Background: The optimal particle size of a beta 2 agonist or anticholinergic aerosol in patients with severe airflow obstruction is unknown.
Methods: Seven stable patients with a mean forced expiratory volume in one second (FEV1) of 37.9% of the predicted value inhaled three types of monodisperse salbutamol and ipratropium bromide aerosols with particle sizes of 1.5 microns, 2.8 microns, and 5 microns, respectively, and a placebo aerosol. The volunteers inhaled 20 micrograms salbutamol and 8 micrograms ipratropium bromide, after which lung function changes were determined and analysed with repeated measurements analysis of variance (ANOVA).
Results: Greater improvements in FEV1, specific airway conductance (sGaw) and maximum expiratory flow at 75%/50% of the forced vital capacity (MEF75/50) were induced by the 2.8 microns aerosol than by the other particle sizes.
Conclusions: In patients with severe airflow obstruction the particle size of choice for a beta 2 agonist or anticholinergic aerosol should be approximately 3 microns.