Relationship between Lung Function Parameters and CT Measurements of Emphysema, Airways, and Tracheal Collapse in Subjects with Mild COPD

PURPOSE. Excessive expiratory tracheal collapse may be related to chronic obstructive pulmonary disease (COPD). However, the relationship between tracheal changes, CT measurements, and lung function is not very well known. This study aims to assess the correlation between pulmonary function tests (PFT) and CT measurements of emphysema, airways, and tracheal collapse in patients with and without COPD. METHOD AND MATERIALS. A database of 1032 male subjects who received inspiration CT (16x0.75mm, 120-140 kVp, 30-160 mAs), expiration CT (90 kVp, 20 mAs) and PFT on the same day was constructed. 389 participants (38%) had COPD, defined as ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) <70%. The number of patients per GOLD stage (0-3) was 643, 247, 122, 20. CT parameters assessed were tracheal collapsibility (TCo), defined as the highest ratio of cross-sectional area of the trachea in expiration and inspiration; emphysema score (ES), computed as the percentage of lung voxels below -950 HU in inspiration scans; air trapping (AT), defined as the ratio of mean lung density in expiration and inspiration; and square root of the wall area of a hypothetical airway of 10-mm internal perimeter of segmental and subsegmental airways (Pi10). Correlations were evaluated using the Spearman correlation coefficients and differences between normal and COPD subjects with a StudentsAC/a,!a,,C/ t-test. RESULTS. ES, Pi10 and AT correlated (p < 0.01) with FEV1 (r= -0.17, r= -0.53, r= -0.36) and FEV1/FVC (r=-0.48, r=-0.34, r=-0.51). TCo did not correlate with FEV1 (r= 0.01), but with FEV1/FVC (r=-0.14). Mean A,A+- standard deviation (SD) ES, Pi10, AT, and TCo in the no-COPD group were 0.82 A,A+- 0.98, 2.29 A,A+- 0.44, 81.57 A,A+- 5.76, and 0.67 A,A+- 0.13. Mean A,A+- SD ES, Pi10, AT, and TCo in the COPD group were 2.80 A,A+- 4.04, 2.65 A,A+- 0.55, 87.18 A,A+- 4.93, and 0.7 A,A+- 0.14. These values were significantly different between both groups ( p < 0.0001). CONCLUSION. ES, Pi10, and AT are significantly different between normal and COPD subjects and are correlated to PFT. TCo is also significantly different between normal and COPD subjects but does not show a strong correlation with PFT. CLINICAL RELEVANCE/APPLICATION. Emphysema, tracheal collapse, and airway morpholgy obtained from chest CT data may be used to discriminate between normal and mild COPD subjects.