Cool Link on Altitude Related Illness

[Montana_Climber]

So now to totally change the subject from this thread has gone....

 

I was wondering about the physiology of oxygen exchange at extremely high altitudes. Take Everest, for instance. The top has a partial pressure of 243 mmHg. Sea level is 760 mmHg. At sea level only 20% of the atmosphere is oxygen and I'm assuming that the percentages remain the same. This would mean that at the top of Everest, the partial pressure of O2 would be about 45 mmHg, nearly the exact same as the pO2 of venous blood in the body. Normally, the oxygen exchange across the alveoli is driven by a very large gradient (at sea level this gradient is about 150 - 23 mmHg for warming/humidifying air which still roughly corresponds to a gradient of about 75 mmHg difference) but at such high altitudes this would not happen according to the above theoretical values.

 

The humidity on the summit is usually somewhere between 40 and 60% (due to being in the jet stream) so perhaps the warming/humidifying effects are not as pronounced.

 

This of course would be assuming that there is no supplemental oxygen. Perhaps for these above reasons, there are so few people who can actually make it to the top without oxygen. Carrying your own would artificially increase the partial pressures, etc, etc.

[skyclimb]

41% not 21% of earths oxygen level. Summit of Karakoram 2(K2) being regarded with this figure, not Everest. This is the reason in the error of your calculation, 21% is half of what the number is, just as 41% is close to half of what K2 is to sea level. Same difference, however not 1/2 but exponential with altitude gains.

[Figger_Eight]

skyclimb said:

41% not 21% of earths oxygen level. Summit of Karakoram 2(K2) being regarded with this figure, not Everest. This is the reason in the error of your calculation, 21% is half of what the number is, just as 41% is close to half of what K2 is to sea level. Same difference, however not 1/2 but exponential with altitude gains.

 

MC is right on with his explanation. There is very little oxygen exchange that high up because there is no pressure gradiant between the atmosphere and the blood stream. Oxygen makes up only 21% of the atmosphere.

 

Source

[mneagle]

Oxygen makes up 21% of the air at all altitudes. The barometric pressure goes down in a non-linear manner as you go up in altitude or go north or south from the equator at a given altitude. The humidity of the ambient air makes no difference as by the time air has been inhaled and reached the alveoli in the lung it has been completely saturated with water vapor and warmed to your body temperature by the mucosa of the respiratory tract. The formula for calculating the partial pressure in the alveoli is:

 

(P barometric - P H20) .21 - 1.2 (Pa CO2)

 

P barometric varies w/ altitude and latitude

P H20 = 47

Pa CO2 (arterial partial pressure of CO2) depends on how many liters you breath per minute

 

Even in normal lungs some blood will reach the arterial system without being fully oxygenated so that the actual arterial partial pressure of oxygen will be lower than the alveolar amount. This difference is called the alveolar -arterial gradient and it is only affected by the barometric pressure at extreme altitudes when diffusion across the alveolar and capillary walls begins to become a factor. Breathing more to drive down your CO2 will increase the alveolar and hence arterial partial pressure of oxygen (one effect of taking Diamox) as will being at lower altitudes or climbing closer to the equator where barometric pressure is higher per given altitude. Breathing supplemental oxygen will increase the .21 in the above equation to a higher percent oxygen which will also increase the partial pressure.

 

Now the complicated part. Partial pressure does not equal the amount of oxygen but is better thought of as a measure of chemical activity, determined by the concentration and temperature of the gas in the system. The higher the temperature, the faster particles move and the higher the concentration the more particles there are moving around. As you can imagine, the more oxygen molecules there are in a given space and the faster they are moving the more likely they are to move across the alveolar wall and smash themselves into a hemoglobin molucule. The partial pressure is a measure of how likely this is to happen.

 

But it's not even that simple because hemoglobin it turns out is a fascinating and dynamic molecule that has entire textbooks dedicated to it. Each hemoglobin molecule can carry 4 oxygen molecules. It's affinity for oxygen is inversely related to the number of oxygen molecules it has bound, however it's not linear. An oxygen dissociation curve plotting saturation vs. partial pressure of oxygen surrounding it forms an S shaped curve. This means that the hemoglobin saturation is not linearly related to the partial pressure of oxygen in the blood. Other factors including pH, pCO2, temperature and the amount of 2-3 DPG around also affect its ability to pick up and deliver oxygen. The only factor I think that is feasable to mention here is 2-3 DPG which is a molecule our body makes to enhance oxygen delivery to tissues as we more to higher altitudes. This takes a few days to achieve and is one of the known factors involved in acclimatization. What's fascinating about this is that it's action is to DECREASE hemoglobin's affinity for oxygen, allowing more efficient delivery of oxygen to starved tissues. This is all good and fine until you reach extreme altitudes when this becomes a possible detriment as partial pressure falls to a point that diffusion across the alveolar/arterial walls is hampered by the lowered oxygen affinity of the hemoglobin. However, this is mostly theoretical. An interesting experiment would be to see if elite high altitude climbers have a unique response to altitude with regards to 2-3 DPG production.

 

One last area is oxygen content and delivery. The actual amount of oxygen in our blood is determined by the equation:

 

(1.39 x hemoglobin x hemoglobin saturation) + (PaO2 x .003)

 

This actually gives you the grams per deciliter of oxygen in your blood. The 1.39 is a constant. Obviously the best way to get more oxygen in your blood is to increase the amount of hemoglobin or increase the hemoglobin saturation. Incraesing the hemoglobin can be done by blood doping or by the natural effect of acclimatization throught the increase in endogenous production of erythropoetin which stimulated bone marrow production of red blood cells. It's too bad we can't just increase the amount of hemoglobin per red blood cell, but only certain Himalayan birds seem to be able to do this. The saturation of hemoglobin is non-linearly affected by the partial pressure of oxygen in the blood and all the stuff mentioned above. Finally we have oxygen delivery which is expressed by the simple equation:

 

oxygen content x cardiac output

 

When the oxygen content in the blood falls as you go higher, your body makes up for this by first increasing the amount of blood pumped per beat (stroke volume) and then by increasing the heart rate. This is why heart rate is such a good measure of acclimatization. If you are tachycardic at rest your body is already working at near max capacity. As you acclimatize, oxygen content increases (through increasing hemoglobin) and efficiency of delivery increases (effects of 2-3 DPG etc.) which will allow your heart rate to come down.

 

[Figger_Eight]

Increasing the hemoglobin can be done by blood doping or by the natural effect of acclimatization throught the increase in endogenous production of erythropoetin which stimulated bone marrow production of red blood cells.

 

Increased VO2 max also results in a higher RBC count.

[randygoat]

Hey Norman, I had some pretty bad altitude sickness[ probably early cerebral edema] in South America around 15-16'000ft.I wassick as a drunken dog. I was puking everything,including water. Total halucinations/delusions/ and confusion. Couldn't stand, etc....

 

Anyway the guys got me to take some electra lite powder mix[ wasn't gator aid] and forced down the water. I was spyched when the Jolley Ranchers would stay down. Anyway, I also started to take the Diamox. It seamed to start to help a bit within the day. I went down to 9-10'000 ft continueing with the diamox and ate and rested for a day. Next day I ws able to reach 19'800, although I was getting totally hammered again and halucinations came back.

 

It probably did help me to even get that far, probably not as far as actually spending the time to get well aclimated first.

 

I think next time I may bring some with me,just in case. I don't think I would need it anywhere in the western U.S. other than Denali.

[randygoat]

Since it is a diuretic, the last water consumed should be done at least one hour before bedtime and a last trip to the pee hole is usually necessary to keep you from making several more trips throughout the night.

 

Sleep with a pee bottle in yer bag. Keep a water bottle with you to, and drink through the night. The pee bottle can add sometemorary heat to yer bag also. Just don't confuse the 2.

[chelle]

So we've had some good discussion about Diamox. I read about a study a guy at UW did last year to determine if Salmeterol (an asthma drug - subject sin the study were not asthmatics) helped to reduce the incidence of AMS on people who ski at high altitudes (the alps). He conculded that it did. Anyone know of any other info about asthma and high altitidue climbing?

[Attitude]

ehmmic said:

So we've had some good discussion about Diamox. I read about a study a guy at UW did last year to determine if Salmeterol (an asthma drug - subject sin the study were not asthmatics) helped to reduce the incidence of AMS on people who ski at high altitudes (the alps). He conculded that it did. Anyone know of any other info about asthma and high altitidue climbing?

Details?

[pete_a]

Did Mark Twight in Extreme Alpinism write something on the use of silberian ginseng to help with acclimitization and reducing the occurance of AMS? just curious....probably gonna end up bringing a whole pharmacy of herbal supplements to help keep me from needing to dip into the diamox bottle on Denali next month. Anyone have experience with using ginseng at altitude?

[chelle]

No experience with Ginsing, but have heard/read that Ginko Biloba works. I think I read an article in Backpacker Mag about two years ago.

[Squid]

Some links on gingko biloba + AMS

here, here, and here.

 

Edited April 8, 2003 by Squid

[chelle]

Attitude said:

ehmmic said:

So we've had some good discussion about Diamox. I read about a study a guy at UW did last year to determine if Salmeterol (an asthma drug - subject sin the study were not asthmatics) helped to reduce the incidence of AMS on people who ski at high altitudes (the alps). He conculded that it did. Anyone know of any other info about asthma and high altitidue climbing?

Details?

 

Okay. I dug the article out of my files. Skiing Magazine Sep 2002, p. 162. There are actually 2 studies.

 

The researcher at UW is named Erik Swenson. He took X-rays and measured fluid levels of 16 subjects within 14 hours of topping Monte Rosa (previous studies waited 24-48 hours after the onset of symptoms - found fluid in the lungs and inflammation in the lungs and assumed inflamation caused HAPE). Swenson found fluid and no inflammation. His conclusion, inflammation does not cause the fluid buildup, therefore anti-inflammatory drugs may not be useful in treating/preventing HAPE.

 

Swiss researchers (Urs Scherrer) then studied 37 climers who had a history of HAPE, gave 18 a puff of salmeterol and 19 a puff of placebo. The studied how the lungs cleared sodium and by extension water from the lungs. Only 6 climbers in the study group showed signs of HAPE; compared to 14 in the control.

 

Someone with access to a medical journal library may be able to find the original journal articles. Skiing doesn't say where the findings were published, but this looks interesting. Especially to someone who has asthma and likes to chase big mountains.

[erik]

PETE

 

i use ginsing for some endurance activities

 

it is good. but it increases your heart rate.

 

i reccomend two pills to one bong load!

 

 

[fern]

Coca tea gets rid of headaches and nausea but only available

in South America. A proven combatant against altitude illness

that is free and available everywhere is TIME

[Squid]

time is never free

[pete_a]

Erik,

thanks for joggin my memory...I think Twight wrote about ginsing being beneficial for increased endurance not helping with AMS, but he also talks about ginko for AMS and I think he mentions taking garlic tablets as a blood thinner to help with frostbite prevention.