Precooled cryogenic ablation system

Abstract

A method and apparatus for using a secondary refrigerant to precool and liquefy a primary refrigerant, then vaporizing and expanding the primary refrigerant to cool a cold tip of a cryosurgical instrument for ablation of biological tissue, such as cardiovascular tissue, in particular endocardiac tissue and tissue inside a cardiac blood vessel. The secondary refrigerant has a critical temperature above the critical temperature of the primary refrigerant, and a cooling temperature below the critical temperature of the primary refrigerant, thereby facilitating the use of the precooling step to provide liquid primary refrigerant in an operating room environment in which the primary refrigerant could not otherwise be provided in the liquid phase.

Description

[0001]Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,237,355. The reissue applications are application Ser. Nos. 11 / 412,250 (the present application) and 10 / 446,390(which is fully incorporated herein by reference). The present application Ser. No. 11 / 412,250, is a divisional of reissue application Ser. No. 10 / 446,390 and also a reissue of U.S. Pat. No. 6,237,355.<?insert-end id="INS-S-00001" ?>CROSS REFERENCE TO RELATED APPLICATIONS[0002]Not ApplicableSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0003]Not ApplicableBACKGROUND OF THE INVENTION[0004]1. Field of the Invention[0005]This invention is in the field of cooling biological tissues to very low temperatures, for treatment of medical conditions, as in cryosurgery.[0006]2. Background Information[0007]It is desirable to be able to selectively cool miniature discrete portions of biological tissue to very low temperatures in the performance of cryosurgery, without ...

AI Technical Summary

Benefits of technology

[0010]The present invention comprises a miniature refrigeration system, including a method for operating the system, including precooling of the primary high pressure refrigerant below its critical temperature, to liquefy the primary refrigerant, with a secondary refrigeration cycle using a second refrigerant with a higher critical temperature, to maximize the available cooling power of the primary refrigerant, and to achieve the lowest possible temperature.

[0011]The cooling power is an important design parameter of a cryosurgical instrument. With greater cooling power, more rapid temperature decreases occur, and lower temperatures can be maintained at the probe tip during freezing. This ultimately leads to greater tissue destruction. The power of a J-T cryosurgical device is a function of the enthalpy difference of the primary refrigerant and the mass flow rate. Pre-cooling a refrigerant below its critical temperature and liquefying the refrigerant will increase the enthalpy difference available for cooling power.

[0014]The primary-to-secondary heat exchanger is part of the secondary refrigeration system, which can have a secondary compressor and a secondary expansion element, in addition to the primary-to-secondary heat exchanger. The liquid high pressure secondary refrigerant, having a higher critical temperature than the primary refrigerant, can be at a temperature which is relatively higher than the critical temperature of the primary refrigerant. However, the vaporized and expanded low pressure secondary refrigerant is at a temperature which is low enough to cool the primary refrigerant below its critical temperature. Since the secondary refrigerant has a critical temperature above normal operating room temperature, it can easily be provided in the liquid state in an operating room environment, whereas the primary refrigerant, which has a critical temperature significantly below normal operating room temperature, can not.

Problems solved by technology

This ultimately leads to greater tissue destruction.

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