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 (ICpeak), peak workload (W peak), forced expiratory volume in 1 s (FEV1) and COPD Assessment Test (CAT) score (outcome variables), and in longitudinal (Anderson-Gill) models with "symptom-based" and "event-based" exacerbations. Results are reported as parameter estimates or hazard ratios (HRs) with 95% confidence intervals per interquartile range dome height increment.

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 ICpeak (0.21 (95% CI 0.13-0.29) L and 0.13 (95% CI 0.07-0.19) L), W peak (9.54 (95% CI 5.03-14.04) W and 6.04 (95% CI 2.45-9.62) W), FEV1 (0.17 (95% CI 0.10-0.25) L and 0.08 (95% CI 0.02-0.14) L) and CAT score (-1.36 (95% CI -2.39- -0.33) and -0.82 (95% CI -1.63-0.00)). LDDH alone was associated with both symptom-based (HR 0.82 (95% CI 0.74-0.91)) and event-based (HR 0.83 (95% CI 0.73-0.95)) exacerbations. Of 167 out of 304 participants with confirmed dynamic hyperinflation (ΔIC -0.47±0.25 L), LDDH alone was associated with all outcomes (ICpeak, W peak, FEV1, CAT and symptom-based/event-based exacerbations).

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.