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Deep Air and Adaptation


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Posted by Kendall Raine on June 30, 2006 at 09:04:01:

It is unfortunate that the recent controversy over the Sea Divers expedition to Osborne Banks devolved as it did. Lost in the hysteria was a fundamental question of impairment by divers using air at depth. The topic of performance impairment using air, and the relatively shallow depths of such impairment, is discussed in numerous articles written by scientists. Furthermore, the controversial issue of adaptation is also examined extensively. In the interest of depersonalizing the topic a bit, the following are abstracts of articles appearing in peer reviewed scientific journals which summarize findings that, not surprisingly, noted performance decrement at depths in the 140-170 foot range. There are more where these came from. The articles also noted that while divers often perceived an adaptive effect to narcosis after repetitive dives, there was no evidence of improvement in performance, particularly for more complex functions. This last bit is important because it illustrates the truly insidious nature of narcosis. In effect, the studies illustrate the analog to the person who believes they drive better after a drink or two. While personal comfort with the slowed motor response inherent in narcosis may increase, the physiochemical processes involved with perception speed, response and cognitive acuity are not influenced by repetition. Put another way, while a diver feels a little buzz but otherwise in control when everything is going along as planned, the effects of impairment are not fully manifest until something unexpected happens. Adaptation is in the mind and the “experienced” diver, having gotten away with deep air diving across a long career, is perhaps most vulnerable to the self-deception otherwise known as “being good on deep air.”

For the record, and before the idiotic flaming starts, I don’t care how anyone else dives and have no interest in converting anyone, teaching anyone, jousting, rabbit punching or making friends. Please consider this nothing more than a public service announcement.

Dissociation of the behavioral and subjective components of nitrogen narcosis and diver adaptation.
• Hamilton K,
• Laliberte MF,
• Fowler B.

Defence and Civil Institute of Environmental Medicine, North York, Ontario, Canada.

We investigated adaptation to nitrogen narcosis by compressing 11 highly experienced divers in a hyperbaric chamber to the equivalent of 54.6 meters of seawater once a day for 5 consecutive days. The behavioral component of narcosis was assessed with a serial choice-reaction time (RT) task, and the subjective component with a global magnitude estimate. Supplementary magnitude estimates were obtained with adjectives describing work effectiveness and body sensations. The results showed that there was no adaptation on the RT task, although learning was evident. In contrast, the global estimate dissociated from RT and showed clear adaptation by Day 3. The work effectiveness adjectives followed RT and did not show adaptation. Some body sensation adjectives showed clear adaptation, but others did not. These results lead to the conclusion that the anecdotal reports of adaptation by divers can probably be attributed to the subjective rather than the behavioral component of narcosis. Dissociation of these components suggests mediation by different brain mechanisms, and it is speculated that the gamma-aminobutyric acidA/benzodiazepine receptor complex, which has been implicated in both the anesthetic and anxiolytic properties of agents such as nitrous oxide, may be involved.
PMID: 7742709 [PubMed - indexed for MEDLINE]

Subjective and behavioral effects associated with repeated exposure to narcosis.
• Hamilton K,
• Laliberte MF,
• Heslegrave R.
Human Factors Division, Defence and Civil Institute of Environmental Medicine, North York, Ont., Canada.
Below 30 m, nitrogen narcosis can severely degrade the performance of air breathing divers. Within the diving community it is generally thought that this effect can be reduced by repeating deep air dives on successive days but laboratory studies have found no strong evidence to support the notion of adaptation to narcosis. One possible explanation for this discrepancy is that one's subjective impression or perception of narcosis may decrease during repeated exposure to hyperbaric air without parallel improvement on task performance. To examine this possibility, symptoms and performance were examined over the course of 5 days of repeated exposure to 30% nitrous oxide at 1 ATA. While the results revealed no clear cut changes in global perceptions of narcosis across days, several symptoms from an adjective checklist showed unequivocal signs of adaptation. With respect to performance effects, reaction time yielded no indications of improvement over days relative to the control. These findings suggest that subjective adaptation can occur without parallel performance improvement, an effect which could compromise safety and which may be of concern in other operational settings that involve repeated exposure to stimulus conditions which impact on performance and symptoms.
PMID: 1417647 [PubMed - indexed for MEDLINE]

Diving experience and emotional factors related to the psychomotor effects of nitrogen narcosis.
• Biersner RJ,
• Hall DA,
• Linaweaver PG,
• Neuman TS.
Simple and complex psychomotor performance were tested among 21 Navy divers under normal conditions and during nitrogen narcosis in simulated dives to 170 ft of sea water. Complex psychomotor performance was impaired significantly during narcosis, while simple psychomotor performance remained essentially normal. Differences between baseline scores for complex psychomotor performance (pre- and post-dive combined) and scores obtained from the two combined testing sessions administered during narcosis were correlated with official Navy records of diving experience and self-reported moods. None of the diving experience measures was associated significantly with these difference scores. The moods of Fatigue and Happiness were, however, correlated significantly with impairment. These results indicate that, although previous experience with nitrogen narcosis and diving tasks do not mediate the performance effects of nitrogen narcosis, the complex psychomotor effects nitrogen narcosis are related to emotional traits.
PMID: 678246 [PubMed - indexed for MEDLINE]




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