Cryotherapy probe
A method of cooling a material including the steps of (i) providing a cryotherapy instrument, (ii) positioning a portion of the cryotherapy instrument adjacent the material to be cooled, and (iii) circulating a cryogenic fluid through the cryotherapy instrument under physical conditions near a critical point of a liquid-vapor system for the cryogenic fluid. The critical point defines a point in a phase diagram of the liquid-vapor system where molar volumes are substantially equivalent for liquid and gas, whereby vapor lock associated with cooling of the cryotherapy instrument is avoided.
1. A method of cooling a material comprising the steps of:
providing a cryotherapy instrument;
positioning a portion of the cryotherapy instrument adjacent the material to be cooled;
circulating a cryogenic fluid through the cryotherapy instrument under physical conditions near a critical point of a liquid-vapor system for the cryogenic fluid, wherein the critical point defines a point in a phase diagram of the liquid-vapor system where molar volumes are substantially equivalent for liquid and gas, whereby vapor lock associated with cooling of the cryotherapy instrument is avoided.
2. The method of claim 1 , wherein the step of circulating the cryogenic fluid comprises circulating the cryogenic fluid for an initial period of time.
3. The method of claim 2 , further comprising the step of maintaining the pressure of the cryogenic fluid during the initial period at a near critical pressure of the cryogenic fluid.
4. The method of claim 3 , wherein the step of circulating the cryogenic fluid comprises circulating cryogenic fluid for a freeze period subsequent to the initial period.
5. The method of claim 4 , wherein the pressure of the cryogenic fluid during the freeze period is less than the pressure of the cryogenic fluid during the initial period.
6. The method of claim 1 , wherein the cryotherapy instrument comprises a shaft having a distal section with a closed distal end and an active freeze region in the distal section.
7. The method of claim 6 , wherein the material to be cooled is human tissue.
8. The method of claim 7 , wherein the shaft comprises a metal material adapted for percutaneous insertion into the human tissue.
9. The method of claim 6 , wherein a length of the active freeze region is approximately 1 cm.
10. The method of claim 7 , wherein the human tissue is a tumor.
11. The method of claim 1 , wherein the circulating step comprises circulating liquid nitrogen at a pressure of about 33.5 atm.
12. The method of claim 1 , wherein the circulating step comprises circulating the cryogenic fluid through an inlet tube, an outlet tube, and a hollow cavity of the cryotherapy instrument.