Three-dimensional quantification of large central airway collapses during expiration*

Expiratory Central Airway Collapse (ECAC), an increasingly recognized disorder particularly among individuals with Chronic Obstructive Pulmonary Disease (COPD), is often combined with other pulmonary obstructions and not understood well. Like many other physiological structures, the central airway consisting of the trachea and the first generation is distensible and subjected to collapses during expiration under diseased conditions. Flow through a collapsible tube is commonly investigated using a straight flexible tube with an imposed driving pressure and transmural pressure (pressure difference between inside and outside of the tube). As a model for large central airways, the current experimental study employs a straight tube, having material properties similar to the large airways and subjected to pressures replicating normal and forced expiration. Observed steady states and self-excited oscillating modes are quantified by reconstructing the tube periphery, both cross-sectionally and along the length of the tube, using stereophotogrammetry. This approach conducted in physiological conditions helps to elucidate the nature of the collapse and subsequently identify the diagnostic procedures.