Shape of the dose-response curve to cold air inhalation in normal and asthmatic subjects

Inhalation of cold air at increasing levels of minute ventilation with assessment of bronchomotor tone between each inhalation (dose-response curve) has been used as a method to assess bronchial hyperresponsiveness. However, no information is available on the shape of the obtained dose-response curve, and it is not known if a plateau of response is reached. We investigated this problem in 13 adult asthmatic subjects (PC20 methacholine results varying from 0.04 to 15.2 mg/ml), 5 normal and 2 former asthmatic individuals (PC20 greater than 8 mg/ml). Inhalation dose-response curves were drawn by asking the subjects to inhale dry cold air (-20 degrees C) for 3 min at progressively increasing degrees of ventilation (5, 10, 15, 20, etc., L/min) until maximal voluntary ventilation (MVV) or sufficient bronchoconstriction was reached. FEV1 was assessed after each degree until no further decline was seen. No functional recovery was observed before asking the subject to inhale the next dose of cold air. Maximal falls in FEV1 ranged from 20.7 to 56.5% in the current asthmatic subjects, whereas no significant (less than 10%) changes in FEV1 were obtained in the normal and former asthmatic individuals. Seven to 13 points on the individual dose-response curves were obtained for each current asthmatic subject. Curves were analyzed using the common pharmacologic logistic model. The coefficients of correlation were, in general, highly statistically significant. Curves obtained for the current asthmatic subjects represented a truncated sigmoidal pattern without a plateau. Curves were flat in the normal and former asthmatic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)