Validity of air-helium DVmax measurements in trials of bronchodilators.

The authors studied the intraindividual variability of DVmax50 He-air in a large homogeneous group of 57 young healthy subjects. They found a 95% confidence interval for a true change between two repeated measurements of DVmax50 of +/- 28%. They compared the discriminant power of FEV1, Vmax50 and DVmax50 in 27 asthmatic young males and 12 normal controls, challenged on different days with fenoterol and ipratropium bromide aerosols given in random order under standardized conditions. FEV1 was not able to discriminate between the effect of the drugs in the normals or asthmatics. Vmax50 increased significantly more after fenoterol than after ipratropium in the asthmatics. DVmax50 was sometimes increased after fenoterol in the asthmatics but not by ipratropium in this group. These results suggest that sympathomimetics are more active on peripheral airways than the antimuscarinics.