Pulmonary hypertension (PH) is a feared complication of interstitial lung disease (ILD) owing to increased risk for hospitalisation and mortality among affected patients. The development of PH in ILD is attributed to several pathobiological mechanisms that often converge to remodel pulmonary arterioles including hypoxic pulmonary vasoconstriction, endothelial dysfunction, inflammation, increased oxidant stress and the pathogenic effects of parenchymal fibrosis on the alveolar-capillary interface.1

The classical definition of precapillary PH used a mean pulmonary arterial pressure (mPAP) ≥25 mm Hg and pulmonary vascular resistance (PVR) ≥3 Wood units (WU), but these haemodynamic criteria were based largely on consensus opinion in the absence of normative data or information on the association between cardiopulmonary hemodynamics and outcomes. A retrospective meta-analysis involving data from healthy volunteers suggested that the upper limit of normal mPAP is ~20 mm Hg, which converged with findings in large referral cohorts suggesting that mPAP>20 mm Hg is common and associated with a substantial increase in mortality risk.2 3 Similarly, data on PVR suggest that values ≥2 WU are clinically important and have significant associations with mortality and hospitalisation for heart failure.4 These and other observations supported the recent revision to the haemodynamic criteria that defines precapillary PH as mPAP>20 mm Hg, PVR>2 WU, and pulmonary artery wedge pressure <15 mm Hg.5 6

Since most outcomes data are from unselected referral cohorts, there is an overarching …