Indirect measurement of lung density and air volume from electrical impedance tomography (EIT) data

Abstract

This paper describes a method for estimating lung density, air volume and changes in fluid content from a non-invasive measurement of the electrical resistivity of the lungs. Resistivity in Ω m was found by fitting measured electrical impedance tomography (EIT) data to a finite difference model of the thorax. Lung density was determined by comparing the resistivity of the lungs, measured at a relatively high frequency, with values predicted from a published model of lung structure. Lung air volume can then be calculated if total lung weight is also known. Temporal changes in lung fluid content will produce proportional changes in lung density. The method was implemented on EIT data, collected using eight electrodes placed in a single plane around the thorax, from 46 adult male subjects and 36 adult female subjects. Mean lung densities (±SD) of 246 ± 67 and 239 ± 64 kg m(-3), respectively, were obtained. In seven adult male subjects estimates of 1.68 ± 0.30, 3.42 ± 0.49 and 4.40 ± 0.53 l in residual volume, functional residual capacity and vital capacity, respectively, were obtained. Sources of error are discussed. It is concluded that absolute differences in lung density of about 30% and changes over time of less than 30% should be detected using the current technology in normal subjects. These changes would result from approximately 300 ml increase in lung fluid. The method proposed could be used for non-invasive monitoring of total lung air and fluid content in normal subjects but needs to be assessed in patients with lung disease.

Coupling of EIT with computational lung modeling for predicting patient-specific ventilatory responses

“…derived by Ref. 57 and similarly observed in several experiments (45,47,48). We used a mean tortuosity of ϭ 1.71, an alveolar conductivity of alv ϭ 0.7284 ⍀/cm and the volumetric strain was converted to the filling factor FF ϭ V air/Vtissue via FF ϭ 5.0•εvol -5.0, which came from the assumption that the filling factor was FF ϭ 3.0 at functional residual capacity (FRC) and FF ϭ 6.0 at total lung capacity (TLC) (57).…”

Correlation between alveolar ventilation and electrical properties of lung parenchyma

“…Results for the resistivity dependence on the filling factor in our model and in literature. Nopp, 1993[36] Nopp 1997, ρ(FRC)=10Ω m Nebuya, 2011[35] Wang, 2014 ventilation, even though they do not match exactly. This can be explained by the neglect of surrounding soft tissues, which clearly has an influence on the image reconstruction (Adler and Lionheart 2006).…”

Ocena regionalnej wentylacji w zespole ostrej niewydolności oddechowej za pomocą elektrycznej tomografii impedancyjnej

“…It has been demonstrated that an increase in lung volume from the residual volume to the vital capacity volume can result in an increase in electrical resistance by more than double [20]. Electrical impedance tomography provides information about thoracic resistance on each section and thereby, degree of their aeration.…”