# US 2019/0168000 A1 · Improved Feedback Control of Neuromodulation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0168000 A1 - Document ID: US20190168000A1 - Status: Published application - Kind: A1 - Application number: 16/091,428 - Filed: 2017-04-05 - Published: 2019-06-06 - Earliest claimed: 2016-04-05 - Assignees: Saluda Medical Pty Ltd - Applicants: Saluda Medical Pty Ltd - Inventors: James Hamilton LAIRD-WAH - Web page: https://patentgrep.com/patent/US20190168000A1 ## CPC - A61N 1/36132: {using patient feedback} - A61B 5/0031: {Implanted circuitry} - A61B 5/388: Nerve conduction study, e.g. detecting action potential of peripheral nerves - A61B 5/4836: {Diagnosis combined with treatment in closed-loop systems or methods (A61B5/0036 takes precedence)} - A61N 1/0551: {Spinal or peripheral nerve electrodes} - A61N 1/18: Applying electric currents by contact electrodes - A61N 1/36067: {Movement disorders, e.g. tremor or Parkinson disease (stimulating motor muscle A61N1/36003)} - A61N 1/36071: {Pain} - A61N 1/36075: {Headache or migraine} - A61N 1/36139: {with automatic adjustment} - A61N 1/36146: {specified by the stimulation parameters} - A61N 1/36185: {Selection of the electrode configuration} - A61N 1/37264: {Changing the program; Upgrading firmware} - A61N 1/3787: {from an external energy source} - A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B) - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract An automated method of controlling neural stimulation. A neural stimulus is applied to a neural pathway in order to give rise to an evoked action potential on the neural pathway, and 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 such as observed ECAP voltage (V) is derived. A feedback loop is completed by using the feedback variable to control the at least one stimulus parameter value for a future stimulus. The method adaptively compensates for changes in a gain of the feedback loop caused by electrode movement relative to the neural pathway. A compensating transfer function is applied to the feedback variable, the compensating transfer function being configured to compensate for both (i) a distance-dependent transfer function of stimulation, and (ii) a distance dependent transfer function of measurement which is distinct from (i). ## Claims ### Claim 1 An automated method of controlling a neural stimulus, the method comprising: applying the neural stimulus to a neural pathway in order to give rise to an evoked action potential on the neural pathway, the stimulus being defined by at least one stimulus parameter; measuring a neural compound action potential response evoked by the stimulus, and deriving from the measured evoked response a feedback variable; completing a feedback loop by using the feedback variable to control the at least one stimulus parameter value; and adaptively compensating for changes in a gain of the feedback loop caused by electrode movement relative to the neural pathway, by applying a compensating transfer function to the feedback variable, the compensating transfer function being configured to compensate for both (i) a distance-dependent transfer function of stimulation, and (ii) a distance dependent transfer function of measurement which is distinct from (i). ### Claim 2 (depends on 1) The method of claim 1 wherein constant recruitment is effected by use of single measurement pairs of stimulation current (I) and observed ECAP voltage (V). ### Claim 3 (depends on 1) The method of claim 1 wherein the compensating transfer function comprises a single parameter k reflecting both a recruitment parameter n and a measurement parameter m, m≠n. ### Claim 4 (depends on 3) The method of claim 3 wherein the total number of fibres recruited N varies as N ∝ Ixn−T0, the measured ECAP voltage amplitude V is approximated as ∝ Nx−m, and k=m/n. ### Claim 5 (depends on 4) The method of claim 4 wherein k is selected to take a value which is suitable for the stimulation and recording configurations in use. ### Claim 6 (depends on 5) The method of claim 5 wherein tripolar stimulation is delivered using the first to third electrodes of a SCS lead, and recordings are taken using the sixth electrode of the same lead, and wherein k is selected to be in the range 0.1 to 0.7. ### Claim 7 (depends on 6) The method of claim 6 wherein k is selected to be in the range 0.22 to 0.53. ### Claim 8 (depends on 7) The method of claim 7 wherein k is selected to be about 0.37. ### Claim 9 (depends on 3) The method of claim 3 wherein k is determined clinically using a recruitment datum. ### Claim 10 (depends on 9) The method of claim 9 wherein the recruitment datum comprises one or more of: the patient's perceptual threshold, discomfort threshold, coverage of a certain area or body part, a qualitative characteristic of the patient's perception of a stimulation, patient's perception of optimal comfort, an electrophysiological measure, the onset of muscle response/twitching, and a measure of neural activity. ### Claim 11 (depends on 9) The method of claim 9 further comprising the patient assuming a series of postures; in each posture adjusting the stimulus intensity until the required recruitment datum is achieved; and estimating k from constant recruitment data in differing postures. ### Claim 12 (depends on 3) The method of claim 3 wherein k is partly or wholly determined clinically by using the recording electrode to measure neural responses to peripheral stimulation in a number of postures to obtain Vi data in each posture; using the stimulus electrode to deliver stimulation in each posture adjusted to a current level Ii which yields the respective Vi, and using the set of (Ii, Vi) pairs of constant recruitment to derive k. ### Claim 13 (depends on 3) The method of claim 3 wherein k is partly or wholly determined clinically by placing the patient in a range of postures i, in each posture sweeping the stimulus intensity and recording a growth curve, linearly fitting the growth curve for each respective posture to determine the respective threshold Ti and growth slope Mi, and comparing log Ti against log TiMi; to derive k. ### Claim 14 (depends on 1) The method of claim 1 wherein an incoming measurement of an ECAP (V) is multiplied with an exponentiated version (Ik) of the stimulus current (I) used to generate that ECAP, and an error signal is generated relative to a setpoint and fed into a controller which determines the next stimulus intensity. ### Claim 15 An implantable device for controllably applying a neural stimulus, the device comprising: a plurality of electrodes including one or more nominal stimulus electrodes and one or more nominal sense electrodes; a stimulus source for providing a stimulus to be delivered from the one or more stimulus electrodes to a neural pathway in order to give rise to an evoked action potential on the neural pathway; measurement circuitry for recording a neural compound action potential signal sensed at the one or more sense electrodes; and a control unit configured to: control application of a neural stimulus as defined by at least one stimulus parameter; measure via the measurement circuitry a neural compound action potential response evoked by the stimulus; determine from the measured evoked response a feedback variable; complete a feedback loop by using the feedback variable to control the at least one stimulus parameter value; and adaptively compensate for changes in a gain of the feedback loop caused by electrode movement relative to the neural pathway, by applying a compensating transfer function to the feedback variable, the compensating transfer function being configured to compensate for both (i) a distance-dependent transfer function of stimulation and (ii) a distance dependent transfer function of measurement which is distinct from (i). ### Claim 16 (depends on 15) The implantable device of claim 15, wherein the control unit is configured to adaptively compensate by multiplying measurements of ECAPs (V) with an exponentiated version (Ik) of the stimulus current (I) used to generate the respective ECAP, and further configured to generate an error signal relative to a setpoint and feed the error signal into a controller which determines a future stimulus intensity. ### Claim 17 A non-transitory computer readable medium for controllably applying a neural stimulus, comprising the following instructions for execution by one or more processors: computer program code means for applying the neural stimulus to a neural pathway in order to give rise to an evoked action potential on the neural pathway, the stimulus being applied as defined by at least one stimulus parameter; computer program code means for measuring a neural compound action potential response evoked by the stimulus and deriving from the measured evoked response a feedback variable; computer program code means for completing a feedback loop by using the feedback variable to control the at least one stimulus parameter value; and computer program code means for adaptively compensating for changes in a gain of the feedback loop caused by electrode movement relative to the neural pathway, by applying a compensating transfer function to the feedback variable, the compensating transfer function being configured to compensate for both (i) a distance-dependent transfer function of stimulation and (ii) a distance dependent transfer function of measurement which is distinct from (i).