Ventilatory response to bronchospasm induced by methylcholine and histamine in man

In 9 normal subjects, we compared mouth occlusion pressure (P0.1) and breathing pattern in bronchospasm of the same magnitude induced by inhalation of acetyl-beta-methylcholine (M) and histamine phosphate (H). The measurements were performed on two different days, in a single blind randomized crossover design, under basal conditions first, then after control inhalation of isotonic buffered saline and finally after inhalation of M or H. For a same mean decrease in FEV1 (+/- SD) by 22.2% (+/- 7.2) after M and 22.3% (+/- 9.4) after H (P less than 0.001), the increases in P0.1 were similar (P less than 0.01 for both drugs) and were correlated to the magnitude of the bronchospasm (r = 0.775, P less than 0.01 for M; r = 0.692, P less than 0.05 for H). However, the minute ventilation and breathing pattern parameters did not differ from each other and from basal or control conditions. Thus, although we can assume that both drugs have different effects on vagal airway receptors, they induce the same respiratory response. We conclude that only receptors indirectly stimulated via airway smooth muscle contraction contribute to the mediation of drive and breathing pattern in drug induced bronchospasm in humans.