Airway Response to Inhaled Methacholine in Normal Human Subjects

Abstract Summary: The individual airway responsiveness to inhaled, nebulized methacholine (MeCh) was estimated in normal volunteers, measuring specific airway conductance (s G AW). The dose of MeCh was increased logarithmically until a 60-65% reduction from baseline s G AW or an asymptotic approach to a maximal response was attained. The concentration of MeCh that caused a 35% reduction in s G AW (PC 35 ), the dose that caused a 62.5% reduction in s G AW, the slope of the straight, central part of the log-dose-response curve (LDRC), the slope of the straight, initial part of the dose-response curve, the maximal response attainable (E max ) and the dose causing a half-maximal response (ED 50 ) were derived. These parameters were transformed as necessary to attain normality of distribution. Relationships between them were examined by measuring the correlations between their transformed values. The ED 50 was taken to represent the least biased estimate of the sensitivity to MeCh. The PC 35 was the best practical estimate of sensitivity. The E max was taken to represent the least biased estimate of the reactivity to MeCh. The slope of the LDRC was the best practical estimate of reactivity. The sensitivity and reactivity varied independently in these normal subjects. Each was also independent of the baseline s G AW.