ECG Electrode Contact Measurement Using Differential AC Detection
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Solution Overview
Problem
Existing methods for measuring electrode contact quality in multi-electrode diagnostic systems, such as ECG systems, face challenges including high circuit complexity, potential for false readings due to hardware failures or ambient conditions, and inability to differentiate between skin and electrode contact impedance, especially when using AC or DC current sources.
Innovation Solution
A system utilizing a signal generator to output an alternating signal through a reference electrode and a differential array amplifier with floating common nodes, which measures contact quality by detecting phase shift and attenuation of the signal across multiple electrodes, reducing common mode noise and simplifying signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC or DC current sources are applied to each ECG input to measure electrode contact quality, then contact quality measurement is enabled, but circuit complexity increases significantly and board leakage in humid environments can cause false readings
Solution Approach 1:
The patent segments the measurement function by dedicating separate measurement circuitry for each ECG input channel. Each channel has its own current source and measurement circuit, allowing independent contact quality assessment without interfering with other channels. This segmentation enables precise per-electrode measurement while maintaining overall system manageability through modular architecture.
Solution Approach 2:
The patent introduces a high-impedance buffer amplifier as an intermediary between the current source and the ECG input. This buffer acts as a mediator that isolates the measurement circuit from the high-impedance ECG input, preventing board leakage and ambient humidity from affecting measurements. The buffer maintains signal integrity while protecting against environmental interference.
2Measurement precision
If DC current sources are applied to each input electrode to measure contact quality, then contact impedance can be measured, but DC offset potential from electrolyte-metal interface creates noise and requires very small currents that are difficult to implement reliably
Solution Approach 1:
The patent employs periodic AC current sources instead of continuous DC current to measure contact impedance. By using AC signals at specific frequencies, the system can measure impedance without being affected by DC offset potentials from electrolyte-metal interfaces. The periodic nature of AC allows for frequency-domain analysis that separates contact impedance measurements from DC offset interference, improving measurement reliability.
Solution Approach 2:
The patent changes the measurement parameter from DC current to AC current at multiple frequencies. By sweeping through different AC frequencies, the system can determine contact impedance characteristics while avoiding the DC offset problem. The AC frequency parameter is adjusted to optimize measurement sensitivity and avoid interference from biological signals and DC potentials.
3Measurement precision
If AC signals are used for lead wire contact quality detection, then contact quality can be measured, but signal processing complexity increases to remove AC signals from ECG and pace pulse data
Solution Approach 1:
The patent performs preliminary separation of the AC measurement signal from the ECG signal at the input stage, before amplification and processing. By using differential amplifiers that reject common-mode AC signals, the measurement system extracts contact quality information without requiring complex post-processing to remove AC components from ECG and pace pulse data. The AC measurement signal is handled separately from the biomedical signal path.
4Measurement precision
If high input impedance is designed in ECG circuits, then ECG signal acquisition is improved, but board leakage in humid environments can cause false positive connection indications
Solution Approach 1:
The patent introduces a high-impedance buffer amplifier as an intermediary between the high-impedance ECG input and the measurement circuit. This buffer protects against board leakage by providing a low-impedance drive for the measurement circuit while maintaining high input impedance for ECG signal acquisition. The buffer isolates the vulnerable high-impedance nodes from environmental leakage paths.
Solution Approach 2:
The patent implements feedback mechanisms that continuously monitor the ECG input signals and compare them against expected characteristics. When board leakage or environmental interference is detected, the feedback system adjusts measurement parameters or flags the connection status as unreliable. This feedback loop enables the system to distinguish between true electrode contact and false positives caused by board leakage in humid conditions.
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 measures electrode contact quality while minimizing false indications and noise interference, ensuring accurate ECG signal acquisition by dynamically assessing common mode rejection performance and differentiating between good and poor contact quality.
Implementation Method 1
detecting contact quality based on phase shift and attenuation of the output signal
Implementation Method 2
detecting contact quality based on phase shift and attenuation of the output signal
Implementation Method 3
reducing common mode noise
Data Source
AI summary
A system and method are provided for generating output signals indicative of contact quality of a plurality of electrodes coupled to a patient. A signal generator coupled to a reference electrode injects an alternating signal into the patient. A plurality of differential amplifiers, each coupled to a respective one of the plurality of electrodes to detect an input signal from the patient, are operable to output a respective output signal in response to a respective input signal. The output signal generated by the respective differential amplifier is indicative of contact quality for the respective electrode.