Tetrapolar Bioimpedance Circuit for Extracellular Fluid and ECG Sensing
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Solution Overview
Problem
Existing impedance monitoring devices are inadequate for real-time monitoring of tissue hydration levels, particularly extracellular fluid, and do not effectively integrate with ECG signals to provide comprehensive hemodynamic assessments.
Innovation Solution
A bioelectric impedance monitoring device using a four-electrode system measures impedance at multiple frequencies to determine extracellular and intracellular hydration levels, integrates ECG data for heart performance analysis, and calculates parameters like heart rate, stroke volume, and cardiac output through signal processing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a four-electrode system with multiple frequency measurements is implemented, then measurement precision for tissue hydration levels is improved, but device complexity increases
Solution Approach 1:
The patent divides the impedance measurement into multiple frequency segments (low frequency for ECF, high frequency for total body water) and uses separate electrode pairs for current injection and voltage measurement. This segmentation allows precise measurement of different fluid compartments while managing device complexity through modular signal processing circuits.
Solution Approach 2:
The patent introduces intermediate signal processing stages including differential amplifiers, filters, and rectifiers that mediate between the raw impedance signals and the final hydration metrics. These intermediary components enable precise extraction of hydration information from complex multi-frequency impedance data without requiring overly complex direct measurement circuits.
2Productivity
If real-time monitoring capability is implemented, then productivity of clinical assessment is improved, but use of energy increases
Solution Approach 1:
The patent implements periodic impedance measurements at multiple frequencies rather than continuous monitoring, with measurement intervals optimized to provide real-time clinical data while allowing the device to enter low-power states between measurements. This periodic operation enables real-time assessment productivity while controlling energy consumption through duty-cycled measurement and processing.
Solution Approach 2:
The patent dynamically adjusts measurement parameters such as frequency selection, current amplitude, and sampling rate based on clinical needs and battery status. By changing operational parameters rather than maintaining fixed high-performance settings, the device achieves real-time monitoring capability when needed while conserving energy during stable periods or when clinical urgency is low.
3Reliability
If integration of ECG data with impedance signals is implemented, then reliability of hemodynamic assessment is improved, but device complexity increases
Solution Approach 1:
The patent merges ECG signal acquisition with impedance measurement by using the same electrode array and synchronized timing circuits. The ECG leads are combined with the impedance electrodes, allowing simultaneous capture of electrical cardiac activity and thoracic impedance changes. This merging improves hemodynamic assessment reliability through correlated multi-parameter measurement while avoiding the complexity of completely separate sensing systems.
Solution Approach 2:
The patent designs the electrode array and signal processing circuitry to serve multiple functions: ECG voltage measurement, impedance current injection, and impedance voltage detection. This multi-functionality enables reliable hemodynamic assessment through integrated ECG-impedance analysis while reducing device complexity by eliminating redundant dedicated circuits for each measurement type.
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
Enables real-time monitoring of tissue hydration and hemodynamic parameters, providing accurate and reliable data for clinical assessments.
Implementation Method 1
at least four electrodes capable of being physically adhered and electrically coupled to the human subject; and circuitry coupled to four of the at least four electrodes to measure a bioelectric tissue impedance
Data Source
AI summary
A portable bioelectric impedance monitor and methods using the monitor can measure and monitor extracellular fluid levels and/or cardiac signals. The monitor may include a tetrapolar electrode array lead with four electrodes arranged sequentially and axially along the lead, and circuitry coupled with the at least four electrodes configured to measure bioelectric impedance extracellular fluid and/or cardiac signals in a human subject at various frequencies. The electrodes are adhered to a human subject/patient on the patient's torso or one of the patient's limbs. One embodiment includes a Tetrapolar Analog Front End Patient Interface circuit configured to convert two electrode operation of a commercial Impedance Converter, Network Analyzer into a tetrapolar operation for excitation and impedance measurement of the human subject.