Thoracic electrical impedance tomography using a two-plane electrode configuration in horses.

Overview

• This study compares two different electrode configurations (one-plane and two-plane) for electrical impedance tomography (EIT) to image lung ventilation in horses.
• The researchers aimed to determine whether the two-plane (twoP) configuration provides a more accurate and representative imaging of lung ventilation than the traditional one-plane (oneP) method.

Background

• Electrical Impedance Tomography (EIT): A non-invasive imaging technique used to visualize ventilation distribution in the lungs by measuring electrical impedance changes caused by air movement.
• One-Plane (oneP) Electrode Configuration: Traditional method using electrodes placed in a single plane around the thorax, which captures a convex lens-shaped lung slice.
• Limitation of oneP: Mainly overrepresents central lung regions while potentially underrepresenting peripheral lung areas.
• Two-Plane (twoP) Electrode Configuration: Involves electrodes placed in two planes to capture lung impedance data, hypothesized to provide a more vertically uniform and representative image of the lungs.

Objectives

• To compare ventilation distribution between oneP and twoP EIT configurations using single slice reconstructions.
• To assess whether twoP improves imaging of lung ventilation, especially in peripheral and vertical lung regions.

Methods

• Computational Modelling: Developed finite element simulation models for the oneP and twoP configurations to predict the volume and distribution of lung fields captured.
• In Vivo Experimental Trial: Data collected from 20 standing horses at baseline, during stance changes, and during rebreathing challenges.
• EIT Data Collection: Voltage data acquired from both oneP and twoP electrode belts placed around the thorax.
• Region of Interest (ROI): Defined visually to represent the lung field for reconstruction and analysis of EIT data.
• Parameters Analyzed:
  • Centres of Ventilation (CoV): Representing the mean position of ventilation distribution.
  • Regional ventilation changes (∆Z): Measured for left (L), right (R), dorsal (D), central dorsal (CD), central ventral (CV), and ventral (V) lung areas.
  • Tidal Impedance Variation (TIV): Represents the overall changes in impedance during breathing cycles, correlated with tidal volume.
• Statistical Tests Used:
  • Wilcoxon matched pairs signed rank test for paired comparisons of parameters.
  • Mixed-effect models to evaluate effects of different conditions.
  • Paired t-tests for proportional changes during challenges.

Results

• Simulation Findings:
  • TwoP configuration exhibited a more evenly distributed vertical sensitivity pattern compared to oneP, suggesting better capture of lung impedance across lung height.
• Baseline In Vivo Findings:
  • Regional ventilation change (∆Z) for both left and right lungs was significantly higher with twoP than oneP.
    • Left lung ∆Z: 7.1 vs. 2.2 (twoP vs. oneP)
    • Right lung ∆Z: 6.4 vs. 1.5 (twoP vs. oneP)
  • Centre of ventilation (CoV) was higher with twoP (47.7) compared to oneP (43.3), indicating a more central or balanced ventilation depiction.
• Rebreathing Challenge:
  • Both configurations showed increases in TIV and CoV, indicating increased ventilation and shifts in ventilation distribution during this respiratory challenge.
  • TwoP retained higher CoV values during intervention, supporting improved vertical representation.

Conclusions

• The two-plane EIT electrode configuration provides a more vertically uniform representation of lung ventilation both in computational models and real-life horse measurements.
• TwoP likely enhances the detection and imaging of ventilation in peripheral lung areas that oneP tends to underrepresent.
• This suggests twoP EIT could improve clinical or research evaluations of lung function by offering more accurate spatial representation of ventilation distribution.