Diffusing Capacity is an Independent Predictor of Outcomes in Pulmonary Hypertension Associated with Chronic Obstructive Pulmonary Disease.
Patients with chronic obstructive pulmonary disease (COPD) who develop pulmonary hypertension (PH) have worse mortality than those with COPD alone. Predictors of poor outcomes in COPD-PH are not well described. Diffusing capacity of the lung (DLCO) assesses the integrity of the alveolar-capillary interface and thus may be a useful prognostic tool among those with COPD-PH.Using a single center registry, we sought to evaluate DLCO as a predictor of mortality in a cohort of COPD-PH patients.This retrospective cohort study analyzed 71 COPD-PH patients from the Johns Hopkins Pulmonary Hypertension Registry with right heart catheterization (RHC)-proven PH and pulmonary function testing (PFT) data within 1 year of diagnostic RHC. Transplant-free survival was calculated from index RHC. Adjusted transplant-free survival was modelled using Cox proportional hazard methods, with age, pulmonary vascular resistance (PVR), FEV1, oxygen use, and N-terminal pro-brain natriuretic peptide (NT-proBNP) included as covariates.Overall unadjusted transplant-free 1-, 3-, and 5-year survival was 87%, 60%, and 51% respectively. Survival was associated with reduced DLCO across the observed range of pulmonary artery pressures and PVR. Severe DLCO impairment was associated with poorer survival (log-rank ꭕ2 13.07, p<0.001), and adjusting for covariates, for every percent predicted decrease in DLCO, mortality increased by 4% (HR 1.04; 95% CI:1.01-1.07).Among patients with COPD-PH, severe gas transfer impairment is associated with higher mortality, even when adjusting for airflow obstruction and hemodynamics, suggesting that DLCO may be a useful prognostic marker in this population. Future studies are needed to further investigate the association between DLCO and morbidity, and to determine the utility of DLCO as a biomarker for disease risk and severity in COPD-PH.