Abstract:
A device, 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.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is of a device, system and method for thermal insulation for a cryosurgical instrument and in particular, for such a device, system and method for maintaining a controlled external temperature for at least a portion of the probe shaft. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cryoprobes (rigid cryosurgical instruments) frequently experience problems of temperature control, particularly with regard to maintaining temperature differential between the contents of the cryoprobe, which are very cold, and the outer shaft, which is desirably maintained at a higher temperature, outside of the tip itself. The outer shaft is in contact with body tissues which may be damaged by excessively cold temperatures, as only the portion of the body tissues which are in contact with the cryotip should be frozen. 
         [0003]    At the same time the closed distal end (cryotip) of such a probe must provide in many cases high specific freezing capacity at sufficiently low temperatures. 
         [0004]    Various attempted solutions to this problem have been provided with regard to thermal insulation of lateral non-operating walls of cryosurgical instruments. 
         [0005]    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. 
         [0006]    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. The patent teaches vacuum insulation of the return lumen. Such a construction is very expensive and has low reliability. Besides, this vacuum insulation limits flexibility of the probe, especially when it has significant length and is used as a catheter. 
         [0007]    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 with drawbacks as described above. 
         [0008]    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. However, this construction is only useful for applications involving a balloon, such as restenosis. 
         [0009]    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. The 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. Unfortunately this system requires the application of additional high pressure. 
         [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 which has disadvantages. 
         [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, with the previously noted disadvantages. 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, all of which require active electrical elements which are disadvantageous. 
         [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 and which are not suitable for most cryosurgical applications. 
       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. 
         [0015]    The present invention overcomes these drawbacks of the background art, by providing a device, 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. 
         [0016]    A cryosurgical instrument and its accessory system, according to some embodiments, are based on application of cryogen liquids with sufficiently low boiling temperatures at pressures in the interval from below one atmosphere through several atmospheres. It should be noted that mixtures of some gases can be applied as the cryogen and/or as thermo-insulating gas. 
         [0017]    In other embodiments, the proposed cryosurgical instrument operates according to the Joule-Thomson principle, which includes expansion of highly pressurized gas flowing via a distal orifice installed on the distal end of the central feeding tube and application of a miniature built-in counter-flow heat exchanger. 
         [0018]    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 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 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 intermediate lumen. 
         [0019]    There is an additional active controller for controlling the temperature differential between the external shaft and the intermediate lumen, termed herein a temperature controller, which preferably comprises an outer coating on a significant section of the external shaft with a layer of material with very high thermal conductivity, for example, with a thick diamond film obtained by CVD (chemical vapor deposition) process. The proximal section of the diamond coating should be heated by an outer heating source installed on a handle of the cryosurgical instrument. An electrical inductor, electrical heater or heating gas can optionally serve as such outer heating source. 
         [0020]    In another embodiment, the internal middle section of the shaft comprises a tubular piece from metal or another material with very high specific thermal conductivity, for example, copper, silver, graphite or the like, or a combination thereof. The outer side of the shaft is protected with a tubular piece from a metal, which is compatible with human tissue (stainless steel, titanium or the like, for example). The internal distal section of the shaft is preferably fabricated from a metal tubular piece (or pieces) with relatively low specific thermal conductivity (stainless steel, titanium or the like for example) in order to minimize propagation of a formed ice ball in the backward direction. The internal proximal section of the shaft is a tubular piece from a material with relatively low specific thermal conductivity, such as a metal for example; this minimizes a flux of lower temperatures in the axial direction of the cryosurgical instrument. 
         [0021]    In some embodiments, the instrument comprises two portions which are connected through a quick coupling connection, featuring a male unit and a female unit; the former preferably is connected to the portion with the cryotip, while the latter is in contact with body tissue. For such an embodiment, the material with low specific thermal conductivity is preferably installed so as to minimize the flux of lower temperatures from the male unit to the female unit. 
         [0022]    In a preferred embodiment, the heating means features a gas with high relative humidity; this allows to achieve very high heat transfer coefficient for heating the middle section of the external shaft and, additionally, to heat this middle section of the shaft up to a place of penetration of the cryosurgical instrument into a tissue. 
         [0023]    In another preferred embodiment the heating gas has low relative humidity or a high level of dryness (without wishing to be limited by a single hypothesis, it prevents formation of microorganism colonies in a passageways of the heating gas). 
         [0024]    In a further embodiment of the present invention, there is a displaceable cap, which can be slidingly shifted along the external shaft of the cryosurgical instrument. In its initial position, the cap is adjacent to a bushing with nozzles providing the heating gas and it is joined with this bushing by a set of small magnets, which are installed on the bushing and the cap itself. After penetration of the cryosurgical instrument into a tissue, the cap is shifted until it contacts with the site of tissue penetration of the cryosurgical instrument. In such a way, the cap protects the tissue from contacting the gaseous heating jets. Among other advantages, this protection obviates the need for sterilizing the heating gaseous medium supplied into the nozzles. 
         [0025]    After termination of the cryosurgical procedure, a surgeon or other medical personnel can return the cap to its initial location and then can remove the cryosurgical instrument from the tissue. 
         [0026]    In other embodiments of the present invention, the heating means are realized as an electrical heating element installed in the female unit of the quick coupling. 
         [0027]    This electrical heating element is separated preferably from the other parts of the female quick coupling unit by a ring from a material with very low thermal conductivity; which may optionally comprise, for example, foamed polyurethane. 
         [0028]    In a further embodiment, the heating means is a fluid medium (gaseous or liquid), which flows via an annular chamber in a bushing, which is provided with an inlet and outlet connections. 
         [0029]    This bushing is separated from the female unit of the quick coupling of the cryosurgical instrument by a ring from a material with very low thermal conductivity; which may optionally comprise, for example, foamed polyurethane. 
         [0030]    The distal end of the central feeding lumen is preferably terminated by an inlet connection for receiving cryogen, while the distal section of the elongated external shaft, which bounds 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 with an inlet connection. In another embodiment, this last inlet connection can serve alternatively as an inlet and outlet connection. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1   a  is an axial cross-section of a cryosurgical instrument according to the present invention with heating an external shaft by streams of gaseous medium; 
           [0032]      FIG. 1   b  is an axial cross-section of an external shaft with a middle internal tubular piece from a material with high specific thermal conductivity. 
           [0033]      FIG. 1   c  is an axial cross-section of an external shaft with a middle outer coating by a thick diamond film. 
           [0034]      FIG. 2  is an axial cross-section of the cryosurgical instrument with heating the external shaft by an outer electrical coil. 
           [0035]      FIG. 3  is an axial cross-section of the cryosurgical instrument with heating the external shaft by a warming fluid medium flowing via an annular chamber. 
           [0036]      FIG. 4   a  is an axial cross-section of the cryosurgical instrument, which is assembled from a disposable unit comprising an external shaft, a cryotip and a central feeding lumen; and a permanent unit, which comprises a connection element and an elongated electrical heater installed on a cylindrical elongated thermal insulator. 
           [0037]      FIG. 4   b  is an axial cross-section of the disposable unit of  FIG. 4   a.    
           [0038]      FIG. 4   c  is an axial cross-section of the permanent unit of  FIG. 4   a.    
           [0039]      FIGS. 5A-5C  relate to an exemplary, non-limiting embodiment with an electrical heater. 
           [0040]      FIG. 6  shows another non-limiting, exemplary embodiment with an elongated vacuum insulated chamber applied instead of the electrical heater. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0041]      FIG. 1  shows an axial cross-section of a cryosurgical instrument  100  according to the present invention with heating an external shaft by streams of a gaseous medium, which preferably have a high water content (ie are humidified). This embodiment of cryosurgical instrument  100  comprises the elongated external shaft  101 , which terminates at its distal edge with cryotip  102 . 
         [0042]    There is a central feeding pipe  103 , which is situated in shaft  103 . 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  preferably protrudes at least partially to prevent movement past a certain point with regard to male unit  119 . 
         [0043]    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 flanging  106  ensures stable positioning of the intermediate tube  104  relative to the elongated external shaft  101 . 
         [0044]    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. 
         [0045]    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. 
         [0046]    The inner surface of the first bushing  107  is preferably also stepped: it preferably has distal, intermediate and proximal sections  116 ,  115  and  112  with progressively reduced diameters. 
         [0047]    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 . There is a first channel  114 , which communicates between the internal and external spaces of inner intermediate section  115  and outer middle section  109  of the first bushing  107 , for receiving the temperature controlling fluid medium, such as a gas for example. 
         [0048]    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 . 
         [0049]    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. 
         [0050]    In a similar manner, the inner surface of the second bushing  120  preferably comprises proximal and distal cylindrical sections  127  and  128  and a middle section  129 ; the proximal and distal sections  127  and  128  have the same diameter, while diameter of the middle section  129  is somewhat larger. 
         [0051]    There are preferably a plurality of nozzles  130  in the distal section  128  of the male unit  133  of a quick coupling; the axes of these nozzles  130  form acute angles with the axis of the external shaft  101 . Nozzles  130  preferably receive a humidified warming gas from an external source through channel  114  (not shown), at a sufficiently high temperature so as to protect the tissue contacted by the instrument (not shown) and then emit this gas onto the tissue. 
         [0052]    The external shaft  101  is divided into the proximal, middle and distal sections; these sections preferably include a common outer tubular piece  140 , an internal middle tubular piece  141  from a material with high specific thermal conductivity (including but not limited to silver, copper, brass, aluminum and the like), an internal proximal tubular piece  143  from a material with relatively low specific thermal conductivity (including but not limited to stainless steel, titanium and the like) and an internal distal tubular piece  142  from a material with relatively low specific thermal conductivity (including but not limited to stainless steel, titanium and the like). The common outer tubular piece  140  is preferably from a metal with good compatibility with human tissue, for example, stainless steel, silver, titanium, gold or any other suitable material. Thus, the low temperature of cryotip  102  is blocked from moving to the portion of the instrument in contact with the tissue, while the warmer temperature of the portion in contact with the tissue cannot heat cryotip  102 . 
         [0053]      FIG. 1   b  is an axial cross-section of an external shaft with a middle internal tubular piece from a material with high specific thermal conductivity. 
         [0054]    The external shaft  150  comprises the outer tubular piece  140  with a turned down proximal section  144 , which serves for installation a male unit of a quick coupling. This outer tubular piece is fabricated preferably from a metal with good biological compatibility which also has low thermal conductivity (stainless steel, titanium). 
         [0055]    In addition, there are an internal distal tubular piece  142 , an internal middle tubular piece  141  and a proximal tubular piece  143 , which are joined by tightly fitting with the outer tubular piece  140 . 
         [0056]      FIG. 1   c  is an axial cross-section of an external shaft with a middle outer coating by a diamond film. 
         [0057]    It comprises a tubular piece  145  with a middle turned section  147  and a proximal turned section  146 . The middle turned section  147  is coated with a diamond film  148  which is optionally and preferably a thick diamond coating, more preferably at least about  100  microns for example. Diamond film  148  provides excellent thermal conductivity, which is higher than that of metal. 
         [0058]      FIG. 2  demonstrates an axial cross-section of the cryosurgical instrument  200  with heating of the external shaft by an outer electrical coil. Elements with the same reference number as for  FIG. 1  have the same or at least a similar function. 
         [0059]    In addition, the inner surface of the face plane of housing  220  is provided with blind holes  222  and helical springs  226 , which are partially situated in these blind holes  222 . In such a way, in the process of coupling, the male unit of the coupling pair is spring-actuated by these helical springs  226 . 
         [0060]    There is a second through channel  221  with an outlet connection  224  installed on the outer end of the second through channel  221 , which communicates the annular channel formed between the middle section of bushing  107  and the outside space of housing  220 . 
         [0061]    In such a way, these annular channels and second through channel  221  serve for exhausting evaporated cryogen from the cryosurgical instrument  200 . There is a thermo-insulating ring  228 , which is installed on the distal face plane of housing  220 , the distal face plane of this thermo-insulating ring  228  serves in turn for installation of ring  227  with an electrical heating spiral  235  on its inner cylindrical surface. Electrical contacts  237  serve for power supply to the electrical heating spiral  235  which therefore heats the external shaft  101 . 
         [0062]      FIG. 3  is an axial cross-section of the cryosurgical instrument  300  with heating the external shaft by a warming fluid medium flowing via an annular chamber. Elements with the same reference number as for  FIG. 1  or  2  have the same or at least a similar function. 
         [0063]    The distal face plane of thermo-insulating ring  228  serves in this embodiment for installation of an annular heating chamber  327  with an internal radiator  329  on its inner cylindrical surface. The annular heating chamber  327  is provided with an inlet and outlet connections  328  and  330  for delivery and removal of a heating fluid medium into the annular heating chamber  327  which therefore is heating the proximal section of the elongated external shaft  101 . 
         [0064]    The inner cylindrical surface of the annular heating chamber  327  is provided with fins  329  in order to improve heat transfer between this surface and the heating fluid medium. 
         [0065]      FIG. 4   a  is an axial cross-section of the cryosurgical instrument  400 , which is assembled from a disposable unit comprising an external shaft, a cryotip and a central feeding lumen; and a permanent unit, which comprises a connection element and an elongated electrical heater installed on a cylindrical elongated thermal insulator;  FIG. 4   b  is an axial cross-section of the disposable unit and  FIG. 4   c  is an axial cross-section of the permanent unit of  FIG. 4   a.    
         [0066]    The disposable unit of the cryosurgical instrument comprises: an elongated external shaft  101  with cryotip  102  and a proximal bushing  413 , which is installed on the outer side of the elongated external shaft  101  and provided with threading  416 . A central feeding lumen  403  is held in the elongated external shaft  101  by two perforated disks  404  and  405 . 
         [0067]    It should be noted that the central feeding lumen  403  preferably protrudes significantly outside the proximal edge of the elongated external shaft  101 . 
         [0068]    A permanent unit  411  of the cryosurgical instrument  400  comprises bushing  417  with a distal cylindrical cavity  419  and a distal internal threading  428 . A cylindrical surface  420  of a smaller diameter in bushing  417  serves for installation of the proximal section of an outer tubular piece  408  with an elongated electrical heater  407 ; opening  425  serves for passage of wires  423  of the elongated electrical heater  407  outside bushing  417  with joining these wires  423  with connectors  422 . The elongated electrical heater  407  is fabricated from an electrically isolated wire, which is wound on the outer tubular piece  408 . In addition, there is a second tubular piece  406 , which is joined with the first tubular piece  408  by two sealing rings  409  and  418 . The distal end of the outer tubular piece  408  is provided with a stationary bushing  410  in order to protect the elongated electrical heater  407  in the assembling process. 
         [0069]    There is a hole  424  in bushing  417  for installation of an outlet connection  414  and a central hole  412 , which is in fluid communication with the inlet connection  415 . In addition, there is a sealing O-ring  421 , which is installed near the edge of the central hole  412 . There is a second tubular piece  406 , which is joined with the first tubular piece  408  by two sealing rings  409  and  418 , the proximal edge of the first tubular piece  408  is installed on the cylindrical surface  420  of bushing  417 . The distal end of the first tubular piece  408  is provided with a stationary bushing  410  in order to protect the elongated electrical heater  407  in the assembling process. 
         [0070]    A cylindrical surface  427  in the internal cavity of bushing  417 , which is of a smaller diameter than the cylindrical surface  420 , is provided with hole  424  for installation of an outlet connection  414 . There is a central hole  412  in the proximal face plane of bushing  417 ; this central hole  412  is in fluid communication with the inlet connection  415 . 
         [0071]    Central feeding lumen  403  receives cryogen which then passes to cryotip  102  for cooling, for example for a cryotherapeutic process, which is preferably a cryosurgical process. To prevent or at least reduce tissue damage, electrical heater  407  heats outer tubular piece  408  to a sufficient extent. 
         [0072]      FIG. 5   a  is an axial cross-section of the cryosurgical instrument  500 , which is assembled from a disposable unit comprising an external shaft, a cryotip and a distal member of a central feeding lumen; and a permanent unit, which comprises an inlet and outlet connection elements, an elongated electrical heater installed on a cylindrical elongated thermal insulator and a central feeding lumen;  FIG. 5   b  is an axial cross-section of the disposable unit and  FIG. 5   c  is an axial cross-section of the permanent unit of  FIG. 5   a.    
         [0073]    The disposable unit of the cryosurgical instrument comprises: an elongated external shaft  501  with cryotip  502  and a proximal bushing  528 , which is installed on the outer side of the elongated external shaft  501  and provided with threading  534 . A distal member of the central feeding lumen is installed in cryotip  502  by disks  536  with holes  537 . This distal member comprises a stationary fastened tubular piece  532  with metal spirals  531 , which serve for the cryogen droplets&#39; separation. The proximal section of the stationary fastened tubular piece  532  is provided with a displaceable tubular piece  533  with conically flanged edge  539 . This displaceable tubular piece  533  is joined with the stationary fastened tubular piece  532  by a wire  538 . The displaceable tubular piece  533  with conically flanged edge  539  should be joined in the process of the cryosurgical instrument assembling with the main section  503  of the central feeding lumen, which is installed in the permanent unit  511 . 
         [0074]    It should be noted that the central feeding lumen  503  preferably protrudes significantly outside the proximal edge of the elongated external shaft  501 . 
         [0075]    A permanent unit  511  of the cryosurgical instrument  500  comprises bushing  517  with a distal cylindrical cavity  519  and a distal internal threading  528 ; a cylindrical surface  520  of a smaller diameter serves for installation of the proximal section of a first tubular piece  508  with an binary wire spiral  507 , which serves as an electrical heater; opening  525  serves for passage of wires  523  of the binary wire spiral  507  outside bushing  517  with joining these wires  523  with connectors  522 . The binary wire spiral  507  is provided with a layer of electrical isolation. 
         [0076]    There is a second tubular piece  506 , which is joined with the first tubular piece  508  by two sealing rings  509  and  518 . The distal end of the first tubular piece  508  is provided with a stationary bushing  510  in order to protect the binary wire spiral  507  in the assembling process. 
         [0077]    In addition, the face plane of bushing  517  is provided with a through opening  524  for installation of an outlet connection  514 , which serves for removal of exhausted gases, and a central hole  512 , which serves for installation of the proximal section of the central feeding lumen  503  and is in fluid communication with the inlet connection  515 . 
         [0078]      FIG. 6  is an axial cross-section of a permanent unit of a cryosurgical instrument with an elongated vacuum insulated chamber applied instead of the electrical heater. A disposable unit of this cryosurgical instrument has the same design as in  FIG. 5   b . A permanent unit  611  of the cryosurgical instrument comprises bushing  617  with a distal cylindrical cavity  619  and a distal internal threading  628 ; a cylindrical surface  620  of a smaller diameter serves for installation of the proximal section of a tubular piece  608 . 
         [0079]    There is a second thermo-insulating tubular piece  606 , which is joined with the first thermo-insulating tubular piece  608  by two sealing rings  609  and  618 , and air in the interior between these first and second tubular pieces  608  and  606  is evacuated to form a vacuum. 
         [0080]    In addition, the face plane of bushing  617  is provided with a through opening  624  for installation of an outlet connection  614 , which serves for removal of exhausted gases, and a central hole  612 , which serves for installation of the proximal section of the central feeding lumen  603  and is in fluid communication with the inlet connection  615 . 
         [0081]    While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.