[Quantitative analysis of emphysema and air trapping at inspiratory and expiratory phase multi-slice spiral CT scan in smokers: correlation with pulmonary function test].

Objective: To quantify emphysema and air trapping at inspiratory and expiratory phase multi-slice spiral CT(MSCT) scanning in smokers without respiratory symptoms, and analyze the correlation between the CT quantifiable parameters and lung function parameters. Methods: A total of 72 smokers, who underwent medical examinations from September 2013 to September 2016 in Changzheng Hospital were enrolled in this research and were divided into two groups: 24 smokers with COPD and 48 smokers without COPD.Besides, thirty-nine non-smokers with normal pulmonary function were enrolled as the controls.All subjects underwent double phase MSCT scanning and pulmonary function tests.CT quantifiable parameters of emphysema included the low attenuation area below a threshold of -950 Hounsfield Units (HU)(LAA%(-950)), the lowest 15th percentile of the histogram of end-inspiratory attenuation values (P(15-IN)), the lowest 15th percentile of the histogram of end-expiratory attenuation values (P(15-EX)), relative volume change(RVC) and the expiratory to inspiratory ratio of mean lung density (E/I(MLD)). Pulmonary function parameters included forced expiratory volume in 1 second expressed as percent predicted (FEV(1)%), forced expiratory volume in one second to forced vital capacity ratio (FEV(1)/FVC), residual volume to total lung capacity ratio (RV/TLC) and carbon monoxide diffusion capacity corrected for alveolar volume (DLCO/VA). The differences of CT quantifiable parameters and pulmonary function parameters among the three groups were analyzed by using one-way analysis of variance or Kruskal - Wallis H test.The correlation between CT quantifiable parameters and pulmonary function parameters was analyzed by using Spearman ' s correlation analysis. Results: The differences of LAA%(-950)(the values for the controls, the group of smokers with out COPD and the group of smokers with COPD were 0.5%±0.7%, 0.7%±1.2% and 2.0%±2.4% respectively), P(15-IN)(the values of the three groups were (-892±33), (-905±15) and (-907±22) HU respectively), FEV(1)%(the values of the three groups were 88.4%±8.8%, 84.2%±7.5% and 82.1%±8.0% respectively), FEV(1)/FVC(the values of the three groups were 78.0%±3.8%, 76.6%±4.3% and 67.3%±5.5% respectively), DLCO/VA (the values of the three groups were (1.36±0.25), (1.30±0.22) and (1.21±0.22) mmol·min(-1)·kPa(-1)·L(-1) respectively) and RV/TLC (the values of the three groups were 49.5%±6.6%, 45.9%±6.0% and 53.0%±6.4% respectively) among the three groups were statistically significant (all P <0.05). In the control group, LAA%(-950) negatively correlated with FEV(1)/FVC and DLCO/VA( r =-0.32, P =0.04; r =-0.69, P =0.00) and neither did P(15-IN) with FEV(1)%( r =-0.14, P =0.02). Inversely, P(15-IN) positively correlated with DLCO/VA ( r =0.55, P =0.00). In the group of smokers without COPD, LAA%(-950) negatively correlated with FEV(1)/FVC and DLCO/VA( r =-0.31, P =0.04; r =-0.42, P =0.00), and P(15-IN) positively correlated with FEV(1)/FVC and DLCO/VA ( r =0.33, P =0.02; r =0.30, P =0.04). In the group of smokers with COPD, LAA%(-950) negatively correlated with DLCO/VA ( r =-0.62, P =0.00), but positively correlated with RV/TLC ( r =0.59, P =0.00). And P(15-IN) positively correlated with DLCO/VA( r =0.53, P =0.01). Conclusions: Smokers emphysema and air trapping can be effectively evaluated by double phase MSCT. Moreover, two of the CT quantifiable parameters, LAA%(-950) and P(15-IN), are highly sensitive to changes in pulmonary function.