Functioning with high CO2

silent running · 14th December 2006, 10:44

Quote: (Originally Posted by CharlieT)

Thank you Mike for starting this educational and very relevant post.

This is the bad one for us CCR divers, worse than the possibility of an O2 hit.

I have a great fear of overbreathing my scrubber so stop and rest if I have over-exerted myself.

Charlie

I agree Charlie, thanks to Mike for furthering the discussion of CO2 production.

But I have not had any occaision to worry about overbreathing my radial scrubber. Having a low WOB to begin with has given me some comfort after having had to work hard at the end of my scrubber life many times. Efficeincy, optimal insulation and minimizing WOB are all effective hedges against CO2 hits. But I still like the idea of a BOV for the multiple reasons listed above... -Andy

jhaaja · 14th December 2006, 10:58

Quote: (Originally Posted by Mike)

Dynamic apnea or freediving clearly must, almost by definition.

Sprinting, I'd still consider falls somewhere in between. Being somewhat oldschool, I consider that breathing slows you down. (Neil Brooks was once quoted as saying "30 seconds? I can hold my breath that long, why breath?)

Even if we are to just consider dynamic apnea, why don't we see the same CO2 hit symptoms there? Or perhaps that's part of what a Samba is? But doing apnea stuff I get really recognisable symptoms like diaphram contractions before really needing to breath. If it only happened in dynamic apnea I'd be suggesting that it could be due to the other exercise related breathing triggers, but as it happens in static apnea as well, that doesn't seem likely.

I am no expert on the matter but I will stick my spoon in

In breath-hold diving you accumulate CO2 that is for sure but the time span is short 1-3mins or more if you are really good. And usually this is done shallow, so partial pressures stay low. While diving Rebreather you are usually deeper so the partial pressures can be a lot higher and the time span for you to accumulate CO2 can be a lot longer (if you have a small by pass in the scrubber for example).

I have thought that those diaphram contractions start when the CO2 level rises to a certain point. PpO2 can still be in acceptable level if you have not hyperventilated before apnea.

Just my thoughts...

**nigelh** · 14th December 2006, 11:35

In Freediving the received wisdom is that a samba, a shallow water black out, is caused by low O2. However I have seen a guy, well more than one, samba and noticed what Gordon Henderson pointed out - no blue lips.

I've been conscious down to the 'blue lips' point without feeling any more twitchy than normal so I suspect CO2 is part of the equation in a samba.

That was sitting by my hospital bed as relaxed as you can be if you think you're probably going to be dead in a few minutes. Also I had all hell breaking out around me - you just aren't allowed to have a heart attack when the consultant is doing rounds. I think I've done a samba too but I wasn't looking in the mirror as it was my first time over 25 meters on 'Free Immersion' (no fins, just a rope), passing the 15m mark on way back up (5 stories yet to climb) and knowing you've overdone it was bad and I was grabbed by the safety diver as I surfaced.

CharlieT · 14th December 2006, 11:42

Nigel

Isn't diving a CCR enough of a challenge! Thank goodness for safety divers

Charlie

6Gill · 14th December 2006, 14:28

CO2 hits seems to have slightly different effects on different people. From personal experience a BOV is a great thing, not a guarantee, but an excellent safety tool.

Quote: (Originally Posted by Mark Chase)

A few points from my perspective:

1: I know two people who have had Co2 hits both experienced deep divers one is an instructor. Both said they couldn't force them selves to take the loop out of their mouths. They were breathing to fast to allow them selves to switch over. One solved the problem by doing a rapid ascent on loop. He was at 20m on the shot. The other dill flushed until he got confident enough to bailout which was apparently immediately after he ran out of diluent

2: Breathing elevated PP02 can delay the onset of symptom of a C02 hit so you don't realize you have a problem till its too late.

3: A BOV will make you more inclined to bailout early because its simple. We loose the habit of reg switching on CCR and we don't like re filling bailout cylinders. As a result we are less likely to switch to OC when a problem occurs. Having made this fundamental error a couple of times I opted for a BOV plumbed into a large off board cylinder.

ATB

Mark Chase

Gene_Hobbs · 14th December 2006, 15:08

Quote: (Originally Posted by dteubner)

Didn't mean to make your head explode mate.

The "breathing is a response to hypercapnea" business does not explain what happens in esercise. Hyperventilation in exercise starts without the CO2 changing. There are many many inputs to the respiratory centres and large muscle movements are themselves enough to make you breathe harder.

The concept of oxygen debt is about the lactate. As you said, lactic acid is the end point of anaerobic metabolism as energy is derived from the conversion of sugar to lactate, without oxygen being required. Once there is available oxygen again then the lactate needs to be converted all the way through to CO2 - which requires oxygen. My understanding is that it's this use of oxygen to get rid of lactate which represents the 'debt'.

Body cells need a relatively normal pH to function efectively. Anaerobic exercise produces lactic acid, which makes the blood acidic. If you add hypercarbia (which also makes the blood acidic) on top of this, the pH falls quite dramatically and normal function becomes impossible.

Dave T

Edit - some evidence apart from "I reckon this" Entrez PubMed

Nice Dave! Just to bring things back some. The key wording to the abstract posted is "transition to steady state". Since some don't read this stuff all the time, published research is on "steady state" unless they are intentionally looking at changes like this example or a VO2max, etc. It takes somewhere on the order of three to five minutes to reach a steady state (and yes, this does include the same workload with the mouthpiece from the start, changes in workload would not allow for a "steady state").

So, if we are diving for more than 3-5 minutes (with the same workload), we will reach a steady state. So now, simply put, we have an increase in O2 consumption and increase in CO2 production and the body adjusting so that it is maintaining pH (for the already mentioned sub max workload). Now, to pull this away from BASIC respiratory and exercise physiology back to applied physiology. If the CCR is working properly, there will be no CO2 accumulation in the loop. Now, lets assume we start to overbreathe. What is the change in the loop? An increase in inspired CO2. What is we have a scrubber break through? Still an increase in inspired CO2. From here the symptoms get fun.

(you notice I don't talk about cognitive changes here, I feel this has been covered pretty well in other threads)

Just as much fun as looking at resting circuits without absorbent is following that up with a short run to boost CO2 production and doing it again (not a steady state since you would be recovering but it will not take long with an empty circuit). (And again, I am NOT saying this is safe. If you do try this, please do so with someone else present.) Too bad we don't all have etCO2 monitors at home to play with... Do something like this once and the expense for a BOV will probably start to seem less.

Janos · 14th December 2006, 16:43

I'm fairly sure I once heard [1] that high ppO2's reduced the initial symptoms of CO2 breakthough. So tunnel vision, dizzyness, etc. was less likely with a ppO2 of > 1.0 than witha ppO2 of 0.21.

Has anyone got any facts to support or disprove this?

Janos

[1] - A prefix that comes second to "I read on the internet that..." in terms of reliability

Gene_Hobbs · 14th December 2006, 19:26

Quote: (Originally Posted by Janos)

I'm fairly sure I once heard [1] that high ppO2's reduced the initial symptoms of CO2 breakthough. So tunnel vision, dizzyness, etc. was less likely with a ppO2 of > 1.0 than witha ppO2 of 0.21.

Has anyone got any facts to support or disprove this?

Well, I did not know of anything so I asked Piantadosi. Here is his reply:

I am not sure what you mean by CO2 breakthrough--this is not a physiological term. There is CO2 breakpoint in breath-hold diving which O2 will help with some. For CO2 narcosis, I don't know of any data or any reason why O2 should help prevent that. A high PO2 and a high PCO2 is of course going to hasten the onset of CNS O2 toxicity, which contributes to the shortening of seizure latency in closed circuit O2 diving and 36%Nitrox diving.

dteubner · 14th December 2006, 23:02

Quote: (Originally Posted by Mike)

Thanks Dave

Dynamic apnea or freediving clearly must, almost by definition.

Even if we are to just consider dynamic apnea, why don't we see the same CO2 hit symptoms there? Or perhaps that's part of what a Samba is? But doing apnea stuff I get really recognisable symptoms like diaphram contractions before really needing to breath. If it only happened in dynamic apnea I'd be suggesting that it could be due to the other exercise related breathing triggers, but as it happens in static apnea as well, that doesn't seem likely.

Perhaps I need to get someone to take some blood samples at the pool...

Mike - learning stuff today!

It is very clear that different people have different responses to CO2, and you can be trained to reduce the response.

Great breathhold divers are able to tolerate much higher levels of CO2 than crap ones - this is about the concept of the "break point" which is the CO2 at which you just have to breathe.

When people started to measure CO2's in elite military divers at depth they were surprised to find that many of them were running levles as much as twice normal, obviously without discomfort, and apparently without much risk.

I think that there are a couple of important points.

If your CO2 is high but it doesn't bother you then that's probably mostly OK apart from a likely higher risk of O2 toxicity and maybe worse narcosis.

If, on the other hand, your CO2 is high and it is bothering you (either because of breakthrough, scrubber failure, too high a work of breathing or whatever) then you are in big trouble. Many people find that they cannot hold their breath in this situation, and therefore will have big problems bailing out - as Mark has pointed out.

Sometimes symptoms other than dyspnoea will predominate (Maybe more often in great breathold divers) and in these guys ordinary bailout will be just fine (as long as they recognise the problem).

To look at it another way there are two different groups of hypercapnic divers. In one, all their gear is working just fine and they 'like' to have a high CO2. The others have a problem which their body is trying to correct but is prevented from doing so by an equipment issue. These people will feel very short of breath and dyspnoea casues panic. Panic is bad. The more complicated the fix is the less likely it will work. This is why I think BOV's are good.

You don't need to do blood samples at the pool, BTW. You can get a good idea of what the aterial CO2 is by measuring it at the end of a breath with a thing called a capnometer. If you ever come to Adelaide give me a ring and maybe we can do an experiment!

dave

**wedivebc** · 15th December 2006, 18:35

Quote: (Originally Posted by Gene_Hobbs)

I am not sure what you mean by CO2 breakthrough--this is not a physiological term. There is CO2 breakpoint in breath-hold diving which O2 will help with some. .

I think he means breakthrough as in in scubber breakthrough as when CO2 gets past the scrubber medium either by channeling or expended scrubber material.

14th December 2006, 10:44	#21 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Functioning with high CO2 Quote: (Originally Posted by CharlieT) Thank you Mike for starting this educational and very relevant post. This is the bad one for us CCR divers, worse than the possibility of an O2 hit. I have a great fear of overbreathing my scrubber so stop and rest if I have over-exerted myself. Charlie I agree Charlie, thanks to Mike for furthering the discussion of CO2 production. But I have not had any occaision to worry about overbreathing my radial scrubber. Having a low WOB to begin with has given me some comfort after having had to work hard at the end of my scrubber life many times. Efficeincy, optimal insulation and minimizing WOB are all effective hedges against CO2 hits. But I still like the idea of a BOV for the multiple reasons listed above... -Andy
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14th December 2006, 10:58	#22 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 885	Re: Functioning with high CO2 Quote: (Originally Posted by Mike) Dynamic apnea or freediving clearly must, almost by definition. Sprinting, I'd still consider falls somewhere in between. Being somewhat oldschool, I consider that breathing slows you down. (Neil Brooks was once quoted as saying "30 seconds? I can hold my breath that long, why breath?) Even if we are to just consider dynamic apnea, why don't we see the same CO2 hit symptoms there? Or perhaps that's part of what a Samba is? But doing apnea stuff I get really recognisable symptoms like diaphram contractions before really needing to breath. If it only happened in dynamic apnea I'd be suggesting that it could be due to the other exercise related breathing triggers, but as it happens in static apnea as well, that doesn't seem likely. I am no expert on the matter but I will stick my spoon in In breath-hold diving you accumulate CO2 that is for sure but the time span is short 1-3mins or more if you are really good. And usually this is done shallow, so partial pressures stay low. While diving Rebreather you are usually deeper so the partial pressures can be a lot higher and the time span for you to accumulate CO2 can be a lot longer (if you have a small by pass in the scrubber for example). I have thought that those diaphram contractions start when the CO2 level rises to a certain point. PpO2 can still be in acceptable level if you have not hyperventilated before apnea. Just my thoughts...
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14th December 2006, 11:35	#23 (permalink)
nigelh New member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 883	Re: Functioning with high CO2 In Freediving the received wisdom is that a samba, a shallow water black out, is caused by low O2. However I have seen a guy, well more than one, samba and noticed what Gordon Henderson pointed out - no blue lips. I've been conscious down to the 'blue lips' point without feeling any more twitchy than normal so I suspect CO2 is part of the equation in a samba. That was sitting by my hospital bed as relaxed as you can be if you think you're probably going to be dead in a few minutes. Also I had all hell breaking out around me - you just aren't allowed to have a heart attack when the consultant is doing rounds. I think I've done a samba too but I wasn't looking in the mirror as it was my first time over 25 meters on 'Free Immersion' (no fins, just a rope), passing the 15m mark on way back up (5 stories yet to climb) and knowing you've overdone it was bad and I was grabbed by the safety diver as I surfaced. __________________ nigelh
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14th December 2006, 11:42	#24 (permalink)
CharlieT Custom Title Allowed! Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Nov 2005 Location: London Posts: 449	Re: Functioning with high CO2 Nigel Isn't diving a CCR enough of a challenge! Thank goodness for safety divers Charlie
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14th December 2006, 14:28	#25 (permalink)
6Gill Custom Title Allowed! Current Rebreather/s: Megalodon Classic Kiss Other Rebreather/s: Join Date: Apr 2006 Location: Washington state Posts: 112	Re: Functioning with high CO2 CO2 hits seems to have slightly different effects on different people. From personal experience a BOV is a great thing, not a guarantee, but an excellent safety tool. Quote: (Originally Posted by Mark Chase) A few points from my perspective: 1: I know two people who have had Co2 hits both experienced deep divers one is an instructor. Both said they couldn't force them selves to take the loop out of their mouths. They were breathing to fast to allow them selves to switch over. One solved the problem by doing a rapid ascent on loop. He was at 20m on the shot. The other dill flushed until he got confident enough to bailout which was apparently immediately after he ran out of diluent 2: Breathing elevated PP02 can delay the onset of symptom of a C02 hit so you don't realize you have a problem till its too late. 3: A BOV will make you more inclined to bailout early because its simple. We loose the habit of reg switching on CCR and we don't like re filling bailout cylinders. As a result we are less likely to switch to OC when a problem occurs. Having made this fundamental error a couple of times I opted for a BOV plumbed into a large off board cylinder. ATB Mark Chase __________________ "It's a shame ignorance isn't painful!"
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14th December 2006, 15:08	#26 (permalink)
Gene_Hobbs Resident bibliophile Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Sep 2006 Location: Durham, NC, USA Posts: 133	Re: Functioning with high CO2 Quote: (Originally Posted by dteubner) Didn't mean to make your head explode mate. The "breathing is a response to hypercapnea" business does not explain what happens in esercise. Hyperventilation in exercise starts without the CO2 changing. There are many many inputs to the respiratory centres and large muscle movements are themselves enough to make you breathe harder. The concept of oxygen debt is about the lactate. As you said, lactic acid is the end point of anaerobic metabolism as energy is derived from the conversion of sugar to lactate, without oxygen being required. Once there is available oxygen again then the lactate needs to be converted all the way through to CO2 - which requires oxygen. My understanding is that it's this use of oxygen to get rid of lactate which represents the 'debt'. Body cells need a relatively normal pH to function efectively. Anaerobic exercise produces lactic acid, which makes the blood acidic. If you add hypercarbia (which also makes the blood acidic) on top of this, the pH falls quite dramatically and normal function becomes impossible. Dave T Edit - some evidence apart from "I reckon this" Entrez PubMed Nice Dave! Just to bring things back some. The key wording to the abstract posted is "transition to steady state". Since some don't read this stuff all the time, published research is on "steady state" unless they are intentionally looking at changes like this example or a VO2max, etc. It takes somewhere on the order of three to five minutes to reach a steady state (and yes, this does include the same workload with the mouthpiece from the start, changes in workload would not allow for a "steady state"). So, if we are diving for more than 3-5 minutes (with the same workload), we will reach a steady state. So now, simply put, we have an increase in O2 consumption and increase in CO2 production and the body adjusting so that it is maintaining pH (for the already mentioned sub max workload). Now, to pull this away from BASIC respiratory and exercise physiology back to applied physiology. If the CCR is working properly, there will be no CO2 accumulation in the loop. Now, lets assume we start to overbreathe. What is the change in the loop? An increase in inspired CO2. What is we have a scrubber break through? Still an increase in inspired CO2. From here the symptoms get fun. (you notice I don't talk about cognitive changes here, I feel this has been covered pretty well in other threads) Just as much fun as looking at resting circuits without absorbent is following that up with a short run to boost CO2 production and doing it again (not a steady state since you would be recovering but it will not take long with an empty circuit). (And again, I am NOT saying this is safe. If you do try this, please do so with someone else present.) Too bad we don't all have etCO2 monitors at home to play with... Do something like this once and the expense for a BOV will probably start to seem less. __________________ http://rubicon-foundation.org/ Home of the Rubicon Research Repository. For help getting started with the Repository, please visit our FAQ page. PLEASE support our work. "Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991
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14th December 2006, 16:43	#27 (permalink)
Janos "Two Sheds" Current Rebreather/s: Classic Kiss Other Rebreather/s: Classic Kiss Join Date: Feb 2005 Location: East Surrey Posts: 632	Re: Functioning with high CO2 I'm fairly sure I once heard [1] that high ppO2's reduced the initial symptoms of CO2 breakthough. So tunnel vision, dizzyness, etc. was less likely with a ppO2 of > 1.0 than witha ppO2 of 0.21. Has anyone got any facts to support or disprove this? Janos [1] - A prefix that comes second to "I read on the internet that..." in terms of reliability __________________ You can lead a horse to water but you can't climb a ladder with a large bell in both hands - Vic Reeves www.hellfins.com/shed
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14th December 2006, 19:26	#28 (permalink)
Gene_Hobbs Resident bibliophile Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Sep 2006 Location: Durham, NC, USA Posts: 133	Re: Functioning with high CO2 Quote: (Originally Posted by Janos) I'm fairly sure I once heard [1] that high ppO2's reduced the initial symptoms of CO2 breakthough. So tunnel vision, dizzyness, etc. was less likely with a ppO2 of > 1.0 than witha ppO2 of 0.21. Has anyone got any facts to support or disprove this? Well, I did not know of anything so I asked Piantadosi. Here is his reply: I am not sure what you mean by CO2 breakthrough--this is not a physiological term. There is CO2 breakpoint in breath-hold diving which O2 will help with some. For CO2 narcosis, I don't know of any data or any reason why O2 should help prevent that. A high PO2 and a high PCO2 is of course going to hasten the onset of CNS O2 toxicity, which contributes to the shortening of seizure latency in closed circuit O2 diving and 36%Nitrox diving. __________________ http://rubicon-foundation.org/ Home of the Rubicon Research Repository. For help getting started with the Repository, please visit our FAQ page. PLEASE support our work. "Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991
(Offline)

14th December 2006, 23:02	#29 (permalink)
dteubner Pedant Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Join Date: Mar 2005 Location: Adelaide, Australia Posts: 221	Re: Functioning with high CO2 Quote: (Originally Posted by Mike) Thanks Dave Dynamic apnea or freediving clearly must, almost by definition. Even if we are to just consider dynamic apnea, why don't we see the same CO2 hit symptoms there? Or perhaps that's part of what a Samba is? But doing apnea stuff I get really recognisable symptoms like diaphram contractions before really needing to breath. If it only happened in dynamic apnea I'd be suggesting that it could be due to the other exercise related breathing triggers, but as it happens in static apnea as well, that doesn't seem likely. Perhaps I need to get someone to take some blood samples at the pool... Mike - learning stuff today! It is very clear that different people have different responses to CO2, and you can be trained to reduce the response. Great breathhold divers are able to tolerate much higher levels of CO2 than crap ones - this is about the concept of the "break point" which is the CO2 at which you just have to breathe. When people started to measure CO2's in elite military divers at depth they were surprised to find that many of them were running levles as much as twice normal, obviously without discomfort, and apparently without much risk. I think that there are a couple of important points. If your CO2 is high but it doesn't bother you then that's probably mostly OK apart from a likely higher risk of O2 toxicity and maybe worse narcosis. If, on the other hand, your CO2 is high and it is bothering you (either because of breakthrough, scrubber failure, too high a work of breathing or whatever) then you are in big trouble. Many people find that they cannot hold their breath in this situation, and therefore will have big problems bailing out - as Mark has pointed out. Sometimes symptoms other than dyspnoea will predominate (Maybe more often in great breathold divers) and in these guys ordinary bailout will be just fine (as long as they recognise the problem). To look at it another way there are two different groups of hypercapnic divers. In one, all their gear is working just fine and they 'like' to have a high CO2. The others have a problem which their body is trying to correct but is prevented from doing so by an equipment issue. These people will feel very short of breath and dyspnoea casues panic. Panic is bad. The more complicated the fix is the less likely it will work. This is why I think BOV's are good. You don't need to do blood samples at the pool, BTW. You can get a good idea of what the aterial CO2 is by measuring it at the end of a breath with a thing called a capnometer. If you ever come to Adelaide give me a ring and maybe we can do an experiment! dave
(Online)

15th December 2006, 18:35	#30 (permalink)
wedivebc Dave Tomblin Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,508	Re: Functioning with high CO2 Quote: (Originally Posted by Gene_Hobbs) I am not sure what you mean by CO2 breakthrough--this is not a physiological term. There is CO2 breakpoint in breath-hold diving which O2 will help with some. . I think he means breakthrough as in in scubber breakthrough as when CO2 gets past the scrubber medium either by channeling or expended scrubber material. __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
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