Active Electrode Bioimpedance Measurement System
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Solution Overview
Problem
Existing electrical bioimpedance measurement devices face challenges such as unstable and poorly defined contact resistances between electrodes and the body, difficulty in accurately determining the trajectory of the excitation current, and limitations in measurement accuracy due to large contact resistances and small impedance changes.
Innovation Solution
The introduction of an active electrode system with an operational amplifier and a current-impeding circuit, along with an analog interface that includes a summator and demodulator, allows for the reduction of contact resistance effects and the optimization of excitation current distribution. Long strip electrodes are used to minimize current leakage and ensure accurate impedance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a classic 4-electrode impedance measurement system is used, then the measurement can be performed with simple equipment, but the contact impedances remain outside the measured body impedance and measurement accuracy deteriorates
Solution Approach 1:
The patent introduces an active electrode system with operational amplifiers as intermediary components between the electrodes and the measurement circuit. These amplifiers actively compensate for contact impedances by injecting compensating currents that cancel out the voltage drops across contact resistances, thereby including contact impedances within the measured body impedance and improving measurement accuracy without significantly increasing system complexity
Solution Approach 2:
The patent employs feedback mechanisms through operational amplifiers that continuously monitor the voltage at electrode interfaces and adjust the excitation current to compensate for contact impedance variations. This feedback control ensures that the measured voltage accurately reflects only the body impedance, eliminating the influence of unstable contact impedances from the measurement
2Measurement precision
If additional electrodes and compensation signal generators are introduced, then contact impedance effects can be compensated, but device complexity increases
Solution Approach 1:
The patent makes the active electrode system multi-functional by using the same operational amplifier circuitry to perform multiple tasks: amplifying the measurement signal, compensating for contact impedances, and rejecting common-mode voltages. This eliminates the need for separate compensation circuits and additional electrodes, achieving accurate measurements while keeping device complexity manageable
Solution Approach 2:
The patent merges the functions of signal amplification and contact impedance compensation into a single active electrode system. The operational amplifiers simultaneously perform voltage amplification and compensate for contact resistance effects, combining what would traditionally be separate functions into one integrated circuit that reduces overall device complexity
3Measurement precision
If short strip electrodes placed perpendicularly to the biological object are used, then sensitivity may be increased, but current trajectory cannot be determined accurately and measurement reliability deteriorates
Solution Approach 1:
The patent employs dynamic current distribution through the active electrode system that adapts to the biological object's geometry. The operational amplifiers dynamically adjust the current paths based on real-time voltage feedback, ensuring that the excitation current flows through the intended tissue region regardless of electrode placement variations, thereby maintaining both sensitivity and measurement reliability
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 solution significantly improves the accuracy and reliability of electrical bioimpedance measurements by minimizing the impact of contact resistances and ensuring that the excitation current passes through the intended region of the body, resulting in more precise and stable measurement results.
Implementation Method 1
an active electrode system (1), comprising an operational amplifier (9)
Implementation Method 2
a generator (4), wherein the generator (4) generates and directs an excitation current (i) through the biological object (100) via the excitation current electrodes (5, 6)
Implementation Method 3
the voltage drop caused by the current passing through the body impedance is picked up by the first voltage electrode (7) and the second voltage electrode (8)
Implementation Method 4
a current-impeding circuit (10), wherein the current-impeding circuit (10) is connected to the inverting input (−) of the operational amplifier (9)
Data Source
AI summary
The invention belongs to the field of medical technology and relates to wearable electrical devices and a method for using the device to measure and monitor the patient's vital signs during the postoperative period in a hospital. The device enables more accurate measurement of the electrical bioimpedance of the patient's tissues, primarily arteries and other organs, which in turn provides an opportunity to determine the vital signs, such as the volume, frequency and nature of the heart beating and breathing, indicating whether the patient's health condition is improving or deteriorating towards the life-threatening direction. The device is distinguished by the methodology for creating and deploying a system of active electrodes specific to the measurement site of the body, and by the means for generating, forming and processing the electrical current and voltage signals necessary for measuring the electrical bioimpedance including the methods for applying the technology.