The concept of airway "sensitivity" and "reactivity".

Linear dose-response relationships can be obtained in vivo by measuring changes in airway conductance induced by graded doses of aerosolized bronchoconstrictor agents. Bronchial Sensitivity is defined as the dose causing the threshold response whereas Reactivity is the rate of response (slope of dose-response line). Determinants of bronchial response are complex and factors other than airway smooth muscle may play an important role (e.g. mucosal thickness). Examples are given of situations in which the concept of Reactivity and Sensitivity may be useful. Differences between in vitro and in vivo dose-response relationships are discussed.