Spirometrically gated high-resolution CT findings in COPD - Lung attenuation vs lung function and dyspnea severity

Study objectives: The aim of this study was to investigate the relationship between high-resolution CT (HRCT) lung attenuation measurements, acquired under spirometric control of inspiratory and expiratory lung volume, and pulmonary dysfunction as well as dyspnea severity in patients with COPD. Patients and design: In 51 patients with COPD, we compared by linear regression, univariate and multivariate logistic regression airflow limitation (FEV1/vital capacity [VC]), hyperinflation (percentage of predicted residual volume [RV%]), parenchymal loss (percentage of predicted diffusing capacity of the lung for carbon monoxide [DLCO%]) and Medical Research Council (MRC) dyspnea scale with relative area with attenuation values < -950 HU at 90% of VC [RAI(950)] and < -910 HU at 10% of VC, respectively, and with mean lung attenuation measured at the same levels of VC (mean CT lung density at 10% of VC, and mean CT lung density at 90% of VC [MeanCT(EXP)]). Results: All HRCT attenuation measurements were significantly related with functional abnormalities and dyspnea severity. In multivariate logistic models, with I indicating worse changes in dichotomous outcome variables, MeanCT(EXP) independently predicted FEV1/NC (odds ratio [OR], 0.24; 95% confidence interval [CI], 0.11 to 0.56), RV% (OR, 0.57; 95% CI, 0.42 to 0.77), and MRC dyspnea scale (OR, 0.63; 95% CI, 0.48 to 0.82), while RAI(950) independently predicted DLCO% (OR, 1.90; 95% CI, 1.37 to 2.65). Conclusions: Spirometrically gated measurements of HRCT lung attenuation reflect differently functional changes and dyspnea perception in COPD. Inspiratory measurements assess the extent of emphysematous tissue loss, and expiratory measurements may reflect airflow limitation and lung hyperinflation with attendant dyspnea perception. Pulmonary dysfunction in COPD cannot be assessed by a single modality of lung attenuation measurement.