In asthma positive phase III slopes can result from structural heterogeneity of the bronchial tree

Abstract

Conceptually, the simplest way to obtain a sloping phase III during a washout exhalation is when there is convective flow sequencing between two lung units, such that the better ventilated unit contributes relatively more to exhaled flow at the beginning of phase III in the exhalation. Here, we show how compliance heterogeneity across the serial and parallel arrangement of branch points in bronchial trees of patients with asthma leads to flow sequencing, and thus phase III slopes of positive sign at the patient’s mouth.