[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.目的： 定量分析无症状吸烟者在多层螺旋CT(MSCT)呼吸双相扫描下肺气肿及空气潴留(AT)，并探讨其与肺功能的相关性。 方法： 收集2013年9月至2016年9月在第二军医大学长征医院进行体检的72例吸烟者，根据肺功能检查结果分为吸烟慢性阻塞性肺疾病(COPD组)24例和吸烟非COPD组48例，另纳入39名不吸烟且肺功能正常的健康志愿者作为对照组。所有受试者均接受MSCT呼吸双相扫描和肺功能检查。CT肺气肿定量参数包括：深吸气末阈值－950 HU以下低衰减区占全肺体积的百分率(LAA%(－950))、深吸气末全肺像素CT值直方图上第15百分位点对应的CT值(P(15-IN)),深呼气末全肺像素CT值直方图上第15百分位点对应的CT值(P(15-EX))、呼吸相对容积改变(RVC)及平均肺密度呼吸比值(E/I(MLD))。肺功能参数包括：第1秒用力呼气容积实测值占预计值百分率(FEV(1)%)、FEV(1)与用力肺活量的比值(FEV(1)/FVC)、残气量与肺总量比值(RV/TLC)及单位肺泡容积一氧化碳扩散量(DLCO/VA)。运用单因素方差分析或Kruskal-Wallis H检验比较三组间CT定量参数、肺功能指标的差异，采用Spearman相关分析评价CT定量参数与肺功能指标的相关性。 结果： 对照组、吸烟非COPD组及吸烟COPD组间肺气肿参数LAA%(－950)(三组数值分别为0.5%±0.7%、0.7%±1.2%及2.0%±2.4%)、P(15-IN)[三组数值分别为(－892±33)、(－905±15)及(－907±22) HU]差异均有统计学意义(均P<0.05)；肺功能参数FEV(1)%(三组数值分别为88.4%±8.8%、84.2%±7.5%及82.1%±8.0%)、FEV(1)/FVC(三组数值分别为78.0%±3.8%、76.6%±4.3%及67.3%±5.5%)、DLCO/VA[三组数值分别为(1.36±0.25)、(1.30±0.22)及(1.21±0.22) mmol·min(－1)·kPa(－1)·L(－1)]、RV/TLC(三组数值分别为49.5%±6.6%、45.9%±6.0%及53.0%±6.4%)差异均有统计学意义(均P<0.05)。不吸烟对照组的LAA%(－950)与FEV(1)/FVC、DLCO/VA(r＝－0.32，P＝0.04；r＝－0.69，P＝0.00)，P(15-IN)与FEV(1)%(r＝－0.14，P＝0.02)均存在负相关性；P(15-IN)与DLCO/VA(r＝0.55，P＝0.00)存在正相关性。吸烟非COPD组的LAA%(－950)与FEV(1)/FVC、DLCO/VA(r＝－0.31，P＝0.04；r＝－0.42，P＝0.00)均存在负相关性；P(15-IN)与FEV(1)/FVC、DLCO/VA(r＝0.33，P＝0.02；r＝0.30，P＝0.04)均存在正相关性。吸烟COPD组的LAA%(－950)与DLCO/VA存在负相关性(r＝－0.62，P＝0.00)，与RV/TLC存在正相关性(r＝0.59，P＝0.00)；P(15-IN)与DLCO/VA存在正相关性(r＝0.53，P＝ 0.01)。 结论： MSCT呼吸双相扫描能有效评价吸烟者肺气肿及空气潴留的改变，且LAA%(－950)及P(15-IN)指标能更敏感评价吸烟者肺功能改变。.