Partial flow-volume curves to measure bronchodilator dos-response curves in normal humans

We examined the use of partial expiratory flow-volume (PEFV) curves to obtain dose-response curves to an inhaled beta 2-adrenoceptor agonist (salbutamol) in eight normal subjects. Maximum expiratory flow at low lung volumes increased on both PEFV and full expiratory flow-volume curves, but the increase was always considerably greater on PEFV (28.4%) than on full (14.5%) curves. The percent increase in flow on the PEFV curve was not significantly influenced by the preceding volume history being 90-120 s of tidal breathing, forced expiration to residual volume, or breath holding after a full inflation. These results suggest that normal tone during tidal breathing is temporarily reduced but not abolished by a full inflation, and once basal tone has been restored it is not enhanced by a full expiration. In seven of the eight subjects a satisfactory cumulative dose-response curve to inhaled salbutamol was obtained with a plateau value of maximum flow at a dose of 110 microgram. The relatively good reproducibility of PEFV curves and the considerable bronchodilator signal obtained (29-70% increase in flow above base line in different individuals) suggest that such dose-response curves may be useful in studying normal bronchial pharmacology in vivo.