Effective site of bronchodilation by antiasthma drugs in subjects with asthma

We studied the effective sites of airway response to atropine and fenoterol aerosols and to the intravenous injection of aminophylline in patients with stable and spontaneous asthma, by the simultaneous assessment of respiratory resistance (Rrs) and anatomic dead space (VD). Central airway response was determined by VD, and overall response was determined by Rrs. Peripheral airway response was inferred from Rrs when the change in VD was slight. Atropine (4 mg/ml) or fenoterol (0.4 mg/ml) was continuously inhaled during tidal breathing for 5 minutes. Inhalation of both atropine and fenoterol increased Grs (reciprocal of Rrs) (p less than 0.01) with a simultaneous increase in VD (p less than 0.01) in the patients with stable and spontaneous asthma. Fenoterol increased Grs more than did atropine at an equivalent increase in VD in patients with spontaneous asthma (p less than 0.05). Intravenous injection of aminophylline (250 mg) had no effect on either Grs or VD in patients with stable asthma, but it significantly increased Grs (p less than 0.01) without change in VD in patients with spontaneous asthma. These results suggest that the predominant sites of bronchodilation induced by inhaled atropine are the central airways, that those sites induced by intravenous injection of aminophylline are the peripheral airways, and that inhaled fenoterol dilates both the central and peripheral airways in subjects with asthma. Differences among clinically used bronchodilators on the effective sites may be considered in the treatment of bronchial asthma.