Acute effects of aerosolized metaproterenol on breathing pattern of patients with symptomatic bronchial asthma.

We studied the effect of two sequential puffs of metaproterenol (650 micrograms each puff) delivered with an auxiliary aerosol delivery system on the breathing pattern of patients with symptomatic bronchial asthma who were monitored noninvasively with respiratory inductive plethysmography. Particular attention was directed to respiratory center drive as reflected by mean inspiratory flow and minute ventilation. Both these components were elevated in the eight patients whose mean FEV1.0 was 1.43 L (45% predicted normal). Two puffs of metaproterenol produced a maximal increase over baseline in FEV1.0 of 50 +/- 25% (SD), whereas no change took place in FEV1.0 with placebo administration. This dose of metaproterenol did not alter heart rate nor blood pressure throughout the study period of 2 hours. Neither mean inspiratory flow, minute ventilation, nor any component of the breathing pattern changed with this partial reversal of bronchoconstriction. These results suggest that the neural mechanism accounting for heightened respiratory center drive in patients with symptomatic bronchial asthma does not wholly depend on bronchoconstriction.