Relationships of methacholine and AMP responsiveness with peak expiratory flow variability in children with asthma

Background: Both bronchial responsiveness (BR) and peak expiratory flow (PEF) variability are increased in asthma. PEF variability is presumed to reflect the degree of BR in asthma. BR is commonly assessed by bronchial challenges using direct or indirect stimuli. Objective: The aim of this study was to compare methacholine and adenosine 5′-monophosphate (AMP) responsiveness with regard to their relationships with PEF variability in children with asthma. Methods: Methacholine and AMP challenge tests were performed in 79 children with mild to moderate asthma, and a provocative concentration causing a 20% decline in forced expiratory volume in 1 s (PC ₂₀) was calculated for each challenge. Subjects recorded PEF each morning and each evening for 14 consecutive days. PEF variability was expressed as amplitude percentage mean (amp%mean; high PEF minus low PEF on each day, expressed as a percentage of their mean, averaged over 14 days), and as the lowest percentage highest (low%high; the lowest PEF expressed as a percentage of the highest PEF recorded over the period). Results: Methacholine PC ₂₀ correlated significantly but weakly with both indices of PEF variability (amp%mean: r=-0.285, P=0.011; low%high: r=0.238, P=0.034). However, there was a significant and strong correlation between AMP PC₂₀ and both amp%mean (r=-0.583, P=0.000) and low%high (r=0.496, P=0.000). For AMP PC₂₀, the correlations were stronger than for methacholine PC ₂₀ (comparison of correlation coefficients with amp%mean: P=0.021; with low%high: P=0.063). Conclusion: Both methacholine PC₂₀ and AMP PC₂₀ correlated significantly with PEF variability. However, the stronger correlations for AMP PC₂₀ than for methacholine PC ₂₀ suggest that PEF variability may be better reflected by BR assessed by AMP than by methacholine.