Bronchial hyperresponsiveness to methacholine/AMP and the bronchodilator response in asthmatic children

Bronchodilator response (BDR) is assessed to estimate the reversibility of airflow obstruction. Bronchial hyperresponsiveness (BHR) is a characteristic feature of asthma and is usually measured by means of bronchial challenges using direct or indirect stimuli. The aim of the present study was to compare BHR to methacholine (direct) and that to adenosine 5'-monophosphate (AMP) (indirect) with regard to their relationships to BDR in asthmatic children. Methacholine and AMP challenge tests were performed on 138 children with mild-to-moderate asthma, and the provocative concentration causing a 20% decline in forced expiratory volume in 1 s (FEV₁) (PC₂₀) was determined for each challenge. BDR was calculated as the change in FEV(1), expressed as a percentage of the initial value, after inhalation of 400 μg salbutamol. Methacholine PC₂₀ correlated significantly but weakly with BDR (r = -0.254; p = 0.003). However, there was a significant and strong correlation between AMP PC₂₀ and BDR (r = -0.489; p = 0.000). For AMP PC₂₀, the relationship was closer than for methacholine PC₂₀ (p = 0.024 for comparison between correlation coefficients). The same figures were observed when BDR was expressed as a percentage of the predicted value. A stronger correlation of BDR with AMP PC₂₀ than with methacholine PC₂₀ suggests that BDR may be better reflected by BHR as assessed by AMP challenge than by methacholine challenge.