Tests of small airway dysfunction: their correlation with the "conventional" lung function tests.

"Sensitive" and "conventional" lung function tests were compared in a group of 114 males, aged 35-55 years, including healthy non-smokers, asymptomatic smokers with normal spirometry, and smokers with chronic bronchitis with or without mild airflow limitation. In non-smokers, with the exception of a MEF vs. FEV1 correlation, "sensitive" and "conventional" tests were independent of each other. In asymptomatic smokers the phase III slope and the closing volume were significantly related to FEV1, RV/TLC and CO transfer factor. In smokers with chronic bronchitis all the "sensitive" tests were related to the "conventional" tests (with the exception of the total lung capacity). Hyperinflation and CO transfer impairment suggest that early emphysema may accompany mucus hypersecretion in smokers.