CO2 Washout ???

There have been a number of posts recently which use the phrase "CO2 Washout". I find myself puzzled as to what some of these are trying to say.

Virtually all commercially available xPAP masks are "vented", that is, there is intentionally a constant flow of air into the mask from the tubing and out through the vent holes. This is done to "wash out" of the mask the air we exhale, which is slightly oxygen depleted and carbon dioxide enriched with respect to room air. If a mask is adequately designed (as all commercially available models presumably are), virtually all of the exhaled air will be "washed out" before our next inhalation, so that we are breathing in "unadulterated" room air.

Yet some posts citing "CO2 washout" appear to be using this phrase as though xPAP were "washing" carbon dioxide out of our bodies, and thereby affecting our breathing and the efficacy of treatment. There also seem to be suggestions that different masks produce different results due to differences in "CO2 washout" characteristics.

To the best of my understanding, xPAP does not directly affect CO2 levels in our bodies, except to the extent that by reducing or eliminating apneas and hypopneas and thus restoring "normal" breathing, oxygen and CO2 levels are "normalized". xPAP does not otherwise change the rate (exception for T-type bipaps) or depth of breathing, and we are breathing ordinary room air.

I'd be grateful if the posters who have utilized this phrase would be so kind as to explain how they feel "CO2 Washout" affects their breathing or their xPAP treatment. Thanks. Velbor

You are correct, washout of a XPAP mask is set by the vent holes, and correct for normal use levels. The different designs of the shape of the masks does change washout some, but not to the level that it matters. Some masks have a larger internal volume so rebreathing may be higher. I think some like to blame the way they feel on wrong conclusings. I take what sounds right, and throw the rest out.

CO2 levels do make a difference in how our bodies tell out mind to control breathing, it's a automatic function of our brain, if we need to breath more, we do, also the depth of breath is controlled. By changing our CO2 levels, we change the requirements, our brain does the math and sends the signal to breath. Normal people can't force themselves to stop breathing, if you pass out you start breathing again.

You can change the vent rates of a mask by changing the vent holes, not a good idea, but I have done it, you must be careful not to close the vent too much. So "Don't try This at Home, kid's". Don't Run with Scissors either. Jim

Velbor,

Do some Google searches on "CO2 washout" and "Carbon Dioxide washout" and there are lots of links that come up.
As Jim said, CO2 is a trigger for our bodies to breathe. With XPAP and a pressure that is too low and/or with a mask that has a "Vent Flow Rate" that is too low it hinders the oxygen getting into our systems.

Den

this discussion can become dangerous for some patients so no experimentation should be attempted with your equipment.

this subject matter is more a factor if you experience idiopathic Central Apnea. While it is true most vented masks vent your exhaled CO2, a greater portion of that exhaled air is mixed with the incoming air where you rebreathe your exhaled CO2 in mixed form. It may also be true that use of some mask interfaces can exhaust too much CO2 out of your system essentially vacuuming CO2 out of your system including that contained in the lungs. CO2 washout is the amount of CO2 that gets washed-out of your exhaled breathe. The opposite is just as true where you retain too much CO2.

I have my own simple theory on this and will state up front I don't believe Central Apnea is a problem. I see it as they bodies own way of controlling the amount of CO2 maintained in your system. CO2 is used in your respiratory drive with many checks and balances in the form of chemoreceptors. Your body stops the respiratory drive because it needs to retain more CO2, that is all a central apnea is (my theory) it is NOT a dysfunction of the neurological drive signal as suggested by the medical profession.

If you want to reduce or stop Central Apnea, you manipulate your breathing so you retain more CO2, this retention in CO2 encourages the respiratory drive the result is you breathe.

Effects of inhaled CO2 and added dead space on idiopathic central sleep apnea:
http://jap.physiology.org/cgi/content/full/82/3/918

IDIOPATHIC CENTRAL SLEEP APNEA SYNDROME (ICSAS) is an uncommon disorder characterized by recurrent central apneas during sleep in the absence of ventilatory failure, cardiac failure, or neuromuscular diseases and in association with symptoms of central sleep apnea (7). Central apneas in patients with ICSAS are precipitated by abrupt increases in tidal volume (VT) and minute ventilation (I), often in association with arousals from sleep, which are accompanied by reductions in PCO2 (30). These observations indicate that central apneas in ICSAS are posthyperventilatory in nature. In addition, our laboratory has previously demonstrated that compared with healthy control subjects, those with ICSAS chronically hyperventilate in association with hypocapnia both while they are asleep and while awake (29). Furthermore, both central and peripheral chemoresponsiveness in patients with ICSAS are increased compared with healthy control subjects, suggesting that increased ventilatory responsiveness to chemical respiratory stimuli may play a role in provoking hyperventilation and hypocapnia (29, 30). Taken together, these data led us to propose that chronic and acute hyperventilation interact in such a way as to precipitate central apneas during sleep: the former may maintain arterial PCO2 (PaCO2) close to the apnea threshold, and the latter may drive PaCO2 below this threshold, resulting in central apneas. Arousals may facilitate this process by causing abrupt increases in I and reductions in PaCO2.

If recurrent reductions in PaCO2 below the threshold for apnea are the mechanism responsible for central apneas during sleep in patients with ICSAS, we reasoned that raising and maintaining PaCO2 above the apneic threshold should abolish central apneas in these patients. To test this hypothesis, we examined the effects of raising PaCO2 on central apneas in patients with ICSAS. This was accomplished either by having them inspire a CO2-enriched gas mixture or by having them breathe through a face mask with added dead space during sleep to increase the fraction of inspired CO2 (FICO2). To this end, patients with ICSAS were studied overnight under four different conditions: 1) room air breathing; 2) alternating room air and CO2 inhalation, 3) CO2 inhalation all night, and 4) breathing through a face mask with added dead space all night.

lookie there these guys agree with me

If you want to know how the Adapt SV functions with central sleep apnea, it works by carefully controlling your breathing so you retain more CO2, by retaining more CO2 it encourages respiratory drive and you breathe normally again. Look at CSR and how that gets resolved, same principle.

I've always said if Central Apnea is showing up on your reports there is something wrong with the CO2 retention level of your circuit. Use a mask like a Swift or Nasalaire in their earlier form and these were like a vacuum cleaner as it relate to CO2. However a mask interface that retains more CO2 feels more humid or stuffy compared to one that exhausts or "washes" out more CO2. Most people generally prefer the latter when it comes to comfort, may not be the best for their sleep but it may feel better. In order to understand this you almost have to have used a dozen different mask interfaces to "feel" the difference, CO2 washout characteristics are different from interface to interface.

In fact after the Harvard CSDB study most mask mfgs like Resmed and Respironics redesigned the exhaust ports on their masks, before that exhaust ports were a crude undertaking. Now you will notice they are computer designed with "square" exhaust holes. The UMFF for example, changed completely from the silicone horseshoe to the Quattro's exhaust port. All of Respironics masks changed to a similar design.

I have some Central Apnea, I use a Soyala which retains more CO2 than say a ComfortGel or Mirage II. It can even been seen in the different flow rates on the mask flow chart. You can feel the difference simply by switching masks from one to the other, one may feel refreshing the other stuffy, and depending on your disorder the latter may be better suited for your therapy. We are all different.

Can I tell the difference? Absolutely! My Silverling reports spit that information out daily. I can use a UltraMirage II nasal mask and see the CA's show up. I can use a UMFF and watch it get even worse yet. I could not use a Swift or a Nasalaire or even a Breeze, I couldn't make it through the night with those. I can switch to the Soyala while the incoming air doesn't feel as refreshing, the proof is in the pudding in my reports with Zero CA's compared to a dozen or more with the others.

For all tense and purpose, I have have a mild form of CSDB with all the mixed apnea seen on my PSG's. I've been dealing with it probably 3-4 years before the study on CSDB ever came out. I never could use straight CPAP or Autopap effectively or for very long, things seemed to always turn into a train wreck. Purchased and tried every machine out there, only one that truly allows me any sleep is the 420e, it avoids the centrals and responds to the obstructive when needed. Sometimes I need 14cm to clear an obstructive apnea most other times over 9 cm and the CA's show up with vengeance. Now that I know how to control it with use of the right machine and mask, I rarely have a train wreck.

Resmed, in the Swift LT manual wrote:•• As with all masks, some rebreathing may occur at low CPAP pressures.

And I"ve seen that said, similarly, in other manuals.

On the other hand, people with CSDB stop breathing when they don't have enough CO2 in their system. (No typo in those last words). Their ventilation on an Adapt SV machine is set to 90% or their target, in order to force them to take breaths.

Look at the multimedia presentation on vpapadaptsv.resmed.com to understand more, especially the third part (use FF to move to the end of the part you don't want to watch) where they start explaining they apneic threshold, and the fact the people with csdb don't breathe because their CO2 (carbon dioxide level) is too low.

O.

Velbor wrote:There have been a number of posts recently which use the phrase "CO2 Washout". I find myself puzzled as to what some of these are trying to say.

Virtually all commercially available xPAP masks are "vented", that is, there is intentionally a constant flow of air into the mask from the tubing and out through the vent holes. This is done to "wash out" of the mask the air we exhale, which is slightly oxygen depleted and carbon dioxide enriched with respect to room air. If a mask is adequately designed (as all commercially available models presumably are), virtually all of the exhaled air will be "washed out" before our next inhalation, so that we are breathing in "unadulterated" room air.

Yet some posts citing "CO2 washout" appear to be using this phrase as though xPAP were "washing" carbon dioxide out of our bodies, and thereby affecting our breathing and the efficacy of treatment. There also seem to be suggestions that different masks produce different results due to differences in "CO2 washout" characteristics.

To the best of my understanding, xPAP does not directly affect CO2 levels in our bodies, except to the extent that by reducing or eliminating apneas and hypopneas and thus restoring "normal" breathing, oxygen and CO2 levels are "normalized". xPAP does not otherwise change the rate (exception for T-type bipaps) or depth of breathing, and we are breathing ordinary room air.

I'd be grateful if the posters who have utilized this phrase would be so kind as to explain how they feel "CO2 Washout" affects their breathing or their xPAP treatment. Thanks. Velbor

Velbor, I think in most discussions here, when they talk about 'CO2 washout', they are referring to the effectiveness with which the CO2 is washed out of your out breath remaining in the mask and the tube. CO2 is not removed 100%, before you take your next breath in any cpap system, so there is a some recirculation of CO2 (which is in a higher concentration than in the normal outside air). As a result of this, it also indirectly affects the CO2 levels in the lungs. Very interestingly this wash out rate varies considerably among mask models -- and that may indeed be one of the reasons why people feel better with one mask over other --, depends a lot on the pressure, as well as if you are using Cflex, Aflex or such exhale pressure reliefs, and the setting of such pressure reliefs.

One item often not mentioned though is that, because of the higher than normal outside air pressure that is used in cpap (the pressure is needed to split open obstructed passages -- that is the fundamental principle of xPAP) there is more quantity of effective air circulated thru your lungs and this increases more removal of CO2 from your lungs than when you are not using xPAP. In some cases (possibly most?) these two factors (higher pressure induced better washout, and the less than 100% of washout from the cpap system) tends to compensate each other!

But more washout or less washout than normal, which is a side effect of xPAP, for some people may cause some other problems.

ozij wrote:

Resmed, in the Swift LT manual wrote:•• As with all masks, some rebreathing may occur at low CPAP pressures.

And I"ve seen that said, similarly, in other manuals.

On the other hand, people with CSDB stop breathing when they don't have enough CO2 in their system. (No typo in those last words). Their ventilation on an Adapt SV machine is set to 90% or their target, in order to force them to take breaths.

Look at the multimedia presentation on vpapadaptsv.resmed.com to understand more, especially the third part (use FF to move to the end of the part you don't want to watch) where they start explaining they apneic threshold, and the fact the people with csdb don't breathe because their CO2 (carbon dioxide level) is too low.

O.

This might be a better link either that or I have DNS problems:
http://www.vpapadaptsv.com/ResMed.htm

Snoredog wrote: I have my own simple theory on this and will state up front I don't believe Central Apnea is a problem. I see it as they bodies own way of controlling the amount of CO2 maintained in your system. CO2 is used in your respiratory drive with many checks and balances in the form of chemoreceptors. Your body stops the respiratory drive because it needs to retain more CO2, that is all a central apnea is (my theory) it is NOT a dysfunction of the neurological drive signal as suggested by the medical profession.

Snoredog, I quoted only a small portion of your good post above. I also tend to think that this is a natural balancing mechanism of the body.

However the centrals, I believe, do disrupt the normal rem dream patterns and disrupt sleep and, IMO, may cause some unwanted bad effects on the body. That may be one of the reasons the majority of medical literature out there tends to say centrals are an undesirable thing.

feeling_better wrote:

Snoredog wrote: I have my own simple theory on this and will state up front I don't believe Central Apnea is a problem. I see it as they bodies own way of controlling the amount of CO2 maintained in your system. CO2 is used in your respiratory drive with many checks and balances in the form of chemoreceptors. Your body stops the respiratory drive because it needs to retain more CO2, that is all a central apnea is (my theory) it is NOT a dysfunction of the neurological drive signal as suggested by the medical profession.

Snoredog, I quoted only a small portion of your good post above. I also tend to think that this is a natural balancing mechanism of the body.

However the centrals, I believe, do disrupt the normal rem dream patterns and disrupt sleep and, IMO, may cause some unwanted bad effects on the body. That may be one of the reasons the majority of medical literature out there tends to say centrals are an undesirable thing.

Oh I wasn't discounting the arousal factor associated with the CA, sleep quality definitely suffers, that is the reason you want to avoid the conditions which allow them to persist. The CA's are an indicator of unstable breathing, your body is shutting down breathing to regulate the amount of CO2. The idea is not to fight it but use the device so it gives the body what it wants. So if you can use the machine to manipulate breathing where it retains more CO2 the CA's should go away on their own. Ideally, you do this before the CA's show up. Maybe we have little valves on our masks that allow us to customize the exhaust rate for our particular disorder.

Snoredog wrote:

ozij wrote:

Resmed, in the Swift LT manual wrote:•• As with all masks, some rebreathing may occur at low CPAP pressures.

And I"ve seen that said, similarly, in other manuals.

On the other hand, people with CSDB stop breathing when they don't have enough CO2 in their system. (No typo in those last words). Their ventilation on an Adapt SV machine is set to 90% or their target, in order to force them to take breaths.

Look at the multimedia presentation on vpapadaptsv.resmed.com to understand more, especially the third part (use FF to move to the end of the part you don't want to watch) where they start explaining they apneic threshold, and the fact the people with csdb don't breathe because their CO2 (carbon dioxide level) is too low.

O.

This might be a better link either that or I have DNS problems:
http://www.vpapadaptsv.com/ResMed.htm

You're right, Snoredog.
O.

did you guys notice from the Resmed video that the effects of CSDB are more likely to show up worse in Stage 2 sleep vs REM?

It may also suggest you probably will never make REM, could be why patients with a form of this syndrome feel so fatigued even with what they "think" is effective CPAP therapy.

I remember when this first came about, I'm sure SWS remembers also, it was thought to be extremely "rare" for one to have this disorder, now they say 15% or more of those with SDB have the disorder. This really is important in selecting a particular machine in my opinion.

Snoredog: I find it interesting that you seem to have a pretty complex sleep issue, including centrals, yet find that one of the least expensive machines , Goodnight 420 E, seems to work best for you. I have been looking at getting a second machine for travel for my BIPAP ST, but have hesitated because of the $5,000 cost of the auto bipaps with ST. Do you find that with your machine that your CO2 is regulated to where you don't need the ST? Just curious - I find your theory extremely interesting and am exploring how it might apply to others with centrals - the ST is working OK but I don't think it is giving me the best results and my centrals continue to be high, forcing the machine initiated breaths to be high. It is all inter-related somehow and that all seems too complicated for my sleep doctor (or his nurse who is the "gate-keeper"). Right now I am leaning towards trying the Bipap Auto SV or Bipap AVAPS, but don't want to pay $5K out of pocket unless pretty sure it is the right thing for somebody with limited obstructive events, but higher hyponia and centrals.

On the co2-washout thingy stuff,

Yes, the role of co2 in the air, lungs, and blood is a complicated thing and little understood in some respects. But mask manufacturers make sure their masks have safe washout within normal operating pressures. So mask-washout discussions are a red herring. We adapt to a little rebreathing much as we adapt to changes in altitude and o2 levels.

For bilevel users, for example, a much more significant impact on co2 is made by where ipap is set at and its relation to epap. (Want easier access to o2? Kick your epap up a notch. Want less co2 in ya? Kick your ipap up a notch. Tidal volume makes a difference.) I would think that any human body that is able to adjust to the constant ipap and epap changes in an auto-bilevel without ill effects would have no problem dealing with any of the masks on the market as far as co2 washout.

jnk

Snoredog wrote:did you guys notice from the Resmed video that the effects of CSDB are more likely to show up worse in Stage 2 sleep vs REM?

It may also suggest you probably will never make REM, could be why patients with a form of this syndrome feel so fatigued even with what they "think" is effective CPAP therapy.

I remember when this first came about, I'm sure SWS remembers also, it was thought to be extremely "rare" for one to have this disorder, now they say 15% or more of those with SDB have the disorder. This really is important in selecting a particular machine in my opinion.

And, considering the "quality" of the doctors practicing sleep medicine these days, that makes it pretty scary if you ask me.......for those that have CSDB.

Den

Snoredog wrote:

feeling_better wrote:

Snoredog wrote:Maybe we have little valves on our masks that allow us to customize the exhaust rate for our particular disorder.

Well, that is exactly the direction I am experimenting now with my Swift LT mask, which has 56 out port holes. Not giving details of any dangerous experiments here