Great article, both informative and detailed. One thing I would add is that most sea-level habituated people are measurably hypoxic over 5,000 feet or so. It's

Great article, both informative and detailed. One thing I would add is that most sea-level habituated people are measurably hypoxic over 5,000 feet or so. It's just not as obvious. If you're a pilot, there's an interesting self-test you can do on yourself the next time you fly VFR at night. At about 8 or 9,000MSL, without oxygen, take a look at the landscape below. Looks normal, right? Now breathe some oxygen while continuing to look. For most people, it's like having the contrast turned way down on a TV and not realizing it. Once the contrast comes back up, there's all this depth of color, vibrance and detail you had been missing -- and have not been aware of it. If you're like me, the crazy part isn't that you were hypoxic. It's that everything seems completely normal. You can't use an out-of-whack system (your brain) to judge whether it's out-of-whack or not.