ELECTRODE TO NERVE DISTANCE ESTIMATION
Estimating a nerve-to-electrode distance involves applying a stimulus from a stimulus electrode to a nerve. Neural measurements of at least one evoked compound action potential are obtained, and processed in order to estimate an originating state of stimulation exhibiting at least one characteristic defined by a single fibre size. A single fibre model is then applied to produce a measure of the nerve-to-electrode distance. Also provided for is estimation of a distribution of recruited fibres. Measurements of a compound action potential are obtained from sense electrodes spaced apart along a neural pathway. A conduction velocity of the compound action potential is determined from the latency between the measurements. From the conduction velocity a dominant recruited fibre diameter is determined. A rate of dispersion of the compound action potential between the sense electrodes is determined. From the rate of dispersion a distribution of diameters of the recruited fibre population is determined.
1 . A medical device, the device comprising:
one or more processors configured to:
apply a plurality of stimuli from at least one stimulus electrode to a spinal nerve, each stimulus having defined stimulus parameters;
process from at least one sense electrode a plurality of neural measurements of respective compound action potentials evoked by the respective stimuli; and
process the plurality of neural measurements and the respective stimulus parameters in order to estimate a rheobase of a single fibre-size of the spinal nerve.
2 . The device of claim 1 , wherein the one or more processors are configured to determine a stimulus threshold at at least two different pulse widths, and wherein the rheobase is calculated from the stimulus thresholds.
3 . The device of claim 2 , wherein four stimuli of the plurality of stimuli are applied to determine the stimulus thresholds.
4 . The device of claim 3 , wherein at least two stimuli of the four stimuli are controllable to have a therapeutic level of charge.
5 . The device of claim 1 , wherein the one or more processors are configured to estimate the rheobase from a slope of a charge duration curve that plots pulse width of the plurality of stimuli against charge delivered by the plurality of stimuli.
6 . The device of claim 1 , wherein the one or more processors are configured to apply a single fibre model to the estimated rheobase and the stimulus parameters to produce a measure of nerve-to-electrode distance comprising a distance between the at least one sense electrode and the spinal nerve.
7 . The device of claim 6 , wherein the single fibre model comprises a fitted relationship between the rheobase and the nerve-to-electrode distance.
8 . The device of claim 6 , wherein the measure of nerve-to-electrode distance is produced by determining a fibre-size of the single fibre-size of the spinal nerve associated with the estimated rheobase, and applying the estimated rheobase and the determined fibre-size to the single fibre model.
9 . The device of claim 8 , wherein the fibre-size is determined by calculating a conduction velocity associated with the plurality of neural measurements of compound action potentials evoked by the stimuli.
10 . The device of claim 1 , wherein the one or more processors are further configured to treat a neurological condition by administering or modifying a therapy in a manner responsive to the estimated rheobase, or to a change in the estimated rheobase over time.
11 . The device of claim 1 , wherein the device comprises an implantable device that is configured to function intra-operatively, as part of a surgical procedure.
12 . The device of claim 1 , wherein the device comprises an implantable device configured to function as part of a postoperative fitting procedure of the device.
13 . A method of estimating a rheobase of a spinal nerve, the method comprising:
applying a plurality of stimuli from a stimulus electrode to the spinal nerve, each stimulus having defined stimulus parameters;
obtaining a plurality of neural measurements of respective compound action potentials evoked by the respective stimuli; and
processing the plurality of neural measurements and the respective stimulus parameters in order to estimate a rheobase of a single fibre-size of the spinal nerve.
14 . The method of claim 13 , wherein the method comprises determining a stimulus threshold at at least two different pulse widths, and calculating the rheobase from the stimulus thresholds.
15 . The method of claim 14 , wherein the method comprises applying four stimuli of the plurality of stimuli to determine the stimulus thresholds.
16 . The method of claim 15 , wherein the method comprises controlling at least two stimuli of the four stimuli to have a therapeutic level of charge.
17 . The method of claim 13 , wherein the method comprises estimating the rheobase from a slope of a charge duration curve that plots pulse width of the plurality of stimuli against charge delivered by the plurality of stimuli.
18 . The method of claim 13 , wherein the method comprises applying a single fibre model to the estimated rheobase and the stimulus parameters to produce a measure of nerve-to-electrode distance comprising a distance between the electrode and the spinal nerve.
19 . The method of claim 18 , wherein the single fibre model comprises a fitted relationship between the rheobase and the nerve-to-electrode distance.
20 . The method of claim 18 , wherein the method comprises producing the measure of nerve-to-electrode distance by determining a fibre-size of the single fibre-size of the spinal nerve associated with the estimated rheobase, and applying the estimated rheobase and the determined fibre-size to the single fibre model.
21 . The method of claim 20 , wherein the method comprises determining the fibre-size by calculating a conduction velocity associated with the plurality of neural measurements of compound action potentials evoked by the stimuli.
22 . The method of claim 13 , wherein the method further comprises treating a neurological condition by administering or modifying a therapy in a manner responsive to the estimated rheobase, or to a change in the estimated rheobase over time.
23 . A non-transitory computer readable medium for estimating a rheobase of a spinal nerve, comprising instructions which, when executed by one or more processors, causes performance of the following:
applying a plurality of stimuli from a stimulus electrode to the spinal nerve, each stimulus having defined stimulus parameters;
obtaining a plurality of neural measurements of respective compound action potentials evoked by the respective stimuli; and
processing the plurality of neural measurements and the respective stimulus parameters in order to estimate a rheobase of a single fibre-size of the spinal nerve.