Delivering refrigerant to catheters for cryotherapy
A method and system for controlling flow of refrigerant through a medical device are disclosed. According to one aspect, a system for delivering refrigerant to an expansion cavity portion of the medical device comprises a first path and a second path in communication with the expansion cavity portion. The system also includes a first PID controller in communication with a first proportional valve in the first path, the first PID controller being configured to operate the first proportional valve based on a pressure measurement in the first path; and a second PID controller in communication with a second proportional valve in the second path, the second controller being configured to operate the second proportional valve based on a pressure measurement in the second path or in the expansion cavity portion.
1 . A system for delivering refrigerant to a medical device, the system comprising:
a first path for delivering the refrigerant to an expansion cavity portion of the medical device from a refrigerant source, the first path including a first solenoid valve;
a second path for removing the refrigerant from the expansion cavity portion, the second path including a second solenoid valve and a vacuum pump connected to draw the refrigerant from the expansion cavity portion through the second solenoid valve; and
a control circuit including:
a first controller to control the first solenoid valve based on a pressure measurement in the first path and further based on a first setpoint value, and
a second controller to control the second solenoid valve based on a pressure measurement in the second path or in the expansion cavity portion and further based on a second setpoint value,
wherein the first controller is configured to operate the first solenoid valve based on a sum of a first plurality of terms including a term proportional to a first error signal, a term proportional to an integral of the first error signal, and a term proportional to a derivative of the first error signal, the first error signal representing a difference between the pressure measurement in the first path and the first setpoint value.
2 . The system of claim 1 ,
wherein the medical device comprises a cryoablation or cryomapping catheter; and
wherein the expansion cavity portion is an inflatable portion of the cryoablation or cryomapping catheter.
3 . The system of claim 1 , wherein the second controller is configured to operate the second solenoid valve based on a sum of a second plurality of terms including a term proportional to a second error signal, a term proportional to an integral of the second error signal, and a term proportional to a derivative of the second error signal, the second error signal representing a difference between the pressure measurement in the second path and the second setpoint value.
4 . The system of claim 3 , wherein the second plurality of terms further includes a term proportional to a derivative of the pressure measurement in the first path at an earlier time.
5 . The system of claim 1 , wherein the control circuit is configured to change the second setpoint value when the expansion cavity portion is being filled with the refrigerant supplied through the first path.
6 . The system of claim 1 , further comprising a third path end-connected at a first end thereof to a section of the first path downstream from the first solenoid valve, the third path including a third solenoid valve,
wherein the control circuit is configured to open the third solenoid valve to vent the refrigerant from the first path.
7 . The system of claim 6 , wherein the third path further includes a fourth solenoid valve between a second end thereof and the third solenoid valve,
wherein the control circuit is configured to operate the fourth solenoid valve to selectively connect the vacuum pump to the third path.
8 . The system of claim 1 , wherein the control circuit includes an electronic controller connectable to a set of sensors selected from the group consisting of a first pressure sensor in the first path, a second pressure sensor in the second path, a third pressure sensor in the expansion cavity portion, a temperature sensor in the expansion cavity portion, and a flow meter in the second path.
9 . The system of claim 8 , further comprising a third path end-connected at a first end thereof to a section of the first path downstream from the first solenoid valve, the third path including a third solenoid valve and a fourth solenoid valve,
wherein the electronic controller is configured to operate the third solenoid valve and the fourth solenoid valve based on a stream of measurements by the set of sensors.
10 . The system of claim 1 , wherein the refrigerant comprises nitrous oxide.
11 . A method of delivering refrigerant to a medical device, the method comprising:
providing a first path for delivering the refrigerant to an expansion cavity portion of the medical device from a refrigerant source, the first path including a first solenoid valve;
providing a second path for removing the refrigerant from the expansion cavity portion, the second path including a second solenoid valve and a vacuum pump connected to draw the refrigerant from the expansion cavity portion through the second solenoid valve;
controlling, with a control circuit, the first solenoid valve based on a pressure measurement in the first path and further based on a first setpoint value;
controlling, with the control circuit, the second solenoid valve based on a pressure measurement in the second path or in the expansion cavity portion and further based on a second setpoint value; and
operating, with the control circuit, the first solenoid valve based on a sum of a first plurality of terms including a term proportional to a first error signal, a term proportional to an integral of the first error signal, and a term proportional to a derivative of the first error signal, the first error signal representing a difference between the pressure measurement in the first path and the first setpoint value.
12 . The method of claim 11 , further comprising operating, with the control circuit, the second solenoid valve based on a sum of a second plurality of terms including a term proportional to a second error signal, a term proportional to an integral of the second error signal, and a term proportional to a derivative of the second error signal, the second error signal representing a difference between the pressure measurement in the second path and the second setpoint value.
13 . The method of claim 12 , wherein the second plurality of terms further includes a term proportional to a derivative of the pressure measurement in the first path at an earlier time.
14 . The method of claim 11 , further comprising operating, with the control circuit, the second solenoid valve based on a sum of a second plurality of terms including a term proportional to a second error signal, a term proportional to an integral of the second error signal, a term proportional to a derivative of the second error signal, and a term proportional to a derivative of the pressure measurement in the first path at an earlier time, the second error signal being a difference between the pressure measurement in the second path and the second setpoint value.
15 . The method of claim 11 , further comprising changing the second setpoint value when the expansion cavity portion is being filled with the refrigerant supplied through the first path.
16 . The method of claim 11 , wherein the control circuit is connectable to a set of sensors selected from the group consisting of a first pressure sensor in the first path, a second pressure sensor in the second path, a third pressure sensor in the expansion cavity portion, a temperature sensor in the expansion cavity portion, and a flow meter in the second path.
17 . The method of claim 16 , further comprising:
providing a third path end-connected at a first end thereof to a section of the first path downstream from the first solenoid valve, the third path including a third solenoid valve and a fourth solenoid valve; and
operating, with the control circuit, the third solenoid valve and the fourth solenoid valve based on a stream of measurements by the set of sensors.
18 . A system for delivering refrigerant to a medical device, the system comprising:
a first path for delivering the refrigerant to an expansion cavity portion of the medical device from a refrigerant source, the first path including a first solenoid valve;
a second path for removing the refrigerant from the expansion cavity portion, the second path including a second solenoid valve and a vacuum pump connected to draw the refrigerant from the expansion cavity portion through the second solenoid valve; and
a control circuit including:
a first controller to control the first solenoid valve based on a pressure measurement in the first path and further based on a first setpoint value, and
a second controller to control the second solenoid valve based on a pressure measurement in the second path or in the expansion cavity portion and further based on a second setpoint value,
wherein the second controller is configured to operate the second solenoid valve based on a sum of a plurality of terms including a term proportional to an error signal, a term proportional to an integral of the error signal, a term proportional to a derivative of the error signal, and a term proportional to a derivative of the pressure measurement in the first path at an earlier time, the error signal being a difference between the pressure measurement in the second path and the second setpoint value.