Acute mountain sickness is not repeatable across two 12-hour normobaric hypoxia exposures

Area of Science:

• Altitude research
• Human physiology
• Environmental medicine

Background:

• Acute mountain sickness (AMS) is a common condition at high altitudes.
• Understanding AMS repeatability is crucial for research and prevention strategies.

Purpose of the Study:

• To assess the repeatability of AMS, its symptoms, and physiological responses.
• To compare outcomes across two identical hypoxic exposures.

Main Methods:

• 25 subjects underwent two identical normobaric hypoxia exposures (4000m) and one sham exposure (1000m).
• AMS severity (Lake Louise score), incidence, heart rate, oxygen saturation, blood pressure, and exhaled nitric oxide were measured.
• Physiological variables were also monitored during sleep.

Main Results:

• AMS incidence did not differ significantly between exposures (84% vs 56%).
• AMS severity (LLS) was significantly lower on the second hypoxic exposure (3.1) compared to the first (4.8).
• Headache was the most consistently severe AMS symptom; physiological variables showed moderate to strong repeatability but did not predict AMS susceptibility.

Conclusions:

• The Lake Louise score (LLS) for AMS was not repeatable across identical hypoxic exposures.
• Reduced AMS severity on re-exposure may be due to environmental familiarity rather than physiological acclimatization.
• Headache emerged as the most reliable indicator of AMS symptoms.