Nerve-to-Electrode Distance Estimation via Compound Action Potential
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Solution Overview
Problem
Current neuromodulation systems face challenges in maintaining effective and comfortable neural stimulation due to variations in nerve-to-electrode distance caused by electrode migration and postural changes, leading to suboptimal therapeutic effects and unwanted side effects, while also requiring efficient energy use to prolong battery life.
Innovation Solution
A method and device that estimate nerve-to-electrode distance by applying stimuli with defined parameters, obtaining compound action potential measurements, and processing them to apply a single fibre model, allowing for adjustments in therapeutic regimes and efficient energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed current stimulation is used in spinal cord stimulation, then the system is simple to operate, but the therapeutic effect deteriorates due to variations in nerve-to-electrode distance from electrode migration and postural changes
Solution Approach 1:
The system measures compound action potentials (CAPs) in response to electrical stimuli and uses this feedback to dynamically adjust stimulation parameters. The processor continuously monitors CAP amplitude and modifies stimulus delivery to maintain optimal therapeutic effect despite changes in electrode-nerve distance caused by migration or postural variations
Solution Approach 2:
The stimulation system transitions from fixed current delivery to dynamic parameter adjustment. The processor automatically modifies stimulus amplitude, pulse width, or frequency based on real-time CAP measurements, allowing the system to adapt to changing anatomical conditions while maintaining consistent therapeutic outcomes
2Reliability
If stimulus amplitude is increased to maintain recruitment above threshold, then neural recruitment is effective, but uncomfortable or painful percepts arise due to recruitment of Aδ fibres
Solution Approach 1:
The system optimizes stimulation parameters by adjusting amplitude, pulse width, and frequency based on CAP feedback. This allows the system to deliver minimal effective stimulus that achieves adequate neural recruitment without exceeding the comfort threshold, thereby preventing unwanted percepts while maintaining therapeutic effectiveness
Solution Approach 2:
The system uses sub-threshold or threshold-level stimuli that are just sufficient to recruit the desired neural fibers (typically Aβ fibres for pain modulation) without excessively recruiting more sensitive Aδ fibres that cause discomfort. The feedback mechanism ensures adequate recruitment while avoiding over-stimulation
3Reliability
If higher stimulus amplitude is applied to compensate for increased nerve-to-electrode distance, then neural recruitment is maintained, but energy consumption increases
Solution Approach 1:
The CAP measurement system provides continuous feedback on neural response quality, allowing the processor to adjust stimulus amplitude only to the extent necessary to maintain effective recruitment. This prevents excessive energy consumption by avoiding unnecessarily high stimulus levels while ensuring adequate neural activation despite distance variations
Solution Approach 2:
The system dynamically optimizes stimulus parameters based on real-time CAP feedback, adjusting amplitude, pulse width, or frequency to achieve minimal effective stimulation. This efficient parameter optimization maintains neural recruitment consistency while minimizing energy consumption compared to fixed high-amplitude approaches
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise estimation of nerve-to-electrode distance, optimizing stimulus delivery, reducing side effects, and minimizing energy consumption, thereby enhancing the effectiveness and longevity of neuromodulation systems.
Implementation Method 1
An electrical pulse applied to the dorsal column by an electrode causes the depolarisation of neurons, and generation of propagating action potentials
Implementation Method 2
A CAP measurement system measures a compound action potential (CAP) in response to electrical stimuli applied by a stimulus electrode
Data Source
AI summary
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.