To investigate whether histamine (His) and methacholine (MCh) have different effects on airways and lung parenchyma, 11 healthy subjects were given aerosol MCh until a response plateau was obtained and then two doses of His. At the plateau, forced expiratory volume in 1 s and forced expiratory flow at 40% of vital capacity from partial flow-volume curves were reduced by 19 +/- 3 (SE) and 80 +/- 4%, respectively. Aerosol His decreased forced expiratory volume in 1 s by an additional 12 +/- 1% but left partial forced expiratory flow unchanged. The bronchodilator effect of deep inhalation, as inferred from the ratio of forced expiratory flow from maximal to that from partial flow-volume curves, increased after MCh and plateaued but decreased after His. Quasi-static transpulmonary pressure-volume area determined in seven subjects was unchanged after MCh but was increased by 57 +/- 10% after His. We conclude that adding His after the response to MCh plateaued does not increase the maximal degree of bronchoconstriction but may increase parenchymal hysteresis, thus blunting the bronchodilator effect of deep inhalation. These results suggest that His and MCh have similar effects on airway smooth muscle but different effects on lung tissue properties.
- Copyright © 1993 the American Physiological Society