Flow distribution through human and canine airways during inhalation and exhalation

Airflow distribution through the tracheobronchial tree is influenced by many factors. In a hollow cast of the central airways, the only factors involved are resistance and inertia of the airflow. Distribution of steady flow during both inhalation and exhalation was measured at different total flow rates in human and canine tracheobronchial casts. The resulting airflow rates in peripheral segments were measured with a sensitive apparatus, which did not disturb the distribution of flow. Inertia of the airflow was found to be small but significant in airways of the human cast and substantially greater in the canine airway cast than in the human cast during inhalation. The influence of airflow inertia during inhalation was largely responsible for the different distributions of flow during inhalation and exhalation through the airway casts. Airflow resistance was found to be considerably greater during exhalation and may have contributed to the redistribution of flow. The forces involved are small but should be considered when modeling the in vivo distribution of airflow.