Association Between DLCO and Echocardiographic Right Ventricular-Pulmonary Arterial Coupling in Idiopathic Pulmonary Fibrosis

Background: Idiopathic pulmonary fibrosis (IPF) is frequently complicated by pulmonary vascular involvement and right ventricular (RV) dysfunction, both of which adversely affect prognosis. The relationship between impaired gas exchange and echocardiographic indices of RV function, particularly the TAPSE/PAPs (tricuspid annular plane systolic excursion/systolic pulmonary artery pressure) ratio as a marker of RV-pulmonary arterial (RV-PA) coupling, has not been fully characterized. Methods: We retrospectively evaluated 198 consecutive patients with IPF assessed at a single tertiary referral center between 2020 and 2026; 188 with complete pulmonary function testing were included in the main analyses. The primary exposure was gas exchange, measured by single-breath DLCO% (diffusing capacity of the lung for carbon monoxide) and stratified into four categories (Normal ≥ 80%, n = 21; Mild 60-79%, n = 56; Moderate 40-59%, n = 70; Severe < 40%, n = 41). The main outcome measures were echocardiographic indices of RV function-TAPSE, systolic pulmonary artery pressure (PAPs), and the TAPSE/PAPs ratio. Associations were assessed using Pearson's correlation, one-way ANOVA, and multivariable linear regression adjusted for age, sex, and smoking status, with the Mild group as the reference for categorical analyses. Results: Lower DLCO values were independently associated with higher PAPs (adjusted β = -0.24 mmHg per 1% DLCO, p = 0.004) and with a lower TAPSE/PAPs ratio (adjusted β = +0.005 per 1% DLCO, p = 0.040). Compared with the Mild reference group, patients with Severe DLCO reduction had markedly higher PAPs (+14.6 mmHg, p = 0.002) and a lower TAPSE/PAPs ratio (-0.37, p = 0.002), with attenuated findings in the Moderate category; the small Normal group did not differ significantly from the Mild one. TAPSE alone showed only a weak, non-significant trend (r = 0.195, p = 0.083). Conclusions: In patients with IPF, lower DLCO was independently associated with higher pulmonary artery pressure and, to a lesser extent, with reduced RV-PA coupling (a lower TAPSE/PAPs ratio), whereas RV longitudinal systolic function (TAPSE) appeared preserved. Among pulmonary function parameters, DLCO showed the strongest association with PAPs. In this exploratory, cross-sectional analysis, combined evaluation of DLCO and the TAPSE/PAPs ratio may help characterize right heart involvement in IPF; its value for pulmonary hypertension (PH) screening requires prospective confirmation.