Oxygen and narcosis

[waynne fowler]

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.

I think your response concerns toxicity and really isn't addressing the narcotic effects of O2... IIRC lipid solubility & density play the major roles in a gases narcotic effects. I don't recall all the spacifics but to my recollection it is generally accepted (by those that accept that O2 is narcotic) that theoretically O2 is actually 3 times more narcotic than N2... The fact that quite a bit of it is matabolized works in our favor. I'll see if I can find the paper I read last year about this.. If I can I'll post it or a link.. it was actually a good read. Wish I had a better memory...

 

[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).

.

Where does it say that in your atricle?

 

[radinator]

I believe there is a correlation based on the size of the molecule. N2 and O2 are approximately the same size (note I said approximately), they have similar narcotic effects. He is much smaller, and has much less of an effect.

Similarly, CO2 is a larger molecule, and is much more narcotic than the others.

 

[BigJetDriver]

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.

Our reader, Rockjock, states that he is not an expert. He then goes on to say that the doctor in the quote above is "cracked".

This is an interesting opinion from someone who, admittedly, is NOT an expert. The good doctor whom he refers to IS in fact, an EXPERT!

The man he refers to is Dr. David Sawatzky, a noted researcher in decompression and related subjects, who works for DCIEM (now DRDC) in Canada. When someone who has no standing or professional training in the field posits that a noted resercher in that field does not know what he is talking about, I would suggest that it is NOT the good doctor who is more than slightly cracked in the old toboggan!

To add to Dr. Sawatzky's comments, I will report the findings of Dr. David Teubner, who is both a Hyperbaric Medicine and Trauma physician, and who is a technical rebreather diver with far more hours underwater than our reader, Rockjock.

Re: O2 Narcosis - 28th November 2005, 17:33-by Dr. Dave Teubner

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 explanation 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.

Even if oxygen were as narcotic as nitrogen, then you can see why the contribution of oxygen to the narcosis is negligible, 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.

Dave T

I think that explains the issue fairly well, but perhaps Rockjock feels that ALL of the experts are wrong, other than himself. Oh, sorry, he did say he wasn't one. :11:

 

[Solitude Diver]

Greetings:

Although I have followed the forums for some months now, I just got around to signing up today so I could access another forum. I ran across this thread inadvertantly, and thought I'd throw in my opinion (for what it's worth).

PADI/DSAT definately has an opinion on this, and teaches it in their Technical Deep Diving class (TecRec Deep).

According to PADI, the prevailing theory about narcosis is that oxygen is equal to or more than narcotic than nitrogen. To quote PADI/DSAT (Diving Science and Technology), “nitrogen and oxygen are both narcotic, and your equivalent narcotic depth (END) does not change as you challenge the ratio of oxygen and nitrogen”.

This is based on the “Meyer-Overton hypothesis” that says: gas absorption into the nerve cell lipids interferes with nerve impulse transmissions, which results in narcosis.

Gas solubility varies with different gasses depending on the solubility; the higher the solubility the higher the potential for narcosis. Since Oxygen is twice as soluble as nitrogen; it suggests that it is potentially more narcotic than nitrogen. The theory also suggests however, that this is offset somewhat by your body metabolizing oxygen. Not enough to make it less narcotic however.

This seems further backed up by Dr. Hamilton's real world tests in which commercial divers where tested at depths using various mixed of air/nitrogen. His statements were that there was no noticable difference in the effects of narcosis with the different blends.

Althought there are some varying opinions, and I am certainly no expert, I trust PADI/DSAT's expertise. The theory seems valid.

In my own experience, I have used regular air and also maximum O2 mixes at depths. Granted the deeper you go, the less O2 you can use do to the risk of oxygen toxicity, so at 130' when I would feel some effects of narcosis, I cannot use more than about 28% O2 anyway. This difference does not produce a noticable narcotic difference for me.

Anyway, that's my 1-1/2 cents worth. Hope it adds something to the mix.

-Steve

 

[BigJetDriver]

Greetings:

PADI/DSAT definately has an opinion on this, and teaches it in their Technical Deep Diving class (TecRec Deep).

According to PADI, the prevailing theory about narcosis is that oxygen is equal to or more than narcotic than nitrogen. To quote PADI/DSAT (Diving Science and Technology), “nitrogen and oxygen are both narcotic, and your equivalent narcotic depth (END) does not change as you challenge the ratio of oxygen and nitrogen”.

This is based on the “Meyer-Overton hypothesis” that says: gas absorption into the nerve cell lipids interferes with nerve impulse transmissions, which results in narcosis.

Gas solubility varies with different gasses depending on the solubility; the higher the solubility the higher the potential for narcosis. Since Oxygen is twice as soluble as nitrogen; it suggests that it is potentially more narcotic than nitrogen. The theory also suggests however, that this is offset somewhat by your body metabolizing oxygen. Not enough to make it less narcotic however.

This seems further backed up by Dr. Hamilton's real world tests in which commercial divers where tested at depths using various mixed of air/nitrogen. His statements were that there was no noticable difference in the effects of narcosis with the different blends.

Althought there are some varying opinions, and I am certainly no expert, I trust PADI/DSAT's expertise. The theory seems valid.

In my own experience, I have used regular air and also maximum O2 mixes at depths. Granted the deeper you go, the less O2 you can use do to the risk of oxygen toxicity, so at 130' when I would feel some effects of narcosis, I cannot use more than about 28% O2 anyway. This difference does not produce a noticable narcotic difference for me.

Steve

Hamilton's "study" consisted of anecdotal remarks and observations collected from divers. It was by no means scientific in its methodology compared to actual research.

The Meyer-Overton Hypothesis is exactly that; a hypothesis. It has not been proven to the point that it can be accepted as fact. It may well be so, but saying it does not make it so.

With all due respect to PADI, which in the last few years has suddenly started billing itself as the authority on technical diving, it would be best to look to the researchers in the field, such as Dr. Sawatzky, for the answers.

He is not saying that the gas, oxygen, is or is not narcotic per se. Simply that in practical terms, given the way it is utilized in the body and the concentrations achieved, for all intents and purposes it does not act as a narcotic on the diver.

Ref: Bennett and Elliott, Pysiology and Medicine of Diving, 5th Edition, 2003, page 34, paragraph 3--"Excess dissolved oxygen can theoretically act as an inert gas under some circumstances. Some evidence of this is suggested in the animal experiments of Donald (1955), and Berhage and McCraken (1979)...(Ed. note: emphasis mine) Human trials on things like this are difficult, expensive, and very hard to get approval from the ethics committees to do, as you might expect.

 

[cmay]

With all due respect to PADI, which in the last few years has suddenly started billing itself as the authority on technical diving, it would be best to look to the researchers in the field, such as Dr. Sawatzky, for the answers.

This is actually pretty comical considering they avoided technical training like the “plaque” for so long. Of course until they saw the revenue streams it was generating for other agencies.

This reminds me of how PADI was one of the “Head Drum Majors” leading the Band Wagon declaring Nitrox as a “Voodoo Gas” when it was trying to be introduced to the recreational community. It is worth noting that the Enriched Air Diver Specialty Course is now PADI’s most popular (profitable) Specialty course.

Not trying to start a fight, just brought up a few memories. Also, before anyone accuses me of PADI bashing, I am a PADI Instructor. (and have been one for quite a while)

 

[lamont]

just do a gas switch from 30/30 to EAN50 at 70 fsw and come to your own conclusions...

 

[JeffG]

just do a gas switch from 30/30 to EAN50 at 70 fsw and come to your own conclusions...

What was yours?

 

[waynne fowler]

just do a gas switch from 30/30 to EAN50 at 70 fsw and come to your own conclusions...

I know this feeling... it's not like I get spanked or anything but I can definatly precieve a bit of fuzzyness. I get roller coaster knees sometimes at the gas switch.