CFD simulations of respiratory airflow in human upper airways response to walking and running for oral breathing condition

Walking and running are common types of physical activities that people do in day to day living, to improve health and physical fitness or for recreation. During a physical activity, rate and depth of breathing increase because working muscles need extra oxygen in order to produce energy. In this study, computational fluid dy-namics (CFD) simulations were used to investigate respiratory airflow dynamics in human upper airways response to walking and running for oral breathing. The numerical simulations were done in a realistic CT-scan airway model using ANAYS Fluent 19.0 software. Flow fields were analysed numerically and flow patterns were inves-tigated in the airway model during inspiration and expiration response to walking and running. The axial velocity distributions and secondary flow patterns for the two respiratory phases were analysed response to the two physical activities at different cross-sections of the airway model. The maximum velocity, wall pressure and wall shear stress values for running were respectively 3.2, 9.4 and 5.9 times higher than that of walking during inspiration. The mixing of flow streamlines was observed to be higher during running than walking because of more significant turbulence. More skewed flows at airway curvatures were observed at inspiration than expira-tion. The results of this study supported the fact that running is a more intense activity than walking from a respiratory dynamics point of view.