Airflow limitation and airway dimensions assessed per bronchial generation in older asthmatics

Abstract

Computed tomography (CT) has been used for non-invasive quantitative assessment of airway dimensions, potentially showing airway remodeling, in asthma. However, most studies have examined either only one airway or only airways in anatomically unidentified cross-sections. Using software capable of precisely identifying the generation of airways and measuring airway dimensions perpendicular to the long axis of airways, we examined, in older patients with stable asthma, how inter-subject variation in airway dimensions correlated among the 3rd to 6th generation of airways, and then examined relationships between airway dimensions of each generation and indices of airflow limitation. Subjects aged ≥55 years old comprised 59 asthmatic patients who underwent CT and pulmonary function tests on the same day. We measured airway wall area (WA%) and inner luminal area (Ai) from the 3rd to the 6th generation of eight bronchi in the right lung. Excellent correlations were identified for both WA% and Ai among the generations (r=0.744-0.930 for WA%) when we took the average of all measured bronchi per generation as a personal representative value. Significant correlations of airflow limitation indices with both WA% and Ai/BSA were found at each of the 3rd to 6th generations with similar correlation coefficients (WA% for FEV(1) %predicted, r=-0.410 to -0.556). In older patients with stable asthma, airway wall thickening and narrowing mightoccur in a parallel manner through 3rd to 6th generation airways. Airway dimensions at these areas of airways may thus have significant and similar correlations with indices of airflow limitation.