Comparison of three techniques of inhalation on the airway response to terbutaline

The relative efficiency of the metered dose inhaler (MDI), the MDI attached to a pear shaped extension tube (PET), and the Inspiron Mini-Neb nebuliser were assessed in eight normal and eight asthmatic subjects. Subjects inhaled the same increasing doses of terbutaline with each technique on different occasions and the response was measured as specific airway conductance (sGaw) and, in the asthmatic patients only, as FEV1. The PET produced greater bronchodilatation than either the MDI or the nebuliser in both normal and asthmatic subjects. Serum terbutaline concentrations were similar after the PET and MDI in the normal subjects, but were lower with the PET in the asthmatic patients. The nebuliser produced about the same amount of bronchodilatation as the MDI--slightly less in the normal subjects and slightly more when assessed as FEV1 in the asthmatic subjects. Serum terbutaline concentrations were lower after the nebuliser than after the MDI in both groups of subjects. For patients with moderately severe airways obstruction requiring large doses of beta agonist, the nebuliser will produce an amount of bronchodilatation similar to the MDI with lower blood levels. Overall, the PET produced greater bronchodilatation than either of the other two methods of inhalation, with low serum terbutaline concentrations similar to those produced by the nebuliser in the asthmatic patients.