Maximal airway response to methacholine in cough-variant asthma: comparison with classic asthma and its relationship to peak expiratory flow variability.
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 x 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.
Kang
Hee
H
Department of Pediatrics, Seoul National University Hospital, 28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea.
Koh
Young Yull
YY
Yoo
Young
Y
Yu
Jinho
J
Kim
Do Kyun
DK
Kim
Chang Keun
CK
D000367:Age Factors; D001249:Asthma / Q000175:diagnosis / Q000503:physiopathology*; D016535:Bronchial Hyperreactivity / Q000175:diagnosis* / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003371:Cough / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D016210:Methacholine Chloride; D010366:Peak Expiratory Flow Rate / Q000502:physiology*; D011336:Probability; D011379:Prognosis; D012016:Reference Values; D012307:Risk Factors; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
D016210:Methacholine Chloride