Inert Gas Narcosis and Environmental Factors

[JS1scuba]

In another thread a comment was made about how visibility and water temperature can have an effect on the narcotic effect of nitrogen under pressure.

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HMMMM, I just learned something new. Water temp, visibility etc all effect END and here all this time I thought it was PN2....

Go figure....
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Deep air diving has been commented on for a long time that one has less narcosis in the "clear blue warm waters" than they do in colder darker waters. Many who have done dives with air or light helium mixtures in both environments will usually attest to being "more narked" when it was colder and darker than when it was warmer and brighter. This prompted me to pull out some earlier material that I created with Dr. Hamilton in one of our books to create the basis of this new discussion.

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Nitrogen and narcosis

Air as a diving gas creates two main problems for the recreational diver, narcosis and the need for decompression when dive times are longer than no-stop times.

"Narcosis" means "numbing" or a state of stupor, with the apparent implication that it is caused by a narcotic drug, but this is not always the case. Surgical anesthesia can be induced by small amounts of specific gaseous agents, some requiring only a few percent of the breathing mixture at one atmosphere (a partial pressure of 0.01 to 0.15 atm).

Nitrogen is indeed a similar "drug," but in a context different from habit-forming or addictive narcotics. Instead, nitrogen belongs in the class of gaseous anesthetics. It behaves in the same manner as a gaseous anesthetic, but requires much higher partial pressures to have its effects.

Nitrogen becomes noticeably narcotic at around 3 or 4 atm PN2 (air at 100-130 fsw or 30-40 msw) for most people, and when 7 atm (200 fsw or 60 msw) is reached almost everyone is seriously affected. A facetious rule of thumb (that actually works) known as "Martini's Law" states that for every 50 fsw (15 msw) of depth breathing air a person is narcotized to the extent of a dry gin martini. Thus the diver on air at 150 fsw has a degree of narcosis equivalent to 3 quick martinis. This diver can be seriously impaired, and probably will not recognize it.

Narcosis is sneaky, because for most people it is a pleasant, euphoric, feeling, yet the diver can be profoundly affected. Although the biochemical mechanism is different, the effects are like alcohol, even to slurred speech, numb lips, inability to concentrate, short attention span, easy distraction, and, amusingly, a tendency to giggle or break out in raucous laughter when stimulated. Sensitivity to narcosis is an individual matter; different people are affected in different ways, but the effects are generally consistent for an individual.

Narcosis has been found by psychologists to work by slowing down processing of information by the brain; it is not a matter of nerve conduction velocity. Narcosis is likely to be the same as the phenomenon of general anesthesia, and both seem to be related to solubility of the narcotic gas in fat.

In recreational diving narcosis is an insidious and dangerous hazard. It is insidious because it induces a feeling of well-being that tends to disguise the threat. Numerous fatalities have resulted with divers who were apparently comfortable until something went a little wrong. Even a slight degree of narcosis can leave a person unable to deal with a problem. In the depth range where narcosis is substantial, if one adds stress, multiple tasks, and a complicated job, most people become dangerously ineffective.

It is said that divers accommodate or acclimate to narcosis. This seems to be valid, but it is not a pharmacological adaptation as much as an improved ability to cope as a result of recent experience (see Brauer, 1985).

The question of whether one can benefit (have reduced narcosis) by replacing some of the nitrogen in a mix with oxygen (such as diving with enriched air) is uncertain. Anecdotes say both that it is better and worse, and laboratory studies are equivocal (Bennett, 1997; Linnarsson et al, 1990). It is best to plan for a narcotic level based on both nitrogen and oxygen, or to assume that the narcotic effect of an enriched air nitrox mix will be the same as that of air at the same depth.
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Copyright Silverstein, JD - Hamilton RW 1997
NAUI Nitrox: A Guide to Diving with Oxygen Enriched Air
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We know that both helium and neon are less dense and less soluble than nitrogen, and they do not cause narcosis. Helium is the gas of choice for diving deeper than the air range. Neon is too expensive to be of much benefit as a diving gas, but it has been used experimentally. By adjusting the nitrogen component in a gas mixture the diver can "set" an "equivalent narcotic level" to help offset the effects of nitrogen narcosis. In theory and in practice this does work. Commercial and military divers routinely breathe a "heliox" mixture of 90/10 (90 % helium 10% oxygen) and virtually eliminate any narcosis at all. Some commercial companies and now technical divers have been using "trimix" to create a more reasonable mixture for decompression purposes and for cost benefits.

I've not seen any studies performed that take into consideration visual acuity when it comes to narcosis but empirical evidence points to this having some positive effects for the diver to "tolerate" high pressure inert gas narcosis better in clear bright waters than in darker colder waters.

As mentioned earlier """Narcosis has been found by psychologists to work by slowing down processing of information by the brain; it is not a matter of nerve conduction velocity."""

People are more alert when it is bright and sunny out than when it becomes darker and overcast. In bright areas the mind is stimulated and can process many more bits of information than when it is dark. This is why lighting in schools is important and why your mother would always turn on the lights when you read a book. It's also why one can fall asleep easier in a dark room than a bright one.

This may be one of the reasons why divers have reported being "good" on air in the 200 foot range while diving in the Caribbean and are virtually ineffective in 100 feet of water in the darker colder waters.

If we examine some of the signs and symptoms of inert gas narcosis, one is dizziness, the other is tunnel vision or visual disturbances. These symptoms also appear with divers in shallow waters on night dives where the ability to see becomes restricted by the lack of overall light.

Can inert gas narcosis be a combination of both partial pressure and environment?

What are your thoughts ?

[LCF]

As someone who has had some very unpleasant experiences with narcosis, I think some of it has to do with orientation information. When you are in warm water with bright sunlight and good structure on which to orient yourself, you can feel a little drunk and not notice it. But, when you are in cold water (already stressful) and limited visibility, you are deprived of the sensory information you normally use to orient yourself, and you're drunk, too. It would be as though you were taken from a well-lit living room full of friends, after a half bottle of wine, and put in a sensory deprivation chamber. The effects of the drug on your brain will be magnified, if there is no other information to compete.

For those of us who find the weightless environment of diving a bit of a challenge from an orientation standpoint, when you add poor visibility AND narcosis, you have an unhappy situation. Put me at 130 feet, on air, in Molokini, and I'm probably equally impaired, but I'm not unhappy about it.

[Doppler]

Interesting question Joel.

In anything I've written on the subject recently (and I'm just editing a chapter on gas choices) there's been some attempt to break one long-standing misunderstanding about narcosis... I believe that perception of its effects can be considered independent of partial pressure.

The bio-physics of narcotic loading is pretty much "solid-state." The interaction of high partial pressures of nitrogen with the nervous system can be taken as roughly lineal... the higher the partial pressure the greater the effect... I suspect there's a wee curve at the top end but essentially, the anesthetic properties are known and can be accounted for.

There has been some interesting work that points to multi-day exposure to high ppN2 builds tolerance, but let's ignore that to keep things simple.

The question then becomes: if narcosis is more or less lineal, how come it affects individuals differently and varies from day-to-day?

The only logical answer is that narcosis does not vary, but our perception of it does... and this leads to some very interesting sidebars.

Clearly cold, poor vis, workload, and other stressors play a role... Each of these issues seems to interfere with clear thinking and clouds judgment. Cold and CO2 are the real bete noirs in my opinion... regardless of what END my mix delivers, if I'm cold, my reaction times are hugely affected. And poor vis freaks most people out.

But as influential as these factors may be, so too must mental pre-conditioning: If I've been told I'll get narced at 20 metres, then there's a good chance I'll feel more narced than a control subject going to the same depth.

The corollary then is: If I am well-drilled in managing my equipment package, if my surroundings and the team I am diving with are all familiar, can I tolerate a higher narcotic load? My answer is yes... for what that's worth.

Anyhow, interesting topic... and one that too many divers trivialize... perhaps because there is no simple answer.

[LCF]

Cold and CO2 are the real bete noirs in my opinion.

The more incident reports I read, the more suspicious I become that elevated CO2 levels are playing a role in a great many problems underwater, especially given that there is research supporting the idea that some people routinely operate at higher than normal CO2 levels when diving. It's a profoundly narcotic gas, and surely additive with nitrogen (which might quite reasonably be expected to blunt the ventilatory response to elevated CO2).

[Gene_Hobbs]

There has been some interesting work that points to multi-day exposure to high ppN2 builds tolerance, but let's ignore that to keep things simple.

But Steve, this was the most interesting part of the topic. In the studies I have read they never controlled for many things, most important being a learning effect (Some tried but failed in my view). My thoughts tend to be in line with Bennett's (on this topic anyway). His presentation at the DAN Tech Conference is a good listen if anyone has not yet.

Clearly cold, poor vis, workload, and other stressors play a role... Each of these issues seems to interfere with clear thinking and clouds judgment. Cold and CO2 are the real bete noirs in my opinion... regardless of what END my mix delivers, if I'm cold, my reaction times are hugely affected. And poor vis freaks most people out.

CO2 is a huge factor as has been seen in the literature over and over again. Even the early studies on the narcotic effect of O2 could not separate the CO2 enough to draw a solid conclusion though they did guess it was a CO2 effect and not one from O2 directly (higher O2 leading to increased CO2). But my thoughts on respiratory physiology have been documented on this board before so no need to get off tangent with that.

I think the one factor too often neglected is one of breathing gas impurities. One recent paper we can not release yet (3 year embargo so we have to wait) shows a high risk of impurities in our breathing gas that could be a huge problem.(1) There are several "reports" on the internet that point to this, though one stands out among them.(2) Breathing gas standards for commercial diving have been getting tougher based on their experience with toluene and other gasses.

At lease we can say narcosis is not a dead topic in diving medicine. There has been some very cool work from the French in recent years as well as a current project by the US Navy at the Naval Submarine Medical Research Lab.

1. Millar IL, Mouldey PG. Compressed breathing air - the potential for evil from within. Diving and Hyperbaric Medicine. 2008. 38: 145-51 (NOTE: Diving and Hyperbaric Medicine is the new name for the Journal of the South Pacific Underwater Medicine Society following a merge with the European Underwater and Baromedical Society Journal)
2. Mouldey PG (Swampdiver). 2004. Toluene Gas Contamination Incident TheDecoStop Internet forum.

[Doppler]

Hi Gene: I have not heard Bennett's presentation... and cannot get at it... is there a transcript somewhere?

You certainly have a point on the impurity issue... more later.

[Gene_Hobbs]

Hi Gene: I have not heard Bennett's presentation... and cannot get at it... is there a transcript somewhere?

There is not but they have made the videos available for free. I can probably get a copy to you. (email sent)

You certainly have a point on the impurity issue... more later.

Looking forward to it!

[JS1scuba]

The more incident reports I read, the more suspicious I become that elevated CO2 levels are playing a role in a great many problems underwater,

Be careful about reading too many reports. It's known to cause headaches........



With open circuit scuba equipment today it is virtually impossible to have increased CO2 loads from a mechanical standpoint. The gas flow once the second stage is open is of such great volume that there is no CO2 build up from the previous exhalation. This has to do with the ease of which regulators crack and the large exhale ports.

In the 1990s the great commercial diving pioneer Andre Galene' had installed some ocean simulator chambers in his facility on City Island NY. (this was the hyperbaric facility i ran in the 1990s) Andre was fascinated with creating diving equipment and procedures that would keep his commercial divers in the water longer, thus getting more work out of them. He had found that at 150 feet his workers were not able to perform the tasks as well as they did at 75 feet. He believed it had to do with CO2 and the "ventilation of the helmet" and the "gas flow" through the hose more than it did with the increased partial pressure of nitrogen.

He conducted the studies on stationary bicycles in the wet chamber at various depths. He found that when he increased the gas flow to the helmet he could virtually eliminate narcosis to working depths of 200 feet. Standard operations for helmets was to have "50 psi over bottom pressure" to make them breathable. Andre had increased that to well over 200 psi over bottom pressure. (The discussion of impairment from high oxygen pressures was also addressed)

Modern scuba regulators of the balanced design take ambient pressure into consideration. A typical regulator is set at 140 psi IP. If it was not balanced the gas delivery at 130 fsw would be 66.5psi over bottom pressure. It would be like sucking gas through a straw. However the balanced design puts the IP at depth at 213.5 psi delivering 140 psi over bottom pressure. This dramatically higher than needed "over bottom pressure" makes the breathing resistance virtually zero.

In recent years some high profile divers has advocated lowering the IP on regulators to around 120 psi to prevent them from having seat problems and because the use of helium in the mixtures would still have them breathing easily. While this may in some respects work well for some divers who have good breathing habits it may be having a negative effect on ventilation and flushing of any small amounts of CO2 left in the breathing box after an exhalation. While some may not agree that 20 psi would be a big thing, regulators are tested for ventilation at design time and lowering the IP will affect the overall performance. The use of helium in the mixture may make it FEEL the same way from ease of inhalation but the actual gas exchange will be affected.

It's important to realize that increasing an IP over a manufactures specification may NOT be beneficial either. It may adversely affect the performance of the regulator.

The bottom line here is that if you have a top performance regulator that is delivering the correct IP at depth then CO2 build up should not be a problem from an equipment standpoint. Of course we have persons that are CO2 retainers and that's a medical issue that needs to be addressed outside of diving equipment.

Divers need to be conscious of work loads and breathing habits. If the workload goes up, slow down and regroup the breathing. If the regulator seems out of tune, get it serviced properly. CO2 should not be a problem causing issue in modern scuba diving. Rebreather diving is another area outside the scope of this post.

Cheers
JDS

[PeteJ]

I am in no way an expert on decompression and narc theory, I can only relate to what I have done in the past.

At one time I would say I was not narced at 130. Then I started taking a camera down with me and tried to figure out F-stops. I'm narced.

But what I find is that as long as I am focused on the dive I seem to be under control and can and have, handled a number of complex problems including entrapments. I think of it as my drinking days in my 20's a six pack was a starter for the night and consumed over about 90 minutes. I was in "drinking shape." If I tried to do a 6-pack in 90 minutes today, you would be picking me up off the floor.

I n cold dark water I tend to get even more focused on what I am doing. Last January on the B-29 on air, I think I was aware of what was going on, but I know the next dive on mix was a lot more brighter and I remember many more details. In warm clear water, my sensory loading is less and I seem to have more ability to do those F-stops or fix the picture of a wreck in my mind.

Last, back in the 80's I took a ride in the City Island, NY chamber to 150 feet with a dive group. In the chamber there is nothing to keep focused on, and you are a lot warmer, and all I can say is that I was completely worthless for at least 10 minutes. Laughing, giggles, etc., just completely worthless.

So, it may be that the total sensory load and an individuals capacity to handle that load is a major part of the perceived narcosis.

Think of it as band width, some days you have a lot, some days not so much.

[dsteding]

I'm assuming you mean CO2 in this throughout, and not CO, which is caused by incomplete combustion (and would indicate a much bigger equipment issue).

I've never really thought of CO2 retention as an equipment issue.

I am, however, one of those "CO2 tolerant" types. I can (apparently) have increased blood CO2 levels without exhibiting the typical physiological responses. Note that I am pretty good shape, do a fair amount of cardio work each week and have a resting heartrate in the high 40s/low 50s.

I know this because I've had splitting CO2 headaches after a few dives, all of them were where I was working hard on the bottom, and, in retrospect, not breathing deep enough to exchange CO2 efficiently through my lungs to exhaled gas. Lynne explained these in terms of the residual effects of vasodilation (constriction) due to CO2 buildup-the CO2 is long-gone, but the physiological effects are still causing the headache.

My first experience with those headaches was a benign profile in Hood Canal as a new (stupid) diver wanting to extend the bottom time on a 95 cubic foot tank. I felt really good about the 70 minute bottom time but had a horrible headache on the way home.

I know enough about myself to know that if I feel a bit of narcosis (and I don't really dive deep on nitrox anyways) I can slow down, take a few breaths, and really diminish the effects of that narcosis. This says to me that CO2 plays a huge antagonistic roll in nitrogen narcosis, or is directly responsible for its own narcotic effect.

One of the reasons I love helium . . .

The bottom line here is that if you have a top performance regulator that is delivering the correct IP at depth then CO build up should not be a problem from an equipment standpoint. Of course we have persons that are CO2 retainers and that's a medical issue that needs to be addressed outside of diving equipment.

Divers need to be conscious of work loads and breathing habits. If the workload goes up, slow down and regroup the breathing. If the regulator seems out of tune, get it serviced properly. CO2 should not be a problem causing issue in modern scuba diving. Rebreather diving is another area outside the scope of this post.

Cheers
JDS

[JS1scuba]

I'm assuming you mean CO2 in this throughout,

yes it was a Tyepo

[JS1scuba]

My first experience with those headaches was a benign profile in Hood Canal as a new (stupid) diver wanting to extend the bottom time on a 95 cubic foot tank. I felt really good about the 70 minute bottom time but had a horrible headache on the way home.

Consider that you may have been dehydrated. I can get a screaming headache here in the desert when its cool If i forget to drink enough water.

I've had divers who do not drink enough water to be "clear and copious" have a headache after a diver and then drink water and it goes away.

Breathing dry, compressed air puts enormous hydration strains on the body. If this was your first time on a long dive this may have been your headache cause.

Just a thought.

Cheers
JDS

[dsteding]

Good thought, but even back then I was religious about hydrating ~24 hours beforehand. I was definitely "clear and copious" pre-dive.

Our whole nation is probably slightly dehydrated most of the time, however.

Consider that you may have been dehydrated. I can get a screaming headache here in the desert when its cool If i forget to drink enough water.

I've had divers who do not drink enough water to be "clear and copious" have a headache after a diver and then drink water and it goes away.

Breathing dry, compressed air puts enormous hydration strains on the body. If this was your first time on a long dive this may have been your headache cause.

Just a thought.

Cheers
JDS

[gcbryan]

...
Can inert gas narcosis be a combination of both partial pressure and environment?

What are your thoughts ?

The way I look at it gas narcosis is gas narcosis and is a linear thing. The overall feeling one has is also based on the environment. I don't look at the environment aspect as being gas narcosis. The narcosis is caused by the gas not the environment. Stress, anxiety, workload effect the feeling so to me they are two separate but related things.

If you have a drink when you're happy and with friends the overall feeling is different than if you were unhappy and trying to drink your sorrows away. The intoxicated aspect is the same as far as a breathalyser would measure however.

Where diving is concerned if you aren't used to cold water with poor viz then you will have a different feeling. If you are used to it there may not be much difference between warm and cold water.

I knew someone who was an experienced diver (whatever that means) who was OK up to about 130 fsw and after than he felt like he was having a heart attack he was so stressed out. I've never been on a dive with him and haven't witnessed this myself but he was certain that he would never go below 130 fsw on air again.

This is a good decision perhaps but since narcosis is linear surely just based on narcosis one isn't OK at 130 fsw and totally freaking out at 140 fsw. I think many people misuse the term nitrogen narcosis to include their personal response to many different things rather than the actual narcosis.

[Montana]

Consider that you may have been dehydrated. I can get a screaming headache here in the desert when its cool If i forget to drink enough water.

I've had divers who do not drink enough water to be "clear and copious" have a headache after a diver and then drink water and it goes away.

Breathing dry, compressed air puts enormous hydration strains on the body. If this was your first time on a long dive this may have been your headache cause.

Just a thought.

Cheers
JDS

Would humidifying the compressed air assist to relieve the dehydration issue or are products such as the bio-filter more hype than praticality?

Enjoying the thread.