A numerical study of the aerosol behavior in intra-acinar region of a human lung

Abstract

The determination of the particle dynamics in the human acinar airways having millions of alveoli is critical in preventing potential health problems and delivering therapeutic particles effectively to target locations. Despite its complex geometrical structure and complicate wall movements, the advanced calculation simulations can provide valuable results to accurately predict the aerosol deposition in this region. The objective of this study was to numerically investigate the aerosol particle transport and deposition in the intra-acinar region of a human lung for different breathing scenarios (i.e., light, normal, and heavy activities) during multiple breaths. Idealized intra-acinar models utilized in this study consisted of a respiratory bronchial model, an alveolar duct model, and an alveolar sac model. The particles with 5 μ m in diameter released from the inlet of the model were tracked until they deposited or escaped from the computational domain. The results showed that due to the rhythmic alveolar wall movement, the flow field was divided into two regions: one is the low-speed alveolar flow and the other is the channel flow. It was found that the chaotic acinar flow irreversibility played a significant role in the aerosol transport in higher generations. During the succeeding breaths, more particles deposited or escaped to the relating acinar generation and reached the more distal regions of the lung. The number of particles remaining in the suspension at the end of the third cycle ranged from 0.016% to 3%. When the mouth flow rate increased, the number of particles remaining in the suspension reduced, resulting in higher deposition efficiency. The total deposition efficiencies for each flow rate were 24%, 47%, and 77%, respectively. The particle simulation results also showed that more breathing cycle was required for full aerosol particle deposition or escape from the model. In addition to the alveolar wall motion, the type of breathing condition and breathing cycle had a significant effect on the accurate prediction of the aerosol deposition in the intra-acinar region of the human lung.

Numerical simulation of the unsteady flow field in the human pulmonary acinus

“…The models presenting the human pulmonary acinus are validated with the numerical results of Darquenne et al [28] and Ciloglu et al [43], and, applied for three breathing conditions with mouth flow rates 15 (light), 30 (normal), and 60 (heavy) LPM for an average human adult with tidal volume 500 mL, FRC of 3 L and total lung capacity 6 L. During one breathing cycle, equal inspiration and expiration times are assumed.…”

“…The pulmonary region of the lung consists of the respiratory bronchioles (with partly surrounding alveoli), the alveolar ducts (completely covered by alveoli), and the alveolar sacs (the blind-ending terminations of alveolar ducts) [42]. To represent the airflow in these generations, i.e., generation 17 (G17), 18 (G18), and 23 (G23), idealized models developed in the author's previous study [43] have been employed, as shown in figure 1.…”

“…Hence, the alveolar wall deformation rate, assuming isotropic volume change spatially, was taken as 25%, except for the rigid-walled alveolar ducts. The respiratory parameters for an average human adult under different breathing conditions were described in detail in the previous study [43]. In this study, the Reynolds numbers at the inlet of airway generations were varied between 0.01 and 1.16 for inhalation flow rates.…”

SARS CoV-2 aerosol: How far it can travel to the lower airways?

“… Madas et al (2020) employed a lung model based on a stochastic deposition, which was developed by Koblinger and Hofmann (1990) to find out the deposition of viral loads and revealed that over 60% of the inhaled viral masses were deposited in the extrathoracalis (upper), which are the portion of the human lung airways, and suggested to affect the upper airways and if not diagnosed, could eventually develop into pneumonia. Other researchers focused on aerosol behavior in the intra-distal region of a simplistic lung model in the presence of different breathing conditions ( Ciloglu, 2020 ), gravity and surface tension effects on micro-bubbles in simplistic bifurcated airways ( Munir and Xu, 2020 ), mask-wearing effects in upper respiratory geometry ( Xi et al , 2020 ), aerosol transport in phantom lung bronchioles ( Mallik et al , 2020 ), cough exhalation from a 18-generation simplistic airways ( Si et al , 2021 ), etc.…”

A note on the stability characteristics of the respiratory events

“…This event is analogous to the breakup of liquid thread that breaks up due to P–R instability. In parallel, other respiratory events such as coughing and sneezing are the spasmodic and complex event [3] , [22] , [26] , [27] that triggers the involuntary discharge of fluid from the lungs [1] , [33] . A cough is a spontaneous and persistent reflex that effectively clears the large breathing passages of fluids and other foreign particles.…”