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Signs of Gas Trapping in Normal Lung Density Regions in Smokers
Journal article   Open access   Peer reviewed

Signs of Gas Trapping in Normal Lung Density Regions in Smokers

Sandeep Bodduluri, Joseph M Reinhardt, Eric A Hoffman, John D Newell Jr, Hrudaya Nath, Mark T Dransfield, Surya P Bhatt and COPDGene Investigators
American journal of respiratory and critical care medicine, Vol.196(11), pp.1404-1410
12/01/2017
DOI: 10.1164/rccm.201705-0855OC
PMCID: PMC5736979
PMID: 28707983
url
https://doi.org/10.1164/rccm.201705-0855OCView
Published (Version of record) Open Access

Abstract

A substantial proportion of subjects without overt airflow obstruction have significant respiratory morbidity and structural abnormalities as visualized by computed tomography. Whether regions of the lung that appear normal using traditional computed tomography criteria have mild disease is not known. To identify subthreshold structural disease in normal-appearing lung regions in smokers. We analyzed 8,034 subjects with complete inspiratory and expiratory computed tomographic data participating in the COPDGene Study, including 103 lifetime nonsmokers. The ratio of the mean lung density at end expiration (E) to end inspiration (I) was calculated in lung regions with normal density (ND) by traditional thresholds for mild emphysema (-910 Hounsfield units) and gas trapping (-856 Hounsfield units) to derive the ND-E/I ratio. Multivariable regression analysis was used to measure the associations between ND-E/I, lung function, and respiratory morbidity. The ND-E/I ratio was greater in smokers than in nonsmokers, and it progressively increased from mild to severe chronic obstructive pulmonary disease severity. A proportion of 26.3% of smokers without airflow obstruction had ND-E/I greater than the 90th percentile of normal. ND-E/I was independently associated with FEV (adjusted β = -0.020; 95% confidence interval [CI], -0.032 to -0.007; P = 0.001), St. George's Respiratory Questionnaire scores (adjusted β = 0.952; 95% CI, 0.529 to 1.374; P < 0.001), 6-minute-walk distance (adjusted β = -10.412; 95% CI, -12.267 to -8.556; P < 0.001), and body mass index, airflow obstruction, dyspnea, and exercise capacity index (adjusted β = 0.169; 95% CI, 0.148 to 0.190; P < 0.001), and also with FEV change at follow-up (adjusted β = -3.013; 95% CI, -4.478 to -1.548; P = 0.001). Subthreshold gas trapping representing mild small airway disease is prevalent in normal-appearing lung regions in smokers without airflow obstruction, and it is associated with respiratory morbidity. Clinical trial registered with www.clinicaltrials.gov (NCT00608764).
 Female Forced Expiratory Volume - physiology Gases Humans Lung - diagnostic imaging Lung - physiopathology Male Middle Aged Pulmonary Disease, Chronic Obstructive - diagnostic imaging Pulmonary Disease, Chronic Obstructive - etiology Pulmonary Disease, Chronic Obstructive - physiopathology Severity of Illness Index Smokers Smoking - adverse effects Smoking - physiopathology Surveys and Questionnaires Tomography, X-Ray Computed Walk Test

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