Abstract:
The disclosure pertains to an intravascular catheter, comprising an elongate member having a proximal end and a distal end, a balloon having an interior surface, an exterior surface, a lumen defined by the interior surface and a cylindrical wall extending between the interior surface and the exterior surface, the cylindrical wall having a proximal end and a distal end, the balloon having a plurality of weeping windows disposed in the wall and able to pass an electric current between the interior surface and the exterior surface and wherein the balloon wall is otherwise electrically insulative, and an electrode disposed in the balloon. The intravascular system is suited for modulation of renal nerves, for example.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/693,066, filed Aug. 24, 2012, the entirety of which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The invention generally pertains to percutaneous and intravascular devices for nerve modulation and/or ablation. 
       BACKGROUND 
       [0003]    Certain treatments require the temporary or permanent interruption or modification of select nerve function. One example treatment is renal nerve ablation which is sometimes used to treat conditions related to congestive heart failure. The kidneys produce a sympathetic response to congestive heart failure, which, among other effects, increases the undesired retention of water and/or sodium. Ablating some of the nerves running to the kidneys may reduce or eliminate this sympathetic function, which may provide a corresponding reduction in the associated undesired symptoms. 
         [0004]    Many body tissues such as nerves, including renal nerves, brain tissue, cardiac tissue and the tissue of other body organs are in close proximity to blood vessels or other body cavities and thus can be accessed percutaneously or intravascularly through the walls of the blood vessels. In some instances, it may be desirable to ablate perivascular nerves using a radio frequency (RF) electrode. In other instances, the perivascular nerves may be ablated by other means including application of thermal, ultrasonic, laser, microwave, and other related energy sources to the vessel wall. 
         [0005]    In treatments involving perivascular nerves such as renal nerves, treatment methods employing such energy sources have tended to apply the energy to the full circumference of the renal artery and/or vein to ensure that the nerves are modulated. However, such a treatment may result in thermal injury to the vessel wall near the electrode and other undesirable side effects such as, but not limited to, blood damage, clotting, weakened vessel wall, and/or fouling of the electrode. 
       SUMMARY 
       [0006]    It is therefore desirable to provide for alternative systems and methods for tissue treatment such as intravascular nerve modulation treatments that distribute ablation or modulation sites along and around the vessel or other body cavity. 
         [0007]    Some embodiments of the invention are directed to a balloon catheter configured for tissue modulation such as nerve modulation and/or ablation. The balloon catheter includes an inflatable balloon at or proximate a distal end of the device. The wall of the balloon is constructed so as to only allow fluid through at desired locations. 
         [0008]    An RF transmitter extends through the lumen of the balloon to supply the RF energy. In use, the balloon is inflated with an ionically conductive fluid such as saline and positioned at a desired location for treatment. In some embodiments, the balloon may be in circumferential contact with a wall such as a blood vessel wall at the treatment location. The RF transmitter is activated and the RF energy is converted to ionic energy creating ionically charged fluid, which exits through micropores in the balloon wall to modulate or ablate tissue. 
         [0009]    The balloon may be a multilayer balloon with a first layer made from weeping material and a second layer made from an electrically insulative material. The weeping material comprises a plurality of micro-pores and therefore has a passageway for fluid and hence ionic conduction. When a balloon is filled the micropores are therefore permeable to an ionically conductive fluid. The micropores may, or may not, permit any significant fluid flow. The weeping material may be formed by forming holes of the appropriate size in an otherwise fluid impermeable material or may be formed of a woven or knitted material to create a mesh-like structure. In other embodiments, the balloon wall may be a balloon wall having a single layer of generally non-conductive and fluid-impermeable material with the windows created by forming a pattern of micro-pores through the layer of the balloon wall. 
         [0010]    The balloon catheter may include other elements such as a multi-lumen catheter shaft. The multi-lumen catheter shaft may include a guidewire lumen and one or two fluid lumens as well as conductive members to connect the electrode and one or more sensors to a power and control system. For embodiments that include two fluid lumens, one fluid lumen may be used to introduce the conductive fluid into the balloon and the other fluid lumen may be used to evacuate the conductive fluid from the balloon. In this manner, the conductive fluid may be circulated through the balloon. In some embodiments, it may be considered beneficial to influence the fluidic flow within the balloon by the placement of the inlet and outlet flow lumens. The RF transmitter may be constructed of any suitable material and geometry that efficiently converts RF energy to ionic energy and may, for example, be a ribbon electrode that is helically wound about the catheter shaft within the balloon lumen and may be made from any suitable material such as gold, copper, or silver. 
         [0011]    In one illustrative method of use, a balloon catheter according to an embodiment of the invention is inserted percutaneously and/or intravascularly to a treatment location using a guidewire, a guide catheter or other conventional means. The balloon is inflated with the conductive fluid and the conductive fluid is circulated through the balloon. The transmitter is activated and RF energy is converted to ionic energy creating ionically charged fluid, which exits through micropores in the balloon wall into the tissue of the desired treatment area. 
         [0012]    The treatment may be ended after a predetermined time or after a predetermined condition is met. For example, impedance may be measured through the electrode and the treatment may be ended after a predetermined change in the measured impedance. The above summary of some example embodiments is not intended to describe each disclosed embodiment or every implementation of the invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    The invention may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a schematic view illustrating a renal nerve modulation system in situ. 
           [0015]      FIG. 2  is a schematic view illustrating the distal end of a renal nerve modulation system. 
           [0016]      FIG. 3  is a cross-sectional view of the renal nerve modulation system of  FIG. 2 . 
           [0017]      FIG. 4  is another cross-sectional view of the renal nerve modulation system of  FIG. 2 . 
           [0018]      FIG. 5  is a cross-sectional view of a renal nerve modulation system. 
           [0019]      FIG. 6  is a schematic view illustrating the renal nerve modulation system of  FIG. 2  in situ. 
           [0020]      FIG. 7  is a projection view of the outer surface of a balloon of a renal nerve modulation system. 
           [0021]      FIG. 8  is a projection view of the outer surface of a balloon of another renal nerve modulation system. 
           [0022]      FIG. 9  is a cross-sectional view of a portion of a balloon window of a renal nerve modulation system. 
           [0023]      FIG. 10  is a detail view of the outer surface of a balloon of another renal nerve modulation system illustrating an example window. 
       
    
    
       [0024]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
       DETAILED DESCRIPTION 
       [0025]    The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The drawings, which are not necessarily to scale, are not intended to limit the scope of the claimed invention. The detailed description and drawings illustrate example embodiments of the claimed invention. 
         [0026]    All numbers are herein assumed to be modified by the term “about.” The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
         [0027]    As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include the plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0028]    It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it would be within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described unless clearly stated to the contrary. 
         [0029]    While the devices and methods described herein are discussed relative to renal nerve modulation through a blood vessel wall, it is contemplated that the devices and methods may be used in other applications where nerve modulation and/or ablation are desired. The term modulation refers to ablation and other techniques that may alter the function of affected nerves and other tissue such as brain tissue or cardiac tissue. When multiple ablations are desirable, they may be performed sequentially by a single ablation device. 
         [0030]      FIG. 1  is a schematic view of an illustrative renal nerve modulation system  10  in situ. System  10  may include one or more conductive element(s)  16 , such as wires or the like, for providing power to a renal ablation system including a renal nerve modulation device  12  disposed within a delivery sheath  14 , which may be adapted to slidably contain the renal nerve modulation device  12  when the radially expanding region (not shown) of the elongate member is in a non-expanded configuration, the details of which can be better seen in subsequent figures. A proximal end of conductive element(s)  16  may be connected to a control and power element  18 , which supplies necessary electrical energy to activate one or more electrodes to which the distal end of conductive element(s)  16  are attached at or near a distal end of the renal nerve modulation device  12 . When suitably activated, the electrodes are capable of ablating tissue as described below. The terms electrode and electrodes may be considered to be equivalent to elements capable of ablating adjacent tissue in the disclosure which follows. Suitable materials for the delivery sheath  14 , device  12  and elements capable of ablating adjacent tissue may include those materials disclosed herein (and/or other suitable materials) and may include internal and/or external layers of lubricious material(s). In some instances, return electrode patches  20  may be supplied on the legs or at another conventional location on the patient&#39;s body to complete the circuit. A proximal hub (not illustrated) having ports for a guidewire, an inflation lumen and a return lumen may also be included. A conductive fluid source  24  such as a syringe, bag, or the like may be included. The conductive fluid source  24  may include a pump, regulator valve, or the like. The conductive fluid source  24  may be fluidly connected to the device by a line  22  or other conventional means. A fluid collection device  28  such as a bag may also be fluidly connected to the device by a line  26 . The fluid collection means may include an aspiration means such as a pump, syringe or the like. 
         [0031]    The control and power element  18  may include monitoring elements to monitor parameters such as power, temperature, voltage, pulse size, impedance, and/or shape and other suitable parameters, with sensors mounted along the renal nerve modulation device  12 , as well as suitable controls for performing the desired procedure. In some embodiments, the power element  18  may control a radio frequency (RF) electrode. The electrode may be configured to operate at a frequency of approximately 460 kHz. It is contemplated that any desired frequency in the RF range may be used, for example, from 450-500 kHz. It is further contemplated that other ablation devices may be used as desired, for example, but not limited to resistance heating, ultrasound, microwave, and laser devices and these devices may require that power be supplied by the power element  18  in a different form. 
         [0032]      FIG. 2  illustrates the distal portion of a renal nerve modulation device  12 . The renal nerve modulation device  12  includes a balloon  30  and an electrode  36 . When in use, the balloon is preferably filled with a conductive fluid such as saline to allow the ablation energy to be transmitted from the electrode  36  through windows  40  that are permeable to RF radiation and/or energy transfer via ionic conductivity. Other appropriate conductive fluids include hypertonic solutions, contrast solution and mixtures of saline or hypertonic saline solutions with contrast solutions. The conductive fluid may be introduced through a fluid inlet port  32  and evacuated through a fluid outlet port  34 , both in a central shaft  42 . One or more sensors  38 , such as a thermocouple, may be included and may be disposed on the shaft  42 , on the balloon  30 , or at another suitable location. 
         [0033]    A cross-sectional view of the shaft  42  of the renal nerve modulation device  12  proximal to the balloon is illustrated in  FIG. 3 . The shaft  42  may include a guidewire lumen  46 , a first lumen  48  (e.g., which may be connected to the fluid outlet  34 ), and a second lumen  50  (e.g., which may be connected to the fluid inlet  32 ). The electrode  36 , or a conductive element to supply power to the electrode may extend along the outer surface of the shaft  42  or may be embedded within the shaft  42 . The electrode  36  proximal to the balloon is preferably electrically insulated and is used to transmit power to the portion of the electrode disposed in the balloon. Conductors  44 , two of which are illustrated in  FIG. 3 , may be used to supply power and to allow information to return from the one or more sensors  38 . In some embodiments, the guidewire lumen and/or one of the fluid lumens  48 ,  50  may be omitted. In some embodiments, the guidewire lumen  46  extends from the distal end of the device  12  to a proximal hub. In other embodiments, the guidewire lumen  46  can have a proximal opening that is distal the proximal portion of the system  10 . In some embodiments, the fluid lumens  48 ,  50  can be connected to a system to circulate the fluid through the balloon  30  or to a system that supplies new fluid and collects the evacuated fluid. It can be appreciated that embodiments may function with merely a single fluid lumen and a single fluid outlet into the balloon  30 . It can also be appreciated that other lumen configurations are contemplated. For example, the three lumens may be disposed within each other, may be concentric, or may be non-concentric. In some embodiments, the guidewire lumen may be the innermost lumen and may be surrounded by the fluid inlet lumen, which, in turn may be surrounded by the fluid outlet lumen. In another contemplated embodiment, only one of the fluid inlet and fluid outlet lumens is disposed around the guidewire lumen and the other of the fluid inlet and fluid outlet lumens extends parallel to and spaced apart from the guidewire lumen. Another contemplated embodiment lacks the fluid outlet lumen and the fluid inlet lumen is disposed around or concentrically around the guidewire lumen. In another contemplated embodiment, the guidewire lumen is omitted and the system includes only the fluid inlet lumen or only the fluid inlet and outlet lumens. Of course, it is also contemplated that any of these shaft variations may be included with any of the balloon and window variations discussed herein. These are just examples. 
         [0034]    A cross-sectional view of the shaft  42  distal to the fluid outlet port  34  is illustrated in  FIG. 4 . The guidewire lumen  46  and the fluid inlet lumen  50  are present, as well as an electrode  36 . In the presently illustrated embodiment, conductors  44 , which are connected to one or more sensors  38 , are not present in this cross-sectional view. It can be appreciated that in embodiments that have one or more distal sensors, one or more conductors  44  may be present to connect with then. 
         [0035]    Balloon  30  is shown in cross-section as having a first layer  54  and a second layer  56 . A window  40  is formed in the balloon  30  by the absence of the second layer  56 . The first layer  54  is preferably made from a weeping material. A weeping material is a material that permits only insignificant fluid flow and does not permit the transmission of ordered streams or jets of fluid. A suitable material may be one in which micropores are formed. Micro-pores are pores having a maximum width of less than 40 micro-inches, less than 35 micro-inches, less than 30 micro-inches, or less than 25 micro-inches. Further, the micropores may have a mean pore size of between 15 and 30 micro-inches. Such a material may be formed by forming holes of a suitable size in an otherwise fluid impermeable material or by providing a material formed of a tight mesh or weave. Suitable materials include polymers materials with micropores and are produced by microporous processing of, for example, PET, nylon 12, polyamid block copolymer, polyester block copolymer, fluoropolymers such as PTFE or ePTFE, and Goretex materials; or mesh or woven materials using many polymers such as nylon or PEBA. Some embodiments may further include a reinforced substructure or a braided substructure. Suitable materials for the fibers of the substructure include UHMWPE, Kevlar, PET, carbon, and the like. 
         [0036]    The second layer  56  may include an electrically non-conductive polymer such as a non-hydrophilic polyurethane, Pebax, nylon, polyester or block-copolymer. Other suitable materials include any of a range of electrically non-conductive polymers. In some embodiments, the materials of the first layer and the second layer may be selected to have good bonding characteristics between the two layers. In other embodiments, a suitable tie layer (not illustrated) may be provided between the two layers. As illustrated, the windows  40  are formed in the wall  52  of the balloon  30  by the absence of the second layer  56 . 
         [0037]      FIG. 5  illustrates a cross-sectional view of another embodiment of a renal nerve modulation device. The cross-section is taken along the same lines as that of  FIG. 4  and the device is similar to that of  FIGS. 2-4  except as otherwise noted herein. The device of  FIG. 5  has a balloon wall  52  that has a single layer  56 . The layer  56  is a generally non-conductive and fluid impervious material except for the windows  40 , which are formed by providing micro-pores through the balloon wall  52  at the area where the window is desired.  FIG. 9  illustrates an example cross-sectional view through a portion of a window  40  through a balloon wall  52 . Micropores  62   a - 62   g  illustrate some of the profiles a micropore may take. Micropores  62   a - 62   g  may be formed by a laser or through some other suitable means.  FIG. 10  is a detail view illustrating an example window  40 . The window  40  comprises a plurality of micropores  62 . Micropores  62  may be provided in a random pattern within the boundaries of a predetermined window shape or may be provided in a regular and repeating pattern. 
         [0038]    The device illustrated in  FIG. 6  is similar to that of the distal end of device  12  in situ. Preferably, the device  12  is available in various sizes, and a size is selected that will allow the windows  40  of the balloon  30  to contact the wall of a blood vessel  60 . 
         [0039]    The particular balloon illustrated in  FIG. 5  may be suitable for use in a renal nerve modulation application. The renal nerve extends generally longitudinally around the outside of a renal artery. This means that one can vary the longitudinal position of any particular circumferential treatment and achieve the same nerve modulation effect. Thus windows  40  are arranged to achieve complete circumferential coverage of the blood vessel while spaced apart longitudinally. In this particular case, the four windows  40  each cover a different 90 degree arc of the blood vessel. Each window may cover more than a 90 degree arc. For example, the windows  40  may cover a 100 or 110 degree arc to allow for some overlapping coverage of the windows  40 . Windows  40  of this embodiment are four in number and generally circular in shape. It can be appreciated that variations in the number of windows and the shape of the windows are contemplated. For example, embodiments are contemplated which include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more windows and which include windows that are circular, oval, rectangular, or polygonal. Moreover, the windows having a different length and width may be oriented so that the largest dimension is parallel to the longitudinal axis, perpendicular to the longitudinal axis, or at another angle with respect to the longitudinal axis such as a 45 degree angle. In some embodiments, each window may have an aspect ratio of 2:1, 3:1 or 4:1, where the major dimension is perpendicular to the longitudinal axis of the balloon. In some embodiments, the window or windows may have a custom pattern to provide a particular treatment pattern. 
         [0040]    The electrode  36  may be a flat ribbon electrode made from platinum, gold, stainless steel, cobalt alloys, or other non-oxidizing materials. In some instances, titanium, tantalum, or tungsten may be used. The electrode  36  may extend along substantially the whole length of the balloon  30  or may extend only as far as the distal edge of the most distal window  40 . The electrode  36  may have a generally helical shape and may be wrapped around the shaft  42 . In some cases, the electrode  36  may be bonded to the shaft  42 . The electrode  36  and windows  40  may be arranged so that the electrode extends directly under the windows  40 . In some embodiments, the electrode  36  may be a wire or may be a tubular member disposed around the shaft  42 . In some embodiments, a plurality of electrodes  36  may be used and each of the plurality may be fixed to the shaft  42  under the windows  40  and may share a common connection to the conductive element  16 . In other embodiments that include more than one electrode, each electrode may be separately controllable. In such embodiments, the balloon may be partitioned into more than one chamber and each chamber may include one or more electrodes. The electrode may be selected to provide a particular level of flexibility to the balloon to enhance the maneuverability of the system. It can be appreciated that there are many variations contemplated for electrode  36 . 
         [0041]      FIGS. 7-8  illustrate projections of the cylindrical central portion of a balloon wall  52  (i.e. the figure illustrates the cylindrical central portion of the balloon wall as if it were cut open and laid flat). The balloon wall  52  of these figures may be readily incorporated into any of the nerve modulation systems described herein. The balloon  30  includes a plurality of windows  40 . The windows may be defined by an absence of a second layer  56  as in the  FIG. 4  embodiment, or by a pattern of micropores through a single layer as in the  FIG. 5  embodiment. The windows are arranged on the balloon such that their greatest dimension extends circumferentially (i.e. along a circumference of the cylindrical balloon wall) and their narrowest dimension extends axially (i.e. in the direction of the central longitudinal axis of the balloon  30 ). The windows  40  are arranged such that any line drawn from the proximal end of the cylindrical balloon wall to the distal end of the cylindrical balloon wall passes through at least one window. 
         [0042]    The windows may overlap circumferentially while being spaced apart axially. If a line drawn from the proximal end of the cylindrical balloon wall to the distal end of the cylindrical balloon wall passes through two windows, those two windows are said to circumferentially overlap. 
         [0043]    The degree of circumferential overlap may be expressed in terms of the circumferential dimension of a window  40 , in terms of the circumference of the balloon or in terms of an absolute dimension. For example, two adjacent windows may exhibit circumferential overlap that is between 0.2 and 2.0 mm, that is between 0.3 and 0.7 mm, that is between 0.4 and 0.6 mm, that is at least 0.3 mm, that is at least 0.4 mm, or that is at least 0.5 mm, or that is between 20% and 30% of the circumferential dimension of one of the two windows, that is between 24% and 26% of the circumferential dimension of one of the two windows, that is between 5% and 15% of a circumferential dimension of the cylindrical balloon, that is between 6% and 7% of a circumferential dimension of the cylindrical balloon, or that is between 10% and 14% of a circumferential dimension of the cylindrical balloon, for example. 
         [0044]    The windows  40  preferably have a greater circumferential dimension than axial dimension. For example, the ratio of circumferential dimension to axial dimension for a window may be greater than 1.5:1, greater than 2:1, greater than 7 to 1 or some other suitable number. A window may have an axial dimension of 1 mm, 1.25 mm, 1.5 mm, 1.75 mm, 2 mm, 2.25 mm, 2.5 mm or other suitable dimension and a circumferential dimension of greater than 3 mm such as 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or 7 mm. The circumferential dimension of a window  40  may be 20%, 25%, 30%, 100% or other suitable percentage of the circumferences of the cylindrical portion of the balloon wall. 
         [0045]    The windows  40  of  FIGS. 7 and 8  are shown as being arranged in a generally helical manner in that each adjacent window is offset axially and circumferentially (while overlapping circumferentially) from the previous window. Any number of windows sufficient to provide complete circumferential coverage may be used. In the embodiment of  FIG. 6 , five windows  40  are illustrated. Some embodiments may include 3, 4, 5, 6, 7, 8, 9, 10 or more windows and, if arranged helically as illustrated in  FIG. 6 , may extend for more than one turn around the balloon wall. It will be appreciated that a helical configuration is not necessary to provide complete circumferential coverage. Complete circumferential coverage means that the windows are arranged such that any axially parallel line drawn from the proximal end of the cylindrical balloon wall to the distal end of the cylindrical balloon wall passes through at least one window. The windows may be any suitable shape such as oval, oblong, bowtie or diamond shaped. 
         [0046]    Multilayer balloons  30  having windows  40  may be made according to one of the methods described herein or by another suitable method. In one method, the first layer  54  and the second layer  56  of the balloon are manufactured separately, using blow-molding techniques or other suitable methods. Holes to define the windows  40  are formed in second layer  56  by a laser, hole punch, mechanical or hydraulic cutting element or other suitable technique. The first layer  54  is positioned inside of the second layer  56  and the two layers  54 ,  56  are fused together using heat, a chemical solvent, an adhesive or other suitable technique. In some cases, the two layers may be positioned inside of a mold and/or pressure may be exerted inside inner layer  54  to fuse the two layers in an expanded position using heat, solvents, or adhesives. In some instances, the two layers are not directly joined but rather are separately attached to shaft  42 . 
         [0047]    In another method of manufacture, the inner layer  54  is formed over a flexible mandrel. The flexible mandrel has a shape like that of the inner layer  54  in the expanded position but it is made from a material, such as silicon, that does not adhere well to the material of the inner layer  54 . The inner layer  54  may be formed over the flexible mandrel by dip coating, spray coating, blow molding or other suitable techniques. A masking material is applied over the inner layer where the one or more windows  40  are desired. The masking material may be fixed to the inner layer using a removable or temporary adhesive. The flexible mandrel, with the inner layer and masking material thereon is then dip coated again using a non-conductive polymer to form the outer layer  56 . The outer layer is cut at the edges of the masking material and the masking material along with the outer layer material that is on the masking material is removed, thus forming the balloon  30 . Finally, the flexible mandrel is removed from within the balloon  30 . 
         [0048]    In use, a renal ablation system such as system  10  is provided. The system may be used with a standard guide catheter such as a 6 French guide catheter. Then the system  10  may be introduced percutaneously as is conventional in the intravascular medical device arts by using a guide catheter and/or a guide wire. For example, a guide wire such as a 0.014″ diameter guidewire may be introduced percutaneously through a femoral artery and navigated to a renal artery using standard radiographic techniques. In some embodiments, a delivery sheath  14  may be introduced over the guide wire and the guide wire may be withdrawn, and the device  12  may be then introduced through the delivery sheath. In other embodiments, the device  12  may be introduced over the guidewire, or the system, including a delivery sheath  14  may be introduced over a guidewire. In embodiments involving a delivery sheath  14 , the device  12  may be delivered distally from the distal end of the delivery sheath  14  into position, or the delivery sheath may be withdrawn proximally to expose the device  12 . A conductive fluid  58  is introduced into the balloon through fluid inlet lumen  50  and fluid inlet port  32 . The conductive fluid expands the balloon to the desired size. The balloon expansion may be monitored indirectly by monitoring the volume of conductive fluid introduced into the system or may be monitored through radiographic or other conventional means. Optionally, once the balloon is expanded to the desired size, fluid may be circulated within the balloon by continuing to introduce fluid through the fluid inlet port  32  while withdrawing fluid from the balloon through the fluid outlet port  34 . The rate of circulation of the fluid may be between 0 and 100 ml/min, 2 and 45 ml/min, 3 and 30 ml/min, or other desired rate of circulation. The rate of weeping, or seepage, through the balloon windows  40  may be between 0 mL/min and 15 mL/min, between 0.1 microliter/min and 0.1 mL/min, or other desired rate (with a possible dependence on pore size and pore count). The balloon may be kept at or near a desired pressure such as an absolute pressure of between 1 and 6 atmospheres, between 1.5 and 4 atmospheres, between 2.5 and 3.5 atmospheres or other desired pressure. The electrode  36  is then activated by supplying energy to the electrode. The energy may be supplied at 400-500 kHz and at between 1 and 50 watts. The energy is transmitted through the medium of the conductive fluid and through the windows  40  to the blood vessel wall to modulate or ablate the tissue. The lack of a conductive pathway through the non-window portions of the balloon may prevent effective energy transmission through the balloon wall except at the window  40  and like structures. The progress of the treatment may be monitored by monitoring changes in impedance through the electrode. Other measurements such as pressure and/or temperature measurements may be conducted during the procedure as desired. The circulation of the conductive fluid  58  may mitigate the temperature rise of the tissue of the blood vessel  60  in contact with the windows  40 . The electrode  36  is preferably activated for an effective length of time, such as 1 minute or 2 minutes. Once the procedure is finished at a particular location, the balloon  30  may be partially or wholly deflated and moved to a different location such as the other renal artery, and the procedure may be repeated at another location as desired using conventional delivery and repositioning techniques. 
         [0049]    Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and principles of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth hereinabove. All publications and patents are herein incorporated by reference to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.