Nitrogen Narcosis

[DCBC]

Like most subjects, I think the two sides start to agree if you take it far enough. One side says that you don't adapt to narcosis. The other side says that with experience you do somewhat.

One side says that sure, for something that you're practiced you might be OK but what about the novel, unexpected situation.

The other side could well respond that if you have enough experience there is very little that you haven't experienced already.

The same outcome simply viewed differently by the two sides.

I don't really think that anyone disagrees with the statement that experience is a mitigating factor when it comes to nitrogen narcosis. This has long been accepted by the hyperbaric research community, the military and the commercial diving industry. I don't see two sides here.

 

[Garth]

there is something that has bit me from scuba, im wondering if narcosis is it?

.. at first I wanted to see the reefs and fish, .. now I just love being underwater however cold, or visable the environment is. Its possible the good feeling I feel when i'm under water is related to this discussion but as for now I've only been below 100' a handfull of times.

thanks everybody

 

[Bubbletrubble]

The this study tested "eleven very experienced Navy divers from DCIEM" (many members of my old team no doubt). There is no comparison between these very experienced divers and inexperienced ones.

The only mention of this is on page 47 of this study. The author states "The strong adaptation effect observed in the present study contrasts with the unreliable effect observed by Hamilton et al (7). This difference could be explained by the substitution of experienced divers for inexperienced non-divers..... we favor the experienced hypothesis..." Improved performance was observed after day 3.

Table one shows a definite drop in the number of errors as the test proceeded. On the last two days the error rate started to increase. This may have been caused by the divers getting bored of the tests (perhaps it was the end of the week and they were looking forward to Beer call).

@DCBC: (Sorry I didn't reply to this yesterday.)

Regardless of whether the diver is experienced or inexperienced, his performance in the reaction test will be worse at depth. What is open for debate is whether the reaction test is a good objective measure for narcosis. One could also criticize the study for being too small (not many subjects).

To clarify, the authors discuss adaptation within two separate contexts: the objective serial choice-response time test AND the subjective measures consisting of a global magnitude estimate (How narc'ed do I think I am?), work capability adjectives (Am I able to concentrate? Am I able to work hard? Am I alert?), and body sensation adjectives (Am I uninhibited? Am I dreamy? Am I intoxicated?).

Adaptation (beyond the expected learning from repeating the task) was not observed in the objective measure. However, it was observed in the subjective measures of global magnitude estimate and body sensation adjectives. It's interesting to note that the divers in this study seemed to be aware that their ability to accomplish a task was impaired at depth -- this is evidenced by no adaptation occurring in the work capability adjectives. The authors point out that perhaps the experience of the divers in this study was what made this task-oriented self-awareness possible.

In the discussion (pg. 47), the authors mention the contrasting findings of the 1992 study by Hamilton et al. because it used inexperienced non-divers and, unlike the current study, showed adaptation in the work capability adjective measure. The authors suggest that experienced divers simply have better self-awareness than non-divers when it comes to gauging how narcosis affects their work. I think that's a reasonable statement. It's pretty interesting that despite having this self-awareness as it relates to task-related work...the experienced divers still thought that they weren't quite as narc'ed with each successive day (represented by the global magnitude estimate trending down over time). The authors conclude that the experienced divers could be mistaking waning body sensation changes for "behavioral" adaptation to narcosis. In other words, the divers were probably thinking: "I don't feel quite as narc'ed now, so I must be adapting to narcosis."

Unfortunately, the authors failed to investigate the effect of whether the divers were looking forward to beer call. Huge mistake IMO. Canadians love their beer, eh?

Hope this clears up a few things...

 

[Diver0001]

@DCBC: (Sorry I didn't reply to this yesterday.)

Regardless of whether the diver is experienced or inexperienced, his performance in the reaction test will be worse at depth.
...

Ok.... so..... just translating this into ga-ga-goo-goo: People thought things were getting easier but the people watching them couldn't see any improvement, right?

If that's the case then you can't argue with it, I guess. A fact is a fact. But man-o-man am I surprised.

If I make a series of say 10 deep dives over a short period of time, by the time dive 10 happens I don't feel the narcosis nearly as much as by the first dive. I could swear that I've adapted. Maybe not in terms of what it's doing to my body. I believe that part stays the same, but I could swear that I "got used to it". To be honest, I'd be very surprised to hear that my performance on dive 10 isn't any better than it is on dive 1. I would have even put money on it.

R..

 

[Bubbletrubble]

Ok.... so..... just translating this into ga-ga-goo-goo: People thought things were getting easier but the people watching them couldn't see any improvement, right?

If that's the case then you can't argue with it, I guess. A fact is a fact. But man-o-man am I surprised.

If I make a series of say 10 deep dives over a short period of time, by the time dive 10 happens I don't feel the narcosis nearly as much as by the first dive. I could swear that I've adapted. Maybe not in terms of what it's doing to my body. I believe that part stays the same, but I could swear that I "got used to it". To be honest, I'd be very surprised to hear that my performance on dive 10 isn't any better than it is on dive 1. I would have even put money on it.

A few points that might be helpful...

1. If you do a repetitive task at 150 fsw or at 10 fsw, you'll improve a little over time. See Figure 1 -- with each successive day, a small but measurable improvement is seen as represented by slightly shorter response times at each depth.
2. Over time, with this reaction-based test, performance on Day 5 at 150 fsw improved enough to be about equal to performance on Day 1 at 10 fsw. However, this is not evidence of adaptation to narcosis. It is only evidence of learning.
3. Other studies show similar results. It's important to note what objective test is used in comparing studies, though. One study used a "standing-steadiness task" (whatever that is), which is different from the serial choice-reaction time task used in this study.

So what would be evidence of adaptation? Well, in this study, in Figure 1, we would expect the slope of the performance line at 150 fsw to be steeper than the slope of the trials conducted at 10 fsw. That's not the case, though. The slopes are similar.

What's confusing is the distinction between "adaptation" and "learning."

To summarize:
In this study, over time, the experienced divers thought they were less narc'ed with regard to "body sensation" but they did have an awareness that their "work capability" was still impaired. Results of the reaction test confirm that they were still impaired.

The take-home message is:
We probably can't trust our subjective assessment of adaptation to narcosis.

Hope this clarifies things a little...

 

[Diver0001]

Er.... yeah. Summary: adaptation is a myth.

R..

 

[Bubbletrubble]

@Diver0001: To apply this knowledge to your previous example...
If you did 10 deep dives over a short period of time, by the time you do Dive #10, you probably won't feel as narc'ed, but your performance on reaction-based tests will still show impairment.

 

[DCBC]

@DCBC: Regardless of whether the diver is experienced or inexperienced, his performance in the reaction test will be worse at depth.

Thanks for the response. I might best describe what I'm trying to say, by using an analogy:

STUDY 1 (as presented by DCBC)

Group 1

A group of non-drinkers were tested to see how Beer affected them. This group was instructed to relax and enjoy the experience. Their performance was tested. The results after 2 Beers: X, after 6 Beers: Y, after 12 Beers: Z

Group 2

A group of non-drinkers were tested to see how Beer affected them. This group was instructed to concentrate and remain in their seats. Their performance was tested. The results after 2 Beers: F, after 6 Beers: G, after 12 Beers: H

Group 3

A group of Navy drunks were tested to see how Beer affected them. No additional instruction was given. Their performance was tested. The results after 2 Beers: A, after 6 Beers: B, after 12 Beers: C

Study 1 Findings

1. The performance of all Groups was reduced as alcohol consumption increased.

2. The performance of non-drinkers in Group 1 was lower than non-drinkers in Group 2.

3. The performance of the Navy drunks in Group 3 was much better than both Groups 1 and 2.

Study 1 Observations

1. Group 3 performed to satisfactory standards after 12 beers.

2. Researcher's believe that the increased performance of the NAVY drunks in Group 3 was attributable to the fact that they were more accustomed to alcohol and better able to cope with its debilitating effects.

3. It was observed that the NAVY drunks were eager to finish the testing so they could go to the Bar for more Beer.


Study 2 (as presented by Bubbletrubble)

Results on file.


The results of study 1 and study 2 were never compared.


The performance of all people is reduced when subjected to inert gas narcosis. This is without question. It is also without question, that the performance of diver's experienced with nitrogen narcosis is better than those who are not experienced in dealing with its effects.

Unfortunately, the authors failed to investigate the effect of whether the divers were looking forward to beer call. Huge mistake IMO. Canadians love their beer, eh?

Absolutely; even when Canadians try to come up with an analogy, they cannot help but talk about Beer.

 

[Diver0001]

@Diver0001: To apply this knowledge to your previous example...
If you did 10 deep dives over a short period of time, by the time you do Dive #10, you probably won't feel as narc'ed, but your performance on reaction-based tests will still show impairment.

I get it.... equal impariment, check.

Surprising.

R..

 

[Bubbletrubble]

@DCBC: BTW, I want to say that I found your study design very entertaining. When I was in college, one of my roommates was a Psych major who wrote his thesis on the effects of alcohol consumption on the perception of pain. We all got paid to drink, have a weight pressed against a thumbnail, and rate how much pain we were in. Then we all went to a local bar and made a$$es of ourselves. Afterwards, another roommate of mine proposed writing his thesis on the effects of alcohol consumption on the perception of beauty (beer-goggling). Good times!

[-]That being said, it probably isn't fair to compare inert gas narcosis to alcohol intoxication. For all intents and purposes, they are two separate beasts. When you drink alcohol, that alcohol is broken down by liver enzymes. We know that experienced alcohol drinkers have upregulated expression of the liver enzymes that break down alcohol. Moreover, there is probably a desensitization which occurs in brain cells that makes an experienced drinker feel less buzzed when his brain is exposed to the same amount of blood alcohol. These two effects are actually forms of adaptation. It explains why a naive tea-totaler might get hammered by one glass of wine whereas an alcoholic might not feel buzzed at all after drinking that same glass of wine.[/-]

Based on what I've read, there doesn't appear to be adaptation for reaction-based tests in inert gas narcosis.

If your personal experience suggests that adaptation might occur, I'm not saying that's wrong. I'm just saying that your subjective assessment might not be the best indicator of adaptation, since it's easy to confuse learning with adaptation. I think the door's still open for the possibility of adaptation...especially in tasks that are unrelated to reaction time.