Mechanism of mosaic attenuation of the lungs on computed tomography in induced bronchospasm

The purpose of this study was to investigate whether hypoxic pulmonary vaso constriction is the major determinant of the computed tomography (CT) patte rn of mosaic attenuation in asthmatic patients with induced bronchoconstric tion. Thin-section CT was performed at suspended full inspiration immediate ly and 30 min after methacholine bronchoprovocation in 22 asthmatic subject s, who were randomly assigned to breathe room air (group A, n = 8), oxygen via nasal prongs at 5 l/min (group B, n = 8), and oxygen via face mask at 1 2 l/min (group C, n = 6). CT changes were quantified in terms of global lun g density and density in hypodense and hyperdense areas. Lung parenchymal d ensity increases were greatest in group C and greater in group B than in gr oup A, globally (P = 0.03) and in hypodense regions (P = 0.01). On bivariat e analysis, the only change in cross-sectional area was related to change i n global density. In hypodense regions, density change was related both to reduction in cross-sectional area (P < 0.0005) and to oxygen administration (P = 0.01). After correction for changes in global lung density, only oxyg en was independently related to density increase in hypodense areas (P = 0. 02). In induced bronchoconstriction, the CT appearance of mosaic attenuatio n can be largely ascribed to hypoxic vasoconstriction rather than to change s in lung inflation.