During the past three decades or so a vast amount of research has been done in an effort to discover a procedure, or find some agent, which would increase man's tolerance to hypoxia. For the most part, early studies were concerned with attempts to raise the ceiling of aircraft pilots, that is, enable them to withstand a more severe degree of hypoxia, and so improve their mental and physical performance at altitude. Presently, of course, this is not so important as it once was, because planes now are equipped with a pressurized cabin, and, also, pilots not in a pressurized cabin are required to use oxygen masks if they fly at altitudes over approximately 8,000 feet.
It should be pointed out, however, that in the event of an emergency, it might be helpful, even lifesaving, if the pilot and copilot could withstand a relatively high degree of hypoxia for even
VAN LIERE EJ. Resistance to Hypoxia. Arch Intern Med. 1964;113(3):418-427. doi:10.1001/archinte.1964.00280090104018