Early smoking-induced lung lesions in asymptomatic subjects. Correlations between high resolution dynamic CT and pulmonary function testing.

PURPOSE: To evaluate the prevalence and significance of the pathological effects of cigarette smoking on the lung and the sensitivity of high-resolution CT (HRCT) in the recognition of early smoking-induced lesions in asymptomatic former or current smokers.
MATERIALS AND METHODS: We performed a prospective and consecutive analysis of 36 volunteers (16 males, 20 females), 10 non-smokers (3 males; 7 females) and 26 smokers (13 males; 13 females / 17 current smokers; 9 former smokers), all asymptomatic and with normal respiratory flows. These subjects underwent lung function testing and HRCT, after providing written informed consent for the study. The HRCT scans were obtained at three pre-selected levels (aortic arch, tracheal carina and venous hilum). The same scans were obtained in post-expiration phase. At the level of the apical segmental bronchus of the right upper lobe, we measured on the monitor wall thickening, and the total and internal diameters using the techniques reported in literature. Each study was independently evaluated by two radiologists that were blinded to all clinical and functional data; they also evaluated the presence, prevalence and type of emphysema, areas of patchy hyperlucency and oligoemia in the inspiration phase and areas of expiratory air trapping. The extension was evaluated with the visual score method. The data obtained were analysed with the Windows SPSS package for statistical analysis.
RESULTS: The two groups (non smokers and smokers) showed significant differences in some functional tests such as FEV1 (p<0.005) and Tiffeneau index (p<0.005), which were lower in current-smokers or former-smokers, although still within the normal range. The HRCT study did not show areas of emphysema or air trapping in non smokers. In the smokers' group, air trapping was observed in 30.7% of cases: 33.3% former-smokers and 29.4% current smokers (mean extension was 21.36% in former smokers and 9.48% in current smokers). Mean extension in the smokers' group was 13.94%. Pulmonary emphysema was found in 34.6% of cases in the smokers' group: 33.3% former-smokers and 35.2% current-smokers. Emphysema was prevalent in the upper lobes (88.8%). Mean extension was 8.76% in the former smokers group and 18.81% in current-smokers, with a total mean extension of 15.47% in the smokers' group. Statistically, there was a significant difference between non-smokers and smokers as regards emphysema extension and expiratory air trapping (p=0.034 and p=0.050, respectively). The smokers' group had a significantly wider diameter of the apical segmental bronchus of the right upper lobe than the controls. There was no significant statistical correlation between this dilatation and the emphysema score (r=0.051; p=0.81). The entity of smoking history did not correlate with emphysema extension or air trapping or with the size of the apical segmental bronchus of the right upper lobe.
CONCLUSIONS: Our study demonstrates that HRCT is more sensitive and specific than commonly-used functional tests for the evaluation of initial emphysema in asymptomatic smokers. We observed expiratory air trapping only in the smokers' group, and only of the lobular type, without evidence of disease in inspiratory scans. Among the smokers and former-smokers, air trapping was found in 30.7% of subjects, with a mean extension lower than 10%. Our results therefore suggest that, even in asymptomatic subjects, expiratory air trapping is probably pathological and, once bronchial asthma has been excluded, it may be related to cigarette smoking and indicate early inflammatory bronchiolar damage. HRCT may therefore be regarded as a useful tool in the early diagnosis of smoking-related lung disease.