BDSC
Contributor
While nitrogen may begin to build immediately in the tissues upon descent, I would not agree that the narcotic effect takes place immediately.
Nitrogen Narcosis
- Thread starter Karel26
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Bubbletrubble
Contributor
I read the abstract of your citation. In the study, the 15 divers (breathing air) were given a battery of psychomotor tests at pressures of 1, 2, 3, and 4 bars. Results indicated impaired performance on a subset of the tests from 2 to 4 bars, which presumably correlated more impairment with greater ambient pressure (not sure about this because I couldn't read the full paper).
The results of the study suggest that there is some detectable impairment when comparing 1 bar to 2 bar. No tests were conducted between these two pressures.
I guess that's my point. We really don't know the "threshold pressure" at which nitrogen narcosis manifests. Due to the variable nature of the condition, it would be hard to prove that it occurs immediately upon descent from the surface.
What is "common sense" anyway? If it's an opinion shared by many, then it has little do with what is accurate or correct.
@DCBC: Are you sure about this? (This should stimulate some discussion.)
I can only speak from my personal experience and agree that it may generate some discussion.
At DCIEM, I was involved in extensive hyperbaric (dry and wet) testing to determine the parameters of inert gas narcosis. Upon completion, the Researchers believed that the potential for narcosis existed as soon as the diver begins to descend.
There were measurable differences in most divers at 33 FSW (some at 10'). These same divers did not usually recognize the first symptoms of narcosis until 100 FSW. Clearly they were affected by it long before they recognized that they were being affected.
As you know, divers have varying levels of susceptibility; this varies day-to-day and in different conditions. Although the DCIEM testing was extensive, it only had a small control group.
The U.S. Navy has also tested this with similar results. They found that a definite alteration in thinking skills occurred when divers reached 33 feet FSW. I believe it's reasonable to conclude that the process starts upon descent.
Bubbletrubble
Contributor
@DCBC: Thank you for sharing your personal experience. I'm glad that the US Navy and DCIEM are doing that type of testing. It challenges the notion that narcosis only manifests at a depth of about 100 fsw.
I think it's very instructive to note that cognitive skills may be impaired at depths as shallow as 33 fsw. I wouldn't be surprised if some subtle impairment were detected at even shallower depths.
Another interesting point you raise is the diminished self-awareness that obscures one's recognition of the narcotic effect.
As a side note, I think that the question posed by Karel26's AOW instructor...was a stroke of genius. I can't think of a better way to introduce the concept in a class format. What a great way to stimulate discussion!
I think it's very instructive to note that cognitive skills may be impaired at depths as shallow as 33 fsw. I wouldn't be surprised if some subtle impairment were detected at even shallower depths.
Another interesting point you raise is the diminished self-awareness that obscures one's recognition of the narcotic effect.
As a side note, I think that the question posed by Karel26's AOW instructor...was a stroke of genius. I can't think of a better way to introduce the concept in a class format. What a great way to stimulate discussion!
Is there any evidence that no narcotic effects are present at 1atm? It's easy to say that the effect starts at elevated pressures, but are the mechanisms of nitrogen narcosis present at any concentration of Inert gas? Stated another way, are we always under some miniscule amount of narcosis, even on the surface? I suspect it would be difficult to ever measure if that were the case.
(just for discussion, I'm not making any claims)
(just for discussion, I'm not making any claims)
HEFFAY
Contributor
We're all narc'd right now.... at 1 atmosphere (assuming we're close to sea level)
The following question is on the ACUC diver examination: When does the narcotic effects of nitrogen start to occur? The correct answer is "Immediately upon descent."
Bubbletrubble
Contributor
I guess it all depends on how you define presence/absence of the "narcotic effect." By convention, with respect to nitrogen narcosis, normal cognitive/psychomotor functioning occurs at 1 atm. This forms the comparative baseline.
Is it possible that having a lower level of inert gas dissolved in one's tissues might result in measurably improved cognitive/psychomotor testing? Sure, why not? Anything's possible. Likely? Not sure about that.
Bubbletrubble
Contributor
This may be one of those cases which distinguishes the answer sought by the examiners (or whoever constructed the test) from an answer that is evidence-based.
I'd take issue with that answer, but that's just me.
At the very least, the "correct" answer on the ACUC test is the most conservative one...and cannot be faulted for urging students to dive more safely, eh?
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