From Air to Trimix at depth

[Tigerman]

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- I've noticed two significant symptoms of CO2 retention ... a feeling of "I can't get enough air", and sometimes a moderate headache. During those times when those symptoms were noticeable, I've never felt like I was narc'ed ...
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Ive had it once. I was laying down a 4-inch plastic water intake hose in a lake. It was weighed down, but full of air. Moving it around and getting it properly sunk took some hard work and the effect on my breating and mental state was profound. I KNOW the regulator provide plenty of air, but the feeling of not getting as much air as you want while being submerged certainly ain't pleasant. Stopping to have a breather and lower the hart rate definetly helps a lot though

 

[dumpsterDiver]

Yes, we have played with this, and had results similar to what's already been reported. You don't notice a huge difference going from Nitrox to 21/35, but you sure notice the fog coming in when you go back.

There are significant data indicating that some, if not many, scuba divers retain CO2 while diving, even if they are not making a specific effort to skip breathe. Elevated CO2 levels almost certainly contribute to narcosis -- CO2 is definitely a narcotic gas, as can be noted in ill patients who are unable to clear their CO2. The deeper you go, the denser the gas, and the less linear the flow through the small airways is. At what depth this actually begins to impede CO2 eliminated is not entirely clear, and the big effects are probably at significant deeper depths than 40 meters. But CO2 retention can be markedly worsened by ineffective breathing strategies (panting) or overexertion at depth, at which point the diver might note a marked narcotic effect (or his buddies might ).

I've seen the effects clearly myself. Sometimes we hunt (spearfish) in deep water on air.. maybe around 180 ft. Sometimes when we see a fish in the distance, we decide to take a deep breath and hold it as we swim toward it trying to close the distance (bubble scare fish). I've swam 75 feet horizontally like that.

In general, I am not feeling much narcosis when doing this. But then, you make the shot and have to grab the fish and maybe wrestle with it a little and you resume breathing hard and fast. The narcosis that hits is very strong, not unusual for the tongue to immediately go numb, lips feel weird, bubbles sound strange and you can hear your pulse throbbing in your eardrums. The narcosis comes on extremely fast (10 seconds or something) in these situations, I can only assume it is primarily associated with CO2 build up. It is NOT a good situation at all.

You want to pant and gulp the air, but you need to concentrate on making full exhalations and also immediately curtail all strenuous activity. If you pushed it too far, you will find it very hard to catch your breath at that depth. You can die from it.

The effects of Co2 at depth are a very significant concern. People say don't descend too fast or the narcosis may come on too strong...A fast descent (as long as it is not excessively strenuous) is NOTHING like CO2 build up!

Also, the ensuing headache has left me puking over the gunnel as I breath oxygen.

 

[Remy B.]

Thanks for your inputs guys, nice straight forward and educated thread, lots of great experience shared, please continue.

 

[kr2y5]

I've seen a video. I had some friends who had a chamber ride, just for fun and experimentation. At about 180' you could see everyone was all giddy and definitely feeling the effects. They switched to breathing trimix (no idea what composition) and it seemed like almost instantly everyone sobered up after they had been breathing it.

This sounds like an interesting experience. Any idea how this could be arranged?

 

[Michael Guerrero]

But in any case CO2 isn't what's narcing you - it's nitrogen. CO2 isn't supposed to be part of the equation.

CO2 does not cause narcosis. I don't know who the "experts" are you mention but they are not remotely expert. There is no significant amount of CO2 in compressed breathing gasses, it is an issue on rebreathers where the diver re-uses their exhaust gas. There is more Argon than CO2 in atmospheric air and that is very narcotic. Composition of Air

According to DAN's Deeper Into Diving, 2nd Edition, pg 113, written by John Lippmann and Simon Mitchell, "Hypercapnia does appear to increase the narcotic effects of nitrogen. The depressive effects of both CO2 and nitrogen, as well as the increased delivery of nitrogen, combine to increase narcosis."

Also, CO2 is a factor in open circuit diving due to gas density and work of breathing. Hypercapnia is the buildup of CO2 in the body due to insufficient ventilation. Ventilation is impeded by depth (at 100ft work of breathing is twice that on the surface), the inherent resistance of your breathing apparatus, and gas density. All of these, in addition to increased work at depth causing increased production of CO2, contribute to hypercapnia.

On top of that, some people are naturally CO2 retainers, and so a rise in arterial CO2 levels does not stimulate a corresponding rise in ventilation as it does with most people. This is not good.

So, to answer your question, if you regularly experience narcosis at 130 feet, without doing significant work at that depth and assuming your equipment is functioning properly, trimix should improve the situation. The benefits grow as you go deeper, not only from the displacement of nitrogen, but also from the gas density which affects CO2 retention and work of breathing.

And yes, if you're experiencing hypercapnia to a significant degree, it's an issue whether you have helium or nitrogen in your breathing gas. But, depending on the circumstances, switching to helium may not make any difference. For example, if you're shallow and experiencing hypercapnia and feelings of narcosis because you're working hard against a current at 80 ft, it's most likely the work that's causing the problem, not your breathing gas.

 

[John C. Ratliff]

TSandM, I have a question for you. Hypercapnia has to do with the buildup of carbon dioxide in the person's sytem. But my question has to do with the exercise not only building up carbon dioxide (hypercapnia), but also contributing to an oxygen debt. Could oxygen debt also contribute to the increased narcosis experienced by these divers? I realize that the divers are getting oxygen at a higher partial pressure, but I'm still wondering.

Concerning Hypercapnia, Wikipedia actually has a decent write-up on its causes and effects during diving. We noticed it during the Warm Mineral Springs Underwater Archaeological Research Project in 1975, when FFM was used for communication at depths of 200+ feet. Apparently sometimes a purge of the FFM was required, and that led to loss of gas from the scuba tanks, necessitating the use of twin 100 cubic foot tanks when using the FFM.

SeaRat

 

[TONY CHANEY]

I think that true hypoxemia situation very seldom presents itself with OC in that the inspired FiO2 is the same unless you are hypoventilating, have CO in the mix, a PFO, etc., and these create a different situations. The ppO2 will increase with depth. CCR is a different thing altogether and I am not well versed to discuss them. I, as a RRT, will second or third what others have said about CO2 buildup + nitrogen Narcosis = a very bad situation. Please look at it like medications. 1+1=3. Nitrogen narcosis, hypoxemia and CO2 buildup all have a lot of the same symptoms.

 

[johngayle]

CO2 certainly is narcotic on OC. I once got narcosis on a south fl wreck Hydro Atlantic at 150 feet diving 21/35 trimix. We went out in rough seas on a very hot day after gearing up i was breathing heavy and sweating before hitting the water. On ascent was breathing heavy and felt narced on the wreck only after about 10 minutes into the dive after i caught my breathe did it subside.

 

[Omisson]

CO2 certainly is narcotic on OC. I once got narcosis on a south fl wreck Hydro Atlantic at 150 feet diving 21/35 trimix. We went out in rough seas on a very hot day after gearing up i was breathing heavy and sweating before hitting the water. On ascent was breathing heavy and felt narced on the wreck only after about 10 minutes into the dive after i caught my breathe did it subside.

I think hypoxia and narcosis are different things- though they share some sensation similarities.

 

[dumpsterDiver]

I think hypoxia and narcosis are different things- though they share some sensation similarities.

A diver breathing gas at depth should normally be getting enough Oxygen. The partial pressure of oxygen at depth is high (hopefully below 1.4 or 1.6) but each inhalation is delivering MUCH more oxygen that you get at the surface.

So the issue is not so much low oxygen, but rather high CO2 that is the issue here.


With regard to too little oxygen: An individual who is getting too little oxygen, but no build up in CO2 may not feel much discomfort at all and can lose the ability to function before they realize they have a problem.

But for divers, the issue is CO2 build up not hypoxia. That does cause stress, discomfort and confusion.

This video is very cool, it shows the effects of low oxygen, when the guy does not have the benefit of a warning that there is a problem because he IS venting CO2. He is significantly impaired. This video is probably most useful to freedivers who do expose themselves to hypoxia (as well as high CO2 levels)


[video=youtube;WTNX6mr753w]https://www.youtube.com/watch?v=WTNX6mr753w[/video]