USRE40815E1 - Control system for cryosurgery - Google Patents

Abstract

An apparatus and method for automatic operation of a refrigeration system to provide refrigeration power to a catheter for tissue ablation or mapping. The primary refrigeration system can be open loop or closed loop, and a precool loop will typically be closed loop. Equipment and procedures are disclosed for bringing the system to the desired operational state, for controlling the operation by controlling refrigerant flow rate, for performing safety checks, and for achieving safe shutdown.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

Not ApplicableThis application is a continuation-in-part of application Ser. No.09/344,423 filed Jun.25,1999, now U.S. Pat. No.6,237,355.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is in the field of methods and apparatus used to generate and control the delivery of cryosurgical refrigeration power to a probe or catheter.

2. Background Information

In a cryosurgical system, contaminants such as oil, moisture, and other impurities are often deposited in the impedance tubing or other restriction through which the refrigerant is pumped. In the impedance tubing, the temperature is very low, and the flow diameter is very small. Deposit of these impurities can significantly restrict the flow of the cooling medium, thereby significantly reducing the cooling power.

BRIEF SUMMARY OF THE INVENTION

A cryosurgical catheter used in a cardiac tissue ablation process should be able to achieve and maintain a low, stable, temperature. Stability is even more preferable in a catheter used in a cardiac signal mapping process. When the working pressure in a cryosurgery system is fixed, the flow rate can vary significantly when contaminants are present, thereby varying the temperature to which the probe and its surrounding tissue can be cooled. For a given cryosurgery system, there is an optimum flow rate at which the lowest temperature can be achieved, with the highest possible cooling power. Therefore, maintaining the refrigerant flow rate at substantially this optimum level is beneficial.

In either the ablation process or the mapping process, it may be beneficial to monitor the flow rates, pressures, and temperatures, to achieve and maintain the optimum flow rate. Further, these parameters can be used to more safely control the operation of the system.

A cryosurgical system which is controlled based only upon monitoring of the refrigerant pressure and catheter temperature may be less effective at maintaining the optimum flow rate, especially when contaminants are present in the refrigerant. Further, a system in which only the refrigerant pressure is monitored may not have effective safety control, such as emergency shut down control.

It may also be more difficult to obtain the necessary performance in a cryosurgery catheter in which only a single compressor is used as a refrigeration source. This is because it can be difficult to control both the low and high side pressures at the most effective levels, with any known compressor. Therefore, it can be beneficial to have separate low side and high side pressure control in a cryosurgical system.

Finally, it is beneficial to have a system for monitoring various parameters of data in a cryosurgery system over a period of time. Such parameters would include catheter temperature, high side refrigerant pressure, low side refrigerant pressure, and refrigerant flow rate. Continuous historical and instantaneous display of these parameters, and display of their average values over a selected period of time, can be very helpful to the system operator.

The present invention provides methods and apparatus for controlling the operation of a cryosurgical catheter refrigeration system by monitoring pressures, temperature, and/or flow rate, in order to automatically maintain a stable refrigerant flow rate at or near an optimum level for the performance of cryosurgical tissue ablation or mapping. Different refrigerant flow rates can be selected as desired for ablation or mapping. Flow rate, pressures, and temperature can be used for automatic shut down control. Refrigerant sources which provide separate high side and low side pressure controls add to the performance of the system. Continuous displays of temperature, high side refrigerant pressure, low side refrigerant pressure, and refrigerant flow rate are provided to the operator on a single display, to enhance system efficiency and safety.

The novel features of this invention, as well as the invention itself, will be best understood from the attached drawings, taken along with the following description, in which similar reference characters refer to similar parts, and to which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic of a first embodiment of the apparatus of the present invention, using a pressure bottle as the primary refrigerant source;

FIG. 2 is a schematic of a second embodiment of the apparatus of the present invention, using a compressor as the primary refrigerant source;

FIG. 3 is a schematic of a third embodiment of the apparatus of the present invention, using two compressors connected in series as the primary refrigerant source;

FIG. 4 is a schematic of a first embodiment of a control system apparatus according to the present invention, for use with the apparatus shown inFIG. 1;

FIG. 5 is a schematic of a second embodiment of a control system apparatus according to the present invention, for use with the apparatus shown inFIG. 2 or3;

FIG. 6 is a schematic of a parameter display for use with the control equipment of the present invention; and

FIG. 7 is a flow diagram showing one control sequence for use with the control apparatus of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to certain embodiments of the invention, the refrigeration system may be a two stage Joule-Thomson system with a closed loop precool circuit and either an open loop or a closed loop primary circuit. A typical refrigerant for the primary circuit would be R-508b, and a typical refrigerant for the precool circuit would be R-410a. In the ablation mode, the system may be capable of performing tissue ablation at or below minus 70° C. while in contact with the tissue and circulating blood. In the mapping mode, the system may be capable of mapping by stunning the tissue at a temperature betweenminus 10° C. and minus 18° C. while in contact with the tissue and circulating blood. These performance levels may be achieved while maintaining the catheter tip pressure at or below a sub-diastolic pressure of 14 psia.

As shown inFIG. 1, one embodiment of theapparatus10 of the present invention is an open loop system using a pressure bottle for the refrigerant source. Such a system can include a primaryrefrigerant supply bottle200, a primaryrefrigerant fluid controller208, acatheter300, a primaryrefrigerant recovery bottle512, asecondary refrigerant compressor100, aprecool heat exchanger114, and various sensors. In certain embodiments, all but thecatheter300 and theprecool heat exchanger114 may be located in a cooling console housing. Theprecool heat exchanger114 is connected to the console byflexible lines121,221. Pressure of the refrigerant in the primaryrefrigerant supply bottle200 is monitored by a primary refrigerantsupply pressure sensor202. Output of primary refrigerant from thesupply bottle200 is regulated by apressure regulator204, which, in certain embodiments, can receive refrigerant from thebottle200 at a pressure above 350 psia and regulate it to less than 350 psia. A primaryrefrigerant relief valve206 is provided to prevent over pressurization of the primary system downstream of thepressure regulator204, for example, above 400 psia. The flow rate of primary refrigerant is controlled by thefluid controller208, which can be either a pressure controller or a flow controller. A feedback loop may be provided to control the operation of thefluid controller208. The feedback signal for thefluid controller208 can come from apressure sensor310 or aflow sensor311, on the effluent side of thecatheter300, discussed below.

A primary refrigeranthigh pressure sensor210 is provided downstream of thefluid controller208, to monitor the primary refrigerant pressure applied to theprecool heat exchanger114. Thehigh pressure side212 of the primary loop passes through the primary side of the cooling coil of theprecool heat exchanger114, then connects to a quick connect fitting304 on theprecool heat exchanger114. Similarly, the low side quick connect fitting304 on theprecool heat exchanger114 is connected to thelow pressure side412 of the primary loop, which passes back through the housing of theprecool heat exchanger114, without passing through the cooling coil, and then through theflow sensor311. The cathetertip pressure sensor310 monitors catheter effluent pressure in the tip of thecatheter300. The control system maintains catheter tip pressure at a sub-diastolic level at all times.

Thelow pressure side412 of the primary loop can be connected to theinlet402 of avacuum pump400. A primary refrigerantlow pressure sensor410 monitors pressure in thelow side412 of the primary loop downstream of theprecool heat exchanger114. Theoutlet404 of thevacuum pump400 can be connected to theinlet502 of arecovery pump500. A3 way, solenoid operated,recovery valve506 is located between thevacuum pump400 and therecovery pump500. Theoutlet504 of therecovery pump500 is connected to the primaryrefrigerant recovery bottle512 via acheck valve508. A primary refrigerantrecovery pressure sensor510 monitors the pressure in therecovery bottle512. A 2 way, solenoid operated,bypass valve406 is located in abypass loop407 between thelow side412 of the primary loop upstream of thevacuum pump400 and thehigh side212 of the primary loop downstream of thefluid controller208. A solenoid operated bypassloop vent valve408 is connected to thebypass loop407.

In thecatheter300, the high pressure primary refrigerant flows through an impedance device such as acapillary tube306, then expands into the distal portion of thecatheter300, where the resultant cooling is applied to surrounding tissues. A cathetertip temperature sensor307, such as a thermocouple, monitors the temperature of the distal portion of thecatheter300. Acatheter return line308 returns the effluent refrigerant from thecatheter300 to theprecool heat exchanger114. The high and low pressure sides of thecatheter300 are connected to the heat exchanger quick connects304 by a pair of catheter quick connects302. As an alternative to pairs of quick connects302,304, coaxial quick connects can be used. In either case, the quick connects may carry both refrigerant flow and electrical signals.

In the precool loop, compressed secondary refrigerant is supplied by aprecool compressor100. An after cooler106 can be connected to theoutlet104 of theprecool compressor100 to cool and condense the secondary refrigerant. Anoil separator108 can be connected in thehigh side117 of the precool loop, with anoil return line110 returning oil to theprecool compressor100. A high pressureprecooler pressure sensor112 senses pressure in thehigh side117 of the precool loop. Thehigh side117 of the precool loop is connected to an impedance device such as acapillary tube116 within the housing of theprecool heat exchanger114. High pressure secondary refrigerant flows through thecapillary tube116, then expands into the secondary side of the cooling coil of theprecool heat exchanger114, where it cools the high pressure primary refrigerant. The effluent of the secondary side of theprecool heat exchanger114 returns via thelow side118 of the precool loop to theinlet102 of theprecool compressor100. A low pressureprecooler pressure sensor120 senses pressure in thelow side118 of the precool loop.

Instead of using primary refrigerant supply and return bottles, the apparatus can use one or more. primary compressors in a closed loop system.FIG. 2 shows a second embodiment of the apparatus of the present invention, with a single compressor system. This embodiment would be appropriate in applications where the high side and low side pressures can be adequately controlled with a single compressor. In theapparatus10′ of this type of system, thelow side622 of the primary loop conducts the effluent of thecatheter300 to theinlet602 of aprimary refrigerant compressor600. Thecompressor600 compresses the primary refrigerant, and returns it from thecompressor outlet604 via thehigh side612 of the primary loop to the primary side of theprecool heat exchanger114. A primary refrigeranthigh pressure sensor614 is provided in thehigh side612 of the primary loop, to monitor the primary refrigerant pressure applied to theprecool heat exchanger114. A primary refrigerant highpressure flow sensor312 can be provided in thehigh side612 of the primary loop. A primary refrigerantlow pressure sensor610 monitors pressure in thelow side622 of the primary loop downstream of theprecool heat exchanger114. Aprimary loop filter608 can be provided in thelow side622 of the primary loop. A 2way, solenoid operated, primaryrefrigerant charge valve626 and aprimary refrigerant reservoir628 can be provided in thelow side622 of the primary loop. A high pressure after-cooler605 can be provided downstream of theprimary refrigerant compressor600.

As further shown inFIG. 2, a 2 way, solenoid operated, primaryloop bypass valve606 is located in abypass loop607 between thelow side622 of the primary loop upstream of thecompressor600 and thehigh side612 of the primary loop downstream of thecompressor600. Opening of the primaryloop bypass valve606 can facilitate startup of theprimary compressor600. Aprecool loop filter101 can be provided in thelow side118 of the precool loop. Further, a 2 way, solenoid operated, precoolloop bypass valve111 is located in abypass loop119 between thelow side118 of the precool loop upstream of thecompressor100 and thehigh side117 of the precool loop downstream of thecompressor100. Opening of the precoolloop bypass valve111 can facilitate startup of theprecool compressor100.

Apurification system900 can be provided for removing contaminants from the primary refrigerant and the secondary refrigerant. Solenoid operated 3way purification valves609,611 are provided in the high side and low side, respectively, of the primary loop, for selectively directing the primary refrigerant through thepurification system900. Similarly, solenoid operated 3way purification valves115,113 are provided in the high side and low side, respectively, of the precool loop, for selectively directing the secondary refrigerant through thepurification system900.

The remainder of the precool loop, theprecool heat exchanger114, and thecatheter300 are the same as discussed above for the first embodiment.

In applications where separate low side and high side pressure control is required, but where a closed loop system is desired, a two compressor primary system may be used.FIG. 3 shows a third embodiment of the apparatus of the present invention, with a dual compressor system. In theapparatus10″ of this type of system, thelow side622 of the primary loop conducts the effluent of thecatheter300 to theinlet616 of a low sideprimary refrigerant compressor618. Thelow side compressor618 compresses the primary refrigerant, and provides it via itsoutlet620 to theinlet602 of a high sideprimary refrigerant compressor600. A low pressure after-cooler623 can be provided downstream of thelow side compressor618. Thehigh side compressor600 further compresses the primary refrigerant to a higher pressure and returns it via itsoutlet604 and via thehigh side612 of the primary loop to the primary side of theprecool heat exchanger114. A primary refrigeranthigh pressure sensor614 is provided in thehigh side612 of the primary loop, to monitor the high side primary refrigerant pressure upstream of theprecool heat exchanger114. A primary refrigerantlow pressure sensor610 monitors pressure in thelow side622 of the primary loop downstream of theprecool heat exchanger114. A primary refrigerantintermediate pressure sensor624 monitors pressure between theoutlet620 of thelow side compressor618 and theinlet602 of thehigh side compressor600. Thehigh side compressor600 and thelow side compressor618 are separately controlled, using feedback from the cathetertip pressure sensor310 and/or theflow sensors311,312.

As further shown inFIG. 3, a 3 way, solenoid operated,bypass valve606′ is located in abypass loop607 between thelow side622 of the primary loop upstream of thelow side compressor618 and thehigh side612 of the primary loop downstream of thehigh side compressor600. A third port is connected between the high side and low side compressors. The precool loop, theprecool heat exchanger114, and thecatheter300 are the same as discussed above for the first and second embodiments.

FIG. 4 shows a control diagram which would be suitable for use with the apparatus shown inFIG. 1. A computerizedautomatic control system700 is connected to the various sensors and control devices to sense and control the operation of the system, and to provide safety measures, such as shut down schemes. More specifically, on the sensing side, the lowpressure precool sensor120 inputs low side precool pressure PA, the highpressure precool sensor112 inputs high side precool pressure PB, the primarysupply pressure sensor202 inputs supply bottle pressure P1, the primaryrecovery pressure sensor510 inputs recovery bottle pressure P2, the high pressureprimary sensor210 inputs high side primary pressure P3, the low pressureprimary sensor410 inputs low side primary pressure P4, the cathetertip pressure sensor310 inputs catheter tip pressure P5, thetemperature sensor307 inputs catheter tip temperature T, and theflow sensor311 inputs primary refrigerant flow rate F. Further, on the control side, thecontrol system700 energizes the normally closedbypass valve406 to open it, energizes the normallyopen vent valve408 to close it, and energizes therecovery valve506 to connect thevacuum pump outlet404 to therecovery pump inlet502. Finally, thecontrol system700 provides a pressure set point SPP or flow rate set point SPF to thefluid controller208, depending upon whether it is a pressure controller or a flow controller.

FIG. 5 shows a control diagram which would be suitable for use with the apparatus shown inFIG. 2 orFIG. 3. A computerizedautomatic control system700 is connected to the various sensors and control devices to sense and control the operation of the system, and to provide safety measures, such as shut down schemes. More specifically, on the sensing side, the lowpressure precool sensor120 inputs low side precool pressure PA, the highpressure precool sensor112 inputs high side precool pressure PB, the high pressureprimary sensor614 inputs high side primary pressure P3, the low pressureprimary sensor610 inputs low side primary pressure P4, the cathetertip pressure sensor310 inputs catheter tip pressure P5, thetemperature sensor307 inputs catheter tip temperature T, and theflow sensors311,312 input primary refrigerant flow rate F. Further, on the control side, thecontrol system700 energizes the normally closed primaryloop bypass valve606,606′ to open it, and thecontrol system700 energizes the normally closed precoolloop bypass valve111 to open it. Thecontrol system700 also energizes the primaryloop purification valves609,611 to selectively purify the primary refrigerant, and thecontrol system700 energizes the precoolloop purification valves113,115 to selectively purify the secondary refrigerant. Finally, thecontrol system700 provides a minimum high side pressure set point PL2 to thecontroller601 of theprimary compressor600 in the system shown in FIG.2. Alternatively, in the system shown inFIG. 3, thecontrol system700 provides a minimum high side pressure set point PL2B to thecontroller601 of the high sideprimary compressor600, and thecontrol system700 provides a maximum low side pressure set point PL2A to thecontroller619 of the low sideprimary compressor618.

A numeric digital display, or a graphical display similar to that shown inFIG. 6, is provided on the cooling console to assist the operator in monitoring and operating the system. For example, on a single graphical display, graphs can be shown of catheter tip temperature T, high side primary pressure P3, low side primary pressure P4, and primary flow rate F, all versus time. Further, on the same display, the operator can position a vertical cursor at a selected time, resulting in the tabular display of the instantaneous values of T, P3, P4, and F, as well as the average, maximum, and minimum values of these parameters.

The present invention will now be further illustrated by describing a typical operational sequence of the open loop embodiment, showing how thecontrol system700 operates the remainder of the components to start up the system, to provide the desired refrigeration power, and to provide system safety. The system can be operated in the Mapping Mode, where the cold tip temperature might be maintained atminus 10 C., or in the Ablation Mode, where the cold tip temperature might be maintained at minus 65 C. Paragraphs are keyed to the corresponding blocks in the flow diagram shown in FIG.7. Suggested exemplary Pressure Limits used below could be PL1=160 psia; PL2=400 psia; PL3=500 psia; PL4=700 psia; PL5=600 psia; PL6=5 psia; PL7=diastolic pressure; PL8=375 psia; and PL9=5 psia. Temperature limits, flow limits, procedure times, and procedure types are set by the operator according to the procedure being performed.

Perform self tests (block802) of the control system circuitry and connecting circuitry to the sensors and controllers to insure circuit integrity.

Read and store supply cylinder pressure P1, primary low pressure P4, and catheter tip pressure P5 (block804). At this time, P4 and P5 are at atmospheric pressure. If P1 is less than Pressure Limit PL2 (block808), display a message to replace the supply cylinder (block810), and prevent further operation. If P1 is greater than PL2, but less than Pressure Limit PL3, display a message to replace the supply cylinder soon, but allow operation to continue.

Read precool charge pressure PB and recovery cylinder pressure P2 (block806). If PB is less than Pressure Limit PL1 (block808), display a message to service the precool loop (block810), and prevent further operation. If P2 is greater than Pressure Limit PL4 (block808), display a message to replace the recovery cylinder (block810), and prevent further operation. If P2 is less than PL4, but greater than Pressure Limit PL5, display a message to replace the recovery cylinder soon, but allow operation to continue.

Energize the bypass loop vent valve408 (block812). Thevent valve408 is a normally open two way solenoid valve open to the atmosphere. When energized, thevent valve408 is closed.

Start the precool compressor100 (block814). Display a message to attach thecatheter300 to the console quick connects304 (block816). Wait for the physician to attach thecatheter300, press either the Ablation Mode key or the Mapping Mode key, and press the Start key (block818). Read the catheter tip temperature T and the catheter tip pressure P5. At this time, T is the patient's body temperature and P5 is atmospheric pressure.

Energize thebypass loop valve406, while leaving therecovery valve506 deenergized (block820). Thebypass valve406 is a normally closed 2 way solenoid valve. Energizing thebypass valve406 opens the bypass loop. Therecovery valve506 is a three way solenoid valve that, when not energized, opens the outlet of thevacuum pump400 to atmosphere. Start the vacuum pump400 (block822). These actions will put a vacuum in the piping between the outlet of thefluid controller208 and the inlet of thevacuum pump400, including the high and low pressure sides of thecatheter300. Monitor P3, P4, and P5 (block824), until all three are less than Pressure Limit PL6 (block826).

Energize therecovery valve506 and the recovery pump500 (block828). When energized, therecovery valve506 connects the outlet of thevacuum pump400 to the inlet of therecovery pump500. De-energize thebypass valve406, allowing it to close (block830). Send either a pressure set point SPP (if a pressure controller is used) or a flow rate set point SPF (if a flow controller is used) to the fluid controller208 (block832). Where a pressure controller is used, the pressure set point SPP is at a pressure which will achieve the desired refrigerant flow rate, in the absence of plugs or leaks. The value of the set point is determined according to whether the physician has selected the mapping mode or the ablation mode. These actions start the flow of primary refrigerant through thecatheter300 and maintain the refrigerant flow rate at the desired level.

Continuously monitor and display procedure time and catheter tip temperature T (block834). Continuously monitor and display all pressures and flow rates F (block836). If catheter tip pressure P5 exceeds Pressure Limit PL7, start the shutdown sequence (block840). Pressure Limit PL7 is a pressure above which the low pressure side of thecatheter300 is not considered safe.

If F falls below Flow Limit FL1, and catheter tip temperature T is less than Temperature Limit TL1, start the shutdown sequence (block840). Flow Limit FL1 is a minimum flow rate below which it is determined that a leak or a plug has occurred in thecatheter300. FL1 can be expressed as a percentage of the flow rate set point SPF. Temperature Limit TL1 is a temperature limit factored into this decision step to prevent premature shutdowns before thecatheter300 reaches a steady state at the designed level of refrigeration power. So, if catheter tip temperature T has not yet gone below TL1, a low flow rate will not cause a shutdown.

If P3 exceeds Pressure Limit PL8, and F is less than Flow Limit FL2, start the shutdown sequence (block840). PL8 is a maximum safe pressure for the high side of the primary system. Flow Limit FL2 is a minimum flow rate below which it is determined that a plug has occurred in thecatheter300, when PL8 is exceeded. FL2 can be expressed as a percentage of the flow rate set point SPF.

If P4 is less than Pressure Limit PL9, and F is less than Flow Limit FL3, start the shutdown sequence (block840). PL9 is a pressure below which it is determined that a plug has occurred in thecatheter300, when flow is below FL3. FL3 can be expressed as a percentage of the flow rate set point SPF.

An exemplary shutdown sequence will now be described. Send a signal to thefluid controller208 to stop the primary refrigerant flow (block840). Energize thebypass valve406 to open the bypass loop (block842). Shut off the precool compressor100 (block844). Continue running thevacuum pump400 to pull a vacuum between the outlet of thefluid controller208 and the inlet of the vacuum pump400 (block846). Monitor primary high side pressure P3, primary low side pressure P4, and catheter tip pressure P5 (block848) until all three are less than the original primary low side pressure which was read inblock804 at the beginning of the procedure (block850). Then, de-energize therecovery pump500,recovery valve506, ventvalve408,bypass valve406, and vacuum pump400 (block852). Display a message suggesting the removal of thecatheter300, and update a log of all system data (block854).

Similar operational procedures, safety checks, and shutdown procedures would be used for the closed loop primary system shown inFIG. 2 orFIG. 3, except that theprimary compressor600 orcompressors600,618 would provide the necessary primary refrigerant flow rate in place of the supply and recovery cylinders, the fluid controller, and the vacuum and recovery pumps. As with the open loop system, the closed loop system can be operated in the Mapping Mode, where the cold tip temperature might be maintained atminus 10 C., or in the Ablation Mode, where the cold tip temperature might be maintained at minus 65 C. As a first option to achieve the desired cold tip temperature, theprecool bypass valve111 can be adjusted to control the liquid fraction resulting after expansion of the secondary refrigerant, thereby adjusting the refrigeration capacity. Under this option, primary refrigerant high and low pressures are kept constant. As a second option, or in combination with the first option, primary refrigerant flow rate can be by means of operatingcontrollers601,619 on theprimary compressors600,618 to maintain a high pressure set point SPP which will achieve the desired flow rate, resulting in the desired cold tip temperature.

A Service Mode is possible, for purification of the primary and secondary refrigerants. In the Service Mode, the normallyopen bypass valves111,606 are energized to close. The primaryloop purification valves609,611 are selectively aligned with thepurification system900 to purify the primary refrigerant, or the precoolloop purification valves113,115 are selectively aligned with thepurification system900 to purify the secondary refrigerant.

In either the Mapping Mode or the Ablation Mode, the desired cold tip temperature control option is input into thecontrol system700. Further, the type of catheter is input into thecontrol system700. The normally closedcharge valve626 is energized as necessary to build up the primary loop charge pressure. If excessive charging is required, the operator is advised. Further, if precool loop charge pressure is below a desired level, the operator is advised.

When shutdown is required, the primary loop highside purification valve609 is closed, and theprimary loop compressors600,618 continue to run, to draw a vacuum in thecatheter300. When the desired vacuum is achieved, the primary loop lowside purification valve611 is closed. This isolates the primary loop from thecatheter300, and thedisposable catheter300 can be removed.

While the particular invention as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages hereinbefore stated, it is to be understood that this disclosure is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended other than as described in the appended claims.

Claims (19)

1. Apparatus for performing cryosurgery, comprising:

a refrigerant supply source connectable to a high pressure duct;

a cryosurgery catheter having an inlet connectable to said high pressure duct, said catheter having a tip;

a refrigerant expansion element in said catheter;

a temperature sensor on said catheter;

a pressure sensor adapted to sense pressure inside said catheter tip;

a low pressure duct connectable to an outlet of said catheter;

a flow sensor in said low pressure duct downstream of said catheter; and

a control system connected and programmed to maintain a selected catheter temperature, in response to signals from said temperature sensor, said pressure sensor, and said flow sensor.

2. An apparatus as recited inclaim 1, further comprising:

a precool heat exchanger in said high pressure duct;

a precool compressor for compressing a secondary refrigerant; and

a precool expansion element connected to said precool compressor for expanding said secondary refrigerant to cool said precool heat exchanger.

3. An apparatus as recited inclaim 2, further comprising a bypass valve connected between an outlet of said precool compressor and an inlet of said precool compressor.

4. An apparatus as recited inclaim 1, wherein:

said refrigerant supply source comprises a pressure bottle; and

a fluid controller in said high pressure duct; and

further comprising a recovery bottle connected to said low pressure duct.

5. An apparatus as recited inclaim 4, wherein said fluid controller comprises a pressure controller.

6. An apparatus as recited inclaim 4, wherein said fluid controller comprises a flow controller.

7. An apparatus as recited inclaim 4, further comprising:

a vacuum pump having an inlet connected to said low pressure duct;

a recovery pump having an inlet connected to an outlet of said vacuum pump, said recovery pump having an outlet connected to said recovery bottle;

a bypass valve in a bypass duct connected between said high pressure duct and said low pressure duct; and

a vent valve connected to said bypass duct between said bypass valve and said high pressure duct.

8. An apparatus as recited inclaim 1, wherein:

said refrigerant supply source comprises a compressor;

said high pressure duct is connected to an outlet of said compressor;

a compressor controller; and

said control system operates said compressor controller to maintain refrigerant pressure above a selected level in said high pressure duct.

9. An apparatus as recited inclaim 8, further comprising a second compressor with a second compressor controller;

wherein:

said low pressure duct is connected to an inlet of said second compressor;

an outlet of said second compressor is connected to an inlet of said first compressor;

said control system operates said first compressor controller to maintain refrigerant pressure above a selected level in said high pressure duct; and

said control system operates said second compressor controller to maintain refrigerant pressure below a selected level in said low pressure duct.

10. An apparatus as recited inclaim 8, further comprising a bypass valve in a bypass duct connected between said high pressure duct and said low pressure duct.

11. An apparatus as recited inclaim 1, further comprising:

a precool heat exchanger in said high pressure duct;

a precool compressor for compressing a secondary refrigerant;

a precool expansion element connected to said precool compressor for expanding said secondary refrigerant to cool said precool heat exchanger; and

a bypass valve connected between an outlet of said precool compressor and an inlet of said precool compressor

wherein:

said refrigerant supply source comprises a primary compressor;

said high pressure duct is connected to an outlet of said primary compressor; and

said control system operates said bypass valve to maintain catheter temperature at a selected level.

12. Apparatus for performing cryosurgery, comprising:

a primary refrigerant pressure bottle connectable to a high pressure duct;

a fluid pressure controller in said high pressure duct;

a precool heat exchanger in said high pressure duct;

a precool compressor for compressing a secondary refrigerant;

a secondary expansion element connected to expand said secondary refrigerant to cool said precool heat exchanger;

a cryosurgery catheter having an inlet connectable to said high pressure duct;

a primary expansion element in said catheter connected to expand said primary refrigerant to cool a portion of said catheter;

a temperature sensor on said catheter;

a low pressure duct connectable to an outlet of said catheter;

a pressure sensor in said low pressure duct;

a flow sensor in said low pressure duct;

a vacuum pump having an inlet connected to said low pressure duct;

a recovery pump having an inlet connected to an outlet of said vacuum pump;

a recovery bottle connected to an outlet of said recovery pump;

a bypass valve in a bypass duct connected between said high pressure duct and said low pressure duct; and

a control system connected and programmed to operate said pressure controller to maintain a selected primary refrigerant flow rate, in response to signals from said temperature sensor, said pressure sensor, and said flow sensor.

13. A method for controlling a cryosurgical instrument, comprising:

providing a refrigerant supply, a cryosurgery catheter including an expansion element, a temperature sensor, a pressure sensor, a flow sensor, a precool loop, and a control system connected to said sensors;

flowing said refrigerant via a high pressure duct into said cryosurgery catheter;

precooling said refrigerant in said precool loop;

expanding said refrigerant in said catheter with said expansion element;

sensing the temperature of said catheter with said temperature sensor;

sensing the pressure of said expanded refrigerant with said pressure sensor;

sensing the flow rate of said refrigerant with said flow sensor; and

controlling said refrigerant with said control system, to maintain a selected catheter temperature, in response to signals from said temperature sensor, said pressure sensor, and said flow sensor.

14. A method as recited inclaim 13, wherein:

said refrigerant supply source comprises a pressure bottle; and

a fluid controller in said high pressure duct;

said method comprising operating said fluid controller to maintain a selected pressure at said pressure sensor.

15. A method as recited inclaim 14, wherein said fluid controller comprises a pressure controller, said method comprising modifying a pressure setpoint of said pressure controller to maintain a selected pressure at said pressure sensor.

16. A method as recited inclaim 14, wherein said fluid controller comprises a flow controller, said method comprising modifying a flow setpoint of said flow controller to maintain a selected pressure at said pressure sensor.

17. A method as recited inclaim 13, wherein:

said refrigerant supply source comprises a compressor; and

a compressor controller;

said method comprising operating said compressor controller to maintain a selected pressure at said pressure sensor.

18. A method as recited inclaim 17, further comprising:

providing a second compressor with a second compressor controller, wherein a low pressure duct is connected between said catheter and an inlet of said second compressor, and an outlet of said second compressor is connected to an inlet of said first compressor;

operating said control system and said first controller to maintain refrigerant pressure above a selected level in said high pressure duct; and

operating said control system and said second controller to maintain refrigerant pressure below a selected level in said low pressure duct.

19. A method as recited inclaim 13, wherein:

said refrigerant supply source comprises a compressor; and

a precool bypass valve in said precool loop;

said method comprising operating said precool bypass valve to maintain a selected catheter temperature.

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