Mailing List Archive Mailing List Archive
At 04:19 23/12/99 , Michael J. Black wrote: >Just stating the facts about nitrogen narcosis. I am not defending >deep diving on air, and have said before that I think it is great that >most of you are taking a clear stand against it. You don't have to >convince me about the dangers of nitrogen narcosis. However, some >adaptation to its effects is the current belief (my references are >Bruce Bassett, John Lippmann, and others but not Timothy Leary). >It appears to be physiologic and not just overlearning of mechanical >skills. Michael, I think I see what's happening here. Allow me to clarify. In your original post you wrote "Prolonged and frequent exposures give some degree of adaptation." This is a straight 'borrow' from Lippmann who, in 'Deeper into Diving' wrote "Acclimatization - prolonged and frequent exposure gives some degree of adaptation." The key here is to understand what is meant by "prolonged and frequent exposure" and to determine whether Lippmann (a mathematician, not a physiologist) and other commentators are using it in the way it was intended. So let's go to one of the sources which Lippmann quotes - Edmonds, Lowry and Pennefather's book 'Diving and Subaquatic Medicine' second edition, where we find: "Frequent or prolonged exposure produces tolerance. Air saturation diving allows for safer excursions to greater depths than is possible from surface orientated diving." And "The narcosis is evident within a few minutes of reaching a given depth (partial pressure) and is not progressive with time.... After some time at depth, tolerance appears to develop slowly." And "A card-sorting test using caisson workers showed some impairment at 2 to 3 ATA, especially in those who had relatively little exposure to pressure. However, with repeated testing i.e. practice, this difference disappeared and no loss of performance was noted even deeper than 3 ATA." And "Visual evoked responses as a measure of nitrogen narcosis were employed in US Navy divers. The investigators concluded that there were reliable and significant differences in visual evoked responses while breathing compressed air at depths which were not apparent on breathing helium-oxygen. A further study using visual evoked responses during a shallow 2 week saturation exposure with excursion dives suggested that some adaptation to narcosis occurs, but was not complete." This is not selective quoting. I merely exerpted the book's every reference to adaptation to narcosis. What this indicates is that when Edmonds, Lowry and Pennefather wrote "prolonged and frequent exposures" in relation to adaptation to narcosis they were referring to SATURATION diving and CAISSON WORKER experiments. Lippmann borrowed the phrase "Prolonged and frequent exposures" but changed the meaning to refer to what he calls "work-up dives". Other commentators then believe a few bounce dives in a row, over a few days or over a number of weekends count as "work up dives" insofar as acclimatisation to narcosis is concerned. And then we get the HESSIANS types who make the assumption that 'experience' is the same as "multiple bounce dives" which are the same as "work up dives" which count as "prolonged and frequent exposures" which are the same as "saturation and working caisson dives" for the purposes of claiming acclimatisation to narcosis. They're not only buying a myth. They're perpetuating it. I would suggest there is actually NO IMPROVEMENT IN PERFORMANCE WHILE NARCOSED DURING REPEATED SPORT TECHNICAL DIVING EXPOSURES OTHER THAN THAT WHICH WOULD BE EXPECTED DUE TO THE REPETITION OF THE ACTIVITIES INVOLVED. Or to put it more usefully, deep air divers are as out of it on the last dive as they are on the first, even if they don't feel that way. And they've got to stop kidding themselves that it's otherwise. regards billyw -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]