[Volumetric correction of the maximal expiratory flow 25-75% in chronic obstructive bronchopneumopathies]

After inhalation of a bronchodilator aerosol, indices of airway obstruction usually improve whereas the forced expiratory flow between 25 and 75% (FEF25-75%) of the forced vital capacity (FVC) commonly remains the same or may decrease. This is due to the fact that the FEF25-75% after bronchodilatation is measured at lower absolute lung volumes with subsequently less elastic recoil pressure. A goal of this study was to analyze this test after volume adjusting so that the flows before and after a bronchodilator are compared at equal volumes (isovolume). Thirty-seven men with chronic obstructive pulmonary disease (COPD) performed maximal forced expiratory maneuvers before and 15 minutes after isoproterenol (0.15 mg) inhalation. The mean value of isovolume (0.56 +/- .30 1. sec-1) was significantly greater (p less than 0.001) than the FEF25-75% recorded before (0.45 +/- .26 1. sec-1) and after (0.50 +/- .27 1. sec-1, p less than 0.01) bronchodilator inhalation. The FVC was improved in 18 patients but only 6 (33%) had an improved conventional FEF25-75%. On the other hand, isovolume FEF improved in 12 (66%) patients. Isovolume FEF also improved twice as frequently as conventional FEF25-75% in those demonstrating an improvement in forced expiratory volume in the first second (FEV1). Furthermore, when the conventional FEF25-75% demonstrated no improvement after isoproterenol inhalation, isovolume improved in 8/26 (31%) of these patients. Our results suggest that volume adjusting the FEF25-75% after isoproterenol inhalation increases its sensitivity for detecting acute bronchodilation in patients with COPD, and that this methods appears practical in routine pulmonary function testing.