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Targeted cooling of tissue within a bodyRelated Patent Categories: Surgery: Light, Thermal, And Electrical Application, Light, Thermal, And Electrical Application, Thermal Applicators, With Fluid Supply, Internally AppliedTargeted cooling of tissue within a body description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060142826, Targeted cooling of tissue within a body. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This invention relates to cooling a target tissue region inside a body. BACKGROUND [0002] Myocardial ischemia, and in severe cases acute myocardial infarction (AMI), can occur when there is inadequate blood circulation to the myocardium due to coronary artery disease. Evidence suggests that early reperfusion of blood into the heart, after removing a blockage to blood flow, dramatically reduces damage to the myocardium. However, the reestablishment of blood flow into the heart may cause a reperfusion injury to occur. Reperfusion injury is believed to be due to the build up of waste products on the myocardium during the time blood flow was inadequate and the reaction of these waste products with oxygen in the blood when normal blood flow is reestablished. It is possible to reduce reperfusion injury to the myocardium by cooling the myocardial tissue prior to reperfusion. Mild cooling of the myocardial tissue to a temperature between 28 and 36 degrees Celsius provides a protective effect, likely by the reduction in the rate of chemical reactions and the reduction of tissue activity and associated metabolic demands. [0003] One method of cooling myocardial tissue is to place an ice pack over the patient's heart. Another method involves puncturing the pericardium and providing cooled fluid to a reservoir inserted into the pericardial space near the targeted myocardial tissue. Cooling of the myocardial tissue may also be accomplished by perfusing the target tissue with cooled solutions. A catheter having a heat transfer element located in the catheter's distal tip may also be inserted into a blood vessel to cool blood flowing into and through the heart. It is also possible to cool the myocardial tissue by supplying cool blood to the heart through a catheter placed in the patient's coronary sinus. SUMMARY [0004] The invention features devices and methods to cool a target tissue region inside the body. In an aspect, the invention features a method of cooling a target tissue region that includes providing fluid cooled below normal body temperature and blood at a normal body temperature to the tissue region in proportions to cool the tissue region and maintain, for an extended period of time, the temperature of the tissue region within a target temperature range that is below normal body temperature. [0005] Implementations may include providing the cooled fluid and the blood at normal body temperature to the tissue region simultaneously. The providing of the blood at normal body temperature to the tissue region may be performed using a catheter that occludes a vessel upstream from the tissue region and permits a selected amount of blood to flow through a lumen in the catheter and to the tissue region. The catheter may also perform the providing of cool fluid to the tissue region. The providing of blood to the tissue region can be performed by occluding a vessel upstream from the tissue region to restrict normal blood flow and then removing the occlusion to permit normal blood flow. A catheter may also provide blood to the tissue region by partially occluding a vessel in fluid communication with the tissue region to permit a restricted amount of blood to flow to the tissue region. In other implementations, a catheter positioned in a vessel in fluid communication with the tissue region may provide the fluid to the tissue region through a lumen that extends longitudinally through the catheter, the lumen having a diameter of at least twenty thousandths of an inch. [0006] In another aspect, the invention features a method of cooling a target tissue region inside a body that includes occluding a body vessel to prevent normal blood flow to the tissue region. While the body vessel is occluded, cooled fluid is provided to the tissue region to cool the tissue region below normal body temperature. Normal blood flow to the tissue region is recommenced by removing the occlusion in the body vessel. Normal blood flow to the tissue region is prevented again by occluding the body vessel before the temperature of the tissue region returns to normal body temperature. While the body vessel is occluded, cooled fluid is provided to the tissue region again to maintain the temperature of the tissue region below normal body temperature. [0007] In implementations, the body vessel may be occluded to prevent normal blood flow to the tissue region by inflating a balloon positioned in the vessel. In addition, a catheter positioned in a vessel at a location upstream from the tissue region may provide the fluid to the tissue region through a lumen extending longitudinally through the catheter, the lumen having a diameter of at least twenty thousandths of an inch. [0008] In another aspect, the invention features a method of cooling a target tissue region inside a body that includes restricting normal blood flow to the tissue region so that only a desired amount of blood is provided to the tissue region. Cool fluid is provided to mix with the blood provided to the tissue region so as to cool the tissue region below normal body temperature and to maintain, for an extended period of time, the temperature of the tissue region within a target tissue range that is below normal body temperature. [0009] In implementations, the providing of the blood at normal body temperature to the tissue region can be performed using a catheter that occludes a vessel upstream from the tissue region and permits a selected amount of blood to flow through a lumen in the catheter and to the tissue region. The providing of blood at normal body temperature to the tissue region may also be performed using a catheter to partially occlude a vessel upstream from the tissue region and permit a selected amount of blood to reach the tissue region. In other implementations, a catheter positioned in a vessel in fluid communication with the tissue region may provide the fluid to the tissue region through a lumen that extends longitudinally through the catheter, the lumen having a diameter of at least twenty thousandths of an inch. [0010] Implementations of the various aspects of the invention may include one or more other features. For example, the tissue region may be maintained within the target temperature range that is below normal body temperature for a time period beyond the normal length of time a tissue region is deprived of oxygenated blood during a heart procedure, or about two minutes. The temperature of the tissue region can be within a target temperature range of about 28 to 36 degrees Celsius. In addition, the providing of fluid and blood to cool the target tissue region can be performed during a procedure to open a lesion in a vessel. Further, a control system may control the providing of fluid and blood to the tissue region to maintain the temperature of the tissue region below normal body temperature. [0011] In another aspect, the invention features a system for controlling the temperature of a target tissue region inside the body. The system includes a catheter for providing cooled fluid to the tissue region and for controlling normal blood flow to the tissue region. The system also includes a control system that controls the amount of the cooled fluid and blood that the catheter provides to the tissue region so as to cool and to maintain, for an extended period of time, the tissue region within a target temperature range that is below normal body temperature. [0012] Implementations may include one or more of the following. The catheter for providing fluid and controlling normal blood flow to the tissue region may be a perfusion catheter. The catheter for providing fluid and controlling normal blood flow to the tissue region may also be a balloon catheter. The catheter may include an infusion lumen for providing fluid to the tissue region that has a diameter of at least twenty thousandths of an inch. The catheter may also include a temperature sensor that may be advanced to a location distal to the catheter to measure the temperature of the tissue region. [0013] The control system may include a controller that controls the cooling of the tissue region without measuring the temperature of the tissue region. The control system may also include a controller that controls the cooling of the tissue region without measuring the temperature of the cool fluid as it exits the catheter and is provided to the tissue region. In addition, the system may have a temperature monitor that receives temperature information from a temperature sensor of the catheter. In other implementations, the control system may include an infusion pump to control the amount of cool fluid provided to the tissue region. An inflation pump to inflate and deflate a balloon on the catheter may also be provided. [0014] In another aspect, the invention features a catheter for providing cool fluid to a tissue region inside a body. The catheter includes an elongated member having a lumen extending longitudinally therethrough to a distal end of the elongated member and a temperature sensor that extends to a location distal to the distal end of the elongated member to sense the temperature of the tissue region. [0015] In implementations, the temperature sensor may be a thermocouple that has two conductors of different material extending from a proximal end of the catheter and joined at a distal end to form a junction. The temperature sensor may sense the temperature of the tissue region by measuring the temperature of a vessel wall located distal to the distal end of the elongated member and adjacent to the target tissue region. In other implementations, the temperature sensor may sense the temperature of the tissue region by measuring the temperature of the cool fluid provided to the tissue region distal to the distal end of the elongated member and adjacent to the target tissue region. [0016] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. DESCRIPTION OF DRAWINGS [0017] FIGS. 1A and 1B are diagrams showing a side view of a distal end of a balloon catheter positioned in a coronary artery, shown in cross-section, and illustrate a method of cooling a target tissue region in the heart. [0018] FIG. 2 is a cross-sectional view of the balloon catheter along the line 2-2 shown in FIG. 1A. [0019] FIG. 3 is a graph that shows the temperature of the target tissue region during the application of the cooling method illustrated in FIGS. 1A and 1B. [0020] FIG. 4 is a diagram of a side view of a distal end of a perfusion catheter positioned in a coronary artery, shown in cross-section, and illustrates an alternative method of cooling a target tissue region in the heart. 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