Effect of aerosol particle size on bronchodilatation with nebulised terbutaline in asthmatic subjects

Abstract

The bronchodilatation achieved by the β2 agonist terbutaline sulphate given as nebulised aerosol from different devices has been measured in seven patients with mild asthma (mean FEV1 76% predicted) over two hours after inhalation. The subjects were studied on four occasions. On three visits they received 2.5 mg terbutaline delivered from three different types of nebuliser, selected on the basis of the size distribution of the aerosols generated; and on a fourth (control) visit no aerosol was given. The size distributions of the aerosols expressed in terms of their mass median diameter (MMD) were: A: MMD 1.8 μm; B: 4.6 μm; C: 10.3 μm. The aerosols were given under controlled conditions of respiratory rate and tidal volume to minimise intertreatment variation. Bronchodilator response was assessed by changes in FEV1, forced vital capacity (FVC), peak expiratory flow (PEF), and maximal flow after expiration of 50% and 75% FVC (V̇max50, V̇max25) from baseline (before aerosol) and control run values. For each pulmonary function index all three aerosols gave significantly better improvement over baseline than was seen in the control (p < 0.05) and had an equipotent effect on FEV1, FVC, and PEF. Aerosol A (MMD 1.8 μm) produced significantly greater improvements in V̇max50 and V̇max25 than did B or C (p < 0.05). These results suggest that for β2 agonists small aerosols (MMD < 2 μm) might be advantageous in the treatment of asthma.