Operation Everest II.

Area of Science:

• Environmental Physiology
• Human Physiology
• High-Altitude Medicine

Background:

• Operation Everest II (OE II) simulated a 40-day ascent to Mt. Everest summit in controlled altitude chambers.
• This study investigated human physiological responses to extreme simulated high-altitude conditions.

Purpose of the Study:

• To comprehensively assess human physiological and psychological responses during a simulated prolonged ascent to extreme altitude.
• To investigate the effects of severe hypoxia on multiple organ systems, including cardiovascular, respiratory, muscular, and neurological functions.

Main Methods:

• Eight subjects underwent gradual decompression over 40 days in United States Army Research Institute for Environmental Medicine (USARIEM) altitude chambers.
• Extensive physiological measurements were taken across various organ systems throughout the simulated ascent and descent.

Main Results:

• Subjects experienced significant reductions in V(O)(2)max and arterial oxygenation due to ventilation-perfusion inequality and diffusion limitation.
• Cardiac function showed resilience to hypoxia, while lungs were significantly impaired with increased pulmonary vascular resistance.
• Persistent neurological deficits (cognition, memory) were observed post-expedition, particularly in individuals with high hypoxic ventilatory responsiveness.
• Significant body weight and muscle mass loss occurred, exceeding predictions based on energy balance.

Conclusions:

• Simulated extreme altitude exposure causes profound physiological stress, particularly affecting respiratory function and leading to neurological and muscular changes.
• The study highlights the limitations of the human respiratory system at extreme altitudes and the complex interplay of physiological adaptations.
• Operation Everest II provided unique, in-depth data complementing field studies, advancing our understanding of high-altitude physiology.