Adaptation of Lung Transplant Recipients at Extreme Altitude

Assessment of Pulmonary Function and Physiological Adaptation of Lung Transplant Recipients at Extreme Altitude: The Mount Aconcagua (6971 m) Expedition

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.

Study Overview

• Status: Active, not recruiting
• Conditions: Hypoxia; Immunosuppression; Lung Transplantation; Microbiota; Physical Fitness; Altitude; Oxygen Saturation Measurement; High-altitude Adaptation

• Study Type: Observational
• Enrollment (Estimated): 30

Contacts and Locations

Study Locations

• Austria
  • Vienna
    • Vienna, Vienna, Austria, 1090
      • Medical University of Vienna

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Lung transplant recipients and Healthy controls

Description

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)

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort
Healthy volunteers
Lung transplant recipients

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Change in forced expiratory volume in one second (FEV₁)	From enrollment to the end of the expedition at 3 weeks
Change in peripheral oxygen saturation (SpO₂) as a marker of physiological adaptation	From enrollment to the end of the expedition at 3 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Heart Rate Variability (HRV)		From enrollment to the end of the expedition at 3 weeks
Blood gas analysis (BGA)		From enrollment to the end of the expedition at 3 weeks
Acute mountain sickness (AMS)		From enrollment to the end of the expedition at 3 weeks
Level of immunosuppression		From enrollment to the end of the expedition at 3 weeks
Level of Torque Teno Virus (TTV)		Before enrollment until approx. 4 weeks after the end of the expedition
Voice analysis	Voice-based heart failure detection developed by Noah Labs uses artificial intelligence to analyze short voice recordings from patients with heart failure. Patients regularly record a standardized speech sample using a smartphone. Deep-learning algorithms extract numerous acoustic features such as frequency patterns and subtle variations in vocal cord vibration. The system identifies these changes as "voice biomarkers" and compares them with previous recordings. If patterns suggest worsening heart failure, clinicians can be alerted early, potentially allowing timely therapeutic adjustments and preventing hospitalizations. The study aims to investigate changes in height and in patients following lung transplantation.	Prior to enrollment to the end of the expedition at 3 weeks
Gut Microbiota Dynamics	The composition of the gut microbiota is being studied longitudinally using stool samples collected prior to the expedition and following successive ascents to high altitudes over the course of several weeks. The samples are analyzed to determine bacterial diversity and taxonomic composition. Microbial diversity indices, including Shannon, Simpson, and Chao1, are calculated to assess changes in community structure. In addition, the Bray-Curtis distance and the Jaccard index are used to assess differences in species distribution across time points. The relative abundance of bacterial taxa is quantified to identify shifts in pathogenic and beneficial microbial populations during altitude exposure.	Prior to enrollment to the end of the expedition at 3 weeks
Transthoracic echocardiography		Prior to enrollment to the end of the expedition at 3 weeks
Lung Ultrasound Score		Prior to enrollment to the end of the expedition at 3 weeks
Renin-angiotensin-aldosterone system		Prior to enrollment to the end of the expedition at 3 weeks
End-tidal CO₂ measurements		Prior to enrollment to the end of the expedition at 3 weeks
Continuous glucose monitoring		Prior to enrollment to the end of the expedition at 3 weeks

Collaborators and Investigators

• Sponsor: Medical University of Vienna

Publications and helpful links

Helpful Links

• Description of the project and the expedition

Study record dates

Study Major Dates

• Study Start (Actual): January 10, 2026
• Primary Completion (Estimated): May 30, 2026
• Study Completion (Estimated): June 30, 2026

Study Registration Dates

• First Submitted: January 19, 2026
• First Submitted That Met QC Criteria: March 15, 2026
• First Posted (Actual): March 18, 2026

Study Record Updates

• Last Update Posted (Actual): March 18, 2026
• Last Update Submitted That Met QC Criteria: March 15, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Signs and Symptoms, Respiratory; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Hypoxia
• Other Study ID Numbers: 2105/2025; EK Nr: 2105/2025 (Other Identifier: Ethics Committee of the Medical University of Vienna (MUW))

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No