@article {1433653,
	title = {Association Between Expiratory Central Airway Collapse and Respiratory Outcomes Among Smokers},
	journal = {JAMA},
	volume = {315},
	number = {5},
	year = {2016},
	month = {2016 Feb 02},
	pages = {498-505},
	abstract = {IMPORTANCE: 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). However, its prevalence and clinical significance are unknown.

OBJECTIVE: To determine whether ECAC is associated with respiratory morbidity in smokers independent of underlying lung disease.

DESIGN, SETTING, AND PARTICIPANTS: Analysis of paired inspiratory-expiratory computed tomography images from a large multicenter study (COPDGene) of current and former smokers from 21 clinical centers across the United States. Participants were enrolled from January 2008 to June 2011 and followed up longitudinally until October 2014. 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).

EXPOSURES: Expiratory central airway collapse.

MAIN OUTCOMES AND MEASURES: The primary outcome was baseline respiratory quality of life (St George{\textquoteright}s Respiratory Questionnaire [SGRQ] scale 0 to 100; 100 represents worst health status; minimum clinically important difference [MCID], 4 units). Secondary outcomes were baseline measures of dyspnea (modified Medical Research Council [mMRC] scale 0 to 4; 4 represents worse dyspnea; MCID, 0.7 units), baseline 6-minute walk distance (MCID, 30 m), and exacerbation frequency (events per 100 person-years) on longitudinal follow-up.

RESULTS: The study included 8820 participants with and without COPD (mean age, 59.7 [SD, 6.9] years; 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 ,
	keywords = {Aged, Aged, 80 and over, Disease Progression, Dyspnea, Exercise Tolerance, Exhalation, Female, Forced Expiratory Volume, Humans, Inhalation, Longitudinal Studies, Male, Middle Aged, Pulmonary Atelectasis, Pulmonary Emphysema, Quality of Life, Respiration, Smoking, Tomography, X-Ray Computed, Tracheal Diseases},
	issn = {1538-3598},
	doi = {10.1001/jama.2015.19431},
	author = {Bhatt, Surya P and Terry, Nina L J and Nath, Hrudaya and Zach, Jordan A. and Tschirren, Juerg and Bolding, Mark S and Stinson, Douglas S and Wilson, Carla G and Curran-Everett, Douglas and Lynch, David A and Putcha, Nirupama and Soler, Xavi and Wise, Robert A and Washko, George R and Hoffman, Eric A and Foreman, Marilyn G and Dransfield, Mark T}
}