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.
HMMMM, I just learned something new. Water temp, visibility etc all effect END and here all this time I thought it was PN2....
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.
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.
Copyright Silverstein, JD - Hamilton RW 1997
NAUI Nitrox: A Guide to Diving with Oxygen Enriched Air
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 ?