New assessment of airway responsiveness. Effect of pretreatment with procaterol on allergen-induced bronchoconstriction.
We examined airway responsiveness to allergen inhalation using a novel technique by which dynamic compliance (Cdyn) and pulmonary resistance (Rl) are simultaneously calculated by Fourier-series analysis of flow and transpulmonary pressure during tidal breathing. C0 and C0.5 (Cdyn at the frequency of zero and 0.5 Hz, respectively) were computed using the regression line of Cdyn versus frequency measured at the fundamental and first three harmonics in each breathing cycle. First, the validity of this system was tested by comparing Rl, C0 and C0.5 during five consecutive breaths with those obtained by the conventional method. A good correlation was seen in Rl, C0 and C0.5 between the two methods. Second, we studied airway response to allergen inhalation before and after oral administration of a long-acting beta 2-stimulant (procaterol, 50 micrograms or 100 micrograms) or placebo in a double-blind crossover trial in six atopic asthmatic subjects. In control allergen inhalation tests by administration of placebo, Rl increased progressively, and C0.5, expressed as percentage of control compliance at zero frequency (C0.5/COcont), decreased progressively. After 100 micrograms procaterol, Rl response to allergen was almost completely inhibited. However, a decrease in C0.5/C0cont was still observed. These findings suggest that pretreatment of asthmatic patients with procaterol can release allergen-induced bronchoconstriction of the central airways, but cannot release that of the peripheral airways.