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 Oxygen content in air changing with elevation
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LongShadow
Founder

Big pack hiker who sleeps with bears in tent and falls on slippery logs

Langley, BC
Canada

7687 Posts

 Posted - 08/25/2003 :  11:07 AM  Show Profile  Reply to this posting
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.

Tad Tired
Junior Member



425 Posts

 Posted - 08/25/2003 :  1:53 PM  Show Profile  Reply with Quote
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.

mick range
Extreme Hoser

Trail running, bike hucking, fast packing, beer drinking collector of pine cones on a day pass

AKA

Dances with Trees

Forest Gnome Cabin
Canada

13551 Posts

 Posted - 08/25/2003 :  7:50 PM  Show Profile  Reply with Quote
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

LongShadow
Founder

Big pack hiker who sleeps with bears in tent and falls on slippery logs

Langley, BC
Canada

7687 Posts

 Posted - 08/25/2003 :  11:36 PM  Show Profile  Reply with Quote
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.

Tad Tired
Junior Member



425 Posts

 Posted - 08/26/2003 :  08:11 AM  Show Profile  Reply with Quote
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

TT

iamcanjim
Junior Member



162 Posts

 Posted - 08/26/2003 :  2:00 PM  Show Profile  Reply with Quote
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.

Trail Blaizer
Intermediate Member

Trail burning speed demon who sports insanely heavy packs

Chilliwack, B.C.
Canada

719 Posts

 Posted - 08/30/2003 :  12:26 AM  Show Profile  Reply with Quote
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!

You Must go over the Mountain to see whats on the other side!

Andrew Strain
Intermediate Member


Whistler, BC
Canada

633 Posts

 Posted - 08/30/2003 :  11:04 AM  Show Profile  Reply with Quote
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).

Rapscallion
Junior Member


Vancouver, BC
Canada

148 Posts

 Posted - 09/06/2003 :  11:43 PM  Show Profile  Reply with Quote
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).



David E. E Vogel
Starting Member


Baltimore, Maryland
2 Posts

 Posted - 10/12/2003 :  03:57 AM  Show Profile  Reply with Quote
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

LongShadow
Founder

Big pack hiker who sleeps with bears in tent and falls on slippery logs

Langley, BC
Canada

7687 Posts

 Posted - 10/14/2003 :  8:21 PM  Show Profile  Reply with Quote
Thanks for the info and the email David. The info is greatly appreciated.

squishylaroo
Starting Member



2 Posts

 Posted - 10/30/2003 :  12:30 PM  Show Profile  Reply with Quote
Hi Guys,

Great site you got here. The actual formula for calculating partial pressure of oxygen in your alveoli (lungs) is PAO2 = [(Barometric Pressure - 47).21] - [PaCO2 / 0.8]. Barometric pressure varies slightly but can be estimated based on your elevation. You use .21 when you're breathing atmospheric air (that's the % of O2). Your PaCO2 is normally 38 - 40, but if you breathe deeper or faster you can bring it down substantially so you have more room for oxygen in your lungs. And with those portable hyperbaric chambers, even if there's no supplemental oxygen added inside, you're going to increase the barometric pressure so you get substantially more oxygen in your blood for your tissues. This is the basic answer but I don't know if it's user friendly so if you have any particular questions, let me know.

squishylaroo
Starting Member



2 Posts

 Posted - 10/30/2003 :  12:47 PM  Show Profile  Reply with Quote
Whoops. That's the partial pressure of oxygen in the lungs. If you have normal lungs (not diseased) then just subtract 2-5 off the PAO2 to get PaO2 (that's the partial pressure of O2 in the blood). But actual oxygen content is mostly based on your hemoglobin since about 97% of the oxygen feeding your body is transported on hemoglobin. So the actual Oxygen Content equation is: CaO2 = (Hgb X 1.34)SaO2 + (PaO2 X .003). 1.34 is a constant, as is the .003. SaO2 is related to paO2 so that a paO2 of 60 = a SaO2 90, and a 97 = 97. (it's a non linear relationship). I guess if you know your hemoglobin and the normal difference of your PAO2 - PaO2 (from an analyzed blood sample) then you could estimate your oxygen content. However, there's no guarantee from me that your lung condition will stay the same as you climb. I could guess what might happen but I bet other people who study the effects of high altitude on the lung would have some better input about that.

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