Chest
Volume 128, Issue 6, December 2005, Pages 3881-3887
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Clinical Investigations
PULMONARY FUNCTION
Maximal Airway Response to Methacholine in Cough-Variant Asthma: Comparison With Classic Asthma and Its Relationship to Peak Expiratory Flow Variability

https://doi.org/10.1378/chest.128.6.3881Get rights and content

Background:

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.

Objective:

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.

Methods:

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 FEV1 (PC20). 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.

Results:

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 × 10-4). In patients with CVA, no significant relationship was found between PC20 and PEF variability. However, the absence of a maximal response plateau and a higher plateau level were associated with increased PEF variability.

Conclusions:

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.

Section snippets

Methods and Materials

Children with a diagnosis of CVA were enrolled in this study. Initially, the patients were referred to our clinics for a cough that had persisted for a minimum of 2 months (range, 9 weeks to 2 years). The cough was usually dry or productive with minimal amounts of clear sputum, and was mainly nocturnal. None of the patients had a history of wheezing or dyspnea, nor was any wheeze or prolonged expiratory phase detected on physical examination. At the time of diagnosis, all had a PC20 level < 16

Results

Ninety-one patients with CVA and 91 PC20-matched patients with CA were enrolled. Of these, two patients with CVA and three patients with CA could not tolerate the high-dose methacholine challenge test, and three patients with CVA had a PC20 value > 16 mg/mL on the test. These eight subjects and their eight matched counterparts were excluded from the comparative study. The clinical characteristics of the two studied groups are shown in Table 1. The two groups were similar in terms of age, sex

Discussion

This study shows that levels of maximal airway response on the dose-response curves to methacholine were significantly lower in patients with CVA than in patients with CA. In patients with CVA, PEF variability was not found to correlate with PC20, but the absence of a maximal response plateau or a higher level of maximal response plateau, when present, was associated with increased PEF variability.

In normal subjects, the dose-response curve achieves a plateau at mild degrees of airway

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  • Cited by (0)

    This study was supported in part by BK 21 Project for Medicine, Dentistry, and Pharmacy and by grant No. 11–2003-022 from the Seoul National University Hospital Research Fund.

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