Background -The optimal particle size of a P2 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 gm, 2.8 rtm, and 5 gm, respectively, and a placebo aerosol. The volunteers inhaled 20 ftg salbutamol and 8 ftg 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%150% of the forced vital capacity (MEF75/50) were induced by the 2.8 gm aerosol than by the other particle sizes. Conclusions -In patients with severe airflow obstruction the particle size of choice for a 2 agonist or anticholinergic aerosol should be approximately 3 ftm.(Thorax 1996;51:977-980) Keywords: aerosols, particle size, bronchodilators. the greatest bronchodilatation.4 To reach the smaller airways in such cases it may be necessary for the particle size of the inhaled aerosol to be decreased. In patients with severe airflow obstruction, aerosols with a smaller particle size may be more suitable. We therefore carried out experiments to determine the most suitable particle size for bronchodilator aerosols in patients with severe airflow obstruction. Methods PATIENTSEight patients (six men) started the trial but one dropped out for personal reasons. The mean (SD) age of the remaining seven was 55 (4) years, and the mean forced expiratory volume in one second (FEVI) was 37.9 (7.3)% of the predicted value. In all patients a more than 15% increase in baseline FEV1 after inhalation of 200 jg salbutamol had been measured just before the trial. None of the patients was smokers. All used inhaled corticosteroids and none used disodium cromoglycate or oral antiasthma medications. Their regular medication other than corticosteroids was discontinued 6-8 hours before the start of the trial, and long acting 12 agonists were stopped 15 hours before the trial. All patients gave their written consent before entry into the study which was approved by the hospital ethics committee.

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By changing the polydisperse characteristic of inhaled aerosols to a monodisperse pattern, the dose of the drug administered can be reduced without loss of efficacy.