DEMONSTRATION OF DILATATION OF PERIPHERAL AIRWAYS

To investigate the ability of various lung-function tests to demonstra te 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 per ipheral deposition, and a high inspiratory flow with a short post-insp iratory pause favoured central deposition of drug in the airways. Ordi nary spirometry, maximum expiratory flow rates after breathing air as well as a helium-oxygen mixture, a single breath N-2-test and resistan ce of the respiratory system were obtained before and after each of fi ve terbutaline doses with both inhalation techniques. By using a doubl e-dummy technique, the study could be performed double blinded. Effect s were compared at doses giving equal effects on PEF, assumed to repre sent equal deposition of bronchodilator and effects on central airways . At such 'iso Delta PEF doses', particularly FVC and the slope of pha se III of the N-2-test improved more following the slow inhalation tec hnique. It is concluded that changes in those tests reflect dilatation in peripheral airways in asthmatics.