Background Quantitative CT (QCT) scans of the lungs have been recently introduced for directing clinicians to the most appropriate lobes needing treatment with lung volume reduction (LVR) therapies. Changes in QCT have been considered as a key marker of procedure success. However, despite procedures aiming to improve quality of life and exercise tolerance, there has been no understanding if the degree of emphysema on QCTs correlates with the subjective and objective parameters used in patient selection for LVR.

Methods The pre-treatment QCT used was able to segment the lungs by tracing inter-lobar fissures thus providing data on the volume of each lobe. It was also able to digitally assess the proportion of emphysematous tissue area (defined by Hounsfield units of – 910 or less) in each lobe. Utilising these two properties we calculated the volume of the lungs affected by emphysema by the summation of the emphysema volumes in all lobes. Values and percentage predicted of FEV1, residual volumes (RV) and gas transfer for carbon monoxide (TLco) were obtained from standard measurements; along with a 6 min walk distance (6’WD) and COPD assessment test (CAT) score. Spearman non-parametric correlation test was used to correlate emphysema volume with these parameters.

Results A total of 47 patients (19 female), mean age (SD) of 66.2 (8.9) years were included. Their mean (SD) FEV1 was 0.81 L (0.28). There was no correlation between the total emphysema volume and CAT score (r=-0.21, p=0.2) or with 6’WD (r=-0.34, p=0.054). Total emphysema volume and the value of RV were strongly correlated; r=0.68, p<0.0001. There was no correlation with FEV1 or TLco values. However, percentage of predicted values of lung function tests weakly correlated with total emphysema volume; for FEV1 (r=-0.36, p=0.01), for RV (r=0.34, p=0.02) and for TLco (r=-0. 32, p=0.04).

Conclusion The lack of strong correlation between anatomical changes and lung function is probably due to changes in airway diameter (as well as tissue destruction) which is not captured by QCT. To add to that, the lack of correlation with 6’WD or CAT score is probably due to non-pulmonary factors affecting the values of these two measurements.