Evaluation of a metered-dose aerosol delivery system using partial flow-volume curves

In 12 normal subjects, FEV1, FVC, peak expiratory flow rate, and flow at 25% of FVC on maximal (MEFV) and partial (PEFV) expiratory flow volume maneuvers were measured before and after inhalation of 2.6 mg of metaproterenol from a metered-dose inhaler (MDI) or from an MDI-holding chamber (MDI-HC) delivery system. The 2 delivery systems were studied on separate days using a randomized crossover design. Premetaproterenol pulmonary function results were very similar on both days. However, on the MDI-HC day, significantly greater bronchodilatation was observed; this was only detectable on PEFV maneuvers. Compared with those on the MDI day, postmetaproterenol PEFV rates on the MDI-HC day were approximately 11% higher (p less than 0.02); premetaproterenol to postmetaproterenol increments in PEFV rates were also larger on the MDI-HC day (p less than 0.05). These results can be explained by the phenomenon of airway hysteresis. The deep breath taken prior to performance of the FVC maneuver reduced bronchomotor tone in almost all subjects, thereby limiting the magnitude of possible change from inhaled bronchodilator. Partial flow-volume curves were not preceded by deep inspiration and were more sensitive in detecting bronchodilatation.