Regional lung function in nonsmokers and asymptomatic current and former smokers

Electrical impedance tomography (EIT) is able to detect rapid lung volume changes during breathing. The aim of our observational study was to characterise the heterogeneity of regional ventilation distribution in lung-healthy adults by EIT and to detect the possible impact of tobacco consumption. A total of 219 nonsmokers, asymptomatic ex-smokers and current smokers were examined during forced full expiration using EIT. Forced expiratory volume in 1 s (FEV(1)), forced vital capacity (FVC) and FEV(1)/FVC were determined in 836 EIT image pixels for the analysis of spatial and temporal ventilation distribution. Coefficients of variation (CVs) of these pixel values were calculated. Histograms and medians of FEV(1)/FVC(EIT) and times required to exhale 50%, 75%, 90% of FVC(EIT) (t(50), t(75) and t(90)) were generated. CV of FEV(1)/FVC(EIT) distinguished among all groups (mean±sd: nonsmokers 0.43±0.05, ex-smokers 0.52±0.09, smokers 0.62±0.16). Histograms of FEV(1)/FVC(EIT) differentiated between nonsmokers and the other groups (p<0.0001). Medians of t(50), t(75) and t(90) showed the lowest values in nonsmokers. Median t(90) separated all groups (median (interquartile range): nonsmokers 0.82 (0.67–1.15), ex-smokers 1.41 (1.03–2.21), smokers 1.91 (1.33–3.53)). EIT detects regional ventilation heterogeneity during forced expiration in healthy nonsmokers and its increase in asymptomatic former and current smokers. Therefore, EIT-derived reference values should only be collected from nonsmoking lung-healthy adults.