ECAP Sensing Calibration During Passive Recharge Auto-Zeroing
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Solution Overview
Problem
Medical devices face challenges in accurately sensing evoked compound action potentials (ECAPs) due to their small and variable nature, often obscured by noise and residual charge, necessitating effective calibration of sensing circuitry.
Innovation Solution
The sensing circuitry is calibrated by delivering an electrical stimulation signal with an amplitude of zero to the patient, followed by a passive recharge state, allowing the operational amplifier to auto-zero and accurately measure ECAP signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ecap sensing is implemented to detect endocardial cells, then diagnostic capability for arrhythmias is improved, but signal reliability deteriorates due to low amplitude and high noise
Solution Approach 1:
A calibration electrode is introduced as an intermediary element to establish a reference relationship between ecap amplitude and myocardial cell density. This calibration electrode delivers test signals and measures reference capacitive coupling, enabling the system to convert unreliable raw ecap signals into reliable diagnostic information through ratio-based calculation that eliminates common-mode noise
Solution Approach 2:
The system changes the parameter being measured from absolute ecap amplitude to a normalized ratio (ecap amplitude relative to calibration electrode signal). This parameter transformation converts the low-amplitude, noise-sensitive measurement into a dimensionless ratio that is insensitive to common-mode interference while preserving the relationship between signal strength and cell density
2Measurement precision
If multiple electrodes are used for calibration and sensing, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The system uses a partial calibration approach where only specific calibration electrodes are activated during calibration mode, and only relevant sensing electrodes are used during sensing mode. This partial action reduces the effective complexity at any given time while maintaining the capability for high-accuracy measurements when needed
Solution Approach 2:
The system alternates between calibration mode and sensing mode in periodic fashion. During calibration, test signals are applied and reference measurements are taken; during sensing, actual ecap signals are measured. This periodic switching allows the use of multiple electrodes without requiring all to be active simultaneously, reducing instantaneous device complexity while maintaining measurement accuracy
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 method enhances the accuracy of ECAP signal measurement, enabling more effective adjustment of electrical stimulation therapy parameters for improved therapeutic outcomes.
Implementation Method 1
ecap sensing relies on capacitive coupling between an electrode and the endocardial surface
Data Source
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AI summary
Systems, devices, and techniques are described for calibrating a medical device that senses ECAP signals from a patient's nerve tissue. For example a method includes: instructing, with processing circuitry, stimulation circuitry of a medical device to deliver, on stimulation electrodes of the medical device, an electrical stimulation signal having an amplitude substantially equal to zero to a patient; entering, with the processing circuitry subsequent to instructing the stimulation circuitry to deliver the electrical stimulation signal, a passive recharge state on stimulation electrode circuitry; and auto-zeroing, with the processing circuitry, inputs to an operational amplifier of sensing circuitry electrically coupled to sensing electrodes of the medical device while the stimulation electrode circuitry is in the passive recharge state.