Flow Dynamics and PM2.5 Deposition in Healthy and Asthmatic Airways at Different Inhalation Statuses

Abstract

Public health reports indicate that high PM 2.5 concentration can impair the respiratory health of the residents, especially for those affected by asthma. Therefore, there is a need to determine the deposition mechanism and efficiencies for PM 2.5 in asthmatic human airways. In this study, gas flow dynamics and deposition fractions (DFs) of PM 2.5 in generations 10-11 of Weibel's lung model were investigated where the two-phase gas-solid flow behaviors in healthy and asthmatic airways were considered. The gas phase was modeled as a transient laminar and incompressible flow while the discrete phase model (DPM) was applied for the particle phase. Three different air flow rates under rest, light activity, and moderate exercise were considered. For the healthy airways, higher total mass DFs were observed during a moderate exercise as compared to rest and light activity conditions. Deposition fractions were higher in asthmatic airways compared to those of healthy ones, stemming from tapering in the airways as well as complex secondary flow fields, namely, Dean vortices, in the folds. Deposition was mainly due to inertial forces of particles, but a small amount of PM 2.5 was deposited near the entrance of asthmatic tube, as a result of the secondary flow. The numerical results revealed that the Dean vortices was an important factor for particle deposition. With increased DF, asthmatic people have a higher total respiratory dose of PM 2.5 for a given exposure compared to healthy individuals. Thus contributing to their increased susceptibility to adverse health effects caused by PM 2.5 .

An Overview of Experiments and Numerical Simulations on Airflow and Aerosols Deposition in Human Airways and the Role of Bioaerosol Motion in COVID-19 Transmission

“…The walls in airways are commonly assumed to be rigid and smooth with a circular cross-section (Chang and El Masry, 1982;Chen et al, 2018a). The concept of hydraulic diameter is important as it equates the circular cross-sections in idealized models to the bronchial surface over which airflow experiences a shear force in the real human airway (Hammersley and Olson, 1992…”

“…Since asthma and COPD are the most prevalent obstructive pulmonary diseases, there is a relatively higher volume of literature covering aerosol motion and deposition in human airways affected by these conditions (Yang et al, 2006;Luo et al, 2007;Zhang and Papadakis, 2010;Chen et al, 2018a). Geometric characteristics of the obstructed human airways such as for asthma and COPD can be represented by slightly altered geometries from the regular idealized ones.…”

“…Those approaches are useful in the assessment of the performance of existing drug-aerosol delivery technologies to the human lungs (Asgharian et al, 2001;Darquenne, 2012). Findings from these studies can be applied in the accurate estimation of risk levels caused by toxic aerosols or in design modifications to overcome the limitations of inhalers used by patients with respiratory diseases (Kolanjiyil and Kleinstreuer, 2017;Chen et al, 2018a).…”

“…Important items before the implementation of a CFD study include the generation of geometry, solving the governing equations along with appropriate boundary conditions, and sometimes incorporating user-defined functions (UDFs). The shape and size of geometry are not only dependent on the generation of the human airways under investigation but also on whether it is healthy or affected by a disease (Sul et al, 2014;Chen et al, 2018a). COPD has been represented by an axisymmetric constriction at the center of a bifurcation, while asthma has been represented by sinusoidal folds at the circumference of the affected bifurcation (Yang et al, 2006;Zhang and Papadakis, 2010).…”

“…Skewed airflow velocities influenced the mass flow ratios at bifurcations in the generations affected by the obstruction and subsequent ones (Mutuku and Chen, 2018). Sudden reduction in the effective cross-sectional area for asthma cases caused increased airflow velocities and high complex secondary flows, which in turn led to higher deposition fractions for PM 2.5 as compared to healthy human airways (Chen et al, 2018a). Airflow resistance, which is normally represented by the ratio of total pressure drop, has been applied to characterize and evaluate obstructions in the human lungs (Sul et al, 2014).…”