The physiological definition of respiration should not be confused with the biochemical definition of respiration, which refers to cellular respiration: the metabolic process by which an organism obtains energy by reacting oxygen with glucose to give water, carbon dioxide and 38ATP (energy).

Scientists who climbed to the summit of Everest and took samples of their own blood have shown that the human body can survive with much lower oxygen levels than was previously thought possible. They say the findings, based on blood taken at higher altitudes than ever before, will help doctors to treat patients in intensive care more effectively.