"High" Altitude Sickness

[HooKooDooKu]

Most airlines pressurize the planes to what you would see at an altitude of 6000 to 8000 feet.

That makes pretty good sense.
I live at an elevation of about 700'
If I go to Clingman's Dome in GSMNP at an elevation of about 6,600', I don't notice a big difference.
When I hiked the JMT coming out of Yosemite Valley, it wasn't until I reached 9,000' that I noticed the thinner air impacting my ability to hike (started getting very winded as the trail climbed from 9,000' to 10,000').

[Daybreak]

The percent of oxygen in (dry) air does not change with altitude, only the pressure drops. The amount of oxygen in a lungful of air decreases since you breathe in proportionally less air mass. This is what the table shows. Air pressure drops from about 14.7 psia at sea level to about 12.2 psia at 5000'. So at 5000' feet the air pressure is 83.0% of that at sea level. The total air mass is 83% and the total oxygen mass is 83% of that at sea level.
0.83 x 20.9% oxygen in air = 17.3 effective oxygen%.
I think looking at percent of sea level pressure is more intuitive. This is the same as the percent of total air and total oxygen mass per lungful compared to sea level.
sea level 100 %5,000' 83 %6,643' 78 % Clingman's Dome10,000' 69 % 14,505' 58 % Mount Whitney20,320' 45 % Mount McKinley29,032 31 % Mount Everest
Pressure Calculator https://www.mide.com/air-pressure-at...ude-calculator

[Daybreak]

• sea level 100 %
• 5,000' 83 %
• 6,643' 78 % Clingman's Dome
• 10,000' 69 % 14,505' 58 % Mount Whitney
• 20,320' 45 % Mount McKinley
• 29,032 31 % Mount Everest

This might be a better table for %pressure versus altitude

[gpburdelljr]

• sea level 100 %
• 5,000' 83 %
• 6,643' 78 % Clingman's Dome
• 10,000' 69 % 14,505' 58 % Mount Whitney
• 20,320' 45 % Mount McKinley
• 29,032 31 % Mount Everest

This might be a better table for %pressure versus altitude

The above isn’t indicative of SpO2 (blood oxygen) level decrease with altitude. For acclimatized people, SpO2 levels drop, on average, from 99% at 145m to 97% at 2000m. I don’t know how long it takes for your body to adjust when increasing your altitude. I do know that with a fingertip monitor I can see my SpO2 increase in minutes if I take deeper breaths.

https://thorax.bmj.com/content/73/8/776

[HooKooDooKu]

Acclimation takes "days"... Basically the time it takes for your body to accumulate additional blood cells.
When I hiked the JMT, 4 days is all it took for me to acclimate to elevations of 10,000' to 11,000' (Coming from home with an altitude below 1,000').