Mount Everest climber Frank Smythe stood at 27,000 feet, near the top of the world, in 1933. Later, Smythe recounted an exceptionally odd experience. He saw "two curious looking objects floating in the sky. [One] possessed what appeared to be squat underdeveloped wings, and the other a protuberance suggestive of a beak. They hovered motionless but seemed slowly to pulsate."1 But in reality, he saw nothing; he just lacked oxygen. Into Thin Air's author Jon Krakauer's own Everest hypoxic delusion involved a green cardigan, wingtips, and an eerie bodily detachment.1 Most people will never experience such a dramatic lack of oxygen; even so, less than "normal" levels of oxygen can have profound physiological effects throughout the body.
Just what is normal? Ambient air at sea level contains approximately 21% oxygen (O2) (~150 mmHg or torr), but the highest partial pressure (pO2) detected in the human body is around 16% (100 ...
