Diagnostic Uses

The airways of asthma subjects are exquisitely sensitive (hyperresponsive) to the bronchoconstrictor actions of specific (e.g., bronchoconstrictor agonist) and nonspecific (e.g., airway irritants) stimuli. Indeed, the degree of airway hyper-responsiveness has been shown to correlate with the severity of asthma [101]. This characteristic is exploited by clinicians in the diagnosis of asthma, particularly in subjects who do not exhibit clinical manifestations of the disease. Pulmonary function tests that assess airway caliber (e.g., forced expiratory volume in one second, FEV1) are performed before and after administration of incrementally increasing concentrations of bronchoconstrictor aerosol. The concentration producing a specified level of bronchoconstriction (e.g., 20% reduction in FEV1) permits an assessment of the airway reactivity relative to established figures for normal subjects and mild and severe asthmatics (Fig. 4). In these studies, aerosols of bronchoconstrictor agonists, such as methacholine (a selective agonist of muscarinic cholinoceptors) and histamine, are used [102]. Other stimuli that are not direct bronchoconstrictors, such as exercise and inhaled adenosine monophosphate, have also been proposed for use in bronchial provocation tests [102,103].

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