Method and device for feedback control of neural stimulation
A method of controlling a neural stimulus by use of feedback. The neural stimulus is applied to a neural pathway in order to give rise to an evoked action potential on the neural pathway. The stimulus is defined by at least one stimulus parameter. A neural compound action potential response evoked by the stimulus is measured. From the measured evoked response a feedback variable is derived. A feedback loop is completed by using the feedback variable to control the at least one stimulus parameter value. The feedback loop adaptively compensates for changes in a gain of the feedback loop caused by electrode movement relative to the neural pathway.
1. A method of suppressing pain by applying a neural stimulus, the method comprising:
delivering stimuli from at least one stimulus electrode to a tissue in the dorsal column of a patient, each stimulus defined by a stimulus intensity parameter;
measuring a neural response sensed at at least one sense electrode and evoked in response to a stimulus;
determine from the measured evoked neural response a feedback variable;
complete a feedback control loop by applying a proportional adjustment to the stimulus intensity parameter, wherein the proportional adjustment in proportion to an error between the feedback variable and a target intensity; and
setting a gain based a characteristic of a neural response growth curve, wherein the neural response growth curve is a relation of a neural response intensity to the stimulus intensity parameter,
wherein the proportional adjustment is determined by multiplying the error by the gain.
2. The method of claim 1 , wherein setting the value of the gain comprises:
comparing each of a plurality of measured neural responses to a corresponding stimulus intensity parameter to determine the characteristic of a neural response growth curve, and
setting the gain based on the determined characteristic of the neural response growth curve.
3. The method of claim 2 , wherein the characteristic is a slope of the neural response growth curve.
4. The method of claim 3 , wherein setting the value of the gain comprises setting the gain such that the feedback control loop has a predetermined corner frequency.
5. The method of claim 4 , wherein setting the value of the gain comprises setting the value of the gain to be the predetermined corner frequency divided by the slope.
6. The method of claim 4 , wherein the predetermined corner frequency is between a heartbeat frequency and a sample rate of the feedback control loop.
7. The method of claim 1 , wherein the gain is set when the patient is in a most sensitive posture, being a posture in which the characteristic is greatest.