Bronchial hyperresponsiveness in children and adolescents

The frequency distribution of bronchial responsiveness to both inhaled histamine and exercise both exhibit a unimodal distribution, different from a normal distribution, whereas PC20 values exhibited a lognormal distribution. BHR to both inhaled histamine (PC20 < or = 8.0 mg/ml (21 (II))) and exercise (delta % FEV1 < or = 10% (22 (III)) was found in 16% of the children and adolescents, while 6% of the population had BHR to both stimuli (22 (III)). Although a significant relationship between responsiveness to inhaled histamine and exercise existed (rs = 0.3, p < 0.001), the lack of overlap indicates that the association between the two stimuli is more complex (20 (I)). Worldwide, considerable differences in the prevalence of children with BHR to both inhaled agents and exercise have been observed. The prevalence of BHR to histamine and exercise observed in the present study was similar to findings in other industrialized countries, while the prevalence of BHR in e.g. Africa is low. All subjects with asthma had BHR to histamine and 77% had BHR to exercise, but only 35% of those with BHR to histamine (20 (I)) and 25% of those with BHR to exercise (delta FEV1 > or = 10%) (22 (III)) had symptomatic asthma. Thus low PVpos indicates that bronchial challenges are inadequate tools for screening in epidemiologic studies of asthma. The present study, however, showed that the predictive values of a negative test (PVneg) was high (100% (23 (IV) and 99% (22 (III)), respectively) supporting that bronchial challenge testing can exclude the diagnosis of asthma. Furthermore, asymptomatic subjects with BHR had reduced increase in height and lung function (FEV1) during the follow-up period of 18 months. The present observation indicate that BHR may induce permanent impairment of the lung function. The degree of responsiveness was significantly influenced by the presence of asthmatic symptoms and atopy of which house-dust mites and horse epithelium were of specific importance, whereas no association was demonstrated between BHR and recent viral infection, smoke or level of lung function. In conclusion, BHR is frequently observed in population samples and the degree of responsiveness was closely related to asthma and atopy. In children and adolescents with BHR, the increased responsiveness remained unchanged and those who developed asthma had a preexisting asymptomatic BHR.