Are all airways equal?

Abstract

BRONCHOCONSTRICTION IS A CARDINAL feature of asthma. It involves airway narrowing, increase in airway resistance, impairment of breathing, and can in very severe cases even lead to death. The severe narrowing of the airway lumen during bronchoconstriction is caused by a shortening of the airway smooth muscle in response to agonists or vagal stimulation. However, does a simple stimulus-response relationship, easily observed in isolated airways or tissue strips, apply in vivo equally to all airways? More than two decades ago, investigators using the multiple inert gas elimination technique (MIGET) showed that bronchoconstriction in asthma resulted in inhomogeneous ventilation-perfusion distributions (2). That suggested that airway lumen narrowing throughout the bronchial tree must have been highly heterogeneous to cause the heterogeneity in ventilation consistent with the measured ventilation-perfusion distributions in asthma. However, it was unclear if such heterogeneity in bronchoconstriction was caused by a random variability in the response of airways and, thus, randomly distributed within the lungs, or if it was predominantly located in contiguous regions of the lungs. During the last decade, pulmonary imaging studies using PET, MRI, and synchrotron CT, found that bronchoconstriction leads to substantial patchy patterns char