A study was carried out in 6 patients with bronchial asthma to investigate the effects of clenbuterol, a β2-sympathomimetic bronchodilator, on peripheral airway obstruction. The basal lung functions of the patients were almost within normal range in both vital capacity (VC) and forced expiratory volume in 1 second (FEV1), but their maximal flow rates were lower in effort-independent phase of both maximal expiratory flow volume (MEFV) curve and partial expiratory flow volume (PEFV) curve. Furthermore, they demonstrated marked basal frequency dependence of dynamic compliance [CDdyn]. Oral administration of clenbuterol (40 μg) produced a significant increase in the maximal flow in effort-independent phase of both MEFV and PEFV curves, and markedly decreased frequency dependence of CDdyn in comparison with the baseline values, while it improved both VC and FEV1 to a lesser extent. These results suggest that clenbuterol preferentially reduced the peripheral airway obstruction in bronchial asthma.
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