RE: AW: Denver, BEWARE!

["Neil, David M" <neildm@id.doe.gov>]

While I am not a physiologist, I do remember a few things from my college zoology degree.



By "oxygen tension", I believe they are meaning partial pressure, which certainly does change with altitude (Well, actually it changes with total pressure, which changes with altitude).  Absolute pressure at sea level is about 14.7 pounds per square inch (PSIA). Of this oxygen accounts for 21%. Therefore 14.7 * 0.21 = 3.087 PSIA(O2).  As long as this partial pressure of oxygen is present, there is not a problem with oxygen transport, whether it is 100% 02 at 3.5 PSIA or normal atmospheric conditions. That's why the space program used 100% oxygen - the lower pressure was easier to contain. (After the capsule fire, they went to a different set of priorities.)  



Conversely, too much pressure raises the O2 partial pressure to toxic levels.  This is one of the reasons that deep divers use a custom gas mixture - for the extreme depths, the mixture is unbreathable at sea level pressure; not enough oxygen. (Nitrogen narcosis and nitrogen embolisms are the other reasons.) 



It's been a while (20+ years) so if I have misrecalled something I was too lazy to look up :-) it was not with intent to mislead.



Dave N



-----Original Message-----

From: John R Johnson [mailto:idias@interchange.ubc.ca]

Sent: Monday, December 20, 2004 1:25 PM

To: jjcohen; Bradshaw, Keith; radsafe@list.vanderbilt.edu

Subject: RE: AW: Denver, BEWARE!





Jerry, Keith et al



I agree with the statement that "increased levels of free radicals which

tend to have carcinogenic effects" but I'm not sure if there is a change in

"oxygen tension" with altitude. In addition food is both necessary for life

but too much of the wrong kind causes fat deposited that can result in death

due to cardiovascular diseases.



John

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-----Original Message-----

From: owner-radsafe@list.vanderbilt.edu

[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of jjcohen

Sent: December 20, 2004 10:36 AM

To: Bradshaw, Keith; radsafe@list.vanderbilt.edu

Subject: Re: AW: Denver, BEWARE!





Several years ago, Daniel Koshland, chairman of AAAS & editor  of  SCIENCE,

published an article implicating oxygen as a mild carcinogen. In this

article, he noted the inverse relationship between altitude and cancer

incidence and postulated that increased oxygen tension increased levels of

free radicals which tend to have  carcinogenic effects.[That is why dietary

anti-oxidants, such as vitamin E are recommended for avoiding cancer). Of

course, OTOH, oxygen is necessary for life. Many people have trouble with

the concept that the same substance can simultaneously cause both beneficial

and harmful effects. That is likely that is why Radiation Hormesis has such

problems gaining acceptance.





----- Original Message -----

From: Bradshaw, Keith <keith.bradshaw@niras.co.uk>

To: <radsafe@list.vanderbilt.edu>

Sent: Monday, December 20, 2004 9:02 AM

Subject: RE: AW: Denver, BEWARE!





> >>When I'm a mile high, I breathe harder than at sea level, so I naturally

> >>thought that the body makes up for the thinner air by trying to inhale

> >>more of it.

>

> >I hear people say the body makes up for the thinner air by making more

red

> >blood cells. (It takes a few days to adapt.) The implication is: we don't

> >inhale a larger volume, but I have never seen any data. I would

appreciate

> >a reference to real data, if anyone can provide it.

>

> My theory:

> The haemoglobin oxygen saturation stays pretty constant down to about 14%

> oxygen, or the equivalent in altitude, then it falls away quickly.  Once

you

> are in this steeply falling region of the curve, the actual tissue

> concentration of oxygen will be significantly reduced.  The haemoglobin

acts

> as a buffer for oxygen concentration in the tissues.

>

> I think the real issue is the oxygen tension or partial pressure.  I

suppose

> you could argue any increased number of red blood cells, as a result of

> adaptation at altitude, would deliver the same oxygen to the tissues, but

> perhaps that only happens when the tissues demand it.  Irrespective of the

> actual amount of haemoglobin, the saturation curve is the same shape.

>

> If this is the correct way of looking at it, that means there is

> significantly less oxygen-generated free radical damage at altitude.  This

> more than makes up for the increased cosmic ray dose, possibly explaining

> the longevity of people who live up mountains.

>

> Perhaps we need a proper physiologist to comment !!

>

> Personal views only

>

> keith.bradshaw@niras.co.uk

>

>

> web:  www.niras.co.uk

>

>

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