Systems and methods for adjusting electrical therapy based on impedance changes

1. A method for controlling a patient therapy device, comprising:

applying or directing application of a therapeutic electrical signal to a patient via an implanted portion of a patient stimulation system that includes a signal delivery device in electrical communication with a target neural population of the patient, the electrical signal being delivered to a first implanted electrical contact set in accordance with a signal delivery parameter having a first value;

using the implanted portion of the patient stimulation system, detecting or directing detection of an increase in an impedance of an electrical circuit that includes the signal delivery device; and

based at least in part on the detected impedance increase, automatically adjusting or directing adjustment of the value of the signal delivery parameter from the first value to a second value different than the first value, without human intervention, wherein automatically adjusting or directing adjustment of the value of the signal delivery parameter includes applying or directing application of the electrical signal to a second implanted electrical contact set, at least one of the first and second contact sets having a different member than the other.

2. The method of claim 1 wherein automatically adjusting or directing adjustment of the value of the signal delivery parameter includes halting or directing the halting of delivery of the electrical signal.

3. The method of claim 1 wherein automatically adjusting or directing adjustment of the value of the signal delivery parameter includes changing or directing a change of at least one of a strength, pulse width, and duty cycle of the signal.

4. The method of claim 1 wherein detecting or directing detection of an increase in an impedance of an electrical circuit includes detecting or directing detection of an increase in an impedance of an electrical circuit that includes the target neural population.

5. The method of claim 1 wherein applying or directing application of a therapeutic electrical signal includes applying or directing application of the electrical signal via an implanted electrical contact carried by the signal delivery device and exposed to the patient's tissue.

6. The method of claim 1 wherein applying or directing application of a therapeutic electrical signal includes applying or directing application of the signal to the patient's spinal cord region.

7. The method of claim 1 wherein automatically adjusting or directing adjustment of the value of the signal delivery parameter includes increasing or directing an increase of a strength of the signal.

8. A method for controlling a patient therapy device, comprising:

applying a therapeutic electrical signal to a patient via an implanted portion of a patient stimulation system that includes a signal delivery device in electrical communication with a target neural population of the patient, the electrical signal being delivered in accordance with a signal delivery parameter having a first value;

using the implanted portion of the patient stimulation system, detecting an increase in an impedance of an electrical circuit that includes the signal delivery device, wherein detecting an increase in an impedance includes detecting an open circuit; and

based at least in part on the detected impedance increase, automatically adjusting the value of the signal delivery parameter from the first value to a second value different than the first value, without human intervention, wherein automatically adjusting the value of the signal delivery parameter includes reducing a strength of the electrical signal and then ramping up the strength of the electrical signal after the circuit is closed.

9. The method of claim 8 wherein detecting an increase in an impedance includes detecting an increase in impedance resulting from a build up of scar tissue on the signal delivery device.

10. The method of claim 8 wherein detecting an increase in an impedance includes detecting an increase in impedance resulting from a change in position of the signal delivery device relative to the patient.

11. The method of claim 8 wherein detecting an increase in an impedance includes detecting an increase in impedance resulting from a change in the patient's posture.

12. The method of claim 8 wherein detecting an increase in an impedance includes detecting an increase in impedance as a function of time, and wherein the method further comprises establishing a trend for future increases in impedance.

13. The method of claim 8 wherein detecting an increase in an impedance includes detecting an increase in impedance by monitoring the therapeutic electrical signal.

14. The method of claim 8 wherein detecting an increase in an impedance includes applying an electrical signal in addition to the therapeutic electrical signal and detecting an increase in impedance by monitoring the additional electrical signal.

15. The method of claim 8 wherein automatically adjusting a signal delivery parameter includes automatically adjusting a compliance value in accordance with which the electrical signal is delivered, in response to the detected impedance increase.

16. The method of claim 8 wherein automatically adjusting a signal delivery parameter includes automatically adjusting a compliance margin in accordance with which the electrical signal is delivered, in response to the detected impedance increase.

17. A method for controlling a patient therapy device, comprising:

applying or directing application of a therapeutic electrical signal to a patient via a patient stimulation system that includes a signal delivery electrical contact in electrical communication with a target neural population of the patient, the electrical signal having a signal delivery parameter with a first value;

automatically identifying or directing identification of changes in an impedance of an electrical circuit that includes the signal delivery electrical contact, as a function of time;

based at least in part on identifying the changes in impedance as a function of time, predicting or directing prediction of a future value of the impedance by extrapolating or directing extrapolation of the future value based on past values; and

based at least in part on the predicted future value of the impedance, automatically performing a task or directing performance of the task.

18. A patient therapy system, comprising:

a patient-implantable portion that includes a pulse generator and a signal delivery device having an electrical contact positioned to be in electrical communication with a target neural population of a patient when implanted;

an impedance detector carried by the implantable portion, the impedance detector being operatively coupled to an electrical circuit that includes the electrical contact to detect an impedance of the electrical circuit;

a processor carried by the patient-implantable portion, the processor having a computer-readable medium programmed with instructions that, when executed:

receive an indication of an impedance change from the impedance detector; and

based at least in part on the detected impedance change and without human intervention, automatically adjust a value of a signal delivery parameter in accordance with which the patient-implantable portion delivers an electrical signal to the electrical contact; and

a constant current source carried by the implantable portion and having a compliance voltage level with a first value, and wherein automatically adjusting the value of the signal delivery parameter includes:

increasing the compliance voltage level from the first value to a second value higher than the first; and

increasing a strength of the signal beyond a strength available with the first value.

19. A patient therapy system, comprising:

a patient-implantable portion that includes a pulse generator and a signal delivery device having an electrical contact positioned to be in electrical communication with a target neural population of a patient when implanted;

an impedance detector carried by the implantable portion, the impedance detector being operatively coupled to an electrical circuit that includes the electrical contact to detect an impedance of the electrical circuit; and

a processor carried by the patient-implantable portion, the processor having a computer-readable medium programmed with instructions that, when executed:

receive an indication of an impedance change from the impedance detector; and

based at least in part on the detected impedance change and without human intervention, automatically adjust a value of a signal delivery parameter in accordance with which the patient-implantable portion delivers an electrical signal to the electrical contact, wherein automatically adjusting a value of a signal delivery parameter includes automatically adjusting at least one of a compliance value and a compliance margin in accordance with which the electrical signal is delivered.