By Dr. David Sawatzky
All of us enjoy diving or we would not be doing it. Often we feel better when we are diving. A subset of divers seem to really enjoy diving deep on air. Is diving addictive? Narcosis is a fascinating topic and supports the conclusion that there might be an addictive component to some types of diving. Narcosis can be defined as ‘a general and non-specific reversible depression of neuronal excitability, produced by a number of physical and chemical agents, usually resulting in stupor’. This complex definition simply states that narcosis is a result of central nervous system (CNS) depression, as narcosis increases our brains are slowly put to sleep.
Since 1835, narcosis has been a known effect of breathing air under increased pressure. Junod stated that when breathing compressed air, “the functions of the brain are activated, imagination is lively, thoughts have a peculiar charm and in some persons, symptoms of intoxication are present”. Approximately 100 years later Albert Behnke suggested that this narcotic effect was due to the raised partial pressure of nitrogen.
In addition to nitrogen, the inert gases (Argon, Krypton, Xenon) and even carbon dioxide (CO2) are narcotic. Narcosis is also an effect of ‘narcotic drugs’ like morphine, demerol, codeine and heroine to name a few. Finally, the effects of narcotic gases are very similar to the effects of anesthetics and Xenon produces anesthesia at surface pressure (the elevated partial pressures as a result of diving are not required).
Periodically someone suggests that oxygen (O2) might be just as narcotic as nitrogen. This is a very complex topic but basically there is no clear data to show that O2 is narcotic. However, high partial pressures of O2 do interfere with the elimination of CO2 from the body and CO2 is narcotic.
The signs and symptoms of narcosis are similar to alcohol. They include laughter, excitement, euphoria, over-confidence, terror, panic, impaired manual dexterity, idea fixation, decreased perception, hallucinations, stupor, and unconsciousness. These signs and symptoms are in rough order of onset and represent the brain slowly being shut down.
An obvious question is why the first symptoms seem to be excitement and increased brain activity. The answer is simply that the first neurons in the brain to be inactivated are the negative feedback loops that keep brain activity suppressed. On a personal level, the first part of brain function to be suppressed is the conscious control on behaviour. That is why when a person drinks alcohol they soon present their ‘true’ personality. A ‘nasty’ drunk is a nasty person who controls their behaviour when they are sober and ‘pretends’ to be a nice person. This characteristic of alcohol is very useful. Before you can say you really know a person, I believe you need to see them when they are drunk. If there is a difference between the sober and the drunken personality, the drunken personality is the real person. At the same time, if there is no difference between the sober and the drunken personality, the person is fundamentally ‘honest’ in that the person they appear to be when they are sober is the person they really are.
Many years ago I had the opportunity to be a research subject on dives to 300 fsw (90 msw) while breathing air in the chamber. I will never forget my experience on the first dive. As we were passing 200 fsw (60 msw) I remember thinking the experience equated to the ‘maximum effects I’d ever experienced from alcohol’. At 250 fsw (75 msw) I was thinking that ‘if this is what street drugs are like, I understand why people get addicted’. At 300 fsw (90 msw) I was in ‘nirvana’. Because of the increased gas density I could hear the blood being pumped through my ears. I could quite happily
have sat and listened to the sound until I died… but we had a task to perform.
We sat in a chair and looked at a computer screen on which a name would appear and our job was to decide if it was male or female (no ambiguous names were used) and then – as previously instructed – press a button with either our left or right hand. We had practiced while on the surface until our responses were consistent and reproducible. The names appeared at a rate of 100 per minute. On the surface the name would appear, we’d choose and press the appropriate button, the name would disappear and after a while the next name would appear. At 300 fsw (90 msw) the name would appear and disappear before we could make a decision; we would decide and be pressing a button as the next name appeared. This was a very clear example of how narcosis slowed brain function. In addition, we were on the bottom for 15 minutes but subjectively it seemed to be only a minute or two.
The Martini Measure
Narcotic effects start as soon as the brain is exposed to the increased partial pressure of nitrogen and because the brain has a very high blood flow the effects are experienced a few seconds after a diver arrives at depth (actually the effects build as the diver descends). If the diver descends very rapidly, the level of narcosis when they initially arrive at depth is greater than expected for that depth but it subsides to the appropriate level within a few minutes. The effects of the narcosis immediately go away when the diver ascends and there is no ‘hangover’ making narcosis a farbetter experience than alcohol! However, as with alcohol, severe narcosis can result in partial amnesia.
Everyone experiences the effects of narcosis on the functioning of their brain. As with alcohol, some individuals are very aware of these effects and some are unaware. Martini’s Law is a rough approximation of these effects. It states: “breathing air at depth has an effect that is similar to drinking one Martini on an empty stomach for every 50 fsw (15 msw) of depth”.
The narcotic effect of breathing air under pressure begins as soon as a diver starts to descend, but most new divers are completely unaware of the effect until the first time they dive to 100 fsw (30 msw) or more. Suddenly they notice that they are quite ‘drunk’. Once a diver has become aware of the narcotic effect, they should be able to sense the effect, at a reduced level, at shallower depths. Some individuals never become aware of the narcotic effect and noted diving explorer Sheck Exley stated that he did not experience narcosis, even at depths of 400 fsw (120 msw) while breathing air. This is probably the most dangerous situation for a diver to be in since he or she thinks they’re functioning normally when in reality they are experiencing the effects of narcosis just like everyone else.
Several factors are known to make the effects of narcosis worse. Anxiety, apprehension, task loading, cold, fatigue, exercise, sedatives, alcohol, and increased levels of CO2 all increase the level of narcosis at a given depth. At the same time, task learning, positive motivation, frequent or prolonged exposure, high intelligence and experience are all known to reduce the level of narcosis.
These effects can be relatively easily explained. First, never forget that breathing nitrogen at a given partial pressure will have a specific depressive effect on the brain (it will put the brain partially to sleep). If you add another gas or drug or factor that also has a depressive effect on the brain or limits the ability of the brain to function, the level of narcosis will be increased.
Fatigue, sedatives, alcohol and increasing levels of CO2 all work this way. The most common sedatives divers take before diving are found in decongestants. Therefore, if you have a stuffy nose or sinuses and you take medication before a dive, check carefully the effects of the drugs in that medication and if they have sedative effects, limit your diving to shallow depths where the narcotic effects will be minimal. Obviously alcohol and ‘street drugs’ should never be taken before diving. Many prescription drugs also have a sedative effect and any drug where the pharmacist has cautioned you about driving a motor vehicle can be a problem while diving.
Exercise and cold most likely have their effect by increasing the level of CO2 in the body. I was diving my rebreather on an expedition in a remote area once and I had already pretty well used up the recommended time on my CO2 absorbent canister. The next dive was to be to a maximum depth of 60 fsw (18 msw) on a small wreck so I decided to do one last dive before changing it. I followed the wreck down to 60 fsw (18 msw) and then swam around on the bottom to a depth of approximately 85 fsw (25 msw) where I found myself at the top of an underwater cliff. I love cliffs so I dropped down to have a look (this was a tech trip where we routinely dived to depths of up to 300 fsw (90 msw). At approximately 150 fsw (45 msw) I suddenly noticed that I was experiencing a level of narcosis appropriate for a depth of about 250 fsw (76 msw), far more than I should have been experiencing. I immediately realized that I was getting CO2 through the scrubber and back into the loop and that the narcotic effect was due to the CO2 effect adding to the nitrogen effect. I quickly ascended to the wreck at 60 fsw (18 msw) where the narcotic effects abated and I finished the dive at shallow depths. The short period of increased narcosis after a rapid descent is also most likely a CO2 effect.
The remaining factors that affect the apparent level of narcosis can be explained by thinking about the brain as having a certain amount of ‘power’ or ‘data processing ability’. Narcosis takes part of this brainpower away. To be conducted safely, all dives require a certain amount of data processing ability. When the dive requires more brainpower than the diver has left, there is a high risk of the diver having an accident or dying.
Apprehension and anxiety severely limit our ability to think, thereby removing a significant amount of our data processing ability. Task loading, trying to keep track of several things at once, requires a lot of brainpower. Open water recreational diving requires the diver to keep track of about five things at the same time – depth, time, orientation/location, air supply, buddy, etc. Cave diving ads another five or so things to this list. Surveying adds about five more things to the list. Many divers are capable of cave diving safely but when they try to survey in a cave, either the survey data that they produce is so full of errors that it is useless or they fail to keep track of the 10 factors important for them to survive the cave dive, and they have an accident. High intelligence simply means that you start with a larger capacity to process data and you‘ll have more left after some has been taken away by the narcosis. On the other end of the spectrum, there are individuals who quite simply do not have the data processing ability to learn to dive safely. Still others have the brainpower to perform easy shallow dives but that’s it. These divers cannot deal with any noticeable level of narcosis.
A complex dive requires a lot more brainpower to conduct safely than a simple dive. Learning to dive new equipment or a new equipment configuration requires more brainpower. Therefore, you should always perfect new skills in shallow water before going deeper. An experienced diver does not need nearly as much brainpower to dive safely as a less experienced diver because most diving becomes automatic. A very experienced diver will already have experienced most diving emergencies. The second time the mouthpiece comes off your regulator is much less stressful than the first time! Always ensure that you have sufficient brainpower left during a dive to deal with an emergency.
The biggest danger with narcosis is that you lose awareness of it with frequent exposure. As part of an experiment I made dives in a chamber to 180 fsw (55 msw) for 30 minutes on air, five days in a row. The first day the narcosis was a huge rush. The fifth day I was unable to detect any narcosis. We had to perform a series of tasks while we were on the bottom. My performance on these tasks did not improve from day one to day five, even though my awareness of the narcosis completely disappeared.
Narcosis slows the ability of the brain to function. If you attempt to perform a task while experiencing narcosis at the same speed you would on the surface, you will make a lot of mistakes. However, if you slow down and concentrate, you should be able to perform the task accurately. The problem is that while diving, some tasks require rapid information processing. Dealing with an out of air emergency, dealing with some equipment malfunctions, etc., may not be possible in the time available if you are experiencing a significant degree of narcosis.
This factor is critical. Divers often make a deep air dive, have no problems on the dive and assume that it’s safe for them to go even deeper on the next dive. This continues until they have an emergency to deal with and then they often die.
Why is nitrogen narcotic? The short answer is that no one really knows, but there are a number of facts and some pretty good theories. All inert gases are narcotic (inert gases do not take part in any chemical reactions in the body). Some inert gases are more narcotic than others. Xenon is more narcotic than Krypton > Argon > Nitrogen > Hydrogen > Neon > Helium. Carbon dioxide is also narcotic and some people believe oxygen is narcotic.
The obvious way to control narcosis is to limit the partial pressure of nitrogen. You can do this by limiting your diving to shallow depths but if you want or need to dive deeper, the only option is to replace some or all of the nitrogen in air with a gas that is less narcotic. Historically, deeper dives were made on Heliox, a mixture of helium and oxygen. Helium causes such a low level of narcosis that dives to more than 1,000 feet (300m) have been completed. At such depths a new problem arises that is called High Pressure Neurological Syndrome (HPNS). This problem becomes more severe as you dive deeper.
Helium is expensive and often the diver only requires a partial reduction in the level of narcosis. Therefore, technical divers have perfected the use of Trimix for intermediate depths. Trimix is a mixture of nitrogen, helium and oxygen. To determine the correct mixture for a dive you simply calculate the percentage of oxygen based on the maximum partial pressure of 02 that is appropriate for the dive. You then decide what level of narcosis is reasonable for the planned dive and calculate the percentage of nitrogen. The rest of the gas has to be helium.
You determine the level of narcosis that is reasonable by evaluating the planned dive to determine how clear your head has to be. If you are simply going to be looking at the sea life on a wall, you might decide on a reasonable level of narcosis is the equivalent to diving air to 130 fsw (40 msw). If you are going to be laying line into an unexplored cave and surveying, you might decide to limit the narcosis to that experienced breathing air at 60 fsw (18 msw).
Other advantages of Trimix are that it is less expensive to make than Heliox and it feels warmer to breathe than Heliox, although there is actually a greater heat loss from the body at the same depth. And Trimix might require less decompression than Heliox; research is ongoing to clarify this and it looks promising. On very deep dives a small amount of nitrogen (5-10 percent) is added to Heliox to try and control HPNS.
Hydrox (hydrogen and oxygen) has been used for deep dives as hydrogen produces little narcosis and has minimal breathing resistance, but oxygen has to be less than 6 percent of the mixture or it is explosive. Tetrox (helium, nitrogen, hydrogen, oxygen) and Neox (neon, oxygen) have also been used for deep dives.
The question still remains, why are these gases narcotic? There are several theories but the best correlation with narcotic potency is lipid solubility. Molecular weight seems to be a factor for the heavier inert gases, but not the lighter. Therefore, this effect could be due to gas density, its effect on breathing difficulty and resulting elevated levels of CO2. The most widely accepted idea at the moment is that the inert gas molecules dissolve in the fatty part of the nerve cell membranes and interfere with the functioning of the membrane in some way to produce the narcotic effect. Exactly how this occurs is unknown. If you are having trouble sleeping some night, just try reading the chapter on narcosis in the textbook referenced in the table!
So is diving addictive? Addiction comes in two forms, physical and psychological. There does not seem to be any evidence that diving produces any type of physical addiction. However, we all enjoy pleasurable experiences and want to repeat them. Therefore, you could say that some individuals experience a psychological addiction to diving.
Narcosis can be a very pleasurable experience and I personally believe that divers who dive deep on air on a regular basis might be suffering from a true psychological addiction to the narcosis. However, diving deep on air is like gambling. Eventually the diver is going to experience an emergency while compromised by a high level of narcosis and the most likely result will be death.
Narcotic effects can be reliably measured on divers breathing air at depths of 100 fsw (30 msw) or more, and the effects increase with depth. Most training agencies recommend recreational diving be limited to a maximum depth of 130 fsw (40 msw), primarily because of narcosis, though limited bottom time before decompression is also a factor. Many training agencies also recommend that if you are diving in cold water or doing a dive that is intellectually challenging, you limit your maximum depth to 100 fsw (30 msw) or less. Narcosis is always a factor when breathing compressed air and should be considered before and during every dive.
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