Delivering refrigerant to catheters for cryotherapy

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.

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.