a favorite topic here
and one of mine, personally and professionally
tremendous personal variation makes hard rules hard. even within the same person it is hard. I have had AMS at 10,000 and 19,000. Different circumstances, not just the height.
I had an eye opening experience in Mexico in November 2012 that was different from my time there in 1997, and places elsewhere. This was the fastest I had ever gone above Whitney height without more lengthy staging
Leaving sea level Virginia one morning, flew/drove to 12,000 for the night. Next am climb on Toluca. Despite Diamox(that does not fix everything) I knew immediately at the trailhead I was slow. No headache or nausea ,etc, but at reaching 15,000 ft I was huffing and puffing and pounding, and turned around while the others (4 of whom also came from sea level LA) went to 15,500 top.
After then spending one night each at (in order) 12,000, 10,000 and 8,000 and watching it rain/ no hiking I became acclimatized. Drove to 14,000 hut of Orizaba and immediately hiked to 15,500 as if the symptoms of Toluca were imaginary. Later summitted 18,500
Scientifically: My cardiovascular status was no different in a few days, I had not yet made much more blood (max takes 3-4 weeks), I was breathing LESS hard and thereby not hyperventilating and did not shift my O2/Hgb curve beneficially leftward, and so the conclusion to me is that the mysterious, poorly understood metabolic changes at the tissue level had set in. Oxygen supply (assuming breathing plain air) is a combination of ambient oxygen pressure, oxygen pickup in the lungs, oxygen delivery by the blood, oxygen unloading from blood at the tissue level, and oxygen utilization at the intracellular level. All of the above are called into action on Everest, but on Orizaba I'd say most of my improvement in a few days was the latter two.
Harvey
