Small airway function in smokers without airway obstruction

Early detection of small airway (SA) dysfunction may help to identify smokers at risk of developing chronic airway obstruction. As there is no single accepted parameter to measure SA dysfunction, a combination of different techniques may be useful. 47 smokers (≥ 10 PY, mean age 49±12) without airway obstruction (FEV 1 /FVC and FEV 1 Z-Score ≥ -1.64) and 35 nonsmokers (mean age 44±12) were recruited. We performed standard lung function and three different small airway tests: Impulse oscillometry (IOS), nitrogen mulitple-breath washout (N 2 -MBW) and double-tracer gas single-breath washout (DTG-SBW). SA indices were defined as follows: Resistance at 5Hz (R5), fall in resistance from 5 to 20Hz (R5-20), resonant frequency (Fres), area index of low frequent reactance (AX), index of acinar ventilation heterogeneity (Sacin x Vt) and the slope of phase III (SIII DTG x Vt). Smokers had slightly lower values for FEV 1 (96±9% vs. 101±11%, p=0.02) and FVC (96±11% vs. 104±12%, p DTG x Vt (-0.263±0.159 g/mol vs. -0.206±0.102 g/mol, p=0.05). 26/47 smokers and 12/35 nonsmokers had at least one abnormal SA index. 15/47 smokers, but only 1/35 nonsmokers showed at least two abnormal SA indices. We detected two or more abnormal SA indices derived by gas washout and IOS in about one third of smokers. This test combination may help to define a subgroup of smokers at risk to develop rapid FEV 1 -decline.