ECG Noise-Grounding Circuit Using Capacitive Patient Coupling
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Solution Overview
Problem
Electrical noise generated by external equipment, such as powered injectors, interferes with electrocardiogram (ECG) signals displayed on monitors, causing signal distortions due to shared electromagnetic frequency spectrum with cardiac signals.
Innovation Solution
A filtering circuitry system using an array of capacitors connected in series between a non-magnetic conductive element, like a wrist strap, and ground to filter out electrical noise from ECG signals while maintaining safe impedance to limit patient leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a powered injector is positioned near the patient for contrast injection, then angiographic imaging can be performed, but electrical noise is generated that distorts ECG signals
Solution Approach 1:
A filtering circuit is introduced as an intermediary component between the patient's body and ground. This circuit includes a capacitor connected in series with a resistor, where the capacitor blocks DC currents while the resistor provides a path to ground for electrical noise. The intermediary filtering circuit selectively allows AC noise signals to pass to ground while blocking DC currents, thus resolving the contradiction between maintaining imaging capability and eliminating ECG signal distortion.
Solution Approach 2:
The filtering circuit changes the electrical parameters (impedance characteristics) between different frequency ranges. By using a capacitor with specific capacitance value and a resistor with specific resistance value, the circuit presents high impedance to DC currents (blocking them) while presenting low impedance to AC noise signals (allowing them to pass to ground). This parameter change resolves the contradiction by differentiating between harmful DC currents and useful AC ECG signals.
2Measurement precision
If filtering circuitry is added to suppress electrical noise, then ECG signal quality is improved, but device complexity increases
Solution Approach 1:
The filtering function is segmented into two distinct components: a capacitor element and a resistor element connected in series. The capacitor segment handles DC current blocking, while the resistor segment handles AC noise routing to ground. This segmentation allows each component to be optimized independently and simplifies the overall circuit design compared to using a single complex filter, thus improving ECG signal quality without excessive complexity.
Solution Approach 2:
The filtering circuit acts as a simple intermediary device with only two passive components (capacitor and resistor), avoiding the need for complex active filters with multiple op-amps or transistors. This minimalistic intermediary approach provides effective noise filtering while maintaining low complexity, resolving the contradiction between measurement precision and device complexity.
3Object-affected harmful factors
If a conductive path to ground is provided for noise routing, then electrical noise is suppressed, but patient safety may be compromised due to potential DC current leakage
Solution Approach 1:
The circuit parameters (capacitance and resistance values) are specifically chosen to change the electrical characteristics in a way that blocks DC currents while allowing AC noise to pass. The capacitor's reactance is very high at DC frequencies (infinite theoretically), while the resistor provides a controlled path for AC signals. This parameter change ensures noise suppression without compromising patient safety from DC current leakage.
Solution Approach 2:
The filtering circuit exploits the frequency-dependent behavior (phase transition in electrical terms) of the capacitor. At DC (0 Hz), the capacitor acts as an open circuit, blocking current flow. At AC frequencies (including ECG and noise frequencies), the capacitor's impedance decreases, allowing signals to pass. This frequency-based phase transition resolves the contradiction by differentiating between safe DC blocking and useful AC noise routing.
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
Effectively suppresses noise distortions in ECG signals, ensuring clear cardiac signal display without hazardous DC currents, adhering to safety standards.
Implementation Method 1
The filtering circuitry employs an array of capacitors, which allows the system to filter to ground the electrical noise generated by the injector and related equipment while the cardiac signals generated by the heart are still picked up by the electrodes
Data Source
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AI summary
A system for suppressing electrical noise in an electrocardiogram (ECG) signal displayed on an ECG monitor includes: a conductive material provided in contact with a surface of a patient; and filtering circuitry connected in series between the conductive material and ground. The filtering circuitry may be configured to filter to ground the electrical noise present within the patient.