Results of a clinical trial show that patients with pulmonary hypertension (PH) have a lower capacity for exercise during hypoxia. Investigators conducted a randomized controlled, single-blinded, crossover trial (ClinicalTrials.gov Identifier: NCT03592927) between August 2018 and April 2019 at the University Hospital Zürich in Zürich, Switzerland. They sought to explore the effect of hypoxia compared to normoxia on constant-work-rate-exercise-test (CWRET) time in patients with PH and to evaluate the physiologic mechanisms that are involved in the process. Adult patients who had been diagnosed with pulmonary arterial hypertension (PAH)/chronic thromboembolic pulmonary hypertension (CTEPH) — both summarized as PH herein — were recruited from outpatients of the PH-center Zürich. All of the participants were randomly assigned to breathe ambient air (normoxia, fraction of inspired oxygen [FiO2]: 21%) initially, followed by normobaric hypoxia (FiO2: 15%), or vice versa, using a sealed facemask with a non-rebreathing 2-way valve during 20 or more minutes of rest. This was followed by use of a symptom-limited cycle-ergometer CWRET until exhaustion. Get the full story at pulmonaryadvisor.com.