High Altitude and Central Apneas

[nicholb]

I recently took a vacation to Estes Park. While there my AHI went from a normal 2-4 up to 30-40. I also had a horrible time sleeping and many times felt like I was suffocating with the mask on. Upon returning home I found almost all the AHI increase to be central apneas. I did some Googling and found that this is common. Here's a couple articles on the subject. Just something I was not aware of before and thought I'd share.

(sorry, I am evidently too new to here to post links so you'll have to Google it yourselves)

"As the oxygen levels are low, the oxygen sensors in the body signals the brain to increase breathing (hyperventilation) which in turn, leads to increase in oxygen and decrease of carbon dioxide in the body. The low carbon dioxide levels then send across signals to the brain to stop breathing to cover up the low CO2 levels and thus, breathing stops for about 12 seconds and resumes again taking in more oxygen. This results in an irregular pattern of breathing causing trouble sleeping."

[Clay L]

In one of the conversations I had with my sleep doc he mentioned that CO is the central apnea king because of altitude.

[richb]

I recently took a vacation to Estes Park. While there my AHI went from a normal 2-4 up to 30-40. I also had a horrible time sleeping and many times felt like I was suffocating with the mask on. Upon returning home I found almost all the AHI increase to be central apneas. I did some Googling and found that this is common. Here's a couple articles on the subject. Just something I was not aware of before and thought I'd share.

(sorry, I am evidently too new to here to post links so you'll have to Google it yourselves)

"As the oxygen levels are low, the oxygen sensors in the body signals the brain to increase breathing (hyperventilation) which in turn, leads to increase in oxygen and decrease of carbon dioxide in the body. The low carbon dioxide levels then send across signals to the brain to stop breathing to cover up the low CO2 levels and thus, breathing stops for about 12 seconds and resumes again taking in more oxygen. This results in an irregular pattern of breathing causing trouble sleeping."

Some of the best study of Central Apnea has come from research on High Altitude Sickness.

[TyroneShoes]

...The low carbon dioxide levels then send across signals to the brain to stop breathing to cover up the low CO2 levels ...

Wouldn't "slow the respiration" be a more accurate physical response than "stop breathing"?

This is all very fascinating, and I wish I understood it better. It does not seem to make sense to me, however, that high altitude would make CA worse. My first thought is that since there are fewer O2 molecules per breath available, that this would spur you to breathe quicker because the O2 would deplete quicker, meaning that you would flag less CAs because the period would be shorter.

This makes me think that it could not be all that simple. To actually "stop" breathing, which for a CA event can be 10 seconds or more than a minute, this means that something must be fundamentally wrong with the respiratory feedback system that regulates it.

While CPAP for OSA is an actual cure, it removes the obstacle that prevents respiration, a ventilator is a workaround, a forced breath is a workaround, and supp O2 is a workaround. If you are not breathing, what machine outside a clinical setting could ever jump start your breathing for you?

Still guessing here, but what seems to make the most sense as to why the feedback system does not regulate breathing properly might be tied to the efficiency of gas exchange, which would explain why high altitude might increase CAs; not only is the O2 concentration lower, the actual gas exchange might work somewhat differently, and not as in sync with respiratory feedback as it would at lower altitudes, especially if you are not fully conditioned to higher altitudes. "Too much" CO2 might be part of what fools the feedback system too, because that seems to be part of the equation. IOW, O2 concentration is not the only stimulus in that cycle.

But I am guessing.

More, please.

[eseedhouse]

Well I suppose you could say that there is "something wrong" with the human breathing mechanism in that we can't breath vacuum. As we go higher the air pressure becomes lower and lower and the percentage of oxygen in the atmosphere also gets lower and lower. We can adapt up to a point, but there is a limit for each of us. I think we first became recognizably "human" at or around sea level, so we are adapted to breath well there. A few populations have nevertheless adapted to continuous life at high altitude, such as many Tibetans.

But most of us are adapted to breath at sea level.

As pressure decreases it becomes harder and harder for oxygen to pass through cell walls in the lungs. As O2 decreases less is breathed, and therefore less is oxidized and turned to CO2, so the air we breath out has less CO2 in it than it would normally have and the brain centres that control our breathing are getting wrong information.

The limit of human ability to move and function without supplemental oxygen is slightly higher than the summit of Mount Everest (demonstrated by the fact that this mountain has been climbed without it) and that is only available to superbly adapted and conditioned super athletes. Even so, above about 25,000 feet everyone who is not breathing oxygen is slowly dying, though not as slowly as the rest of us are dying.

[archangle]

CO2 supplementation at high altitudes would be interesting, especially EERS (enhanced expiratory rebreathing space).

[richb]

Keep in mind that the body does not measure O2 levels. Breathing is controlled (for the most part) by the measurement of CO2 levels. Specifically the acidity of the blood is the key factor. Dissolved CO2 forms carbonic acid which lowers blood pH. Breathing removes CO2 and raises blood pH. At high altitude there is a tendency to over breathe causing hyperventilation. This in turn removes CO2 raising blood pH and suppressing breathing. This has been looked at in sleep studies of people suffering from High Altitude Sickness.

[eseedhouse]

CO2 supplementation at high altitudes would be interesting, especially EERS (enhanced expiratory rebreathing space).

There's already barely enough oxygen at high altitudes and it doesn't seem like a good idea to reduce it further to me.

The CO2 in your bloodstream that stimulates your respiratory system comes from your body burning oxygen. Your lungs transfer oxygen into the blood and CO2 out of it, if I recall rightly. If so all you'd be doing is adding more oxygen starvation into the situation.

If the level of CO2 is too low to stimulate normal breathing it seems better to supplement with oxygen which will allow your body to burn more carbon and raise the level of CO2 in your blood.

I use supplemental oxygen during sleep and my central apneas have reduced to the point where they are not concerning. Of course that means I'm tied to not one, but two machines every night.

[archangle]

CO2 supplementation at high altitudes would be interesting, especially EERS (enhanced expiratory rebreathing space).

There's already barely enough oxygen at high altitudes and it doesn't seem like a good idea to reduce it further to me.

The CO2 in your bloodstream that stimulates your respiratory system comes from your body burning oxygen. Your lungs transfer oxygen into the blood and CO2 out of it, if I recall rightly. If so all you'd be doing is adding more oxygen starvation into the situation.

If the level of CO2 is too low to stimulate normal breathing it seems better to supplement with oxygen which will allow your body to burn more carbon and raise the level of CO2 in your blood.

I use supplemental oxygen during sleep and my central apneas have reduced to the point where they are not concerning. Of course that means I'm tied to not one, but two machines every night.

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.

Increasing the CO2 level in your inhaled air may increase your blood CO2 level, increase your respiratory drive, and reduce central apnea for some people. Some experiments have been done with an external CO2 supply and it helped some. EERS increases CO2 in the air at the cost of some O2, but the reduced central apnea and increased respiratory drive increases the SpO2 level in the blood for some people.

Central apnea at altitude is similar in some ways. Increasing the CO2 level by EERS, even at the cost of reduced O2 in the air, may increase the respiratory drive to the point where SpO2 increases in some people.

I believe the idea is sound. However, it needs appropriate study. I definitely DO NOT recommend someone tinker with their own home grown EERS system.

[eseedhouse]

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?