Neural Response Measurement With High-Impedance Stimulus Artefact Isolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge of isolating a compound action potential (CAP) signal is complicated by electrode artefacts arising from the stimulus, which often have a decaying exponential characteristic and can obscure the neural response, especially when the neural response is contemporaneous with the stimulus.
Innovation Solution
Implementing a method and device that apply an electrical stimulus, impose a delay during which the stimulus electrodes are open circuited, and measure the neural response signal at sense electrodes with a measurement amplifier, ensuring a sufficiently high impedance to constrain the stimulus-induced voltage at the sense electrode interface, thereby isolating the neural response voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high stimulation currents and close proximity between electrodes are used to characterize dorsal column responses, then measurement sensitivity is improved, but stimulus artefact increases and obscures the neural response
Solution Approach 1:
The patent applies preliminary action by performing charge recovery between stimuli through switching arrangements that short-circuit electrodes or use capacitive coupling. This preparatory charge management occurs before the neural response measurement, enabling high-current stimulation with close electrode proximity while preventing artefact contamination of the CAP signal.
Solution Approach 2:
The patent introduces intermediary elements including capacitors in series with electrodes and switching networks that act as mediators between the stimulus source and tissue. These intermediaries enable charge recovery and artefact reduction while maintaining the ability to deliver high stimulation currents for sensitive neural response characterization.
2Reliability
If electrode capacitors or star network of resistors are used for charge recovery, then DC charge injection is prevented, but considerable artefact is generated that interferes with small CAP signal measurement
Solution Approach 1:
The patent applies parameter changes by carefully selecting capacitor values and resistor configurations to optimize the balance between charge recovery and artefact reduction. By adjusting these electrical parameters, the system achieves reliable charge management while minimizing artefact that would interfere with CAP signal detection.
Solution Approach 2:
The patent employs dynamic switching arrangements that change the circuit configuration between stimulation and measurement phases. Switches dynamically connect or disconnect capacitors and resistors based on operational phase, enabling effective charge recovery during stimulation while minimizing artefact during the subsequent CAP measurement window.
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 effectively reduces stimulus-induced artefacts, allowing for accurate measurement of neural responses by constraining the stimulus-induced voltage to a level that permits assessment of the neural response voltage, even in the presence of significant stimulus artefacts.
Implementation Method 1
ensuring that an impedance between the sense electrodes is sufficiently large that a voltage arising on the sense electrode tissue interface in response to the stimulus is constrained
Data Source
AI summary
Measuring a neural response to a stimulus comprises applying an electrical stimulus, then imposing a delay during which the stimulus electrodes are open circuited. During the delay, a neural response signal present at sense electrodes is measured with a measurement amplifier, while ensuring that an impedance between the sense electrodes is sufficiently large that a voltage arising on the sense electrode tissue interface in response to the stimulus is constrained to a level which permits assessment of the neural response voltage seen at the sense electrode. For example the input impedance to the measurement amplifier (ZIN) can be, where ZC is the sense electrode(s) constant phase element impedance, Vs1−Vs2 is the differential voltage arising on the sense electrode tissue interface, and VE is the neural response voltage seen at the sense electrode.