Revisiting pulmonary acinar particle transport: convection, sedimentation, diffusion, and their interplay

Abstract

It is largely acknowledged that inhaled particles ranging from 0.001 to 10 m are able to reach and deposit in the alveolated regions of the lungs. To date, however, the bulk of numerical studies have focused mainly on micrometer sized particles whose transport kinematics are governed by convection and sedimentation, thereby capturing only a small fraction of the wider range of aerosols leading to acinar deposition. Too little is still known about the local acinar transport dynamics of inhaled (ultra)fine particles affected by diffusion and convection. Our study aims to fill this gap by numerically simulating the transport characteristics of particle sizes spanning three orders of magnitude (0.01-5 m) covering diffusive, convective, and gravitational aerosol motion across a multigenerational acinar network. By characterizing the deposition patterns as a function of particle size, we find that submicrometer particles [formulae see text (0.1 m)] reach deep into the acinar structure and are prone to deposit near alveolar openings; meanwhile, other particle sizes are restricted to accessing alveolar cavities in proximal generations. Our findings underline that a precise understanding of acinar aerosol transport, and ultrafine particles in particular, is contingent upon resolving the complex convective-diffusive interplay in determining their irreversible kinematics and local deposition sites.

Image‐based computational fluid dynamics in the lung: virtual reality or new clinical practice?

“…They also indicated that the exact shape of alveoli may have less influence on the presence of alveolar recirculation. Many other works have also shown this convective mixing effect both qualitatively and quantitatively . Hofemeir and Sznitman showed that alveolar geometric topology influences localized flow characteristics and deposition sites for finer particles.…”

“…Nevertheless, understanding of airflow mechanics and particle transport in the acinar region has significantly advanced due to CFD. One important question that has been investigated is the role of proximal and distal acinar airways as mixing chambers . Existence of mixing in these submillimeter alveolar units has applications in both pharmacological and clinical sectors.…”

“…One important question that has been investigated is the role of proximal and distal acinar airways as mixing chambers. 65,[69][70][71][72][73] Existence of mixing in these submillimeter alveolar units has applications in both pharmacological and clinical sectors. Further reviews on computational models to simulate transport can be found elsewhere.…”

Do nanoparticles provide a new opportunity for diagnosis of distal airspace disease?

“…The former is achieved by large nanoparticles, while the latter increases for small nanoparticles. 47,[86][87][88] Based on the analysis explained, the optimal particle size range for AiDA is 40-100 nm, but experiments and detailed model calculations, especially for diseased lungs, are necessary to confirm these theoretical predictions. …”

Numerical assessment of airflow and inhaled particles attributes in obstructed pulmonary system

“…Multi-scale computational models of the airways have been established by [19] to identify the pathophysiological mechanisms in asthma and COPD. An anatomically-inspired model of the lung acinus featuring a bifurcating tree of alveolated airways with moving walls has been developed [20], [21]. Moreover, the airflow characteristics of human airways between the 8 th and 14 th generations have been examined [22].…”