Unpleasant Experience

[wedivebc]

This is sort of an answer to a question that has been bouncing around in my pea brain as of late, which is " Is enriched air(nitrox) less or more narcotic than regular air at deeper depths?". My thought was that the lower nitrogen levels would make nitrox slightly less narcotic than air, considering that O2 takes the place of nitrogen. Considering all of this, however, possibly the reverse is actually true?

UP's experience notwithstanding most divers report feeling less narcosis with higher O2 mixes. This issue is so confusing to many that even within PADI, training material contradictions on this subject exist. In the PADI tec deep manual it states that oxygen should be treated as being equally narcotic as nitrogen yet in the rebreather training material they state that care must be taken to avoid narcosis due to high nitrogen levels in the breathing loop. This shows a clear lack of definate information on the subject.
To look at UP's observation from a different angle there are many who experience a noticable reversal of narcosis effects in the presents of helium to a degree greater than the actual percentage of the helium mix. This leads us to believe that helium is like an "antidote" to nitrogen narcosis. This would offer another explaination for UP's noticable increase of impairment when switching to EAN 50 from trimix.

 

[Kestrell]

I said supposedly because that is what I have read concerning the narcotic potential of CO2.

If the lipid solubility of a gas is an indicator of its narcotic potential then CO2 would be 25x more narcotic than nitrogen according to the Bunsen Solubility coefficient of each gas. (nitrogen 0.052 vs CO2 1.340 btw O2 is 0.110)

This may or may not be the case... but CO2 buildup (hypercapnia) certainly seems to exacerbate nitrogen narcosis and of course causes shortness of breath (SOB) as well as anxiety.

I'm not sure if the solubility is the only indicator of a gas' narcotic effect. Nitrogen is narcotic because it suppresses communication between nerves.

It may have been a combination of things; Nitrogen Narcosis, exacerbated by CO2 build up and borderline Oxygen toxicity.

 

[Kestrell]

Maybe because Meyer - Overton deals with inert gas narcosis and O2 isn't inert. Therefore does not follow the M-O theory.

Exactly, it isn't the level of nitrogen or oxygen in the tank that effects you, it is the amount in your body. O2 is utilized by your body and will take longer to build up. Nitrogen isn't utilized by your body and therefore will build up in your body. There is also the fact, as I stated in another post, that Nitrogen inhibits nerve to nerve communication. Helium probably helps with narcosis because it is absorbed more quickly than Nitrogen and therefore displaces the Nitrogen that would have been absorbed by your body. Since Helium is less narcotic, it is an effective way to control narcisis due to Nitrogen build up.

 

[Uncle Pug]

" Is enriched air(nitrox) less or more narcotic than regular air at deeper depths?". My thought was that the lower nitrogen levels would make nitrox slightly less narcotic than air, considering that O2 takes the place of nitrogen.

I know I am not the only one to feel it when switching from 21/35 to EAN50. A friend mentioned the trouble he had doing some simple math at 70' during the gas switch stop. I said that I could feel it too and Shane concured. It would be interesting to hear if others have detected the same thing.

At any rate here are some things to consider and then I'll ask questions:
1. Most folks can't discern nitrogen narcosis at 70' (though it is present to some degree) while on 79% nitrogen (air.)

2. Switching from 21/35 to EAN50 adds 6% nitrogen and 29% oxygen to the breathing gas and subtracts all of the helium. In other words a 13.7% increase in the N2 but a 138% increase in the O2 and a 100% decrease in the helium.

3. The N2 fraction in EAN50 is still only 50% compared to air at 79% and yet a narcotic effect can be detected at 70'.

What causes it? Is it the increased fraction of O2? That would mean that O2 is narcotic.

Does helium do more than just displace nitrogen in the mix... does it have an *anti narcotic* effect? If so then removing the helium from the breathing gas still wouldn't explain how I could detect narcosis at 70' on 50% nitrogen.

Is it the sudden introduction of the additional 6% nitrogen into the breathing mix? Or the sudden removal of all the helium?

Or am I just crazy?

 

[Uncle Pug]

Exactly, it isn't the level of nitrogen or oxygen in the tank that effects you, it is the amount in your body.

It isn't the amount in your body... it is the amount in your blood... and it doesn't take much time to build up. This is different than the ongassing that we are concerned about from a decompression standpoint.

For example: what is the recommendation for relief from narcosis and how long does it take?

2xBTW
the onset of a CO2 hit can be very rapid
I don't think O2 toxity had anything to do with this

 

[jonnythan]

It isn't the amount in your body... it is the amount in your blood... and it doesn't take much time to build up. This is different than the ongassing that we are concerned about from a decompression standpoint.

For example: what is the recommendation for relief from narcosis and how long does it take?

Ascend slightly to relieve narcosis.. and the relief is almost instantaneous.

So it's not the amount in your blood...

 

[Kestrell]

It isn't the amount in your body... it is the amount in your blood...

Perhaps I was being too non-specific in my use of the word, "body". Either way Nitrogen in your blood and your body contribute to nitrogen narcosis. Nitrogen narcosis is causes by the effect on the nerves in you body. Nitrogen inhibits the electro-chemical communication that occurs between nerves, specifically in your brain. The blood only carries the nitrogen around.

On-gassing is relevent, because that indicates the amount of nitrogen absorbed by the body (brain mostly) and therefore affecting nerve to nerve communication. Also at play is the pressure at which the nitrogen is at, similar to oxygen partial pressure. That is why when you decrease your depth, it relieves the effects of narcosis.

 

[Uncle Pug]

The point is, it doesn't take time to build up in your *body*... it only takes moments to enter your blood and affect your brain. Yes... the effect is in your brain... but it has to be present in your blood to effect your brain. And it happens fast. Relieve the pressure by ascending and even though the blood gas level will take a few minutes to drop the narcosis subsides.