Computed tomography for evaluation of the small airway disease in asthma.

Small airway dysfunction and remodeling are known to influence the disease control and progression in asthma. We investigated the small airway involvement in asthmatic patients by correlating data derived from computed tomography (CT) and pulmonary function test (PFT). The CT lung scans were acquired at full inspiration and expiration using a portable spirometer to control the respiratory manoeuvers. PFT was performed before and after bronchodilator test with salbutamol 400 mcg, measuring lung volumes and flows, airway resistance (Raw) and single-breath nitrogen washout (SBN2W). Up to now, 25 patients with mild-to-moderate asthma were studied. Fifteen had a good control of the disease at the time of the study as reflected by an Asthma Control Test (ACT) score ≥ 20. The mean lumen area (LA), measured in the left lower lobe posterior-basal segmental bronchus (LB10), correlated directly with the forced expiratory volume in 1 sec (FEV1) (r=0.60, p=0.002) and inversely with Raw (r=-0.52, p=0.011). The wall area percent (WA%) in the LB10 correlated inversely with FEV1 (r=-0.55, p=0.004)and directly with Raw (r=0.50, p=0.014). Air trapping, expressed as expiratory Voxel Index -856 HU (%), correlated inversely with FEV1 (r=-0.82, p<0.0001) and directly with both residual volume (RV)(r=0.72, p<0.0001) and the change in N2 concentration in phase 3 of the SBN2W test (r=0.67, p=0.001). A trend toward a significant increase in air trapping was found in the 10 patients with a poor control of the disease in comparison with the 15 patients in good control (p=0.083). These preliminary data show that both CT and PFT including Raw and SBN2W provide useful information for the study of the small airways in asthma.