Abstract:
A configuration for a cryo-catheter which optimizes both the catheter&#39;s outer diameter and the size of the catheter&#39;s internal refrigerant flow path is described. Specifically, the inner dimensions of the cryo-catheter are configured to accommodate a pre-selected flow of refrigerant into the catheter&#39;s distal tip, and a return flow of refrigerant from the distal tip. The return flow is established in the void spaces between a refrigerant supply line and the inner wall of the catheter body. The available void space varies along the catheter length and depends on the presence/absence of various catheter accessories (i.e. pull wires, pressure tubes, etc.) which typically only extend through a portion of the catheter length. The disclosed configuration ensures that the cryo-catheter does not operate in a refrigerant limited condition, maintains the refrigerant as a liquid in the supply tube, and maintains the return line pressure at about 1 atmosphere.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to systems and methods for cryoablating tissue. More particularly, the present invention pertains to a configuration for a cryo-catheter having an active articulation system. The present invention is particularly, but not exclusively, useful as a configuration for a cryo-catheter which optimizes both the catheter&#39;s outer diameter and the size of the catheter&#39;s internal refrigerant flow path. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cryoablation has been successfully used in various medical procedures to destroy or deactivate selected tissues. In this context, it has been determined that cryoablation procedures can be particularly effective for curing heart arrhythmias, such as atrial fibrillation. It is believed that at least one-third of all atrial fibrillations originate near the ostia of the pulmonary veins, and that the optimal treatment technique is to treat these focal areas through the creation of circumferential lesions around the ostia of these veins. 
         [0003]    Typically, to cryoablate selected tissue in and around the heart in a non-invasive procedure, a cryo-catheter Is employed. In this regard, tissue in and around the heart is typically accessed from a peripheral artery such as the femoral or brachial artery. From the peripheral artery, the distal end of the catheter must navigate through the curves and bends of a narrow and tortuous vascular tree to reach a targeted area. In some cases, an introducer sheath is first inserted into the vasculature to establish a mechanical pathway to the treatment site. This allows the cryo-catheter to pass within the sheath from the peripheral artery to the treatment site. To be successful in locating the distal tip of a cryo-catheter at a treatment site, it is important that the catheter be flexible and have a relatively small outside diameter. On the other hand, modern cryo-catheters typically require the incorporation of a number of sophisticated, internal catheter systems that must all somehow fit within the thin, low profile catheter. These systems often include a first passageway to deliver a refrigerant from an extracorporeal location to the distal tip for expansion at the distal tip. A second passageway is also required to evacuate the expanded refrigerant from the tip. 
         [0004]    In addition to the internal systems described above, various monitoring systems are often employed to measure tip temperature, tip pressure and electrical signals from the heart (i.e. EKG signals). These systems often require pressure tubes, wires, sensors, electrode bands and other monitoring components. Lastly, but perhaps equally important, modern cryo-catheters often include internal systems to articulate the distal tip of the catheter. These articulation systems can be used to steer the cryo-catheter during its journey through the vasculature and to manipulate the distal tip of the catheter into contact with selected tissue at a treatment site. For this purpose, these articulation systems typically include pull wires, sheath springs, deflection support structures such as springs, and other peripheral components. Thus, all of these system components need to somehow fit within a low profile cryo-catheter while still leaving sufficient room along the entire length of the catheter to deliver an ample quantity of refrigerant to the distal tip and evacuate expanded refrigerant from the tip. 
         [0005]    With the above in mind, for a typical medical procedure, cryoablation begins at temperatures below approximately minus twenty degrees Centigrade (−20° C.). For the effective cryoablation of tissue, however, much colder temperatures are preferable. With this goal in mind, various fluid refrigerants (e.g. nitrous oxide N 2 O) have normal boiling point temperatures (i.e. the boiling point temperature at 1 atmosphere pressure) as low as minus eighty eight degrees Centigrade (−88° C). An important consideration in this regard is the fact that the temperature at which a refrigerant boils is dependant on the pressure that the refrigerant is experiencing. Specifically, for a refrigerant such as nitrous oxide, the boiling temperature increases with increases in boiling pressure. 
         [0006]    A low ablation temperature, however, is typically not sufficient to efficiently cryoablate tissue. Specifically, it is also necessary that there is a sufficient refrigeration potential to effectively freeze tissue. In order for a system to both attain and maintain a suitable cryoablation temperature, while providing the necessary refrigeration potential to effect cryoablation of tissue, several physical factors need to be considered. 
         [0007]    In this regard, it is well known that when a fluid boils (i.e. changes from a liquid state to a gaseous state) a significant amount of heat is transferred to the fluid from its surroundings. With this in mind, consider a liquid that is not boiling, but which is under a condition of pressure and temperature wherein effective evaporation of the liquid ceases. A liquid in such condition is commonly referred to as being “fully saturated.” It will then happen, as the pressure on the saturated liquid is reduced, the liquid tends to boil and extract heat from its surroundings. Initially, the heat that is transferred to the fluid is generally referred to as latent heat. More specifically, this latent heat is the heat that is required to change a fluid from a liquid to a gas, without any change in temperature. For some fluids, this latent heat transfer can be considerable. In this context, the refrigeration potential is a measure of the capacity of a system to extract energy from its surroundings at a fixed temperature. 
         [0008]    An important consideration for the design of any refrigeration system is the fact that heat transfer is proportional to the difference in temperatures (ΔT) between the refrigerant and the body that is being cooled. Importantly, heat transfer is also proportional to the amount of surface area of the body being cooled (A) that is in contact with the refrigerant. In addition to the above considerations (i.e. ΔT and A); when the refrigerant is a fluid, the refrigeration potential of the refrigerant fluid is also a function of its mass flow rate. Specifically, the faster a heat-exchanging fluid refrigerant can be replaced (i.e. the higher its mass flow rate), the higher the refrigeration potential will be. This notion, however, has it limits. 
         [0009]    As is well known, the mass flow rate of a fluid through a duct/tube results from a pressure differential on the fluid. More specifically, it can be shown that as a pressure differential starts to increase on a refrigerant fluid in a system, the resultant increase in the mass flow rate of the fluid will also increase the refrigeration potential of the system. This increased flow rate, however, creates additional increases in the return pressure (i.e. back pressure) that will result in a detrimental increase in the boiling point temperature of the refrigerant. Thus, for relatively low mass flow rates, increases in the mass flow rate of the refrigerant will cause lower temperatures. Refrigerant flow in this range is said to be “refrigeration limited.” On the other hand, for relatively high mass flow rates, increases in the mass flow rate actually cause the temperature of the refrigerant to rise. Flow in this range is said to be “surface area limited.” Because a cryo-catheter refrigeration system is least efficient at higher temperatures, operation under “refrigeration limited” conditions is generally avoided. 
         [0010]    From the above discussion, it can be appreciated that a cryo-catheter refrigeration system must be capable of performing three basic functions. First, it must deliver the refrigerant to the distal tip of the cryo-catheter in a liquid state so that the liquid can boil at the tip and absorb latent heat. Second, the system must evacuate the expanded refrigerant and maintain the pressure where the refrigerant boils at a preselected pressure to ensure that the refrigerant boils at a low temperature. Lastly, the system must perform the first two functions at a sufficient refrigerant mass flow rate to generate the necessary refrigeration potential to efficiently cryoablate tissue. It is to be further appreciated that the satisfaction of these three requirements is highly dependent on the size of the flow passages and expansion chambers used to deliver the refrigerant to the cryo-catheter&#39;s distal tip and evacuate the expanded refrigerant from the tip. 
         [0011]    In light of the above, it is an object of the present invention to provide a cryo-catheter configuration which optimizes both the catheter&#39;s outer diameter and the size of the catheter&#39;s internal refrigerant flow path. It is another object of the present invention to provide a cryo-catheter configuration that ensures that the cryo-catheter does not operate in a refrigerant limited condition. It is yet another object of the present invention to provide a configuration for a cryo-catheter that cooperates to maintain a refrigerant in a liquid state as it transits through a supply tube and simultaneously maintains the pressure in a refrigerant return line at about 1 atmosphere. Yet another object of the present invention is to provide a cryo-catheter configuration which is easy to assemble, relatively simple to implement, and comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention is directed to a configuration for a cryo-catheter which optimizes both the catheter&#39;s outer diameter and the size of the catheter&#39;s internal refrigerant flow path. In particular, the outer diameter of the catheter is minimized to allow the catheter to be advanced, percutaneously, through a patient&#39;s vasculature. On the other hand, the inner dimensions of the cryo-catheter are configured to accommodate a pre-selected flow of refrigerant into the catheter&#39;s distal tip, and importantly, a return flow of refrigerant from the distal tip. 
         [0013]    In greater structural detail, the cryo-catheter has a proximal end and a distal end and includes a tip at the distal end. The proximal end of the cryo-catheter is attached to a catheter handle. Between the handle and the tip, the cryo-catheter includes a two-part catheter body having an articulation segment and a braided segment. The braided segment extends distally from the catheter handle to the proximal end of the articulation segment. For the cryo-catheter, the articulation segment is positioned between the distal end of the braided segment and the cryo-catheter tip. Together, the braided segment and articulation segment establish a central lumen which extends from the catheter handle to the catheter tip. With this cooperation of structure, the central lumen has a first cross-sectional area in the articulation segment and a second cross-sectional area in the braided segment. 
         [0014]    To cool the cryo-catheter&#39;s distal tip, a two-part refrigerant supply line is disposed in the central lumen. More specifically, the supply line includes a high pressure supply tube and a flow restricting tube (e.g. capillary tube). Structurally, the capillary tube is attached to and extends from a distal end of the high pressure supply tube. In the operation of the cryo-catheter, a regulated flow of liquid refrigerant is introduced into the proximal end of the high pressure supply tube. With this arrangement, the refrigerant traverses the supply tube, passes through the capillary tube and then outflows into an expansion chamber at the cryo-catheter&#39;s distal tip. Expanded refrigerant is then exhausted from the chamber through a low pressure return line that is established in the void spaces between the outer wall of the supply line and the inner wall of the catheter body. It is important to note that the exact nature and dimensions of these void spaces varies along the length of the cryo-catheter. Specifically, at each location along the length of the catheter, the available void space will depend on the size and extent of other catheter structures (i.e. accessories) that are present in the central lumen at that particular location. These catheter accessories can include, but are not necessarily limited to, pull wires, sheath springs, sheath spring guide tubes, thermocouple wires, electrode wires and pressure measurement tubes. For the cryo-catheter, each of these accessories extends through some or all of the length of the catheter. 
         [0015]    The dimensions of the refrigerant flow paths are functionally significant and typically must be sized with several operational objectives in mind. Specifically, these dimensions control the pressures and flow rates at critical points along the refrigerant flow path. In greater detail, the pressure within the high pressure supply tube must be sufficient to maintain the refrigerant in a liquid state throughout the length of the supply tube. On the other hand, the pressure in the expansion chamber must be sufficiently low to allow for full refrigerant vaporization within the chamber. As a consequence, the capillary tube must create the necessary pressure reduction between the high pressure supply tube and the low pressure expansion chamber. 
         [0016]    In addition to the requirements described above, the refrigerant pressures and flow path dimensions are generally designed to avoid operation of the cryo-catheter in a refrigerant limited condition. This condition is typically characterized as having a relatively low supply pressure for refrigerant entering the supply tube together with a relatively low return pressure. In the refrigerant limited condition, the catheter is typically unable to achieve the lowest possible cryoablation temperature at the catheter&#39;s distal tip. Quantitatively, the expansion chamber is generally maintained at a pressure of approximately 1 atm. In addition, the accessories and fluid supply line are arranged to leave a portion of a first cross-sectional area void in the articulation segment and leave a portion of said second cross-sectional area void in the braided segment. These voids establish a return path for a flow of gaseous refrigerant through the central lumen. Preferably, the cryo-catheter is configured with the second cross-sectional area void being greater than about thirty percent of the first cross-sectional area. As a consequence, the return path in the articulation segment has a somewhat greater flow capacity than the return path in the braided segment. With this interactive cooperation of structure, refrigerant is maintained as a liquid in the high pressure supply tube while maintaining the expansion chamber at a pressure of about 1 atm. to ensure that the cryo-catheter does not operate in a refrigerant limited condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0018]      FIG. 1  is a perspective view of a cryo-catheter and catheter handle in accordance with the present invention; 
           [0019]      FIG. 2  is a side plan view of a distal portion of the cryo-catheter shown in  FIG. 1 , shown juxtaposed with a layout of internal catheter accessories to illustrate the distal extent of each of the catheter accessories; 
           [0020]      FIG. 3  is a cross-sectional view of the cryo-catheter including internal accessories as seen along line  3 - 3  in  FIG. 2 ; and 
           [0021]      FIG. 4  is a cross-sectional view of the cryo-catheter including internal accessories as seen along line  4 - 4  in  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring initially to  FIG. 1 , a system (generally designated  10 ) having a cryo-catheter  12  and catheter handle  14  is shown. For the present invention, the system  10  can be used as part of a cryoablation apparatus to cryoablate a lesion in a body conduit of a patient (patient not shown). Although the system  10  is described herein for a catheter  12 , those skilled in the pertinent art will appreciate that the systems and methods described herein can be implemented with other applicators such as a cryo-probe (not shown) that is configured to contact and ablate exposed tissue. 
         [0023]    As indicated in  FIG. 1 , the cryo-catheter  12  includes an articulation segment  16  that can be deflected using the catheter handle  14  into different configurations and orientations.  FIG. 1  further shows that the cryo-catheter  12  includes a braided segment  18  that extends distally from the catheter handle  14  to the articulation segment  16 . It can be further seen that the cryo-catheter  12  includes a distal tip  20  that is attached to and extends distally from the articulation segment  16 . In use, the distal tip  20  of the cryo-catheter  12  is typically inserted into a patient through a peripheral artery, such as the femoral artery, and advanced through the patient&#39;s vasculature until the distal tip  20  is positioned at a targeted location such as a location inside a heart chamber. Although the system  10  is capable of performing a cryoablation procedure in an upper body vessel, such as a pulmonary vein, those skilled in the pertinent art will quickly recognize that the use of the system  10 , as herein described, is not limited to use in any one type of vessel, but, instead can be used in vascular conduits and other ductal systems throughout the human body. 
         [0024]    Referring now to  FIG. 2 , a distal portion of the cryo-catheter  12  is shown together with the distal portions of the various internal catheter accessories. A sectional view of the internal catheter accessories that are present in the articulation segment  16  is shown in  FIG. 3  and a sectional view of the internal catheter accessories that are present in the braided segment  18  is shown in  FIG. 4 . As seen in  FIG. 2 , the cryo-catheter  12  includes the supply line  22  having a high pressure supply tube  24  and a capillary tube  26 . In a typical arrangement, the supply tube  24  is sized to impart a negligible impedance to the flow of refrigerant through the supply tube  24 . An exemplary supply tube  24  has an inside diameter in the range of 0.017-0.022 inches, an outside diameter in the range of 0.025-0.030 inches and a length of about 73 inches. On the other hand, for the system  10 , the capillary tube  26  is typically sized with a much greater impedance than the high pressure supply tube  24 , to thereby cause most of the supply line pressure drop to occur in the capillary tube  26 . Functionally, this results in a concentration of cooling power at the distal tip  20  of the catheter  12 . Comparing  FIGS. 3 and 4 , it can be seen that the capillary tube  26  has a much smaller inside diameter than the high pressure supply tube  24 . As best seen in  FIG. 2 , the high pressure supply tube  24  terminates at a distal end  28  in the braided section  18 . For the embodiment shown, the distal end  28  is located several inches proximal to the articulation segment  16 .  FIG. 2  also shows that the capillary tube  26  is attached to the distal end  28  of the supply tube  24 , extends therefrom through the articulation segment  16 , and terminates at a distal end  30  in the distal tip  20 . An exemplary capillary tube  26  has an inside diameter in the range of 0.006-0.008 inches, an outside diameter in the range of 0.016-0.018 inches and a length in the range of 4.9 inches to 9.8 inches. 
         [0025]    For the system  10  shown in  FIG. 1 , a refrigerant supply unit (not shown) is attached to the handle  14  to supply a refrigerant to the supply line  22 . At the refrigerant supply unit, various valves, pre-cooling circuits, control systems and other components are connected to a refrigerant tank and configured to produce a regulated flow of sub-cooled, liquid refrigerant which is then directed into the supply line  22 . In particular, a fluid refrigerant, such as Nitrous Oxide, is used that transitions from a liquid state to a gaseous state as it outflows from the capillary tube  26  to cool the distal tip  20 . A suitable refrigerant supply unit for delivering a refrigerant in a liquid state to a supply line  22  for transition to a gaseous state during outflow from a capillary tube  26  is disclosed in co-pending, co-owned U.S. patent application Ser. No. 10/243,997, entitled “A Refrigeration Source for a Cryoablation Catheter” and filed on Sep. 12, 2002. Co-pending U.S. patent application Ser. No. 10/243,997 is hereby incorporated by reference herein. In a typical application, Nitrous Oxide refrigerant is input into the proximal end of the high pressure supply tube  24  at a pressure in the range of about 300 to 500 psi. 
         [0026]    With reference to  FIG. 2 , refrigerant from the supply unit (not shown) traverses the supply tube  24 , passes through the capillary tube  26  and then outflows into an expansion chamber formed in the cryo-catheter&#39;s distal tip  20 . Heat absorbed by the refrigerant during the liquid to gas phase transition (i.e. latent heat) cools the distal tip  20 . Expanded refrigerant is then exhausted from the expansion chamber through a low pressure return line. As best seen in  FIGS. 3 and 4 , the low pressure return line is established in the void spaces  32  that are formed in the central catheter lumen. Typically, suction is applied to the low-pressure return line via an extracorporeally located vacuum pump. Refrigerant suction pressures and flow path dimensions are generally designed to avoid operation of the cryo-catheter  12  in a refrigerant limited condition. Quantitatively, the pressure in the distal portion of the return line is generally maintained in a range between 0.5 atm. and 2 atm. 
         [0027]    Comparing  FIG. 3  with  FIG. 4 , it can be seen that the exact nature and dimensions of these void spaces  32  varies along the length of the cryo-catheter  12 . Specifically, at each location along the length of the cryo-catheter  12 , the available void space  32  will depend on the size and extent of the catheter accessories present in the central lumen at that particular location. These catheter accessories will now be described in greater detail. 
         [0028]    With cross reference to  FIGS. 2 and 3 , an understanding of the articulation segment  16  and the accessories that are present in the articulation segment  16  can be obtained. As shown there, the articulation segment  16  of the cryo-catheter  12  includes a deflection structure  34 , which for the embodiment shown is a metal, helically coiled, spring. For the articulation segment  16 , the deflection structure  34  is positioned in a flexible outer tube  36 . In terms of size, the outer tube  36  has a catheter French size that is in the range of 8-10, allowing the catheter  12  to pass through a patient&#39;s vasculature. As detailed further below, the size of the outer tube  36  is preferably as small as possible, subject to the condition that an adequately sized, low pressure return line is established. 
         [0029]    With regard to the deflection structure  34 , although a spring is shown, it is to be appreciated that other types of deflection structures can be used. For example, a deflection structure made of a thin walled, stainless steel material (e.g. 304 alloy) that has been cut with a laser to form transverse slits can be used. A more detailed description of the laser cut deflection structure  34  can be found in co-pending, co-owned U.S. patent application Ser. No. 10/774,665, filed Feb. 9, 2004, which is hereby incorporated by reference in its entirety herein and co-pending, co-owned U.S. patent application Ser. No. 10/876,312 which is also hereby incorporated by reference herein. 
         [0030]    To deflect the articulation segment  16 , the cryo-catheter  12  includes a pull wire  38  having a distal end  40  that is attached to the distal tip  20  and a proximal end (not shown) that is operationally attached to a control wheel (not shown) on the handle  14  (see  FIG. 1 ). In use, the control wheel can be activated to place the pull wire  38  in tension to deflect the distal tip  20 .  FIGS. 2 and 4  show that a central portion of the pull wire  38  is disposed in a metal, helically coiled, sheath spring  42 . The proximal end (not shown) of the sheath spring  42  is rigidly attached to the handle  14  (see  FIG. 1 ), extends therefrom and terminates in a distal end  44  that is located approximately adjacent to the joint where the braided segment  18  attaches to the articulation segment  16 . Functionally, the sheath spring  42  provides a compression force in response to the pull wire force, which in turn, allows for articulation of the distal tip  20 . An exemplary sheath spring has an inside diameter in the range of 0.008-0.020 inches, an outside diameter in the range of 0.0115-0.025 inches and is made of a wire having a diameter in the range of 0.004-0.006 inches and an overall length of about 40 inches. It can be further seen in  FIGS. 2 and 4  that a portion on the sheath spring  42  is disposed within a sheath spring guide tube  46 . Typically, the sheath spring guide tube  46  extends from the handle  14  (see  FIG. 1 ) and terminates at a distal end  48  that is located about one and one-half inches proximal to the articulation segment  16 . Functionally, the sheath spring guide tube  46  is used for support and to prevent gas leakage into the sheath spring/pull wire assembly. 
         [0031]      FIG. 2  also shows that the cryo-catheter  12  includes an EKG band electrode  50  and corresponding electrode wire  52 . As shown, for the cryo-catheter  12 , the electrode  50  is located near the distal end of the articulation segment  16 . From the electrode  50 , the electrode wire  52  extends proximally through the central lumen and extends within both the articulation segment  16  and the braided segment  18  (see also  FIGS. 3 and 4 ). From the braided segment  18 , the electrode wire  52  typically passes through the handle  14  (see  FIG. 1 ) to an EKG monitor (not shown). For the cryo-catheter  12 , the electrode wire  52  is typically a Nickel wire having an outside diameter in the range of 0.008-0.011 inches that is disposed in a polyimide sleeve  54 . The use of a sleeve  54  over the wire  52  prevents electrical shorts with other components of the cryo-catheter  12 .  FIGS. 2 and 3  also show that a thermocouple wire set  56  is disposed in the central lumen of the cryo-catheter  12  to measure a distal tip  20  temperature. As shown, the thermocouple wire set  56  extends through both the braided segment  18  and articulation segment  16  and terminates in a distal end  58  that is located in the distal tip  20 . For the cryo-catheter  12 , the thermocouple wire set  56  extends through the handle  14  to a temperature monitor (not shown). 
         [0032]    As best seen in  FIGS. 2 and 4 , the cryo-catheter  12  includes a pressure measurement tube  60  that is disposed in the central lumen of the braided segment  18 . As shown, the pressure measurement tube  60  has a distal end  62  that is positioned at a location proximal to the joint where the braided segment  18  attaches to the articulation segment  16  (i.e. about 1 inch proximal to the articulation segment  16 ). From its distal end  62 , the pressure measurement tube  60  extends proximally through the handle  14  (see  FIG. 1 ) to a pressure monitor (not shown) which measures a pressure at the proximal end of the pressure measurement tube  60 . Together, the pressure measurement tube  60  and pressure monitor cooperate to provide an estimate of the pressure in the low pressure return line near the distal tip  20 . An exemplary pressure measurement tube  60  has an inside diameter in the range of 0.017-0.022 inches, an outside diameter in the range of 0.025-0.030 inches and a length of about 73 inches. 
         [0033]    As indicated above, an important functional consideration for the cryo-catheter  12  is its ability to transfer a fluid refrigerant to the catheter&#39;s distal tip  20  as a liquid, and to then exhaust the refrigerant back through both the articulation segment  16  and the braided segment  18 , as a gas. As also indicated above, however, the outside dimensions of the cryo-catheter  12  are constrained by anatomical requirements. Operationally, these outside dimensions necessarily impact on the economies that can be obtained for fluid refrigerant flow inside the cryo-catheter  12 . With these constraints in mind, the consequent requirement is that there be the maximum possible void space within the cryo-catheter  12  for exhausting the gas refrigerant from the cryo-catheter  12 . Both the articulation segment  16  and the braided segment  18  are involved here. 
         [0034]    Table A, shown below, provides exemplary maximum and minimum dimensions for specified components that may be incorporated into the cryo-catheter  12  and positioned in the articulation segment  16 . Table A is, perhaps, best appreciated by cross-referencing it with  FIG. 3 . 
         [0000]                                                                                                                                                                                TABLE A                       Min Meas.   Max Meas.                                    Deflection Structure (34)                Inner Diameter    7.8E−02   7.900E−02   in.           Area   4.778E−03   4.902E−03   sq. in.            Capillary Tube (26)                Outer Diameter   1.600E−02   1.800E−02   in.           Area   2.011E−04   2.545E−04   sq. in.            Pull Wire (38)                Outer Diameter    1.0E−02   1.100E−02   in.           Area   7.854E−05   9.503E−05   sq. in.            Electrode Wire (52)                Outer Diameter   8.000E−03   1.100E−02   in.           Area   5.027E−05   9.503E−05   sq. in.            Thermocouple Wire Set (56)                Outer Diameter   7.000E−03   8.000E−03   in.           Area   3.848E−05   5.027E−05   sq. in.           Void Space   4.410E−03   4.407E−03   sq. in.           Area (32)                        
Using the numbers provided above, it is easily determined that the void space within the articulation segment  16  will be in a range of about 89.4% to about 91.4% of the space available inside the deflection structure  34  of articulation segment  16 .
 
         [0035]    Similar to Table A, Table B shown below, provides exemplary maximum and minimum dimensions for specified components that may be positioned in the braided segment  18 . Table B is, perhaps, best appreciated by cross-referencing it with  FIG. 4 . 
         [0000]                                                                                                                                                                                                            TABLE B                       Min Meas.   Max Meas.                                    Catheter Cross Section                Inner Diameter   9.900E−02   9.950E−02   in.           Area   7.698E−03   7.776E−03   sq. in.            Supply Tube (24)                Outer Diameter   2.500E−02   3.000E−02   in.           Area   4.909E−04   7.069E−04   sq. in.            Spring Sheath (42)                Outer Diameter   1.150E−02   2.500E−02   in.           Area   1.039E−04   4.909E−04   sq. in.            Pressure Measuring Tube (60)                Outer Diameter   2.500E−02   3.000E−02   in.           Area   4.909E−04   7.069E−04   sq. in.            Electrode Wire (52)                Outer Diameter   8.000E−03   1.100E−02   in.           Area   5.027E−05   9.503E−05   sq. in.            Thermocouple Wire Set (56)                Outer Diameter   7.000E−03   8.000E−03   in.           Area   3.848E−05   5.027E−05   sq. in.           Void Space   6.524E−03   5.726E−03   sq. in.           Area (32)                        
Using the numbers provided above, it is easily determined that the void space within the braided segment  18  will be in a range of about 73.0% to about 84.2% of the space available inside the braided segment  18 .
 
         [0036]    An important observation to be made from Tables A and B is the fact that, although the percentage of void space in articulation segment  16  is greater than the percentage of void space in the braided segment  18 , the actual void space in the braided segment  18  is greater. As indicated above, this relationship is established to ensure maximum operational efficiency. 
         [0037]    While the particular Cryo-applicator Cross-Section Configuration and corresponding methods of use as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.