Joyce Denise Schroeder MD, Presenter: Research grant, Siemens AG

John D. Newell MD, Abstract Co-Author: Research Consultant, Siemens AG Research grant, Siemens AG Consultant, WebMD Health Corp (WebMD, Inc) Author, The Humana Press

Jordan Zach, Abstract Co-Author: Nothing to Disclose

James R. Murphy, Abstract Co-Author: Nothing to Disclose

Carla G. Wilson, Abstract Co-Author: Nothing to Disclose

Eric A. Hoffman PhD, Abstract Co-Author: Shareholder, VIDA Diagnostics Medical Advisory Board, Siemens AG

David Augustine Lynch MB, Abstract Co-Author: Consultant, Actelion Ltd Research support, Siemens AG Consultant, Gilead Sciences, Inc Consultant, Novartis AG Scientific Advisor, Perceptive Informatics, Inc

In individuals with COPD, quantitative CT (QCT) has the potential to quantify emphysema and air trapping as distinct components of COPD which may be important for phenotyping of the disease and for subsequently devising individualized treatment. The purpose of this study is to evaluate the relationship between QCT measurements of emphysema and gas trapping and physiologic measures of disease severity.

QCT analysis (Pulmonary Workstation, VIDA Diagnostics) and spirometric evaluation were completed on 1759 subjects in the COPDGene Study (771 smoking controls without evidence of airway obstruction, 140 with GOLD Stage 1, 427 with GOLD Stage 2, 272 with GOLD Stage 3, and 149 with GOLD Stage 4). Subjects underwent volumetric CT at full inspiration (N=1759) and at the end of a normal expiration (N=1630). QCT analysis was performed using VIDA software. On QCT, % emphysema is defined as % lung voxels <= -950 Hounsfield units (HU) on inspiratory CT and % air trapping is defined as % lung voxels <= -856 HU on expiratory CT. Multivariate analysis was performed to evaluate the relationship between demographic, clinical and QCT variables and FEV1 % predicted and FEV1/FVC ratio.

Univariate R-squared regression values for the relationship between physiologic parameters and QCT for FEV1 % predicted are: 0.43 (% emphysema) and 0.61 (% air trapping). R-squared values for FEV1/FVC ratio are: 0.53 (% emphysema) and 0.71 (% air trapping.) P<0.0001 for all regression slopes. On multivariate analysis, significant predictors of lower FEV1 % predicted and FEV1/FVC ratio are: % air trapping on QCT (t ratios -42, -50), BMI (t ratios -8, -2), male gender (t ratios 2, 0), age at enrollment (t ratios 4, -0.8), and hours of supplemental oxygen use per day (t ratios -10, -8). These models account for 66% and 73% of variability in FEV1 % predicted and FEV1/FVC ratio, respectively. Of these ratios, % air trapping is the most powerful predictor based on its proportion of the total variance.

QCT is strongly associated with spirometric impairment in cigarette smokers. In particular, % air trapping, combined with clinical parameters, strongly correlates with physiologic measurements of airway obstruction.

Quantitative CT measurements of gas trapping and emphysema describe distinct components of COPD which may be important for phenotyping the disease and devising individualized treatment.

Schroeder, J, Newell, J, Zach, J, Murphy, J, Wilson, C, Hoffman, E, Lynch, D, Quantitative CT Measurements of Emphysema and Air Trapping Correlate with Physiologic Airway Obstruction in Smokers with Chronic Obstructive Pulmonary Disease (COPD): The COPD Gene Study.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9006365.html