Refrigerant flow control

Abstract

The present application relates to cryogen flow control. An apparatus includes a probe comprising a first lumen and a second lumen and having a distal end that contacts tissue of a living body. A fluid supply device delivers cryogenic fluid through the first lumen to the distal end, and receives cryogenic fluid returned via the second lumen. A temperature sensor is located at the distal end. A pressure sensor located at a proximal end of the first lumen measures pressure of the cryogenic fluid. A processor controls a delivery rate of the cryogenic fluid from the fluid supply device such that the delivery rate is a preset low rate when a temperature measured by the temperature sensor is less than a preset protection temperature, and the delivery rate is set in response to a pressure measured by the pressure sensor when the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature.

Description

Invention Field

[0001] This invention relates generally to the flow of refrigerants, and more particularly to the effective control of the flow of refrigerants. Background of the Invention

[0002] Pumps used with cryogenic materials must be able to overcome the limitations caused by extreme cold (such as reduced elasticity) in order to operate efficiently. Vapor lock is also an issue for cryogenic pumps. Systems and methods for improving the efficiency of cryogenic pumps are known in the art.

[0003] U.S. Patent 6,007,571 to Neilson et al. describes a liquid coolant supply system for supplying liquid coolant to a thermotherapy catheter. The system has a sensor control unit that includes a pump, cooling equipment, a temperature sensor, and a pressure sensor.

[0004] U.S. Patent 6,471,694 to Kudaravalli et al. describes a control system for cryosurgery. It discloses procedures for bringing the system to a desired operating state, for controlling operation by controlling the refrigerant flow rate, for performing safety checks, and for achieving a safe shutdown.

[0005] U.S. Patent 6,939,346 to Kannenberg et al. describes a device for controlling a temperature-controlled probe. The device includes a controller coupled to the probe and a thermal element for changing the probe temperature.

[0006] Ryba's U.S. Patent 7,357,797 describes a system for altering return pressure to control the tip temperature of a cryoablation catheter. In this system, the distal end of the refrigerant supply line is located within the central lumen and at a distance from the distal tip of the catheter to establish an expansion chamber.

[0007] Levin's U.S. Patent 7,731,711 describes an oscillating flow within the central lumen of a cryosurgery instrument. In this instrument, the cryopressor is provided in the form of a separate portion on the inner surface of the distal cryogenic tip.

[0008] U.S. Patent 7,780,657 to Abboud et al. describes a cooling system. The system's control panel includes: a first cooling system that directs coolant along a coolant supply line to a medical device at a first temperature; and a second cooling system that cools the coolant within the coolant supply line to a temperature below the first temperature before the coolant reaches the connection point.

[0009] U.S. Patent 7,921,657 to Littrup et al. describes a system for cooling an object with a refrigerant having a critical point defined by a critical point pressure and a critical point temperature. The pressure of the refrigerant is increased above the determined pressure value, thereby providing a refrigerant with a reduced molar volume, thus preventing gas sealing.

[0010] U.S. Patent 10,098,685 to Lalonde et al. describes a system that provides feedback data or information related to the depth of damage to myocardial tissue during cryoablation procedures.

[0011] U.S. Patent 10,213,244 to Fourkas et al. describes a cryogenic needle for a cryogenic system coupled to a heater. The power supplied to the heater is used to interpolate the performance of the needle and / or the operating parameters of the cryogenic system.

[0012] Geiselhart's U.S. Patent 10,485,602 describes a temperature regulator for adjusting the temperature of a freezing probe. The freezing probe supplies at least a portion of liquid refrigerant at a first pressure to an evaporation zone, causing the refrigerant to evaporate at least temporarily in the presence of a second pressure to cool the cooling portion of the freezing probe.

[0013] U.S. Patent 10,828,080 to George et al. describes a method for adjusting pressure in a cryotherapy balloon catheter to reduce temperature.

[0014] U.S. Patent Application 2005 / 0159735 by Walton et al. describes a device for the automated operation of a refrigeration system that provides refrigeration power to catheters used for tissue ablation or mapping. The main refrigeration system can be open-loop or closed-loop, while the pre-cooling circuit is typically closed-loop.

[0015] US Patent Application 2005 / 0198972 by Lentz et al. describes a pressure-temperature control system for a cryoablation catheter system. A temperature sensor is mounted at the distal end of the cryoablation catheter. The system controller communicates electronically with the pressure regulator and the temperature sensor.

[0016] U.S. Patent Application 2019 / 0175395 by Kim et al. describes an apparatus and method for cooling living tissue for medical and other purposes. The cooling apparatus includes a container configured to contain a cooling medium and thermally coupled to the cooling medium through direct contact. Invention Overview

[0017] An embodiment of the present invention provides an apparatus comprising:

[0018] A probe comprising a first lumen and a second lumen and having a distal end configured to contact living tissue;

[0019] A fluid supply device is connected to deliver cryogenic fluid through a first cavity to the distal end of the probe and to receive cryogenic fluid returning from the probe via a second cavity.

[0020] A temperature sensor located at a remote location;

[0021] A pressure sensor, located at the proximal end of the first cavity and configured to measure the pressure of a cryogenic fluid within the first cavity; and

[0022] The processor is configured to control the delivery rate of the cryogenic fluid from the fluid supply device such that when the temperature measured by the temperature sensor is less than a preset protection temperature, the delivery rate is a preset low rate, and when the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the delivery rate is set in response to the pressure measured by the pressure sensor.

[0023] In the disclosed implementation, when the temperature measured by the temperature sensor is greater than or equal to a preset protection temperature, the delivery rate is set in response to that temperature.

[0024] In a further disclosed embodiment, when the temperature measured by the temperature sensor is greater than or equal to a preset protection temperature, the conveying rate is set in response to a preset target temperature that is greater than the preset protection temperature. Typically, the preset target temperature is in the range of -10°C to -50°C.

[0025] In a further disclosed embodiment, when the temperature measured by the temperature sensor is greater than or equal to a preset protection temperature, the delivery rate is less than or equal to the maximum delivery rate calculated based on a preset function of pressure. Typically, the first derivative of the preset function at the pressure measured by the pressure sensor is negative.

[0026] In an alternative implementation, when the temperature measured by the temperature sensor is greater than or equal to a preset protection temperature, the delivery rate is set in response to a pressure compared to a parameter pressure, which is selected in response to the critical pressure of the cryogenic fluid. Typically, the parameter pressure is greater than the critical pressure.

[0027] In another alternative implementation, the processor is a proportional-integral-derivative (PID) controller. Typically, the PID controller operates as a PI controller.

[0028] According to an embodiment of the present invention, a method is also provided, the method comprising:

[0029] A probe is provided that includes a first lumen and a second lumen and has a distal end configured to contact tissue in a living organism.

[0030] A fluid supply device is connected to deliver cryogenic fluid through the first cavity to the distal end of the probe and to receive cryogenic fluid returning from the probe via the second cavity.

[0031] Position the temperature sensor at a remote location;

[0032] The pressure sensor is positioned at the proximal end of the first cavity and configured to measure the pressure of the cryogenic fluid within the first cavity; and

[0033] The delivery rate of the cryogenic fluid from the fluid supply device is controlled such that when the temperature measured by the temperature sensor is lower than the preset protection temperature, the delivery rate is a preset low rate, and when the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the delivery rate is set in response to the pressure measured by the pressure sensor.

[0034] According to an embodiment of the present invention, an apparatus is also provided, the apparatus comprising:

[0035] A probe comprising a first lumen and a second lumen and having a distal end configured to contact tissue of a living organism;

[0036] A fluid supply device is coupled to deliver cryogenic fluid through a first cavity to the distal end of the probe and to receive cryogenic fluid returning from the probe via a second cavity.

[0037] Temperature sensor, located at a remote location;

[0038] A pressure sensor, located at the proximal end of the first cavity and configured to measure the pressure of a cryogenic fluid within the first cavity; and

[0039] The processor is configured to control the delivery rate of the cryogenic fluid from the fluid supply device, such that, in response to a preset target temperature and pressure sensor at a remote location, the temperature sensor measures a pressure that oscillates around the preset target temperature by a preset amplitude.

[0040] Typically, the processor is configured to control the delivery rate of the cryogenic fluid in response to a ratio of the pressure measured by a pressure sensor to a predetermined pressure. The predetermined pressure may be greater than the critical pressure of the cryogenic fluid.

[0041] Typically, the conveying rate is at least a preset minimum conveying rate.

[0042] Typically, the processor is a proportional-integral-derivative controller, and the controller's coefficient values ​​are selected to cause the temperature to oscillate at a preset amplitude.

[0043] Typically, the preset range is between 8°C and 12°C.

[0044] This disclosure will be more fully understood from the following detailed description of embodiments thereof, taken in conjunction with the accompanying drawings, in which: Brief description of the attached diagram

[0045] Figure 1 This is a schematic diagram of an apparatus used in cryogenic medical procedure according to an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of a probe according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic block diagram of an apparatus according to an embodiment of the present invention, illustrating how the components of the apparatus are connected together;

[0048] Figure 4 This is a flowchart illustrating the operations performed by the processor according to an embodiment of the present invention during the first phase of surgery when executing the algorithm; and

[0049] Figure 5 According to an embodiment of the present invention Figure 4 A set of schematic graphs obtained during the operation of the flowchart. Detailed Implementation

[0050] Overview

[0051] One of the problems encountered in the operation of cryogenic probes during cryosurgery is reduced efficiency or even complete inoperability due to gas sealing. Gas sealing occurs in cryogenic systems when cryogenic vapors from the evaporating cryogenic liquid impede or stop the flow of the liquid; that is, the flow rate of the liquid is reduced or even completely stopped. This reduced flow prevents the probe from cooling the tissue in contact with it during surgery. The gas sealing problem is exacerbated if the cryogenic liquid is practically incompressible, and this is the case when the probe operates at low pressures that are significantly different from the critical pressure of the cryotropic agent used. For example, liquid nitrogen has a critical pressure of approximately 33.5 atm (atmospheres) and is therefore relatively incompressible in the pressure range of approximately 1 atm to 10 atm.

[0052] Embodiments of the present invention overcome the gas-sealing problem of cryogenic probes by configuring the probe to operate periodically for short periods at high pressures close to the critical pressure of the refrigerant (here assumed to be liquid nitrogen), while operating the probe primarily at relatively low pressures. During these time periods, liquid nitrogen is relatively compressible and can flow more freely to alleviate any initial gas-sealing.

[0053] To achieve high pressure for a short time, embodiments of the present invention configure the temperature at the distal end of the probe to oscillate around a target temperature, rather than attempting to maintain the distal end at the target temperature. The processor measures the pressure of the refrigerant in the probe and the temperature at the distal end. The processor uses the measured temperature and pressure values ​​to control the rotational rate of the refrigerant pump, i.e., to control the flow rate of the refrigerant discharged from the pump into the probe, and the processor is configured such that the flow rate (pump rotational rate) varies oscillatingly between high and low values.

[0054] The oscillations in flow rate provide the aforementioned short time period of high pressure, as well as the oscillations with respect to the target temperature.

[0055] Embodiments of the present invention provide an apparatus comprising a probe having a first lumen and a second lumen and having a distal end configured to contact tissue of a living organism. A fluid supply device is provided, coupled to deliver cryogenic fluid through the first lumen to the distal end of the probe, and to receive cryogenic fluid returning from the probe via the second lumen.

[0056] A temperature sensor is located at the distal end of the probe, and a pressure sensor is located at the proximal end of the first cavity. The pressure sensor measures the pressure of the cryogenic fluid flowing within the first cavity.

[0057] The processor is configured to control the delivery rate of the cryogenic fluid from the fluid supply device such that when the temperature measured by the temperature sensor is lower than a preset protection temperature, the delivery rate is a preset low rate, and when the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the delivery rate is set in response to the target temperature at a remote end and the pressure measured by the pressure sensor.

[0058] Detailed description

[0059] In the following description, the same elements in the accompanying drawings are identified by the same numbers.

[0060] For reference Figure 1 This is a schematic diagram of a device 20 used in cryomedical surgery according to an embodiment of the present invention. For example, the surgery described below is assumed to be for a breast tumor; however, it should be understood that the device 20 can be used for other surgeries, such as treating prostate tumors or kidney tumors, and all such surgeries are considered to be included within the scope of the present invention.

[0061] The cryosurgery for breast tumors is performed in two phases: a first phase in which the temperature of the distal end 112 of the probe 60 is reduced to an initial temperature, typically between approximately -10°C and approximately -30°C; and a second phase in which the distal temperature is further reduced to a subsequent temperature below the initial temperature. In one embodiment, the subsequent temperature is approximately -160 ± 10°C.

[0062] The procedure is performed on patient 28 by physician 24, and the physician is able to observe the results on monitor 32 contained in device 20. (Typically, the first stage of breast tumor surgery includes an ultrasound scan of patient 28's breast, and the scan results are presented on monitor 32.) The scan is typically performed by an ultrasound specialist rather than physician 24. Details of the ultrasound scan are not relevant to this disclosure, and for simplicity, an ultrasound specialist is not described. Figure 1 As shown in the diagram. Alternatively or additionally, the first stage may include a CT (computed tomography) scan of the breast.

[0063] Device 20 is controlled by processor 36, which is coupled to memory 40, which stores software 44 for device operation. Processor 36 and memory 40 are mounted in an operation console 42. For example, the software 44 in memory 40 can be downloaded electronically to the processor via a network. Alternatively or additionally, the software may be provided on a non-transitory tangible medium (e.g., optical, magnetic, or electronic storage media). Software 44 includes software for device operation algorithm 48, comprising steps executed by the processor operating device 20. Device operation algorithm 48 is described in more detail below.

[0064] In the first and second stages of breast tumor surgery, device 20 is used to inject cryogenic fluid 52 into probe 60, which has a distal end 112 inserted near the tumor. The cryogenic fluid 52 is initially typically held in pump 56 (also referred to herein as fluid supply device 56). Pump 56 includes a Dewar flask 72 that holds the cryogenic fluid 52 in liquid form within a lower space 80 of the Dewar flask. Above the liquid in the Dewar flask, in an upper space 84, is a gas formed by the evaporation of the cryogenic liquid. A pump similar to pump 56 is described in U.S. Patent Application 16 / 785,686 entitled "Cryogen Pump" by Hilleli et al., which is incorporated herein by reference.

[0065] Fluid 52 is initially in liquid form, but during the procedure, it may change from liquid to a liquid / gas mixture, or even become entirely gaseous. Unless otherwise stated, by way of example, cryofluid 52 is assumed herein to include liquid or gaseous nitrogen. However, it should be understood that other cryofluids, such as cryoargon, may be used in device 20, and all such cryofluids are considered to be included within the scope of the invention. Pump 56 is connected to probe 60, and physician 24 manipulates probe 60 to properly position the distal end of the probe relative to the tumor. (Manipulation is typically assisted by the physician observing the aforementioned ultrasound scan.) Probe 60 will be described in more detail below.

[0066] Figure 2 This is a schematic diagram of a probe 60 according to an embodiment of the present invention. The probe 60 includes a handle 104 attached to a shaft 108 of the probe at a proximal end. The shaft 108 terminates at a distal tip 112, which allows the shaft to pierce tissue, such as a portion of the breast of the patient 28. (A marker 102 on the outer wall of the shaft indicates the distance from the distal end and can be used by the physician 24 during placement of the probe 60 during surgery.) As shown in section 116, the shaft 108 includes three concentric tubes typically formed of thin-walled stainless steel. A first inner tube 120 surrounds a central lumen 124 and is surrounded by a second tube 128. The first and second tubes are spaced apart by an intermediate space 132. A third outer tube 136 surrounds the second tube 128, and the second and third tubes are spaced apart by a space 140. The marker 102 may be provided on the outer wall of the tube 136.

[0067] Temperature sensor 144 (typically a thermocouple or thermistor) is fixedly located within distal end 112, typically near heat exchanger 146 located at distal end, which surrounds tube 120. Cable 148 for the temperature sensor is typically located within space 140. The cable connects to processor 36 and enables the processor to measure the temperature sensed by sensor 144.

[0068] During operation of device 20, the space 140 between the second and third tubes of shaft 108 remains in a sealed, evacuated state. As explained in more detail below, the central cavity 124 is used to deliver cryogenic fluid from pump 56 to distal end 112, and the intermediate space 132 is used to return cryogenic fluid from distal end to pump.

[0069] A flexible tube 152, having an internal structure substantially similar to that of shaft 108, is connected to the shaft via handle 104. The inner cavity within tube 152 is configured to deliver cryogenic fluid from pump 56 to central cavity 124 and to transfer returning cryogenic fluid from intermediate space 132 to pump.

[0070] Figure 3 This is a schematic block diagram of device 20 according to an embodiment of the present invention, showing how the components of the device are connected together. The block diagram illustrates the flow of cryogenic fluid and the transmission of signal data between the components.

[0071] The processor 36 controls the operation of the device 20 by providing pump motor control signals to the motor 68. Upon startup, the motor operates the pump 56, causing the cryogenic fluid to be discharged from the Dewar flask 72 at a flow rate dependent on the motor's rotational speed. Therefore, in this description, unless otherwise stated, the speed of the motor, i.e., the motor's rotational speed, is proportional to the flow rate of the discharged cryogenic fluid; thus, a large rotational speed corresponds to a large flow rate, and a small rotational speed corresponds to a small flow rate. The flow rate is also referred to herein as the delivery rate.

[0072] In this description, flow rates are given in rpm (revolutions per minute), and in one embodiment, the pump has a motor with a gear ratio of 1:50, so 3000 rpm of the motor corresponds to 60 rpm of the pump. When the fluid is 100% liquid, the approximate conversion factor between pump rpm and flow rate is: 60 rpm = 0.36 liters / minute.

[0073] The discharged cryogenic fluid flows out of the Dewar flask, through the flexible tube 152, the handle 104, and the inner cavity 124 of the tube 120 to the distal end 112.

[0074] In the disclosed implementation, processor 36 is a PID (proportional-integral-derivative) controller.

[0075] The cryogenic fluid typically returns from the distal end 112 to the Dewar flask 72 in the form of a liquid / gas mixture via the space 132 in the probe 60, the handle 104, and the flexible tube 152.

[0076] As shown, a temperature sensor 144 located at the distal end of the probe provides a signal to the processor 36 indicating the temperature of the probe tip. The processor 36 also receives a signal from a pressure sensor 100 in the handle 104 indicating the pressure of the cryogenic fluid entering the inner cavity 124. The sensor 100 is located in the handle 104, typically close to the inner tube 120, such that the sensor is in contact with the entering cryogenic fluid.

[0077] Processor 36 uses signals from pressure and temperature sensors to run algorithm 48, which enables the processor to generate output signals that control pump motor 68. The output signals transmitted to the pump motor control the motor's rotational speed and, consequently, the flow rate of the cryogenic fluid discharged from Dewar flask 72.

[0078] Figure 4This is a flowchart of the operations performed by the processor 36 according to an embodiment of the present invention during the first stage of the operation, using algorithm 48. In the description of the flowchart, it is assumed that the processor 36 includes a PID (proportional-integral-derivative) controller, whose output is given by equation (1):

[0079]

[0080] Where u(t) is the control signal output by the processor at time t, and

[0081] K C t i and t d These are the coefficients of the proportional term, integral term, and differential term, respectively.

[0082] For processors that differ from PID controllers, those skilled in the art will be able to adjust the flowchart description with necessary modifications without excessive experimentation.

[0083] In the first step 150, parameters of processor 36 (here, as described above, it is assumed to include a PID controller) are input to the processor. In the following description, it is assumed that the PID controller has K... C =0.1 and t i =0.05 and t d =0 coefficient value, that is, processor 36 operates as a PI controller, and those skilled in the art will be able to target K without excessive experimentation. C t i and t d Other values ​​are adjusted in the description.

[0084] In step 150, the target temperature T is provided to the processor 36. t Target temperature T t This is the nominal temperature to which the distal end 112 is cooled. Typically, temperature T... t Within the range of -10°C to -50°C, but in some implementations T t Outside of this range. A protective temperature T is also provided to processor 36. g Protection temperature T g It is less than T t Temperature, protection temperature T g Used as the nominal temperature limit value for the remote end. In one implementation, when T... t = -20℃, T g = -23℃.

[0085] The processor also sets the minimum motor speed M applied to the pump motor 68 according to the steps of the flowchart, corresponding to the minimum flow rate or minimum delivery rate. mIn one implementation, the minimum motor speed is set to 224 rpm.

[0086] In the initial step 150, a function f(P) is also provided to the processor, which uses f(P) to calculate the maximum motor speed M to be applied to the pump motor. u Maximum motor speed M u This corresponds to the maximum flow rate or maximum conveying rate, i.e.

[0087] M u =f(P) (2)

[0088] Where f is a function of the pressure P measured by pressure sensor 100.

[0089] In an embodiment of the invention, f(P) is configured such that if P increases, the maximum motor speed M... u The flow rate decreases, thus the maximum flow rate decreases, and if P decreases, then M... u This increases, thus increasing the maximum flow rate. In this implementation, the two derivatives... and All are negative.

[0090] In one disclosed implementation, equation (2) is set as equation (3):

[0091]

[0092] Where P arb It is a parameter pressure with a fixed value, which is set to be greater than the critical pressure of the cryogenic fluid used by device 20; and

[0093] K1 is a proportionality constant, which is used to convert the expression on the right side of equation (3) into M. u The unit.

[0094] According to equation (3), the gradient of the first derivative of the equation is... Given by equation (3a):

[0095]

[0096] In one example of the disclosed implementation, when P is measured in psi (pounds per square inch) and M u When measured in rpm (revolutions per minute), K1 = 960 rpm and P arb =800psi, making per psi.

[0097] In the initial step 154 ​​of the surgery, the doctor 24 inserts probe 60 into patient 28 and activates pump 56 to inject cryogenic fluid into probe.

[0098] In the first determination step 158, the processor compares the temperature T measured by sensor 144 with the protection temperature T by evaluating the following expression. g Comparison:

[0099] T <T g (4)

[0100] If expression (4) returns positive, that is, the temperature T is less than the protection temperature T g Then the processor proceeds to the first flow rate setting step 162, in which the processor sets the motor speed to the minimum speed M. m This corresponds to setting the flow rate to the minimum flow rate. Then control returns to decision step 158.

[0101] If expression (4) returns negative, i.e., temperature T is greater than or equal to the protection temperature, then control continues to the second decision step 166. In step 166, the processor compares temperature T with the target temperature T by evaluating the following expression. t Comparison:

[0102] T <T t (5)

[0103] If step 166 returns a positive result, meaning the temperature T is less than the target temperature T... t In step 168, the processor calculates the target motor speed M corresponding to the reduced target flow rate. T .

[0104] If step 166 returns a negative result, that is, the temperature T is greater than or equal to the target temperature T. t In step 170 of increasing motor speed, the processor calculates the increased target motor speed M corresponding to the increased target flow rate. T .

[0105] In steps 168 and 170, the processor calculates u(t) according to equation (1) and determines the target motor speed M according to equation (6). T :

[0106] M T =K2·u(t) (6)

[0107] Where K2 is a proportionality constant, which is used to convert u(t) into the unit of motor speed.

[0108] In the publicly available implementation, K2 = 640 rpm.

[0109] The control in steps 168 and 170 continues at the maximum speed in step 172.

[0110] In step 172, the processor accesses the value of pressure P provided by pressure sensor 100 and uses this value to calculate the maximum motor speed M according to equation (2). u .

[0111] In the third decision step 174, the processor compares the motor speed M by evaluating the following expression. T and M u That is, the processor compares the target flow rate with the maximum flow rate:

[0112] M T <M u (7)

[0113] If expression (7) returns positive, that is, the target motor speed M T Less than the maximum motor speed M u Then the processor proceeds to the second flow rate setting step 178, in which the processor sets the motor speed to the target motor speed M. T That is, the processor sets the flow rate to the target flow rate.

[0114] If expression (7) returns negative, that is, the motor speed M T Equal to or greater than the maximum speed M u Then the processor proceeds to the third step 182, which sets the flow rate, whereby the processor sets the motor speed to the maximum motor speed M. u That is, the processor sets the flow rate to the maximum flow rate.

[0115] Figure 4 The flowchart is repeated by returning from the flow rate steps 162, 178, and 182 to the decision step 158.

[0116] The steps in the flowchart corresponding to Algorithm 48 are in the reference. Figure 1 The procedure is performed during the first phase of the surgery. The first phase terminates when the surgeon stops iterating through the flowchart steps, i.e., stops running algorithm 48. At this point, the surgeon can proceed to the second phase of the surgery to further reduce the temperature of the distal end 112. In the second phase, algorithm 48 is not activated, and the lower temperature is typically achieved by increasing the flow rate of pump 56.

[0117] Figure 5 According to an embodiment of the present invention Figure 4The flowchart is a set of schematic graphs obtained during the execution of the process, i.e. during the activation algorithm 48. The first graph 200 plots the temperature of the distal 112 measured by the sensor 144 as a function of time; the second graph 204 plots the pressure measured by the sensor 100 as a function of time; and the third graph 208 plots the refrigerant flow rate (which corresponds to the input from the processor 36 to the pump 68) measured by the pump motor speed as a function of time.

[0118] As shown in the graph, when the distal temperature T is lower than the protection temperature T g At this point, the flow rate and motor speed are low and approximately constant, corresponding to the first flow rate step 162 in the flowchart. The low flow rate allows the distal temperature to rise to the protection temperature T. g The above, and the pressure can also be increased. Typically, as shown at time 212, away from the protective temperature T. g At that time, the pressure is initially low, resulting in the maximum flow rate and maximum motor speed M. u (Calculated in step 172) There is a high value, and since T is less than T t Therefore, decision 166 returns affirmative and the processor begins to reduce the flow rate and motor speed in step 168. Decision 174 then returns affirmative, so this corresponds to the second flow rate step 178, where the motor speed is set to the target speed M. T Set the flow rate to the target flow rate.

[0119] However, when T is greater than or equal to T t At that time, in step 170, the processor begins to increase the target flow rate and the target motor speed M. T Due to the maximum flow rate and maximum motor speed M u The value is still very high, therefore decision 174 returns to positive, allowing the second flow rate step 178 to remain enabled, and increasing the target flow rate and target motor speed M. T You can continue.

[0120] The increased flow rate continues until the pressure increases sharply due to the increased flow rate, for example, as shown at time 80 in graph 204. The high pressure releases any initial gas seal because any liquid refrigerant is more compressible at high pressure than at low pressure. Furthermore, near or above the critical pressure, the refrigerant is, or behaves, as a supercritical fluid. Therefore, the refrigerant flows more easily in the probe.

[0121] The increased flow rate also caused a sharp drop in temperature to T. g The following is illustrated in graph 200. Increased pressure means that the maximum motor speed M is now present. uThe set maximum flow rate is low, so decision 174 returns negative, and the third flow rate step 182 is enabled. Therefore, the flow rate drops sharply, corresponding to a low maximum motor speed M. u And this flow rate continued until time 216.

[0122] As is evident from the graph, the processing implemented by processor 36 is iterative, with one iteration occurring between times 212 and 216. During the iteration, as shown in graph 200, the temperature at the distal end reaches the target temperature T. t The pressure oscillates around the sensor. Graph 204 also shows that the pressure measured by the pressure sensor 100 oscillates between relatively low values ​​of approximately 100 psi and relatively high values ​​of approximately 300 psi. The oscillations in temperature, pressure, and flow rate are finite, and the corresponding upper and lower limits, among other things, depend on the minimum flow rate and motor speed M. m The settings and the maximum flow rate and the motor speed M given by equation (3) u Therefore, the oscillation also depends on the coefficient of the PID controller term used in equation (1).

[0123] In an embodiment of the present invention, when the temperature at the distal end is at the target temperature T t When the surrounding area oscillates, the amplitude of the temperature oscillation at the far end is approximately 10°C, where the amplitude is the temperature difference between the local maximum temperature and the local minimum temperature at the far end.

[0124] As used herein, the terms “approximately” or “approximately” for any numerical value or range indicate an appropriate dimensional tolerance that allows a part or assembly of parts to be used for its intended purpose as described herein. More specifically, “approximately” or “approximately” can refer to a value range of ±20% of the mentioned value; for example, “approximately 80%” can refer to a value range from 64% to 96%.

[0125] It will be understood that the embodiments described above are cited as examples, and the invention is not limited to what is specifically shown and described above. Rather, the scope of the invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications thereto that would occur to those skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Claims

1. An apparatus comprising: A probe comprising a first lumen and a second lumen and having a distal end configured to contact tissue of a living organism; A fluid supply device is coupled to deliver cryogenic fluid through the first cavity to the distal end of the probe, and to receive cryogenic fluid returning from the probe via the second cavity; A temperature sensor, located at the distal end; A pressure sensor is located at the proximal end of the first cavity and is configured to measure the pressure of the cryogenic fluid in the first cavity; as well as A processor is configured to control the delivery rate of the cryogenic fluid from the fluid supply device such that when the temperature measured by the temperature sensor is below a preset protection temperature, the delivery rate is a preset low rate, and when the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the delivery rate is set in response to the pressure measured by the pressure sensor. When the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the delivery rate is set in response to a pressure compared with a parameter pressure, which is selected in response to the critical pressure of the cryogenic fluid.

2. The apparatus according to claim 1, wherein, When the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the conveying rate is set in response to the temperature.

3. The apparatus according to claim 1, wherein, When the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the conveying rate is set in response to a preset target temperature that is greater than the preset protection temperature.

4. The apparatus according to claim 3, wherein, The preset target temperature is in the range of -10°C to -50°C.

5. The apparatus according to any one of claims 1-3, wherein, When the temperature measured by the temperature sensor is greater than or equal to the preset protection temperature, the conveying rate is less than or equal to the maximum conveying rate calculated based on a preset function of pressure.

6. The apparatus according to claim 5, wherein, The first derivative of the preset function at the pressure measured by the pressure sensor is negative.

7. The apparatus according to claim 1, wherein, The parameter pressure is greater than the critical pressure.

8. The apparatus according to any one of claims 1-3, wherein, The processor includes a proportional-integral-derivative (PID) controller.

9. The apparatus according to claim 8, wherein, The PID controller operates as a PI controller.

10. An apparatus comprising: A probe comprising a first lumen and a second lumen and having a distal end configured to contact tissue of a living organism; A fluid supply device is coupled to deliver cryogenic fluid through the first cavity to the distal end of the probe, and to receive cryogenic fluid returning from the probe via the second cavity; A temperature sensor, located at the distal end; A pressure sensor is located at the proximal end of the first cavity and is configured to measure the pressure of the cryogenic fluid in the first cavity; as well as A processor is configured to control the delivery rate of the cryogenic fluid from the fluid supply device, such that, in response to a preset target temperature at the remote end and a pressure measured by the pressure sensor, the temperature measured by the temperature sensor oscillates around the preset target temperature at a preset amplitude. The processor is configured to control the delivery rate of the cryogenic fluid in response to a ratio of the pressure measured by the pressure sensor to a predetermined pressure.

11. The apparatus according to claim 10, wherein, The predetermined pressure is greater than the critical pressure of the cryogenic fluid.

12. The apparatus according to claim 10, wherein, The conveying rate is at least a preset minimum conveying rate.

13. The apparatus according to claim 10, wherein, The processor is a proportional-integral-derivative controller, and the coefficient values ​​of the controller are selected such that the temperature oscillates at the preset amplitude.

14. The apparatus according to claim 10, wherein, The preset range is between 8°C and 12°C.

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