Demonstration of dilatation of peripheral airways

To investigate the ability of various lung-function tests to demonstrate dilatation of peripheral airways, ten asthmatics inhaled increasing doses of a beta 2-agonist by two different and controlled techniques. Low inspiratory flow with a long post-inspiratory pause favoured peripheral deposition, and a high inspiratory flow with a short post-inspiratory pause favoured central deposition of drug in the airways. Ordinary spirometry, maximum expiratory flow rates after breathing air as well as a helium-oxygen mixture, a single breath N2-test and resistance of the respiratory system were obtained before and after each of five terbutaline doses with both inhalation techniques. By using a double-dummy technique, the study could be performed double blinded. Effects were compared at doses giving equal effects on PEF, assumed to represent equal deposition of bronchodilator and effects on central airways. At such 'iso delta PEF doses', particularly FVC and the slope of phase III of the N2-test improved more following the slow inhalation technique. It is concluded that changes in those tests reflect dilatation in peripheral airways in asthmatics.