Patent Document

CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    Not applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         FIELD OF THE INVENTION  
         [0003]    The present invention relates to medical devices, and in particular, to cooling mechanisms for cryogenic devices.  
         BACKGROUND OF THE INVENTION  
         [0004]    Catheter-based devices for use in surgical procedures and other medical applications are becoming well known. Recently, the use of low temperature fluids, or cryogens, with such catheters to cold-treat target areas has begun to be explored.  
           [0005]    The application of cold to selected body tissues provides a number of advantages over prior catheter devices which alternatively use heat, RF energy, laser light, or other means for treating targeted tissue. A device uses the energy transfer derived from thermodynamic changes occurring in the flow of a cryogen through the device. This energy transfer is then utilized to create a net transfer of heat flow from the target tissue to the device, typically achieved by cooling a portion of the device to very low temperature through conductive and convective heat transfer between the cryogen and target tissue.  
           [0006]    Structurally, cooling of the device can be achieved through injection of high pressure cryogen through an orifice into an enclosed expansion chamber. Because the cryogen is supplied at high pressure, ranging up to 800 psia, it is generally a liquid-vapor mixture as it travels through the device to the expansion chamber. Upon injection into the expansion chamber, the cryogen undergoes two primary thermodynamic changes: (i) expanding to low pressure and temperature through positive Joule-Thomson throttling, and (ii) undergoing a phase change from liquid to vapor, thereby absorbing heat of vaporization. The resultant flow of low temperature cryogen through the expansion chamber acts to absorb heat from the target tissue and thereby cool the tissue to the desired temperature.  
           [0007]    As is well known in the art, of the two processes contributing to the cooling power of the device, evaporative boiling through a change in phase creates a far greater cooling effect through the absorption of latent heat of vaporization, on a specific basis, than merely that of Joule-Thomson cooling alone. Therefore, it is highly desirable to supply the device with a cryogen that is as much in liquid rather than gaseous phase, before the fluid is injected into the expansion chamber to cool tissue. Unfortunately, during transit to the expansion chamber, such as through an elongate catheter, the cryogen supplied typically passes through a region of comparatively high temperature, such as a region of the human body preceding the target area, and is thereby warmed. This warming coupled with head losses in the flow of cryogen down a length of several hundred diameters of tubing, acts to degrade the quality of cryogen from its high pressure liquid form, to a lower pressure, higher temperature, mixed phase form, leading to significantly degraded cooling power of the device. Furthermore, vapor bubbles may form in the injection line, disrupting the smooth flow of cryogen. As is well known to those skilled in the art, the additional adverse effects of sputtering, turbulence, cavitation, and unsteady flow all degrade cooling power.  
           [0008]    It is therefore desirable to provide a device which maximizes the cooling power of the flow of cryogenic fluid therethrough, namely through maintaining a steady, uniform supply of high pressure cryogen in liquid phase. It is also desirable to provide a medical device which minimizes cooling losses in the flow of cryogen as it is applied to tissue, as well as maximizing the ratio of the cooling power of the device versus its internal flow lumen diameter.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a medical device to cold treat desired regions. The device includes an injection tube member defining an injection lumen therein. The injection tube member includes a proximal end, an open distal end, and at least one aperture proximate the distal end. A second cooling member is disposed around the injection tube member, defining a cooling lumen therebetween. A third outer tube member is disposed around the second cooling member, defining a return lumen therebetween. A first fluid pathway is thereby provided for fluid to flow from the injection lumen, through to the aperture in the injection tube, and thereafter through the cooling lumen. A second fluid pathway is provided for fluid to flow from the injection lumen, through the distal end of the injection tube, and thereafter through the return lumen. The device may be coupled to a supply of fluid regulated by a controller mechanism to provide for a pressure gradient throughout the first and second fluid pathways. The flow of fluid through the first fluid pathway insulates and cools the fluid supplied into and flowing through the injection lumen. The flow of fluid through the second pathway cools the surrounding areas external to and proximate the distal end of the device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:  
         [0011]    [0011]FIG. 1 is a schematic diagram of a medical system that includes enhanced cooling structures in accordance with the invention;  
         [0012]    [0012]FIG. 2 is a longitudinal cross-sectional view of the distal portion of a catheter, taken along line  2 - 2 , which is part of the system of FIG. 1;  
         [0013]    [0013]FIG. 3 is a transverse cross-sectional view of the distal portion of the device taken from section  3 - 3  in FIG. 2;  
         [0014]    [0014]FIG. 4A is an enlarged view of an alternate arrangement of the device as shown in FIG. 3, taken from section  3 - 3  in FIG. 2;  
         [0015]    [0015]FIG. 4B is an enlarged view of another alternate arrangement of the device as shown in FIG. 3, taken from section  3 - 3  in FIG. 2;  
         [0016]    [0016]FIG. 5 is a longitudinal cross-sectional view of the distal portion of an alternate arrangement of a catheter which is part of the system shown in FIG. 1;  
         [0017]    [0017]FIG. 6 is a longitudinal cross-sectional view of the distal portion of another alternate arrangement of the catheter; and  
         [0018]    [0018]FIG. 7 is an enlarged longitudinal cross-sectional view of the distal portion of yet another arrangement of the catheter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    As used herein, the term “cryogen” refers to a fluid substance with properties suitable for: (i) steady flow through ducts of small diameter, (ii) high pressure compression into liquid phase, and (iii) evaporation and expansion to low temperatures. The cryogen may preferably be any suitable, relatively inert “working fluid”, such as gases like nitrogen, nitrous oxide, or carbon dioxide, liquids such as chlorodifluoromethane, ethyl alcohol, or Freon (a trademark of DuPont), or any number of other refrigerants or fluids with a high thermal energy transfer capacity and low boiling point, as are commonly known to those skilled in the art.  
         [0020]    As used herein, the term “tube” refers to an elongate duct or conduit suitable for conveying a fluid. The tube may comprise of any number of elements or members, and may have a varying range of properties and dimensions, such as length, thickness, and cross-sectional shape.  
         [0021]    Referring now to the drawings, in which like reference designators refer to like elements, there is shown in FIG. 1 a schematic of a system constructed in accordance with the principles of the present invention, and designated generally as  100 . Cryocatheter system  100  preferably includes a controller  102 , a cryogen supply  103 , and a catheter  104  comprising a distal portion  105 , and tip  106 . During application, a portion of the catheter  104  is introduced into the body and is placed in contact with or proximate to selected tissue. FIG. 1 illustrates the catheter distal portion  105 .  
         [0022]    A user  101  interfaces with the controller  102 , to control, actuate and operate the components of the system  100 . For example, the controller  102  regulates the flow of cryogen into the catheter  104  in response to a command input from user  101  into the controller  102 . The controller  102  is preferably any number of suitable mechanical or electronic device components that are capable of receiving and executing programmed instructions, sensor signals, or manual user input as is known in the art.  
         [0023]    The cryogen supplied may be either in a liquid or a gaseous state. The cryogen is cooled and/or compressed to a predetermined initial temperature and initial pressure before introduction into the catheter  104 . The catheter  104  contains multiple tubes (not shown), preferably made of flexible material such a polymer, fiber, metal, or any combination thereof. The tubes are arranged to create a plurality of lumens (not shown) for the flow of cryogen therethrough. These lumens are arranged to create a closed loop flow path for cryogen such that it circulates through the catheter during operation of the device. This includes an injection lumen (not shown) through which the cryogen is introduced into the catheter  104  to flow from the supply  103  through to the tip  106 , and a vacuum return lumen (not shown), through which cryogen eventually flows back from the tip  106 . The controller  102  is used to create vacuum pressure conditions (or negative gauge pressure) at the proximate portion of the vacuum return lumen. The initial supply pressure of the cryogen is preferably on the order of 30 to 40 atmospheres, or 400 to 600 psia, much higher than the eventual final pressure in the vacuum return lumen. The resultant negative pressure gradient drives the high pressure cryogen drawn from supply  103  to flow through an injection lumen in catheter  104 , to the tip  106 , and thereafter to flow back through a vacuum return lumen.  
         [0024]    During operation of the device, the catheter  104  is typically introduced into a body, such that the distal portion  105  is disposed in close proximity to a tissue region that is a source of heat Q, thereby warming the cryogen flowing therethrough. In many cryosurgical applications, the length of the distal portion  105  exposed to heat Q may include up to a few hundred diameters of catheter  104 . The overall length of catheter  104  from its proximal end to its tip  106  may be several hundred diameters, such that significant head losses are present in the flow of high pressure cryogen therethrough, as is well known to those skilled in the art. Because the cryogen supplied is at as a high pressure and as low a temperature as possible, the dual effect of heat transfer from tissue and head losses through the length of catheter  104  serves to degrade the overall performance of the system  100 .  
         [0025]    [0025]FIG. 2 shows a longitudinal cross-sectional view of the distal portion  105  of the catheter  104 , of an exemplary embodiment of the present invention. Referring now to FIG. 2, distal portion  105  comprises an outer tube  201 , an injection tube  202 , a sub-cooling tube  203 , an adhesion element  204 , a catheter tip  205 , an expansion chamber  206 , an injection lumen  207 , a sub-cooling lumen  208 , a return lumen  209 , an injection orifice  210 , and at least one sub-cooling aperture  211 . Outer tube  201  circumferentially encloses injection tube  202  and sub-cooling tube  203 , such that all tubes are preferably coaxially disposed with respect to each other, such that a longitudinal centerline (not shown) of outer tube  201  coincides with the longitudinal centerline of both the injection tube  202  and sub-cooling tube  203 . Sub-cooling tube  203  is also disposed coaxially around injection tube  202 , such that the longitudinal centerline (not shown) of injection tube  202  coincides with the longitudinal centerline (not shown) of sub-cooling tube  203 . It is emphasized that the foregoing spatial arrangement of tubes  201 ,  202  and  203  are but one particular arrangement, and that any number of alternative arrangements may be used so as to provide for the suitable operational enablement of the present invention.  
         [0026]    All of tubes  201 ,  202 , and  203  are preferably made of a flexible solid material, such as polyimide, or other polymer, metal, or combination thereof, suitable for the transport of high pressure fluids, as is well known to those skilled in the art. The distal end of sub-cooling tube  203  is coupled to the distal end portion of injection tube  202 , through adhesion provided by adhesion element  204 , such that the absolute distal end of sub-cooling tube  203  circumferentially circumscribes the distal end portion of injection tube  202 , at a point slightly more proximate than the absolute distal end of injection tube  202 . It is understood that any number of adhesion or coupling mechanisms or devices may be used for adhesion element  204 , preferably including, nut not limited to, a glue, epoxy, or other suitable coupling agent, as is well known to those skilled in the art. Alternatively, injection tube  202  and sub-cooling tube  203  may be formed as a single element, such that the use of adhesion element  204  to couple the distal ends of injection tube  202  and sub-cooling tube  203  is not necessary.  
         [0027]    Outer tube  201  is coupled to the catheter tip  205 , the catheter tip  205  being disposed at the absolute distal end of the catheter. The tip  205  is preferably made of a thermally-transmissive material, such as a metal or other suitable material of high thermal conductivity. Although many materials and structures may be thermally conductive or thermally transmissive if cooled to a very low temperature, as used herein, a “thermally-transmissive” element is intended to broadly encompass any element that readily conducts heat.  
         [0028]    The absolute distal end of injection tube  202  is disposed at a point proximate the tip  205 , such that an expansion chamber  206  is defined by the space enclosed by tip  205  inside the distal end of catheter  104 , proximate the distal end of injection tube  202 . The injection tube  202  further defines an injection lumen  207 . High pressure, low temperature cryogen is supplied to the catheter  104 , and initially enters the catheter  104  as it flows through the injection lumen  207  towards the expansion chamber  206 . At the absolute distal end of the injection lumen  207 , the injection tube  202  further comprises an injection orifice  210 . Injection orifice  210  is disposed transverse to the flow of cryogen through injection lumen  207 . Injection orifice  210  may be an adiabatic nozzle, choked-flow orifice, or other flow regulating structure. Cryogen, upon flowing through the injection lumen  207 , exits the injection tube  202  through the injection orifice  210 , and flows into the expansion chamber  206 . After flowing into the expansion chamber  206 , cryogen is induced through a negative pressure gradient to flow back towards the proximate portion of the catheter  104  through the return lumen  209  defined by the interior surface of the outer tube  201  and the exterior surface of the sub-cooling tube  203 .  
         [0029]    Cryogen flowing through the injection lumen  207  is in mixed liquid and gas phase, at several atmospheres pressure and at a temperature well below standard room temperature. Upon injection into the expansion chamber, the cryogen undergoes two thermodynamic changes. First, the gas phase of the cryogen expands through a positive Joule-Thomson throttling process, which may be substantially isenthalpic, but acts to substantially lower the pressure and the temperature of the cryogen. The resulting low pressure, very low temperature cryogen gas flows through the expansion chamber  206 , through to the return lumen  209 . This flow of cryogen creates both conductive and convective heat transfer with respect to target region R proximate the catheter tip  205 . The cumulative effect of this heat transfer, shown as Qc in FIG. 2, serves to cool any tissue in region R to a desired temperature. Second, upon injection through orifice  210 , a portion of the liquid phase of the cryogen evaporatively boils, absorbing latent heat vaporization from the surrounding target region R. This evaporative absorption of heat, labeled in FIG. 2 as Qe, further cools the target tissue. The magnitude of heat transfer rates Qc and Qe may vary widely depending on the particular refrigerant used, although Qc is generally smaller than Qe, such that the overall cooling power of the device is mainly attributable to evaporative cooling rather than conductive or convective heat transfer.  
         [0030]    The arrangement of sub-cooling tube  203  coaxially around injection tube  202  defines a sub-cooling lumen  208 , circumferentially disposed around the exterior of injection tube  202 . At a point proximate the distal end of injection tube  202 , injection tube  202  contains at least one sub-cooling aperture  211 . At least one aperture  211  is preferably of much smaller diameter than orifice  210 . As cryogen flows through the injection lumen  207 , before exiting the lumen  207  through orifice  210 , the cryogen flows past the sub-cooling apertures  211 . The proximate ends of all of tubes  201 ,  202 ,  203 , and lumens  207 ,  208 ,  209  are coupled to the controller  102  shown in FIG. 102, such that the static pressures in all of lumens  207 ,  208 , and  209  may be regulated and controlled during operation of the device. The static pressure in the sub-cooling lumen  208  is maintained at a level above atmospheric pressure, above that of the static pressure in return lumen  209 , but still well below the static pressure in the injection lumen  207 . Because of this pressure differential, although a majority of the cryogen flows from the injection lumen  207  through orifice  210 , a portion of the cryogen flow is directed through the apertures  211  to flow into the sub-cooling lumen  208 . This cryogen then flows through the sub-cooling lumen  208  back to the proximate portion of the catheter, whereupon the return lumen and sub-cooling lumen are joined (not shown) and all of the cryogen flowing back towards the controller  102  after circulating through the device is collected and either disposed of or recirculated.  
         [0031]    The flow of cryogen through the sub-cooling lumen  208  acts to insulate the flow of cryogen in the injection lumen  207  from the heat being transferred therein by the surrounding warm tissue in region R, shown in FIG. 2 as Qh. Although, the warming effects of Qh may be minimized by the use of low thermal-transmissivity materials in outer tube  201 , as the cryogen flows in the injection tube throughout the length of the distal portion  105  of the cryocatheter, the effects of Qh may significantly (i) change a portion of the supplied cryogen from liquid to gaseous phase, and (ii) increase head pressure losses and raise the temperature of the cryogen supplied, such that by the time the cryogen is injected into expansion chamber  206 , the cooling power of the device is degraded. Thus, arrangement of the sub-cooling tube  203  around injection tube  202  creates a heat exchanger for the cryogen flowing therethough. The heat exchanger acts in two ways, such that the overall effect of the flow of cryogen through the sub-cooling lumen  208  is to “sub-cool” the cryogen flowing in injection lumen  207 . First, the flow of cryogen through sub-cooling lumen  208  both insulates the injection lumen  207  from the warming effects of Qh, and provides for thermal energy transport and diffusion of heat away from the injection tube  202 . Second, the flow of cryogen through sub-cooling lumen  208  itself provides for additional condensation and cooling of the cryogen in injection lumen  207  through the conductive and convective heat transfer with the flow of low pressure and temperature cryogen in the sub-cooling lumen  208 . All of these effects serve to provide a greater proportion of liquid phase cryogen flow through the injection lumen  207  to the orifice  210 , prevent unnecessary warming the cryogen, and thus enable greater evaporative cooling and more efficient gas expansion of the cryogen upon injection into the expansion chamber.  
         [0032]    [0032]FIG. 3 shows a transverse cross-sectional view of the catheter  104  taken along section  3 - 3  in FIG. 2, illustrating the spatial arrangement of outer tube  201 , injection tube  202 , sub-cooling tube  203 , injection lumen  207 , sub-cooling lumen  208 , and apertures  211 . Referring now to FIG. 3, the arrangement of the apertures  211  in injection tube  202  allows for the flow of cryogen from the injection lumen  207 , through the apertures  211  and into the sub-cooling lumen  208 . Apertures  211  may be of any number, and may be disposed along multiple cross-sections of injection tube  202 . Preferably, the injection tube inner diameter ranges from 0.004 to 0.06 inches; the sub-cooling tube inner diameter is approximately 0.09 inches; and the outer tube inner diameter is approximately 0.15 inches. As is well known to those skilled in the art, it is understood that the particular dimensions of the device may vary depending on the particular application of the invention and without comprising its fundamental functionality.  
         [0033]    [0033]FIGS. 4A and 4B show additional cross-sectional views of the injection tube  202  and sub-cooling lumen  203  taken from section  3 - 3  in FIG. 2. Referring now to FIGS. 4A and 4B, the apertures  211  may be arranged radially in any number of patterns, either using a four-aperture configuration as in FIG. 4A, or a three-aperture configuration as in  4 B, so as to maximize the sub-cooling efficiency gained through the flow of cryogen from injection lumen  207 , through apertures  211 , into sub-cooling lumen  208 . The cryogen, by entering the sub-cooling lumen  208  through apertures  211  positioned in a variety of locations along the injection tube  202 , is uniformly and optimally dispersed through the sub-cooling lumen so as to flow therethrough with a minimum of turbulence, cavitation, unsteady mixing, and friction, all of which induce heat flow into the injection lumen  207 , or otherwise degrade the overall cooling efficiency and power of the cryocatheter device.  
         [0034]    [0034]FIG. 5 shows yet another embodiment of the present invention, further enhancing the overall cooling efficiency of the device. Referring now to FIG. 5, there is shown an additional longitudinal cross-sectional view of the distal portion of catheter  104 , comprising an outer tube  201 , an injection tube  202 , a sub-cooling tube  203 , an adhesion element  204 , a catheter tip  205 , an expansion chamber  206 , an injection lumen  207 , a sub-cooling lumen  208 , a return lumen  209 , an injection orifice  210 , and at least one sub-cooling aperture  211 . The shape of the distal end  501  of the sub-cooling tube  203 , as well as the spatial orientation of the coupling of injection tube  202  with sub-cooling  203 , may be arranged to provide for enhanced quality flow of cryogen through the expansion chamber  206  upon exiting orifice  210  and flowing through to return lumen  209 . In this embodiment, the distal end  501  of sub-cooling tube  203  is curved and coupled to injection tube  202  by means of adhesion element  204 . This curvature allows for cryogen exiting the injection tube to flow through the expansion chamber with less turbulence, friction losses, and other unsteady flow effects, than that of the embodiment shown in FIG. 2. This in turn provides for enhanced convective heat transfer between the tip  205  and the cryogen, thereby enhancing the overall cooling power and efficiency of the device. It is understood that the particular coupling arrangement for injection tube  202  and sub-cooling tube  203  is not limited to those embodiments shown in FIGS. 2 and 5, but may be of any number of arrangements suitable for enabling the present invention.  
         [0035]    [0035]FIG. 6 shows a longitudinal cross-sectional view of the distal portion of another yet another embodiment of the catheter  104 . Referring now to FIG. 6, there is shown an outer tube  201 , an injection tube  202 , a sub-cooling tube  203 , an adhesion element  204 , a catheter tip  205 , an expansion chamber  206 , an injection lumen  207 , a sub-cooling lumen  208 , a return lumen  209 , an injection orifice  210 , at least one sub-cooling aperture  211 , and an insulation tube  601 . The insulation tube  601  covers at least a portion of the outer surface of sub-cooling lumen  203 , and is coupled thereto by means of a suitable adhesive or coupling element (not shown). The insulation tube  601  preferably comprises a material of relatively low thermal transmissivity. Heat transfer into the sub-cooling lumen  208 , and injection lumen  207  enclosed therein, is significantly reduced by the presence of the insulation tube  601 , thereby keeping the cryogen supplied and flowing in injection tube  202  at better conditions for injection into expansion chamber  206 . Therefore, the objective of sub-cooling and insulating the cryogen flowing in injection lumen  207  is advanced beyond merely the effects of using a sub-cooling tube  203  alone. It is understood that any number of insulation tubes  601 , or other insulation elements such as thin films or coatings may be disposed circumferentially around the injection tube  202  and sub-cooling tube  203 , so as to achieve the objectives of the present invention.  
         [0036]    [0036]FIG. 7 shows an enlarged, longitudinal, cross-sectional view of the distal portion of catheter  104 , including an outer tube  201 , an injection tube  202 , a sub-cooling tube  203 , an adhesion element  204 , a catheter tip  205 , an expansion chamber  206 , an injection lumen  207 , a sub-cooling lumen  208 , a return lumen  209 , an injection orifice  210 , at least one sub-cooling aperture  211 , and a blocking tube  701 . Blocking tube  701  is slidably disposed in contact with a part of the inner surface of injection tube  202 , and extends along a desired length of the injection lumen  207 . A suitable control mechanism (not shown) is coupled to blocking tube  701 , allowing for the positioning of blocking tube  701  along a plurality of longitudinal positions within the injection lumen  207 . In this particular embodiment of the present invention, a set of two apertures  211  are located along two cross-sectional planes of injection tube  202 . By sliding the blocking tube from a first position, shown as  701  in FIG. 7, to a second position, shown as  701   a  in FIG. 7, the number of apertures  211  through which the cryogen may flow from injection lumen  207  through to sub-cooling lumen  208  may be controlled. Thus, the positioning of blocking tube  701  acts to control the flow of cryogen in sub-cooling lumen  208 . This in turn allows the user to control the cooling power of the cryocatheter device.  
         [0037]    It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.

Technology Category: 1