Correlation of bronchial responsiveness to diluent and to histamine.

Histamine inhalation tests were performed in 113 subjects, who were then classified by their response to histamine as normal (n = 26), mild bronchial hyperreactivity (n = 32), moderate bronchial hyperreactivity (n = 48) and marked bronchial hyperreactivity (n = 7). The response to inhaled sterile isotonic saline, the diluent, was measured as the percentage of change in FEV1 and the four groups were compared. Over-all there was a wide range of bronchial response to diluent, between +12 and -29% FEV1 change. There was little difference in the mean FEV1 change of the diluent (all less than 2%) in normals, mildly and moderately hyperreactive subjects. However, the markedly hyperreactive subjects were significantly more responsive to diluent than any other group, showing 11.7 +/- 4.4% FEV1 fall. We conclude that the mean bronchial responsiveness to diluent increases with increasingly severe nonspecific bronchial responsiveness to inhaled histamine.