Patent ID: 7004936

Claim:
A refrigeration system for cooling a tip section of a cryoablation catheter which comprises: a source for a primary fluid refrigerant wherein the primary fluid refrigerant is nitrous oxide (N 2 O); a closed-cycle refrigeration unit for pre-cooling the primary fluid to a sub-cool temperature (T sc ) at a working pressure (p w ) wherein the sub-cool temperature is approximately minus forty degrees Centigrade (T sc =−40° C.) and the working pressure is approximately four hundred psia; a catheter tube formed with a lumen and having an open proximal end and a closed distal end, with the closed distal end of said catheter tube defining a tip section; a supply line having a distal end and a proximal end, said supply line being positioned inside the lumen of the catheter tube with the distal end thereof positioned in the tip section of said catheter tube, wherein said supply line includes a supply tube and a coaxial capillary tube extending distally therefrom, and further wherein said capillary tube has a fluid flow impedance greater than a fluid flow impedance of said supply tube; a means for introducing the sub-cooled primary fluid into the proximal end of said capillary tube at approximately −40° C. and at substantially the working pressure (p w ) for transfer therethrough and outflow therefrom into the tip section of said catheter tube in a substantially liquid state at approximately −88° C. and at an outflow pressure (p o ); and a vacuum means connected in fluid communication with the proximal end of said catheter tube for removing the primary fluid therefrom at a return pressure (p r ), while maintaining the outflow pressure (p o ) in the tip section substantially at a predetermined value to allow the primary fluid to boil in the tip section substantially at its normal boiling point of approximately minus eighty eight degrees Centigrade.