Cryogenic apparatus

Abstract

The invention relates to cryosurgical instruments in which gas cooling by Joule-Thomson expansion is employed in an applicator adapted to contact and thermally cool human tissue, the gas in the cooling mode being carried to an orifice, for expansion therethrough, by a first duct and led away to atmosphere after expansion by a second duct. The invention resides in apparatus and a method of obtaining rapid warming of the applicator by providing valve means for connecting the second duct directly to a source of high pressure refrigerant gas so that gas condenses within the applicator upon any cold surface thereof.

Description

This invention relates to cryogenic apparatus and in particular to cryosurgical instruments of the type in which pressurised refrigerant gas, such as nitrous oxide for example, is expanded through an orifice to thereby produce a cooling effect by Joule-Thomson expansion, the cooled gas impinging upon the internal surfaces of a hollow working tip, applicator or probe whereby animal tissue in contact therewith may be frozen. Such instruments are described in U.S. Pat. No. 3,502,081 which also shows electrical heaters associated with the probes for the purpose of rapidly heating a working tip so that it may be readily detached from frozen tissue when so desired.

Such instruments have an exhaust passage leading from the hollow working tip to atmosphere whereby the refrigerant after expansion is ducted away, and may use the bottled refrigerant in the liquid phase, drawing-off the refrigerant as a gas from above the liquid surface.

Non-electrical methods have been proposed for reheating the working tips of similar instruments, which methods do not suffer from the need to regulate the heating, or to monitor the tip temperature when so doing, as with electrical methods. Such a non-electrical method is disclosed in U.S. Pat. No. 3,696,813 and involves restricting or completely closing the exhaust passage so that refrigerant fluid, still flowing through the orifice, raises the pressure within the working tip to that, or nearly so, of the refrigerant source. In the case of a Joule-Thomson, gas-cooled instrument, as the pressure of gas rises within the working tip, gas begins to condense on the cold surfaces, the latent heat of condensation serving to warm the surfaces and bring about a rapid "defrost" as it is generally known.

Although the method described may be satisfactory in small instruments, it is believed that the rate of warming can be accelerated in larger instruments by by-passing the orifice and pressurising the interior of a working tip directly from the source of refrigerant thus avoiding delays due to exponential rates of pressure rise arising from the restriction to flow of an orifice.

The rate of pressure rise in a working tip is also affected by the size of the isolated volume and the size of orifice (which however is normally fixed to produce the required cooling power). It is believed that U.S. Pat. No. 3,696,813 seeks to minimise the restricted or isolated volume by providing a manually operated valve within the normally hand-held instrument so that the surgeon may initiate cooling and reheating of the working tip by respectively depressing and releasing the valve with his finger/s. In view of the high refrigerant pressures employed, for example 700 p.s.i. in the case of nitrous oxide, such a valve requires either a large force, or an exaggerated finger movement if levers are employed to reduce the force for operation thereof, and which may make precise movements or manipulations of the instrument difficult during surgery. By removing the valve and placing it remote from the instrument, although permitting the surgeon greater sensitivity of operation, the isolated volume in the warming mode would be greatly increased resulting in slower defrost.

It is therefore an aim of the invention to provide a method for initiating a cooling mode and for causing the cooled working tip of a cryosurgical instrument to rapidly rewarm sufficiently for detachment from tissue frozen theret, i.e., a warming mode, in which the rate of warming is independent of any isolated volume; and it is also an aim to provide apparatus in which such cooling and rewarming is achieved by valve or other control means which may be either within or separate from the instrument.

Accordingly the invention provides a cryosurgical instrument for use with a remote source of pressurised gas and adapted to operate in a cooling mode and in a rapid warming mode, comprising:

a body enclosing a cavity having a wall of high thermal conductance, said wall being shaped externally for contacting human tissue and being of sufficient structural integrity to withstand the full source pressure and providing heat transfer with the tissue;

a first conduit extending through said body and connected to said cavity terminating therein in a restricted orifice through which pressurised gas may expand into said cavity, experiencing Joule-Thomson cooling in so doing, and thereby cool said wall when said first conduit is connected to said source of gas;

a second conduit connected to said cavity; cross-over valve means to which connects said first and second conduits, said source of pressurised gas and an exhaust passage leading to atmosphere, which valve means, in the cooling mode connect said source to said first conduit and connect said second conduit to said exhaust passage, and in the warming mode connect said source to said second conduit;

all such that, in the cooling mode, pressurised gas from said source expands through said orifice and into said cavity wherefrom it is ducted to atmosphere via said second conduit and said exhaust passage and, that in the warming mode, gas from said source is fed via said second conduit directly into said cavity wherein, if the wall is cold it condenses thereupon, thus liberating latent heat and warming said wall in consequence.

The valve means may conveniently comprise a two position valve, either within or remote from said body, which in a second position provides connection for the warming mode and in a first position provides connection for a cooling mode. Such a valve may be biased, by a spring for example, towards said second position, and may be adapted for foot, hand or pressure control.

When such a two-position valve is used it is preferable to include means, such as for example a non-return valve in series with said first conduit, in order to prevent continuous reversal of flow when in the warming mode. The valve itself, when in its second position, may be adapted to close said first conduit, or the conduit may be permitted to remain connected to said source since no flow will occur when the pressure in said first and second conduits is equal.

In order to isolate the source of gas and/or to vent said first and second conduits when the instrument is not in use, the valve means may comprise a three-position valve having the same first and second positions as the aforementioned two-position valve but having a third position whereat the source is isolated and, if so desired, at least the first conduit of said first and second conduits may be connected to said exhaust passage.

If the valve is adapted to pass through the second position when changing from the first to third positions, and vice versa and is biased normally towards said third position, the instrument may then be operated by a single movement, automatically passing through the warming mode in each direction of valve movement. Should the time of transit through the second position be insufficient for thorough warming to take place, the invention provides for delay means which temporarily maintain the valve in its second position when changing from first to third positions. Such delay means in its simplest form may comprise a dashpot operatively connected to the movable member of the valve, or may, in a preferred form, comprise a pressure operated detent which includes a bleed orifice through which any gas pressure in the detent may leak away when the detent is fluidly isolated. The detent may be operated by said three-position valve which may be adapted to connect the detent to said source of gas only when in said first position, and means may be provided to fluidly isolate the detent when the valve is in said second position, the valve, when changing from first to third positions, being maintained in its second position by said detent for a period determined by the rate of bleed of gas from the now fluidly isolated detent. The detent isolation means may comprise a non-return valve, or be part of said three-position valve. The three-position valve may be adapted for hand, foot or pressure operation.

When a three-position valve is used, said first conduit when a warming mode is selected, may be either closed, open to atmosphere and shut off from the source, or remain connected to said source. If open to atmosphere, reverse flow through said restricted orifice being only for such time that the valve is maintained in its second position. It is therefore within the scope of the invention to connect said first conduit to atmosphere by said three-position valve when in its second position particularly when delay means are incorporated which ensure such connection holds for only a brief period. Such momentary reversal of gas flow is advantageous in that contaminants may be flushed out of said first conduit.

It has been found in practice that when cryosurgical instruments according to the invention are used in the cooling mode for excessively long periods, such as for example when freezing a large volume of human tissue, the second conduit, and even the valve means when remote, are cooled by the effluent gas to such an extent that they fill or partially fill with condensed liquid when pressurised in the warming mode. With a three-position valve which when in the third position, vents the second conduit, such liquid is expelled. However, by including a pressure operated shuttle valve within said instrument body, cold effluent may be vented to atmosphere directly from said body thus minimising the regions which may be cooled by such gas flow.

Accordingly the invention provides a cryosurgical instrument for use with a remote source of pressurised gas and adapted to operate in a cooling mode and in a rapid warming mode, comprising:

a body defining a chamber and enclosing a cavity having a wall of high thermal conductance, said wall being shaped externally for contacting human tissue and providing heat transfer with the tissue and being of sufficient structural integrity to withstand the full source pressure, a wall of which chamber is provided with an exhaust passage leading to atmosphere adjacent a first end thereof;

a first conduit connecting with said remote source of pressurised gas, extending through said body and into said cavity terminating therein in a restricted orifice through which gas from said source may expand into said cavity and thereby cool said wall;

a second conduit leading from said cavity into said first end of said chamber;

a valve member slidably mounted in said chamber movable therein under the action of pressure and having an axially aligned fluid passage therethrough, said exhaust passage being closeable by said valve member;

a control valve connected to said source and a third conduit leading from said control valve to a second end of said chamber;

all such that; when the control valve is operated for the cooling mode, said third conduit is connected by said valve to atmosphere so that gas entering and expanding in said cavity is ducted to said first end of said chamber thrusting said valve member towards said chamber second end thus opening said exhaust passage and permitting said expanded gas to escape to atmosphere therethrough; when the control valve is released for the warming mode, said third conduit is connected to said source so that said valve member is thrust towards said chamber first end thus closing said exhaust passage and ducting high pressure gas from said third conduit through said fluid passage and into said cavity, via said second passage, wherein said gas will condense upon the wall, if this be cold, giving up latent heat in so doing.

The control valve may be adapted for hand, foot or pressure operation.

With the possible exception of the aspect of the invention in which reverse flow is permitted in the warming mode, it is also advantageous to provide a non-return valve in said restricted orifice being such that, in the cooling mode gas flow is restricted and that, in the reverse sense of flow, gas flow is relatively unrestricted. Such an arrangement permits said first conduit to be flushed if so desired and therefore constitutes a facility for unblocking a blocked restricted orifice.

The invention contemplates a method for controlling the cooling and subsequent reheating of the working tip of a cryosurgical instrument of the type described in which an exhaust passage leads normally to atmosphere from the interior of the working tip, which method involves connecting by valve means the exhaust passage to atmosphere during a cooling operation, and directly to a source of gaseous refrigerant during a reheating operation. The refrigerant leading to the orifice in operation, may be permanently connected to its source, since all flow through that orifice will cease as the pressure difference thereacross equalises. However, it is within the scope of the invention to interrupt the supply of refrigerant to the orifice during a warming mode, and even to connect the supply side of the thus isolated orifice briefly to atmosphere so that a modicum of reverse flow occurs therethrough, thus clearing the supply passages of liquid refrigerant which may condense therein, or of contaminants.

The invention will now be exemplified with reference to the accompanying drawings which are as follows:

FIG. 1 illustrates a simple cryosurgical probe or applicator having the general features referred to in the invention;

FIGS. 2 and 3 show, in sectional elevation and end view respectively, a restricted orifice fitted with a ball valve;

FIGS. 4 and 5 are schematic diagrams of cryosurgical instruments which incorporate remote, two-position control valves and such an applicator as illustrated in FIG. 1;

FIG. 6 is a schematic diagram of a cryosurgical instrument having a remote, three-position, control valve and an applicator such as illustrated in FIG. 1.

FIG. 7 shows schematically a cryosurgical instrument, of the type illustrated in FIG. 6, in which a pneumatic delay is provided;

FIGS. 8, 8A and 8B illustrate respectively the three-control positions of an instrument similar to the kind depicted in FIG. 6;

FIG. 9 shows in section a cryosurgical applicator, in the body of which is provided a two-position, pressure operated, shuttle valve; and

FIG. 10 is a schematic diagram of an instrument which incorporates an applicator such as illustrated in FIG. 9.

Referring to FIG. 1, the cryosurgical applicator illustrated comprises a hollow, cylindrical body 1 of stainless steel, closed at one end and having a bore 1H recessed at 1A, into which recess is brazed end 2B of a thin-walled stainless steel tube 2. The other end 2A of tube 2 is closed to define a cavity and constitutes the working tip of the applicator, the external surface of end 2A being, in operation, applied to human tissue in order to extract heat therefrom. The wall of end 2A is thin so that the thermal conductance thereof is high but is sufficient structural integrity to withstand the full source pressure.

A first conduit 3 extends co-axially and sealedly through the wall of the closed end of body 1, extending through bore 1H and tube 2 wherein it terminates in an orifice 3A such that any gas issuing from orifice 3A is directed towards the internal surface of the end 2A. The orifice 3A is restricted in the sense that its cross-sectional area is smaller than that of the bore of conduit 3 leading up to the orifice.

End 3B of conduit 3 is adapted to receive a flexible hose 4 through which a high pressure gaseous refrigerant is, in the cooling operation, ducted to the applicator. Such a refrigerant may, for example, be a polyatomic gas such as carbon dioxide or nitrous oxide and which has an inversion temperature above normal room temperature, normally stored in bottles as a liquid at high pressure (around 700 p.s.i.).

A second conduit 7 also leads sealedly through the wall of the closed end of body 1, opening within a recess 1J of bore 1H. The outer end 7A of the second conduit 7 is adapted to receive a flexible hose 8 through which, in operation, gases expanded from orifice 3A into tube 2 are exhausted away to a region of low pressure, such as the atmosphere.

Body 1 is threaded externally to engagedly receive a thermally insulative handle 9, suitably threaded internally at 9B for this purpose.

The schematic diagram in FIG. 4 shows how such an applicator 16 may be connected to a control valve VI and thereby to a source of gaseous refrigerant 12, the combination of applicator, valve and source constituting a practical embodiment of the invention.

The control valve VI is a two-position, foot-operated, two-way, cross-over valve, shown in FIG. 4 in the defrost or warming mode position. When the valve VI is depressed, gaseous refrigerant from gas bottle 12 is ducted to the applicator 16 via isolation valve 14, duct 13, flexible hose 4 and non-return valve 4A, leaving the applicator via hose 8 and escaping to atmosphere via valve port 15.

High pressure gas expands through orifice 3A, cooling as it does so as a result of the Joule-Thomson effect, thus cooling application surface 2A, the expanded gas being led away by hose 8 as described above.

When the valve VI is released, refrigerant gas from gas bottle 12 is ducted into hose 8 thus immediately pressurising the bore of tube 2 of the applicator so that gas condenses on the cold inner surfaces thereof, thus liberating latent heat and rapidly rewarming the surfaces including application surface 2A. The non-return valve 4A, in this particular embodiment, prevents a reversal of gas flow.

It is to be noted that in this last-described case, while there is reversal of the sense of direction of the pressurized gas supply, there is reversal of gas flow only to the extent required to charge the cavity and connected spaces with the pressurized gas. The valve provisions may be such that, as in the case where there is a valve 4A, there is no continuous reverse flow in the warming mode; or it may be such that the valve port 15 is so restricted that virtually the whole of the source pressure is applied within the cavity and connected spaces, there being only a very reduced continuous flow. The device of FIGS. 2 and 3 (described in full below) may be used in either case.

The system illustrated in FIG. 5 is similar to that of FIG. 4, but has a different control valve, now V2, which achieves the same result as follows:

In the warming mode position as illustrated, hoses 8, 4 and gas bottle 12 are all connected together so that, when the pressures in hoses 4 and 8 have equalised, no reverse flow can occur. When the valve V2 is depressed, the applicator 16 is connected as before.

A three-position valve V3 is used in the instrument of FIG. 6, and is shown in its intermediate position corresponding to the warming mode, but is naturally biased towards the "OFF" position whereat gas bottle 12 is isolated. When valve V3 is fully depressed, and as illustrated it is foot operated, applicator 16 receives high pressure gas as described before, via duct 13, isolation valve 14 which may now comprise the gas bottle valve and be normally left open, and duct 4. Hose 8 is connected to atmosphere via valve port 15.

As valve V3 is released, it passes through the intermediate position illustrated, and if necessary may be momentarily checked in this position by the operator, whereat hose 4 is isolated and hose 8 connected to bottle 12. When valve V3 reaches its final, or "OFF" position, bottle 12 is isolated and applicator 16 vented of high pressure through valve-port 15.

In order to ensure that valve V3 dwells in the intermediate position long enough for adequate warming of the application surface 2A, means may be provided for detaining the valve in the intermediate position when it is released. Such an arrangement is shown in FIG. 7 in which the control valve V4, a foot-operated, three-position valve, normally biased towards the "OFF" position, is illustrated in the intermediate position. The plunger 19 by which the valve is operated, is provided with a collar 20 which acts as a stop in co-operation with a pneumatically operated detent 18, such that when bellows 17 are inflated by high pressure gas, detent 18 is thrust into the path of the collar 20.

Valve V4 has ports and associated passages such that: it behaves as valve V3 of FIG. 6 as regards controlling applicator 16; in the intermediate position, duct 22, which connects bellows 17 to the valve, is closed; in the first or operating position, bellows 17 is connected to the gas bottle 12. The bellow 17 is also provided with a bleed valve 21, through which gas is bled from the bellows at a rate determined by the valve 21 setting.

When valve V4 is fully depressed, applicator 16 is put into the cooling mode and bellows 17 are pressurised thus extending detent 18 into the path of collar 20 which is now below and spaced from the detent 18. Upon releasing the valve V4, it moves into the intermediate position whereat it is held by detent 18. In this position, the applicator 16 is put into the warming mode, and the pressure in the now isolated bellows 17 falls at a rate determined by the now setting of bleed valve 21, until the detent 18 moves clear of collar 20 and permits the valve to move to the "OFF" position whereat both applicator and bellows are vented to atmosphere. By adjusting bleed valve 21, the length of the warming mode period may be varied.

FIGS. 8, 8A and 8B depict schematically a variation of the instrument of FIG. 7 in which the control valve is so modified that the valve may be changed directly from the "OFF" to the first, or operational position, without passing through the intermediate position, but does pass through temporarily and is held in the intermediate position when changing in the reverse sense.

Applicator 16 is connected to control valve assembly generally indicated as V5, hose 4 connecting with two-position valve V5A and hose 8 connecting with another two position valve V5B which has a ported body 31 moveable axially relative to the fixed body of valve V5A, the valve member 32 of V5B being connected by rod 33 to member 30 of V5A.

A lever 35, pivotally mounted at 37, extends through a slot 34 in rod 33 such that when button 35A on the lever is pressed, i.e., the lever is urged in a clockwise direction, valve members 30 and 32 are moved to the left against the action of the valve biasing spring 36. Valve body 31 may be moved axially against the action of compression springs 43 by means of a bellows 38 which, when pressurised, extends and thrusts upon end 31B of the valve body 31. The bellows fluidly connect with hose 4 via a spring loaded non-return valve, and a bleed valve 39 permits any pressurised gas within the bellows 38 to gradually bleed to atmosphere.

A gas-bottle 12 is connected to valve V5A via duct 13 and to valve-body 31 of valve V5B via a duct 13A which has sufficient flexibility to permit movement of body 31, likewise hose 8 is sufficiently flexible.

FIG. 8 illustrates the "OFF" position and FIG. 8A the operational position. Referring then to FIG. 8A, when button 35A is depressed, V5A takes up the position shown in which duct 13 connects with hose 4, V5B remains unchanged, the valve body 31 not having moved relative to member 32 which engaged with end stops 31A, both member 32 and body 31 having moved to the left. Hose 8, in this position of valve V5B, is connected to atmosphere via port 15. As hose 4 received gas from bottle 12, the pressure therein was communicated via duct 41 of non-return valve 40 to bellows 38 which extended leftwards to engage with end 31B of body 31, thus preventing return of the body to its original position, whilst not impeding any subsequent rightwards movement of member 32. When button 35A is released, members 30 and 32 move to the right under the action of spring 36, body 31 remaining held to the left by bellows 38, and FIG. 8B illustrates this, the warming mode position. Hose 4 is now vented to atmosphere via valve V5A and port 42, hose 8 is connected by valve V5B to gas bottle 12 via duct 13A, so that rapid warming of the applicator 16 occurs. Some reverse flow results through orifice 3A of the applicator, but as the warming period is short, this flow is unimportant. Because hose 4 is vented to atmosphere, non-return valve 40 isolates bellows 38 which, after a pre-determined period of time (according to the adjustment of bleed valve 39) retract, permitting body 31 to move to its original "OFF" position (as in FIG. 8) under the action of springs 43.

It has been found that, in some particular surgical operations where prolonged cooling is required, cold effluent gas may cool hose 8 and the associated control valve (such as valve V1 of FIG. 1 for example) sufficiently for condensation of refrigerant gas to occur within these members during a warming mode, thus tending to flood the instrument. FIG. 9 therefore shows an applicator in which a pneumatically operated shuttle valve is included which permits the effluent gas to escape to atmosphere at the applicator and not at some remote point. The total mass that can be cooled is therefore reduced.

Referring to FIG. 9, the cryosurgical instrument illustrated comprises a valve body 51 of stainless steel which is in the form of a hollow chamber having a cylindrical bore 51G in which is a shuttle valve member 55 in axially slidable sealed engagement therewith.

A passing 51D leads axially from the bore 51G, opening thereinto, terminating in a spigot 51B to which is soldered or welded end 52B of a stainless steel tube 52, the other end 52A of which is closed. Where passage 51D opens into bore 51G, a valve seat 51C, comprising a lip, is provided with which valve member 55 may sealedly engage. Holes 51E are provided in the valve body wall adjacent the valve seat, leading from the bore 51G into an annular space 59A existing between a handle 59 of insulating material which substantially encloses the instrument, except for a length of tube 52 and the enclosed end 52A thereof which extends from the handle 59 and which constitutes the working tip or application surface of the instrument, i.e., that portion which may be used to contact and cool human tissue.

The handle 59 is in threaded engagement with threaded portion 51F of valve body 51, and the annulus 59A opens to atmosphere.

A conduit extends co-axially and sealedly through the left hand end wall of the valve body 51, it extends through bore 51G and valve member 55 (which has a bore 55A extending therethrough), passage 51D and tube 52 where it terminates in an orifice of chosen diameter or area adjacent closed end 52A. A nylon hose 54 is shown connected to the external end of conduit 53, and leads to a gas-bottle 12 as will be explained in relation to FIG. 10. Another conduit 57 also extends sealedly through the left hand end wall of valve body 51, and opens into bore 51G. Another nylon hose 58 connected to the external end of conduit 57 leads to a control valve V6 as shown in FIG. 10.

The valve member 55, which is provided with an annular seal 56 in slideable contact with bore 51G, may be moved from one end of the bore 51G to the other by the use of pressurised gaseous refrigerant in the following manner: when conduit 57 is, via hose 58, open to atmosphere, and pressurised refrigerant is supplied to conduit 53, the refrigerant issues from orifice 53A, impinges upon the internal wall of tube end 52A which it cools, and exhausts along tube 52, passage 51D, and pushes valve-member 55 into the position illustrated. The exhaust gas may now pass through holes 51E and annulus 59A to atmosphere.

If, now, gaseous refrigerant, from the same gas-bottle 12 is connected via hose 58 to conduit 57, valve member 55 is thrust towards valve seat 51C which it sealedly contacts thus closing the exhaust passage but permitting the gaseous refrigerant to flow through the annulus bounded by conduit 53 and valve member 55A, thus to rapidly raise the pressure within the working tip to that of the source.

Although the annulus extending through the valve member must not be so large that it prevents operation of the valve member, its area can be very much greater than that of the orifice 53A without affecting such operation.

In the arrangement of FIG. 10, valve member 5 is controlled directly from a foot operated valve V6. No reverse flow is contemplated therefore it is sufficient to move valve-member 55 onto seat 51C so that gas is supplied directly from bottle 12 to the interior of tube 52. Flow through orifice 53A ceases as the pressure difference thereacross disappears.

Instruments according to the invention may also be provided with means for clearing a blocked expansion orifice, such blocking occuring occasionally in practice due to the presence in the first conduit of particulate matter which has either escaped the gas filter, if such be provided, or is due to failure to adequately clean the conduit during manufacture.

Such means are illustrated in FIGS. 2 and 3 and comprise a ball 11 situated within tubular conduit 3 in the vicinity of end 3C thereof which has been reduced in diameter (by spinning for example) to form a seat for the ball. The ball 11 is retained within conduit 3 by a stop 3B welded or soldered into the wall thereof. A small nick 3D in the reduced end 3C constitutes the restricted orifice when the ball 11 is seated as shown in FIG. 2.

In operation, when high pressure gas is introduced into conduit 3, the ball is thrust thereby onto its seat, thus closing end 3C with the exception of orifice 3D through which the gas then expands.

When the pressure across ball 11 is equalised, or when a reverse flow occurs, the ball 11 either drops away from end 3C or is lifted by the reverse flow.

So that a blocked orifice may readily be cleared, a further valve may be provided (such as that shown in dotted line in FIG. 6 and annotated 60) which, when the applicator is in the warming mode, may be briefly opened to atmosphere thus flushing conduit 3 and lifting ball 11 clear of its seat permitting particulate matter trapped in orifice 3D to be blown away.

While particular embodiments of the invention have been described, various modifications may be made thereto by practitioners in the art without departing from the spirit of the invention and the scope of the appended claims.

Claims

We claim:

1. A cryosurgical instrument for use with a remote source of pressurized gas and adapted to operate in a cooling mode and in a rapid warming mode, comprising:

a body enclosing a caviyty having a wall of high thermal conductance, said wall being shaped externally for contacting human tissue and providing heat transfer with the tissue and being of sufficient structural integrity to withstand the full source pressure;

a first conduit extending through said body and connected to said cavity terminating therein in a restricted orifice through which pressurized gas may expand into said cavity experiencing Joule-Thompson cooling in so doing and thereby cool said wall when said first conduit is connected to said source of gas;

a second conduit connected to said cavity;

an exhaust passage leading to atmosphere; and

valve means for providing a cooling mode gas-flow path from said source of pressurized gas, through said first conduit and said orifice, into said cavity, and then through said exhaust passage, whereby the expansion of as through said orifice cools said wall, and for selectively providing a heating mode gas-flow path from said source of pressurized gas, through said second conduit, and directly to said cavity for pressurizing said cavity sufficiently to condense said gas on the cooled wall and liberate latent heat to warm the wall.

2. A cryosurgical instrument according to claim 1 in which said valve means are remote from said body and comprise;

a two-position valve which in a second position provides connection for the warming mode and in a first position provides connection for the cooling mode;

means which prevent flow through sad first conduit in the warming mode.

3. A cryosurgical instrument according to claim 2 in which said means for preventing flow in said first conduit is said two-position valve.

4. A cryosurgical instrument according to claim 2 in which said means for preventing flow in said first conduit is a non-return valve.

5. A cryosurgical instrument according to claim 2 in which said valve is biased towards said second position.

6. A cryosurgical instrument according to claim 1 in which said valve means comprise a pressure operated two-position valve situated in said body.

7. A cryosurgical instrument according to claim 1 in which said valve means comprise a three-position valve which, in a first position, provides connection for the cooling mode, in a second position provides connection for the warming mode and in a third position isolates said source of pressurised gas.

8. A cryosurgical instrument according to claim 7 in which said three position valve, when in said third position, also connects at least the first conduit of said first and second conduits to said exhaust passage.

9. A cryosurgical instrument according to claim 8 in which said three-position valve when in said second position connects said first conduit to said exhaust passage.

10. A cryosurgical instrument according to claim 7 in which said three position valve passes through said second position at least when changing from the first to the third position.

11. A cryosurgical instrument according to claim 10 in which delay means are provided which temporarily maintain said three-position valve in said second position when it is urged from said first position towards said third position.

12. A cryosurgical instrument according to claim 11 in which said delay means comprise; a pressure operated detent including a bleed orifice through which any gas pressure in said detent may leak away when said detent is fluidly isolated; in which cryosurgical instrument said three-position valve is adapted to (a) operate said detent by connecting it to said source only when in said first position; and (b) to be maintained in said second position by said operated detent, when changing from said first to said third position, for a period determined by the rate of bleed of gas from said detent when fluidly isolated; means which fluidly isolate said detent from said source when said three-position valve is in said second position.

13. A cryosurgical instrument according to claim 12 in which said detent isolation means is a non-return valve connecting said detent to said first conduit and said three-position valve when in its second position connects said first conduit to said exhaust passage.

14. A cryosurgical instrument according to claim 1 in which said restricted orifice includes a non-return valve such that, in the cooling mode, gas flow is restricted but that gas flow is relatively unrestricted in the reverse sense of flow.

15. A cryosurgical instrument according to claim 14 in which said first conduit terminates in a portion of reduced diameter and in which said non-return valve comprises a free ball of smaller diameter than that of the first conduit bore but greater than that portion of reduced diameter and which seats on the reduced portion under the action of pressure within said first conduit, and is released upon reversal of pressure; in which said restricted orifice is formed in the wall of said reduced portion.

16. A method of cooling and then warming the highly thermally conductive wall of an expension chamber in a cryosurgical instrument, the external surface of the wall providing the applicator surface of the instrument, the method comprising:

introducing a pressurized gaseous refrigerant from a source thereof into said chamber through flow-restricting means while connecting said chamber to a region of pressure lower than the pressure of said source, thereby cooling said wall and said applicator surface by the Joule-Thomson effect; and then

pressurizing said chamber from said source of pressurized gaseous refrigerant through a flow path separate from said flow-restricting means so that said refrigerant condenses on said wall and liberates latent heat thereto, thereby warming said wall and said applicator surface.

17. A method as described in claim 16 wherein the gaseous refrigerant is carbon dioxide.

18. A method as described in claim 16 wherein the gaseous refrigerant gas is nitrous oxide.

19. A method as set forth in claim 16, wherein said introducing is effected through a conduit having said flow-restricting means therein.

20. A method as set forth in claim 19, wherein said conduit is blocked during said warming.

21. A method as set forth in claim 19, wherein said conduit is connected to said source during said warming.

22. A method as set forth in claim 19, wherein said conduit is connected to atmosphere during said warming.

23. A cryosurgical instrument according to claim 1, in which said body is a hollow cylindrical body having said first conduit extending therethrough from one end of the body and into said cavity at the opposite end, said second conduit and said exhaust passage being connected to said body at said one end, said valve means comprising a valve member slidably mounted in said body at said one end of said body and having means for connecting said second conduit and said exhaust passage to said cavity alternately in response to gas pressure in said second conduit, said valve means further comprising a control valve for selectively connecting said second conduit to said source or to atmosphere.