Abstract
<h3>Background:</h3> In asthmatic subjects, not only airway sensitivity but maximal airway response are increased on the dose-response curve to methacholine, and peak expiratory flow (PEF) variability is closely related to airway hypersensitivity and maximal airway response. <h3>Objective:</h3> The aims of this study were to compare the prevalence and the level of maximal response plateau between patients with cough-variant asthma (CVA) and those with classic asthma (CA), and to examine the relationship between airway hypersensitivity or maximal airway response and PEF variability in patients with CVA. <h3>Methods:</h3> A high-dose methacholine inhalation test was performed on 83 patients with CVA and on 83 patients with CA matched for provocative concentration of methacholine causing a 20% fall in FEV<sub>1</sub> (PC<sub>20</sub>). PEF was recorded in the morning and evening for 14 consecutive days in 78 CVA patients, and the amplitude percentage mean was used to express the diurnal PEF variation. <h3>Results:</h3> Fifty-two CVA subjects (62.7%) but only 33 CA subjects (39.8%) showed a maximal response plateau. This difference was significant after correction by the Bonferroni method (corrected p=0.024). Subjects in the CVA and CA groups showing a plateau had significantly different plateau levels (38.0 ± 5.9% vs 42.9 ± 3.9%, corrected p=1.0 × 10<sup>-4</sup>). In patients with CVA, no significant relationship was found between PC<sub>20</sub> and PEF variability. However, the absence of a maximal response plateau and a higher plateau level were associated with increased PEF variability. <h3>Conclusions:</h3> Maximal airway response may be an important confounder in the relationship between airway hypersensitivity and the clinical expression of asthma. The identification of a maximal response plateau and the level of this plateau in patients with CVA provide information relevant to PEF variability.
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