Abstract:
A method and apparatus for inflating a balloon at a distal portion of an elongated delivery catheter to contact surrounding biological tissue, and expanding a refrigerant adjacent the balloon to cool the biological tissue to render it non-viable. The inflation of the balloon can be accomplished with the expanded refrigerant or with a separate pressurized fluid. The balloon can act as a heat transfer element, or there can be a separate heat transfer element on the catheter adjacent the balloon. The apparatus can be used to perform a dilation procedure, such as angioplasty, in conjunction with cooling of the surrounding tissue.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is in the field of equipment and procedures used to apply cooling to living tissue for the purpose of causing, at a minimum, retardation of the proliferation and healing of the tissue. In certain cases, it will be desirable to freeze the tissue so as to render it non-viable. 
     2. Background Information 
     In several systems of the body of a patient, it can be desirable to apply extreme cooling to the living tissues, thereby retarding proliferation and healing of the tissues, or rendering the tissues non-viable. The non-viable tissue may then slough off for eventual removal or disintegration, or the tissue may remain in place. Some systems in which this process may be performed are the cardiovascular system and the female reproductive system. In applying this extreme cooling, it is known to introduce a refrigerant through a flexible transvascular catheter, or through a rigid probe. In known systems, the cooling is then applied to the target tissue with a heat transfer element formed as a part of the catheter or probe. 
     In known systems, the heat transfer element is generally limited to applying the cooling at a relatively small location, since the heat transfer element must be small enough to permit its easy introduction into the treatment area. This means that it may be necessary to apply cooling for a relatively long period of time, in order to freeze surrounding fluid in the system, such as blood in an artery or vein, before the cooling power is applied to the actual target tissue. Alternatively, it may be necessary to shift the heat transfer element to several locations, with repetitive cooling steps, in order to cover the entire target area. It would be helpful, then, to have an apparatus and procedure which will place a heat transfer element which is large enough to contact all the target tissue directly, at one time, thereby allowing the freezing of all the target tissue in one step. 
     Also in known systems, the application of cooling power to the target tissue may be reduced by the flow of warm fluid past the target area, such as blood flowing past an area of target tissue in an artery or vein. It would be helpful, then, to have an apparatus and procedure which will block the flow of any surrounding fluid, to accelerate the freezing process in the target tissue. 
     One procedure which could benefit from the freezing of tissue is the practice of angioplasty, in which a balloon is inflated to open up a region of stenosis in an artery supplying blood to the heart. It is commonly known that, after the performance of the angioplasty procedure, the area of stenosis will often experience restenosis. It would be helpful, then, to have an apparatus and procedure to freeze the arterial wall tissue in the area of the stenosis, thereby rendering it non-viable, to prevent restenosis. 
     BRIEF SUMMARY OF THE INVENTION 
     By way of example, the subject invention provides an apparatus and a method for inserting a balloon catheter into a selected location in a vascular system of a patient. When the balloon is positioned in the selected location, the balloon is inflated to contact the walls of the vascular system, such as the walls of a blood vessel. This inflation may, for example, be achieved by expanding a compressed refrigerant into the balloon, or it may be achieved by introducing a separate pressurized fluid through the catheter into the balloon. The expanded refrigerant cools either the balloon or a separate heat transfer element, to freeze the surrounding tissue. Where used, the separate heat transfer element can be a metallic coil wound around the catheter next to the balloon, or a metallic cylinder on the outside surface of the catheter next to the balloon. If the inflated balloon is used as the heat transfer device, the cooling is applied directly to the walls of the vascular system. If a separate heat transfer element is used, freezing of surrounding fluid in the vascular system, such as blood, may be necessary, forming an ice ball which will ultimately freeze the walls of the vascular system. The apparatus and method of the invention may be used, for example, to open restricted areas of a blood vessel. 
     The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and in which: 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a longitudinal section view of a first embodiment of the apparatus according to the present invention; 
     FIG. 2 is a longitudinal section view of an embodiment similar to FIG. 1, with two inflatable balloons; 
     FIG. 3 is a longitudinal section view of a second embodiment of the apparatus according to the present invention, with a metallic coil heat transfer element; and 
     FIG. 4 is a longitudinal section view of an embodiment similar to FIG. 3, with a metallic cylinder heat transfer element rather than a metallic coil. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, a first embodiment of the apparatus  10  of the present invention includes a delivery element  12 , an inflatable balloon  14 , a refrigerant supply lumen  18 , a refrigerant return lumen  20 , and one or more expansion elements  22 , shown as orifices in the supply lumen  18 . The delivery element  12  can be an elongated flexible catheter or an elongated rigid probe. The delivery element  12  is shown as a multi-lumen element with coaxial conduits, but it also could be a bundle of separate conduits, or a bundle of separate conduits attached to a guiding element. The balloon  14  is attached adjacent to the distal end  16  of the delivery element  12 . The distal end  16  of the delivery element  12  can be a formable tip or a remote manipulator, to aid in guiding the delivery element  12  through the system of a patient. Where the delivery element  12  is a flexible catheter, the distal end  16  of the delivery element  12  can be provided with a guidewire channel  24 , facilitating the insertion of the catheter through the vascular system of a patient. The distal portion of the delivery element  12  and the balloon  14  can also be provided with instrumentation, such as a thermocouple. 
     The apparatus  10  may include a plurality of balloons  14 , as shown in FIG. 2, with, for example, refrigerant being expanded into the interior of each balloon. 
     The delivery element  12 , with the balloon  14  in a collapsed state, is passed into a selected system of a patient, such as a vascular system. This process can be aided by the use of a remote manipulator tip or formable tip on the distal end  16  of the delivery element  12 . When the distal end  16  of the delivery element  12  has been placed at a selected location in the system of a patient, next to targeted biological tissues, a source of compressed refrigerant, such as a compressor or pressure bottle (not shown), can be used to flow compressed refrigerant through the supply lumen  18  of the delivery element  12 . The compressed refrigerant undergoes expansion through one or more expansion elements, such as the orifices  22 , near the distal end  16  of the delivery element  12 , thereby lowering the temperature of the refrigerant to a desired, lower, temperature, which is sufficiently cold to freeze the target tissues. The expanded refrigerant passes into the interior of the balloon  14 , thereby expanding the balloon  14 . 
     When expanded, the balloon  14  may contact the targeted tissues, such as the walls of a blood vessel. This reduces or blocks the flow of any fluid in the vascular system, such as blood flow, and it achieves an intimate contact with the walls of the system of the patient. The expanded refrigerant cools the walls of the balloon  14 , which in turn cools the targeted tissues, preferably to a temperature sufficient to retard proliferation and/or healing of the tissue or render the tissue non-viable, for example, to a temperature below their freezing point. Expanded refrigerant escapes from the balloon through the return lumen  20 , to return to the inlet of the refrigerant source. Circulation of the refrigerant is continued, to maintain the temperature of the balloon  14  at the desired temperature to insure freezing of the targeted tissue. 
     As an alternative, a separate source (not shown) of pressurized inflation fluid can first be used to inflate the balloon  14  through the supply lumen  18  or the return lumen  20 , followed by introduction of the refrigerant as described above, to achieve the freezing temperature. 
     FIG. 3 shows a second embodiment of the apparatus  10 ′ of the present invention, which includes a delivery element  12 , two inflatable balloons  14 , a refrigerant supply lumen  18 , a refrigerant return lumen  20 , and an expansion element  22 , shown as an orifice or the open end of a capillary tube containing the supply lumen  18 . A single inflatable balloon  14  can also be used. In this embodiment, the delivery element  12  also includes an inflation lumen  26  connected to an inflation fluid source (not shown). The inflation lumen  26  has one or more inflation ports  28  exposed to the interiors of the balloons  14 . 
     The delivery element  12  can be an elongated flexible catheter or an elongated rigid probe. The delivery element  12  is shown as a multi-lumen element, but it also could be a bundle of separate conduits, or a bundle of separate conduits attached to a guiding element. The balloons  14  are attached adjacent to the distal end  16  of the delivery element  12 . The distal end  16  of the delivery element  12  can be a formable tip or a remote manipulator, and it can be provided with a guidewire channel, as discussed above. The distal portion  16  of the delivery element  12  and the balloons  14  can also be provided with instrumentation, such as a thermocouple. 
     Also provided in this embodiment is a separate heat transfer element  30 , which can be a metallic coil formed around the delivery element  12  between the balloons  14 . Rather than being within the balloons  14 , as above, the expansion element  22  in this embodiment may be within the heat transfer element  30  on the delivery element  12 . In this embodiment, a plug  32 , made of a conductive material such as metal, is provided on the delivery element  12  where it will be exposed to the expanded refrigerant issuing from the expansion element  22 . This cools the plug  32 , which in turn cools the metallic coil  30 , by contact therewith. 
     Alternatively, the heat transfer element can be a metallic tube  30 ′ surounding the delivery element  12  between the balloons  14 , as shown in FIG.  4 . One or more openings  34  are provided in the delivery element  12 , to expose the metallic tube  30 ′ to the expanded refrigerant issuing from the expansion element  22 . This cools the metallic tube  30 ′. 
     The delivery element  12 , with the balloons  14  in a collapsed state, is passed into a selected system of a patient, such as a vascular system. This process can be aided by the use of a remote manipulator tip or formable tip on the distal end  16  of the delivery element  12 , as discussed above relative to the first embodiment. When the distal end  16  of the delivery element  12  has been placed at a selected location in the system of a patient, next to targeted biological tissues, inflation fluid is introduced throught the inflation lumen  26  to inflate the balloons  14  against the walls of the surrounding organ or vessel. This reduces or blocks the flow of any fluid in a vascular system, such as blood flow. 
     A source of compressed refrigerant, such as a compressor or pressure bottle (not shown), can be used to flow compressed refrigerant through the supply lumen  18  of the delivery element  12 . The compressed refrigerant undergoes expansion through the orifice  22 , near the distal end  16  of the delivery element  12 , thereby lowering the temperature of the refrigerant to a desired, lower, temperature, which is sufficiently cold to freeze the target tissues. The expanded refrigerant passes through the expansion element  22 , thereby cooling the heat transfer element  30 ,  30 ′ which in turn cools the fluid in the surrounding vascular system, forming an ice ball. The ice ball in turn cools the targeted tissues below their freezing point. Formation of the ice ball is facilitated by blockage of the flow of the surrounding fluid by the balloons  14 . Expanded refrigerant returns through the return lumen  20 , to the inlet of the refrigerant source. Circulation of the refrigerant is continued, to maintain the temperature of the heat transfer element  30 ,  30 ′ at the desired temperature to insure freezing of the targeted tissue. 
     While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.