A Comparison of Bronchial Reactivity in Methacholine and Histamine Inhalation Challenge with a Continuous Tidal Breathing Method

Potential differences in pharmacologic provocation of the airway may exist among asthmatics. To compare the bronchial responsiveness to methacholine and histamine, we studied 7 normals and 12 asymptomatic asthmatic subjects with the oscillation method during continuous tidal breathing. While none of the normal healthy subjects demonstrated hyperresponsiveness to the administered agonists, all of the asthmatics had a positive challenge to both methacholine and histamine. Elevation of respiratory resistance (Rrs) values occurred in the asthmatics after provocation. Although the correlation between methacholine and histamine sensitivity in asthmatics patients was good, we did observe 2cases where the differences in the provocative cumulative dose (Dc) between methacholine and histamine were greater than 10 units. We conclude that intra-individual variability should be considered when comparing bronchial responsiveness to methacholine and histamine in asthmatics.