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Original Research: COPD |

Not All Measures of Hyperinflation Are Created EqualGas Trapping and Hyperexpansion in COPD: Lung Structure and Clinical Correlates of Gas Trapping and Hyperexpansion in COPD: The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study

Benjamin M. Smith, MD; Eric A. Hoffman, PhD; Robert C. Basner, MD; Steven M. Kawut, MD; Ravi Kalhan, MD; R. Graham Barr, MD, DrPH
Author and Funding Information

From the Department of Medicine (Drs Smith, Basner, and Barr), College of Physicians and Surgeons, Columbia University, New York, NY; Department of Medicine (Dr Smith), McGill University Health Center, Montreal, QC, Canada; Department of Radiology (Dr Hoffman), University of Iowa Carver College of Medicine, Iowa City, IA; Department of Medicine (Dr Kawut), Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA; Asthma and COPD Program (Dr Kalhan), Division of Pulmonary and Critical Care, Feinberg School of Medicine, Northwestern University, Chicago, IL; and Department of Epidemiology (Dr Barr), Mailman School of Public Health, Columbia University, New York, NY.

Correspondence to: R. Graham Barr, MD, DrPH, Columbia University Medical Center, Presbyterian Hospital 9 E Room 105, 630 W 168th St, New York, NY 10032; e-mail: rgb9@columbia.edu


Part of this work has been presented in abstract form at the American Thoracic Society International Conference, May 17-22, 2013, Philadelphia, PA.

Funding/Support: This study was funded by the National Institutes of Health, National Heart, Lung, and Blood Institute [Grants R01-HL093081, R01-HL077612, and R01-HL075476; Contracts N01 HC 95159 through N01 HC 95165 and N01 HC 95169] and Fonds de la recherche en santé Québec.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2014;145(6):1305-1315. doi:10.1378/chest.13-1884
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Background:  Hyperinflation refers to a nonspecific increase in absolute lung volumes and has a poor prognosis in COPD. The relative contribution of increased airways resistance and increased parenchymal compliance to hyperinflation of each absolute lung volume is poorly understood. We hypothesized that increased residual volume (RV) and RV/total lung capacity (TLC) would be associated with reduced airway lumen dimensions, whereas increased functional residual capacity (FRC), TLC, and reduced inspiratory capacity (IC)/TLC would be associated with emphysema on CT scan. We examined whether clinical characteristics differed accordingly.

Methods:  The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study recruited smokers aged 50 to 79 years who were free of clinical cardiovascular disease. Gas trapping was defined as RV or RV/TLC greater than the upper limit of normal and hyperexpansion as FRC or TLC greater than the upper limit of normal or IC/TLC less than the lower limit of normal. Airway lumen diameters and percent emphysema < −950 Hounsfield units were quantified on CT images. Analyses were adjusted for age, sex, body size, race/ethnicity, education, and smoking.

Results:  Among 116 participants completing plethysmography, 15% had gas trapping, 18% has hyperexpansion, and 22% had both. Gas trapping was associated with smaller airway lumen diameters (P = .001), greater dyspnea (P = .01), and chronic bronchitis (P = .03). Hyperexpansion was associated with percent emphysema (P < .001), lower BMI (P = .04), and higher hemoglobin concentration (P = .001).

Conclusions:  Gas trapping and hyperexpansion on plethysmography were associated with distinct differences in lung structure and clinical characteristics. Absolute lung volumes should not be considered equivalent in their estimation of hyperinflation and provide insight into the extent of airway and parenchymal abnormalities in COPD.

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