Nitrox and Narcosis

[PfcAJ]

For one thing, self assessment of impairment is NOT a good indicator of anything.

How many drunks have you heard say 'I'm fine to drive', but everyone on the outside knows better? A similar situation exists in regard to narcosis, where the person making the judgement on if they are impaired IS impaired. For science, its gotta be an outside observer making objective observations. Anything 1st person subjective is automatically baloney as far as science is concerned.

 

[Nirvana]

I don't think the OP was confusing the mechanisms of DCS and narcosis. It does seem logical that narcosis should be, to some extent, time dependent. It is a phenomenon that affects the central nervous system and is caused by the partial pressured of the breathing gases, and these gases take some time from entering ours lungs to reaching our nervous cells and acumulating in them. Therefore, if narcosis is a function of the degree of saturation of N2 and O2 (mainly) of the CNS, it should take some time from exposure to a certain partial pressure of nitrogen or oxygen to the onset of narcosis.

If the saturation level of the CNS is not the trigger of narcosis, then what is? If it was the rate of transfer of gases from the blood to the nervous cells, then narcosis should alleviate with time, as the transfer rate gets smaller as the saturation increases. If it is neither of the above described mechanisms, what is it then?

 

[PfcAJ]

The correct answer is "we don't really know".

The wiki article on nitrogen narcosis goes into technical detail.

Fwiw, most neural tissue (brain, spinal cord) gets a lot of bloodflow, hence the 'immediate' affects of narcosis. Inert gas is rapidly transferred to these tissues, and it also rapidly moved out of these tissues when you ascend.

 

[waterpirate]

The way to reduce the potential for narcosis is to eliminate the amount of n2 in any given mix. Sooo by enriching the 02 where feasible and also adding he the amount of n2 is greatly reduced, thus greatly reduceing the potential. As far as the who is and who is not narced. It can happen to anyone on any given Sunday irregardless of their previous experiance. I dove with a guy who swore he was never impaired on 21%. I have never been so entertained as to watch him try and open a ghost trap at 150fsw. He got it open, but it sure took a long time?????
Eric

 

[dfx]

The way to reduce the potential for narcosis is to eliminate the amount of n2 in any given mix. Sooo by enriching the 02 where feasible ...

Not necessarily. You may wanna check out this (quite, uhm, interesting) thread: http://www.scubaboard.com/forums/ad...4199-narcosis-properties-different-gases.html

 

[Nirvana]

Fwiw, most neural tissue (brain, spinal cord) gets a lot of bloodflow, hence the 'immediate' affects of narcosis. Inert gas is rapidly transferred to these tissues, and it also rapidly moved out of these tissues when you ascend.

That is a possible explanation. In fact, it is an explanation I myself had offered a few posts back (post #3):

I haven't ever read anything relating time at depth and narcosis. It may be because the CNS is very well perfused, causing the partial pressure of gases in the CNS to reach levels similar to the blood rapidly enough for the time of exposure until the commencement of narcotic effects to be insignificant.

This explanation, however, assumes that the amount of N2 and O2 dissolved in nervous tissues is responsible for narcosis. As well perfused as they may be, it still takes some minutes for them to reach saturation, which would imply the effects of narcosis should become progressively worse for some time upon reaching a given depth.

 

[elan]

It does not make sense. The body has residual amount of n2, o2 and co2 at 1 ata. The partial pressure of those gasses changes instantaneously as you descend as it is all dissolved in liquid and the liquid transfers the pressure instantaneously. So you get the partial pressure changing in real time - there is no delay.

I don't think the OP was confusing the mechanisms of DCS and narcosis. It does seem logical that narcosis should be, to some extent, time dependent. It is a phenomenon that affects the central nervous system and is caused by the partial pressured of the breathing gases, and these gases take some time from entering ours lungs to reaching our nervous cells and acumulating in them. Therefore, if narcosis is a function of the degree of saturation of N2 and O2 (mainly) of the CNS, it should take some time from exposure to a certain partial pressure of nitrogen or oxygen to the onset of narcosis.

 

[Nirvana]

elan, with all due respect, you seem to be confusing some physics principles. When you say "the liquid transfers the pressure instantaneously", if you are talking about mechanical pressure exerted on the liquid (as in the brake system of a car), then, yes, the transfer is, for most purposes, instantaneous. But when someone refers to partial pressure of N2 dissolved in blood the word "pressure" has a completely different meaning. If you say the partial pressure of nitrogen in a given liquid is of 2atm, it means the liquid is holding as much nitrogen in it as it would if it were let to reach equilibrium with an atmosphere of pure nitrogen if that atmosphere was at 2atm. The partial pressure of gas in solution, therefore, refers to the quantity of molecules that are in solution.

That this process diffusion from gas to liquid takes some time becomes clear when you remember that it is the mechanism responsible for controlling DCS risk. The NDL is the time a diver can stay at a given depth before the amount of dissolved gas in some tissues (i.e., the partial pressure of inert gas in the tissue) becomes so great that it would take longer for a safe release of gas than would be possible through a direct ascent to the surface.
As the NDL is different from zero for most depths, it becomes clear that the diffusion takes a few minutes before the tissue can be considered saturated (even the fastest tissues, which control the NDL at greater depths).

 

[elan]

I understand your point but it does not seem to be that simple. The gases are not completely dissolved in liquid (say in blood), they do exist in a form of bubbles and I would guess mean they will have partial pressure changed in the bubble almost instantaneous. How that will affect narcosis though I have no idea. And even if we do not take into account those bubbles and only consider ongassing blood is a fast tissue and saturates fairly quickly and I doubt it matters whether one breathes air of nitrox.

From my own experience the bigger enemy is not N2 but CO2. I clearly feel a difference in the level of narc between scootering and finning at 100ft. And you do not need to transfer it from lungs to the tissues as we know.

elan, with all due respect, you seem to be confusing some physics principles. When you say "the liquid transfers the pressure instantaneously", if you are talking about mechanical pressure exerted on the liquid (as in the brake system of a car), then, yes, the transfer is, for most purposes, instantaneous. But when someone refers to partial pressure of N2 dissolved in blood the word "pressure" has a completely different meaning. If you say the partial pressure of nitrogen in a given liquid is of 2atm, it means the liquid is holding as much nitrogen in it as it would if it were let to reach equilibrium with an atmosphere of pure nitrogen if that atmosphere was at 2atm. The partial pressure of gas in solution, therefore, refers to the quantity of molecules that are in solution.

That this process diffusion from gas to liquid takes some time becomes clear when you remember that it is the mechanism responsible for controlling DCS risk. The NDL is the time a diver can stay at a given depth before the amount of dissolved gas in some tissues (i.e., the partial pressure of inert gas in the tissue) becomes so great that it would take longer for a safe release of gas than would be possible through a direct ascent to the surface.
As the NDL is different from zero for most depths, it becomes clear that the diffusion takes a few minutes before the tissue can be considered saturated (even the fastest tissues, which control the NDL at greater depths).

 

[wve]

You hear folks say that using Nitrox reduces Narcosis. I think it is a bit more nuanced than that. My understanding is the following. Suppose that I do two dives to the identical depth with identical ascent and descent profiles. One is on air and one on Nitrox, say 30%. For each dive I stay down until within a minute or two of NDL and then start to ascend. It would seem to me that

1. The Nitrox dive would last longer but since NDL is based on compartment loading I would be equally narced at the end of bottom part of both dives since I have equal Nitrogen loading. So Nitrox does not reduce the maximum ammount of narcosis reached although it does reduce it early on in the bottom time.

2. Since I start the ascent with the same Nitrogen loading I will offgas Nitrogen faster with the Nitrox and thus might be a bit clear headed at the end of the Nitrox dive. This being diver dependent.

Anything wrong with this?

Having given your questions more consideration, I may have misunderstood what you were asking.

1. Given the parameters of the dives that you specified, then yes, the Nitrox dive will take longer to reach the NDL, but once you have reached it, the total nitrogen loaded will be the same as the dive on air.

2. In theory, yes, you should eliminate nitrogen a little faster while ascending on Nitrox due to the greater gradient, and you might notice a difference in how you feel upon surfacing.

But the actual risk for the euphoric/dysphoric effects of nitrogen that we call "narcosis" is more directly related to the partial pressure of nitrogen which is determined by both the depth and amount of nitrogen in your breathing mix. Thus if your dives are to the same depth, then you are less likely to experience "narcosis" on the Nitrox dive because your partial pressure of nitrogen will not be as great as it is on the air dive.