Absolute Electrical Impedance Tomography (aEIT) Guided Ventilation Therapy in Critical Care Patients: Simulations and Future Trends

Abstract

ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract-Thoracic electrical impedance tomography (EIT) is a noninvasive, radiation-free monitoring technique whose aim is to reconstruct a cross-sectional image of the internal spatial distribution of conductivity from electrical measurements made by injecting small alternating currents via an electrode array placed on the surface of the thorax. The purpose of this paper is to discuss the fundamentals of EIT and demonstrate the principles of mechanical ventilation, lung recruitment, and EIT imaging on a comprehensive physiological model, which combines a model of respiratory mechanics, a model of the human lung absolute resistivity as a function of air content, and a 2-D finite-element mesh of the thorax to simulate EIT image reconstruction during mechanical ventilation. The overall model gives a good understanding of respiratory physiology and EIT monitoring techniques in mechanically ventilated patients. The model proposed here was able to reproduce consistent images of ventilation distribution in simulated acutely injured and collapsed lung conditions. A new advisory system architecture integrating a previously developed data-driven physiological model for continuous and noninvasive predictions of blood gas parameters with the regional lung function data/information generated from absolute EIT (aEIT) is proposed for monitoring and ventilator therapy management of critical care patients.

Robust real‐time inversion of electrical impedance tomography data for human lung ventilation monitoring

“…Let us consider a 2D EIT problem where Ω is the cross section of a human thorax probed by V electrodes displaced along its external perimeter (Figure ). EIT data are collected with the adjacent‐electrode‐pair strategy by successively applying a low‐frequency ( f < 100kHz) current to a pair of adjacent electrodes and measuring the arising impedance values on all remaining pairs of neighboring electrodes, the total number of independent measurements being M = V ( V − 3)/2. The DUT Ω is characterized by a real (purely resistive) conductivity distribution σ ( r ) piecewise constant within Q = 5 subregions {Γ q , q = 1, …, Q }, Ω = ∪ Γ q , modeling fat ( σ ( r ) = σ F ,∀ r ∈ Γ 1 ‐ Figure ), muscle ( σ ( r ) = σ M ,∀ r ∈ Γ 2 ‐ Figure 1), hearth ( σ ( r ) = σ H ,∀ r ∈ Γ 3 ‐ Figure 1) and left/right lungs ( σ ( r ) = σ L / R ,∀ r ∈ Γ 4/5 ‐ Figure 1), respectively.…”

“…To numerically solve the forward problem (ie, the computation of the electrodes impedances), the finite‐element method (FEM) is used by partitioning Ω into N triangular mesh cells. Moreover, under the low‐frequency approximation, the potential distribution produced by the injected currents and affected by the conductivity distribution of the DUT is computed with the Poisson equation and the electrodes impedances, , are determined as. where and Ψ(. ) is the forward EIT‐FEM operator.…”

“…EIT is based on the measurement of the potentials caused by the conductivity spatial‐distribution when injecting low‐frequency currents, generated by an array of boundary electrodes, in the domain under test (DUT). A very interesting application of the EIT is the continuous monitoring of the human lungs ventilation of patients under mechanical ventilation in intensive care units (ICUs) . Indeed, while X‐ray radiography and computed tomography (CT) provide high‐spatial resolution images of the human thorax, they also imply the exposure to non‐negligible radiation.…”

“…Electrical impedance tomography (EIT) is a promising noninvasive and radiation-free imaging technique with a wide range of medical (eg, lung ventilation, breast cancer, gastric emptying and cardiac/brain activity monitoring) and nonmedical (eg, minerals detection in soil and crack detection) applications. [1][2][3][4][5] EIT is based on the measurement of the potentials caused by the conductivity spatial-distribution 1 when injecting low-frequency currents, generated by an array of boundary electrodes, in the domain under test (DUT). A very interesting application of the EIT is the continuous monitoring of the human lungs ventilation of patients under mechanical ventilation in intensive care units (ICUs).…”

Lung impedance measurements to monitor alveolar ventilation

“…One step further, information on regional distribution of ventilation might be fused with other relevant parameters such as blood gas values and thus being the basis for a computerized advisory system facilitating the application of the least injurious ventilation [7 ].…”