New considerations about measuring airway hyperresponsiveness

Measuring airway responsiveness to inhaled bronchoconstrictor stimuli, such as methacholine or histamine, has become an important tool in the diagnosi s of asthma. This is measured by patients inhaling increasing doses or conc entrations of the bronchoconstrictor stimulus until a given level of bronch oconstriction is achieved. Inhaled allergens initiate processes that increa se airway inflammation and enhance airway hyperresponsiveness in asthmatic subjects. Studies using inhaled allergen challenges have provided insight i nto how changes in airway hyperresponsiveness are regulated by induced infl ammatory processes. These changes in airway hyperresponsiveness (1-2 doubli ng doses) have been shown to be of much smaller magnitude than those demons trated when asthmatics with stable airway hyperresponsiveness are compared to normals (4-8 doubling doses). These allergen-induced changes would be of little relevance in subjects with normal airway responsiveness, because th ey would not increase the degree of airway responsiveness into the asthmati c range. They are, however, important in asthmatics who already have airway hyperresponsiveness because they are similar to changes associated with wo rsening asthma control. It is likely that the mechanisms responsible for th e changes in airway hyperresponsiveness following experimental allergen exp osure are similar to those producing transient worsening of control in asth matics. Nevertheless, it is unlikely that the mechanisms of the transient a llergen-induced airway hyperresponsiveness will explain the underlying mech anisms of the persistent airway hyperresponsiveness in asthmatic patients w hen compared with normal individuals.