Effect of fenoterol on small airways and regional lung function in asymptomatic asthma.

Lung function tests for small airways were performed before and after inhalation of fenoterol by 11 young asymptomatic asthmatics and in 8 control subjects. In the asthmatics, minimal impairment in the tests was found except for increased expansion of the lower part of the lung (133Xe regional lung volumes) and an "abnormal" distribution pattern of a bolus of Xe inhaled from the residual volume. This suggests enhanced airway closure, especially in the lower area of the lung. Usual therapeutic doses of fenoterol (0.4 to 0.6 mg in puffs) could not correct these abnormalities, but 1.2 mg given to 2 patients resulted in changes similar to those observed in normals. The results suggest that small airway impairment in asymptomatic asthmatics is not only related to enhanced bronchomotor tone, but also to anatomical changes located especially at the base of the lung.