[Significance of specific time constant and F-V curve configuration in evaluating small airway function for smokers]

To evaluate the clinical significance of the specific time constant (S tau) and F-V curve configuration in testing small airway functions for smokers, routine ventilatory functions, S tau and F-V curve configuration were studied in 116 passive and light, heavy active smokers. Routine ventilatory functions and F-V curve configuration were determined with routine method. S tau were calculated from S tau = 1/V. The results showed that the distribution of convex type rose with the degree of smoking, and the decrease of V50, V25 and elongation of S tau 50, S tau 25 in convex type were just consistent with heavy smokers. The range of elongation of S tau 50 and S tau 25 was 120%-130% of predicted value in both heavy smokers and convex type. These showed there were slight disturbances in functions of small airways. Compared with COPD patients previously measured, their S tau 75, S tau 50, S tau 25 all prolongated to higher degree and meant both large and small airways were affected. Therefore, the convex type, elongation of S tau 50 and S tau 25, and decrease of V50 and V25 were sensitive indices for detecting small airway functions. They can be recommended for clinical application.