Functioning with high CO2

Mike

How much of the problem with CO2 is driven by the primary effects of CO2 (imperative to breath), vs the secondary effects (Narcosis, increased sensitivity to O2)?

So far, I've decided that a OC BOV isn't worth the complexity it introduces - but I'm not 100% convinced.

So I try to play around with increasing CO2 in me, and seeing what sort of effect it has, and what effective capability I have. Last night I was in the pool, swimming laps, trying to recapture a bit of fitness. After a bit of distance I did a sprint set of 10 by 50m sprints, with minimal recovery time between sprints. At the end of this set, I normally have a pulse rate in the 200 to 220 range, and my breathing is, umm, rather rapid.

At this point I took a medium breath and submerged, looking at my watch and taking my pulse. Pulse averaged 180 over the 20 seconds I managed to hold my breath for, and I was able to adjust my goggle strap one handed at the same time.

Now - it's a pretty inexact measure, but I'm willing to bet that my CO2 levels were pretty high at that point - my breathing had been pretty shot on the last break, I had a stitch etc. But, while I had the reasurance of the surface being 50cm away and wasn't mentally stressed, I was still able to do a 20 second breath hold and function pretty normally. My reasoning is that 20 seconds is plenty of time for me to get a bailout reg in my mouth, even including turning the tank on or doing some basic untangling.

Afterwards, it took me a few minutes to recover afterwards, and my SAC would have been over 100 litres/minute for a couple of minutes - but I'd been well aware of rapid breathing for a good 5 minutes prior, and there is no way I wouldn't have noticed the condition I was in for the last couple of sprints way earlier and done something about it.

All this is giving me a (false?) sense of confidence about CO2 - that I will recognise it well before I get to the point where I'm not able to do anything about it.

However, I also know that this is not the experience of people who have had CO2 issues, so what's the difference?
Can we, through exercise, push our CO2 levels high enough to experience the sort of symptoms of a CO2 hit?
Is experiencing CO2 at the surface completely neglecting some other important variables such as narcosis?
Does a scrubber breakthorugh (for instance) evidence as an insiduous increase in CO2 until some tipping point is reached where we go from not noticing to incapacitated in a couple of seconds? (this is the one that I don't quite believe, and hence the basis for thinking I don't need an OC DSV)

Mike

__________________
Open ....... Closed
Mind ........ Loop

Scuttle

Non functioning would be a better word, Mike.
next time your down my way ask me about my life threatening CO2 hit in Tasmania.
Having a BOV is the quickest way to check if you think there is an break through issue. Clears the head enough to realise in time before it all goes belly-up. Quarter turn & your on O/C makes the task loading simple even with a muddled mind.
All breathers should have one in my opinion, & that is one of the reasons I choose the Classic Kiss.

dive2dive2000

Hi Mike,

You bring up an interesting topic and some interesting points.

I don't believe your test is accurate because during an unexpected CO2 hit by the time you realise you are experiencing a CO2 hit your motor skills might be greatly reduced. I personally believe a BOV is safer and quicker than going straight to bail out If diving a FFM I personally feel a BOV is a must not an option. Being a cold water wreck diver and a PRISM user I feel I can get a sanity breath in the right amount of time from holding the ADV dn (I am not sure if all units are capable of this, on a prism your dil feed is right under inhalation CL fitting and hose to your mouthpiece, so you can get a sanity breath by inhaling crushing lung flat and depressing adv simultanisly) the only neg to this is your buoyancy can and will become negative (if done wrong then positive). Being a wreck diver I am on or near bottom or structure or near a line. If I was an avid cave diver or wall diver I would feel stronger towards a BOV just because of the buoyancy factor.

Basically what I am saying is that a BOV can and should be used over a DSV depending on your CCR and the type of diving you do.










just my PPO2

__________________
Safe Diving,
Martin

"but what's the fun of getting what you need, instead of what you want?"

Steve

Well, for what it is worth Mike the way a CO2 issue whilst diving makes me feel is very different to the way an experiment like yours makes me feel. Anecdotal I know but I'm no medical researcher.

PS. Buy a OC/CC DSV

__________________
WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.

Genesis

I know this is not a scientific or "in water" test but for grins and giggles while playing with the K1 on the couch early on I tried breathing it with no scrubber media in the can at all.

Within a minute or two of starting I got VERY lightheaded and, well, "weird". There was breath hunger (which of course isn't sated by breathing faster!) but there were also what could only be described as coordination and mental deficits that started to snowball FAST.

I dropped the mouthpiece, but if I hadn't (or turned it to OC) I suspect I would have passed out.

Had plenty of O2 (setpoint control was running) but of course way too much CO2.

Underwater I can easily see where that could kill you almost without warning. I'm not sure that if I was finning hard against a current or otherwise preoccupied that I would recognize the incipient symptoms until my coordination and mental faculties were severely compromised, and at that point I'm not certain I could successfully bail if I had to swap mouthpieces. I DID have enough left to turn the knob.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

dteubner

In your experiment it is very unlikely that your CO2 was at all high - it may even have been a bit low.

The sensation of dyspnoea (shortness of breath) with exercise is not related to an elevation in CO2 (hypercarbia), it is not well understood but relates to a whole host of factors.

Dyspnoea post exercise is also not related to hypercarbia.

If you do vigorous exercise and then hold your breath for a few seconds, your CO2 will not rise much at all.

Genesis's experiment, on the other hand, almost certainly did cause hypercarbia and he was significantly incapacitated even on a couch with no task loading.

The main point about a BOV is that if your CO2 rises moderately high it will be almost impossible to hold your breath long enough to swap to a different gas source, which might take longer than you hope because of loss of coordination.

Dave T

Gene_Hobbs

Hi Mike,

First, congrats on playing with your physiology. What you did was not a very good measure for what you seem to want to know but the key is asking the question and actually doing something to test it. The quick test 'Genesis' did was similar to a CO2 test we do here to determine CO2 production of individual subjects. It can also be a pretty good way to "feel" the onset. (I am NOT saying this is safe. If you do try this, please do so with someone else present.)

As for reading material, I just added this paper a few days ago for one of our Hyperbaric Fellows. This is a good starting point for information worth reading.

Carbon Dioxide Tolerance and Toxicity. Lambertsen, CJ
RRR ID: 3861, Citation: IFEM Report No. 2-71

More reports by Dr. Lambertson can be found here: EBSDC Research Components Chris designed the early systems so his work should always be at the top of your list when asking questions about rebreathers.

Hope this helps!
G

__________________
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

Skipbreather

Hi Mike-

I appreciate that you’ve gone to considerable effort to get some insight to the CO2 issue, but DUDE- with respect- they were great efforts, but bear little resemblance to what you might expect to go thru in an underwater hypercapnia event. A closed breathing loop w/ limited scrubbing ability combined with elevated ambient pressures make it an entirely different game.

Courtesy of having dived a single scrubber configured IDA71 homebuilt conversion for several years I’ve experienced CO2 breakthru in many different forms. The two opposite ends of the spectrum are, arguably, Case 1- a scrubber that’s just mostly used up and finally cannot cope w/ the ambient workload and, on the other end, Case 2- hard swimming causing over breathing a scrubber that’s marginal for the set up and then immediately dropping several ATA deeper before the effect of the over breathing makes itself known.


Case 1 is not fun but not all that big a deal. Things don’t feel right. PpO2 looks fine so you do a dil flush and things feel better for a few breaths. The improvement lasts for fewer and fewer breath between successive flushes until it dawns on you the scrubber’s toasted. In my case, when I did an orderly bail to OC, it was like when you finally hit the correct point while focusing binoculars- things simply snapped rapidly into sharp clarity. BOV would be nice, but at most just a convenience. Grabbing stage reg was simple.

Case 2 is, IMHO, the killer. It produced in me the so-called “dark nark”. In spades. WAY back inside a wreck. Solo. Even though ppO2 was fine, I was absolutely, positively, and completely convinced I was going to die right then and there. I had one hand on my stage reg and physically could not bring myself to close the DSV with my other, let alone take it out of my mouth. Only decades of serious emergency training in full motion simulators gave me the mental discipline to calm myself enough to exit the wreck and ascend. The very next day I started design of my BOV. I haven’t dove one of my own rigs without one since it was finished.

Hope this helps answer your question.

Ken

__________________
"Entropy RULES! Enjoy the interim."

Mike

I figure it must be... I'd like to understand why though.
There is definately the issue of a closed system with the rebreather vs the open system when exercising, but I'm surprised it's that great.

I figure there are three scenarios diving;
1: the 'upside down scrubber', where there is no scrubbing at all
2: the 'I forgot the bucket O-ring' where there is reduced scrubbing capacity
3: the 'do I feel lucky' (I know what your thinking, did I put 5 hours on this scrubber or six? Well, to tell you the truth, in all this excitement I kind of lost track myself. You've got to ask yourself a question: Do I feel lucky? Well, do ya, punk? ) where there is reduced scrubber capacity but still some remaining.

The first one should get picked up in the boat on prebreathe (on the basis that we have a loop volume of say 15 litres and are producing a minimum of .5 of a litre of CO2 a minute, therefore we will hit 5% co2 in 90 seconds)

Both 2 and 3 should be analogous to any anerobic exercise - you are getting rid of some, but not all, the CO2 each breath. Therefore CO2 will build up to uncomfortable levels over time - but it should take a minimum of 90 seconds to get to the dehibilitating stage, and that should be long enough to recognise and react?

Mike

__________________
Open ....... Closed
Mind ........ Loop

silent running

Hi Marty, I'm wrestling with the BOV issue for the Prism also. My current opinion is that it would be good to have for 2 reasons:

1) Another easy way to add dil to the loop, say during a rapid descent if the ADV whip popped off or that crude little shrader valve blocked up-redundancy

2) ADV shrader valve can't flow as much as a good reg down deep.

That being said, would you really need a whole lung full of fresh gas to bring down the CO2 level enough to gain relief? The Prism ADV being right next to the inhale hose does provide nearly instant fresh gas, without it mixing with with the gas already in the IN CL and it might still flow enough to bring down the CO2 enough to get it together. While depressing the ADV with my right hand I use my left to vent the exhaled gas through the OPV in the EX CL, bringing the CO2 down further and keeping my bouyancy the same-open loop. I've practiced this a bit and it's pretty easy, but no doubt, turning the BOV lever would be easier so I would still rather have one, if only for the dil add redundancy.

But then there's the WOB issue. How will any of the currently available BOVs work with the Prism loop? If I can add one without increasing the WOB over the stock DSV, then I'd be all for it. Otherwise, it might be foolish to add something in anticipation of a possible CO2 hit which might actually increase the chance of that happening by increasing the WOB. Tough call. Anybody have a BOV on their Prism right now?

Mike, sorry if this seems like a hijack, but I think it's still relevent... -Andy