Effects of volume history and time dependence of flow-volume curves on assessment of bronchial response to inhaled methacholine in normals.

The behavior of maximum expiratory flow-volume curves and partial expiratory flow-volume curves with and without volume history of total lung capacity was studied in 11 healthy subjects before and after methacholine inhalation challenge. Flow-volume curves were superimposed at absolute lung volumes by measuring thoracic gas volumes at which inspiratory maneuvers began. The results show that maximum inspiratory effort reduced significantly residual volume, either before or after challenge, while flow rates at 40% of control total lung capacity achieved with partial expiratory flow-volume curves with history of total lung capacity were significantly greater than those without history of maximal inflation. These findings are explained by the stress relaxation as an effect of volume history ot total lung capacity and by the appearance of time dependence as an index of inhomogeneity of lung emptying. After methacholine the effects of volume history on maximum flows and residual volume were increased. In conclusion, the results of this study emphasize the probability of errors when only maximum expiratory flow-volume curve are used in assessment of bronchial responses.