Abstract:
An improved guide wire brake that is particularly suited to ablative rotational atherectomy devices is disclosed. The guide wire brake ensures that a guide wire is prevented from rotating or moving axially prior to activation of a primary mover such as a turbine. In one embodiment a pressure relief valve delays the activation of the prime mover on start up, and a check valve delays the release of the guide wire brake on shut down. In a second embodiment the guide wire brake is serially connected to the prime mover such that the prime mover is not connected to the pressurized gas source until after the guide wire brake is engaged. In a third embodiment a guide wire is disposed through a flexible tube within a rigid cylinder that is serially connected to the prime mover, such that when pressurized gas is provided to the prime mover the flexible tube will collapse on the guide wire, to prevent guide wire movement. In a fourth embodiment a mechanical brake, in a single action, engages the guide wire prior to opening a flow path between the pressurized gas source and the prime mover. Methods for manually bypassing the guide wire brake are also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical devices used to differentially ablate or cut deposits from within a patient&#39;s vasculature, and in particular to guide wire braking mechanisms for such medical devices. 
     BACKGROUND OF THE INVENTION 
     A variety of techniques and instruments have been developed for removing health-threatening deposits in a patient&#39;s arteries and similar body passageways. Such deposits may be caused by a number of diseases such as arteriosclerosis, a condition characterized by the buildup of deposits (atheromas) in the intimal layer of a patient&#39;s blood vessels. If the atheroma has hardened into a calcified atherosclerotic plaque, removal of the deposit can be particularly difficult. Deposits in the vasculature can restrict the flow of blood to vital organs, such as the heart or brain, and can cause angina, hypertension, myocardial infarction, strokes, and the like. 
     Several kinds of atherectomy devices have been developed for removing such deposits. One such device that is particularly suited to removing calcified atherosclerotic plaque, is an ablative rotational atherectomy device, such as that disclosed in U.S. Pat. No. 4,990,134 by Auth. Auth teaches using a small burr covered, or partially covered, with an abrasive cutting material, such as diamond grit. The burr is attached to the distal end of a flexible, rotatable drive shaft. A rotational atherectomy device practicing the Auth invention is sold by the assignee of the present invention under the trademark Rotablator® and is described below. 
     The Rotablator® ablative device  10 , depicted in FIG. 1, utilizes a guide wire  26  that is inserted through the patient&#39;s body approximately to the location of the deposit that is to be treated. A hollow, flexible drive shaft  22  having an ablative burr  24  at its distal end is then inserted over the guide wire  26 , and advanced to a location just proximal to the deposit. The drive shaft  22  is covered with a lumen or catheter  20  along most of its length to minimize the impact to surrounding tissue when the drive shaft  22  is rotatably engaged. The drive shaft  22  is connected to a compressed-air driven drive assembly  16  having a turbine (not shown) that can rotate the drive shaft  22  at relatively high rotational speeds, typically in the range of, e.g., about 150,000 to about 190,000 rpm. The drive assembly  16  is slidably mounted in an advancer housing  12  on a track  32 , allowing a surgeon using the device  10  to move the drive assembly  16  transversely, and hence move the drive shaft  22  and burr  24  forward and backward to ablate the atheroma. When the turbine is engaged, that is, when compressed air is being supplied to the drive assembly  16 , a guide wire brake  50  normally clamps onto the guide wire  26 , preventing the guide wire  26  from rotating or moving laterally while the drive shaft  22  is rotating. 
     A prior-art guide wire brake  50  for an ablative rotational atherectomy device is shown in FIG.  2 A. This prior art guide wire brake  50  comprises a brake collet  52  axially supported in a brake cylinder  56  containing a free piston  54  with a lip seal  55 . The guide wire  26  runs axially through the collet  52 , cylinder  56 , and piston  54 . As seen most clearly in FIG. 2B, the brake collet  52  is an elongate member having an upper portion  41  disposed opposite an identical lower portion  42 . The upper and lower portions  41 ,  42  are separated by a narrow gap  47  along most of the length of the brake collet  52 . The brake collet  52  has a tubular back portion  45  and a head portion  46  wherein the head portion  46  upper and lower portions  41 ,  42  generally form a pair of abutting truncated cones that are coaxial with the back portion  45 . The gap  47  separating the upper portion  41  from the lower portion  42  extends entirely through the head portion and most of the way through the back portion  45 , wherein interior flat faces  49  on the upper and lower portions  41 ,  42  are disposed on either side of the gap  47 . A narrow strip of the back portion  45  connects the upper portion  41  to the lower portion  42 , elastically biasing the upper portion  41  and lower portion  42  in an “unclamped” position wherein the gap is wider than the diameter of the guide wire  26 . 
     As shown in FIG. 2A, the piston  54  has a collet engagement orifice  48  that slidably engages the head portion  46  of the collet  52  at the gapped end. Because the head portion  46  is conically tapered, urging the collet engagement orifice  48  axial against the head portion  46  will deflect the upper and lower portions  41 ,  42  of the collet  52  toward each other, into a closed or clamped position. A spring  53  fits over the brake collet  52  and biases the piston  54  away from the collet  52 . During ablation, the compressed air that powers the drive assembly  16  enters the Rotablator®  10  via a manifold  59  having a first outlet port  61  fluidly connected to the brake cylinder  56 , and a second outlet port  62  leading to the drive assembly  16  through tube  30 . When compressed air is provided to the drive assembly  16  it is supplied in parallel to the brake cylinder  56 . The piston  54  is thereby urged distally toward the brake collet  52 , causing the collet engagement orifice  48  to elastically compress the head portion  46  around the guide wire  26  when the turbine is engaged. 
     Under certain circumstances, it is desirable to override the guide wire brake  50  and release the guide wire  26  even when the turbine and the drive shaft  22  are rotating. For example, it is sometimes desirable to engage the turbine when the drive shaft  22  is advanced over the guide wire  26  to the target position within an artery, or when the drive shaft  22  is being removed from the artery. Sometimes it is also useful to override the guide wire brake to permit advancement or retraction of the guide wire  26  within the rotating drive shaft  22 . The Rotablator® provides a “dynaglide” mode wherein the guide wire  26  is enclamped when turbine is operated at a lower velocity in order to facilitate such drive shaft insertion and removal. For these and other situations, a bypass valve  57  is provided between the manifold  59  and the brake cylinder  56 , whereby the first manifold outlet  61  to the brake cylinder  56  may be closed. This allows the pressurized gas to drive the turbine without engaging the guide wire brake  50 . 
     An alternative guide wire brake for an atherectomy device is disclosed in U.S. Pat. No. 5,779,722 to Shturman et al., wherein a mechanical guide wire brake is coupled to a mechanical turbine brake. Shturman et al. teaches a mechanical system wherein translation of the turbine along its track, (which is generally performed to move the burr back and forth over the atheroma), has a range of positions that will engage a turbine brake, and a further range that will then release the guide wire brake. A separate override clamp may be secured to the device to release the guide wire brake without engaging the turbine brake. While the device disclosed by Shturman et al. provides an alternate method of ensuring the guide wire brake is engaged when the turbine is operated, the device has the disadvantages of being relatively complicated to build and to operate. In addition, it is possible that the override clamp could be inadvertently left in place, whereby the guide wire could undesirably be free to move. 
     It is desirable to provide a guide wire brake assembly that ensures that automatically resets any brake override or bypass mechanisms when the drive assembly is engaged. It is further desirable to have a guide wire brake that engages more quickly or earlier than the turbine when the compressed air supply is switched on, and disengages more slowly or later than the turbine, when the compressed air supply is switched off. It is further desirable to provide a guide wire brake that is mechanically simple and easy to operate. 
     SUMMARY OF THE INVENTION 
     A novel guide wire brake particularly suited to ablative rotational atherectomy devices is disclosed. Ablative rotational atherectomy is a procedure for removing unhealthy deposits within a body by inserting an ablative burr proximate a deposit, and rotating the burr to remove the deposit. A fine guide wire is first inserted, typically through the patient&#39;s vasculature, to the deposit site. A flexible, tubular drive shaft, with the ablative burr at its distal end, is then inserted over the guide wire and guided to the proper location. A catheter covers the drive shaft along most of its length to minimize the impact to local tissues. In normal operation, the guide wire is then clamped at its proximal end to prevent axial or rotational motion, and a prime mover, such as a turbine, is engaged to rotate the drive shaft and burr. The guide wire brake of the present invention clamps the guide wire prior to the activation of the prime mover, and slightly delays the release of the clamp to allow the rotational inertia of the prime mover to dissipate prior to unclamping the guide wire. 
     In one embodiment the guide wire brake is connected in parallel to a pressurized gas source that drives the prime mover and utilizes a piston in a cylinder to activate the guide wire brake. A pressure relief valve is provided between the pressurized gas source and the prime mover that has an activation pressure greater than the guide wire brake activation pressure, whereby the guide wire brake will engage the guide wire prior to the pressure relief valve opening to the prime mover. Additionally, a check valve is connected to the guide wire brake cylinder that prevents or impedes the flow of gas out of the brake cylinder, thereby delaying the release of the guide wire brake after the pressurized gas source is disconnected or turned off. 
     In another embodiment of the invention a pneumatic guide wire brake is connected in series between the pressurized gas source and the prime mover. The guide wire brake cylinder includes a side outlet port that leads to the prime mover, whereby the side outlet port does not open until after the guide wire brake has been engaged. 
     In yet another embodiment of the present invention, a pneumatic guide wire brake is connected in series between the pressurized gas source and the prime mover. The guide wire brake consists of a flexible tube through which the guide wire passes that is suspended within a rigid cylinder. When the pressurized gas passes through the rigid cylinder prior, the increased pressure causes the flexible tube to collapse around the guide wire, thereby clamping the guide wire. 
     In still another embodiment of the present invention, a mechanically-engaged guide wire brake is provided, wherein rotation of a valve to a first position will engage the guide wire break prior to opening a channel between the pressurized gas source and the prime mover. 
     In each of the embodiments disclosed herein an optional valve is provided whereby the guide wire brake can be selectively bypassed. 
    
    
     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 is a partially exploded isometric view of a prior art rotational ablation device; 
     FIG. 2A is an exploded isometric view of a prior art guide wire brake assembly; 
     FIG. 2B is an isometric view of a prior art brake collect; 
     FIG. 3A is a schematic representation of a first embodiment of the guide wire brake of the present invention showing a bypass valve in an open position; 
     FIG. 3B is a schematic representation of the guide wire brake shown in FIG. 3A showing the bypass valve in a closed position; 
     FIG. 4A is a schematic representation of a second embodiment of a guide wire brake of the present invention with no pressurized gas supplied to the guide wire brake; 
     FIG. 4B is a schematic representation of the guide wire brake shown in FIG. 4A with pressurized gas supplied to the guide wire brake and with a bypass valve is in an open position; 
     FIG. 4C is a schematic representation of the guide wire brake shown in FIG. 4A with pressurized gas supplied to the guide wire brake and with the bypass valve in a closed position. 
     FIG. 5A is a schematic representation of a third embodiment of a guide wire brake of the present invention with a bypass valve in an open position; 
     FIG. 5B is a cross-sectional view of the guide wire brake shown in FIG. 5A with the guide wire unclamped; 
     FIG. 5C is a cross-sectional view of the guide wire brake shown in FIG. 5A with the guide wire clamped; 
     FIG. 5D is a cross-sectional view of a modified guide wire brake embodiment similar to that shown in FIG. 5A but having brake shoes inserted into an elastic brake tube; and 
     FIG. 6 is a schematic representation of a fourth embodiment of a guide wire brake of the present invention showing the guide wire brake in an unclamped position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As discussed above, FIG. 1 shows a rotational ablation device  10 , illustrating the application for which the present invention was developed. Although the present invention will be illustrated with respect to a rotational ablation device  10 , it is contemplated that the invention will find other applications as well. 
     The ablation assembly  10  includes ablation burr  24  attached to the distal end of drive shaft  22 . The drive shaft  22  is coupled to a drive assembly  16  having a compressed-gas-driven turbine (not shown). The drive assembly  16  is slidably mounted on a single-rail track  32 , whereby the drive assembly  16  can be selectively moved longitudinally. The drive assembly  16  transmits torque to the drive shaft  22  and ablation burr  24 . Given the coupling of the drive shaft  22  to the drive assembly  16 , it will be appreciated that longitudinal motion of the drive assembly  16  will cause the ablation burr  24  to advance and retract, whereby the ablation burr  24  can be maneuvered through an atheroma in a patient&#39;s vasculature. 
     The ablation burr  24  is positioned in a patient&#39;s vasculature over the guide wire  26 . The proximal end of guide wire  26  extends longitudinally through the ablation assembly  10 . To limit undesired movement of the guide wire  26  during the atherectomy procedure, a guide wire brake  50  is provided, through which the guide wire  26  passes. A prior art guide wire brake  50  is depicted in FIG. 2A, and has been described above. 
     A schematic view of an improved guide wire brake  100  in accordance with one embodiment of the present invention is shown in FIGS. 3A and 3B. Pressurized gas, such as air, is provided through an inlet port  102  to a manifold  159 . The manifold  159  has two outlet ports  104  and  105 . The outlet port  104  is connected to a pressure relief valve  106 . When the pressure is sufficiently high to open the pressure relief valve  106 , compressed air flows through the pressure relief valve  106  to a turbine (not shown). The second outlet port  105  fluidly connects the manifold  159  to a check valve  108 , which in turn is fluidly connected to a bypass valve  157 . When the bypass valve  157  is in an open position, as shown in FIG. 3A, the pressurized air flows through an input port  110  and an outlet port  120 . The outlet port  120  is fluidly connected to an inlet port  122  of a brake cylinder  156 . A pair of O-rings  114 ,  116  on a bypass button  112  seal the bypass valve  157 . A spring  118  biases the valve  157  in an open position such that the inlet port  110  and outlet port  120  are fluidly connected. Pressing the bypass button  112  compresses the spring  118  and moves the O-ring  114  such that the outlet port  120  and inlet port  110  are on opposite sides of the O-ring  114  thereby closing the valve  157 . 
     The brake cylinder  156  includes a free piston  154  that moves within the brake cylinder  156 . An O-ring  155  is attached to the piston  154  to provide a seal between the interior of brake cylinder  156  and the piston  154 . A top surface of the piston  154  is in fluid communication with the inlet port  122 . A rear surface of the piston  154  is biased by a spring  153  away from a cylinder base  151  that closes the brake cylinder  156 . The brake cylinder  156  and the piston  154  have a central hole through which a guide wire  26  is passed. A sleeve  158  is secured to the top surface of the piston  154  and extends out of the brake cylinder  156  to seal the hole through which the guide wire extends. Surrounding the hole for the guide wire  26  on the rear surface of the piston  154  is a collet engagement orifice  148 . 
     The cylinder base  151  includes a collet support channel  146  into which the brake collet  52  is slidably disposed. The brake collet  52  has a tubular back portion  45  that fits within the collet support channel  146 . The head portion  46  of the brake collet  52  has a tapered upper portion  41  and a tapered lower portion  42 . The tapered upper and lower portions  41 ,  42  have oppositely disposed, generally parallel flat faces  49  that are separated by a gap  47  that is larger than the diameter of the guide wire  26 . The back portion of collet  52  connects the upper and lower portions  41 ,  42 , whereby the upper and lower portions can be elastically displaced towards each other. 
     In the unpressurized condition, a spring  153  disposed within brake cylinder  156  biases the piston  154  away from the brake collet  52 , such that the brake collet  52  will not engage the guide wire  26 . When pressurized gas is provided at the manifold inlet port  102  and the bypass valve  157  is in the open position, the brake cylinder  156  is fluidly connected to the pressurized gas source. The pressure in the brake cylinder  156  produces a force on the piston  154  sufficient to overcome the biasing force of the spring  153 , causing the collet engagement orifice  148  to engage the tapered upper and lower portions  41 ,  42  of the brake collet  52 , thereby urging the tapered portions  41 ,  42  toward each other, such that the flat faces  49  will clamp onto the guide wire  26 . 
     The pressure relief valve  106  has an activation pressure greater than the pressure required to engage the guide wire brake  100 , whereby the guide wire brake  100  will engage the guide wire  26  prior to spin-up of the turbine. It will be appreciated that when the pressurized gas source is removed, the check valve  108 , in combination with the O-ring  155 , inhibits the flow of gas out of the brake cylinder  156 , and will substantially seal the interior of the brake cylinder  156 . The substantially sealed volume in the brake cylinder  156  will therefore maintain a positive pressure for a period of time, thereby delaying release of the guide wire brake  100 . In prototype tests, the release of the guide wire brake  100  has been found to occur approximately one second after the pressurized gas is shut off, which is approximately four times longer than the release time of the prior art guide wire brake  10  described above. 
     FIG. 3B shows a schematic of the first preferred embodiment of the guide wire brake  100  shown in FIG. 3A, with the bypass valve  157  in a closed position. When the bypass valve  157  is closed by depressing the bypass valve button  112 , the bypass O-ring  114  is moved past the outlet port  120 , so that the guide wire brake  100  is fluidly disconnected from the inlet port  110 . Therefore the brake cylinder  156  is no longer fluidly connected to the manifold  159 , and the pressurized gas entering the inlet port  102  will drive the turbine without engaging the guide wire brake  100 . It will be appreciated that a constant pressure must be applied to the bypass valve button  112  to overcome the biasing force from the spring  118 , in order to bypass the guide wire brake  100 . 
     A schematic view of a second embodiment of a guide wire brake of the present invention is shown in FIGS. 4A,  4 B, and  4 C. In this embodiment the guide wire brake  200  is connected in series between a pressurized gas source (not shown) and a turbine (also not shown). To activate the guide wire brake  200 , pressurized gas is applied to a bypass valve  257 . The valve  257  has a first inlet port  210  and a first outlet port  220 . The bypass valve  257  also has a second inlet port  221  and a second outlet port  211 . When the bypass valve  257  is in the open position, the first inlet port  210  is fluidly connected to the first outlet port  220  and the second inlet port  221  is fluidly connected to the second outlet port  211 . A push button  212  has a pair of O-rings  214 ,  216  that open and close the valve. A spring  218  biases the push button  212  so that the valve  257  is normally open. The first inlet port  210  is connected to a source of compressed air and the second outlet port  211  is connected to a turbine. A brake cylinder  256  is connected in series between the first outlet port  220  and the second inlet port  221 . The brake cylinder  256  has a front end  261  and a back end  262 . An inlet port  222  extends through the front end  261 . An outlet port  223  is provided in the cylinder  256 , located between the front end  261  and the back end  262 . 
     A master piston  264  is disposed inside the cylinder  256 , and is biased toward the front end  261  with a spring  263 . A secondary piston  254  is also disposed in the brake cylinder  256  and is biased toward the back end  262  by the same spring  263 . A cylinder base  251  closes the back end  262  of the cylinder  256 . The secondary piston  254  is biased toward the brake cylinder front end  261  with a second spring  253 , located between the secondary piston  254  and the cylinder base  251 . A guide wire  26  extends through a hole in the secondary piston  254 , the master piston  264 , and the front end  261  of the brake cylinder  256 . The secondary piston  254  includes a collet engagement orifice  248  on its rear surface surrounding the hole through which the guide wire  26  passes. A brake collet  52 , identical to the brake collet described above, projects into the brake cylinder  256 , and is supported by a collet support channel  246  in the cylinder base  251 . The spring  263  and the second spring  253  are selected such that when no pressurized gas is provided at the inlet port  222 , as shown in FIG. 4A, the master piston  264  is disposed adjacent the brake cylinder front end  261  and the secondary piston  254  is disposed between the brake cylinder back end  262  and the outlet port  223 , so that the collet engagement orifice  248  does not engage the tapered upper and lower portions  41 ,  42  of the brake collet  52 . The outlet port  223  is fluidly connected to a second inlet port  221  on the bypass valve  257 . 
     As seen most clearly in FIG. 4A, before a pressurized gas is supplied at the first inlet port  210 , the master piston  264  separates the brake cylinder inlet port  222  from the brake cylinder outlet port  223 . In operation as shown in FIG. 4B, a pressurized gas source is fluidly connected to the first inlet port  210  which is in turn fluidly connected to the brake cylinder  256  through the first outlet port  220  of the bypass valve and the inlet port  222  of the brake cylinder. Initially the fluid path to the turbine is blocked by the master piston  264 . The pressurized gas will cause the master piston  264  to move toward the brake cylinder back end  262 , thereby urging the secondary piston  254  toward the brake collet  52  causing the brake collet  52  to clamp the guide wire  26 . The displacement of the master piston  264  past the outlet port  223  also opens the fluid path between the pressurized gas and the turbine, through the bypass valve second inlet port  221  and second outlet port  211 . It will be appreciated that the guide wire brake  200  and turbine are therefore connected in series, and the guide wire brake  200  will engage the guide wire  26  prior to spin-up of the turbine. 
     As seen most clearly in FIG. 4C, closing the bypass valve  257  by pressing the bypass button  212  fluidly connects the bypass valve first inlet port  210  to the second outlet port  211 , thereby fluidly connecting the turbine to the pressurized gas source without engaging the guide wire brake  200 . When the bypass button  212  is depressed against the biasing force of the spring  218 , the bypass valve O-rings  214 ,  216  are moved such that the first inlet port  210  and the second outlet port  211  lie between the O-rings  214 ,  216  and the first outlet port  220  and the second inlet port  221  lie on opposite sides of the O-rings  214 ,  216 , so that the pressurized gas entering the bypass valve first inlet port  210  is channeled directly to second outlet port  211  to the turbine. As with the first embodiment described above, when the pressure on the bypass valve button  212  is released, the spring  218  will return the bypass valve  257  to an open position and the serial connection to the guide wire brake  200  will be reestablished whereby the guide wire brake  200  will engage the guide wire  26 . 
     A third embodiment of the guide wire brake according to the present invention is shown schematically in FIGS. 5A,  5 B,  5 C, and  5 D. This third guide wire brake  300  embodiment comprises an elastomeric brake tube  350  with an axial channel  351  therethrough, disposed in a brake cylinder cavity  352  of a brake cylinder  356 . An annular transverse flange  354  extends outwardly from each end of the brake tube  350 . As seen most clearly in FIG. 5B, the brake tube  350  is preferably generally elliptical or eye-shaped in cross-section. The brake tube  350  is attached to the brake cylinder  356  with a pair of threaded plugs  370  that are installed at either end of the brake cylinder cavity  352 . The plugs  370  have axial orifices  371  therethrough having a diameter greater than the diameter of the guide wire  26 . The guide wire  26  runs axially through the brake tube  350  and through axial orifices  371  in the plugs  370 . A bypass valve  257 , identical to the bypass valve described above and shown in FIGS. 4A,  4 B and  4 C, is provided as shown in FIG.  5 A. The first outlet port  220  of the bypass valve is connected to an inlet port  322  of the brake cylinder  352 . An outlet port  323  of the brake cylinder  352  is coupled to the second inlet port  221  of the bypass valve  257 . As described in detail above, depressing the bypass valve button  212  against the biasing force of the spring  218  fluidly connects the bypass valve inlet port  210  to the second outlet port  211 , thereby fluidly connecting the turbine to the pressurized gas source without engaging the guide wire brake  300 . 
     In operation, a pressurized gas source is fluidly connected to the first inlet port  210  of the bypass valve  257 , and thereby to the cylinder cavity  352  through the outlet ports  220  and an inlet port  322 . The elastomeric brake tube  350  is a flexible member and the axial channel  351  therethrough is connected to atmospheric pressure through the plug axial orifices  371 . Therefore, when the pressure in the cylinder cavity  352  is increased, the elastomeric tube  350  will collapse, thereby clamping onto the guide wire  26  disposed therethrough, as seen most clearly in FIG.  5 C. The pressurized gas is fluidly connected to the turbine in series with the guide wire brake  300  through the outlet port  323  and the bypass valve  257  via the second inlet port  221  and the second outlet port  211 . The guide wire brake  300  will therefore engage the guide wire  26  prior to the pressurized gas spinning up the turbine. Brake shoes  374  may optionally be inserted in brake tube  350 , as shown in FIG. 5D, to alter the clamping characteristics of the guide wire brake  300 . 
     A fourth embodiment of the guide wire brake of the present invention is shown in FIG.  6 . The guide wire brake  400  includes a cylinder  410  having a cylindrical cavity  409 . The cylinder  410  has oppositely disposed guide wire orifices  412  that are aligned perpendicularly with the longitudinal axis of the cylinder  410  to accommodate a guide wire  26  passing through the cylinder cavity  409  An inlet orifice  414  and an outlet orifice  416  are similarly provided in the cylinder  410 . The inlet orifice  414  and the outlet orifice  416  are oppositely disposed above the guide wire orifices  412 . A brake bypass assembly  430  is slidably disposed within the cylindrical cavity  409 . A first brake shoe  436  is disposed within the cylinder cavity  409 , below the guide wire  26 . A shaft  434  having a knob  432  on its outer end extends axially through the outer cylinder  410  through an orifice  413 , and connects to the first brake shoe  436 , such that the first brake shoe  436  can be moved axially within the cylindrical cavity  409  by moving the knob  432  axially. A spring  438  biases the first brake shoe  436  to a first position wherein the first brake shoe  436  is adjacent the guide wire  26 . By pulling downward on the knob  432 , the first brake shoe  436  can be moved to a second position disposed away from the guide wire  26 . 
     An inner cylinder  450  is rotatably disposed within the cylinder cavity  409 , wherein at least the portion of the inner cylinder  450  that is adjacent inlet orifice  414  and outlet orifice  416  has an outer diameter that is approximately equal to the inner diameter of the cylinder cavity  409 . The inner cylinder  450  has a transverse flow channel  452  therethrough, located such that when inner cylinder  450  is properly oriented, the flow channel  452  fluidly connects the inlet orifice  414  and the outlet orifice  416 . A second shaft  442  having a lever  440  connected on its outer end extends axially through the cylinder  410  through an orifice  411 , and connects to the inner cylinder  450 , such that the inner cylinder  450  can be rotated within the cylinder  410  by rotating the lever  440 . A helical groove  454  is provided on the circumference of the inner cylinder  450 , extending part way around the inner cylinder  450 . The bottom of the inner cylinder  450  comprises a second brake shoe  456 , that is disposed above the guide wire  26 , opposite the first brake shoe  436 . 
     As shown in FIG. 6, a pin  420  having a first end  422  extends through the cylinder  410  such that a first end  422  slidably engages the helical groove  454  and restricts the axial movement of the inner cylinder  450 . Rotation of the inner cylinder  450  will cause the inner cylinder  450  to move axially within the cylinder cavity  409 . The inner cylinder helical groove  454  and the channel  452  are oriented such that the inlet orifice  414  and the outlet orifice  416  are fluidly connected by the channel  452  when the lever  440  is in a first position. Additionally, the length of the inner cylinder  450  is selected such that as the lever  440  is moved to the first position, the second brake shoe  456  moves adjacent the first brake shoe  436  so that the first brake shoe  436  and the second brake shoe  456  clamp the guide wire  26 . When the lever  440  is in a second position, as shown in FIG. 6, the inner cylinder  450  closes the inlet orifice  414  and the outlet orifice  416 , and the second brake shoe  456  is moved away from the guide wire  26 , whereby the guide wire  26  is unclamped. 
     It will be appreciated that the guide wire brake  400  may be disposed in series between a pressurized gas source (not shown) that can be fluidly connected to the inlet port  414  and a turbine (also not shown) that can be fluidly connected to the outlet port  416 , whereby the guide wire brake  400  will engage the guide wire  26  prior to connecting the turbine to the pressurized gas source. 
     The guide wire brake  400  can be effectively bypassed by pulling on the knob  432  of the brake bypass assembly  430 , whereby the first brake shoe  436  will be moved away from the second brake shoe  456 . It will be appreciated that bypassing the guide wire brake  400  requires constant force be applied to the knob  432 , and that upon release of the knob  432  the guide wire brake  400  will re-engage the guide wire  26 .