Patent Document

FIELD OF THE INVENTION 
     The present invention relates to atherectomy devices, in general and in particular to brake systems for use in atherectomy devices. 
     BACKGROUND OF THE INVENTION 
     Arteriosclerosis is a common vascular disease in which a patient&#39;s blood vessels become hardened and blocked by plaque or clots that impede blood flow. Left untreated, this condition is a major contributing factor to the occurrence of high blood pressure, strokes and cardiac arrest. 
     To treat arteriosclerosis, many invasive and non-invasive techniques have been developed. For example, cardiac bypass surgery is now a commonly performed procedure whereby an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is generally successful, it is fairly traumatic because the entire chest cavity must be opened to access the occluded vessel. Therefore, the procedure is not generally performed on elderly or relatively frail patients. 
     One example of a minimally invasive technique that is being performed on a greater number of patients is to remove the occluding material from a patient&#39;s vessel with an atherectomy device. To perform this procedure, a guide catheter is typically inserted into the patient&#39;s femoral artery and advanced until the distal end of the guide catheter is located in the patient&#39;s ostium. A guide wire is then inserted through the guide catheter and traversed into the coronary arteries and past the occluded material to be treated. Then, as described in U.S. Pat. No. 4,990,134, issued to Auth, an atherectomy catheter having a small abrasive burr is advanced through the guide catheter and over the guide wire to the point of the occlusion. The burr is then rotated at high speed and passed through the occlusion during an ablation phase in order to remove particles that are sufficiently small such that they will not reembolize in the distal vasculature. As the burr removes the occlusion, a larger lumen is created in the vessel and blood flow is restored. 
     During the atherectomy procedure, after the burr has been routed over the guide wire to the location of the occlusion, the physician activates a rotational source (i.e. gas turbine) coupled to the burr by depressing a foot pedal so that the rotational source spins the ablation burr up to operational speed. In a conventional atherectomy device, a brake system is activated in unison with the rotational source to prevent rotation of the guide wire during the ablation phase of the atherectomy procedure. If the guide wire is not secured, the rotational inertia of the burr may begin to spin the guide wire and advance it downstream of the occlusion. 
     As shown in FIGS. 1 and 2A, a conventional brake system  20  consists of a brake cylinder  22 , having a bore  24  extending therethrough. The cylinder  22  is mounted to a brake assembly bracket  26 . A cylindrical piston  28  having an inner tapering or partially conical bore  30  linearly reciprocates within the bore  24  of the brake cylinder  22 . A wiper ring seal  32  is seated on a front surface  34  of the piston  28  to create a chamber  38  within the bore  24 . A cylindrically shaped brake collet  40  is disposed adjacent to the rear surface of the piston  28 . The brake collet  40  includes an axial bore  46  for allowing the guide wire  42  to extend therethrough. 
     Referring to FIG. 2A-2B, the distal end of brake collet  40  further includes a pair of tapered jaws  44  that begin at approximately the mid point of the brake collet  40 . The tapered jaws  44  have a conical engagement surface  50  that mates with the tapering bore  30  of the piston  28 . The jaws  44  are separated by a slot  52  that extends from the distal end of the brake collet  40  toward the mid-section such that the jaws are hinged at the proximal end but can bend inward toward the exposed guide wire  42  when the jaws are forced into the tapering bore  30  of the piston  28 . 
     The brake cylinder  22  has a gas inlet  56  that connects the chamber  38  to a source of gas through a gas conduit  58 . Attached to one end of the brake cylinder  22  is a brake bracket  60 . The brake bracket  60  has a centrally located bore  62  to retain the distal end of the brake collet  40  and to retain the brake collet  40  in proper alignment with the piston  28 . Disposed around the brake collet  40  is a return spring  64  which exerts force on the rear face  66  of the piston  28  in order to return the piston  28  to its original location after the brake system  20  is deactivated. 
     With reference to FIGS. 1 and 2A, during the operation of the atherectomy device, the physician rotates the ablation burr via activation of a foot pedal. Depression of the foot pedal allows gas from a gas line  70  to enter manifold  74  having a gas conduit  58  fluidly connected to brake cylinder  22 , and an outlet port  78  leading to the rotation source through tube  80 . Gas entering chamber  38  through gas inlet  56  exerts pressure on the front piston face  68  thereby causing the piston  28  to linearly translate within the bore  24  of the brake cylinder  22 . As the piston  28  moves linearly toward the brake bracket  60 , the inner tapering bore  30  of the piston  28  engages the correspondingly conical engagement surface  50  of the brake collet  40  to urge the jaws  44  radially inward to engage with the guide wire  42 . The jaws  44  of brake collet  40  clamp down onto the guide wire  42  so that the guide wire  42  is prevented from rotating. After the occlusion has been ablated, the physician releases pressure on the foot pedal to deactivate the ablation burr. When the physician releases the foot pedal, the gas is shut off from the chamber  38  allowing the biasing force of the return spring  64  to move the piston  28  linearly back toward the proximal end of the brake cylinder  22  as the gas escapes back through the gas conduit  58 . This disengages the brake collet  40  from the guide wire  42 . To prevent potential rotation of the guide wire, care must be taken to ensure that the driveshaft has stopped rotating before the spring  64  pushes the piston  28  towards the brake cylinder  22  thereby releasing the guide wire. 
     While the brake system illustrated in FIGS. 1 and 2A works well to prevent rotation of the driveshaft during the ablation procedure, the present invention seeks to improve the performance and to simplify the design by eliminating the wiper ring seal  32 . 
     SUMMARY OF THE INVENTION 
     The present invention is a brake activator system comprising several linear actuators using a bellows design to decrease the leakage of gas in the brake cylinder and ensure that the guide wire is prevented from rotating during the activation and deactivation of the atherectomy device. 
     In one embodiment, the brake activator system comprises a housing which includes two coaxially disposed apertures for receiving a guide wire therethrough. At least one bellows is coupled to the linear actuator. A brake collet having a camming surface and a braking surface is engageable with the guide wire. Expansion of the bellows urges the braking surface of the brake collet toward the guide wire to prevent the rotation thereof. 
     In another embodiment, the linear actuator uses two concentrically arranged bellows to form an annular chamber. Expansion of the chamber linearly translates the rear plate of the linear actuator into engagement with a brake collet. The conical shape of each engagement surface results in the brake collet clamping down on the guide wire and thus preventing its rotation. 
     In yet another embodiment, the brake activator comprises a housing, a pair of bellows and a pair of brake shoes. One end of each bellows is secured to opposing interior walls of the housing. Brake shoes are attached to the other end of each bellows to form two chambers. Expansion of the chambers linearly translates the brake shoes radially inward into engagement with the guide wire to prevent its rotation. 
     As will be readily appreciated from the foregoing description, the present invention provides a brake activator system that eliminates the use of a sliding seal commonly used in conventional designs so that the brake activation pressure bleeds down slower, resulting in a tighter grip around the guide wire during activation of the brake. Additionally, slower bleed down provides a longer period of time for the ablation burr to stop rotating during deactivation of the brake system prior to the brake tube disengaging from the guide wire. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 illustrates an assembly view of a conventional brake system of an atherectomy burr device; 
     FIGS. 2A-2B illustrate the operation of a brake collet with the brake system shown in FIG. 1; 
     FIG. 3 illustrates an atherectomy burr device using a brake activator system of the present invention; 
     FIGS. 4A-4C illustrate a first embodiment of the brake activator system of the present invention; 
     FIGS. 5A-5B illustrate a second embodiment of the brake activator system of the present invention; 
     FIGS. 6A-6C illustrate a third embodiment of the brake activator system of the present invention; 
     FIG. 7 illustrates a fourth embodiment of the brake activator system of the present invention, and 
     FIG. 8 illustrates a fifth embodiment of the brake activator system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As will be explained in further detail below, the brake activator system (hereinafter referred to as “brake system”) of the present invention uses a sealed bellows to linearly translate a portion of a linear actuator into engagement with a brake collet in order to urge the brake collet into a clamping engagement with a guide wire. The bellows design provides a system that has an activation source that is more replicable, thus creating a better grip on the guide wire. The bellows design should also activate at lower pressure, thus holding the guide wire better during low pressure operation. Further, because it will have less leakage, it will bleed down after use slower and will hold longer when the burr spins down at deactivation. 
     FIG. 3 illustrates an exemplary brake system  110  of the present invention. The brake system is utilized in conjunction with a rotational ablation burr device  102  operated by a physician in an atherectomy procedure. 
     A rotational ablation burr device  102  utilizes a guide wire  114  that is routed through the patient&#39;s body approximately past the location of the occlusion that is to be treated. A hollow, drive coil  122  having an ablative burr  112  at its distal end is then inserted over the guide wire  114 , and advanced to a location just proximal to the occlusion. The drive coil is covered by a guide catheter  116  to minimize the impact to surrounding tissue when the drive coil  122  is rotatably engaged. The drive coil  122  is connected to a rotational source  120 , such as a gas turbine, housed within an advancer housing  118 . 
     During the atherectomy procedure, a rotational ablation burr  112  is routed over the guide wire  114  that extends from a position outside a patient&#39;s body to a position near the site of a vascular occlusion. Once the rotational ablation burr  112  is at the correct location in the patient&#39;s vasculature, the physician activates the rotational source  120  to rotate the ablation burr  112  so that a new lumen can be created. The brake system  110  is activated in unison with the rotational source  120  for preventing rotation of the guide wire  114  during the ablation phase of the atherectomy procedure and is describe in more detail below. 
     As shown in FIG. 3, the brake system  110  of the present invention is disposed at the proximal end of an advancer housing  118 . As best shown in FIGS. 4A-4C, the brake system comprises a brake tube bracket  130 , a brake cylinder  140 , a linear actuator  160 , and a brake collet  188 . The brake cylinder  140  has a cylindrical bore  146  extending along its longitudinal axis  142  from the open end  148  of the brake cylinder  140  to the closed end  150  of the brake cylinder  140  and a gas inlet  152  that is in communication with a source of gas through a gas line  124  (FIG.  3 ). At the closed end  150  of the brake cylinder  140 , and coaxial with its longitudinal axis  142  is an aperture  154 . A hypotube section  156  is fitted within the aperture such that one end extends from outside the brake cylinder  140  and the other end extends within the bore  146 . The hypotube section  156  has a central lumen  158  to accommodate the insertion of the guide wire  114 . Coupled to the outside surface of the hypotube section  156  is front plate  162  of the linear actuator  160 . 
     The linear actuator  160  consists of a front plate  162 , a rear plate  164 , and a bellows section  166 . The bellows section  166  has a u-shape cross-section and extends annularly around the bore  146  of the brake cylinder  140  so that it creates an open cavity  168  that guide wire  114  extends through while providing a chamber  170  that may be expanded to apply the braking force against a brake collet  188  as described below. The open ends of the u-shape cross-sectioned bellows section  166  are bonded to the proximal surface of the front-plate  162  to create the leak-proof chamber  170 . 
     Still referring to FIGS. 4A-4B, front plate  162  includes an aperture  172  disposed coaxially with central lumen  158  and mateable with the outer surface of the hypotube section  156 . Front plate  162  is secured to the outside surface of hypotube section  156  so that one portion of the linear actuator  160  is fixed or anchored within the brake cylinder  140 . Disposed radially outward of the aperture  172  is a gas inlet  174  that is in communication with the gas inlet  152  of the brake cylinder  140  via a fluid connector  176  such as a tube or pipe so that the chamber  170  receives a gas to expand the bellows section  166 . Bonded to the closed end of the bellows section  166  is the rear plate  164 . 
     As shown in FIG. 4A-4B, the rear plate  164  contains a base portion  178  and a collet engaging ring  180  that extends proximally from the center of the base portion. The base portion  178  is cylindrical in shape and has a diameter just slightly less than the inside diameter of bore  146  so that the rear plate  164  may not only reciprocate within the bore  146  but is also guided by the bore  146  so as not to get misaligned when the bellows section  166  expands. Disposed at the center of base portion  178  is an aperture  182  coaxial with the longitudinal axis  142  of the brake cylinder  140 . The collet engaging ring  180  has an inner surface  184  that tapers radially inward to form a conical engagement surface  186 . The diameter of the conical surface  186  at the position where the taper ends is equal to the diameter of the aperture  182  in the base portion  178 . 
     Referring to FIGS. 4A and 4C, a cylindrically shaped brake collet  188  is disposed adjacent the proximal end of the collet engaging ring  180  of the rear plate  164 . The brake collet  188  includes a bore  190  for allowing the guide wire  114  to extend therethrough. The distal end of brake collet  188  further includes a pair of tapered jaws  192  that begin at approximately the mid point of the brake collet  188 . The tapered jaws  192  have a conical engagement surface  196  that mates with the conical engagement surface  186  of the collet engaging ring  180  of the rear plate  164 . The jaws  192  are separated by a slot  194  that extends from the proximal end of the brake collet  188  toward the mid-section such that the jaws are hinged at the proximal end but can bend inward toward the exposed guide wire  114 . 
     As best shown in FIG. 4A, attached to one end of the brake cylinder  140  is a brake tube bracket  130 . The brake tube bracket  130  contains a bore  132  coaxial with the longitudinal axis  142  of the brake cylinder  140 . The brake tube bracket retains one end of the brake collet  188  to maintain the brake collet  188  in proper alignment with the rear plate  164 . Disposed around the brake collet  188  is a return spring  134  which exerts force on the proximal surface of the rear plate  164  to return the rear plate  164  to its original location after the brake system is deactivated. 
     With reference to FIGS.  3  and  4 A- 4 C, during the operation of the atherectomy device, the physician rotates the ablation burr  112  via activation of a foot pedal. Depression of the foot pedal allows gas from a gas line  124  to enter manifold  126  having a gas conduit  128  fluidly connected to the chamber  170  of the bellows section  166 , and an outlet port  136  leading to the rotation source through tube  138 . Gas entering chamber  170  through inlets  152 ,  174  exerts pressure on the inside of the bellows section  166  thereby causing the rear plate  164  to linearly translate within the bore  146  of the brake cylinder  140 . As the rear plate  164  moves rearward, the conical engagement surface  186  of the rear plate  164  engages the correspondingly conical engagement surfaces  196  of the brake collet  188  to urge the tapered jaws  192  of the brake collet  188  radially inward to engage with the guide wire  114 . 
     As described above, the inside surface of the bore  146  acts as a guide so that the corresponding conical engagement surfaces are aligned properly to force the tapered jaws  192  of the brake collet  188  radially inward. The tapered jaws  192  of brake collet  188  clamp down onto the guide wire  114  so that the guide wire  114  is prevented from rotating. When the physician releases the foot pedal to deactivate the ablation burr, the gas is shut off from the chamber  170  allowing the biasing force of the return spring  134  to move the rear plate  164  linearly back toward the closed end of the brake cylinder  140  as the, gas escapes out through the gas inlets  174  and  152 . This disengages the brake tube  188  from the guide wire  114 . 
     In the presently preferred embodiment of the present invention, the bellows section  166  is made from a flexible material such as rubber, plastic, or the like, and could be fabricated by a technique such as blow-molding, which is well known in the art. Further, it will be appreciated to those skilled in the art that in an alternative embodiment, the brake cylinder  140  could be eliminated and the front plate  166  may include three or four extension or attachment members. The brake tube bracket  130  would then attach to the attachment members of the modified front plate to contain the rear plate  164  and the bellows section  166 . 
     FIGS. 5A-5B illustrates another embodiment of the brake system according to the present invention. Brake system  204  contains multiple cylindrical bellows sections  206  that are disposed radially around the longitudinal axis  242  of the brake cylinder  240 . The ends of the bellows sections  206  are bonded to the distal face of the rear plate  208  and the proximal face of the front plate  210 , respectively, to form chambers  212 . Front plate  210  includes an aperture  216  coaxial with the longitudinal axis  242  of brake cylinder  240  to receive the end of a hypotube  218 . Disposed radially outward of the aperture  216  are gas inlets  274  that are in communication with gas inlets  252  of the brake cylinder  240  via a fluid connector such as a pipe or tube  276  so that the chambers  212  receive a source of gas to expand the bellows sections  206 . The other end of hypotube  218  is secured to the brake cylinder  240  so that the front plate  210  is fixed or anchored. The hypotube includes a central lumen  220  for receiving a guide wire  214  therethrough. 
     As shown in FIG. 5A, rear plate  208  contains a base portion  222  and a collet engaging ring  224 . The base portion  222  is cylindrical in shape and has a diameter just slightly less than the inside diameter of bore  246  so that the rear plate  208  may not only reciprocate within the bore  246  but is also guided by the bore  246  so as not to get misaligned when the bellows sections  206  expands. Disposed at the center of base portion  222  is an aperture  226  coaxial with the longitudinal axis  242  of the brake cylinder  240 . The collet engaging ring  224  has an inner surface  228  that tapers radially inward to form a collet engagement surface  236 . The diameter of the collet engagement  236  surface at the position where the taper ends is equal to the diameter of the aperture  226  in the base portion  222 . 
     As shown in FIG. 5B, four bellows sections are used to reciprocate the rear plate  208  with respect to the stationary front plate  210 . However, it will be appreciated that any number of bellows sections  206  could be used. 
     During operation, similar to the operation described in the first embodiment, gas is supplied to the chambers  212  of the bellows sections  206  through gas inlets  252 ,  274  when the physician activates the foot pedal to rotate the ablation burr. Gas entering chambers  212  exerts pressure on the front face of rear plate  208  thereby causing the rear plate  208  to linearly translate within the bore  246  of the brake cylinder  240 . As the rear plate  208  moves linearly toward the brake tube bracket  230 , the collet engagement ring  236  of the rear plate  208  engages the correspondingly conical engagement surfaces  296  of the brake collet  288  to urge the tapered jaws  292  radially inward to engage with the guide wire  214 . 
     As described above, the inside surface of the bore  246  acts as a guide so that the brake collet  288  and the collet engaging ring  236  are aligned properly to force the tapered jaws  292  of the brake collet  288  radially inward. The tapered jaws  292  of brake collet  288  clamp down onto the guide wire  214  so that the guide wire  214  is prevented from rotating. When the physician releases the foot pedal to deactivate the ablation burr, the gas is shut off from the chambers  212  allowing the biasing force of the return spring  234  to move the rear plate  208  linearly back toward the distal end of the brake cylinder  240  as the gas escapes through the gas conduit  252 . This disengages the brake collet  288  from the guide wire  214 . 
     FIG. 6A-6B illustrates another embodiment of the brake system according to the present invention. The brake system  310  in this embodiment is similar to the first embodiment described above. Identical two-digit reference numerals will be used to designate similar structure found in the first embodiment but with a  300  prefix. For example, the present embodiment uses the brake cylinder  140 , but will instead be numbered  340 . The differences will now be enumerated below. 
     As shown in FIG. 6A, the brake system  310  comprises a brake cylinder  340 , a brake tube bracket  330 , a brake collet  388 , and a linear actuator  360 . The linear actuator  360  uses a different arrangement which will now be described. The linear actuator  360  contains longitudinally disposed inside and outside expandable membranes  362 ,  364 , a front plate  366 , and a rear plate  368 . The front plate  366  is cylindrical in shape and includes a relatively flat base plate  370  with an inside annular flange  372  and an outside annular flange  373 . The inside annular flange  372  is tube-like and contains a bore  376  that is coaxial with the longitudinal axis  342  of the brake cylinder  340  to provide a passage for the guide wire  314  to traverse. The inside annular flange  372  extends proximally from the base plate  370  to provide an inner shoulder on which the inside bellows  362  is secured. 
     The outside annular flange  373  is similar to the inside annular flange  372  in that it extends in the same directions as the inside annular flange  372  and provides an outer shoulder to which the outside expandable membrane  364  is secured. Attached to the distal side of the front plate  366  from inside annular flange  372  is a hypotube section  356 . The hypotube section  356  is coupled to the front plate  366  and has a lumen  358  that is coaxial with the longitudinal axis  342  of the brake cylinder  340 . A gas inlet  374  is disposed through the front plate  366  at a position radially outward from the longitudinal axis  342 . The gas inlet  374  is in communication with a gas inlet  352  of the brake cylinder  340  via a fluid connector such as a pipe or tube  376  so that a chamber  338  receives a gas to expand the bellows created by the expandable membrane  362 ,  364 . 
     Still referring to FIG. 6A, the rear plate  368  is cylindrical in shape and contains a relatively flat base plate  378 , a proximally extending collet engaging ring  380 , and a distal extending outside flange  382 . The collet engaging ring  380  includes a bore  384  that is coaxial with the longitudinal axis  342  of the brake cylinder  340  to provide a passage for the guide wire  314  to traverse. The distal surface of the base plate also includes an inner ring  383  having the same diameter as the annular flange  372  to provide an inner shoulder to which the flexible membrane  362  is secured. The collet engaging ring  380  has an inner surface  386  that tapers to form a conical engagement surface  387  that mates with the tapered jaws of the brake collet  388  in the manner described above. 
     As shown in FIGS. 6A-6B, the inside and outside bellows created by the membrane  362 ,  364  are concentrically arranged around the longitudinal axis  342  of the brake cylinder  340 . The inside and outside membranes  362 ,  364  are bonded to the respective shoulders as best shown in FIG. 6A, to create a substantially sealed annular chamber that may be expanded by the application of compressed gas to apply the braking force against a brake collet. The membranes  362 ,  364  can be secured to the respective shoulders in any manner known in the art such as glued, solvent bonded, press fit, ring clamped, rotational welded, sonically sealed or the like so that they form a leak-proof chamber. 
     During the operation of the brake system  310 , gas is supplied to the chamber  338  created between the membranes  362 ,  364  through gas inlets  352 ,  374  when the physician activates the foot pedal to rotate the ablation burr. The gas is supplied to the gas inlets using the gas lines, manifolds, etc. as described above with respect to FIG.  3 . Gas entering chamber  338  exerts pressure on the front face of the base plate  378  of rear plate  368  thereby causing the rear plate  368  to linearly translate within the bore  346  of the brake cylinder  340 . As the rear plate  368  moves linearly toward the brake tube bracket  330 , the conical engagement surface  387  of the rear plate  368  engages the correspondingly conical engagement surface  396  of the brake collet  388  to urge the tapered jaws  392  of the brake collet  388  radially inward to engage with the guide wire  314 . The inside surface of the brake cylinder bore  346  acts as a guide so that the corresponding conical engagement surfaces are aligned properly to force the tapered jaws  392  of the brake collet  388  radially inward. The brake collet  388  clamps down onto the guide wire  314  so that the guide wire  314  is prevented from rotating. When the physician releases the foot pedal, the gas is shut off from the chamber  338  allowing the biasing force of the return spring  334  to move the rear plate  368  linearly back toward the closed end of the brake cylinder  340  as the gas escapes through the gas inlet  352 . This disengages the brake tube from the guide wire. 
     Alternatively, as will be appreciated to those skilled in the art, the linear actuator  360  of the presently preferred embodiment may use inside and outside membranes  362 ,  364  of a suitable material such as metal to provide a biasing force to return the rear plate  368  to its original or unexpanded position during the deactivation of the brake. Further, as shown in FIG. 6C, the inside and outside membranes could be plastic molded onto a spring. If the membranes are made so as to provide the biasing force, the return spring  334  therefore is not needed. 
     FIG. 7 illustrates yet another embodiment of the brake system according to the present invention. The brake system  410  comprises a housing  412  having an interior cavity  414 , a first and second opposing bellows  416 ,  418 , and a pair of brake shoes  420 ,  422  on the opposing surfaces of the bellows  416 ,  418  respectively. The housing  412  has a rectangular cross-section and an aperture  424 ,  426  on each vertically opposing wall. The apertures  424 ,  426  are coaxially aligned and have a sufficient diameter to receive the guide wire  428  therethrough. Disposed within the cavity  414  are the first and second cylindrically shaped bellows  416 ,  418  that are positioned on opposing sides of the guide wire  428 . The bottom end of the first bellows  416  is bonded to the inside face of the bottom end of the housing  412 . The top end of the first bellows is bonded to the first brake shoe  420  to form a chamber  432 . The top end of the second bellows  418  is bonded to the inside face of the top end of the housing  412 . The bottom end of the second bellows  418  is bonded to the second brake shoe  422  to form a chamber  436 . Each of the chambers  432 ,  436  has a gas inlet  444 ,  442  respectively that delivers gas to the chambers to expand the opposing bellows. The opposing brake shoes  420 ,  422  engage the guide wire  428  during activation of the brake system  410 . The brake shoes  420 ,  422  may have to be constrained by housing  412  to prevent twisting or cocking of the brake shoes by the guide wire&#39;s rotational force. 
     During operating of the brake system  410 , gas is supplied to the chambers  432 ,  436  of the bellows  416 ,  418  when the physician activates the foot pedal to rotate the ablation burr. Gas entering chambers  432 ,  436  exerts pressure on the brake shoes  420 ,  422  thereby causing the brake shoes  420 ,  422  to move radially inward within the cavity  414  of the housing  412  toward the guide wire  428 . As the brake shoes move radially inward, the brake shoes  420 ,  422  engage the guide wire  428  to prevent the guide wire  428  from rotating. When the physician releases the foot pedal, the gas is shut off to the chambers  432 ,  436 , allowing the slight biasing force of the bellows  416 ,  418  to disengage the brake shoes  420 ,  422  from the guide wire  428  as the gas escapes through the gas inlets  442 ,  444 . 
     Alternatively, FIG. 8 illustrates yet another embodiment of the brake system according to the present invention. The brake system  510  comprises a housing  512  having an interior cavity  524 , a bellows  516 , and a pair of brake shoes  520 ,  526 . The housing  512  has a rectangular cross-section and a pair of aligned apertures  514 ,  516  on opposing walls. The apertures  514 ,  516  have a sufficient diameter to receive the guide wire  518 . Disposed within the cavity  524  is a cylindrically shaped bellows  516  which is bonded to the top surface of the housing  512 . Bonded to the bottom end of bellows  516  is a brake shoe  520  to form a chamber  522 . The brake shoe  520  engages the guide wire  518  during activation of the brake system  510 . Attached to the bottom surface of the housing  512  is a second brake shoe  526  having a surface for engaging the guide wire during activation of the brake system  510 . A gas inlet  530  is disposed through the top end of the housing  512  in communication with chamber  522 . The gas inlet  528  is in communication with a source of gas to provide the actuating force to expand the bellows  516 . 
     During operation of the brake system  510 , gas is supplied to the chamber  522  of the bellows  516  when the physician activates the foot pedal to rotate the ablation burr. Gas entering chamber  522  exerts pressure on the inside surface of brake shoe  520  thereby causing the brake shoe  520  to engage the guide wire  518 . When the physician releases the foot pedal, the gas is shut off to the chamber  522 , allowing the slight biasing force of the bellows  516  to disengage the brake shoe  520  from the guide wire  518  as the gas escapes through the gas inlet  530 . The brake shoe  526  releases from the guide wire  518  by slack in the housing  512 , allowing brake shoe  526  to drop downward slightly away from the guide wire  518 . 
     In the presently preferred embodiments illustrated in FIGS. 7 and 8, it will be appreciated by those skilled in the art that the bellows sections could have several arrangements. For example, the bellows section in FIG. 8 could be bonded to the bottom inside surface of the housing and the second shoe could be bonded to the top inside surface of the housing. Further, it will be appreciated by those skilled in the art that the housing  412  and  512  shown in FIGS. 7 and 8, respectively, could have a C-shaped cross-section by using a part such as a C-clamp or caliper. 
     With respect to the above discussed embodiments and any other potential embodiments, the expandable membranes that comprise the bellows could be made of an elastomer such as latex rubber or urethane, a flexible material such as polyethylene, or a more rigid plastic such as polyester or nylon. A thin metal may also be used to form the bellows. Further, the expandable membranes could be plastic or rubber coated fabric. As described in one embodiment above, the bellows made from a metal material can have a pre-set compression biasing force so that a return spring is not needed to disengage the brake tube from the guide wire. A spring with plastic or rubber covering bonded thereto could also be used as an alternative to a metal bellows. See FIG.  6 C. Bellows formed from a metal material could also be used in the embodiments described in FIGS. 7 and 8 to provide a mechanism for disengaging the brake shoe(s) from the guide wire when the ablation burr is deactivated. 
     While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the scope of the invention. It is therefore intended that the scope of the invention be determined from the following claims and equivalent thereto.

Technology Category: a