Airflow velocities in the airways during expiration on different end-expiratory lung volumes: Computational study

We used our computational model of the respiratory system which features non-linear variation of airway dimensions and airway-generation-based structure to show airflow velocities (cm/sec) during natural slow expiration on different end-expiratory lung volumes. Expiratory airflow rates at the mouth can be easily measured using a flow meter. However, because there is no practical non-invasive method that is currently available to measure airflow velocity in the airways, the airflow velocities in airway generations 0~16 were studied using the computational model. An airflow velocity is given by an airflow rate (ml/sec)+a cross sectional area (cm²). The cross sectional areas vary depending on inflation and deflation of a lung during respiration, and thus, knowing expiratory airflow rates at the mouth does not go far along the way to find out airflow velocities in the airways. In this study, we first predicted variation of expiratory airflow rates on six different end-expiratory lung volumes using a concept of a time constant, a product of lung compliance and airway resistance, and computational simulation. Then airflow velocities during expiration on the six end-expiratory lung volumes were computed and compared at the conducting airways, airway generations 0~16