Conductance Catheter Volume Estimation Using Nonlinear Calibration
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Solution Overview
Problem
Current methods for measuring instantaneous ventricular volume in the heart are hindered by parallel conductance from cardiac muscle, leading to inaccurate volume estimates due to the use of linear relationships between conductance and volume, and the electric field around sensing electrodes is not uniform, reducing sensitivity for large volumes.
Innovation Solution
The method involves measuring complex admittance at multiple frequencies to separate muscle and blood contributions, using the phase angle to improve accuracy, and applying a non-linear relationship between conductance and volume to correct for muscle conductance, thereby enhancing the estimation of instantaneous blood volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a linear relationship between conductance and volume is used for calibration, then the measurement method is simple, but the measurement precision deteriorates because the actual relationship is substantially nonlinear
Solution Approach 1:
The patent transforms the linear calibration approach into a nonlinear calibration model that accounts for the actual physical relationship between conductance and volume. By incorporating geometric factors and solving the Laplace equation to model the electric field distribution, the system adapts the calibration parameters to reflect the true nonlinear behavior, thereby improving measurement accuracy without excessive complexity
Solution Approach 2:
The patent replaces the simple linear empirical calibration with a physics-based mathematical model that solves the Laplace equation to describe the electric field and its relationship to volume. This substitution of physical principles for empirical linear relationships enables accurate volume measurement while maintaining computational efficiency through pre-calculated geometric factors
2Ease of operation
If parallel conductance from cardiac muscle is not removed, then the measurement process is simple, but the measurement precision deteriorates because the estimated volume is larger than the actual blood volume
Solution Approach 1:
The patent segments the total measured conductance into distinct components: blood conductance and parallel muscle conductance. By separately identifying and subtracting the parallel conductance component, the system isolates the blood volume signal, thereby improving measurement accuracy while maintaining a relatively simple measurement process through signal decomposition
Solution Approach 2:
The patent extracts and removes the parallel conductance contribution from cardiac muscle from the total conductance measurement. By isolating this interfering component and subtracting it from the total signal, the system recovers the pure blood volume signal, thereby eliminating the source of measurement error without complicating the overall measurement approach
3Device complexity
If a uniform electric field assumption is used, then the calculation is simple, but the measurement precision deteriorates for large volumes because the electric field around sensing electrodes is not uniform
Solution Approach 1:
The patent applies local quality by calculating geometric factors specific to different electrode configurations and positions within the ventricle. Rather than assuming uniform field properties throughout, the system determines location-specific geometric factors that account for local field non-uniformity, thereby improving accuracy for large volumes while keeping calculations manageable through pre-computed factors
Solution Approach 2:
The patent performs preliminary calculation of geometric factors based on the Laplace equation before actual volume measurements are taken. By pre-computing the electric field distribution and geometric factors for the specific catheter configuration, the system eliminates the need for complex real-time field calculations during measurement, thereby maintaining computational simplicity while achieving high precision
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 provides more accurate measurements of ventricular volume by accounting for the frequency-dependent electrical properties of muscle and blood, improving the sensitivity and accuracy of volume estimation, especially in cases with enlarged hearts.
Implementation Method 1
Measurements of electrical conductance using a tetrapolar admittance catheter are used to estimate instantaneous ventricular volume
Implementation Method 2
The technique works because the electrical properties of muscle are frequency-dependent, while those of blood are not
Data Source
AI summary
An apparatus for determining cardiac performance in the patient involving a conductance catheter (12) for measuring conductance and blood volume in a heart chamber of the patient. The apparatus includes a processor (14) for determining instantaneous volume of the ventricle by applying a non-linear relationship between the measured conductance and the volume of blood in the heart chamber to identify mechanical strength of the chamber. The processor (14) is in communication with the conductance catheter (12).