Effect of a deep inspiration on expiratory flow in normals and patients with chronic obstructive pulmonary disease.

Normal control subjects and individuals with chronic obstructive pulmonary disease (COPD) were studied by measuring routine lung function tests as well as maximal (MEFV) and partial expiratory flow-volume (PEFV) curves and lung elastic recoil (Pst,L) before and after a total lung capacity (TLC) volume history. In the normal subjects: before bronchodilators airflow increased significantly, whereas Pst,L and upstream segment resistance (Rus) decreased significantly following inspiration to TLC; after administration of inhaled bronchodilators, flow rates were higher on the PEFV than on MEFV curves; nevertheless, because Pst,L decreased substantially following a deep breath, post-bronchodilator Rus was still somewhat reduced by deep inspiration. In the subjects with COPD flow rates on PEFV curves were as high or exceeded flow rates on MEFV curves in 76/100 studies; the ratio of flow rates (PEFV)/flow rates (MEFV) increased as pulmonary function worsened; as in normal subjects, Pst,L diminished in COPD subjects following deep inspiration; although flow rates increased on both PEFV and MEFV curves after bronchodilators, the increments in flow were considerably larger on PEFV maneuvers.