Oxygen and narcosis

[empressdiver]

In a recent discussion on nitrox I had with a few other divers, they took the position that oxygen was just as narcotic as nitrogen, and therefore using nitrox did not reduce narcosis compared to breathing air. It appears that they may have based this position on a statement made some time ago by Dr. Bill Hamilton of Hamilton Research that he had a little data which says a person's impairment is the same at high and low O2 levels of nitrox and so O2 is just as narcotic as nitrogen.

Dr. David Sawatzky wrote an article in Diver Magazine, December 1996, entitled "Oxygen Narcosis: Fact or Fiction?" He surveyed the research up to that date and concluded that oxygen narcosis is of no significance to recreational divers. Another diver has just stated that the doctor has confirmed that his article is still current.

I would like to ask an expert if there is anything to add to this conclusion.

 

[rockjock3]

He surveyed the research up to that date and concluded that oxygen narcosis is of no significance to recreational divers. Another diver has just stated that the doctor has confirmed that his article is still current.
QUOTE]

First, I am not an expert. Second the doctor is cracked. Oxygen does have narcotic effect, it can also kill you. I guess that part was of no significance to rec divers either.

 

[empressdiver]

My question for the expert was not about oxygen toxicity - it was about whether or not there was any narcotic effect to oxygen as there is with nitrogen.

 

[rjack321]

Modern therory suggests that O2 is narcotic and approximates that of N2. Here's a good paper on its relative potential:

http://jap.physiology.org/cgi/repri...IRSTINDEX=0&sortspec=relevance&resourcetype=1

Thus, when diving air or nitrox your narcosis is similar. Only by adding helium can narcosis be reduced.

Whether narcosis is significant or not to recreational divers is a topic for another post.

 

[wedivebc]

First, I am not an expert. Second the doctor is cracked. Oxygen does have narcotic effect, it can also kill you. I guess that part was of no significance to rec divers either.

I'm sure you're right. That "cracked" Dr is one of the leading experts on dive medicine in our country. But of course if you say so....
I just asked this question on another board and got this very well thought out reply:

O2 does not contribute significantly to narcosis because the partial pressure of oxygen in the neurons doesn't get very high because oxygen is used up.

Moderately complicated explaination follows.

Oxygen is carried in blood in 2 ways, bound to haemoglobin and dissolved in the blood. The haemoglobin in 100mls of normal blood carries about 20ml of oxygen and the dissolved component is 0.003ml per mmHg O2 per 100mls of blood.

You use the dissolved component first. Your brain uses about a quarter of the available oxygen breathing normobaric air, so you have about 15mls of oxygen per 100mls blood in the veins which equates to a partial pressure of oxygen of about 40mmHg. The venous and tissue partial pressures are roughly the same

If you are diving at a setpoint of 1.4, each 100mls of your blood contains a bit more oxygen than usual (20mls bound to haemoglobin and about 3.2 mls dissolved). If you are using the same amount of oxygen then there will be about 18mls O2/100mls blood, which means the haemoglobin is about 90% saturated and the partial pressure of O2 is about 75mmHg.

If oxygen was as narcotic as nitrogen then you can see why the contribution fo oxygen to the narcosis is negligable, and why narcosis worsens as the PO2 falls.

Say you are at 40m with air dil and a setpoint of 1.4. The partial pressure of nitrogen in the brain is 3.6 ATA (or 2736mmHg) and the partial pressure of oxygen in the brain is about .1 ATA (75mmHg) so the total "narcotic load" is 3.7 ATA.

Now say your setpoint changes to 0.2 (for whatever reason) The partial pressure of nitrogen in the brain is now 4.8 ATA (or 3648mmHg) and the partial pressure of oxygen in the brain is about .05ATA (40mmHg) so the total "narcotic load" is 4.85 ATA - much worse.

.

 

[rjack321]

This has been discussed much before, search on "oxygen narcosis" and "O2 narcosis" and judge for yourself.

The applied physiology paper link is from 2003 and post-dates all the previous discussions I found.

 

[wedivebc]

This has been discussed much before, search on "oxygen narcosis" and "O2 narcosis" and judge for yourself.

The applied physiology paper link is from 2003 and post-dates all the previous discussions I found.

I found it a little tough reading but it does state that other toxic effects come in to play before narcosis is an issue. I don't think it is cumulative, as per Dalton's law, each gas acts independantly. Therefore you will tox out at a much lower PPO2 than the partial pressure required to induce narcosis
The actual wording is: "The narcotic effects of O2 and CO2, however will be difficult to discriminate from the effects of their highly reactive secondary reactive products" (pg 891)

 

[rockjock3]

My question for the expert was not about oxygen toxicity - it was about whether or not there was any narcotic effect to oxygen as there is with nitrogen.

Read past the first sentence of my response.

 

[rjack321]

I doubt each gas acts totally independently. At least CO2 and N2 appear to have synergistic effects (the sum being greater than addition of the parts).

Some agencies now teach that O2 is narcotic, some don't and this issue ain't gonna be resolved here (see the raft of previous posts/topics)!

Dr. Sawartzky (I believe he's the expert refered to in the 1st post) has valid reasons for his opinion. And, the link I posted suggests that Dr. Sawartzky's opinion might not reflect all of the available science (of which there ain't much). There are also other valid opinions, e.g. the "I'm not less narced on nitrox" group, which should be respected for their real world applicability.

The exact narcotic potential of O2 is about as precise as decompression science, i.e. not very exacting.

 

[wedivebc]

I doubt each gas acts totally independently. At least CO2 and N2 appear to have synergistic effects (the sum being greater than addition of the parts).

Some agencies now teach that O2 is narcotic, some don't and this issue ain't gonna be resolved here (see the raft of previous posts/topics)!

Dr. Sawartzky (I believe he's the expert refered to in the 1st post) has valid reasons for his opinion. And, the link I posted suggests that Dr. Sawartzky's opinion might not reflect all of the available science (of which there ain't much). There are also other valid opinions, e.g. the "I'm not less narced on nitrox" group, which should be respected for their real world applicability.

The exact narcotic potential of O2 is about as precise as decompression science, i.e. not very exacting.

Ask any rebreather diver this same question. Anyone who has experienced a change in PPO2 at depth a felt an immediate change in perception will support the O2 = less narcosis argument.
When doing SCR bailout drills I was required to shut off my O2 at 100ft and use my diluent (air) to breath my CCR as a semi closed rebreather. After a period of time the drill was over and my PPO2 went from about .6 to 1.3 in a matter of seconds. I noticed an immediate feeling of perception increase, like a fog being lifted. That was enough to convince me.