Determining posture state from ECAPs

1. A system comprising:

stimulation circuitry configured to deliver electrical stimulation;

sensing circuitry configured to sense a plurality of evoked compound action potential (ECAP) signals; and

processing circuitry configured to:

control the stimulation circuitry to deliver a plurality of electrical stimulation pulses having different amplitude values;

control the sensing circuitry to detect, after delivery of each electrical stimulation pulse of the plurality of electrical stimulation pulses, a respective ECAP signal of the plurality of ECAP signals; and

determine, based on the plurality of ECAP signals, a posture state of the patient.

2. The system of claim 1 , wherein the processing circuitry is configured to:

determine characteristic values for the plurality of ECAP signals, each ECAP signal of the plurality of ECAP signals being associated with a respective characteristic value of the characteristic values;

determine a growth curve representing a relationship between the characteristic values of the plurality of ECAP signals and the different amplitude values of the plurality of electrical stimulation pulses from which the ECAP signals were evoked;

compare the growth curve to a plurality of calibration growth curves associated with respective posture states of a plurality of posture states; and

determine, based on the comparison, the posture state of the patient.

3. The system of claim 2 , wherein the processing circuitry is configured to, for each posture state of the plurality of posture states:

control the stimulation circuitry to deliver a plurality of calibration electrical stimulation pulses having different amplitude values while the patient assumes the posture state;

control the sensing circuitry to detect, after delivery of each calibration electrical stimulation pulse of the plurality of calibration electrical stimulation pulses, a respective calibration ECAP signal of a plurality of calibration ECAP signals;

determine calibration characteristic values for the plurality of calibration ECAP signals, each calibration ECAP signal of the plurality of calibration ECAP signals being associated with a respective characteristic value of the calibration characteristic values; and

determine a respective calibration growth curve, of the plurality of calibration growth curves, that represents the relationship between the calibration characteristic values of the plurality of calibration ECAP signals and the different amplitude values of the plurality of calibration electrical stimulation pulses from which the calibration ECAP signals were evoked.

4. The system of claim 1 , wherein the processing circuitry is configured to control the stimulation circuitry to deliver the plurality of electrical stimulation pulses as a sweep of pulses comprising iteratively increasing amplitude values.

5. The system of claim 1 , wherein the plurality of electrical stimulation pulses is a second set of electrical stimulation pulses and the plurality of ECAP signals is a second set of ECAP signals, and wherein the processing circuitry is configured to:

control, during a first period of time, the stimulation circuitry to deliver a first set of electrical stimulation pulses from which respective ECAP signals of a second set of ECAP signals can be detected;

identify, during the first period of time, a transient movement of the patient;

responsive to identifying the transient movement, terminate the first period of time and the delivery of the first set of electrical stimulation pulses and discard the second set of ECAP signals;

determine that the transient movement has ended; and

after the transient movement has ended, control the stimulation circuitry to deliver the second set of electrical stimulation pulses and control the sensing circuitry to detect the second set of ECAP signals.

6. The system of claim 5 , wherein the processing circuitry is configured to, responsive to determining that the transient movement has ended, control the stimulation circuitry to deliver the second set of electrical stimulation pulses and control the sensing circuitry to detect the second set of ECAP signals.

7. The system of claim 5 , wherein the processor is configured to detect the transient movement from an electromyogram signal.

8. The system of claim 5 , wherein the processing circuitry is configured to detect the transient movement from information received from one or more accelerometers.

9. The system of claim 1 , wherein the posture state of the patient comprises at least one of a static posture of the patient or an activity level of the patient.

10. The system of claim 1 , wherein the processing circuitry is configured to determine the posture state by selecting the posture state from a plurality of posture states, the plurality of posture states comprising at least two of a prone position, a supine position, a sitting position, and a standing position.

11. The system of claim 1 , wherein the different amplitude values are lower than a discomfort threshold for the patient.

12. The system of claim 1 , wherein the processing circuitry is configured to adjust, based on the determined posture state, a value of one or more parameters that at least partially define electrical stimulation therapy for the patient.

13. The system of claim 1 , wherein an implantable medical device comprises the stimulation circuitry, the sensing circuitry, and the processing circuitry.

14. A method comprising:

controlling, by processing circuitry, stimulation circuitry to deliver a plurality of electrical stimulation pulses having different amplitude values;

controlling, by the processing circuitry, sensing circuitry to detect, after delivery of each electrical stimulation pulse of the plurality of electrical stimulation pulses, a respective evoked compound action potential (ECAP) signal of a plurality of ECAP signals; and

determining, by the processing circuitry and based on the plurality of ECAP signals, a posture state of the patient.

15. The method of claim 14 , further comprising:

determining characteristic values for the plurality of ECAP signals, each ECAP signal of the plurality of ECAP signals being associated with a respective characteristic value of the characteristic values;

determining a growth curve representing a relationship between the characteristic values of the plurality of ECAP signals and the different amplitude values of the plurality of electrical stimulation pulses from which the ECAP signals were evoked;

comparing the growth curve to a plurality of calibration growth curves associated with respective posture states of a plurality of posture states; and

determining, based on the comparison, the posture state of the patient.

16. The method of claim 15 , further comprising, for each posture state of the plurality of posture states:

controlling the stimulation circuitry to deliver a plurality of calibration electrical stimulation pulses having different amplitude values while the patient assumes the posture state;

controlling the sensing circuitry to detect, after delivery of each calibration electrical stimulation pulse of the plurality of calibration electrical stimulation pulses, a respective calibration ECAP signal of a plurality of calibration ECAP signals;

determining calibration characteristic values for the plurality of calibration ECAP signals, each calibration ECAP signal of the plurality of calibration ECAP signals being associated with a respective characteristic value of the calibration characteristic values; and

determining a respective calibration growth curve, of the plurality of calibration growth curves, that represents the relationship between the calibration characteristic values of the plurality of calibration ECAP signals and the different amplitude values of the plurality of calibration electrical stimulation pulses from which the calibration ECAP signals were evoked.

17. The method of claim 14 , wherein controlling the stimulation circuitry to deliver the plurality of electrical stimulation pulses comprises controlling the stimulation circuitry to provide a sweep of pulses comprising iteratively increasing amplitude values.

18. The method of claim 14 , wherein the plurality of electrical stimulation pulses is a second set of electrical stimulation pulses and the plurality of ECAP signals is a second set of ECAP signals, and wherein the method further comprises:

controlling, during a first period of time, the stimulation circuitry to deliver a first set of electrical stimulation pulses from which respective ECAP signals of a second set of ECAP signals can be detected;

identifying, during the first period of time, a transient movement of the patient;

responsive to identifying the transient movement, terminating the first period of time and the delivery of the first set of electrical stimulation pulses and discard the second set of ECAP signals;

determining that the transient movement has ended; and

after the transient movement has ended, controlling the stimulation circuitry to deliver the second set of electrical stimulation pulses and control the sensing circuitry to detect the second set of ECAP signals.

19. The method of claim 18 , further comprising, responsive to determining that the transient movement has ended, controlling the stimulation circuitry to deliver the second set of electrical stimulation pulses and control the sensing circuitry to detect the second set of ECAP signals.

20. The method of claim 18 , further comprising detecting the transient movement from an electromyogram signal.

21. The method of claim 18 , further comprising detecting the transient movement from information received from one or more accelerometers.

22. The method of claim 14 , wherein the posture state of the patient comprises at least one of a static posture of the patient or an activity level of the patient.

23. The method of claim 14 , wherein determining the posture state comprises selecting the posture state from a plurality of posture states, the plurality of posture states comprising at least two of a prone position, a supine position, a sitting position, and a standing position.

24. The method of claim 14 , wherein the different amplitude values are lower than a discomfort threshold for the patient.

25. The method of claim 14 , further comprising adjusting, based on the determined posture state, a value of one or more parameters that at least partially define electrical stimulation therapy for the patient.

26. A non-transitory computer-readable medium comprising instructions that, when executed, causes processing circuitry to:

control stimulation circuitry to deliver a plurality of electrical stimulation pulses having different amplitude values;

control sensing circuitry to detect, after delivery of each electrical stimulation pulse of the plurality of electrical stimulation pulses, a respective evoked compound action potential (ECAP) signal of a plurality of ECAP signals; and

determine, based on the plurality of ECAP signals, a posture state of the patient.