文献紹介

喫煙者（現喫煙・過去喫煙）のCT画像の気管断面積（呼気時の狭窄）は現在の呼吸機能の悪さと将来の呼吸機能の悪化に関連している。
CT撮影は最大吸気位(total lung capacity),、安静呼気位(functional residual capacity), 、一部の被検者に最大呼気位(residual volume)で撮影。それぞれ呼吸機能検査における肺気量で表現している。

Surya P. et al.
Association Between Expiratory Central Airway Collapse and Respiratory Outcomes Among Smokers
JAMA. 2016;315(5):498-505. doi:10.1001/jama.2015.19431 

Central airway collapse greater than 50% of luminal area during exhalation (expiratory central airway collapse [ECAC]) is associated with cigarette smoking and chronic obstructive pulmonary disease (COPD). 

Analysis of paired inspiratory-expiratory computed tomography images from a large multicenter study (COPDGene) of current and former smokers, enrolled from January 2008 to June 2011 and followed up longitudinally until October 2014.
Computed tomography scans were performed at maximal inspiration (total lung capacity), end-tidal expiration (functional residual capacity), and, at 1 center, at residual volume.
Images were initially screened using a quantitative method to detect at least a 30% reduction in minor axis tracheal diameter from inspiration to end-expiration. From this sample of screen-positive scans, cross-sectional area of the trachea was measured manually at 3 predetermined levels (aortic arch, carina, and bronchus intermedius) to confirm ECAC (>50% reduction in cross-sectional area).

The study included 8820 participants with and without COPD (4667 [56.7%] men; 4559 [51.7%] active smokers). The prevalence of ECAC was 5% (443 cases).
Patients with ECAC compared with those without ECAC had worse SGRQ scores (30.9 vs 26.5 units; P < .001; absolute difference, 4.4 [95% CI, 2.2-6.6]) and mMRC scale scores (median, 2 [interquartile range [IQR], 0-3]) vs 1 [IQR, 0-3]; P < .001]), but no significant difference in 6-minute walk distance (399 vs 417 m; absolute difference, 18 m [95% CI, 6-30]; P = .30), after adjustment for age, sex, race, body mass index, forced expiratory volume in the first second, pack-years of smoking, and emphysema.
On follow-up (median, 4.3 [IQR, 3.2-4.9] years), participants with ECAC had increased frequency of total exacerbations (58 vs 35 events per 100 person-years; incidence rate ratio [IRR], 1.49 [95% CI, 1.29-1.72]; P < .001) and severe exacerbations requiring hospitalization (17 vs 10 events per 100 person-years; IRR, 1.83 [95% CI, 1.51-2.21]; P < .001).
In a cross-sectional analysis of current and former smokers, the presence of ECAC was associated with worse respiratory quality of life.