Time to recover SAC after CO2 hit

matt said:
Yes, I think this is right - any elevation of CO2 (hypercapnia) is described as CO2 retention.

CO2 retention can occur either due to elevated CO2 in the breathing gas (by-pass, etc.) or because of inadequate ventilation. When CO2 rises the brain normally causes ventilation to increase (sub-consciously) to clear the excess CO2. Retention which comes about due to inadequate ventilation isn't anything to do with breakthrough of the scrubber, and wouldn't be detected by the post-scrubber sensor.

It seems that the act of scuba-diving can alter the way the brain works and in some people elevated work-of-breathing due to things like gas-density, depth, equipment-choices, hard-work, etc. can cause CO2 to be retained. CO2 retained in this way is often differentiated in forum-diving-circles from scrubber-breakthrough and I think that is the distinction Mark is alluding to.

CO2 retention due to inadequate ventilation isn't anything to do with the scrubber, and even occurs OC. Some people, called CO2-retainers, are able to tolerate elevated CO2 levels without experiencing the initial symptom of hypercapnia. This is another use of that term.

I'm not an expert, but that is how I understand it. Sorry if this isn't useful to you.

Matt.
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I have only had one C02 hit and it was on OC



Breathig C02 is not retaining C02

Your body is not holding it in or failing to expell it, its doing its best to exhale it but its just going back into the loop arround and back in your mouth. There is no retention involved any more than death by low PP02 on high helium mixes can be called "retaining helium"?
 
Mark Chase said:
I have only had one C02 hit and it was on OC



Breathig C02 is not retaining C02

Your body is not holding it in or failing to expell it, its doing its best to exhale it but its just going back into the loop arround and back in your mouth. There is no retention involved any more than death by low PP02 on high helium mixes can be called "retaining helium"?
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The surplus CO2 that respiration cannot deal with is retained, that's what hypercapnia is.

If it is not retained then there is no issue and we wouldn't need a scrubber at all, would we?
 
matt said:
The surplus CO2 that respiration cannot deal with is retained, that's what hypercapnia is.

If it is not retained then there is no issue and we wouldn't need a scrubber at all, would we?
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Are you kidding me? Of course we would still need a scrubber. The more we exhale the CO2 into the loop, the lower the po2 is going to get. Can you say hypoxia?
 
DSix36 said:
Are you kidding me? Of course we would still need a scrubber. The more we exhale the CO2 into the loop, the lower the po2 is going to get. Can you say hypoxia?
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Nah, the solenoid takes care of PO2, Don. ;-)

Hypercapnia is the other one.
 
Mark Chase said:
Your body is not holding it in or failing to expell it, its doing its best to exhale it but its just going back into the loop arround and back in your mouth.
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I've always understood CO2 retention as a very real danger: having elevated levels of arterial CO2. But it's more a function of physiology than of the machine (or a potential physiological response to some types of rebreather failures).

Thanks to dead air spaces, there's always some level of CO2 on the arterial side.

When one isn't breathing efficiently then what CO2 the body has produced and is TRYING to get into the alveoli to be exhaled and removed isn't getting there properly and the pCO2 starts to elevate.

And then bad things happen.
 
Johan Isaksson said:
There is another option to the end-tidal measurements that I routinely drop into these conversations in the hope that someone would start fiddling around with it and that's transcutaneous monitoring. Basically it's a probe placed on the skin that measures blood CO2 levels. It's in routine use in medicine but there are some technological issues that could present problems. If it works it'd likely be about equal to end-tidal monitoring and could cover hypoxia as well.
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The problem I see with transcutaneous CO2 monitoring is that it's measuring CO2 in one tissue and expects this to be representative of overall CO2 level (ie arterial CO2).

In the case of a resting patient, that's reasonable, because CO2 production will be basal levels everywherish (and even then it's not all that accurate).

In the case of an exerting diver, which is what concerns us, CO2 will be produced in some tissues (legs, diaphragm, ...), but not in others. So what's measured will have gone through veins back to the heart, arteries to the lungs, veins back to the heart, then arteries to the tissues we're measuring from, and through that tissue to the sensor, in an reverse (to normal) gradient. This would magnify the inaccuracy and inevitably add a delay.

It's not the same as a pulse oxymeter which measures oxyhemoglobin saturation and therefore what's coming from the lungs and that's it.

I'm not saying it's a bad idea, far from it, but I can see how etCO2 would be superior in this case.

Cheers,

Matthieu
 
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Mark Chase said:
NO


If your scruber fails you will breath C02

If you retain C02 it is due to a work of breathiung issue causeing a colaps of the avoli in the lungs which will not alow you to properly exhale the C02 YOUR BODY PRODUCES

This can occur on a perfictly packed brand new scrubber

And a C02 scrubber moniter temp stick or RMS device will not detect it

IMHO retained WOB, skip cycle, short sharp or over breathing related C02 issues or equipment failure related C02 issues are more likley to be an issue that scrubber related ones

As seen above you can push a standard inspo scrubber to 10 hours. Personaly I dont go past 6.

Using a C02 monitor on a Inspo sized scrubber when your doing 3 hours max is only catching badly packed scrubbers. Argubly it will also catch faulty lime? but how often does that happen?

The way I pack my scrubber is very repeatable. SOme say its not the best way but I have a ot of hours often under some prety harsh conditions, so I have built up confidance that whilst it might not be the best, it seems to be safe.

C02 monitors and scrubber monitors are IMHO just a way for divers to push the limits on a scrubber. They dont deel with unit failure or retained C02 so I see them as of little benifit in that area.

If it came free with the unit I wouldent take it off but equaly I wouldent spend extra money buying one.

IF they ever produce an End tidal C02 system thats reliable and functional, I would consider one.

ATB
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so how is tis going to work you want somthing that is perfect and cheap but you dont want to support it in the begining.companys that are doing the best they can to keep us alive by ofering what they curently have,so we buy it and they will be able to develop what you want at a price thats cool for everybody. thats why we can dive ccr today cos peopel did buy inspos back in 97 and the company developt better ccrs. if you dont support then develop your own end tidal co2 monitor and have it ript apart on forums by peopel that have never don a thing or supported one
 
matt said:
The surplus CO2 that respiration cannot deal with is retained, that's what hypercapnia is.

If it is not retained then there is no issue and we wouldn't need a scrubber at all, would we?
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"retained" specificly means we can not exhale it

If the scrubber has failed we can exhale it just fine but its not going to help because all we are breathing is more and more C02

retained C02 in CCR terms referes specificly to a physical condition inside the lung which is the result of a presure imbalance caused by friction of the gas as it passes through the avoli. This friction may be the result of gas density or the effort of breathing

If you want to be pedantic then a failed scrubber will eventualy result in this condition due to the massivly accelorated breathing rates. But this totaly misses the diferance between the two conditions one which requires a failed scrubber and the other which can hapen any time on any scrubber in any stage of scrubber life.
 
AlexBerger said:
so how is tis going to work you want somthing that is perfect and cheap but you dont want to support it in the begining.companys that are doing the best they can to keep us alive by ofering what they curently have,so we buy it and they will be able to develop what you want at a price thats cool for everybody. thats why we can dive ccr today cos peopel did buy inspos back in 97 and the company developt better ccrs. if you dont support then develop your own end tidal co2 monitor and have it ript apart on forums by peopel that have never don a thing or supported one
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Where did I say cheep?

Current scrubber monitors & C02 systems are mainly an advantage for people to push the scrubber with

I dont push my scrubber anywhere neer its ultimate limits soits not an advantage for me

I and when they produce an end tidal C02 monitor that works I would consider one and cost wouldn't be a primory consideration.
 
matt said:
Nah, the solenoid takes care of PO2, Don. ;-)

Hypercapnia is the other one.
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You seem to think that breathing C02 is fine as long as we dont retain it?

This is wrong. Breathing IN c02 is very bad. Exhaleing co2 is just fine

Brething in cleen trimix or cleen nitrox but failing to breath OUT c02 is also very bad,

and we call this retained C02
 
I have not experienced any CO2 issues in three years of rebreather diving, but in 20 plus years of OC diving I experienced a number of CO2 issues, as a result of this OC experience I am pretty sure I could pick a building CO2 issue on rebreather, I monitor my breathing closely and general feeling during a dive on rebreather (or OC). Any feeling of unease, increase breathing rate I am stopping and if progresses further to any form of heightened anxiety or feelings of impending doom (I hope never to develop to that extent on rebreather) I am bailing out and getting out of there hopefully before breathing rate gets out of control.
 
Mark Chase said:
You seem to think that breathing C02 is fine as long as we dont retain it?

This is wrong. Breathing IN c02 is very bad. Exhaleing co2 is just fine

Brething in cleen trimix or cleen nitrox but failing to breath OUT c02 is also very bad,

and we call this retained C02
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wow ATB mark is the superman he can breath co2 and not retain it amazing!!!!!!!
 
matt said:
I've no longer any idea what you are going on about. Sorry.

Hypercapnia and CO2 retention are the same thing. I put what I thought in #59.
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Hypercapnia is an excess of CO2 in Arterial Circulation with an imbalance of PH in blood.

CO2 retention (not getting rid of CO2) or failed scrubber (hence excess of inspired CO2) is the root cause of hypercapnia.

Not the same thing in my view ... but I might be wrong

Fabio
 
I would not use the word retention to describe CO2 buildup due to bad gas or a failed scrubber. To me as a MD and pulmonologist CO2 retention is used to describe a state where inadequate ventilation causes increased arterial CO2 levels.
 
Johan Isaksson said:
I would not use the word retention to describe CO2 buildup due to bad gas or a failed scrubber. To me as a MD and pulmonologist CO2 retention is used to describe a state where inadequate ventilation causes increased arterial CO2 levels.
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so what causes co2 in your loop? or what causes inadequate ventilation?
 
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