Relationship of airway wall thickness to airway sensitivity and airway reactivity in asthma

Airway wall thickening has been assumed to cause airway hyperresponsiveness, but a protective effect against airway narrowing has also been suggested. We investigated the relationship between airway wall thickness as assessed by helical computed tomography and two components of airway responsiveness, airway sensitivity and reactivity, in patients with stable asthma with (n = 23) and without (n = 22) inhaled steroid treatment. A cross-section of the apical bronchus of the right upper lobe was obtained. Airway wall area corrected by body surface area was measured as an index of wall thickness. Airway sensitivity and reactivity were measured by continuous inhalation of methacholine, on the basis of the methacholine respiratory resistance dose-response curve. The eosinophil count in sputum was determined in 16 patients [steroid (+) group] and 14 patients [steroid (-) group]. In both groups of patients, airway sensitivity was not related to airway reactivity. Airway sensitivity was related to eosinophil count [r = 0.57 in the steroid (+) group and r = 0.49 in the steroid (-) group], but not to airway wall thickness. In contrast, airway reactivity negatively correlated with airway wall thickness [r = -0.56 in the steroid (+) group and r = -0.55 in the steroid (-) group] but not with eosinophil count. Our results suggest that airway wall thickening attenuates airway reactivity in patients with asthma. These findings may have important implications in pathophysiology and in the treatment of airway remodeling.