Acute effects of normobaric hypoxia on invasively measured exercise hemodynamics in patients with pulmonary vascular disease. The HEXA-RCT

<bold>Introduction:</bold> Short-term normobaric hypoxia does not relevantly alter invasive pulmonary hemodynamics at rest in patients with pulmonary vascular diseases (PVD, pulmonary arterial or chronic thromboembolic pulmonary hypertension, PAH/CTEPH). The aim of this study was to further investigate the attenuated hypoxic pulmonary vasoconstriction by invasive exercise hemodynamics. <bold>Methods:</bold> PVD-patients scheduled for right heat catheterization (RHC) had supine assessments at rest. Thereafter, they were placed in 45°semi-supine position on a cycling ergometer and breathed ambient air (21% FiO2) or normobaric hypoxia (15%FiO2) for 10 min at rest, followed by two 3-min-steps exercise at 10-20 or 20-40 Watts. The sequence was repeated after a wash-out period of >15min with the other FiO2 according to a randomized cross-over design. Main outcomes assessed after >10’ rest and end-exercise with respective FiO2 were arterial PO2, mean pulmonary artery pressure (mPAP), cardiac output (CO, assessed by direct Fick), and mPAP/CO-slope during exercise. <bold>Results:</bold> We included 23 PVD-patients (10 women): 15 PAH, 8 distal CTEPH, 16 prevalent/pretreated, mean±SD age 53±15 years. Arterial oxygenation was lower but hemodynamics at rest and end-exercise as well as the mPAP/CO-slope were similar whilst breathing FiO2 21 vs. 15%. <bold>Conclusion:</bold> This first RCT on the effect of acute exposure to normobaric hypoxia vs. ambient air in PVD-patients assessed during exercise RHC shows that hypoxia equivalent to ≈2500m does not change resting nor end-exercise pulmonary hemodynamics. Pressure-flow-slope during mild exercise remains unalterd despite significantly decreased blood oxygenation.