Numeric Examination of Non-Stationary Dusted Airflow and Quantification of Deposition of Micro-Sized Solid Particles in the Human Airways under Different Breathing Intensity

This study focuses on developing a mathematical model of the respiratory system created by the authors. This model has been created to solve relevant tasks within assessing and predicting health risks caused by negative effects of airborne exposures. In particular, the main focus is on investigating dusted airflow and dust particle deposition in the human airways (from the nasal cavity to the fifth generation of the bronchi) under different breathing intensity. Inhaled air is considered a multi-phase mixture of a homogenous gas and solid dust particles. The three-dimensional geometry of the airways is based on CT scans. The study investigated non-stationary airflow during calm, deep and intense breathing. We quantified deposition of particles with different sizes (diameter between 0.5 µm and 20 µm) and density (1000 kg/m3, 2000 kg/m3, 2700 kg/m3 and 4000 kg/m3) in the airways during an inhalation of different intensity; provided velocity fields for inhaled air and motion paths for particles of various sizes. Large particles (more than 10 µm), which tend to be heavy, are almost completely (more than 90 %) deposited in the airways (predominantly in the nasal cavity, pharynx and larynx). As a particle size and mass (density) declines, the share of deposited particles goes down as well and, accordingly, there is a growth in the share of particles able to reach smaller airways and even the lungs. As breathing intensity grows, the share of deposited particles (diameter 2.5 µm and larger) increases as well. Particle density has a more pronounced effect on differences in deposition of micro-sized particles (sized between 2.5 and 10 µm); the higher is particle density, the higher is their mass (of particles with the same size) and the higher is the share of particles deposited in the airways. Deposition of smaller particles (sized 0.5 µm, 1 µm) differs only slightly depending on their density. Depending on breathing intensity, approximately 28–34 % of particles sized 1 µm or less is deposited in the analyzed section of the airways. These findings are qualitatively consistent with the results obtained by a conducted field experiment aimed at investigating regularities of distribution of ambient dust particles in the human airways.