Effect of Normobaric Hypoxia on Exercise Performance in Pulmonary Hypertension

Background Many patients with pulmonary arterial or chronic thromboembolic hypertension (PH) wish to travel altitude by airplane, but their risk of hypoxia-related adverse health effects is insufficiently explored. Research Question How does hypoxia, compared normoxia, affect constant work-rate exercise test (CWRET) time in PH, and which physiologic mechanisms are involved? Study Design Methods Stable PH resting Pao2 ? 7.3 kPa underwent symptom-limited cycling CWRET (60% maximal workload) while breathing normobaric hypoxic air (hypoxia; Fio2, 15%) ambient (normoxia; 21%) a randomized cross-over design. Borg dyspnea score, blood gases, tricuspid regurgitation pressure gradient, mean artery pressure/cardiac output ratio (mean PAP/CO) echocardiography were assessed before during end-CWRET. Results Twenty-eight (13 women) included: median (quartiles) age, 66 (54; 74) years; pressure, 41 (29; 49) mm Hg; vascular resistance, 5.4 (4; 8) Wood units. Under normoxia times 16.9 (8.0; 30.0) 6.7 (5.5; 27.3) min, respectively, difference (95% CI) –0.7 (–3.1 0.0) min corresponding –7 (–32 0.0)% (P = .006). At end-exercise values differences variables as follows: Pao2: 8.0 vs 6.4, –1.7 (–2.7 –1.1) kPa; oxygen content: 19.2 17.2, (–3 –0.1) mL/dL; Paco2: 4.7 4.3, –0.3 (–0.5 lactate: 3.7 3.7, 0.9 (0.1 1.6) mM < .05 all differences). Values for scale score: 7 6, 0.5 (0 1); gradient: 89 77, –3 (–9 16) PAP/CO: 4.5 3.3, 0.3 (–0.8 1.4) units remained unchanged. In multivariable regression, baseline resistance was the sole predictor hypoxia-induced change time. Interpretation short-time exposure hypoxia well tolerated reduced association hypoxemia, lactacidemia, hypocapnia. Because hemodynamics at unaltered, limitation may be due delivery causing peripheral tissue augmented lactic acid loading hyperventilation. Trial Registry ClinicalTrials.gov; No.: NCT03592927; URL: www.clinicaltrials.gov;