Prospective interventional trial in lowlanders evaluating effect of acute exposure, acclimatization and re-exposure to high altitude.

Low altitude baseline measurements will be performed in Santiago de Chile, 520 m, over the course of 3 days. Participants will then travel by commercial airline (5 h flight) and by bus (3 h ride) to the Atacama large Millimeter Array (ALMA) base camp located at 2900 m near San Pedro de Atacama, northern Chile. Participants will stay there for the next 7 nights and they will be spend the days (6-8 h daily) at the telescope station at 5050 m while undergoing physiological testing. Daily transports from 2900 to 5050 m will be by car (1 h ride, one way). After the first 7 day altitude sojourn participants will return to the Santiago area (520 m) for a 7 day recovery period.

A second altitude sojourn cycle with an identical schedule as the one described above and a final low altitude stay of 3 days will follow.

Measurements on study subjects will be performed at baseline (lowland, Santiago de Chile), then at 2nd day of altitude exposure and 7th day at altitude before returning to lowland; those are repeated in the second altitude sojourn cycle. Measurements will be conducted by qualified specialists using a portable ultrasound device.

Inclusion Criteria:

• Born, raised and currently living <800m
• No overnight stay at altitudes > 1500m 4 weeks before the study

Exclusion Criteria:

• Previous altitude intolerance to altitude <3000m
• Pregnancy
• Health impairment, which requires regular treatment