Abstract:
A balloon catheter is provided with a balloon on the tip of a main shaft. The balloon catheter is provided with: protruding parts that are furnished on the outer surface of the balloon and protrude outward from the outer surface of the balloon at least when the balloon is expanded; and electrodes that are furnished on the leading edges of the protruding parts in the direction of protrusion and are capable of transmitting energy to living tissue. The leading edge electrodes can thereby be delivered near the desired site of treatment by thrusting the protruding parts into living tissue and, in this configuration, energy is transmitted to said treatment site.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a balloon catheter for being inserted into a body cavity and treating a desired living tissue therein, and an energizing (electrification) system incorporating such a balloon catheter. 
       BACKGROUND ART 
       [0002]    There has been a finding that patients with intractable hypertension who find it difficult to improve their high blood pressure even by taking antihypertensive can expect their blood pressure to be lowered by severing or disrupting the sympathetic nerve around the renal artery to block neurotransmission. 
         [0003]    It has been proposed in the art to percutaneously sever the sympathetic nerve around the renal artery using an ablation catheter. For example, Japanese Laid-Open Patent Publication No. 2008-515544 (PCT) discloses an ablation catheter for severing the sympathetic nerve around the renal artery, the ablation catheter including a helical electrode disposed around an inflatable balloon for contacting and energizing the inner wall of a blood vessel. Similarly, Japanese Laid-Open Patent Publication No. 2010-509032 (PCT) discloses an electrode disposed around a positioning member such as a balloon or the like, the electrode being expandable into contact with the inner wall of a blood vessel for energizing. 
       SUMMARY OF INVENTION 
       [0004]    Normally, the sympathetic nerve around the renal artery is disposed in the vicinity of the adventitia. The above ablation catheter according to the background art has its electrode held in abutment with the inner surface of the renal artery and cauterizes the inner surface of the renal artery. Therefore, the ablation catheter tends to cauterize not only the sympathetic nerve in the vicinity of the adventitia, but also the entire blood vessel wall including the intima of the renal artery. In other words, since energy is transmitted to other regions than the target issue to be cauterized, i.e., the sympathetic nerve in the vicinity of the adventitia, the ablation catheter is likely to cause possible problems such as intimal thickening, thrombosis, etc. 
         [0005]    The present invention has been made in view of the above drawbacks of the background art. It is an object of the present invention to provide a balloon catheter which is capable of selectively transmitting energy to a desired living tissue and an energizing system incorporating such a balloon catheter. 
         [0006]    According to the present invention, there is provided a balloon catheter including a balloon on a distal end side of a shaft, comprising a protrusive member disposed on an outer surface of the balloon and extending outwardly from the outer surface of the balloon at least when the balloon is inflated, and an electrode disposed on a projecting tip end portion of the protrusive member, for transmitting energy to a living body tissue. 
         [0007]    According to the present invention, there is also provided an energizing system comprising a balloon catheter including a balloon on a distal end side of a shaft and an electrode disposed on an outer surface of the balloon, for transmitting energy to a living body tissue, and a power supply for supplying a high-frequency current to the electrode, wherein the balloon catheter has a protrusive member disposed on the outer surface of the balloon and extending outwardly from the outer surface of the balloon at least when the balloon is inflated, and the electrode is disposed on a projecting tip end portion of the protrusive member. 
         [0008]    With the above arrangement, the protrusive member which projects outwardly at least when the balloon is inflated is disposed on the outer surface of the balloon, and the electrode for transmitting energy to a living body tissue is disposed on a projecting tip end portion of the protrusive member. The electrode can be reliably delivered to a desired living body tissue which is present deeply in a blood vessel wall, for selectively transmitting energy to the living body tissue and its neighboring region. When the balloon is inflated in a renal artery, for example, the protrusive member cuts into or pushes a wall surface of the renal artery and delivers the electrode on the tip end portion of the protrusive member to a position in the vicinity of the adventitia of the renal artery for energizing. Consequently, the electrode can selectively cauterize a sympathetic nerve that is present around the adventitia of the renal artery while effectively preventing the overall blood vessel wall from being adversely affected by the energization. 
         [0009]    If the protrusive member is insulative, then energy transmission from the protrusive member to the living body tissue is reliably blocked for smoother selective energy transmission to the desired living body tissue. 
         [0010]    The protrusive member may serve as a cutting edge having the electrode on a leading end thereof for cutting into a blood vessel wall to deliver the electrode into the blood vessel wall. Alternatively, the protrusive member may serve as a pushing member having the electrode on a leading end thereof and having an abutment portion with an inner surface of a blood vessel for pushing the inner surface of the blood vessel wall toward an outer surface of the blood vessel wall, thereby deforming the blood vessel wall, to deliver the electrode to a desired position when the protrusive member is pressed against the inner surface of the blood vessel wall. 
         [0011]    If the protrusive member is provided as at least a pair of protrusive members, and the electrodes disposed on the pair of protrusive members serve as a set of bipolar electrodes, then the living body tissue to be energized can be energized more locally, so that energy transmission to other living body tissues is prevented more reliably. 
         [0012]    The protrusive members may be provided in a plurality of arrays disposed along an axial direction of the balloon and at different circumferential phases of the balloon in the arrays. With this arrangement, the protrusive members are prevented from being concentrating circumferentially at a certain position along the direction in which the renal artery extends, and hence from cauterizing the blood vessel wall in an annular pattern at one location. In other words, the electrodes cauterizes the blood vessel wall at axially distributed positions, but prevents the blood vessel wall from being injured intensively at one location along the direction in which the blood vessel extends. Therefore, a sympathetic nerve that extends along the blood vessel is reliably cauterized by the electrodes that are disposed in axially distributed arrays, while at the same time any injury caused to the cauterized blood vessel is distributed to prevent the blood vessel from being greatly injured locally. The protrusive member may be disposed helically on the outer surface of the balloon. 
         [0013]    If the protrusive member is shaped as a thin plate or a needle, then the protrusive member makes it possible to deliver the electrode on the tip end more smoothly deeply into the blood vessel wall. 
         [0014]    The energy may comprise high-frequency energy. The living body tissue may comprise a nerve around a renal artery. 
         [0015]    According to the present invention, the protrusive member which projects outwardly at least when the balloon is inflated is disposed on the outer surface of the balloon, and the electrode for transmitting energy to a living body tissue is disposed on a projecting tip end portion of the protrusive member. The electrode can be reliably delivered to a desired living body tissue which is present deeply in a blood vessel wall, for selectively transmitting energy only to the living body tissue and its neighboring region. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a view showing an energizing system in its entirety which incorporates a balloon catheter according to an embodiment of the present invention; 
           [0017]      FIG. 2  is an enlarged perspective view of a distal end side of the balloon catheter shown in  FIG. 1 ; 
           [0018]      FIG. 3A  is a view showing a cylindrical portion of the balloon of the balloon catheter as it is spread out 360° in the circumferential direction thereof; 
           [0019]      FIG. 3B  is a view showing the cylindrical portion of the balloon as it is spread out 360° in the circumferential direction thereof, with a modified wiring structure for electrodes; 
           [0020]      FIG. 4A  is a cross-sectional view taken along line IVA-IVA of  FIG. 1 ; 
           [0021]      FIG. 4B  is a cross-sectional view taken along line IVB-IVB of  FIG. 1 ; 
           [0022]      FIG. 5A  is a cross-sectional view of the balloon which is inserted into a renal artery; 
           [0023]      FIG. 5B  is a cross-sectional view of the balloon which is inflated from the state shown in  FIG. 5A ; 
           [0024]      FIG. 6  is a cross-sectional view of the balloon with protrusive members pushing the intima of the renal artery toward the adventitia thereof; 
           [0025]      FIG. 7A  is an enlarged perspective view of a distal end side of a balloon catheter according to a first modification; 
           [0026]      FIG. 7B  is a front view of the balloon catheter shown in  FIG. 7A ; 
           [0027]      FIG. 8  is an enlarged perspective view of a distal end side of a balloon catheter according to a second modification; and 
           [0028]      FIG. 9  is an enlarged perspective view of a distal end side of a balloon catheter according to a third modification. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0029]    Balloon catheters according to preferred embodiments of the present invention in relation to an energizing system which incorporates the balloon catheters will be described below with reference to the accompanying drawings. 
         [0030]      FIG. 1  is a view showing an energizing system  12  in its entirety which incorporates a balloon catheter  10  according to an embodiment of the present invention, and  FIG. 2  is an enlarged perspective view of a distal end side of the balloon catheter  10  shown in  FIG. 1 . 
         [0031]    The energizing system  12  is a medical instrument for treating a hypertension by blocking or disabling the neurotransmission function of a sympathetic nerve  26 . In the treatment of the hypertension, the balloon catheter  10  has an elongate shaft  14  inserted into a body cavity, e.g., a renal artery  18  leading to a kidney  16 , and a balloon  20  on a distal end side thereof which has a pair of electrodes  22 ,  24  on its surface. The electrodes  22 ,  24  are delivered into the blood vessel wall and energized to transmit energy to a region around the adventitia of the renal artery  18  for thereby cauterizing the sympathetic nerve  26 . In  FIGS. 1 and 2 , a right side of the shaft  14  which is near a hub  28  will be referred to as a “proximal end (rear end, near region)” side, and a left side of the shaft  14  which is near the balloon  20  as a “distal end (far region)” side. 
         [0032]    As shown in  FIGS. 1 and 2 , the energizing system  12  includes the balloon catheter (cutting catheter, ablation catheter)  10 , and a high-frequency power supply (power supply)  30  for supplying a high-frequency current to a plurality of pairs of electrodes  22 ,  24  mounted on the balloon  20  of the balloon catheter  10 . The high-frequency power supply  30  may have specifications properly selected depending on, e.g., a target to be treated by the balloon catheter  10 . The high-frequency power supply  30  and the electrodes  22 ,  24  are interconnected by energizing paths E 1 , E 2  (indicated by the broken lines in  FIG. 1 ) extending in and along the shaft  14 . 
         [0033]    The balloon catheter  10  includes the shaft  14  which is slender and elongate, the balloon  20  disposed on the distal end side of the shaft  14 , a plurality of protrusive members (protrusive pieces, cutting members, cutting edges, pushing members)  32 ,  34  which protrude radially-outwardly from an outer surface of the balloon  20 , the electrodes  22 ,  24  mounted on respective projecting tip end portions of the protrusive members  32 ,  34  for transmitting energy to a living tissue, and the hub  28  disposed on the proximal end side of the shaft  14 . 
         [0034]    In  FIG. 1 , the balloon catheter  10  illustrated as a so-called rapid-exchange-type structure wherein the shaft  14  has an opening  36  formed in an intermediate portion thereof that is slightly closer to the distal end side, with a guide wire  35  extending out of the opening  36 . However, the balloon catheter  10  may be of an over-the-wire-type structure wherein the guide wire  35  extends out of the hub  28  on the proximal end. 
         [0035]    The balloon catheter  10  according to the present embodiment is of constitution similar to general balloon catheters for use in PTCA (Percutaneous Transluminal Coronary Angioplasty) except that the protrusive members  32 ,  34  and the electrodes  22 ,  24  are disposed on the outer surface of the balloon  20  and the energizing paths E 1 , E 2  are provided which interconnect the high-frequency power supply  30  and the electrodes  22 ,  24 . The constitutive details of the balloon catheter  10  which are similar to those of the general balloon catheters will not be described in detail below. For example, the shaft  14  of the balloon catheter  10  is of a dual-tube structure from the balloon  20  to the opening  36 , which has an inner tube  38  which has a guide wire lumen  37  (see  FIG. 4A ) through which the guide wire  35  is inserted, and an outer tube  40  with an inflating lumen  39  formed between itself and the inner tube  38  for passage therein of an inflating fluid (e.g., a contrast medium) to be supplied to the balloon  20 , and a single-tube structure from the opening  36  to the hub  28  (see  FIG. 4B ), which has the inflating lumen  39  in the outer tube  40  (or a proximal shaft, not shown). The balloon  20  of the balloon catheter  10  can be inflated when the inflating fluid is delivered thereto under pressure from a pressure applying device (not shown) such as an indeflator or the like vie a luer taper mounted on the hub  28 . 
         [0036]    Each of the inner tube  38  and the outer tube  40  of the shaft  14  is in the form of a tube made of a polymeric material such as polyolefin, polyvinyl chloride, polyamide, polyamide elastomer, polyurethane, polyurethane elastomer, polyimide, fluororesin, or the like, or a mixture of these polymeric materials, or a multilayer tube of two or more of the above polymeric materials. The balloon  20  is made of essentially the same material or materials as the inner tube  38  and the outer tube  40 . 
         [0037]      FIG. 3A  is a view showing a cylindrical portion of the balloon  20 , i.e., a portion where the protrusive members  32 ,  34  are disposed, as it is spread out 360° in the circumferential direction thereof. In  FIG. 3A , for an easier understanding of the illustration, a second wire E 1   b  which provides the one energizing path E 1  is indicated by the solid lines, and a second wire E 2   b  which provides the other energizing path E 2  is indicated by the broken lines. This also holds true for  FIG. 3B . 
         [0038]    As shown in  FIGS. 2 and 3A , the protrusive members  32 ,  34  are in the form of thin rectangular plates which are arrayed on an outer surface of the balloon  20  along the circumferential direction thereof and which project radially-outwardly from the balloon  20 . The protrusive members  32 ,  34  are provided as a plurality of (three in the present embodiment) pairs of protrusive members  32 ,  34  juxtaposed in the circumferential direction of the balloon  20  (see also  FIGS. 5A and 5B ). The protrusive members  32 ,  34  are fused or bonded to the surface of the balloon  20 , for example. 
         [0039]    The protrusive members  32 ,  34  may be arrayed in appropriate patterns. For example, the protrusive members  32 ,  34  in each pair may be closely positioned with a spacing of 30° therebetween, and the pairs of protrusive members  32 ,  34 , i.e., one predetermined pair of protrusive members  32 ,  34  and another pair of protrusive members  32 ,  34 , may be spaced from each other by an interval of 90°. Alternatively, all the protrusive members  32 ,  34  may be spaced at equal intervals of 60°, for example. 
         [0040]    As shown in  FIG. 5B , when the balloon  20  is inflated, the protrusive members  32 ,  34  function as cutting edges (blades, cutting members) which cut into the renal artery  18  from an intima  18   c  to a media  18   b  thereof to deliver the electrodes  22 ,  24  on their tip ends into a region near an adventitia  18   a  of the renal artery  18 . In other words, the protrusive members  32 ,  34  should project radially-outwardly from the outer surface of the balloon  20  at least when the balloon  20  is inflated. 
         [0041]    The protrusive members  32  ( 34 ) including the electrodes  22  ( 24 ), i.e., electrode assemblies (cutting edge electrodes, pushing electrodes) of the protrusive members  32  ( 34 ) and the electrodes  22  ( 24 ), should preferably be of a shape having a width W (see  FIG. 2 ) in the range from about 0.1 mm to 0.15 mm, a height H in the range from about 0.25 mm to 0.35 mm, and an axial length L in the range from about 3 mm to 200 mm so that the electrode assemblies can smoothly cut into the blood vessel wall and the electrodes  22  ( 24 ) on the tip end portions of the protrusive members  32  ( 34 ) can be positioned appropriately with respect to the sympathetic nerve  26  in the vicinity of the adventitia  18   a.  The electrodes  22  ( 24 ) may have a height which is in the range from about 5% to 50% of the height H. The electrode assemblies may be of any of various shapes other than parallel thin plate shapes, e.g., a triangular cross-sectional shape, a triangular pyramidal shape, a quadrangular pyramidal shape, or the like. When the balloon  20  with the protrusive members  32 ,  34  mounted thereon is inflated, its tubular portion may have an outside diameter in the range from about 3 mm to 6 mm and a length in the range from about 8 mm to 30 mm. 
         [0042]    The protrusive members  32 ,  34  are made of an insulative material such as resin, e.g., acryl, nylon, PET, PP, ABS, or the like, or ceramics or the like, or are made of metal with its surface coated with an insulating film (e.g., an insulating coating such as a resin coating of parylene, PTFE, or the like). Therefore, the protrusive members  32 ,  34  serve as electrically insulative members. When a living body between the electrodes  22 ,  24  is energized with high-frequency energy, a current is prevented from being applied between the protrusive members  32 ,  34 , but is caused to be applied selectively between only the electrodes  22 ,  24  on the tip ends of the protrusive members  32 ,  34  in each pair. 
         [0043]    The protrusive members  32 ,  34  may be made of a material whose electric resistance is sufficiently greater than the electrodes  22 ,  24 , rather than an insulative material, so that the protrusive members  32 ,  34  can function as electrically insulative members as a current is essentially applied only between the electrodes  22 ,  24 . 
         [0044]    The electrodes  22 ,  24  are mounted in pairs on adjacent ones of the protrusive members  32 ,  34 . According to the present embodiment, three pairs of the electrodes  22 ,  24  are mounted on adjacent ones of the protrusive members  32 ,  34 , and the energizing paths E 1 , E 2  are connected to the electrodes  22 ,  24  (see  FIGS. 2 and 3A ). The electrodes  22 ,  24  in the pairs function as active electrodes and return electrodes, providing bipolar electrodes for bipolar energization of living bodies. Though the electrodes  22 ,  24  are provided as three pairs of bipolar electrodes in the present embodiment, they may be provided as one or two pairs or four or more pairs of bipolar electrodes. 
         [0045]    The electrodes  22 ,  24  are disposed on the respective projecting tip end portions (tip end faces) of the protrusive members  32 ,  34 . The electrodes  22 ,  24  may be in the form of thin metal plates or the like joined to the tip end portions of the protrusive members  32 ,  34  or predetermined electrical conductors applied by brazing and solidified on the tip end portions of the protrusive members  32 ,  34 . However, the electrodes  22 ,  24  may be of any constitution insofar as it is capable of supplying a predetermined high-frequency current to living bodies. 
         [0046]    Next, the energizing paths E 1 , E 2  that are connected from the high-frequency power supply  30  to the electrodes  22 ,  24  comprise first wires E 1   a,  E 2   a  connected by connectors to the high-frequency power supply  30  and extending up to a position near the opening  36  in the shaft  14 , and second wires E 1   b,  E 2   b  connected to the distal ends of the energizing cables E 1   a,  E 2   a  and extending from the position near the opening  36  to the electrodes  22 ,  24 . 
         [0047]    The first wires E 1   a,  E 2   a  may comprise bendable electric wires in the form of electrically conducive wires covered with insulation (insulated-covered electric wires), and have suitable specifications in view of voltages applied to living bodies and compatibility with living bodies. As shown in  FIGS. 1 and 4B , the first wires E 1   a,  E 2   a  extend from the opening  36  in the shaft  14  to the proximal end side thereof, and are disposed on an outer surface of the outer tube  40  of the shaft  14  with the inflating lumen formed therein. The first wires E 1   a,  E 2   a  and the outer tube  40  are covered with a covering member  41  such as a heat-shrinkable tube or the like. The first wires E 1   a,  E 2   a  have their proximal ends spaced from the shaft  14  and connected by connectors to the high-frequency power supply  30 . 
         [0048]    As shown in  FIGS. 2 and 4A , the second wires E 1   b,  E 2   b  may preferably be in the form of printed wires that extend from the ends of the electrodes  22 ,  24  over side faces (front and rear end faces) of the protrusive members  32 ,  34  and are disposed on the outer surface of the balloon  20  and the outer surface of the shaft  14 . The second wires E 1   b,  E 2   b  may have suitable specifications in view of voltages applied to living bodies and compatibility with living bodies. 
         [0049]    In the energizing paths E 1 , E 2 , the first wires E 1   a,  E 2   a  and the second wires E 1   b,  E 2   b  are disposed respectively on proximal and distal end sides of the opening  36 , and are joined to each other in the vicinity of the opening  36 , e.g., at a position immediately prior to the opening  36 . 
         [0050]    The distal end side of the shaft  14 , which will be positioned on the distal side in the body cavity, has its outside diameter minimized by the second wires E 1   b,  E 2   b  in the form of printed wires. The proximal end side of the shaft  14  is of simple low-cost constitution due to the first wires E 1   a,  E 2   a  in the form of electric wires. As connectors can easily be connected to the proximal ends of the first wires E 1   a,  E 2   a,  the first wires E 1   a,  E 2   a  can easily be connected to the high-frequency power supply  30 . The portion of the shaft  14  on the proximal end side of the opening  36  may comprise a base tube, not shown, having a certain large tube rigidity which is coupled to the outer tube  40 . Even with such constitution, the first wires E 1   a,  E 2   a  can easily be fixed to the circumferential surface of the base tube by the covering member  41 . Accordingly, the shaft  14  can be manufactured with increased efficiency. Of course, the first wires E 1   a,  E 2   a  may comprise printed wires as with the second wires E 1   b,  E 2   b,  and the second wires E 1   b,  E 2   b  may comprise electric wires as with the first wires E 1   a,  E 2   a.    
         [0051]    As shown in  FIG. 2 , for example, radiopaque markers M may be disposed on the circumferential surface of the inner tube  38  which extends through the balloon  20  in order to allow the user to visually recognize the positions of the balloon  20  and the electrodes  22 ,  24  when the balloon catheter  10  is used in radioscopy. The radiopaque markers M that are positioned in alignment with the distal and proximal ends of the electrodes  22  ( 24 ) or in alignment with the distal and proximal ends of the cylindrical portion of the balloon  20 , for example, make it possible to visually recognize more accurately the axial positions of the balloon  20  and the electrodes  22  ( 24 ). Of course, the radiopaque markers M may be disposed at the distal and proximal ends of the protrusive members  32  ( 34 ) or at the distal and proximal ends of the electrodes  22  ( 24 ). The radiopaque markers M are made of a material (radiopaque material) opaque to X rays (radiations) such as gold, platinum, tungsten, or the like, so that they are visible under radioscopy even when they are placed in living bodies. 
         [0052]    A process of treating the sympathetic nerve  26  using the energizing system  12  which incorporates the balloon catheter  10  constituted as described above according to the present embodiment will be described by way of example below. 
         [0053]    The balloon catheter  10  and the energizing system  12  which incorporates the balloon catheter  10  are used on patients with intractable hypertension who find it difficult to improve their high blood pressure even by taking antihypertensive, for example. The balloon catheter  10  and the energizing system  12  are used in a treatment for lowering the blood pressure by cauterizing the sympathetic nerve  26  around the renal artery  18  to block its neurotransmission function. 
         [0054]    In substantially the same manner as with a medical procedure for indwelling a general balloon catheter in a renal artery, the guide wire  35  and a guiding catheter  33  (see  FIG. 1 ) are inserted from a femoral artery toward the renal artery  18  with the sympathetic nerve  26  therearound to be cauterized until the guide wire  35  and the guiding catheter  33  reach the renal artery  18  while they are being imaged under radioscopy. 
         [0055]    Then, as shown in  FIG. 5A , the balloon catheter  10  with the balloon  20  folded is inserted into the body through the lumen of the guiding catheter  33  while being guided by the guide wire  35 , and caused to ascend under radioscopy until the balloon  20  with the electrodes  22 ,  24  on the tip ends of the protrusive members  32 ,  34  reaches a position in the vicinity of the center of the renal artery  18 . While the balloon  20  is being folded, the protrusive members  32 ,  34  and the electrodes  22 ,  24  are stored by being surrounded by the folded balloon  20 . Therefore, the balloon catheter  10  can pass smoothly through the guiding catheter  33  and the blood vessel.  FIG. 5A  shows the folded balloon  20  by way of example. The balloon  20  may be folded in other configurations, e.g., the balloon  20  may be folded with the protrusive members  32  lying down. 
         [0056]    Then, the balloon  20  is inflated in the renal artery  18  to cause the protrusive members  32 ,  34  to cut into the blood vessel wall until the electrodes  22 ,  24  reach a region near the adventitia  18   a  for cauterizing the sympathetic nerve  26 . 
         [0057]    An inflating fluid is delivered under pressure into the inflating lumen  39  formed in and extending through the shaft  14 , inflating the balloon  20 . As shown in  FIG. 5B , the protrusive members  32 ,  34  projecting from the outer surface of the balloon  20  puncture the intima  18   c  and the media  18   b  of the renal artery  18  until the electrodes  22 ,  24  on the tip ends reach a region within or in the vicinity of the adventitia  18   a.  In  FIGS. 5A and 5B , the reference character  31  represents an extravascular tissue (surrounding tissue) such as fat or the like which is present around the renal artery  18 . 
         [0058]    The user then turns on a predetermined power supply switch, to energize the high-frequency power supply  30  to supply a high-frequency current through the energizing paths E 1 , E 2  (the first wires E 1   a,  E 2   a  and the second wires E 1   b,  E 2   b ) to be applied between the electrodes  22 ,  24  in the pairs. Regions that are disposed between the electrodes  22 ,  24  in the pairs, which serve as bipolar electrodes, and regions in their periphery (e.g., cauterized regions A surrounded by the broken lines in  FIG. 5B ) are cauterized, damaging the sympathetic nerve  26  together with part of the adventitia  18   a  thereby to block the neurotransmission function thereof. Thereafter, the balloon  20  is shrunk to pull the protrusive members  32 ,  34  out of the blood vessel wall. The balloon catheter  10  is then removed out of the body, and the incision made in the thigh for inserting the balloon catheter  10  is closed. The treating process is now ended. 
         [0059]    With the balloon catheter  10  according to the present embodiment, as described above, the protrusive members  32 ,  34  which project outwardly at least when the balloon  20  is inflated are mounted on the outer surface of the balloon  20 , and the electrodes  22 ,  24  for transmitting energy, e.g., a high-frequency current, to a living body tissue are mounted on the respective projecting tip end portions of the protrusive members  32 ,  34 . When the balloon  20  is inflated in the renal artery  18 , for example, the protrusive members  32 ,  34  cut into the wall of the renal artery  18  to cause the electrodes  22 ,  24  on the tip ends to pass through the intima  18   c  and the media  18   b  of the renal artery  18  until they reach the adventitia  18   a  with ease. As indicated by the cauterized regions A shown in  FIG. 5B , the adventitia  18   a  and the sympathetic nerve  26  in its surrounding can selectively be cauterized while any adverse effects on the intima  18   c  and the media  18   b  of the renal artery  18  are being minimized, so that the neurotransmission function of the sympathetic nerve  26  can be blocked for treating hypertension. 
         [0060]    Since the protrusive members  32 ,  34  are erected on the outer surface of the balloon  20  and the electrodes  22 ,  24  are mounted on the tip end portions of the protrusive members  32 ,  34 , the electrodes  22 ,  24  can be delivered easily and accurately to a desired depth in the body cavity and can selectively supply a high-frequency current only in their neighborhood. Specifically, the height H (see  FIG. 2 ) of the protrusive members  32 ,  34  may be set to an appropriate value depending on an object to be treated, such as the sympathetic nerve  26 , so that only such an object to be treated which may be located deeply in the blood vessel wall can be selectively cauterized while preventing the blood vessel wall from being cauterized in its entirety. Furthermore, as energy is transmitted to only the object to be treated and its vicinity, the efficiency with which to cauterize the object to be treated is high. 
         [0061]    The balloon catheter  10  has at least a pair of protrusive members  32 ,  34 , and the electrodes  22 ,  24  mounted respectively on the protrusive members  32 ,  34  serve as a pair of bipolar electrodes. The electrodes  22 ,  24  can locally energize a living body tissue to be energized, e.g., the sympathetic nerve  26 , while reliably preventing other living body tissues, e.g., the intima  18   c  of the renal artery  18 , from being energized. 
         [0062]    As the protrusive members  32 ,  34 , which serve as a basis for the electrodes  22 ,  24 , are arrayed along the circumferential directions of the balloon  20 , the electrodes  22 ,  24  can be placed in an appropriate position in the renal artery  18  without the need for any special process of positioning the electrodes  22 ,  24  in the renal artery  18  for determining a cauterizing position, and the electrodes  22 ,  24  thus placed can appropriately and reliably disrupt the sympathetic nerve  26  which is disposed along and around the renal artery  18 . Stated otherwise, with the layout of the protrusive members  32 ,  34  (the electrodes  22 ,  24 ) on the surface of the balloon  20  being appropriately set in advance depending on an object to be treated, the electrodes  22 ,  24  do not need to be positioned in a blood vessel under radioscopy, and hence the medical treatment process involving the balloon catheter  10  is simple and highly accurate. 
         [0063]    Inasmuch as the protrusive members  32 ,  34 , which serve as a basis for the electrodes  22 ,  24  for transmitting energy to a living body tissue, are insulative, the region that is energized by the electrodes  22 ,  24  is limited to a desired region. The intima  18   c  and the media  18   b  of the blood vessel are thus prevented from being energized between the protrusive members  32 ,  34 . 
         [0064]    Normally, the blood vessel wall such as of the renal artery  18  or the like is so soft that the protrusive members  32 ,  34  in the form of thin plates to some extent can sufficiently function as cutting edges and cut into the blood vessel wall even if the protrusive members  32 ,  34  are not sharp in shape. However, depending on the nature of the blood vessel wall, the protrusive members  32 ,  34  may not cut into the blood vessel wall sufficiently, and depending on the state and type of the blood vessel wall, it may not be preferable for the protrusive members  32 ,  34  to cut into the blood vessel wall. 
         [0065]    In this case, as shown in  FIG. 6 , the protrusive members  32 ,  34  do not cut into the blood vessel wall, but press the blood vessel wall from within the blood vessel and push the intima  18   c  and the media  18   b  into the blood vessel wall to deliver the electrodes  22 ,  24  on the tip ends to the vicinity of the adventitia  18   a  and the sympathetic nerve  26  therearound. The cauterized ranges A then include part of the intima  18   c  and the media  18   b  that are pushed and curved by the protrusive members  32 ,  34 . However, since the part of the intima  18   c  and the media  18   b  which included in the cauterized ranges A is only a slight proportion of the intima  18   c  and the media  18   b  in their entirety, any adverse effects on the entire blood vessel wall are limitative. 
         [0066]    Accordingly, the protrusive members  32 ,  34  may be arranged as cutting edges (cutting edge electrodes) having the electrodes  22 ,  24  on their leading ends for cutting into the blood vessel wall to deliver the electrodes  22 ,  24  to a desired depth in the blood vessel wall, or as pushing members (pushing electrodes) having the electrodes  22 ,  24  on their leading ends for pushing part of the inner surface of the blood vessel wall toward an outer surface of the blood vessel wall to deliver the electrodes  22 ,  24  to a desired depth in the blood vessel wall when the electrodes  22 ,  24  are pressed against the blood vessel wall. The protrusive members  32 ,  34  may be of any constitution insofar as it can deliver the electrodes  22 ,  24  on the tip ends thereof to a position in the vicinity of an object to be treated. 
         [0067]    The interconnection by energizing paths E 1 , E 2  from the high-frequency power supply  30  to the electrodes  22 ,  24  may be of constitution other than illustrated above. For example, the first wires E 1   a,  E 2   a  may be inserted through a wire lumen (not shown) juxtaposed in addition to the inflating lumen  39 , or may be inserted through the inflating lumen  39 , rather than being disposed on the outer circumferential surface of the shaft  14  by the covering member  41  (see  FIG. 4B ). The second wires E 1   b,  E 2   b  that are wired between the electrodes  22 ,  24  may be connected parallel to the electrodes  22  and also parallel to the electrodes  24 , as shown in  FIG. 3B , rather than being connected in series between the electrodes  22  and also in series between the electrodes  24 . 
         [0068]    The protrusive members for delivering the electrodes  22 ,  24  to a position in the vicinity of an object to be treated may be of constitution and layouts other than those shown in  FIG. 2 . Modified constitution and layouts of the protrusive members will be described below. 
         [0069]      FIG. 7A  is an enlarged perspective view of a distal end side of a balloon catheter  10   a  according to a first modification, and  FIG. 7B  is a front view of the balloon catheter  10   a  shown in  FIG. 7A . In  FIGS. 7A and 7B , those reference characters which are identical to those shown in  FIGS. 1 to 3B  denote identical or similar parts, and those parts will not be described in detail below as having identical or similar functions and advantages. This also holds true for other modifications to be described later. 
         [0070]    As shown in  FIGS. 7A and 7B , the balloon catheter  10   a  includes a balloon  20  having a plurality of pairs of protrusive members  42 ,  44  in the form of short, rectangular thin plates disposed on the outer surface of the balloon  20 . In each pair, the protrusive members  42 ,  44  are adjacent to each other in the circumferential directions of the balloon  20 . The protrusive members  42 ,  44  in pairs or sets are provided in a plurality of (four in the first modification) circumferential arrays along an axial direction from the distal end side to the proximal end side of the balloon  20 , and are disposed at different circumferential phases. The protrusive members  42 ,  44  have respective electrodes  22 ,  24  on their respective tip end portions. The protrusive members  42 ,  44  may be of the same structural details as the protrusive members  32 ,  34  except that the protrusive members  42 ,  44  are of a shape different from the protrusive members  32 ,  34 . 
         [0071]    The balloon catheter  10   a  thus has four circumferential arrays of sets or pairs of protrusive members  42 ,  44  (the electrodes  22 ,  24 ). In each pair or set, the protrusive members  42 ,  44  are adjacent to each other in the circumferential directions and provide a bipolar electrode. The sets or pairs of protrusive members  42 ,  44  are arranged from the distal end side to the proximal end side, and are arrayed at different circumferential phases which are equally angularly spaced (by 90° in this embodiment), in the respective arrays. The sets of the electrodes  22 ,  24  in the arrays are capable of cauterizing the blood vessel wall fully circumferentially at axially spaced positions in a substantially helical pattern. 
         [0072]    As a result, the protrusive members  42 ,  44  (the electrodes  22 ,  24 ) are prevented from being concentrating circumferentially at a certain position along the axial direction in which the renal artery  18  extends, and hence are prevented from cauterizing the blood vessel wall in an annular pattern at one location. In other words, the electrodes  22 ,  24  cauterizes the blood vessel wall at axially distributed positions, but prevents the blood vessel wall from being injured intensively at one location along the axial direction in which the blood vessel extends. Therefore, the sympathetic nerve  26  is reliably cauterized by the electrodes  22 ,  24  that are disposed in axially distributed arrays, while at the same time any injury caused to the cauterized blood vessel is distributed to prevent the blood vessel from being greatly injured locally. 
         [0073]    Since the electrodes  22 ,  24  are mounted on the protrusive members  42 ,  44  which are disposed at the different phases in the plural arrays, the electrodes  22 ,  24  are positioned structurally accurately in the blood vessel. The electrodes  22 ,  24  thus positioned make it unnecessary to perform a medical procedure for cauterizing a desired region while axially moving and rotating the balloon  20 , for example, and hence allow the balloon catheter to be operated simply. 
         [0074]    The protrusive members  42 ,  44  may be of an arrangement other than providing one set of bipolar electrodes in each of the axially distributed arrays as described above. For example, the protrusive members  42 ,  44  may be arranged to provide two sets of bipolar electrodes in each of the axially distributed arrays. In such a case, the protrusive members  42 ,  44  in at least axially adjacent arrays should desirably be disposed in different phases. 
         [0075]      FIG. 8  is an enlarged perspective view of a distal end side of a balloon catheter  10   b  according to a second modification. 
         [0076]    As shown in  FIG. 8 , the balloon catheter  10   b  has protrusive members  46 ,  48  in the form of thin needles, instead of the protrusive members  42 ,  44  of the balloon catheter  10   a  shown in  FIGS. 7A and 7B , with electrodes  22 ,  24  mounted on the tip ends of the protrusive members  46 ,  48 . The protrusive members  46 ,  48  may be of the same structural details as the protrusive members  32 ,  34  except that the protrusive members  46 ,  48  are of a shape different from the protrusive members  42 ,  44 . 
         [0077]    When the balloon catheter  10   b  is applied to the renal artery  18 , for example, the needle-shaped protrusive members  46 ,  48  are effective to reduce ranges in which the intima  18   c  and the media  18   b  are severed, thereby cauterizing the sympathetic nerve  26  while reducing adverse effects on the entire blood vessel wall. Since the protrusive members  46 ,  48  are in the form of needles, they can easily cut into soft blood vessel walls or the like and deliver the electrodes  22 ,  24  smoothly to a desired region to be cauterized. 
         [0078]    Essentially as with the balloon catheter  10   a,  the balloon catheter  10   b  also prevents the blood vessel wall from being injured intensively at one location along the direction in which the blood vessel extends, and allows the electrodes  22 ,  24  to be positioned easily in the blood vessel. The needle-shaped protrusive members  46 ,  48  may be arranged along the circumferential directions, essentially as with the balloon catheter  10   a.  In such a case, the needle shape of the protrusive members  46 ,  48  minimizes injury that is caused to the blood vessel wall when it is cut into. 
         [0079]      FIG. 9  is an enlarged perspective view of a distal end side of a balloon catheter  10   c  according to a third modification. 
         [0080]    As shown in  FIG. 9 , the balloon catheter  10   c  includes a balloon  20  having a pair of helical protrusive members  50 ,  52  in the form of thin rectangular plates mounted on the outer surface of the balloon  20  and extending helically along an axial direction from the distal end side to the proximal end side of the balloon  20 . The protrusive members  50 ,  52  have respective electrodes  22 ,  24  on their respective tip end portions. The protrusive members  50 ,  52  may be of the same structural details as the protrusive members  32 ,  34  except that the protrusive members  50 ,  52  are of a shape different from the protrusive members  32 ,  34 . 
         [0081]    The helical protrusive members  50 ,  52  and the electrodes  22 ,  24  make it possible to cauterize the blood vessel wall along the full circumferential directions thereof at axially different positions, essentially as with the balloon catheters  10   a,    10   b  described above. Consequently, the sympathetic nerve  26  extending along the blood vessel wall can reliably be cauterized by the helical electrodes  22 ,  24  turned along the axial direction, although the blood vessel wall is prevented from being cauterized intensively at one location along the axial direction. As the second wires E 1   b,  E 2   b  may be joined to the electrodes  22 ,  24  at respective single spots, the balloon catheter  10   c  is simplified in structure. Bipolar electrodes provided by the protrusive members  50 ,  52  (the electrodes  22 ,  24 ) may be provided in two or more sets. 
         [0082]    The present invention is not limited to the above embodiments, but various arrangements and processes may be employed without departing from the scope of the invention.