Monitoring and controlling internally administered cryotherapy

1. A method, comprising:

advancing an elongate shaft of a catheter toward a treatment location within a body lumen of a human patient;

directing a flow of refrigerant toward a cryotherapeutic element at a distal end portion of the shaft via a supply line extending along at least a portion of a length of the shaft;

expanding the directed refrigerant to cause cooling within a balloon of the cryotherapeutic element;

exhausting the expanded refrigerant via an exhaust line extending along at least a portion of the length of the shaft;

measuring pressure within the cryotherapeutic element and/or within a distal portion of the exhaust line via a monitoring line extending along at least a portion of the length of the shaft;

calculating a rate of change of the measured pressure;

processing the rate of change of the measured pressure using a first feedback loop during a first monitoring window of a treatment cycle, the first feedback loop being configured to cause the flow of refrigerant through the supply line to stop if the rate of change of the measured pressure falls outside a range from a first lower threshold to a first upper threshold;

switching from the first monitoring window to a second monitoring window of the treatment cycle; and

processing the rate of change of the measured pressure using a second feedback loop during the second monitoring window, the second feedback loop being configured to cause the flow of refrigerant through the supply line to stop if the rate of change of the measured pressure falls outside a range from a second lower threshold to a second upper threshold, wherein (a) the first lower threshold is different than the second lower threshold and/or (b) the first upper threshold is different than the second upper threshold.

2. The method of claim 1 , wherein:

the first monitoring window corresponds to a first portion of the treatment cycle, the first portion of the treatment cycle being characterized by pressure within the balloon increasing and then stabilizing toward a steady-state pressure; and

the second monitoring window corresponds to a second portion of the treatment cycle, the second portion of the treatment cycle being characterized by pressure within the balloon remaining at least generally at the steady-state pressure.

3. The method of claim 1 , further comprising:

starting the flow of refrigerant through the supply line;

measuring a pressure within the cryotherapeutic element and/or within the distal portion of the exhaust line via the monitoring line upon expiration of a predetermined time period immediately following starting the flow of refrigerant; and

performing an inflation check including determining if the measured pressure is within a range characteristic of proper inflation of the balloon.

4. The method of claim 1 , further comprising:

stopping the flow of refrigerant through the supply line;

measuring a pressure within the cryotherapeutic element and/or within the distal portion of the exhaust line via the monitoring line upon expiration of a predetermined time period following stopping the flow of refrigerant; and

performing a deflation check including determining if the measured pressure is below a threshold indicating proper deflation of the balloon.

5. The method of claim 1 , further comprising:

starting the flow of refrigerant through the supply line;

measuring a temperature within the cryotherapeutic element and/or within the distal portion of the exhaust line via a sensor lead extending along at least a portion of the length of the shaft upon expiration of a predetermined time period after starting the flow of refrigerant; and

performing a cooling check including determining if the measured temperature is below a threshold indicating proper cooling of the balloon.

6. The method of claim 1 , further comprising:

stopping the flow of refrigerant through the supply line;

measuring a temperature within the cryotherapeutic element and/or within the distal portion of the exhaust line via a sensor lead extending along at least a portion of the length of the shaft upon expiration of a predetermined time period after stopping the flow of refrigerant; and

performing a warming check including determining if the measured temperature is above a threshold indicating proper warming of the balloon.

7. The method of claim 1 , further comprising measuring a temperature within the cryotherapeutic element and/or within the distal portion of the exhaust line via a sensor lead extending along at least a portion of the length of the shaft, wherein switching from the first monitoring window to the second monitoring window includes switching from the first monitoring window to the second monitoring window based at least partially on the measured temperature.

8. The method of claim 1 , wherein switching from the first monitoring window to the second monitoring window includes switching from the first monitoring window to the second monitoring window based at least partially on the measured pressure.

9. The method of claim 1 , further comprising:

releasing a pulse of refrigerant into the balloon via the supply line;

measuring a pressure within the exhaust line after releasing the pulse; and

performing a pre-inflation check including determining if the measured pressure within the exhaust line is within a range indicating that the balloon is intact.

10. The method of claim 9 , wherein:

releasing the pulse includes releasing a first pulse; and

the method further comprises:

releasing a second pulse of refrigerant into the balloon via the supply line after performing the pre-inflation check,

measuring a pressure within the balloon and/or within a distal portion of the exhaust line after releasing the second pulse, and

performing a pressure-decay test including determining if the measured pressure within the balloon and/or within a distal portion of the exhaust line is within a range indicating that the balloon is intact.

11. The method of claim 1 , further comprising measuring a temperature within the cryotherapeutic element and/or within the distal portion of the exhaust line via a sensor lead extending along at least a portion of the length of the shaft, wherein switching from the first monitoring window to the second monitoring window includes switching from the first monitoring window to the second monitoring window based at least partially on a predetermined time, the measured temperature, the measured pressure, or a combination thereof.

12. The method of claim 11 , wherein switching from the first monitoring window to the second monitoring window includes switching from the first monitoring window to the second monitoring window using a switching algorithm in which switching based on the measured temperature, the measured pressure, or a combination thereof can only occur prior to expiration of the predetermined time.

13. The method of claim 1 , wherein:

measuring pressure and processing the measured pressure using the first feedback loop are executed by a first control algorithm operating at a first cycle speed;

switching from the first monitoring window to the second monitoring window is executed by a second control algorithm operating at a second cycle speed; and

the first cycle speed is faster than the second cycle speed.

14. The method of claim 13 , wherein the first cycle speed is at least 10 times faster than the second cycle speed.

15. The method of claim 13 , wherein:

processing the rate of change of the measured pressure using the first feedback loop includes, within the first control algorithm, accessing a first stored value as the first lower threshold and accessing a second stored value as the first upper threshold; and

switching from the first monitoring window to the second monitoring window includes converting the first feedback loop into the second feedback loop by, within the second control algorithm, (a) changing the first stored value from the first lower threshold to the second lower threshold and/or (b) changing the second stored value from the first upper threshold to the second upper threshold.