Not all measures of hyperinflation are created equal: lung structure and clinical correlates of gas trapping and hyperexpansion in COPD: the Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study.
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 &lt; -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 &lt; .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.
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY; Department of Medicine, McGill University Health Center, Montreal, QC, Canada.
Benjamin M
BM
Smith
Department of Radiology, University of Iowa Carver College of Medicine, Iowa City, IA.
Eric A
EA
Hoffman
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY.
Robert C
RC
Basner
Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.
Steven M
SM
Kawut
Asthma and COPD Program, Division of Pulmonary and Critical Care, Feinberg School of Medicine, Northwestern University, Chicago, IL.
Ravi
R
Kalhan
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY; Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Electronic address: rgb9@columbia.edu.
R Graham
RG
Barr
D000368:Aged; D050197:Atherosclerosis / Q000208:ethnology; D016022:Case-Control Studies; D006801:Humans; D007320:Inspiratory Capacity / Q000502:physiology; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D010641:Phenotype; D010993:Plethysmography, Whole Body; D029424:Pulmonary Disease, Chronic Obstructive / Q000208:ethnology / Q000473:pathology* / Q000503:physiopathology*; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging / Q000503:physiopathology; D012115:Residual Volume / Q000502:physiology; D013147:Spirometry; D014057:Tomography, X-Ray Computed; D014109:Total Lung Capacity / Q000502:physiology