[Measurement of the parameters of dose-response curve obtained after the methacholine challenge test]

To investigate the clinical value in the measurement of parameters of the dose-response curve (DRC) obtained after the methacholine challenge test.

Twenty-seven cases of cough variant asthma (CVA), 29 of mild asthma, 19 of moderate asthma, and 15 healthy volunteers underwent the methacholine challenge test. The dose-response curves were constructed. The following parameters were calculated: position (PC35sGaw), dose-response curve (DRS), ratio of the area under the curve to the logarithm of the maximal concentration (AUC/lg[Cmax]) and maximal response.

A plateau appeared in 11 cases among the healthy subjects, while a plateau appeared only in 2 cases of CVA and 2 of asthma. There were no significant differences among the asthmatic groups in the measurements of PC35sGaw and AUC/lg[Cmax] (geometric mean PC35sGaw: mild asthmatics = 0.369, moderate asthmatics = 0.251, cough variant asthmatics = 0.547), AUC/lg[Cmax] was significantly greater in the asthmatic groups than in the normal group [AUC/lg [Cmax](mean +/- s): mild asthmatics = 24.7 +/- 4.7, moderate asthmatics = 26.6 +/- 4.3, cough variant asthmatics = 25.6 +/- 3.7, normal subjects = 15.5 +/- 4.3, P < 0.01]. DRS of moderate asthmatics was significantly greater as compared with cough variant asthmatics (geometric mean DRS: mild asthmatics = 30.761, moderate asthma-tics = 59.020, cough variant asthmatics = 19.231, P < 0.05), but there was no difference between the other groups. PC35sGaw was negatively correlated with DRS (r = 0.866, P < 0.001) and with AUC/lg[Cmax] (r = 0.502, P < 0.001).

Four parameters of DRC obtained after the methacholine challenge represent airway sensitivity and reactivity respectively. The parameters of DRC of asthmatic patients are different from those of normal subjects. The sensitivity is related to the reactivity, but they are not completely parallel with each other.