Respiratory epithelial permeability is unrelated to bronchial reactivity and small airway function in young smokers and nonsmokers.

We studied eight young smokers and ten nonsmokers, to determine whether respiratory epithelial permeability to radiolabelled diethylenetriamine penta-acetate (99mTcDTPA) was related to small airway function or bronchial reactivity. Permeability was measured in inner (containing central airways) and outer lung zones by gamma camera. Lung-to-blood half-time (LB-T1/2) was corrected for blood background. Histamine was inhaled tidally (2 min inhalations) using doubling concentrations from 2 to 64 mg.ml-1. Results of small airway function tests, and of bronchial reactivity (expressed as the threshold concentration (reducing forced expiratory volume in one second (FEV1) by 2 SD), and as the percentage reduction in FEV1 after histamine 16 mg.ml-1) were similar in smokers and nonsmokers. LB-T1/2 was shorter in smokers than in nonsmokers in both inner (median (range) 21 (5.5-33) vs 63.5 (41-115) min; p less than 0.004) and outer (20.5 (5.5-30) vs 58.5 (39-105) min; p less than 0.004) zones. Neither inner nor outer zone LB-T1/2 was related to small airway function or bronchial reactivity. Bronchial reactivity and small airway tests may be abnormal in middle-aged smokers, but neither is related to the increased respiratory epithelial permeability of young smokers, in whom it appears too sensitive an index of airway integrity.