Dose-response effects of two sizes of monodisperse isoproterenol in mild asthma

The dose-response effect of monodispersed isoproterenol of two different sizes (diameters 2.5 and 5 microns) was examined in eight mild asthmatic subjects (baseline FEV, 81.5% of predicted). Pulmonary and cardiovascular variables were measured before and following 1, 2, 4, 8, and 16 cumulative min of aerosol inhalation. Subjects inhaled 1 to 30 micrograms (2.5-microns particles) or 2 to 50 micrograms (5-microns particles) of isoproterenol. Pulmonary but not cardiac responses were significantly greater for the 2.5-microns particles as compared to equivalent doses of 5-microns particles. Pulmonary dose-related response differences were particularly marked for variables associated with small airway function (FEF25-75 and FEF75-85). These findings suggest that small particles penetrate more deeply into the lung and thereby more effectively dilate small airways and that small amounts of appropriately sized inhaled bronchodilator may produce considerable therapeutic effects.