Bronchial hyperreactivity

The abnormal response of airway smooth muscle has been used to define bronchial hyperreactivity and has been the subject of most investigations, but it has been suggested that hyperreactivity of other systems, such as those regulating mucous secretion, cough, pulmonary vasomotor tone, and the pattern of breathing, might also occur. An increased response of airway smooth muscle is so characteristic of asthma that it has been proposed as a criterion for the diagnosis of the disease and the measurement of bronchial reactivity has been used as a diagnostic test in patients with unexplained cough or dyspnea. Nevertheless, the cause or causes of bronchial hyperreactivity are unknown. The purposes of this article are to review the current methods and problems in the study of airway smooth muscle contraction, to discuss some possible mechanisms of hyperreactivity, and to relate these findings to clinical problems that involve bronchospasm.