Changes in Indices of Airway Hyperresponsiveness During One Year of Treatment with Inhaled Corticosteroids in Patients with Asthma

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Abstract
We analyzed the changes in indices of airway hyperresponsiveness, including hypersensitivity and hyperreactivity, during one year of treatment with inhaled corticosteroids. We then investigated on which of them the inhaled corticosteroids had a primary effect. Fifty outpatients with asthma were recruited and treated with inhaled beclomethasone dipropionate. They underwent bronchoprovocation tests on the initial visit and at 3, 6, and 12 months. The dose of methacholine required to produce a 20% fall in the forced expiratory volume in 1 second (PD20-FEV1) was measured to evaluate airway hypersensitivity. A relatively novel index, the percent change in the forced vital capacity (ΔFVC%) at the PD20-FEV1, was assessed as a marker of airway hyperreactivity. PD20-FEV1 and ΔFVC% were assumed to indicate the horizontal shift of the dose-response curve and the vertical change in the maximal response plateau, respectively. Log(PD20-FEV1) and ΔFVC% continued to improve throughout the year (p < 0.001 and p = 0.002, respectively). Log(PD20-FEV1) improved significantly at the 3-month evaluation (p < 0.001), and ΔFVC% improved at the 6-month evaluation (p = 0.012). Log(PD20-FEV1) had no or weak relationships with ΔFVC% at all evaluation points. In conclusion, inhaled corticosteroids continued not only to reverse the leftward shift of the curve, but also to restore the plateau. Furthermore, their effect was reflected primarily by the former rather than the latter. They should be followed separately to examine how much airway inflammation is reduced.

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