Cryotherapy probe

1. A device for freezing body tissue, the device comprising a main driving system capable of generating nitrogen under physical conditions near a critical point of a liquid-vapor system for the nitrogen, wherein:

(i) 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, and

(ii) the physical conditions comprise a pressure of about 33.5 atm.

2. The device of claim 1 , further comprising a storage vessel to store the nitrogen.

3. The device of claim 1 , further comprising a heat exchanger to over-cool the nitrogen prior to delivery to a distal portion of a cryotherapy instrument.

4. The device of claim 1 , further comprising at least one cryotherapy instrument.

5. The device of claim 4 , wherein the cryotherapy instrument comprises:

at least one supply conduit; and

at least one return conduit.

6. The device of claim 5 , wherein the cryotherapy instrument further comprises insulation.

7. The device of claim 6 , wherein the insulation is in the form of a vacuum.

8. The device of claim 4 , wherein the cryotherapy instrument comprises a plurality of electrical elements.

9. A cryotherapy system comprising:

a main driving system capable of generating nitrogen under physical conditions near a critical point of a liquid-vapor system for the nitrogen, wherein (i) 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 and (ii) the physical conditions comprise a pressure of about 33.5 atm; and

a cryotherapy ablation device comprising:

an inlet capillary for providing a supply flow of the nitrogen; and

an outlet capillary for providing a return flow of the nitrogen,

wherein the inlet capillary and the outlet capillary are configured to circulate the nitrogen through the cryotherapy ablation device, and

wherein vapor lock associated with circulating the nitrogen through the cryotherapy instrument is avoided.

10. The cryotherapy system of claim 9 , further comprising a storage vessel to store the nitrogen.

11. The cryotherapy system of claim 9 , further comprising a heat exchanger.

12. The cryotherapy system of claim 9 , wherein the cryotherapy ablation device further comprises insulation.

13. The cryotherapy system of claim 12 , wherein the insulation is in the form of a vacuum.

14. The cryotherapy system of claim 9 , wherein the cryotherapy ablation device comprises a plurality of electrical elements.

15. A method of freezing body tissue, the method comprising the steps of:

positioning a distal portion of a cryotherapy instrument in the body tissue; and

circulating nitrogen through the cryotherapy instrument under physical conditions near a critical point of a liquid-vapor system for nitrogen,

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, and

wherein the physical conditions comprise a pressure of about 33.5 atm.

16. The method of claim 15 , wherein the circulating step comprises the step of passing the nitrogen through a heat exchanger to over-cool the nitrogen.

17. The method of claim 16 , further comprising the step of reducing the pressure of the nitrogen.

18. A method of avoiding vapor lock in a cryotherapy ablation device, the method comprising:

raising a pressure of liquid nitrogen to about 33.5 atm to generate near critical nitrogen; and

circulating the near critical nitrogen through the cryotherapy ablation device.

19. The method of claim 18 , wherein a diameter of a portion of the cryotherapy ablation device to be placed adjacent to tissue to be ablated is less than 2 mm.

20. The method of claim 18 , wherein the cryotherapy ablation device comprises at least one supply conduit and at least one return conduit.