Background: Associated pulmonary hypertension (APH) is frequently observed in fibrosing interstitial pneumonias (FIP), such as idiopathic pulmonary fibrosis (IPF). APH is associated with worse prognosis, but it remains unclear whether it is associated with greater functional impairment. Six-minute walk distance (6MWD) is widely used to assess functional capacity in pulmonary hypertension and FIP. Objectives: To investigate if APH independently contributes to exercise intolerance in FIP, irrespective of the extent of underlying fibrosis. Methods: Patients diagnosed with FIP (September 2009 to June 2017) were included in the study if they underwent right heart catheterization, high-resolution chest computed tomography (HRCT), and 6MWD within 3 months. Recruitment was not limited only to patients undergoing lung transplant assessment. APH was defined as mean pulmonary artery pressure (mPAP) ≥25 mm Hg. The extent of fibrosis was quantified on HRCT using a visual fibrosis score by 2 separate observers. Results: Seventy-two patients (60 with IPF) were identified. Fifty-five patients had APH. mPAP was not significantly different in subgroups stratified according to the extent of fibrosis on HRCT. Pulmonary vascular resistance (PVR) was the strongest predictor of 6MWD on both univariate and stepwise regression analyses, and remained so considering only patients with normal wedge pressure (< 15 mm Hg) (n = 61). HRCT fibrosis score and pulmonary function tests did not significantly correlate with 6MWD. Conclusions: In patients with FIP, PVR is a significant contributor of 6MWD, independently from the extent of fibrosis on HRCT. These results strengthen both the rationale to use 6MWD as endpoint in FIP and to target APH with specific therapies.

Keywords:
Pulmonary hypertension, Idiopathic pulmonary fibrosis, Pulmonary vascular resistance, Six-min walk distance, Exercise capacity
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