Utility of diaphragm dome height as a marker of operational lung volume changes, disease burden and exacerbations in patients with mild-to-moderate COPD: an observational study within the CanCOLD cohort.

Background: Dynamic hyperinflation is central to dyspnoea, exercise limitation and exacerbations in COPD. While studied previously in moderate-to-severe COPD, the relevance of diaphragm dome height (DDH) on clinically important outcomes has been under-investigated in mild-to-moderate COPD. Methods: Canadian Cohort Obstructive Lung Disease (CanCOLD) participants with spirometry-confirmed COPD, symptom-limited incremental cardiopulmonary exercise testing and computed tomography image data were included. Base-to-apex left DDH (LDDH) and right DDH (RDDH) were automatically segmented, with increased height implying less flattening and thus less hyperinflation. Dynamic hyperinflation was defined as ≥150 mL reduction in inspiratory capacity (IC) from rest to peak exercise. Cross-sectional linear regression models were fitted between LDDH and RDDH (predictor variables) with peak IC (IC Results: Amongst 304 participants (mean±sd age 64.7±10.3 years, 41.8% female, 44.4% with mild COPD), each LDDH and RDDH increment, respectively, was associated with IC Conclusions: LDDH appears to be a clinically important marker for operational lung volume changes, lung function, exercise performance, disease burden and exacerbations in mild-to-moderate COPD.