Hybrid feedback loop control of neuromodulation device

1 . A method of controlling a neural stimulus, the neural stimulus being defined by at least one stimulus intensity parameter, the method comprising:

generating a stimulus intensity parameter to control a stimulator that generates a stimulus for application to a tissue,

measuring a response of the tissue, evoked by the stimulus;

determining a response parameter indicative of the measured response;

in response to the response parameter being less than a first threshold, setting the stimulus intensity parameter to a desired stimulus intensity level that is independent of the measured response; and

in response to the response parameter being greater than a second threshold, adjusting the stimulus intensity parameter according to a feedback variable derived from the measured response.

2 . The method of claim 1 , wherein the desired stimulus intensity level is configured by a user.

3 . The method of claim 1 , wherein setting the stimulus intensity parameter to the desired stimulus intensity level comprises determining a present stimulus intensity parameter of the neural stimulus and setting the stimulus intensity level to the present stimulus intensity parameter.

4 . The method of claim 1 , wherein setting the stimulus intensity parameter to the desired stimulus intensity level comprises iteratively adjusting the stimulus intensity parameter to the desired stimulus intensity level in increments.

5 . The method of claim 1 , wherein the first threshold is equal to the second threshold.

6 . The method of claim 1 , wherein the first threshold and the second threshold represent a level of electrically evoked compound action potential of the tissue.

7 . The method of claim 1 , wherein the first threshold and the second threshold are determined based on the stimulus intensity level at an ECAP threshold.

8 . The method of claim 1 , wherein the response parameter is a function of a plurality of measured response values determined over a time period.

9 . The method of claim 1 , further comprising storing the stimulus intensity parameter in non-volatile memory, and in response to the neural stimulus turning on, setting the stimulus intensity parameter to the stored stimulus intensity parameter.

10 . The method of claim 1 , further comprising:

determining an artefact compensation parameter based on an artefact component of the measured response of the tissue; and

adjusting the measured response based on the artefact compensation parameter.

11 . The method of claim 10 , further comprising determining the artefact component based on the stimulus intensity parameter.

12 . The method of claim 1 , wherein adjusting the stimulus intensity parameter according to the feedback variable derived from the measured response comprises:

in response to the measured response being greater than a target value, reducing the stimulus intensity parameter in accordance with a loss rate; and

in response to the measured response being less than the target value, increasing the stimulus intensity parameter in accordance with a gain rate.

13 . The method of claim 12 , wherein the magnitude of the loss rate is not equal to the magnitude of the gain rate.

14 . The method of claim 12 , further comprising determining the loss rate based on a duration of time for which the measured response is greater than the target value.

15 . The method of claim 1 , wherein the first threshold is determined based on a perception threshold of the tissue.

16 . The method of claim 1 , wherein the second threshold is determined based on a perception threshold of the tissue.

17 . An implantable device for controllably applying a neural stimulus defined by at least one stimulus intensity parameter, the device comprising:

one or more stimulus electrodes to deliver stimulus to a tissue to evoke a compound action potential response of the tissue;

a stimulator for controlling the one or more stimulus electrodes in accordance with the at least one stimulus intensity parameter;

measurement circuitry for measuring the evoked compound action potential response of the tissue; and

a control unit configured to,

generate the stimulus intensity parameter,

measure the response of the tissue, evoked by the stimulus,

determine a response parameter indicative of the measured response,

in response to the response parameter being less than a first threshold, set the stimulus intensity parameter to a desired stimulus intensity level that is independent of the measured response, and

in response to the response parameter being greater than a second threshold, adjust the stimulus intensity parameter according to a feedback parameter derived from the measured response.

18 . The device of claim 17 , further comprising an input for configuring the desired stimulus intensity level.

19 . The device of claim 17 , wherein the control unit is configured to set the stimulus intensity parameter to the desired stimulus intensity level by determining a present stimulus intensity parameter of the neural stimulus and setting the stimulus intensity level to the present stimulus intensity parameter.

20 . The device of claim 17 , wherein the control unit is configured to set the stimulus intensity parameter to the desired stimulus intensity level by adjusting the stimulus intensity parameter to the desired stimulus intensity level in increments.

21 . The device of claim 17 , wherein the first threshold is equal to the second threshold.

22 . The device of claim 17 , wherein the first threshold and the second threshold represent a level of electrically evoked compound action potential of the tissue.

23 . The device of claim 17 , wherein the first threshold is determined based on a perception threshold of the tissue.

24 . The device of claim 17 , wherein the second threshold is determined based on a perception threshold of the tissue.