The prognostic value of DLCO and pulmonary blood flow in patients with pulmonary hypertension

BACKGROUND: Cardiac output is a prognostic marker in patients with pulmonary hypertension. Pulmonary blood flow as a surrogate for cardiac output can be measured non-invasively by inert gas rebreathing. We hypothesized that pulmonary blood flow can predict outcome in patients with pulmonary hypertension. METHODS: From January 2009 to January 2012, we measured pulmonary blood flow by inert gas rebreathing in outpatients with pulmonary hypertension. Patients with pulmonary hypertension confirmed by right heart catheterization and a valid inert gas rebreathing maneuver were followed until January 2016. The investigated outcome was all-cause mortality. RESULTS: We included 259 patients (mean age 65 ± 13 years, 53% female) with pulmonary hypertension and classified into groups 1 (n = 103), 2 (n = 26), 3 (n = 80), and 4 (n = 50) according to the current pulmonary hypertension classification system. The median time between pulmonary hypertension diagnosis and inert gas rebreathing was 9 (IQR 0; 36) months. During a median follow-up time of 51 (IQR 20; 68) months, 109 patients (42%) died. Parameters significantly associated with survival (in order of decreasing statistical strength) were diffusion capacity of the lung for carbon monoxide (DLCO), 6-minute walk distance (6-MWD), age, NTpro-BNP, WHO functional class, group 3 pulmonary hypertension, and tricuspid annular plane systolic excursion (TAPSE), while baseline hemodynamics and pulmonary blood flow were not. In multivariable Cox regression analysis, DLCO, age, 6-MWD, and TAPSE remained significant and independent predictors of the outcome. DLCO as the strongest parameter also significantly predicted survival in aetiological subgroups except for group 4. CONCLUSIONS: DLCO is a strong and independent predictor for survival in patients with pulmonary hypertension of different aetiologies, while pulmonary blood flow measured by inert gas rebreathing is not.