Abstract:
A device, system and method for controlling the temperature differential between the medium within the cryosurgical instrument and the external temperature of the shaft, apart from at the cryotip itself, uses a fluid medium supplied within an internal space between the shaft and an intermediate lumen positioned between the shaft and a central feeding lumen of the cryosurgical instrument. The temperature of the fluid medium is controlled to provide control of the temperature differential.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a system and method for insulating a cryosurgical instrument and in particular, to such a system and method for maintaining a controlled external temperature for at least a portion of the probe shaft. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cryoprobes or catheters frequently experience problems of temperature control, particularly with regard to maintaining a temperature differential between the contents of the cryoprobe or catheter, which are very cold, and the outer shaft, which is desirably maintained at a higher temperature, outside of the cryotips themselves. The outer shaft is in contact with body tissues which may be damaged by excessively low temperatures of this shaft, as only the portion of the body tissues which are surrounding the cryotip should be frozen. 
         [0003]    In addition, cryosurgical catheters must have a great deal of flexibility, especially when they are used for cardiac interventions. At the same time the closed distal end (cryotip) of such a probe or catheter must provide in many cases high specific freezing capacity at sufficiently low temperatures. Various attempted solutions to this problem have been provided with regard to thermal insulation of lateral non-operating walls of cryosurgical instruments. 
         [0004]    For example, U.S. Pat. No. 3,971,383 proposes a cryogenic surgical instrument with a coaxial assembly of flexible lumens; the inner lumen is connected to a supply of cryogenic liquid, and the space between the outer wall of the inner lumen and the next lumen forms a return line for evaporated cryogenic liquid which is vented to the atmosphere. The space between the outermost one of the coaxial lumens and the intermediate lumen contains a gas, such as normal butane, serving for thermal insulation of the inner and intermediate lumens. 
         [0005]    U.S. Pat. No. 5,573,532 describes a cryosurgical instrument, which comprises lumens of cryogenic fluid supply and return of cryogenic fluid vapors; these lumens are situated concentrically and the return lumen is sealed with a cryotip. Vacuum insulation of the return lumen is taught, which is very expensive and has low reliability. In addition, this vacuum insulation limits flexibility of the probe, especially when it has significant length and is used as a catheter. 
         [0006]    U.S. Pat. No. 5,674,218 describes a cryosurgical instrument, a system and method of cryosurgery. According to this patent a cryogenic liquid (preferably, liquid nitrogen) is initially sub-cooled below its normal boiling point and then it is supplied into the open proximal end of the internal supply line. The outer lumen of the cryosurgical instrument is provided with active vacuum insulation. 
         [0007]    U.S. Pat. No. 7,288,089 describes an enhanced method and device intended to treat atrial fibrillation or inhibit or reduce restenosis following angioplasty or stent placement. A balloon-tipped catheter is disposed in the area treated or opened through balloon angioplasty immediately following angioplasty. The balloon, which can have a dual balloon structure, may be delivered through a guiding catheter and over a guidewire already in place. A fluid such as a perfluorocarbon flows into the balloon to freeze the tissue adjacent the balloon, this cooling being associated with reduction of restenosis. A similar catheter may be used to reduce atrial fibrillation by inserting and inflating the balloon such that an exterior surface of the balloon contacts at least a partial circumference of the portion of the pulmonary vein adjacent the left atrium. In another embodiment, blood perfusion is performed simultaneously. In another embodiment, tissue contacted by the cryoablation catheter, which should not be ablated, is protected against damage by a separate heating step. However, this invention is limited to balloon catheters. 
         [0008]    U.S. Pat. No. 7,273,479 describes methods and systems which are applied for cooling an object with a cryogen having a critical point defined by a critical-point pressure and a critical-point temperature. A pressure of the cryogen is raised above a pressure value determined to provide the cryogen at a reduced molar volume that prevents vapor lock. Thereafter, the cryogen is placed in thermal communication with the object to increase a temperature of the cryogen along a thermodynamic path that maintains the pressure greater than the critical-point pressure for a duration that the cryogen and object are in thermal communication. 
         [0009]    U.S. Pat. No. 7,255,693 discloses a cryosurgical catheter which is heated in order to prevent its freezing within the lumen of an endoscope. The catheter is to be used with an endoscope to perform cryoablation on an internal tissue; e.g., the esophagus. Electric conductivity to produce heat employs an electrical conductive coating on the catheter. Also, disclosed is a fitting for use with a catheter comprising both a connection for receiving gas and an electrical connection. 
         [0010]    U.S. Pat. No. 6,562,030 describes a cryocatheter which includes a catheter body defining a coolant flow path, a catheter tip exposed to the coolant flow path, and a heating element associated with the catheter tip. The heating element can be disposed entirely or partially within the catheter tip. Alternatively, the heating element can be external to the catheter tip. The heating element can include an electrically resistive element. However, it should be noted that in any case the heating element is an active electrical element. 
         [0011]    US patent application No. 20070276360 discloses a cryosurgical catheter which is heated in order to prevent its freezing within the lumen of an endoscope. The catheter is to be used with an endoscope to perform cryoablation on an internal tissue; e.g., the esophagus. Electric conductivity to produce heat employs an electrical conductive coating on the catheter. Also, disclosed is a fitting for use with a catheter comprising both a connection for receiving gas and an electrical connection; again note that electrical power is required for the heating element. 
         [0012]    In addition, U.S. Pat. Nos. 6,182,666, 6,095,149, 5,906,612, 5,899,897, 5,658,276 describe different versions of application of electrical heating elements for thermal insulation of untreated tissue. 
         [0013]    U.S. Pat. Nos. 5,910,104 and 6,457,212 describe the application of thermo-insulating disposable sheaths, which are situated on shafts of cryosurgical instruments. 
       SUMMARY OF THE INVENTION 
       [0014]    The background art does not teach or suggest a simple and inexpensive mechanism for maintaining a controlled temperature differential between material inside a cryosurgical instrument and the external temperature of the shaft, away from the tip. The present invention overcomes these drawbacks of the background art, by providing a system and method for controlling the temperature differential between the material within the cryosurgical instrument and the external temperature of the shaft, apart from at the cryotip itself. The present invention uses a fluid within a jacket surrounding the shaft or between an intermediate lumen positioned coaxially with the central feeding lumen containing the cryogen and the outer shaft. The temperature of the fluid is controlled to maintain and/or to induce the above temperature differential. By “&#39;fluid” it is understood that any gas, liquid or other material may optionally be used, alone or in combination. According to some embodiments of the present invention, a gas is preferred. According to other embodiments of the present invention, the cryosurgical instrument is preferably a cryocatheter which is optionally and more preferably flexible. According to other embodiments of the present invention, the cryosurgical instrument is preferably a cryoprobe which may optionally be non-flexible or less flexible. 
         [0015]    A cryosurgical instrument and its accessory system are based on application of cryogen liquids with sufficiently low boiling temperatures at pressures in the interval from below one atmosphere through several atmospheres. On the other hand, these temperatures are sufficiently high for the use of gases with low thermal conductivity such as krypton as a dynamic or static thermal insulator, when the operating pressure of these gases is maintained at such a level that these gases are in their superheated condition, so that they cannot condense at the operating temperatures of the cryogen. 
         [0016]    It should be noted that mixtures of some gases can be implemented as the cryogen and/or as thermo-insulating gas. 
         [0017]    However, as a preferred embodiment, the present invention preferably comprises liquid CF4 (Freon R 14) as a working cryogen and krypton as a thermo-insulating gas. According to another embodiment, liquid nitrogen is used as a freezing agent and warm gaseous nitrogen as an active thermo-insulating medium. Preferably a cryosurgical instrument according to the present invention comprises an external elongated shaft; a central feeding lumen positioned in the external elongated shaft for receiving a cryogen; a cryotip, which is joined sealingly with the distal edge of the external elongated shaft; an intermediate lumen positioned coaxially between the central feeding lumen of the external elongated shaft and joined sealingly with the external elongated shaft by its distal and proximal flanges, which features a fluid medium for controlling the temperature differential between the external shaft and the central feeding lumen. 
         [0018]    In addition, the proximal end of the central feeding lumen is preferably terminated by an inlet connection for receiving cryogen, while the proximal section of the elongated external shaft, which seals the internal space between the central feeding lumen and this shaft, is preferably provided with an outlet connection for permitting the cryogen gas to be exhausted out. A proximal section of the elongated external shaft, which bounds the internal space with the intermediate lumen, is provided as well with an inlet connection. In another embodiment, this last inlet connection can serve alternatively as an inlet and outlet connection. 
         [0019]    The cryosurgical instrument preferably operates as follows. The working cryogen (liquid nitrogen, CF4 or another cryogen with a sufficiently low boiling temperature in the desired range of pressures) is supplied in the form of separated pulses with sufficiently low on-off ratio into the central feeding lumen via its proximal inlet connection. By “sufficiently low on-off ratio” it is meant that the timing of the pulses is such so as to cool the tip sufficiently, preferably while maintaining the presence of continuously boiling cryogen at the tip. The liquid component of the working cryogen accumulates in the internal space of the cryotip and is preferably constantly boiling with cooling of the wall of the cryotip and freezing of the surrounding tissue. 
         [0020]    At the same time a heating and/or thermo-insulating medium is preferably supplied into the space between the elongated external shaft and the intermediate lumen via its inlet-outlet connection. In such a way the pressure in the space between the elongated external shaft and the intermediate lumen is elevated. 
         [0021]    Thereafter the pressurized gas between the elongated external shaft and the intermediate lumen is purged through this inlet-outlet connection. 
         [0022]    After terminating the cryogen pulse, the pressurized heating and thermo-insulating medium again enters the internal space between the elongated external shaft and the intermediate lumen. 
         [0023]    In another embodiment, the thermo-insulating medium is optionally introduced into the space between the elongated external shaft and the intermediate lumen periodically. In yet another embodiment, the distal flange of the intermediate lumen is provided with through openings for passage of the thermo-insulating medium. In such a way, the thermo-insulating medium flows via the gap between the elongated external shaft and the intermediate lumen and mixes with the evaporated cryogen exhausted from the cryotip. This allows the temperature of the exhausted gas to be elevated and, in such a way, to decrease the cooling effect of this exhausted gas on the elongated external shaft. The thermo-insulating medium may optionally be provided to space between the intermediate lumen and the elongated external shaft during the intervals between cryogen pulses or alternatively (and optionally) may be provided continuously if the pressure of the thermo-insulating medium upon entering the gap between the elongated external shaft and the intermediate lumen exceeds the pressure of the exhausted cryogen at the distal section of the gap between the central feeding lumen and the intermediate lumen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1   a  is an axial cross-section of an assembled cryoprobe according to the present invention in some embodiments; 
           [0025]      FIG. 1   b  is an axial cross-section of the male unit of the above cryoprobe;  FIG. 1   c  is an axial cross-section of the female unit of the cryoprobe of  FIG. 1   a ; and 
           [0026]      FIG. 2  is an axial cross-section of another embodiment of a cryoprobe according to the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]      FIG. 1   a ,  FIG. 1   b  and  FIG. 1   c  show an axial cross-section of a cryoprobe according to some embodiments of the present invention with an intermediate lumen for receiving a temperature controlling fluid, preferably a heating and insulating gas, and a quick coupling construction for easy assembly. This embodiment of cryoprobe  100  comprises the elongated external shaft  101 , which terminates at its distal edge with cryotip  102 . A central feeding pipe  103  is situated in shaft  101 . Preferably, the proximal end of the central feeding pipe  103  protrudes from the proximal end of shaft  101 . The proximal sections of the elongated external shaft  101  and the central feeding pipe  103  serve for installation of a male unit  119  for quick coupling. The extreme proximal section of the shaft  101  is preferably somewhat radially projected to prevent movement past a certain point with regard to male unit  119 . 
         [0028]    Thermal insulation of the elongated external shaft  101  is ensured by an intermediate tube  104  with two flanged ends  105  and  106 , wherein the outer diameter of the formed flanges  105  and  106  conforms to the internal diameter of the shaft. Friction between the internal surface of the elongated external shaft  101  and flanged ends  105  and  106  ensures stable positioning of the intermediate tube  104  relative to the elongated external shaft  101 . The proximal section  111  of shaft  101  is preferably provided with at least one and preferably a plurality of openings  121 , which allow fluid communication with the internal space between the intermediate lumen  104  and the elongated external shaft  101  for receiving the fluid temperature controlling material. The male unit  119  of the quick coupling, which is installed on the proximal sections of the elongated external shaft  101  and the central feeding pipe  103 , preferably comprises a first bushing  107 ; the outer and internal surfaces of this first bushing  107  are preferably stepped. 
         [0029]    The outer surface of the first bushing  107  preferably comprises proximal and distal cylindrical sections  108  and  110  and a middle section  109 ; the proximal and distal sections  108  and  110  have the same diameter, while the diameter of the middle section  109  is somewhat smaller. 
         [0030]    The inner surface of the first bushing  107  is preferably also stepped: it preferably has distal, middle and proximal sections  116 ,  115  and  112  with progressively reduced diameters. 
         [0031]    The first bushing  107  is installed on the proximal sections of shaft  101  and the central feeding pipe  103  such that the distal section of the inner surface of the bushing  107  is fitted tightly on the proximal section of the shaft  101 , while the proximal inner surface  112  of bushing  107  is fitted slidingly on the proximal section of the central feeding pipe  103 . After positioning the first bushing  107  on the proximal section of the elongated external shaft  101 , the proximal edge of the central feeding pipe  103  is preferably flanged with application of a deformable o-ring  118 , more preferably constructed from a cryogenically stable polymer, for sealing the gap between the proximal sections of the internal surface of the first bushing  107  and the central feeding pipe  103 . A first channel  114  communicates between the internal and external spaces of inner middle section  115  and outer middle section  109  of the first bushing  107 . 
         [0032]    A second bushing  120  is preferably installed on the longitudinally turned section  111  of the elongated external shaft  101  distally to the first bushing  107  and spaced from this first bushing  107  by a thermo-insulating ring  113 . The outer surface of the second bushing  120  preferably comprises proximal and distal cylindrical sections  124  and  125  and a middle section  126 ; the proximal and distal sections  124  and  125  have the same diameter, while the diameter of the middle section  126  is somewhat smaller. 
         [0033]    In a similar manner, the inner surface of the second bushing  120  preferably comprises proximal and distal cylindrical sections  128  and  127  and a middle section  129 ; the proximal and distal sections  128  and  127  have the same diameter, while diameter of the middle section  129  is somewhat larger. 
         [0034]    Preferably a plurality of openings  130  in the middle section  126  provide fluid communication from the internal space between the intermediate lumen  104  and the elongated external shaft  101  to the external space which is external to cryoprobe  100 . A female unit  135  of the quick coupling mechanism preferably comprises a proximal housing  136 , with the cylindrical inner cavity  137 , wherein the diameter of the cylindrical inner cavity  137  conforms to the outer diameters of the distal and proximal sections  110  and  108  of the first bushing  107  of male unit  119 . 
         [0035]    An opening  138  in the proximal face plane of the inner cavity serves for installation of an inlet connection supplying the cryogen into cryoprobe  100  (this inlet connection is not shown). It should be noted that the tolerance of the space between the first bushing  107  and the cylindrical inner cavity  137  permits the bushing  107  of cryoprobe  100  to be slidingly inserted into the housing  136  of the female unit  135 . The cylindrical inner cavity  137  is preferably provided with a plurality of annular grooves  151  and  139 , which serve for installation of corresponding polymer o-rings  140  and  141 ; these polymer o-rings  140  and  141  ensure sealing of the middle section  126  of the first bushing  107  of cryoprobe  100 . 
         [0036]    In addition, the inner surface of the face plane of the proximal housing  136  is preferably provided with an annular groove  142 , and a helical spring  143 , which is partially situated in annular groove  142 . In such a way, in the process of coupling, the male unit  119  of the coupling pair is spring-actuated by this helical spring  143 , to maintain male unit  119  in tight coupling to female unit  135 . 
         [0037]    Preferably a channel  144  with an outlet connection  145  installed on the outer end of channel  144  communicates between the middle section  109  of the first bushing  107  and the outside space of the proximal housing  136 . The proximal housing  136  comprises an opening  146 , with the axis situated in parallel to the axis of the cylindrical inner cavity  137 ; this opening  146  serves for installation of a joining screw, which is not shown. 
         [0038]    In addition, the female unit  135  preferably comprises a distal bushing  147 , which is separated from the proximal housing  136  by a thermo-insulating ring  148 . The thermo-insulating ring  148  and the distal bushing  147  are preferably provided with an opening  149  and a blind hole  150  with threading  151  for installation of the aforementioned assembling screw (not shown), to close and lock male unit  119  and female unit  135 . 
         [0039]    The cylindrical inner surface of the distal bushing  147  is provided with two annular grooves  152  and  153 , which serve for installation of two polymer o-rings  154  and  155 ; these polymer o-rings  154  and  155  ensure sealing of the middle section  126  of the second bushing  120  of cryoprobe  100 . 
         [0040]    A through channel  156  is provided with an inlet-outlet connection  157  for receiving the temperature controlling fluid material: this inlet-outlet connection  157  is installed on the outer end of the through channel  156  for connecting between the middle section  126  of the second bushing  120  and the inner surface of the distal bushing  147 , and the outside space of the distal bushing  147 . 
         [0041]    In such a way, the distal bushing  147  may be used to supply a heating and thermo-insulating medium into the space between the elongated external shaft  101  and the intermediate lumen  104  through the inlet-outlet connection  157 . 
         [0042]    A spring-actuated ratchet  160  is installed on the outer surface of the distal bushing  147  permitting the male unit  119  and the female unit  135  to be coupled and uncoupled. 
         [0043]      FIG. 2  shows an axial cross-section of another embodiment of a cryoprobe with a plurality of openings in the distal flange of its intermediate lumen for passage of the thermo-insulating medium. 
         [0044]    The embodiment of cryoprobe  200  comprises the elongated external shaft  101 , which ends at its distal edge with cryotip  102 . Numbers which are identical to  FIG. 1  have the same or identical function unless otherwise specified. 
         [0045]    Thermal insulation of the elongated external shaft  101  is ensured by an intermediate tube  104  with two flanged ends  205  and  106 , wherein the outer diameter of the formed flanges  205  and  106  conforms to the internal diameter of the shaft. Friction between the internal surface of the elongated external shaft  101  and flange  106  ensures stable positioning of the intermediate tube  104  within the elongated external shaft  101 . 
         [0046]    The distal flange  205  preferably features a plurality of openings  225 , which ensures passage of a thermo-insulating gaseous medium and its mixture with the gaseous cryogen to be exhausted from cryotip  202 . The medium preferably enters at openings  121  so that the fluid medium travels one way through intermediate tube  104 . This avoids the need for charging and purging intermediate tube  104 , as for the embodiment of  FIG. 1 . 
         [0047]    Persons skilled in the art will appreciate that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the appended claims and includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description.