Biophysics of airflow within the airway: a review

An understanding of the fundamental principles that govern flow through the airway, like anatomy and physiology, is essential for the practising otolaryngologist. Failure to grasp these principles prevents the clinician from understanding why certain things happen clinically and why certain treatments are effective. This review presents the basic concepts of fluid mechanics as applied to the airway, using commonly encountered clinical situations to further illustrate ideas. Since air is a gaseous fluid, a review of the gas laws initiates the reader. Laminar and turbulent flow is discussed as well as the method used to distinguish between the two. Also included is a brief review of the air/liquid interface inside an alveolus, as well as a discussion of airflow through an endotracheal tube.