Numerical investigation of the effects of the bronchial stenosis on airflow in human respiratory tract

Obstructive lung diseases are slowly progressing diseases that are characterized by a narrowing of airway diameter and make it harder to breathe. Although obstructive lung diseases have a high mortality rate, there are many clinical methods for early diagnosis such as impulse oscillometry, thorax computed tomography scans, and pulmonary function tests. The objective of this study is to investigate the effects of obstructions in main bronchitis on the airflow pattern and provide a better understanding to flow characteristics in healthy and obstructed (bronchial obstructions) human airways throughout a tidal breathing pattern. Seven-generation lung airway model of a healthy person was reconstructed from computed tomography (CT) images and additional models were created artificially for investigation of how obstructed airways affect flow characteristics, flow rate, tidal volumes, and air distributions. A person-specific non-uniform pressure inlet boundary condition for 12 breaths per minute was created as a time-dependent pressure profile and implemented in FLUENT software as a macro for distal airways and atmospheric pressure outlet boundary condition defined at the trachea exit. Numerical simulations were carried out in SST k-w turbulence model and validated with an experimental study. Various flow properties such as lobar distribution rates, maximum flow rate changes, and airflow characteristics at different flow rates (quiet breathing-15 L/min and intense activity level-60 L/min) in the carina region, mid-trachea and sagittal section of the trachea were obtained in the human respiratory tract by computationally. The results show that regardless of flow rate, the airflow characteristics are similar for healthy models and models with various stenosis grades during inhalation. In terms of maximum flow rate drop, for both inspiration and expiration phases 16%, 45%, and %80 decreases were observed in OM-I, OM-II, and OM-III, respectively. In line with the decrease in maximum flow rate similar drop, percentages were obtained for tidal volumes. Besides, with the increase of stenosis grade, the inhaled air volume distribution to the right and left upper lobes decreased between 15%-95%.