Distribution of methacholine inhalation challenge responses in a selected adult population

To determine bronchial reactivity patterns in adults, 211 subjects, 22 to 86 years of age, underwent a methacholine challenge in a Natural History of Asthma study. The diagnosis of asthma or nonasthmatic allergic diseases was based on a standardized respiratory questionnaire. Subjects were nonsmokers and had not had an infection for 1 month. Intradermal skin tests were done to a battery of common antigens. The methacholine challenge response was expressed as the area under the dose-response curve integrated to a 35% fall in the FEV₁ or 800 breath units. Thirty-three subjects with asthma, 47 normal subjects from normal families (NF), 59 normal subjects from families with asthma (AF), 31 allergic subjects without asthma, 23 subjects with questionable asthma, and 18 subjects with prior asthma were studied. Overall, 50% of the subjects without asthma had a negative response to methacholine. There was a difference (p < 0.02) in the distribution of log₁₀ methacholine area under the dose-response curve integrated to a 35% fall in the FEV₁ or 800 breath units responses in normal subjects from NFs compared to normal subjects from AFs. The allergic subjects from AF had a greater degree of bronchial reactivity compared to normal individuals from NF. The age of the normal subjects had an influence on the degree of bronchial reactivity. Methacholine challenge studies in adult patients need to be interpreted with age and family history in mind.