Airflow and Particle Deposition in Acinar Models with Interalveolar Septal Walls and Different Alveolar Numbers

Abstract

Unique features exist in acinar units such as multiple alveoli, interalveolar septal walls, and pores of Kohn. However, the effects of such features on airflow and particle deposition remain not well quantified due to their structural complexity. This study aims to numerically investigate particle dynamics in acinar models with interalveolar septal walls and pores of Kohn. A simplified 4-alveoli model with well-defined geometries and a physiologically realistic 45-alveoli model was developed. A well-validated Lagrangian tracking model was used to simulate particle trajectories in the acinar models with rhythmically expanding and contracting wall motions. Both spatial and temporal dosimetries in the acinar models were analyzed. Results show that collateral ventilation exists among alveoli due to pressure imbalance. The size of interalveolar septal aperture significantly alters the spatial deposition pattern, while it has an insignificant effect on the total deposition rate. Surprisingly, the deposition rate in the 45-alveoli model is lower than that in the 4-alveoli model, indicating a stronger particle dispersion in more complex models. The gravity orientation angle has a decreasing effect on acinar deposition rates with an increasing number of alveoli retained in the model; such an effect is nearly negligible in the 45-alveoli model. Breath-holding increased particle deposition in the acinar region, which was most significant in the alveoli proximal to the duct. Increasing inhalation depth only slightly increases the fraction of deposited particles over particles entering the alveolar model but has a large influence on dispensing particles to the peripheral alveoli. Results of this study indicate that an empirical correlation for acinar deposition can be developed based on alveolar models with reduced complexity; however, what level of geometry complexity would be sufficient is yet to be determined.

Nanoparticle Deposition in Rhythmically Moving Acinar Models with Interalveolar Septal Apertures

“…Will it be indispensable to nanoparticle deposition, and how important it is relative to the other two mechanisms? Even though this study was not devoted to this question, some conclusions can be made from the results in this and other studies [34,41,42]. From Figure 6, the inhalation flow induced by the alveolar wall expansion is necessary to carry the particle-entrained bulk flow into the alveolar space to deposit there.…”

“…Even developing a complete model for a single acinar unit can be prohibitive. In this study, a four-alveoli model that was previously developed in Xi et al [41] was adopted for its well-defined shape and dimension. Figure 1a shows the surface geometry of the four-alveoli model in transparent and solid views, while Figure 1b shows the cut-open view of the hollow model, with interalveolar septal apertures (pores) connecting adjacent alveoli.…”

“…By contrast, in a respiratory bronchiole or alveolar duct, particles remain in the alveolar airspace for several cycles, rotating counterclockwise during inhalation and clockwise during exhalation [35,38]. Recent attempts to develop empirical correlations were also reported in alveolar models [34,38,39,40,41,42]. However, most studies have excluded the interalveolar septal walls and apertures (pores) for geometrical simplicity.…”

Design of a multilayer lung chip with multigenerational alveolar ducts to investigate the inhaled particle deposition

“…In this breathing mode, the aerosol remained in the channel for a longer time, resulting in particle concentrations in the 2nd–4th generation ducts that were generally be higher than those concentrations in the quiet breathing mode, and the number of particles in some 5th generation channels was increased. 16,47,48 In the uneven breathing mode (Fig. 5B(c)), the exhalation time was twice as long as in quiet breathing, while the flow rate was half that of the rate during quiet breathing.…”

A comparison of CFPD, compartment, and uniform distribution models for radiation dosimetry of radionuclides in the lung

“…There are also voxels in the lung region that are misidentified as heart voxels, which can overestimate the dose to the heart if particles fall in the vicinity in high concentrations. Third, the current CFPD model cannot model particle deposition in the acinar region, which is characterized by rhythmic wall motions and complex alveolar structures [74][75][76][77]. Despite rapid advances in CT imaging techniques, image-based lung models have rarely gone beyond bifurcation generation 11 due to the trade-off between CT resolution and radiation risk.…”