# Finite element modeling of human thorax for electrical bioimpedance based monitoring of pulmonary fluid accumulation

## TL;DR

This paper explores using electrical impedance to non-invasively monitor fluid buildup in the lungs, which could help track conditions like pulmonary edema.

## Contribution

The study introduces a computational model to assess the feasibility of using tetrapolar electrical impedance for continuous pulmonary fluid monitoring.

## Key findings

- A linear relationship between impedance and fluid volume was observed with high R2 values for both lungs.
- Impedance changes exceeding 2 Ω were predicted for clinically relevant fluid accumulations.
- Frequency-domain analysis showed consistent impedance contrast across a wide frequency range.

## Abstract

Monitoring fluid accumulation in the lungs is critical in conditions such as pulmonary edema and pneumonia. Current diagnostic modalities, including auscultation, chest X-ray, computed tomography, magnetic resonance imaging, and ultrasonography, either involve ionizing radiation or are not suitable for continuous long-term monitoring. This study investigated the feasibility of a non-invasive, non-ionizing electrical impedance–based approach for continuous assessment of pulmonary fluid accumulation using computational modeling. Firstly, CT images of human subjects were used to build a simplified thorax model. Different parts of human thorax including airways, left and right lungs, and soft tissue were segmented using a segmentation software Materialise Mimics® and imported into COMSOL Multiphysics® for finite element analysis. Tetrapolar transfer impedance was computed at multiple vertical electrode positions under baseline (air-filled lung) and fluid-accumulation conditions. The results demonstrated a measurable reduction in impedance in the presence of fluid, particularly at electrode levels corresponding to the fluid-filled lower lobes. A linear relationship between impedance and fluid volume was observed (R2 = 0.9972 for the left lung and R2 = 0.9998 for the right lung), with sensitivities of −466.74 mΩ/100 mL and −754.75 mΩ/100 mL, respectively. For clinically relevant fluid accumulations (≥300 mL), the predicted impedance change exceeded 2 Ω, indicating practical detectability. Frequency-domain analysis (5–1000 kHz) further demonstrated consistent impedance contrast across the investigated range. These findings suggest that tetrapolar electrical impedance measurements have the potential for continuous monitoring of pulmonary fluid changes and provide a foundation for future experimental validation in human subjects.