Maximal Airway Response in Adolescents With Long-term Asthma Remission and Persisting Airway Hypersensitivity
Epidemiologic studies, have demonstrated that many children with asthma go into long-lasting clinical remission at adolescence. Bronchial hyperresponsiveness (BHR) is a characteristic feature of asthma, and its measurement may provide a useful adjunct to the diagnosis of asthma. The correlation of the level of bronchial responsiveness with the clinical severity of the disease, however, is not well established. While some workers have suggested that subjects with a greater degree of bronchial responsiveness had more severe asthma, others have disagreed. Several studies have shown that BHR persists in a considerable proportion of adolescents with asthma in long-term clinical remission, and therefore does not fully explain symptomatology in asthma.
BHR is usually defined as an increased sensitivity of the airways to inhaled nonsensitizing bronchocon-strictor stimuli. However, there is accumulating evidence that BHR is a more complex functional abnormality that comprises more than just hypersen-sitivity. When exposed to high concentrations of inhaled bronchoconstrictors, normal subjects feature a maximal response plateau on the dose-response curve at mild degrees of airway narrowing, whereas asthmatic patients show an excessive airway narrowing as reflected by either an elevated or absent maximal response plateau. It has been argued that the latter is clinically a more relevant component of BHR than the former per se because it reflects the potential severity of airways obstruction in the individual patients.
It has been shown that the maximal response of the airways increases with increasing sensitivity to methacholine in patients with symptomatic asthma, leading to unmeasurable plateau levels when the sensitivity is relatively high.