Question for the Physics/Medical Geeks

[chelle]

Sorry in advance for posting this in the climbers forum, but I figure it is more likely to be seen by someone with an answer to my physics question...studying for a physiology exam tomorrow.

 

We all know that at higher elevations there is less atmospheric pressure, meaning less molecules per volume X.

 

At sea level the difference during normal breathing between the pressure outside and inside the lungs is about 1mmHg. This is one component that helps with normal inhalation. Does this relationship hold at altitude? [i know there is less O2 and understand what the body's response is to compensate, so no need to comment on that.]

 

What I am wondering is if in general the same volume of air (not compostion) is being inhaled at altitude.

 

Thanks for your help.

[lummox]

yur lungs capacity wont change much at altitude.

[chelle]

Yeah that's a set maximum, but does tidal volume remain relatively constant?

[erik]

and there is not less oxygen cuase the atmosphere must stay in balance they molulcules are jsut spaced further requiring you to work harder to get the same amount of o2

 

[chelle]

Yep, presicesly what I said Erik. Fewer molecules per volume 'X' (liter, gallon, cubic foot). Ratios in the volume remain constant for the balance thing, still 20% O2, but the fewer molecules = less O2 delivery on each breath... Thus the need to acclimate.

[fern]

what is tidal volume?

 

this 1mmHg pressure differential ... is this the over/underpressurizing that expels/draws breath?

[klenke]

Geeky engineering solution:

 

Yes, you are breathing in the same volume of "outside" air at 10,000 ft that you are at sea level. However, the air is less dense at altitude. Assuming perfect mixing of components (thus constant partial pressure fractions of elements such as oxygen, nitrogen, and argon), then you couldn't possibly be breathing in the same mass of oxygen at altitude than at sea level.

 

Equationally: mass of O2 breathed in = Volume breathed in X density of O2 in atmosphere in kilograms per cubic meter.

Symbolically: Mass, O2 = V (m^3) x rho (kg/m^3).

 

In the rarified limit approaching space, you'd have to suck pretty hard. But if you could suck in indefinitely in the fringes of the atmosphere, you could eventually fill your lungs with the same volume of "air." The problem is your body processes (needs) the oxygen thus enhaled quicker than you can acquire it from your surroundings. You can try this by attempting to breathe in very very slowly. You will see that the slower you go the harder it is to maintain a slow pace. That is, your involuntary reflex would eventually be to speed up the process, to suck harder.

Edited August 6, 2003 by klenke

[Necronomicon]

Additonally, the concentration of O2 changes with latitude. The closer to the poles, the lower the [c] O2. This is because the O2 is a more massive molecule than N2, and is "flung" to the lower latitudes, as if the Earth were a giant centrifuge. Because of this, it has been said that Everest, if it were at the same latitude as Denali, would be unclimbable without supplemental O2.

[chelle]

fern said:

what is tidal volume?

 

this 1mmHg pressure differential ... is this the over/underpressurizing that expels/draws breath?

 

Tidal volume is the volume of air inhaled/exhaled in a normal resting breath (about 500ml). Yep the pressure differential is what draws the air in and expels it when you exhale. Totally dependent on the volume change in the thoracic cavity when your diaphragm contracts/relaxes.

 

Thanks everybody. I feel prepared now. Time to drink in a couple hours. Yippee!

[texplorer]

Just another side note is that normally breath per minute rate increases initially upon moving to higher alts and your body also responds physiologically by taking larger breaths to compensate for its loss of O2

[Dru]

Necronomicon said:

Additonally, the concentration of O2 changes with latitude. The closer to the poles, the lower the [c] O2. This is because the O2 is a more massive molecule than N2, and is "flung" to the lower latitudes, as if the Earth were a giant centrifuge. Because of this, it has been said that Everest, if it were at the same latitude as Denali, would be unclimbable without supplemental O2.

 

we debunked this "factoid" myth last year.

[Necronomicon]

I love being wrong. Thanks for setting me straight, Dru.

 

Up to about 80 km the composition of atmosphere is highly uniform - term homosphere is applied. The chemical composition of air in the homosphere is shown on the right (Fig. 2.10 from Strahler & Strahler). See also Fig. 3-3.

 

Two groups of atmospheric gases:

 

I. Gases which have minimal effect on weather and climate. Concentration of these gases is constant everywhere throughout the homosphere. By volume:

 

78% - nitrogen (N2); chemically inactive, neutral

21% - oxygen (O2); very active chemically, reacts readily with other substances in the process of oxydation: slow (rock decay) or fast (fuel combustion)

0.93% - argon (Ar); inert

< 0.04% - trace gases: Neon (Ne), Helium (He), Methane (CH4), Krypton (Kr), Hydrogen (H2)

Ozone (O3) - extremely important as a shield for life - absorbs UV rays

II. Gases which are significant for weather and climate. Concentration of these gases (especially water vapor) can vary considerably from one place to another.

 

0-4% - water vapor (< 1% on average) - absorbs longwave radiation, emits counterradiation (greenhouse effect), transfers heat by latent heat transfer

0.033-0.036% - carbon dioxide (CO2) - together with water vapor is responsible for greenhouse effect

[shuksan]

Yep the pressure differential is what draws the air in and expels it when you exhale. Totally dependent on the volume change in the thoracic cavity when your diaphragm contracts/relaxes.

 

I think the pressure differential is more accurately due to the RATE of change of the volume of the thoracic cavity -- if you breathe slowly, you can still get the same lungfull of air, but it will flow thru a lower pressure differential than if you breathe rapidly. The pressure differential is also proportional to the ambient pressure; for a fixed breathing rate, the pressure differential will be lower at altitude than for sealevel. This ties together the idea of the body trying to compensate and tex's remark about change in breaths/minute. By breathing faster, the pressure differential would be maintained (the decrease due to altitude is countered for by the increase in breathing rate). This makes sense since pressure differential is essentially another measurement of O2 flow rate. Eventually the body's preferred acclimation kicks in so that efficiency at using O2 increases and we don't need the same flow rate. Then the pressure differential (and breathing rate) would be expected to go down.

[Alpine_Tom]

"The difference in the barometric pressure at northern latitudes affects acclimatization on Denali and other high arctic mountains. Denali's latitude is 63° while the latitude of Everest is 27°. On a typical summit day in May, the Denali climber will be at the equivalent of 22,000' (6900M) when compared to climbing in the Himalaya in May. This phenomenon of lower barometric pressure at higher elevations is caused by the troposphere being thinner at the poles."

 

from http://cancerclimb.thepeaks.com/facts.htm

 

It's not that the concentration of oxygen molecules is less at the poles, it's that the density of the air is less.

[Dru]

Alpine_Tom said:

"The difference in the barometric pressure at northern latitudes affects acclimatization on Denali and other high arctic mountains. Denali's latitude is 63° while the latitude of Everest is 27°. On a typical summit day in May, the Denali climber will be at the equivalent of 22,000' (6900M) when compared to climbing in the Himalaya in May. This phenomenon of lower barometric pressure at higher elevations is caused by the troposphere being thinner at the poles."

 

from http://cancerclimb.thepeaks.com/facts.htm

 

It's not that the concentration of oxygen molecules is less at the poles, it's that the density of the air is less.

 

Promotional material for a climb for cancer is not reputable source for physiological and meteorological information. They are just chestbeating about Denali. Do the search for the thread from last year in which this factoid was compellingly debunked.

[Alpine_Tom]

Dru said:

 

Promotional material for a climb for cancer is not reputable source for physiological and meteorological information. They are just chestbeating about Denali. Do the search for the thread from last year in which this factoid was compellingly debunked.

 

The only reason I used that quote is because they expressed the information more succinctly than I would have (plus, they had more accurate numbers for the lattitudes of Denali and Everest than my son's globe.) It's a matter of metorological fact that the tropopause (top of the troposphere) is lower near the poles than at the equator, no matter who on this site has "debunked" it.

 

Perhaps a less comercial link would give a little more credibility to the physics? It's actually a far more interesting topic than I'd at first assumed from the factoid I was carrrying around in my head, and so I appreciate being challenged.

 

http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html

 

http://www.atmos.washington.edu/~hakim/tropo/

 

http://www.fofweb.com/Subscription/Science/Helicon.asp?SID=2&iPin=enweath3421

 

If I HAVE to, I suppose I could actually bestir myself to go look up the relevant information in a book, but that's so, well, tedious.

At any rate, it's beside the whole point of ehmmic's question, about which I don't have any useful information...

[fern]

Alpine_Tom said:

It's a matter of metorological fact that the tropopause (top of the troposphere) is lower near the poles than at the equator, no matter who on this site has "debunked" it.

 

did you do the search? nobody questioned that fact, and that is not the nature of the chestbeating. So the tropopause is lower in polar regions than equatorial ... can you quantify the resultant effect in terms of the relative physiological stress experienced climbing in Alaska at a particular altitude versus climbing in the Himalayas at a particular altitude? ... numbers!!!

[Fairweather]

Alpine_Tom said:

"The difference in the barometric pressure at northern latitudes affects acclimatization on Denali and other high arctic mountains. Denali's latitude is 63° while the latitude of Everest is 27°. On a typical summit day in May, the Denali climber will be at the equivalent of 22,000' (6900M) when compared to climbing in the Himalaya in May. This phenomenon of lower barometric pressure at higher elevations is caused by the troposphere being thinner at the poles."

 

from http://cancerclimb.thepeaks.com/facts.htm

 

It's not that the concentration of oxygen molecules is less at the poles, it's that the density of the air is less.

 

If this were true, (it's not) then an altimeter would read 22,000 feet on top of McKinley. (it doesn't) Additionally, altimeters would have to be sold pre-calibrated for the latitude in which the buyer intended to use the device.

[Fence_Sitter]

can you quantify the resultant effect in terms of the relative physiological stress experienced climbing in Alaska at a particular altitude versus climbing in the Himalayas at a particular altitude? ... numbers!!!

yeah right... and win a contest for the hardest thign to prove in the world... barometric pressure changes constantly, sooo it would be reather difficult to get any readings at all...

[Fence_Sitter]

Fairweather said:

Alpine_Tom said:

"The difference in the barometric pressure at northern latitudes affects acclimatization on Denali and other high arctic mountains. Denali's latitude is 63° while the latitude of Everest is 27°. On a typical summit day in May, the Denali climber will be at the equivalent of 22,000' (6900M) when compared to climbing in the Himalaya in May. This phenomenon of lower barometric pressure at higher elevations is caused by the troposphere being thinner at the poles."

 

from http://cancerclimb.thepeaks.com/facts.htm

 

It's not that the concentration of oxygen molecules is less at the poles, it's that the density of the air is less.

 

If this were true, (it's not) then an altimeter would read 22,000 feet on top of McKinley. (it doesn't)

 

no genius... cause you set it for sea level in alaska not in tibet

[Fairweather]

Fence_Sitter said:

Fairweather said:

Alpine_Tom said:

"The difference in the barometric pressure at northern latitudes affects acclimatization on Denali and other high arctic mountains. Denali's latitude is 63° while the latitude of Everest is 27°. On a typical summit day in May, the Denali climber will be at the equivalent of 22,000' (6900M) when compared to climbing in the Himalaya in May. This phenomenon of lower barometric pressure at higher elevations is caused by the troposphere being thinner at the poles."

 

from http://cancerclimb.thepeaks.com/facts.htm

 

It's not that the concentration of oxygen molecules is less at the poles, it's that the density of the air is less.

 

If this were true, (it's not) then an altimeter would read 22,000 feet on top of McKinley. (it doesn't)

 

no genius... cause you set it for sea level in alaska not in tibet

 

I believe this is not the case. Even a device set at sea level on the equator would read 20,320 atop Denali. If this were not the case, the rate of increasing altitude expressed on the device as you climbed would be different at varying latitudes to the point that an altimeter would need to be specifically calibrated for, say every 10 degrees.

 

I could be wrong. I'm certainly no atmospheric scientist.

[philfort]

Fairweather said:

If this were true, (it's not) then an altimeter would read 22,000 feet on top of McKinley. (it doesn't)

 

oh come on

 

Here's an article about why the effective altitude is greater at the south pole. http://www.polar.org/antsun/Sun020203/altitude.html

 

[philfort]

Fairweather said:

the rate of increasing altitude expressed on the device as you climbed would be different at varying latitudes to the point that an altimeter would need to be specifically calibrated for, say every 10 degrees.

 

Well, that's what the link I posted above is claiming (due to cold temps though). So yeah, the relationship between pressure change and altitude change would be different - but that ratio is fixed (at least on my altimeter), so the altimeter is "permanently calibrated" to some norm.

 

But the changing weather is probably going to mess with your altimeter more than the "latitude error"?

[Fairweather]

"A commonly mistaken explanation of pressure altitude is that it is the result of centrifugal forces of Earth's spin that draws the atmosphere toward the equator to form an 'equatorial bulge'."

 

I always assumed that this was the case being made for the 22,000 ft Denali claim. As it turns out the varyance is thermally driven. I still question how this would account for a 1700 foot varyance, and this is still not explained in the article, but now I understand I (and others) have misunderstood the premise. Thanks for the link!

 

 

[Fence_Sitter]

Fairweather said:

Fence_Sitter said:

Fairweather said:

Alpine_Tom said:

"The difference in the barometric pressure at northern latitudes affects acclimatization on Denali and other high arctic mountains. Denali's latitude is 63° while the latitude of Everest is 27°. On a typical summit day in May, the Denali climber will be at the equivalent of 22,000' (6900M) when compared to climbing in the Himalaya in May. This phenomenon of lower barometric pressure at higher elevations is caused by the troposphere being thinner at the poles."

 

from http://cancerclimb.thepeaks.com/facts.htm

 

It's not that the concentration of oxygen molecules is less at the poles, it's that the density of the air is less.

 

If this were true, (it's not) then an altimeter would read 22,000 feet on top of McKinley. (it doesn't)

 

no genius... cause you set it for sea level in alaska not in tibet

 

I believe this is not the case. Even a device set at sea level on the equator would read 20,320 atop Denali. If this were not the case, the rate of increasing altitude expressed on the device as you climbed would be different at varying latitudes to the point that an altimeter would need to be specifically calibrated for, say every 10 degrees.

 

I could be wrong. I'm certainly no atmospheric scientist.

 

nope sorry wouldn't... even if weather was constant, it would be different because of teh rotation of the planet... it forces a higher concentration of air at teh equator at teh expense of air nearer to teh poles.... therefore sea level air would be less dense in AK than equator as would 20,000. Though sea level changes as well, so that is a wholenother fish to fry