Cryogenic Biological Apparatus

Abstract

A spray-type cryogenic probe including a dual stream, cryogenic liquifier for converting stored gas into an ultracold liquid which is ejected from the probe in a fine, controlled stream to freeze tissue.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the field of cryogenic biology (cryobiology) and, more particularly, to a cryogenic system for generating cryogenic liquid specifically for application in the freezing of tissue such as, for example, skin tissue in cryodermatology operations.

Prior methods of freezing tissue have included the direct application of cryogenic liquids such as liquid argon and liquid nitrogen to tissue. However, storage and transfer of cryogenic liquids at temperatures in the order of minus 300.degree. F. have presented many disadvantages. For example, the ultracold liquid must be stored in relatively expensive cryogenic dewars, and a significant portion of the liquid may vaporize during prolonged storage. Even more importantly, the transfer line from the dewar to the probe may become frosted and stiff at low temperatures such that heat must be applied to the transfer line during the operation in order to keep it flexible and frost-free Alternatively, some prior devices have been designed wherein a gas is liquefied and circulated entirely within a closed tip or "cold-finger." Such systems require that the liquid be vaporized within the tip, and the vapor is returned in countercurrent heat exchange with the incoming gas to cool and condense it. While such closed cycle, cold-tip probes solve the liquid problem, they are medically disadvantageous in that the cold tip quickly accumulates frost which substantially reduces the heat transfer rate between the tip and the tissue. On the other hand, if the tip is kept frost-free, the tissue tends to freeze to the tip such that free movement of the tip is hindered, in addition to causing considerable discomfort to the patient.

SUMMARY OF THE INVENTION

The present invention solves all of the above-indicated problems by utilization of a unique, dual stream liquefier wherein gas from the source is divided into first and second streams. The first stream is passed through a heat exchanger and a Joule Thompson expansion orifice whereby it is reduced in temperature to its liquefaction point and liquefied. This first stream is passed in heat exchange relationship with the second stream so as to liquefy the second stream which is then ejected against the tissue in a fine, controlled jet. The first stream is vaporized in liquefying the second stream and is returned in countercurrent heat exchange with the incoming first and second streams before being vented to atmosphere at a relatively warm temperature.

Accordingly, it is a primary object of the present invention to provide a cryogenic system for use in biological applications wherein the refrigerant can be stored as an ambient temperature gas, liquefied, and ejected as a controlled jet of ultracold liquid.

It is a further object of the present invention to provide a cryobiological probe including a dual stream liquefier whereby a first portion of the stored gas refrigerant is liquefied and heat exchanged against a second portion, such that, the first portion is vented as a gas at relatively warm temperature, while the second portion is ejected as a controlled jet of ultracold liquid or gas.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic flow diagram of the complete cryobiological system including the gas storage cylinder, the control unit, and the probe; and

FIG. 2 is a cross-sectional view of the probe illustrating the details of the dual-stream liquefier.

DETAILED DESCRIPTION

Referring first to FIG. 1, numeral 10 indicates a standard, high-pressure cylinder in which a gas such as argon or nitrogen may be stored in a compressed state such as a pressure of 3,000 p.s.i.a. The cylinder includes a standard cylinder valve 12 which is manually opened and which is connected to a flexible line or hose 14 for conducting the high-pressure gas into a control cabinet 16. Of course, it will be understood that the size of cabinet 16 has been greatly enlarged relative to the size of cylinder 10 so as to facilitate the illustration of the control components contained within the cabinet. In practice, the cabinet is sufficiently small so as to be placed on a desk or table in close proximity to the probe 18, whereas, the cabinet may be located at any distance from the cylinder 10. Alternatively, line 14 may be provided with a connector so as to be connected to a high-pressure gas piping system.

Within cabinet 16, line 14 is connected to a pressure gauge 18 which indicates the operating pressure of the cylinder 10, or other source of compressed gas. This gauge indicates that a sufficient source pressure is available for operating the system. Line 14 is also connected to a pressure reduction valve 20 which may be manually variable, or may be set to operate at a predetermined pressure reduction. By way of example, the cylinder 10 may be at a pressure in the order of 3,000 p.s.i.a., whereas, the pressure downstream of valve 20 may be in the order of 1,500 p.s.i.a.

The output side of valve 20 is connected to an adsorber 22 which is provided to remove any impurities in the gas which may solidify and thereby plug the very fine heat exchanger tubing which will be subsequently described. Adsorber 22 may be filled with any conventional adsorbent material such as charcoal, silica gel or other material.

The output side of adsorber 22 is connected through a solenoid valve 24 to a flexible line 26 leading to the probe 18. Solenoid valve 24 is connected via electrical lines 27 to a plug 28 which may be plugged into any standard electrical outlet. Lines 27 include an ON/OFF switch 29 closure of which actuates the solenoid and opens the valve 24. An indicator light 30 is also connected in parallel with the valve so as to indicate the open position of valve 24, and hence, the operating condition of the system.

Reference is now made to FIG. 2 which illustrates the internal details of probe 18. The probe includes a cylindrical casing 30 closed at the rearward end by a cap 32 and including casing portions 34 and 36 which are disposed at an angle relative to the longitudinal axis of cylinder 30. Axially disposed within the casing 30 is an elongated, metallic sleeve 38 which is closed at the rearward end by cap 32 and closed at the forward end by a plug 40. A second metallic sleeve or mandrel 42 is concentrically positioned within sleeve 38 and is closed at opposite ends by plugs 44 and 46. Finned tubing 48 is helically wound on mandrel 42 so as to form a heat exchanger coil 49 in direct engagement with both mandrel 42 and the interior surface of sleeve 38. The forward end of tubing 48 terminates in a reduced diameter tip portion 50 forming a Joule Thompson expansion orifice disposed within a chamber 52. The opposite end of tubing 48 is secured in a fitting 54 which extends through cap 32.

Fitting 54 also includes a lateral port which receives the end of a length of tubing 56 which is helically wound about the external surface of cylinder 38 and forms a second heat exchanger coil 57. Coil 57 terminates in an elongated nozzle portion 58 extending slightly outwardly of casing portion 36 and is supported by a rod 60 having one end rigidly secured in plug 40. Fitting 54 further includes a counterbored portion 62 which receives a plug of filter material 64 and which receives the end of a stem 66 to which flexible line 26 is connected by a suitable coupling 68.

A short length of tubing 70 is provided through cap 32 so as to provide a vent from the interior of sleeve 38 to atmosphere. Lastly, the space between sleeve 38 and casing 30 is filled with a suitable thermal insulation 72 such as, for example, expanded polyurethane foam.

OPERATION

The operation of the cryogenic biological system is as follows. Assuming that cylinder valve 12 is open, the operator closes switch 29 which opens solenoid valve 24 and permits the passage of ambient temperature gas through valve 20, adsorber 22, valve 24 and flexible line 26 to probe 18. The gas passes through stem 66 and filter plug 64 in fitting 54 wherein it is divided into a first stream which flows through tubing 48, coil 49 and tip portion 50 forming a Joule Thompson expansion orifice whereby the gas is rapidly expanded and cooled. As this first stream continues to flow through coil 49 and the expansion orifice formed by the end of tip 50, the gas is precooled by the colder gas flowing countercurrently from chamber 52 around coil 49 and through vent 70 to atmosphere. Thus, the first gas stream is quickly cooled to its liquefaction temperature and cryogenic liquid is formed in chamber 52. Since the liquid in chamber 52, and the cold gas flowing countercurrently around coil 49, are in heat exchange relationship with the second gas stream passing through coil 57 around sleeve 38, the second gas stream is also cooled and liquefied. Thus, as soon as the brief cool-down period is completed, the second stream is ejected from nozzle 58 as a fine, controlled jet of cryogenic liquid having a temperature in the order of minus 320.degree. F., while the first stream of gas is vented at a temperature of in the order of 60.degree. F.

From the foregoing description it will be apparent that by gripping the handle provided by cylinder 30, the operator may direct the fine stream or jet of ultracold liquid against the precise portion of tissue which is to be frozen. In addition to having precise control over the area which is to be treated by the fine jet, the volume or rate of heat transfer may also be varied by presetting or manually varying the pressure reduction occurring in valve 20. For example, valve 20 may be set such as to produce a substantially pure liquid jet or, if desired, the second stream may be ejected from the nozzle 58 as a gas at a cryogenic temperature in the order of minus 300.degree. F. which is slightly above the normal liquefaction temperature of nitrogen, argon, air, etc. It will therefore be apparent that the particular tissue area may be selectively frozen without the disadvantages of maintaining a continuous liquid reservoir, and without the problems incident to the use of closed tip systems previously disclosed. That is, the gas in the cylinder may be stored for extended periods of time with no loss of refrigerant gas and the lines 14 and 26 present no problems of frost accumulation or loss of flexibility since they operate at ambient temperatures.

From the foregoing description of one preferred embodiment of the invention, it will be readily apparent that numerous changes may be made without departing from the scope of the invention. For example, the tubing 56 forming coil 57 may be wound around mandrel 42 along with tubing 48 instead of being separately wound on the outside of cylinder 38. In addition, it will be apparent that an additional flow control valve may be utilized in line 26 in order to control the volume of flow if desired. Lastly, the term "cryogenic" as used hereinabove and in the following claims is intended to denote temperatures lower than minus 200.degree. F., and the term "fluid" is intended to denote gas, liquid and mixed gas-liquid streams at cryogenic temperatures.

Claims

Having described the invention in one preferred embodiment, what is claimed is:

1. A cryogenic system for use in cryobiological applications including, a source of high-pressure gas, a probe including a nozzle for ejecting a stream of cryogenic fluid against tissue to be frozen, and cooling means including a cryogenic heat exchanger having a Joule Thompson expansion orifice intermediate said gas source and said nozzle for cooling said gas to a cryogenic temperature before ejection from said nozzle as said stream of cryogenic fluid.

2. A cryogenic system for use in cryobiological applications including, a source of high-pressure gas, a probe including a nozzle for ejecting a stream of cryogenic fluid against tissue to be frozen, cooling means intermediate said gas source and said nozzle for cooling at least a portion of said gas to a cryogenic temperature before ejection thereof from said nozzle as said stream of cryogenic fluid, said cooling means including means for dividing said high-pressure gas into first and second streams, means for cooling said first stream, means for cooling said second stream in heat exchange with said first stream, means for venting said first stream after warming said first stream in heat exchange with said second stream, and means connecting said second stream to said nozzle for ejection therefrom as said stream of cryogenic fluid.

3. The system as claimed in claim 2 wherein said means for cooling said first stream comprises a first heat exchanger and a Joule Thompson expansion orifice, and said means for cooling said second stream comprises a second heat exchanger connected to said nozzle.

4. The system as claimed in claim 3 wherein said first and second heat exchangers comprise wound tubular coils in heat exchange relationship with each other, and at least one of said coils is composed of finned tubing.

5. A cryobiological probe for use in generating and directing a cryogenic fluid against tissue comprising:

a. a hollow, elongated casing forming a handle having forward and rearward portions,

b. a gas supply tube extending into said rearward portion,

c. means within said casing and connected to said supply tube for dividing said gas into first and second streams,

d. means within said casing forming a first heat exchanger and a Joule Thompson orifice for cooling said first stream,

e. means within said casing forming a second heat exchanger for cooling said second stream in heat exchange with said first cooled stream whereby said first stream is warmed and said second stream is cooled to form a cryogenic fluid,

f. a nozzle located in the forward portion of said casing and connected to said second heat exchanger for ejecting said second stream as a jet of cryogenic fluid, and

g. means for exhausting said warmed first stream from said probe after heat exchange with said second stream.

6. The cryobiological probe as claimed in claim 5 including means forming a liquid chamber for collecting cryogenic liquid produced by said Joule Thompson orifice, and means for passing said second stream in heat exchange relationship with said cryogenic liquid so as to at least partially liquefy the gas in said second stream.

7. The cryobiological probe as claimed in claim 6 wherein said first heat exchanger comprises finned tubing helically wound about a first mandrel, and a sleeve surrounding said finned tubing forming said liquid chamber.

8. A method of freezing tissue comprising:

a. storing a gas at ambient temperature and at high pressure,

b. withdrawing a portion of said stored gas,

c. dividing said withdrawn gas into first and second streams,

d. cooling said first stream by Joule Thompson expansion and heat exchange with itself to produce a first cryogenic fluid,

e. cooling said second stream to a cryogenic temperature in exchange with said first stream so as to warm said first stream,

f. exhausting said warmed first stream, and

g. ejecting a jet of said second stream at a cryogenic temperature against said tissue to freeze said tissue.

9. The method as claimed in claim 8 wherein step (d) includes cooling said first stream to its liquefaction temperature so as to form a cryogenic liquid, and step (e) includes cooling said second stream to its liquefaction temperature so as to liquefy substantially all of said second stream to form a jet of cryogenic liquid as it is ejected from said nozzle.