WO2001070123A1

WO2001070123A1 - Refrigeration instrument and system

Info

Publication number: WO2001070123A1
Application number: PCT/GB2001/001288
Authority: WO
Inventors: Patrick Sparkes; Richard Coleman
Original assignee: Spembly Medical Limited
Priority date: 2000-03-23
Filing date: 2001-03-23
Publication date: 2001-09-27
Also published as: GB2360573B; GB2360573A; GB0007135D0

Abstract

One aspect of the invention provides a refrigeration system (1; 50) comprising a cooling instrument (25) and a refrigerant circuit (3, 5; 52, 54) comprising means (9, 15; 58, 66) for puming refrigerant through the circuit and the instrument wherein the instrument is detachable from the regrigerant circuit, and the refrigerant circuit further comprises means operable to remove regrigerant from the instrument prior to its disconnection from the circuit.

Description

REFRIGERATION INSTRUMENT AND SYSTEM This invention relates to refrigeration instruments and systems. The invention is especially suitable for use in cryosurgical systems, but it is not limited exclusively to this. The invention is also especially suitable for (but is not limited to) use in systems which include an instrument (for example a probe) which is coupled to a refrigeration unit for supplying refrigerant to the instrument.

Cryosurgical systems are generally of two types. The first is an exhausting system in which expended refrigerant (also referred to herein as a cryogen) is vented after use, for example into the atmosphere. One disadvantage of such systems is that they are limited to use with a particular range of cryogens. Another disadvantage is that such systems require refilling with cryogen during use.

The second type of system is a closed loop, or recycling, system in which the refrigerant or cryogen is reprocessed and reused. Such a system can be used with a wider variety of cryogens.. . The present invention provides advantageous improvements to such systems.

One aspect of the invention provides a refrigeration system comprising: a cooling instrument; and a refrigerant circuit comprising means for pumping refrigerant through the circuit and the instrument; wherein the cooling instrument is detachable from the refrigerant circuit, and the refrigerant circuit further comprises means operable to remove refrigerant from the instrument prior to its disconnection from the circuit.

Another aspect of the invention provides: a refrigerant supply system for supplying refrigerant to a cooling instrument, the supply system comprising: connector means for detachably coupling the cooling instrument to the engine, the connector means including a refrigerant delivery path and a refrigerant return path; a refrigerant re-circulation circuit for circulating refrigerant from the return path to the delivery path; and means operable to withdraw refrigerant from the instrument to enable the instrument to be substantially discharged of refrigerant prior to disconnection from the supply system. Another aspect of the invention provides a refrigeration system comprising: a first closed loop circuit for circulating a re-usable refrigerant through a cooling instrument; detachable connector means for enabling the instrument to be detachably connected to the first circuit; and a closed loop pre-cooling refrigerant circuit for pre- cooling the re-usable refrigerant of the first circuit. The various aspects of the invention described herein provide numerous advantages over previously proposed arrangements.

For example, as the instrument can be detachable, cryosurgical procedures which employ different instruments - or more than one instrument - can easily be performed by exchanging one instrument for another. A further advantage associated with the provision of means for withdrawing refrigerant is that at least a substantial proportion of residual refrigerant (which may be potentially harmful) trapped in the instrument is removed. This is advantageous because it avoids potentially harmful or toxic refrigerant being vented to the atmosphere, and also because it avoids the amount of refrigerant in the system being depleted as one instrument is exchanged for another. Avoiding depletion of the amount of refrigerant in the system reduces the chance of the surgeon having to top-up the level of refrigerant during a surgical procedure.

A further advantage of one preferred embodiment of the invention is that means may be provided for removing contaminants (such as moisture or air, for example) from an instrument. This preferred embodiment reduces the likelihood of such contaminants being inadvertently introduced into the refrigerant system where they can impair the efficiency of the system (and in some cases can actually damage the refrigeration circuit). In a recycling refrigeration system, the accidental introduction of contaminants is a major problem. The impact of such a problem is vastly increased when a component of the system is designed to be regularly detached.

A further advantage associated with the provision of a removable

(disconnectable) instrument is that cleaning of the instrument, by autoclaving for example, may more easily be accomplished. This is advantageous as it reduces the chance of cross-infection between patients when one instrument is used for two or more patients. As mentioned above, preferred embodiments of the invention comprise means for decontaminating moisture for example from a cryosurgical instrument.

In one embodiment, at least a portion of the decontaminating means is separate from said refrigerant circuit. In another embodiment, the decontaminating means comprises an integral component of the refrigerant circuit.

In either event it is preferred that the decontaminating means includes a vacuum pump. In the above mentioned other embodiment, the decontaminating means comprises a vacuum pump separate from the refrigerant circuit, and filter means as an integral component of said circuit. In this case, it is preferred that the circuit comprises valve means between said decontaminating means and said means for pumping refrigerant through said circuit.

Preferably, the means for removing refrigerant from said instrument comprises a compressor. More preferably, the compressor for removing refrigerant is operable to withdraw refrigerant from said instrument into an accumulator or other temporary refrigerant store.

It is further preferred that the refrigerant removing means comprises the compressor operable to pump refrigerant through said circuit and said instrument, and wherein refrigerant flow through said circuit is interrupted prior to operation of the refrigerant removing means to withdraw refrigerant from said instrument. Interruption of said circuit may be accomplished by valve means forming an integral part of said circuit.

In one embodiment, a detachable instrument is provided with inlet and outlet automatic self-sealing valved connectors which are respectively engageable with cooperating outlet and inlet automatic self-sealing valved circuit connectors, and wherein interruption of said circuit is accomplished by disconnecting said instrument inlet connector from said circuit outlet connector.

Additionally, or alternatively, a separately operable valve may be provided for shutting off the flow in one of the paths to enable the refrigerant to be pumped out of the instrument, e.g. by the compressor. Preferably, said refrigerant circuit comprises a first circuit from which said cooling instrument may be detached, and a pre-cooling closed loop circuit in heat exchange communication with said first circuit and operable to pre-cool refrigerant in said first circuit.

Preferably, said pre-cooling closed loop circuit comprises a compressor operable to pump refrigerant through a condenser, an expansion valve, said heat exchanger, optionally an accumulator and back to said compressor for recirculation.

In one embodiment, refrigerant in said first circuit comprises R23, and refrigerant in said pre-cooling circuit comprises R134A.

In another embodiment, refrigerant in said first circuit comprises R508B, and refrigerant in said pre-cooling circuit comprises R404A.

Preferably the cooling instrument comprises a cryosurgical probe.

Embodiments of the invention will now be described, by way of example only, with reference to a cryosurgical system as shown in the accompanying drawings, in which: Figure 1 is a schematic representation of a cryosurgical system in accordance with a preferred embodiment of the invention;

Figure 2 is a schematic representation of a cryosurgical system in accordance with a further embodiment of the invention;

Figure 3 is a schematic cross-sectional view of a cryosurgical instrument suitable for use with the systems of Figures 1 and 2;

Figure 4 is a schematic representation of an electronic control system for the cryosurgical system of Figure 1;

Figure 5 is a schematic representation of an electronic control system for the cryosurgical system of Figure 2; Figure 6 is a flow diagram of an illustrative operating procedure for the control system of Figure 4; and

Figure 7 is a flow diagram of an illustrative operating procedure for the control system of Figure 5.

As mentioned above, Figure 1 is a schematic representation of a cryosurgical system 1 according to a first embodiment of the invention. The system 1 comprises a primary refrigeration circuit 3 and a secondary refrigeration circuit 5. The secondary circuit 5 is coupled to the first circuit 3 for heat exchange therebetween by a heat exchanger 7. The use of two circuits is preferred in this embodiment as such an arrangement is particularly useful for the particular refrigerants employed. However, it will be apparent to persons skilled in the art that a single refrigerant circuit or more than two refrigerant circuits may alternatively be employed if desired, and if appropriate for the particular refrigerant(s) to be employed. The primary circuit comprises a compressor 9, a condenser 11, an accumulator 12 and an expansion valve 13. The secondary circuit 5 comprises a compressor 15, an expansion valve 17, a valve 19, a further valve 19a, a pair of self-sealing valved connectors 21, 23 to which a cryosurgical instrument 25 may be connected, an accumulator 22 and a filter unit 24. The cryosurgical instrument 25 is detachable from the secondary circuit 5 so that it can be sterilised or replaced with another instrument, for example, so that the likelihood of cross-patient infection is reduced. This arrangement is advantageous as cryosurgical probes need to be routinely autoclaved at a high temperature (typically at 138°C) in order to sterilise the probe so that the chance of cross infection between patients is reduced.

Associated with the system 1 is an evacuation device 27, for example a vacuum pump, and the purpose of this device will be later described.

The primary circuit 3 acts as a pre-cooling circuit for the secondary circuit 5, and in use the primary compressor 9 pumps high pressure gaseous refrigerant to the condenser 11 where the refrigerant condenses to form a high pressure liquid refrigerant. The high pressure liquid refrigerant is pumped from the condenser 11 , through the expansion valve 13 where its temperature and pressure are lowered. The low temperature, low pressure liquid refrigerant then passes into the section of conduit passing through the heat exchanger 7, where the low temperature/low pressure refrigerant draws heat from the secondary refrigerant circuit 5. As a result of the heat transfer between the secondary circuit 5 and the primary circuit 3 in the heat exchanger 7, the refrigerant changes from its liquid state to a low pressure vapour state and passes back to the compressor 9 for recirculation via the accumulator 12.

When the secondary circuit 5 is in use with a cryosurgical instrument 25 connected to the valved connectors 21, 23, low pressure gaseous refrigerant provided into the compressor is compressed by the compressor 15 to provide high pressure vapour/liquid gaseous refrigerant which is supplied to the heat exchanger 7. The high pressure gaseous refrigerant from the compressor 15 enters the heat exchanger 7 (via oil separator 28) and heat from the high pressure gaseous refrigerant is transferred to the refrigerant in the primary refrigerant circuit 3 so that the refrigerant in the secondary circuit 5 condenses to a high pressure liquid. The valve 19a is closed at this time to prevent the refrigerant from bypassing the heat exchanger 7.

The high pressure liquid refrigerant is then pumped from the heat exchanger 7, through the expansion valve 17 where its temperature and pressure are lowered. The liquid refrigerant then passes into the conduit passing through the instrument 25 connected to the connectors 21, 23 where heat transfer from the surroundings of the instrument (which will typically be a body part of a patient) to the refrigerant takes place. As a result of this heat transfer the refrigerant changes from its liquid state to a low pressure vapour state and passes back to the compressor 15 for recirculation via filter 24 and accumulator 22. As mentioned above, the cryosurgical instrument 25 can be detached from the secondary circuit 5 for cleaning or replacement. When the instrument is detached, the self-sealing valved connectors 21, 23 of the secondary circuit 5 automatically close to prevent escape of refrigerant, and to reduce the likelihood of contaminants entering the circuit. The instrument 25 is provided with complementary self-sealing valved connectors 29, 31 which also automatically close on disconnection from the circuit. The valved connectors 21, 23 of the secondary circuit 5 and the valved connectors 29, 31 of the instrument 25 are configured so that they each open automatically when engaged with one another.

In order to reduce the chance of any refrigerant being released into the atmosphere when an instrument 25 is disconnected from the secondary circuit (and during subsequent cleaning of the instrument), it is important to ensure that any residual refrigerant (or at least a substantial proportion thereof) in the instrument is removed prior to its disconnection from the circuit. Removal of residual refrigerant is accomplished by closing the valve 19, and then operating the compressor 15 to draw residual refrigerant from the instrument 25 back into the secondary circuit 5, and in particular back into the accumulator 22. When all, or at least a significant proportion, of the residual refrigerant in the instrument has been removed, the instrument 25 can be disconnected from the circuit 5. The instrument 25 may then safely be removed for sterilisation procedures without releasing significant amounts of residual refrigerant into the atmosphere.

Whilst it is highly preferred that the valve 19 is provided in order to isolate the self sealing valved connector 23, it will be apparent to persons skilled in the art that the valve 19 could be omitted from the second circuit 5. If such an arrangement were to be employed, removal of refrigerant from the instrument 25 could still be accomplished by disconnecting the instrument connector 31 from the circuit connector 23 (whereupon both connectors 23, 31 will automatically close) and then operating the compressor 15 to draw refrigerant from the instrument through the other open connectors 21, 29 and back into the circuit.

As mentioned above, an evacuation device 27, for example a vacuum pump, is associated with the system 1 in order to reduce the likelihood of moisture contaminants being introduced into the secondary circuit upon reconnection of an instrument 25 thereto. If moisture contaminants were to be introduced into the secondary circuit they could seriously affect the operation of the secondary circuit, and thus it is important to ensure that steps are taken to reduce the amount of contaminants in the instrument to be connected.

In refrigeration systems in general, the principal contaminants are air and water and the evacuation device 27 may be operated to remove at least a significant proportion of both of these by connecting an instrument to complementary connectors 33 of the evacuation device 27, and then operating the evacuation device 27 to create a vacuum in the instrument 25. As a vacuum is created within the instrument 25, the pressure reduces and the boiling point of water reduces correspondingly. Thus by creating a vacuum within the instrument it is possible to remove air and water contaminants in one step by evacuating the instrument 25. Any particulate contaminants will be removed by the filter unit 24 once the instrument has been connected to the system.

Once the instrument 25 has been evacuated to a sufficient extent, the self- sealing valved connectors 29, 31 of the instrument can be disconnected from the connectors 33 of the evacuation device whereupon the instrument connectors will automatically close to maintain the vacuum (and hence the reduced contaminant environment) within the instrument 25. The instrument can then be connected or reconnected to the valved connectors 21, 23 of the secondary circuit 5.

After operating the instrument 25, and prior to removing residual refrigerant therefrom to permit disconnection from the circuit 5, it may be desired to defrost the instrument 25 and thus warm the adjacent tissue of the patient's body. By reheating the adjacent body tissue, the tissue will cease to stick in an ice ball to the instrument 25 and thus will not be pulled away on the instrument when the instrument is withdrawn from the patient's body. The instrument 25 is defrosted by opening the valve 19a (and optionally closing the valve 19) for a period of time and then closing the valve 19a after the instrument 25 (and thus also the adjacent body tissue) have warmed sufficiently. When the valve 19a is open, the hot refrigerant bypasses the heat exchanger 7 and expansion valve 17 and flows into and warms the instrument 25.

Figure 2 is a schematic representation of a cryosurgical system in accordance with a further embodiment of the invention. As with the system of Figure 1, the system 50 of Figure 2 comprises a primary refrigerant circuit 52 and a secondary refrigerant circuit 54. The primary and secondary refrigerant circuits 52, 54 are separate from one another and meet at a heat exchanger 56. The use of two circuits is preferred in this embodiment as such an arrangement is particularly useful for the particular refrigerants employed. However, it will be apparent to persons skilled in the art that a single refrigerant circuit or more than two refrigerant circuits may alternatively be employed if desired, and if appropriate for the particular refrigerants to be employed.

In this embodiment, the primary refrigerant circuit 52 comprises a compressor 58, a condenser 60, an expansion valve 62 and an accumulator 64. The compressor's outlet 58b is coupled by a suitable conduit to the condenser's inlet 60a, and the condenser's outlet 60b is coupled by a suitable conduit to the expansion valve's inlet 62a. The expansion valve's outlet 62b is coupled by a suitable conduit to the accumulator's inlet 64a, and the accumulator's outlet 64b is coupled by a suitable conduit to the compressor's inlet 58a. At least a portion of the conduit between the expansion valve outlet 62b and the accumulator inlet 64a passes through the heat exchanger 56, mentioned above.

In use, low pressure gaseous refrigerant (typically at a pressure of about 6.89 to 68.9 kPa [1 to 10 p.s.i]) at the compressor inlet 58a is compressed by the compressor 58 to provide high pressure gaseous refrigerant (typically at a pressure of about 2.07 MPa [300 p.s.i]) at the compressor outlet 58b. The high pressure gaseous refrigerant from the compressor outlet 58b enters the condenser 60 and heat from the high pressure gaseous refrigerant is radiated to the ambient air so that the refrigerant condenses to a high pressure liquid (typically at a pressure of about 2.07 MPa [300 p.s.i]).

High pressure liquid refrigerant is pumped from the condenser outlet 60b, and through the expansion valve 62 where its temperature and pressure are lowered. The low temperature, low pressure liquid refrigerant then passes into the section of conduit passing through the heat exchanger 56, where the low temperature/low pressure refrigerant draws heat from the secondary refrigerant circuit. As a result of the heat transfer between the secondary circuit 54 and the primary circuit 52 in the heat exchanger 56, the refrigerant changes from its liquid state to a low pressure vapour state and passes back to the inlet 58a of the compressor via the accumulator 64 for recirculation.

The secondary refrigerant circuit 54 comprises a compressor 66, an expansion valve 68, an oil separator 69, a filter unit 70 and an accumulator 72. The compressor's outlet 66b is coupled by a suitable conduit via the heat exchanger 56 to the expansion valve's inlet 68a. The expansion valve's outlet 68b is coupled by suitable conduit to the filter unit's inlet 70a, and the filter unit's outlet 70b is coupled to the accumulator's inlet 72a. The accumulator's outlet 72b is coupled by suitable conduit to the compressor's inlet 66a. The conduit between the expansion valve outlet 68b and the filter unit inlet 70a includes a valve 76 and first and second self-sealing connector valves 78, 80 by means of which various instruments may be connected into and disconnected from the secondary circuit 54.

In use with any given instrument 25, such as a cryosurgical probe, connected to the connectors 78, 80 (i.e. to provide a closed secondary circuit), low pressure gaseous refrigerant (typically at 20.7 to 82.7 kPa [3 to 12 p.s.i.]) at the compressor inlet 66a is compressed by the compressor 66 to provide high pressure gaseous refrigerant (typically at a pressure in the range of 758 kPa to 2.27 MPa [110 to 330 p.s.i.]) at the compressor outlet 66b. The high pressure gaseous refrigerant from the compressor outlet 66b enters the heat exchanger 56 and heat from the high pressure gaseous refrigerant is transferred to the refrigerant in the primary refrigerant circuit 52 so that the refrigerant in the secondary circuit 54 condenses to a high pressure liquid. At this time, a valve 76a is closed to prevent the refrigerant from bypassing the heat exchanger 56.

High pressure liquid refrigerant is pumped from the heat exchanger 56, and through the expansion valve 68 where its temperature and pressure are lowered. The liquid refrigerant then passes into the section of conduit passing through the instrument 25 connected to the connectors 78, 80 where heat transfer from the surroundings of the instrument 25 to the expanded refrigerant takes place. As a result of this expansion and heat transfer the refrigerant changes from its liquid state to a low pressure vapour state and passes back^' to the inlet 66a of the compressor via the filter unit 70 and accumulator 72 for recirculation.

As with the system shown in Figure 1, it is important to remove all of, or at least a substantial proportion of, the residual refrigerant in the instrument 25 before the instrument 25 is disconnected from the system. Removal of residual refrigerant is accomplished by operating the compressor 66 with the valve 76 closed to evacuate residual refrigerant from the instrument 25 connected to the first and second connector valves 78, 80, and to reintroduce that refrigerant into the secondary circuit 54 before the instrument 25 is disconnected. Once the instrument has been disconnected, the connector valves 78, 80 automatically close to seal the system against accidental leakage of refrigerant to the atmosphere.

In contrast to the arrangement shown in Figure 1, the system of Figure 2 has an evacuation device 81 which forms an integral part of the secondary circuit, rather than being provided as a separate entity. To incorporate the evacuation device for contaminant/moisture removal into the system of the second embodiment, further valves 82, 83 are provided between the filter unit 70 and the first self-sealing connector 80, and the evacuation device is connected to the portion of the secondary circuit between the valve 82 and the self-sealing connector 80 via the valve 83.

To remove contaminants from an instrument newly connected to the connectors 78, 80 of the secondary circuit 54 after the instrument has been autoclaved, the valves 76 and 82 are first closed and the evacuation device 81 is operated by opening valve 83 to create a vacuum in the instrument and the portions of the secondary circuit between the valves 82, 76 and the connectors 78, 80. As the vacuum is established in the instrument, any water in the instrument boils off and is removed together with any air for venting to the atmosphere. Once a sufficient vacuum has been established in the instrument to ensure that all, or at least a significant proportion, of any contaminants present in the instrument have been removed, the evacuation device can be switched off after closing valve 83 and the valves 76, 82 opened to allow refrigerant to be re-circulated into the evacuated instrument. The system is then ready for use once more. As with the system of Figure 1, it may in some circumstances be desirable to defrost or warm the instrument 25 after the instrument has operated in a cooling mode and before the refrigerant is recovered from the instrument and the instrument is disconnected. Accordingly, the valve 76a may be provided with its associated conduit which bypasses the heat exchanger 56 and the expansion valve 68. The system of Figure 2 may be switched from the cooling mode to a defrosting mode by opening the valve 76a (and optionally closing the valve 76) so that hot refrigerant is not cooled by the heat exchanger 56 before it enters the instrument 25 to defrost the instrument and thus warm and release adhered body tissue. After sufficient warming, the defrost mode is ended by closing the valve 76a (and opening the valve 76 if appropriate). The instrument 25 may then be removed from the patient's body.

Figure 3 is a schematic representation of an illustrative instrument 25 suitable for use with the cryosurgical systems of Figures 1 and 2 (not shown). In this embodiment, the instrument 25 is a cryosurgical probe and comprises an inlet length of hose 84, an outlet length of hose 86, a handle 88 and a probe tip 90. Internally, a capillary expansion nozzle 92 is connected to the inlet hose 84 and to a heat exchanger 94.

In use, low pressure / low temperature liquid refrigerant is passed from the expansion valve of the secondary circuit of Figures 1 or 2, into the probe via the capillary expansion nozzle 92 and into the heat exchanger 94 in the probe tip 90. The liquid refrigerant expands to draw heat from the surroundings of the probe tip (typically some part of a patient's anatomy) to cause tissue within the patient and in the vicinity of the probe to form a so-called ice ball, or local freezing in the surroundings of the probe tip 90.

The probe tip 90 incorporates a temperature sensor 95 connected via a lead to an external electrical connector 96. The sensor 95 may be used to detect the temperature of the probe (and thus indirectly of the surrounding tissue) during the cooling and defrosting modes of operation.

In the preferred embodiment, the primary circuit of Figure 1 or 2 is filled with a refrigerant known as R134A (which has a boiling point of-23°C), and the secondary circuit of Figure 1 or 2 is filled with a refrigerant known as R23 (which has a boiling point of -82°C). As an alternative, the primary circuit may be filled with a refrigerant known as R404A (which has a boiling point of -51°C), and the secondary circuit may be filed with a refrigerant known as R508B (which has a boiling point of -88.6°C). A variety of alternative refrigerants will be apparent to persons skilled in the art. An illustrative operating sequence for the system of Figures 1 or 2 will now be described, by way of example only, in order to promote a better understanding of the principles of the present invention.

The system of Figure 1 or 2 will normally be left dormant without a probe connected to the secondary circuit. Accordingly, prior to any procedure the operator must first connect a probe 25 to the circuit.

To this end, the operator must first remove moisture contamination from the instrument either before connecting the instrument to the secondary circuit (using a separate evacuation device as in the embodiment of Figure 1) or by closing the valves 76, 82 and operating the integral evacuation device 81 after connecting the instrument to the secondary circuit (as described in relation to the embodiment of Figure 2).

Once contaminants have been removed from the instrument, the instrument can be connected to the circuit (as in the embodiment of Figure 1) and the valves 19 and 21a are opened with the valve 19a remaining closed. If the instrument is already connected to the circuit (as in the embodiment of Figure 2) the valves 76, 82 can be opened after the valve 83 has been closed with the valve 76a remaining closed. The refrigerant will then be re-circulated into the instrument by the compressors of the first and second circuits which may then be operated to circulate refrigerant through their respective circuits and to provide cooling at the instrument connected to the secondary circuit for the duration of the procedure. The cooling may be controlled using feedback from the temperature sensor 95.

After completion of the cooling mode, the defrosting mode may follow for a period of time sufficient to warm the instrument to free it from frozen tissue stuck thereto. In the embodiment of Figure 1, the bypass valve 19a is opened to pass hot refrigerant into the instrument, and is then closed when temperature sensor 95 detects that sufficient warming has occurred. The valve 19 may also be closed and then opened. In the embodiment of Figure 2, the defrosting mode involves opening the valve 76a and closing it when temperature sensor 95 detects that sufficient warming has occurred. The valve 76 may also be closed and then opened.

To remove the instrument from the system once the cooling or defrosting mode has been completed, the valve 19 in Fig 1, or 76 in Fig 2, is closed and the secondary circuit compressor is run to draw refrigerant from the instrument back into the secondary circuit, and in particular into the accumulator that forms a part thereof. When a sufficient vacuum has been generated in the instrument (to indicate the removal of at least a significant proportion of refrigerant contained therein), the instrument may be disconnected from the secondary circuit for cleaning or replacement after closing valve 82 in Fig 2.

The system is then in its dormant state ready for re-use in a subsequent procedure with a different instrument, or with the previously used instrument once it has been cleaned. Use of either system may be automated to some extent by employing a control system such as those shown in Figures 4 and 5.

Figure 4 shows a control system suitable for use with the system of Figure 1. As shown, the system comprises a controller 100 (such as a microcontroller), a display 102 for displaying system information and instructions to an operator, a user operation panel 104, connections 106 to the connectors 21, 23 so that the controller 100 can determine whether or not an instrument is connected to the system, and connections 107 to the compressors 9, 15. The system controller would advantageously be in a power-down mode until an instrument is connected to the connectors 21, 23.

If such a control system were to be employed, then it is preferred that the secondary circuit 5 comprises a further valve 21a (shown in ghost in Figure 1) between the valved connector 21 and the compressor 15 (preferably closer to the connector 21 than the compressor 15), and a pressure sensor 108 so that the controller can verify that a vacuum exists in the instrument. Refrigerant access is provided to the remainder of the secondary circuit by opening the valves 19, 21a. Preferably the valves 19, 19a, 21a would be electronically controllable by and connected to the controller by connections 109 and could comprise, for example, solenoid valves.

The control system also includes an electrical connector 97 at the end of a flying lead which connects to the electrical connector 96 so that the controller receives the probe tip temperature from the temperature sensor 95 of the instrument. An illustrative operating cycle for such a control system is shown in the flow diagram of Figure 6.

As shown, the system is initially in a power down mode 110 with the valves 19, 19a, 21a closed, and continually polls in step 112 to determine whether or not an instrument is connected to the system. If an instrument is connected, then the controller interrogates the pressure sensor 108 in step 114 to determine whether or not the instrument has been evacuated. If no vacuum is detected, then the system warns the operator in step 116 to evacuate the instrument and continues to interrogate the pressure sensor 108 until a vacuum is detected.

Once a vacuum is detected, the controller 100 opens the valves 19, 21a in step 118 to allow access to the remainder of the second circuit and runs, in step 120, the compressors 9, 15 for the duration of the procedure. The controller polls the system in step 122 to determine whether the procedure has been completed, and once completed the operator notifies the controller of this by means of a button, for example, on the user operation panel 104 in Fig 4. The controller then closes the valve 19 and opens the valve 19a in step 123 whilst keeping at least compressor 15 running, in order to defrost the instrument. The controller polls the temperature sensor 95 in step 124 to determine when defrosting is completed. When completed, the controller 100 closes valve 19a in step 125. Thereafter the controller still runs the second circuit compressor 15, in step 126, to draw refrigerant from the instrument until a vacuum is detected by the pressure sensor 108 in step 128. Once a vacuum is sensed, the valve 21a is closed in step 130 and the operator is prompted in step 132 to disconnect the instrument. The controller interrogates the connectors to determine whether or not the instrument has been disconnected in step 134, and if it has been disconnected returns to the power-down mode of step 110.

Figure 5 shows a control system suitable- for use with the system of Figure 2. As shown, the system comprises a controller 200 (such as a microcontroller), a display 202 for displaying system information and instructions to an operator, a system clock 204, a user operation panel 207, connections 206 to the connectors 78, 80 so that the controller 200 can determine whether or not an instrument is connected to the system, connections 208 to the valves 76, 76a, 82, a connection 211 to the evacuation device 81, and connections 210 to the compressors 58, 66. The system controller would advantageously be in a power-down mode until an instrument is connected to the connectors 78, 80. As the system of Figure 2 includes an integral evacuation device 81 the control system requires a pressure sensor 184 such as that used in the system of Figure 1. As with the previously described control system, the valves 76, 76a, 82 are preferably electronically controllable by the controller and could comprise, for example, solenoid valves.

An illustrative operating cycle for such a control system is shown in the flow diagram of Figure 7.

As shown, the system is initially in a power down mode 220 with the valves 76, 76a, 82 closed, and continually polls in step 222 to determine whether or not an instrument is connected to the system. If an instrument is connected, then the controller operates the evacuation device 81 in step 224 to decontaminate the instrument of air or moisture.

Once the evacuation device has been run, in step 224, for a sufficient period of time to ensure that a sufficient vacuum has been established in the instrument as indicated by the pressure sensor 184, the controller 200 opens the valves 76, 82 in step 226 to allow access to the remainder of the secondary circuit and runs, in step 228, the compressors 58, 66 for the duration of the procedure. The controller polls the system in step 230 to determine whether the procedure has been completed, and once completed the operator notifies the controller of this by means of a button, for example, on the user operation panel 207.

The controller then closes the valve 76 and opens the valve 76a in step 231 whilst keeping at least compressor 66 running, in order to defrost the instrument. The controller polls the temperature sensor 95 in step 232 to determine when defrosting is completed. When completed, the controller 200 closes valve 76a in step 233. Thereafter the controller still runs the second circuit compressor 66, in step 234, to draw refrigerant from the instrument for a sufficient period of time to ensure that at least a significant proportion of the refrigerant in the instrument has been removed. The valve 82 is then closed in step 236 and the operator is prompted in step 238 to disconnect the instrument. The controller interrogates the connectors 78, 80 to determine whether or not the instrument has been disconnected in step 240, and if it has been disconnected returns to the power-down mode of step 220. As will be appreciated from the above, the invention provides numerous advantages over previously proposed systems. In addition, the above described control systems enable a system to be provided that is easy to operate, and which reduces the chance of an operator inadvertently introducing contaminants into the refrigeration circuits. It will also be understood, and should be noted, that modifications, alterations and additions may be made to the embodiments described herein without departing from the scope of the invention as defined in the appended claims. All such modifications, alterations and additions are thus within the scope of the invention.

Also it is to be noted/understood that re-circulating and reuse of the refrigerant in the secondary circuit obviates the need for the operator to continually check the quantity of the refrigerant remaining system prior to commencing a surgical procedure. Unlike existing CO₂ and N₂O Joule Thomson cryosurgical systems or LN₂ (liquid nitrogen) cryosurgical systems where the operator needs to frequently change the refrigerant containment cylinders or re-charge storage dewars with LN₂. It should further be noted that the control system described herein is provided by way of example and should not be interpreted as limiting the scope of the invention in any way. A multitude of different control systems will be apparent to persons skilled in the art.

It should further be noted that the provision of pressure sensors (to sense the pressure in the instrument) is not essential, and that the compressor or vacuum pump could instead be operated for a predetermined period of time that is of sufficient length to ensure that residual refrigerant, or contaminants, are at least substantially removed from the instrument.

It should also be noted that, whilst in the preferred embodiment a single instrument is provided for connection to the secondary circuit, a bank of instruments (i.e. more than one instrument) may be provided for simultaneous use with and connection to the secondary circuit.

Finally, it should also be remembered that the present invention is not limited to cryosurgical systems, and that the teachings provided herein may be applied to any number of different systems.

Claims

1. A refrigeration system comprising: a cooling instrument; and a refrigerant circuit comprising means for circulating refrigerant through the circuit and the instrument; wherein the cooling instrument is detachable from the refrigerant circuit, and the refrigerant circuit further comprises means operable to remove refrigerant from the instrument prior to its disconnection from the circuit.

2. A system according to Claim 1, wherein said system further comprises means for decontaminating a cooling instrument.

3. A system according to Claim 2, wherein at least a portion of the decontaminating means is separate from said refrigerant circuit.

4. A system according to Claim 2, wherein the decontaminating means comprises an integral component of the refrigerant circuit.

5. A system according to Claim 3 or 4, wherein the decontaminating means includes a vacuum pump.

6. A system according to Claim 5 when dependent upon Claim 3, wherein the decontaminating means comprises a vacuum pump separate from the refrigerant circuit, and filter means as an integral component of said circuit.

7. A system according to Claim 6, wherein the circuit comprises valve means between said decontaminating means and said means for pumping refrigerant through said circuit.

8. A system according to any preceding claim, wherein said means for removing refrigerant from said instrument comprises a compressor.

9. A system according to Claim 7, wherein said compressor for removing refrigerant is operable to withdraw refrigerant from said instrument into an accumulator or other temporary refrigerant store.

10. A system according to Claim 8 or 9, wherein said refrigerant removing means comprises the compressor operable to pump refrigerant through said circuit and said instrument, and wherein refrigerant flow through said circuit is interrupted prior to operation of the refrigerant removing means to withdraw refrigerant from said instrument.

11. A system according to Claim 10, wherein interruption of said circuit is accomplished by valve means forming an integral part of said circuit.

12. A system according to Claim 10 or 11, wherein said detachable instrument is provided with inlet and outlet automatic self-sealing valved connectors which are respectively engageable with co-operating outlet and inlet automatic self- sealing valved circuit connectors, and wherein interruption of said circuit is accomplished by disconnecting said instrument inlet connector from said circuit outlet connector.

13. A system according to any preceding claim, wherein said refrigerant circuit comprises a first circuit from which said instrument may be detached, and a ^x pre-cooling closed loop circuit in heat exchange communication with said first circuit and operable to pre-cool refrigerant in said first circuit.

14. A system according to Claim 13, wherein said first and pre-cooling circuits communicate with one another for heat exchange by means of a heat exchanger.

15. A system according to Claim 13 and 14, wherein said pre-cooling closed loop circuit comprises a compressor operable to pump refrigerant through a condenser, an expansion valve, said heat exchanger, optionally an accumulator and back to said compressor for recirculation.

16. A system according to any of Claims 13 to 15, wherein refrigerant in said first circuit comprises R23, and refrigerant in said pre-cooling circuit comprises R134A.

17. A system according to any of Claims 13 to 15, wherein refrigerant in said first circuit comprises R508B, and refrigerant in said pre-cooling circuit comprises R404A.

18. A system according to any preceding claim, wherein said cooling instrument comprises a cryosurgical probe.

19. A system according to any preceding claim, further comprising electronic control means operable to control said system.

20. A refrigerant supply system for supplying refrigerant to a cooling instrument, the supply system comprising: connector means for detachably coupling to the instrument, the connector means including a refrigerant delivery path and a refrigerant return path; a refrigerant re-circulation circuit for circulating refrigerant from the return path to the delivery path; and means operable to withdraw refrigerant from the instrument to enable the instrument to be substantially discharged of refrigerant prior to disconnection from the supply system.

21 A method of operation of a refrigerant system, comprising the steps of:

(a) circulating a refrigerant through a cooling instrument using a closed loop refrigerant circuit;

(b) withdrawing the refrigerant from the instrument while the instrument is connected to the refrigeration circuit; and

(c) disconnecting the instrument from the refrigeration circuit.

22. A method according to Claim 21, wherein the withdrawing step comprises closing a first refrigerant flow path to the instrument, and pumping refrigerant from the instrument via a second refrigerant flow path.

23. A method according to Claim 22, wherein the pumping step comprises operating a compressor of the refrigerant circuit to withdraw the refrigerant.

24. A method according to any of Claims 21 to 23, further comprising applying a low pressure to the instrument to decontaminate the instrument prior to circulating the refrigerant in step (a).

25. A method of performing cryosurgery comprising operating a refrigeration system in accordance with the method of any of claims 21 to 24 to cool body tissue.

26. A refrigeration system comprising: a first closed loop circuit for circulating a re-usable refrigerant through a cooling instrument; detachable connector means for enabling the instrument to be detachably connected to the first circuit; and a closed loop pre-cooling refrigerant circuit for pre-cooling the re-usable refrigerant of the first circuit.