Bronchial hyperreactivity.

Bronchial hyperreactivity is characterized by increased responsiveness of bronchial smooth muscle to non-specific constrictor stimuli. Tests used in assessing airway calibre are influenced by a number of factors and should be regarded as providing a qualitative rather than quantitative index of reactivity. One important determinant of bronchial reactivity is the resting state of the airways. An increase in resting bronchomotor tone either by the direct action of spasmogens or by the autonomic nervous system may potentiate a subsequent constrictor stimulus. Bronchial challenge may help in the diagnosis of asthma in patients with normal lung function at the time of testing.