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Maximal Airway Response in Adolescents With Long-term Asthma Remission and Persisting Airway Hypersensitivity: Statistical Analysis

PC20 values were logarithmically transformed before analysis and were expressed as a geometric mean with a range of 1 SD.
Other values were presented as mean ± 1 SD. Values or prevalences between the two groups of adolescents were compared using the Student t test or the x2 test. Screening of data for differences among the three treatment groups was performed using the Kruskall-Wallis test. Changes in PC20 or maximal airway response with respect to the baseline values were analyzed using Wilcoxon signed-rank test. In each case, statistical significance was accepted when the two-sided p values were < 0.05.
Results
A total of 96 subjects (48 subjects in each group) entered the first phase of study. Of these, six subjects (two subjects with asthma remission and four subjects with symptomatic asthma) were excluded due to interruption of the test because of discomfort. The clinical characteristics of the 90 subjects who completed the initial high-dose methacholine inhalation test are shown in Table 1. There were no differences between the two groups in terms of age, sex ratio, atopic status as assessed by total serum IgE, and the pattern of positive skin responses, body mass index, FEV1, or PC20.
The levels of maximal airway response are shown in Figure 1. Thirty-four adolescents with asthma remission (73.9%) and 19 adolescents with symptomatic asthma (43.2%) featured a maximal response plateau on their dose-response curve to methacho-line (x2 test, p = 0.003). In those subjects with a plateau, there was no significant difference in its level between the adolescents with asthma remission (40.9 ± 5.6%) and those with symptomatic asthma (42.8 ± 3.5%; p = 0.141). When the percentage decline in FEV1 at the end of the protocol was taken as the maximal response for the subjects without a plateau in order to allow comparison across all subjects, the level of maximal airway response was significantly lower in the adolescents with asthma remission (44.0 ± 7.2%) than in those with symptomatic asthma (48.6 ± 5.8%; p = 0.001).
Fig1
Figure 1. Comparison of maximal airway response to methacho-line between adolescents with asthma remission and adolescents with symptomatic asthma. Open circle: subject with a maximal response plateau; closed circle: subject with FEV1 fall > 50% without a plateau. Horizontal bars represent mean ± SD.
Table 1—Clinical Characteristics of the Two Adolescent Groups

Characteristics Asthma Remission (n = 46) Symptomatic Asthma(n = 44)
Age, yr 15.0 ± 1.2 14.7 ± 1.0
Male/female sex, No. 32/14 28/16
Serum IgE, IU/mL 288.4 (138.0-602.6) 331.1 (107.2-1023.3)
Pattern of positive skin response t 44/18/9/6/14 41/17/10/8/16
Body mass index Methacholine inhalation test 19.6 ± 2.9 18.9 ± 3.1
FEVj, % predicted 97.3 ± 9.2 96.5 ± 10.1
PC20, mg/mL 5.50 (2.40-12.59) 5.37 (2.40-12.02)