Bronchial reactivity is known to be a component of airway hyperresponsiveness, a cardinal feature of asthma, with bronchial sensitivity, and is increments in response to induced doses of bronchoconstric tors as manifested by the steepest slope of the dose-response curve. However, there is some controversy regarding methods of measuring bronchial reactivity and clinical impact of such measurements. The purpose of this study was to evaluate the clinical significance and assess the clinical use by analyzing the relationship of the bronchial sensitivity, the clinical severity and the changes in pulmonary function with bronchial reactivity.

A total of 116 subjects underwent a methacholine bronchial provocation test. They were divided into 3 groups : mild intermittent, mild persistent, moderate and cough asthma. Severe patients were excluded. Methacholine PC20 was determined from the log dose-response curve and PC40 was determined by one more dose inhalation after PC20. The steepest slope of log dose-response curve, connecting PC20 with PC40, was used to calculate the bronchial reactivity. Body plethysmography and a single breath for the DLCO were done in 43 subjects before and after methacholine test.

The average bronchial reactivity was 38.0 in the mild intermittent group, 49.8 in the mild persistent group, 61.0 in the moderate group, and 41.1 in the cough asthma group. There was a weak negative correlation between PC20 and bronchial reactivity. A heightened bronchial reactivity tends to produce an increased clinical severity in patients with a similar bronchial sensitivity and basal spirometric pulmonary function. There were significant correlations between the bronchial reactivity and the initial pulmonary function before the methacholine test in the order of sGaw, Raw, FEV₁/FVC, MMFR. There were no correlations between the bronchial sensitivity and the % change in the pulmonary function parameters after the methacholine test. However, there were significant correlations between the bronchial reactivity and the PEF, FEV₁, DLCO.

There was weak significant negative correlation between the bronchial reactivity and the bronchial sensitivity, and the bronchial reactivity closely reflected the severity of the asthma. Accordingly, measuring both the bronchial sensitivity and the bronchial reactivity can be of assistance in assessing of the ongoing disease severity and in monitoring the effect of therapy.