Dynamic Lung Morphology of Methacholine-Induced Heterogeneous Bronchoconstriction

investigate airway response in rats following intravenous (i.v.) bolus administration of a contractile agent, methacholine (MCh). The method provides direct visualization of the venti-lated regions within the lung. Heterogeneous bronchoconstric-tion following the i.v. MCh injection was evident using this technique. These 3He dynamic lung images revealed that the inspired fresh air was shunted to the less-constricted regions after the MCh challenge in a similar manner as described by Laplace’s relationship for the stability between adjacent alveoli. The airways in the more-constricted regions became nearly closed, resulting in air trapping, while the airways in the less-constricted regions remained effectively open, leading to over-inflation. These data suggest a lung model of airway constric-tion partitioned into ventilated and nonventilated regions. These nonventilated regions are heterogeneously distributed in the lung and this distribution cannot be deduced from spirometric measurement of the whole lung. We demonstrate that a com-bination of functional 3He images and anatomical 1H images provide an effective method to diagnose regional lung abnor