The effect of asthma on the perimeter of the airway basement membrane

When comparing the pathology of airways in individuals with and without asthma, the perimeter of the basement membrane (Pbm) is used as a marker of airway size, as it is independent of airway smooth muscle shortening or airway collapse. The extent to which the Pbm is itself altered in asthma has not been quantified. The aim of this study was to compare the Pbm from the same anatomical sites in postmortem lungs from subjects with (n = 55) and without (n = 30) asthma (nonfatal or fatal). Large and small airways were systematically sampled at equidistant "levels" from the apical segment of the left upper lobes and anterior and basal segments of the left lower lobes of lungs fixed in inflation. The length of the Pbm was estimated from cross sections of airway at each relative level. Linear mixed models were used to investigate the relationships between Pbm and sex, age, height, smoking status, airway level, and asthma group. The final model showed significant interactions between Pbm and airway level in small (<3 mm) airways, in subjects having asthma (P < 0.0001), and by sex (P < 0.0001). No significant interactions for Pbm between asthma groups were observed for larger airways (equivalent to a diameter of ∼3 mm and greater) or smoking status. Asthma is not associated with remodeling of the Pbm in large airways. In medium and small airways, the decrease in Pbm in asthma (≤20%) would not account for the published differences in wall area or area of smooth muscle observed in cases of severe asthma.