Using DPM CT Analysis to Assess the Contribution of Small Airways Disease in COPD

Introduction: COPD is characterised by airflow limitation, caused by parenchymal destruction and small airways disease. This study aims to use a novel quantitative CT method (DPM) to assess the contribution of small airways disease in COPD. Methods: 38 Mild-moderate COPD subjects, 21 ex (ES) and 17 non-smokers (NS) had CT chest performed in inspiration and expiration. Image analysis was performed by VIDA Lungprints (DPM), which registers inspiratory and expiratory images, classifying each voxel as normal, emphysema or gas trapping due to small airway disease (DPMGT). Results: Minimal emphysema was found (COPD 1.3%, ES 0.0%, NS 0.0%). Significantly more DPMGT in COPD (12.3%) was found compared to ES (2.2%) or NS(1.4%). There were significant associations between DPMGT and FEV1% (-0.67) and peripheral airway resistance (R5-R19) (0.54). Strong associations between overall and lobar values of DPMGT (rho 0.78-0.96) were found. Greater lobar quantities of DPMGT were found in COPD compared to controls (p<0.001) (Table 1). There were significant differences in DPMGT between lobes for all groups, being most marked in COPD (p<0.001). The middle lobe, followed by the upper lobes had the greatest quantity of DPMGT. Conclusion: Even in subjects with mild COPD significant small airways disease was detected using DPM analysis. By exhibiting strong associations with pulmonary function and accurately describing the distribution of gas trapping, this technique demonstrates its potential to study the small airways in COPD.