This prospective observational study investigates the effects of intermittent hypoxic conditioning and real high-altitude exposure in lung transplant recipients compared with healthy controls.

The study includes an eight-week home-based preparatory phase during which participants use a normobaric hypoxic tent with reduced oxygen concentration. Prior to this phase, all participants receive standardized training on the safe use of the equipment. During the preparatory period, daily vital parameters, including heart rate, oxygen saturation, and heart rate variability, are recorded using a sports watch and a pulse oximeter. Symptoms, adverse events, and subjective well-being are documented daily in an electronic diary. All data are transmitted to the study team via encrypted electronic systems, allowing continuous remote monitoring. At the end of the preparatory phase, participants undergo a clinical evaluation to confirm fitness for the expedition phase.

The expedition phase consists of a monitored ascent of Aconcagua (6,971 meters). Before departure, all participants are required to attend a comprehensive safety, protection, and first aid training conducted jointly by the study team and professional expedition providers. The expedition is planned and led by an experienced international expedition company in cooperation with a local provider specializing in high-altitude mountaineering.

The expedition includes arrival in Mendoza, preparatory procedures such as equipment checks and permits, followed by a staged ascent to base camp. Subsequent days involve rest periods and acclimatization hikes with the establishment of progressively higher camps. A summit attempt is planned after sufficient acclimatization, followed by descent to high camp. A weather-dependent buffer period is included before the final descent to the valley and return to Mendoza, where the expedition concludes.

Total study participation is expected to last approximately 15 weeks, including about eight weeks of home-based preparation and approximately three weeks at altitude. A final follow-up examination is conducted 2 to 4 weeks after completion of the expedition, marking the end of study participation.

Inclusion Criteria:

Lung transplant recipients:

• Age ≥ 18 years
• > 1 years after lung transplantation
• Stable lung function over 6 month prior to inclusion, FEV1 +/-10% from baseline
• VO2peak of more than 25 ml/min/kg
• Physical and mental fitness, defined as the ability to complete strenuous day trips lasting 8 to 10 hours independently without suffering from a fear of heights, an altitude exposure of at least 2500m must be confirmed.
• Negative pregnancy test for women of childbearing age
• Written informed consent

Healthy volunteers:

• Age ≥ 18 years
• VO2peak of more than 25 ml/min/kg
• Physical and mental fitness, defined as the ability to complete strenuous day trips lasting 8 to 10 hours independently without suffering from a fear of heights
• Negative pregnancy test for women of childbearing age
• Written informed consent

Exclusion Criteria:

Lung transplant recipients:

• Age < 18 years
• Refusal to participate in the study
• Pregnancy

Healthy controls:

• Age < 18 years
• Refusal to participate in the study
• Pregnancy
• Chronic obstructive pulmonary disease (COPD)

Lung transplant recipients and Healthy controls