Baseline airway hyperresponsiveness and its reversible component: role of airway inflammation and airway calibre.

Airway hyperresponsiveness (AHR), in which airway inflammation has been reported to be a key factor, is an important component of asthma. However the precise role of inflammation in AHR is still unclear. In this report, airway inflammatory changes were assessed using hypertonic saline-induced sputum examination and exhaled nitric oxide analysis, and the relation between AHR to methacholine, airway calibre forced expiratory volume in one second (FEV1) and airway inflammatory indices examined. Furthermore, the changes in these variables were also examined by means of 8 weeks' open uncontrolled inhaled steroid administration (800 microg x beclomethasone x day(-1)). Asthmatic subjects had higher eosinophil counts and bradykinin concentration in induced sputum and higher exhaled NO levels, and showed AHR to methacholine. Baseline AHR significantly correlated with FEV1 but not with indices of inflammation in sputum or exhaled air. Steroid inhalation therapy was associated with a reduction in eosinophil and bradykinin concentration in sputum and NO levels in exhaled air and an improvement in FEV1 and AHR. The changes in FEV1 and AHR were significantly related to changes in markers in sputum and exhaled air (p<0.01 for each). These results suggest that baseline airway hyperresponsiveness can be predicted from the airway calibre but not from inflammatory parameters in sputum or exhaled air. In contrast, the reversible component of airway hyperresponsiveness appeared to be associated with the reduction in airway inflammation.