrane is obtained when the balloon is inflated. In more detail, the balloon membrane can have a central thickness t c  in the region midway between the proximal and distal membrane ends and a membrane thickness t e  at the proximal and distal membrane ends, with t e &gt;t c . 
         [0011]    Also for the balloon system, an inflation unit is included to inflate the balloon. For example, an inflation lumen can be formed in the catheter shaft to establish fluid communication between the inflation unit and the inflation chamber of the balloon. 
         [0012]    During an inflation of the balloon by an inflation pressure P i , a radial distance r c  is established from the outer surface of the shaft to the inter-contact surface of the midway region. In addition, for the balloon system of the present invention, the radial distance r c  varies proportionally with changes in P i  inside the inflation chamber. Typically, the radial distance r c  will be as required by the application. For example, it will usually be less than about 35 mm with a balloon inflation pressure P i  less than about 15 atmospheres. In one embodiment, a balloon is designed to be inflated up to 14 atm of pressure. 
         [0013]    In one aspect of the present invention, the balloon membrane is designed such that sequential configurations of the balloon membrane during an inflation cycle present a substantially same area for the inter-contact surface of the midway region. For example, this functionality can be achieved by controlling the thickness between the proximal and distal ends of the membrane during the balloon membrane manufacturing process. 
         [0014]    For another perspective of the present invention, the elongated balloon membrane can be considered as having three distinguishable regions along its length L. These are, in sequence: a proximal region, an intermediate region, and a distal region. As envisioned for the present invention, the balloon will be made of a compliant material. Moreover, in the intermediate region, the balloon membrane will be thinner than it is in the proximal and distal regions of the balloon. Consequently, the balloon membrane in the intermediate region will be more stretchable and bendable than it is in the proximal and distal regions. 
         [0015]    Structurally, the intermediate region is defined by a curved outer surface that is established by a radius of curvature r 1 . It also has a curved inner surface that is established by a radius of curvature r 2 . For the present invention, r 2 ≦r 1 . 
         [0016]    The extent of the intermediate region between the proximal and the distal regions of the balloon can be varied from balloon to balloon, as needed. More specifically, with the intermediate region always centered midway between the ends of the balloon, the intermediate region can be extended from the midway point to cover as little as 10% of the balloon&#39;s length L, or as much as 90% of the length L. 
         [0017]    It is an important feature of the balloon for the present invention that its thickness at the center of the intermediate region has a predetermined value, t c . On the other hand, the thickness of the balloon membrane in both the proximal and distal regions is greater than or equal to a value t. In this combination, t will always be greater that t c  (t&gt;t c ). With this in mind, the stretchability and bendability within the different regions of the balloon will vary for two reasons. First, these functional characteristics are dependent on the material that is used to manufacture the balloon. Second, they are directly proportional to the thickness of the balloon material. Consequently, depending on selected dimensions for balloon thickness in the different regions, an inflated balloon will assume customized configurations for its generalized shape as a prolate spheroid. 
         [0018]    It is to be noted that the present invention anticipates the creation of discontinuities on the inner surface of the balloon during manufacture. In particular, it is anticipated that discontinuities will occur at the interfaces between the intermediate region and the proximal and distal regions, respectively. Specifically, a discontinuity is to be expected for designs wherein the thickness t c  remains constant throughout the intermediate region. Also, a discontinuity will occur whenever the separation between the surfaces generated by r 1  are r 2  at the interface is less than t. For such discontinuities, and others when experienced, the present invention envisions the creation of minimally intrusive transition zones for smoothing the discontinuities. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAVVINGS 
         [0019]    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: 
           [0020]      FIG. 1  is a schematic/perspective view of the balloon system of the present invention; 
           [0021]      FIG. 2  is a cross-section view of a portion of the balloon system as seen along the line  2 - 2  in  FIG. 1 , shown with the balloon inflated by an inflation pressure P i ; 
           [0022]      FIG. 3  is a cross-section view of a portion of the balloon system as seen along the line  2 - 2  in  FIG. 1 , shown with the balloon inflated by an inflation pressure P i  together with two other balloon configurations (shown by dotted lines) corresponding to two other inflation pressures; 
           [0023]      FIG. 4  is graph showing a balloon inflation pressure (ordinate) as a function of radial distance r c  from the outer surface of the shaft to the inter-contact surface of the midway region (abscissa); 
           [0024]      FIG. 5A  is a cross-section view of a portion of the balloon system, as seen along the line  2 - 2  in  FIG. 1 , showing the incorporation of curved surfaces with different radii of curvature, to create regions of the balloon having different stretchability and bendability structural capabilities; 
           [0025]      FIG. 5B  is a cross-section view of the portion of the balloon system shown in  FIG. 5A , wherein the extent of respective regions have been changed along the length of the balloon; and 
           [0026]      FIG. 6  is a cross-section view of the portion of the balloon system shown in  FIG. 5A , showing a region wherein the curved surfaces have the same radius of curvature. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Referring initially to  FIG. 1  a balloon system in accordance with the present invention is shown and is generally designated  10 . In one application, the balloon system  10  can be used to position a distal end  12  of a catheter  14  at a treatment site within the vasculature of a patient (not shown).  FIG. 1  also shows that the balloon system  10  includes a shaft  16  that defines a longitudinal axis  18 , extends from a proximal end  20  to a distal end  22 , and has an outer diameter d o .  FIG. 1  also shows that the shaft  16  is formed with a lumen  24 . 
         [0028]    Continuing with  FIG. 1 , it can be seen that the balloon system  10  also includes a tubular shaped balloon membrane  26 . Typically, for the present invention, the balloon membrane  26  is made of a compliant material such as urethane.  FIG. 1  also shows that the balloon system  10  can include an inflator  28  that is operationally connected to the proximal end  20  of the shaft  16  to selectively inflate the balloon. Also, as shown, a display  30  can be operationally connected to the inflator  28  to provide information, such as inflation pressure, to a user (not shown), such as a physician, during a balloon inflation. 
         [0029]      FIG. 2  shows that the balloon membrane  26  has a length L. between its proximal end  32  and its distal end  34  and, typically, L will be between about 8-35 mm for use in the coronary and between about 20-150 mm for use in the peripheral arteries. It can also be seen in  FIG. 2  that the proximal end  32  and distal end  34  of the balloon membrane  26  are affixed to an outer surface  36  of the shaft  16 . With this cooperative structural arrangement, an inflation chamber  38  is established between the balloon membrane  26  and the outer surface  36  of the shaft  16 . Also,  FIG. 2  shows that the shaft  16  can be formed with an inflation lumen  40  to establish fluid communication between the inflator  28  (see  FIG. 1 ) and the inflation chamber  38 . 
         [0030]    Continuing with reference to  FIG. 2 , it can be seen that the balloon membrane  26  can be thicker at the ends (i.e. the proximal end  32  and distal end  34 ) than a region  42  that is midway between the proximal end  32  and distal end  34 . As shown, the balloon membrane  26  can have a central thickness t c  in the region  42  midway between the proximal end  32  and distal end  34  and a membrane thickness t e  at the proximal end  32  and distal end  34 , with t e &gt;t c . This arrangement allows for a relatively short and a relatively flat inter-contact surface in the midway region  42  of the membrane  26  to be obtained when the balloon is inflated.  FIG. 2  illustrates that the balloon membrane  26  can have a non-uniform thickness between the proximal end  32  and distal end  34  to establish a selected membrane shape when the balloon is inflated. For the embodiment shown in  FIG. 2 , the selected membrane shape is a prolate spheroid.  FIG. 2  shows the balloon inflated to an inflation pressure P i . As shown, at the inflation pressure P i , the midway region  42  of the membrane  26  is spaced at a radial distance r c  from the axis  18  of the shaft  16 . 
         [0031]      FIGS. 3 and 4  illustrate that the radial distance between the midway region  42  of the membrane  26  and the outer surface  36  of the shaft  16  varies proportionally with changes in P i  inside the inflation chamber  38 . Specifically,  FIG. 3  shows the membrane  26  at an inflation pressure P 1  has a radial distance r c1  between the midway region  42  of the membrane  26  and the outer surface  36  of the shaft  16 . At an inflation pressure P 2 , with P 2 &gt;P 1 , membrane  26 ′ has a radial distance r c2 , with r c2 &gt;r c1 , between the midway region  42 ′ of the membrane  26 ′ and the outer surface  36  of the shaft  16 . Also, at an inflation pressure P 3 , with P 3 &gt;P 2 , membrane  26 ″ has a radial distance r c3 , with r c3 &gt;r c2 , between the midway region  42 ″ of the membrane  26 ″ and the outer surface  36  of the shaft  16 .  FIG. 3  also illustrates that the balloon membrane  26  is designed such that sequential configurations of the balloon membrane  26  during an inflation cycle present a substantially same area for the inter-contact surface of the midway region  42 .  FIG. 4  shows a plot  44  of balloon inflation pressure (ordinate) as a function of radial distance r c  from the outer surface  36  ( FIG. 3 ) of the shaft  16  to the inter-contact surface of the midway region  42  (abscissa). From  FIG. 4 , it can be seen that the radial distance rc between the midway region  42  ( FIG. 3 ) of the membrane  26  and the axis  18  of the shaft  16  varies proportionally with changes in P i  inside the inflation chamber  38 . 
         [0032]    In another aspect of the present invention, balloon membrane  26  can be constructed with separate, identifiable and distinguishable regions. Specifically, as shown in  FIG. 5A , the balloon membrane  26  can be manufactured with an intermediate region  50  that is positioned between a proximal region  52  and a distal region  54 .  FIG. 5A  also shows that with a line  56 , drawn perpendicular to the shaft  16  and centered between the proximal end  58  and the distal end  60  of the balloon membrane  26 , the balloon membrane  26  will have a thickness t c  along the line  56 . Stated differently, t c  is the thickness of the membrane  26  between the outer surface  62  and the inner surface  64  at the midpoint of the intermediate region  50 . 
         [0033]    It is an important feature of the present invention that the extent of the intermediate region  50  is determined by a configuration of the outer surface  62  of the balloon membrane  26 . Specifically, in the intermediate region  50 , the outer surface  62  will conform to a curve having a radius of curvature r 1  around a point  66  on line  56 . Further, in the intermediate region  50 , the inner surface  64  of balloon membrane  26  will conform to a curve having a radius of curvature r 2  around a point  68  on the line  56 . Also, as shown in  FIG. 5A , the balloon membrane  26  will have a thickness t in both the proximal region  52  and the distal region  54 . Typically, the thickness t will be constant, and it will be the same, for both the proximal region  52  and the distal region  54 . As envisioned for the present invention t c  will always be less than t (t c &lt;t), and r 1  will be greater than or equal to r 2  (r 1 ≧r 2 ). 
         [0034]    With the above in mind, and depending on the linear extent of the intermediate region  50  within the length L of the balloon membrane  26 , several different variations for configurations of the present invention are possible, For one variation, as shown in  FIG. 5B , the intermediate region  50 ′ can be diminished to around 5% of L. For this variation, the proximal region  52 ′ and the distal region  54 ′ are appropriately expanded to maintain the intermediate region  50 ′ centered for the balloon membrane  26 . In this case, like the above disclosure for  FIG. 5A , t c  will still be less than t (t c &lt;t), and r 1  will still be greater than or equal to r 2  (r 1 ≧r 2 ). For the variation shown in  FIG. 5B , the intermediate region  50  will function fundamentally as a so-called “living hinge”. 
         [0035]    For another variation in the configuration of the balloon membrane  26 ,  FIG. 6  shows that t c  can be held constant throughout the intermediate region  50 ″. In this case, t c  will still be less than t (t c &lt; and ≠t), but r 1  will equal r 2  (r 1 =r 2 ). In this variation, the present invention envisions the outer surface  62  will conform to a curve in the intermediate region  50 ″ having a radius of curvature r 1  around a point  70  on line  56 , while the inner surface  64  of balloon membrane  26  will conform to a curve having a radius of curvature r 2  around a point  72  on the line  56 . 
         [0036]    It is to be appreciated that the proximal region  52  ( FIG. 5A ) and the proximal region  52 ″ ( FIG. 6 ), as well as the distal region  54  ( FIG. 5A ) and the distal region  54 ″ ( FIG. 6 ) are variable, depending on the extent of intermediate region  50  (Fig,  5 A) or intermediate region  50 ″ ( FIG. 6 ). Specifically, as envisioned for the present invention, the extent of intermediate region  50 , for variations shown in  FIG. 5A  and  FIG. 6 , can be selected to be anywhere in a range between 90% of L and 5% of L. Further, in the variations for the present invention shown in  FIG. 5A  and  FIG. 6 , the present invention anticipates the creation of a discontinuity  74  (best shown in  FIG. 6 ) at the interface between the intermediate region  50  and the regions  52  and  54 . As intended for the present invention, if necessary, the discontinuity  74  can be modified to present a smooth transition on the inner surface  64 . 
         [0037]    In accordance with the above disclosure, it is also to be appreciated that when the regions  50 ,  52  and  54  are respectively rotated around the axis  18 , they will, in combination, form a prolate spheroid. In detail, the intermediate region  50  will be formed as an annulus, and both the proximal region  52  and the distal region  54  will respectively be formed conical surfaces. 
         [0038]    While the particular prolate spheroid-shaped balloon with central hinge 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.