Acute Mountain Sickness Symptoms Depend on Normobaric versus Hypobaric Hypoxia

Area of Science:

• Environmental physiology
• Altitude medicine

Background:

• Acute mountain sickness (AMS) affects unacclimatized individuals ascending to high altitudes.
• AMS symptoms like headache and nausea can be disabling, especially with exercise.
• Previous research suggests normobaric hypoxia (NH) and hypobaric hypoxia (HH) may elicit different physiological responses.

Purpose of the Study:

• To evaluate differences in AMS symptoms between NH and HH during initial exposure.
• To determine if the assessment tool influences the detection of symptom differences.
• To investigate if NH and HH are interchangeable for AMS research.

Main Methods:

• Thirty-six subjects underwent 72 exposures to normobaric normoxia (NN), NH, or HH for 8 hours.
• Environmental Symptoms Questionnaire (ESQ) and Lake Louise Self-report (LLS) were administered.
• Classification tree analysis was used to analyze symptom data.

Main Results:

• Classification tree analysis revealed distinct primary AMS symptoms in NH (feeling sick, shortness of breath) versus HH (feeling faint, appetite loss, light headedness, dim vision).
• These symptom differences were not detected using the LLS assessment tool.
• The findings suggest qualitative differences in AMS experience between NH and HH.

Conclusions:

• Initial AMS symptom profiles differ significantly between NH and HH.
• The choice of assessment tool (ESQ vs. LLS) impacts the ability to detect these differences.
• NH and HH may not be interchangeable environments for studying the initial stages of AMS.