Surgery – Instruments – Cyrogenic application
Patent
1991-07-19
1993-07-06
Aschenbrenner, Peter A.
Surgery
Instruments
Cyrogenic application
606 22, 606 23, A61B 1736
Patent
active
052249433
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to cryosurgical apparatus and in particular to a cryoprobe for freezing human or animal tissue in a surgical procedure.
BACKGROUND OF THE INVENTION
Most cryosurgical probes in use today are cooled by expanding a gas at high pressure in a cavity at the working tip of the probes whereby in accordance with the Joule-Thomson effect, the gas undergoes rapid cooling and the tip is brought quickly to its operating temperature.
Before using a cryosurgical probe of this type it has to be sterilised by a steam process. In this process probe moisture contamination may occur which will either prevent the probe from functioning at all or cause the tip to defrost after a short period of time by clogging the gas flow passages and the Joule Thomson nozzle through which the gas is caused to expand into the tip cavity.
It is normal practice therefore to purge the gas flow passages and Joule-Thomson nozzle of moisture contamination subsequent to the steam sterilisation process, by a purging method which involves passing a low pressure dry gas of the type eventually used for the cooling process, but at a higher pressure, through the probe gas flow passageways including the Joule-Thomson nozzle.
However for small diameter probes the required purging time is unacceptably high which reduces the efficiency of the device in the hands of the surgeon primarily because of the waiting time before it can be used.
Attempts have been made to reduce the purging time. For example, one method entails passing a low pressure gas through the probe in a flow direction reverse to the normal flow direction to effect cooling, i.e. the probe freeze cycle, and increasing the flow rate by drilling two small by-pass holes near the Joule-Thomson nozzle.
An alternative method disclosed in U.S. Pat. No. 3,613,689 utilises a valve which closes a by-pass hole provided close to the Joule-Thompson nozzle under the effect of high-pressure gas flow in the probe freeze cycle, but which is constrained to move away from the by-pass hole under the effect of low pressure gas during the probe purge cycle or warming mode, so increasing the flow rate and consequently the purging time. In this design the gas flow direction in both the purge and freeze cycles is the same.
The increased purging time provided by the prior art is, however, still not short enough fully to satisfy operational requirements. Moreover the introduction of small holes in the vicinity of the Joule-Thomson nozzle has the undesirable effect of decreasing the pressure drop across the nozzle so reducing its efficiency and the cooling effect.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems of the prior art above stated and to provide a cryosurgical probe which is capable of being purged of contaminating moisture to such rapid extent as to constitute an event which to all intents and purposes is unnoticed by the operator.
According to the invention there is provided a cryosurgical probe comprising a probe body, an operating tip at one end of the body, first and second passageways leading to and from a cavity in the probe tip, means for expanding a high pressure gas in said cavity delivered along said first passageway thereby to cool the gas and said tip, and valve means arranged in the probe body and selectively operable between a probe purge cycle position whereat to by-pass said expanding means and direct flow of a purging gas delivered along said second passageway to said first passageway, and a freeze cycle position whereat to direct a high pressure gas along said first passageway to said expanding means then to exhaust from said cavity after expansion, along said second passageway.
With this arrangement it is possible to purge the probe prior to a freezing sequence very rapidly compared with known techniques because purging may be limited to those parts of the probe which have been affected by moisture contamination during the sterilising process and it does not involve any modification of or interfe
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Aschenbrenner Peter A.
Price, Jr,. Stanley J.
Spembly Medical Ltd.
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