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Acute mountain sickness: increased severity during simulated altitude compared with normobaric hypoxia
R C Roach1, J A Loeppky, M V Icenogle
1Copenhagen Muscle Research Center, Rigshospitalet, Denmark.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1996
Summary
Simulated altitude causes more acute mountain sickness (AMS) than low oxygen or low pressure alone. This study clarifies the distinct roles of hypoxia and hypobaria in AMS development.
Area of Science:
- Environmental Physiology
- Altitude Medicine
Background:
- Acute mountain sickness (AMS) is commonly attributed solely to hypoxia at high altitudes.
- Emerging evidence suggests that hypobaria (reduced barometric pressure) may also contribute to AMS pathophysiology.
Purpose of the Study:
- To investigate the independent contributions of hypoxia and hypobaria to AMS development.
- To compare AMS severity under simulated altitude, normobaric hypoxia, and normoxic hypobaria.
Main Methods:
- Nine healthy men were exposed to simulated altitude (4,564 m), normobaric hypoxia, and normoxic hypobaria in a controlled environmental chamber.
- Exposure durations were 9 hours, with AMS symptom scores recorded.
- Inspired partial pressure of oxygen (PO2) was matched across conditions.
Main Results:
- Simulated altitude resulted in significantly higher AMS symptom scores (3.7) compared to normobaric hypoxia (2.0) and normoxic hypobaria (0.4).
- Normobaric hypoxia also induced some AMS symptoms, but less severe than simulated altitude.
- Normoxic hypobaria alone induced minimal AMS symptoms.
Conclusions:
- Simulated altitude is a greater trigger for AMS than either isolated hypoxia or hypobaria.
- Both hypoxia and hypobaria play roles in AMS, with simulated altitude encompassing both factors.
- Understanding these distinct physiological stressors is crucial for managing and preventing AMS.