Oxygen content in air changing with elevation - ClubTread Community

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post #1 of (permalink) Old 08-25-2003, 11:07 AM Thread Starter
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Default Oxygen content in air changing with elevation

All this talk about reduced oxygen when we were doing the climb yesterday got me interested. I haven't found an actual formula yet, just a couple data points. It isn't enough to tell me if it is linear or some curve though. Does anyone know the formula for calculating oxygen content at various elevations? From what I understand, temperature also plays a bit of a role, but I'm looking more for rough calculations - doesn't need to be overly specific.

A couple data points that I did find are:

* At sea level (which is considered normal) the oxygen content is 21%.
* At 9,000ft, the oxygen content is reduced to 16%.

So you can see from our climb to 8,000ft yesterday at Mt. Outram, we definitely did lose a good amount of Oxygen over the course of the climb (from 2,000ft to 8,000ft).

I remember back when I was at Cathedral Lakes, a guy told me that there is 20% less oxygen there. The calculation makes sense if you do the ratios of % oxygen content in the air from above.

I also saw some notes on air density on the web. A couple examples that I saw were:

* Everest base camp (17,700ft) - air density of 51%
* Ali manufacturing plant (15,400ft) - air density of 62%

How does air density play a role in these calculations? Or does it? This is one of the reasons I am suspecting that the calculation of oxygen content isn't linear.

I know there are a bunch of science types on this site. I'm quite interested in knowing this.

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post #2 of (permalink) Old 08-25-2003, 01:53 PM
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The gas ratios should stay the same. The percentage of oxygen in the air should not change to a significant degree with altitude but the absolute O2 content decreases as the overall air pressure decreases.

The good news is that for lower altitudes the oxygen delivery is maintained quite well because of the miracle of hemoglobin and its ability to carry O2. But it comes to a point where the curve gets slippery and O2 delivery capability plummets.

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post #3 of (permalink) Old 08-25-2003, 07:50 PM
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One thing is for sure,exertion at high altitude is tougher with less oxygen!Last year on holiday in Colorado I did a lot of running at 9500-14000 ft(Rocky Mtn Park,Colo trail,Durango,Gunnison,Pike's Peak,etc)and it's vastly different from the sea level to 4000 ft I run here at home.Even after several days acclimatization,you get the occasional headrush.No wonder on Everest they need weeks to get used to it before attempting the summit.I find it really catches up to you on a day when you are really tired,but of course that seems obvious...Mick

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post #4 of (permalink) Old 08-25-2003, 11:36 PM Thread Starter
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In my searches for the "formula" today I actually stumbled across an article about this chamber they built. It can actually simulate the atmospheric pressure and O2 content up to 14,000ft. Quite amazing really - filtering out the O2, etc.

At dinner tonight, Rich told me that people living at sea level start feeling it between 6000-8000ft. It also comes down to how sensitive you are to the effect - everyone is individual.
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post #5 of (permalink) Old 08-26-2003, 08:11 AM
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Yes that industry appears to be florishing. People trying to acclimatize, boost their hemoglobin and shift ther oxygen hemoglobin curve through adaptation the easy way.

I don't remember the actual numbers but I don't think there is actually much fear of high altitude sickness below 8000 or so and occurences that low are uncommon. But people may feel unwell below that but there are a number of things likely feeding in to their subjective symptoms including fitness issues, other medical problems (including an even slightly low hemoglobin), calorie deficiency, thermal issues and dehydration.

Hope you had a good dinner last night with the group in Richmond. Undoubtedly no worries about calorie deficiencies there<img src=icon_smile_big.gif border=0 align=middle>


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post #6 of (permalink) Old 08-26-2003, 02:00 PM
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It is interesting. I attended school in central Alberta (elevation approx 3500 ft) and found the first month I suffered from headaches. Others told me I was just acclimatizing to altitude. It did go away.
It is physically impossible for gas ratios to change at altitude. Oxygen is always 20% of air no matter what. But, air pressure (the amount of air) does decrease. Therefore, there is less oxygen available in total.

This effect not only occurs in humans. If you take your dog for a walk in high altitudes, the dog will be strongly affected, as the amount of oxygen needed per pound increases as mass decreased.

Carborated (sp?) cars have the same problem, as a car depends on a precise fuel/oxygen ratio. The higher the altitude, the less oxygen for the same amount of fuel. Fuel injected cars can compensate, so in modern cars, the effect is less noticable.

When the Olympics were held in Mexico City, the times for footraces were high for long races and low for short races.

Two other effects of altitude are increased moisture loss (the vapour pressure of the water in your lungs is constant, but the externel pressure is lower) and water boils at low temperatures.
In the high Andes, it is difficult to purify water by boiling, as the boiling temperature can be as low as 85 C, not hot enough to kill germs.

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post #7 of (permalink) Old 08-30-2003, 12:26 AM
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Thanks for the great information people, its amazing the questions we can ask and then get a full answer and plus back,is great.CHEERS!

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post #8 of (permalink) Old 08-30-2003, 11:04 AM
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very interesting topic. as i recall, there was an article in National Geographic earlier this year about altitude and its effects on the human body. cant remember what month it was, (the issue about everest) but the article was one of the more interesting ones that ive read in geographic (which is saying alot).

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post #9 of (permalink) Old 09-06-2003, 11:43 PM
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Partial pressures and oxygen saturation are hotly debated in high altitude mountaineering circles. During most of our expeditions we take pulse oximeters and take readings regularly.

In my experience people do not typically experience 'significant' altitude related discomfort until around 3,500 to 4,000 meters (11,500 to 13,200 feet). That said, recently a client on a Kilimanjaro trip I was asked to guide (thankfully I did not go as I was already commited to other activities) contracted cerbral oedema and died. They had only just breached 3,000 meters (9,900 feet).

Mileage varies and each individual is unique...the main priority should be to ascend in a slow and controlled fashion and to treat altitude related illness aggressively...drink and descend.

We had quite extensive medical support for our Everest 2003 expedition and had a couple of oximeters. Oximeters measure the level of oxygen saturation in your blood. They can be a basic indicator of high altitude acclimatization, though the readings they provide are indicators only and need to be taken in context.

We took readings all the way up to 7,300 meters (24,000 feet) and obtained some 'interesting' results. At sea level my oxygen saturation is usually 98-99% with a resting pulse of about 53.

The photo below is my reading after a day's rest at Camp III at 7,300 meters. My reading is 67% oxygen saturation with a resting pulse of 119. Big difference.

This was not my lowest score - I experienced the 'honor' of my lowest scores one night when I had frighteningly severe sleep apnea (when you stop breathing in your sleep). After being awake for some time I took my reading and it was 49%.

I can only begin to imagine what our readings where above 8,000 meters (26,400 feet).

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post #10 of (permalink) Old 10-12-2003, 03:57 AM
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The partial pressure of oxygen at sea level is 14.7 PSI (pounds per square inch).

At 18,000 feet, the partial pressure of oxygen is half that. And at 36,000 feet, the partial pressure of oxygen is half that again. The decay rate is linear. This holds true until we get to outer space. In outer space, the point is moot.

Air is composed of oxygen (20-percent) and nitrogen (80-percent). Let's not quibble about 1-percent inert gasses. The composition remains the same regardless of altitude or temperature.

David E. Vogel, MSGT, USAF, Retired - Aerospace Physiologist

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