Posture-Responsive Neurostimulation With ECAP Feedback Control
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Solution Overview
Problem
Existing neuromodulation systems face challenges in maintaining effective neural recruitment while minimizing energy expenditure and addressing electrode migration and postural changes, which can alter neural recruitment and cause discomfort or ineffectiveness.
Innovation Solution
An implantable device with electrodes and a control unit that measures neural compound action potentials, estimates patient posture, and implements a feedback loop to maintain a constant recruitment level by adjusting stimulus parameters based on measured characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If stimulus amplitude is increased to maintain neural recruitment above recruitment threshold, then therapeutic effect is improved, but patient comfort deteriorates due to recruitment of Aβ fibres causing uncomfortable sensations
Solution Approach 1:
The system measures ECAP amplitude and uses it as feedback to adjust stimulus amplitude dynamically. This closed-loop feedback control maintains neural recruitment at the desired level while preventing excessive stimulation that would cause discomfort, thus resolving the contradiction between reliable neural recruitment and patient comfort.
Solution Approach 2:
The stimulus amplitude is made dynamic rather than fixed, adjusting in real-time based on measured ECAP responses and detected posture changes. This dynamic adaptation allows the system to maintain optimal recruitment levels across varying conditions without causing discomfort.
2Reliability
If stimulus amplitude is increased to compensate for electrode migration or postural changes, then neural recruitment is maintained, but energy consumption increases
Solution Approach 1:
The feedback loop continuously monitors ECAP amplitude and adjusts stimulus amplitude only when necessary to maintain recruitment. This prevents wasteful energy consumption from continuously high stimulation levels while ensuring reliable neural recruitment when needed.
Solution Approach 2:
The system changes stimulus parameters (amplitude, pulse width) based on measured responses and posture detection. By optimizing these parameters dynamically, the system maintains effective neural recruitment at minimal energy expenditure rather than using fixed high-amplitude stimulation.
3Duration of action of stationary object
If stimulus amplitude is kept low to minimize energy consumption, then battery lifetime is extended, but neural recruitment falls below therapeutic threshold
Solution Approach 1:
The feedback mechanism ensures stimulus amplitude is increased only when ECAP measurements indicate neural recruitment is falling below the therapeutic threshold. This maintains reliable therapeutic effect while minimizing energy consumption during periods when lower amplitudes are sufficient.
Solution Approach 2:
The system uses periodic ECAP measurements to monitor neural recruitment status and adjusts stimulation accordingly. This periodic feedback allows the system to maintain therapeutic effectiveness while using lower average power consumption compared to continuous high-amplitude stimulation.
4Measurement precision
If ECAP measurements are taken continuously to monitor neural recruitment, then control precision is improved, but data storage requirements exceed implanted device capacities
Solution Approach 1:
The system extracts only the essential information from continuous ECAP measurements - specifically the amplitude values needed for feedback control - rather than storing complete waveforms. This extraction approach maintains measurement precision for control purposes while dramatically reducing data storage requirements.
Solution Approach 2:
The system performs partial measurement by focusing only on the critical ECAP amplitude parameter needed for feedback control, rather than comprehensively recording all aspects of the neural response. This partial measurement approach provides sufficient control precision while minimizing data volume.
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
The solution ensures consistent therapeutic effects by adapting to postural changes, reducing energy consumption, and minimizing discomfort, thereby extending device lifetime and improving patient comfort.
Implementation Method 1
measurement circuitry for recording a neural compound action potential signal sensed at the one or more sense electrodes
Implementation Method 2
An electrical pulse applied to the neural pathway by an electrode causes the depolarisation of neurons, and generation of propagating action potentials
Data Source
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AI summary
An implantable device is configured to control application of a neural stimulus as defined by a stimulus parameter; measure via the measurement circuitry a characteristic of a neural compound action potential response evoked by the stimulus; and compute, using the stimulus parameter and the measured characteristic of the evoked neural compound action potential response, a characteristic of an evoked response that would be obtained from the neural stimulus if the patient were in a reference posture. A posture of the patient can be estimated from the computed characteristic and/or the computed characteristic can be used as a feedback variable of a feedback loop. Multidimensional histograms of datasets comprising at least one of the stimulus parameter and a feedback variable can be stored.