Correlations between volumetric capnography and automated computed tomography quantitative analysis in patients with severe COPD

Background: In chronic obstructive pulmonary disease (COPD), morphological analysis made by computed tomography (CT) is usually correlated with spirometry as the main functional tool. In this study, quantitative CT analysis (QCT) was compared with volumetric capnography (VCap), besides spirometry and 6-minute walk test (6MWT). Methods: 27 patients with severe/very severe COPD were included, compared with 19 control subjects. All participants performed spirometry and chest high resolution CT scans, analysed with a fully automated software. The COPD group was also submitted to VCap and 6MWT. Results: COPD patients (65.07±8.25 years) showed an average FEV₁ of 1.2 L (44% of the predicted) and the control group (34.36±8.78 years). VCap x QCT: positive correlations were observed with bronchial wall thickening and negative correlations with diameter and area of the bronchial lumen. Spirometry x QCT: positive correlations were observed between post-BD: FVC, FEV₁ and FEF25-75% and diameter and luminal area of the airways and, FVC and lung and vascular volumes (emphysema). Negative correlation between post-BD FVC and FEV₁ when compared to Pi10 (internal perimeter of 10 mm). 6MWT vs. QCT: negative correlations were observed between distance covered: with relative wall thickness (airways) and, vascular volume and peripheral vascular volume (vasculature). Conclusion: Relevant correlations between QCT and pulmonary function variables were found, including the VCap, highlighting the importance of structural analysis in conjunction with a multidimensional functional assessment. This is the first study to correlate airway and parenchyma QCT with VCap.