Airway responsiveness as a direct factor contributing to the dyspnoea perception in asthma

Abstract

It is not clear whether airway responsiveness is directly related to the perception of bronchoconstriction in asthma. The purpose of this study is to directly compare the perception of induced bronchoconstriction among the groups classified according to the degree of airway responsiveness. Two hundred and twenty-seven patients with the definitive or suspected asthma underwent a methacholine provocation test. During the test, the degree of dyspnoea was assessed by a modified Borg scale. The perception of induced bronchoconstriction was indicated by the slope in the linear regression analysis between changes in Borg score and the reduction in forced expiratory volume in 1 sec (FEV1) as a percentage of baseline value. The provocative concentration of methacholine resulting in 20% fall in FEV1(PC20) was calculated. The degree of airway responsiveness to methacholine was categorized as moderate to severe airway hyper-responsiveness (AHR) if PC20was <1 mg ml−1, mild AHR if PC20was ⩾1 but ⩽4 mg ml−1, borderline AHR if PC20was >4 but ⩽16 mg ml−1, and normal airway responsiveness (negative AHR) if PC20was >16 mg ml−1. Positive AHR was defined as PC20⩽4 mg ml−1. Another index of bronchial responsiveness (BR index) was calculated as the log [(% decline in FEV1/log final methacholine concentration as mg dl−1)+10]. We found that the geometric mean of the slope was lower in subjects with positive AHR (0·12, n=115) than in subjects with negative AHR (0·17,n =72;P<0·01). The geometric mean of the slope in subjects with borderline AHR (0·14,n =40) was between the two groups. Furthermore, the slope was decreased in asthmatics with moderate to severe AHR compared with mild AHR (P<0·05), although the baseline FEV1did not differ between the two groups. In multiple regression analysis, airway responsiveness expressed as BR index had a significant effect on the perception of bronchoconstriction. We conclude that the perception of bronchoconstriction is diminished in patients with AHR and the degree of airway responsiveness may be directly related to the perception of bronchoconstriction in asthmatic subjects.