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Marine Science and PhysiologyPost all medical questions related to decompression or diving here. Questions and discussions about the marine life we love to share the ocean with and how to protect them are also welcome.
I got on the web last night to research Nitrogen Narcosis. Every medical discussion I read said that:
1) NN is cause by cell exposure to N2 at excessive pressure.
2) This causes synapse retardation in nerve impulse transmission, causing the symptoms.
3) The pressure level needed can vary due to many factors.
4) Symptoms rapidly dissipate with removal of pressure.
Is there any data that suggests that previously absorbed N2 can lead to increased susceptibility to NN on multiple dives?
Don't know about recorded data, but my personal experience, if "feel" less narced on my second dive than the first. Even if there to the same depths. Don't know if I just get "used" to it, or it has less effect?
How would the absorption of Nitrogen, or retention of residual nitrogen from previous dives, have any effect to increase narcosis - when it is the pressure that causes it?
I don't think saturation, or even super-saturation of nitrogen would have any link with narcosis. If it did, then surely narcosis would present itself on ascent?
Is there any data that suggests that previously absorbed N2 can lead to increased susceptibility to NN on multiple dives?
I'm not a Doctor but NN is caused by a combination of N2 and pressure. So, if you have residual N2 and pressure be it on the first dive of the day or the last, NN is going to happen. The difference is more dependant on your individual physiology than anything else.
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Dave
The plural of anecdote is not data.
Before you criticize someone, you should walk a mile in their shoes. That way, when you criticize them, you're a mile away and you have their shoes.
One must also factor in the individual's physiological response. When I was diving to depths of 200 ft regularly, narcosis even at that depth was present but not a problem. Since I stopped diving that deep, I get narced at depths as shallow as 105 ft... and that never used to happen to me over 48 years of diving. Physiological response IMHO can be conditioned, and can also vary day-to-day.
It has been known for a while that there is no behavioral changes with repeated exposures though some learning does occur and the French researchers have been looking into this on a receptor level. Cecile's work has not shown any changes with repetitive exposure thus far.
The best analogy I heard to illustrate this was (again)...alchohol.
Drink a bottle of whisky once per year and you are carried home (incapacitated).
Drink a bottle of whisky every day and you can still walk home from the bar (inebriated, but not incapacitated).
Familiarity with the effects of being inebriated, enable the brain to develop a form of 'work-around' function. An alchoholic develops a capacity to stagger the right route home from the local bar, get the key in the door and fall into their bed at home.
Exit bar, turn left...stumble stumble stumble...turn right...stumble stumble stumble...turn right..stumble stumble stumble...open gate...stumble...key in left pocket...fumble fumble...open door...stagger stagger...up the stairs....stumble...open bedroom door...stagger....fall onto bed....
They could not, however, perform the same task if they were in a strange city...and had to work out their location, route and use a different type of key/lock in a different door.
Exit bar, turn left...stumble stumble stumble...where am I?!?...stumble stumble stumble...turn right..stumble stumble stumble...this isn't my road?!?...stumble stumble stumble...give up.....sleep behind dumpster...
With divers...it is quite possible (and I believe this from personal experience) that the 'ingrained' training and experience can still be performed when under severe narcosis (depth/time awareness, buoyancy, following a strict dive plan). However, anything that deviates from these 'ingrained' or conditioned behaviours/skills and presents itself as novel... requiring swift and accurate planning and decision making...will be byond their ability to cope with.
The danger of this is that it can lead to the perception of competence, when the reality is that you are severely detrimented. But you will never experience the severity of that detriment unless you are presented with a scenario for which you are not ingrained to react to.
The more experienced the diver...the more situations they have been ingrained to react effectively to.... hence the less likelihood that they will be presented with evidence of their inebriation.
I don't believe the OP was asking about acclimatization to narcosis, but rather than he was asking whether residual nitrogen in the tissues predisposes one to earlier or more severe narcosis on a second or later dive on a given day or trip.
The answer is no, it doesn't; narcosis is dependent on the partial pressure of nitrogen to which the neurons are exposed, and that will always equilibrate to the depth where you are. The total number of molecles of nitrogen that are in the tissues may be higher, but the nitrogen tension is the same, so the symptoms are the same. This is why narcosis will abate so quickly if you just shallow yourself up a bit.
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My dive journal can be read here, and a current dive blog HERE
My personal experience on 50m dives has been that a previous deep dive seems to give me more of a "tolerance" I got "narced" a bit on my first 50m dive, but not in the least on subsequent dives. My diving doc said that this is common, and recent reading seems to support this...i have read that this increased tolerance can last for a week or so...
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