Ultrafine particle deposition in a realistic human airway at multiple inhalation scenarios

Abstract

The scarcity of regional deposition data in distal respiratory airways represents an important challenge for current toxicology and pharmacology research. To bridge this gap, a realistic airway model extending from nasal and oral openings to distal bronchial airways with varying pathway length was built in this study. Transport and deposition characteristics of naturally inhaled ultrafine particles (UFPs) ranging from 1 to 100 nm were numerically investigated, and effects of different inhalation scenarios were considered. To enable intercase particle deposition comparison, an adjusted parameter, unified deposition enhancement factor (UDEF), was proposed for quantifying the localised deposition concentration. Results show that compartment particle deposition peaked around the ultrafine end of the considered size range, and it dropped rapidly with the increase of particle size. Different inhalation modes caused notable deposition changes in the extrathoracic region, while its effects in the TB airway are much less. For UFPs larger than 10 nm, predicted deposition efficiencies in all compartments are all at lowest levels among considered particle size range, implying UFPs ranging from 10 to 100 nm can travel through the whole respiratory airway model and escape to the alveolar region. Furthermore, high enhancement factors were observed at the vicinity of most bifurcation apexes, and more even UDEF distribution was observed from 1‐nm particle cases. While for 100‐nm cases, the deposited particles tend to concentrate at few “hot spots” (areas of high deposition concentration in relation to surrounding surfaces) with greater UDEF in the tracheobronchial airway.

Inhalation Exposure Analysis of Lung-Inhalable Particles in an Approximate Rat Central Airway

“…Many studies presented deposition enhancement factors (DEFs) to quantify the local deposition density within a defined area relative to overall deposition density in the entire region [34,35,36,37]. In this study, the local DEF was defined as:DEF = number of particles deposited within a fixed radius of a surface node/AitalicLocaloverall number of particles deposited in the whole airway/AitalicTotal , where AitalicLocal is the local region with a fixed searching radius of 1 mm, AitalicTotal is the overall surface area of all considered airway regions.…”

“…Many studies presented deposition enhancement factors (DEFs) to quantify the local deposition density within a defined area relative to overall deposition density in the entire region [ 34 , 35 , 36 , 37 ]. In this study, the local DEF was defined as: where is the local region with a fixed searching radius of 1 mm, is the overall surface area of all considered airway regions.…”

“…Due to lack of relevant experimental inhalation exposure studies using rat lung airways, the numerical model presented in this paper was not validated against any measurement data. However, the numerical modeling strategy and most of the model configurations have been extensively validated in the authors’ previous studies, including rat nasal cavity [ 25 ], human nasal cavity [ 42 , 43 ], and human lung airways [ 36 ]. Those previous studies provided substantial benefits to the present work, which ensure consistent and rigorous numerical models.…”

Deposition features of inhaled viral droplets may lead to rapid secondary transmission of COVID-19

“…The details of mesh generation and airflow simulation methods were explained in the authors’ previous studies ( Dong et al, 2019 , Shang et al, 2019 ), which investigated airflow dynamics and nanoparticle deposition characteristics using the same realistic airway model. To better revealing the regular inhalation conditions in the crowded environment, the oral–nasal inhalation scenario mode B ( Dong et al, 2019 ), which inhales air through nostrils and mouth opening simultaneously, was selected in this study. The external sphere was set as pressure inlet with the pressure of zero.…”

Aerosol transmission of COVID-19 and infection risk in indoor environments

“…After being inhaled, particles of >20 µm diameter are predominantly deposited in the upper respiratory tract, while more than 90% of the fine aerosol particles with a diameter smaller than 2.5 µm can penetrate deeply into the lungs (Inthavong et al, 2012;de Gabory et al, 2020). By simulating inhalation and associated turbulent air motions in the respiratory system, it was estimated that 100 µm particles deposit in the nasal fossa, while 15 µm particles have a 62% probability to reach the lungs; and for 1 µm particles this was estimated at 94% (Inthavong et al, 2017;Dong et al, 2019;de Gabory et al, 2020). Since most viruses are contained in the small particles, it may be assumed that they penetrate deeply and, when retained, have the potential to cause infection in the lungs.…”