High Altitude and Central Apneas

[richb]

The theory is this:

Your respiratory drive is driven more by CO2 concentration than by O2 concentration. This is believed to be part of the reason some people get central apnea on CPAP. You may end up "washing out" CO2, which reduces your respiratory drive.

So far this is correct so far as I understand.

Increasing the CO2 level in your inhaled air may increase your blood CO2 level

And this is where I think you go wrong. Why should increasing the level of CO2 you inhale increase your blood levels of CO2? Your lungs are adapted to selectively extract oxygen from inhaled air and NOT to extract other inhaled gasses. The CO2 in your blood is a product of oxidization in your tissues. It is the CO2 in the blood that triggers the breathing reflex, not the CO2 in your lungs.

You have the causation backwards, in my opinion.

Can you cite any studies that support your beliefs?

Breathing into a paper bag is the classic way to increase CO2 level in your blood. The method is used to increase CO2 levels when one hyperventilates. There are experimental devices that can be attached to CPAP machines that increases CO2 levels in this manner. http://www.researchgate.net/profile/Dean...000000.pdf

[PaytonA]

Breathing into a paper bag is the classic way to increase CO2 level in your blood. The method is used to increase CO2 levels when one hyperventilates. There are experimental devices that can be attached to CPAP machines that increases CO2 levels in this manner. http://www.researchgate.net/profile/Dean...000000.pdf

The study that you linked to is a study of the effect of vent location and mask design on amount of rebreathed CO2. Could you clarify how this relates to the discussion of gas transfer by the lungs.

Best Regards,

PaytonA

[richb]

Breathing into a paper bag is the classic way to increase CO2 level in your blood. The method is used to increase CO2 levels when one hyperventilates. There are experimental devices that can be attached to CPAP machines that increases CO2 levels in this manner. http://www.researchgate.net/profile/Dean...000000.pdf

The study that you linked to is a study of the effect of vent location and mask design on amount of rebreathed CO2. Could you clarify how this relates to the discussion of gas transfer by the lungs.

Best Regards,

PaytonA

Why would they be doing a study on re breathing CO2 if it did not occur?
Gas transport in the lungs is explained here: http://people.eku.edu/ritchisong/301notes6.htm
CO2 can be transferred to the blood by breathing just as it can be released from the blood. CO2 in the blood is converted to carbonic acid and incidentally lowers blood pH. The body uses an enzyme Carbonic Anhydrase to release the bound CO2. The higher CO2 concentration in the lungs is diluted by the incoming air with a lower CO2 concentration (Theory of partial pressures). If one breathes air with a higher concentration of CO2 than contained in the blood CO2 will be transferred to the blood. The Carotid Body is an organelle that senses blood acidity and increases respiration to get rid of CO2 and thereby raise blood pH. Under normal sea level conditions it is very difficult to accumulate CO2 in the blood because the body simply raises the rate of respiration. People with a defective Carotid body may not sense that the CO2 level is just right to achieve normal breathing during sleep. For these people (people with periodic breathing and Central Apnea) an idea is to try to raise the concentration of CO2 in air being inhaled. One way suggested is to create some dead air space in the tubing of the CPAP machine. (You can search for this trial.) A problem for some people with periodic breathing and Central Apnea is that an extra amount of CO2 is washed out of their blood by the pressure of the machine. The lungs and sinuses normally retain a small amount of CO2 that is re breathed. The pressures of CPAP machines can wash out this CO2. Greater expansion of the alveoli are also a factor. There have also been studies of directly adding CO2 to the CPAP air stream. http://www.ncbi.nlm.nih.gov/pubmed/9074983 Idiopathic Central Apnea/periodic breathing is difficult to treat. A pharmacological pathway exists that has the effect of breathing extra CO2. People who suffer from High Altitude sickness very often have Central Apnea/ periodic breathing when sleeping. The High altitude sickness medication Acetazolamide is a substance that inhibits the enzyme Carbonic Anhydrase leaving higher concentrations of carbonic acid in the blood. This higher acidity (lower pH) makes the Carotid Body think that there is too much CO2 in the blood and thereby stimulates respiration. Studies have shown that this treatment can reduce Central Apnea and periodic breathing. http://www.nswo.nl/userfiles/files/publi...en%202.pdf

Rich

[eseedhouse]

Why would they be doing a study on re breathing CO2 if it did not occur?
Gas transport in the lungs is explained here: http://people.eku.edu/ritchisong/301notes6.htm
CO2 can be transferred to the blood by breathing just as it can be

Well, I've read that link and don't see what you see, apparently. It seems to me that it agrees with my view.

[richb]

Why would they be doing a study on re breathing CO2 if it did not occur?
Gas transport in the lungs is explained here: http://people.eku.edu/ritchisong/301notes6.htm
CO2 can be transferred to the blood by breathing just as it can be

Well, I've read that link and don't see what you see, apparently. It seems to me that it agrees with my view.

I must be misunderstanding what you see here.

[nicholb]

Interestingly the last time I was in that area about 20 years ago was before I was diagnosed and of course was not using CPAP. I had no issues with altitude other than shortness of breath for the first day or 2. This time it actually got worse during the time I was there. My highest AHI's were the last 2 days of the week and I also felt the worst. I did find this (quoted below) in one of the articles. I read up on acetazolamide and it basically works by changing the blood Ph so the breathing regulation does not get screwed up. I'll have to investigate that option if I am staying at higher elevations again.

"Patients with obstructive sleep apnea who travel to high altitude should continue to use their CPAP machine while traveling as they do at home. Such patients might benefit from preventive treatment with acetazolamide when staying at an altitude higher than 1600 m; they should consult their doctor about this possibility."

[archangle]

Increasing the CO2 level in your inhaled air may increase your blood CO2 level

And this is where I think you go wrong. Why should increasing the level of CO2 you inhale increase your blood levels of CO2? Your lungs are adapted to selectively extract oxygen from inhaled air and NOT to extract other inhaled gasses. The CO2 in your blood is a product of oxidization in your tissues. It is the CO2 in the blood that triggers the breathing reflex, not the CO2 in your lungs.

You have the causation backwards, in my opinion.

Can you cite any studies that support your beliefs?

Can you cite any studies that support your belief that there's some sort of selective transport across the blood-air interface in the lungs?

The lungs are passive gas exchange devices in the technical sense. The gas transport is powered by simple diffusion across the alveolar membrane. Even if they are selective for CO2 and O2, they aren't directionally sensitive.

CO2 flows from the blood to the air because concentration is higher in the blood than the air. O2 flows the other way for similar reasons. There's no need for a selective directional mechanism because O2 and CO2 are always flowing "downhill" across the alveolar membrane in normal circumstances.

Even if the alveolar membrane were some sort of one-way CO2 valve, CO2 in the inhaled air would still increase blood CO2 concentration, because the body is producing CO2 all the time and a higher concentration of CO2 in the air would reduce the rate of flow of CO2 from the blood to the air. CO2 in the blood will never drop below the concentration of CO2 in the air.

Read up on the mechanisms of the lungs and alveola. Also read up on EERS and CO2 supplementation for central apnea. Both involve mechanisms for increasing the CO2 in the air and its effect of increasing CO2 in the blood.

However, I'm not saying that EERS or even CO2 supplementation will cure high altitude induced central apnea. Respiration and central apnea are complicated processes. I'm also not sure that it's been proven that high altitude central apnea is due to CO2 washout. .

It makes sense that EERS might help, but I don't know if it's been studied. EERS/CO2 supplementation for CA needs more study, even at sea level.

I DON'T recommend do it yourself EERS treatment. If you get it wrong badly enough, you could suffocate.

[richb]

Increasing the CO2 level in your inhaled air may increase your blood CO2 level

And this is where I think you go wrong. Why should increasing the level of CO2 you inhale increase your blood levels of CO2? Your lungs are adapted to selectively extract oxygen from inhaled air and NOT to extract other inhaled gasses. The CO2 in your blood is a product of oxidization in your tissues. It is the CO2 in the blood that triggers the breathing reflex, not the CO2 in your lungs.

You have the causation backwards, in my opinion.

Can you cite any studies that support your beliefs?

Can you cite any studies that support your belief that there's some sort of selective transport across the blood-air interface in the lungs?

The lungs are passive gas exchange devices in the technical sense. The gas transport is powered by simple diffusion across the alveolar membrane. Even if they are selective for CO2 and O2, they aren't directionally sensitive.

CO2 flows from the blood to the air because concentration is higher in the blood than the air. O2 flows the other way for similar reasons. There's no need for a selective directional mechanism because O2 and CO2 are always flowing "downhill" across the alveolar membrane in normal circumstances.

Even if the alveolar membrane were some sort of one-way CO2 valve, CO2 in the inhaled air would still increase blood CO2 concentration, because the body is producing CO2 all the time and a higher concentration of CO2 in the air would reduce the rate of flow of CO2 from the blood to the air. CO2 in the blood will never drop below the concentration of CO2 in the air.

Read up on the mechanisms of the lungs and alveola. Also read up on EERS and CO2 supplementation for central apnea. Both involve mechanisms for increasing the CO2 in the air and its effect of increasing CO2 in the blood.

However, I'm not saying that EERS or even CO2 supplementation will cure high altitude induced central apnea. Respiration and central apnea are complicated processes. I'm also not sure that it's been proven that high altitude central apnea is due to CO2 washout. .

It makes sense that EERS might help, but I don't know if it's been studied. EERS/CO2 supplementation for CA needs more study, even at sea level.

I DON'T recommend do it yourself EERS treatment. If you get it wrong badly enough, you could suffocate.

Here is a study of EERS and Central Apnea: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3014237/

[eseedhouse]

The lungs are passive gas exchange devices in the technical sense. The gas transport is powered by simple diffusion across the alveolar membrane. Even if they are selective for CO2 and O2, they aren't directionally sensitive.

CO2 flows from the blood to the air because concentration is higher in the blood than the air. O2 flows the other way for similar reasons. There's no need for a selective directional mechanism because O2 and CO2 are always flowing "downhill" across the alveolar membrane in normal circumstances.

OK, I see your point and agree with your logic. The way I think of it the aveola wall and adjacent capillary walls are in effect semipermeable membranes and gasses permeate them by osmosis. If the partial pressure of CO2 in the ambient air inside the lungs is higher than the partical pressure in the bloodstream then CO2 should flow into the bloodstream.

But CO2 is a lot more poisonous than O2, and I prefer if I have to breath something other than air that it be oxygen. The CO2 in the bloodstream is generally the result of oxidation of organic compounds so more O2 in the blood also increases CO2 in the bloodstream indirectly.

Of course oxygen is also a poison in high enough concentrations.

[Shastzi]

That's right folks. All things in moderation!