What is narcosis and why does it happen?
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SparticleBrane
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A good starting point might be the Rubicon Research Repository's Recommended Reading List.
fisheater
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Short answers:
It's a feeling of intoxication that one has from breathing nitrogen at high partial pressure, that has been compared to alcohol consumption. You get the high partial pressures by breathing air at depths around 100 ft and below, depending upon the gas mixture and individual susceptibility.
As for "how" it happens, no one knows, for sure, the bio-medical mechanism.
It's a feeling of intoxication that one has from breathing nitrogen at high partial pressure, that has been compared to alcohol consumption. You get the high partial pressures by breathing air at depths around 100 ft and below, depending upon the gas mixture and individual susceptibility.
As for "how" it happens, no one knows, for sure, the bio-medical mechanism.
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Another good question showing up here today ... one that's not exactly simple to answer.
When we dive, the increased density of the air we breathe causes nitrogen to build up inside our body tissues. Because the pressure of the air we breathe has to compensate for the pressure of the water surrounding us, we are breathing it in denser and denser quantities, and therefore taking in greater amounts of nitrogen and oxygen with increased depth. Because we are basically "surface" creatures, we reach a point where we are taking in more of these elements than our bodies are designed for. And the deeper we go, the greater those amounts become. At a certain point, our "tolerance" for the gas we're breathing reaches its limit, and we basically "overdose" on the gas elements that comprise the air we're breathing. The symptoms appear as narcosis ... which affects us in ways similar to alcohol.
The chemical process that causes nitrogen narcosis isn't well understood. And although nitrogen is generally considered an inert gas, one theory is that it somehow blocks impulses traveling through our nervous system, affecting our brain's ability to concentrate, and thereby inhibiting our ability to perceive, comprehend, and respond to what's going on around us.
The good news is that narcosis itself isn't harmful ... and simply coming up a few feet is generally all that's needed to make it go away. The bad news is that because it affects our brain function, it amounts to "drunk driving" ... which can have all sorts of harmful effects due to a lack of good judgment or action at a necessary time. And like alcohol, it affects everyone differently ... and for that matter, your tolerance to narcosis will vary from day to day and dive to dive.
Many deep divers develop a tolerance for narcosis through repetition ... basically adapting to the condition. Most modern diving philosophies frown on this technique ... again using the analogy that it amounts to training yourself to drive a car while drunk.
... Bob (Grateful Diver)
Couldn't narcosis be compared to the feeling from nitrous oxide that you get at the dentist? At low concentrations you get a little relaxed and sedated. It higher concentrations you can get pretty heavily sedated. Different persons are affected to differing degrees at the same concentrations
Since the nitrous oxide enters and leaves the body through the lungs just as nitrogen does, the effects of both go away upon reducing the partial pressure quite quickly.
Since the nitrous oxide enters and leaves the body through the lungs just as nitrogen does, the effects of both go away upon reducing the partial pressure quite quickly.
Thanks everyone, especially NWGratefulDiver (Bob). I have read some of your answers on this board and they are very informative. I believe thats what someone new to diving needs. Not that anyone elses answers are irrelevant, I appreciate them all.
Narcosis and alcohol are very different. Narcosis can be eliminated immediatly by ascending, and sometimes you don't feel sick, only to concentrate slower. Otherwise with alcohol, you must wait several hours to eliminate, and you are always sick.
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The effects of nitrogen on divers and nitrous oxide on land-dwellers are probably somewhat similar, and may be produced by similar mechanisms. The interesting thing is that the actual chemical events that lead to narcosis (or general anesthesia) are not understood, despite many years of research. We know what KINDS of gases are likely to produce sedation or anesthesia, and we can even build them, but we cannot really explain why they work.
Most people talk about narcosis as an either/or phenomenon: You are narced, or you are not. It is highly likely that what actually happens is that, from the moment you submerge, your nervous system is affected by nitrogen, and the effect increases as you go deeper. Where you become aware of the narcosis can vary, but most people will say it's at or below 100 fsw. The impairment can be manifested as euphoria (usually in good visibility and warm water) or as paranoia (more common in cold water and poor viz), and frequently involves a degree of tunnel vision (poor situational awareness) and poor judgment, clumsiness with physical skills, and even hallucinations when it is severe.
Bob said that narcosis isn't harmful, and that's true in the sense that it does no permanent harm we know of to the central nervous system. But people have died because of it, because they went too deep, or ran out of gas because they stopped checking gauges. It is not a funny thing, even when the experience is euphoric.
As Bob said, narcosis varies from individual to individual (just as susceptibility to alcohol and anesthetics does) and can also vary from day to day in the same individual. It's also important to know that carbon dioxide is an extremely narcotic gas, so breathing patterns that result in CO2 retention augment nitrogen narcosis, sometimes to a debilitating degree.
This is one of the reasons why new divers are advised to expand their envelope slowly, doing shallower dives until they are comfortable, before they head for the deeps.
Most people talk about narcosis as an either/or phenomenon: You are narced, or you are not. It is highly likely that what actually happens is that, from the moment you submerge, your nervous system is affected by nitrogen, and the effect increases as you go deeper. Where you become aware of the narcosis can vary, but most people will say it's at or below 100 fsw. The impairment can be manifested as euphoria (usually in good visibility and warm water) or as paranoia (more common in cold water and poor viz), and frequently involves a degree of tunnel vision (poor situational awareness) and poor judgment, clumsiness with physical skills, and even hallucinations when it is severe.
Bob said that narcosis isn't harmful, and that's true in the sense that it does no permanent harm we know of to the central nervous system. But people have died because of it, because they went too deep, or ran out of gas because they stopped checking gauges. It is not a funny thing, even when the experience is euphoric.
As Bob said, narcosis varies from individual to individual (just as susceptibility to alcohol and anesthetics does) and can also vary from day to day in the same individual. It's also important to know that carbon dioxide is an extremely narcotic gas, so breathing patterns that result in CO2 retention augment nitrogen narcosis, sometimes to a debilitating degree.
This is one of the reasons why new divers are advised to expand their envelope slowly, doing shallower dives until they are comfortable, before they head for the deeps.
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