Tracheobronchial clearance in bronchial asthma: response to beta-adrenoceptor stimulation

Tracheobronchial clearance was studied in 12 patients with bronchial asthma. They inhaled a test aerosol of 6 mum teflon particles tagged with 99mTc, after which external measurement of the radioactivity in the lungs was made for 2 h in the supine position. Clearance was determined after subcutaneous administration of 0.25 mg of the beta-adrenoceptor stimulating compound terbutaline and vehicle, respectively, in a crossover, double-blind study. The average clearance in the asthmatics did not differ significantly from that of healthy non-smokers. Terbutaline significantly enhanced clearance in the asthmatics, though considerably less than reported for healthy subjects. Alternative explanations for this weak effect of terbutaline in the asthmatics might be that the mucociliary transport system was affected by the asthma disease, or that earlier treatment with beta-adrenoceptor stimulating compounds or other drugs had produced increased tolerance and/or carry-over effects. Ventilatory function measured as FEV1.0 deteriorated significantly during the clearance measurement when vehicle was given, but not when terbutaline was given. Terbutaline thus counteracted the unfavourable effect of the supine position on ventilation.