Implantable Electrode System Localizing Thoracic Fluid via Conductivity Mapping
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Solution Overview
Problem
Current implantable medical devices (IMDs) face challenges in accurately discriminating thoracic fluid conditions, such as pulmonary edema, cardiac dilation, and infections, due to the non-specific nature of intrathoracic impedance measurements, which can be influenced by various factors including fluid levels, vascular changes, and electrolyte imbalances.
Innovation Solution
The implementation of a fully implanted electrode system that uses computational techniques from electrical impedance tomography (EIT) to generate conductivity maps based on intrathoracic impedance measurements, allowing for the discrimination of thoracic fluid conditions by analyzing changes in tissue conductivity across anatomical regions, using a combination of implanted cardiac electrodes and the IMD housing as electrodes for excitation and measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single intrathoracic impedance measurement is used, then the device can detect changes in thoracic fluid status, but it cannot specifically identify the location or underlying cause of the change
Solution Approach 1:
The patent divides the thoracic cavity into multiple anatomical regions (anterior, posterior, lateral, medial segments of lungs; cardiac silhouette; mediastinum; aortic knob) and performs impedance measurements across different electrode pairs to obtain region-specific impedance values. This segmentation allows the system to identify which specific anatomical region contains fluid accumulation rather than just detecting general fluid status changes.
Solution Approach 2:
The patent transitions from single-point impedance measurement to multi-dimensional impedance mapping by using multiple electrode pairs arranged in a grid pattern around the thorax. By measuring impedance along multiple vectors and constructing a three-dimensional impedance map of the thoracic cavity, the system can localize fluid changes to specific spatial regions and differentiate between various anatomical structures.
2Loss of information
If multiple impedance measurements are performed to discriminate thoracic fluid conditions, then location and cause information can be obtained, but the device complexity increases
Solution Approach 1:
The patent utilizes the existing IMD housing and implanted cardiac electrodes to serve dual functions: delivering cardiac pacing/defibrillation therapy and performing impedance measurements for fluid detection. The same electrodes that provide life-saving cardiac therapy are repurposed to create impedance measurement vectors, eliminating the need for separate dedicated impedance measurement electrodes and reducing overall device complexity.
Solution Approach 2:
The IMD housing itself serves as an active electrode for impedance measurements, utilizing its own structure and components (battery can, circuit board, connectors) to generate the electrical fields needed for measurement. This self-service approach eliminates the need for additional external measurement equipment or separate electrode systems.
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 enhances the sensitivity and specificity of detecting and discriminating thoracic fluid conditions, enabling early and appropriate medical intervention by accurately localizing changes in thoracic fluid status and differentiating between various conditions based on conductivity patterns.
Implementation Method 1
Intrathoracic impedance measurements are typically made by measuring the impedance between two implanted cardiac electrodes or between a cardiac electrode and the IMD housing. The intrathoracic impedance measurement provides impedance across a portion of the thorax... Intrathoracic impedance decreases when thoracic fluid level increases, for example with pulmonary edema associated with worsening congestive heart failure. The impedance decreases because of the relatively low resistivity of biological fluids.
Data Source
AI summary
An implantable medical device and associated methods monitor thoracic fluid status and discriminate thoracic fluid conditions. Intrathoracic impedance is measured along multiple intrathoracic measurement vectors using implanted electrodes. A map of thoracic conductivity is computed using the measured intrathoracic impedances. A thoracic fluid condition is detected in response to the computed map.