Saturation
Medical Moderator
Dr Paul Thomas once bubbled...
I entirely agree with you, Saturation, and it frustrates me that many instructors and dive marshalls here treat the CNS oxygen clock as gospel.
As an aside, as you know, any healthy individual can have a surface fit, more than two fits points to a possible diagnosis of epilepsy. These rare events you report may have been in sub-clinical epileptic subjects with a higher than normal tendency towards fitting. (No pre-dive test for that.)
I am convinced CO2 is the major factor as I have posted elsewhere on this site. I am going away for a day or two but will PM you with the reference when I get back as I would greatly value your comments.
I'm taking this opportunity to comment issues raised in this thread without addressing anyone specifically, to keep peace.
The USN had an Oxygen Tolerance Test to determine a diver's inherent tolerance to high pp02. Besides genetics and c02, suspected modifiers to convulsion thresholds included drugs and vitamins, but data is scanty and did not undergo further verification.
I have tried not to call 02 convulsions seizures, as its likely two separate biological issues, there are no EEG findings to suggests epileptic foci in 02 convulsions. In the 2 2002 cases posted here, no information suggests they were epileptic prior to their 02 convulsions.
No short term harm has yet been recorded for recreational divers following the CNS clock within 132' depth limits of nitrox diving keeping pp02 < 1.4, however the lower one is from 1.4, the safer you are.
"Technical" implies they delve deeper into aspects of diving, and it was technical divers who first brought to my attention the controversies of recreational curricula.
I would read "technical" literature and give their comments thought and consideration, most of the information is on the Internet, as printed texts are quickly obsolete.
Technical diving is the future of sport diving today. They push the envelope and provide subjects to refine decompression theory, equipment, and procedures that are of little interest to traditional funding sources [USN, NASA, DoD]. It requires a different strategy to address reliable data collection but the numbers of divers, large in comparison to subjects in controlled studies, offers great promise to the researcher who can work with them and find alternative funding sources.
Technical diving has a dark side, and their good messages are at times drowned by poor diplomacy, hubris and machismo. They too may take a procedure as gospel, like in recreational diving. Scuba training suffers from a huge variation in quality control, and that includes technical diving.
A young technical agency is at the vanguard in re-examining and applying knowledge of diving. FAD within hours of a trimix dive and 02 decompression is one such insight, it is physiologically sound but unstudied in the classical medical sense. Dr. Vann's recent paper reinforces FAD potential:
http://www.scuba-doc.com/MFFAD.pdf
Time will tell whether they persevere in maintaining exceptional quality standards or yield to the sins of general humanity as has afflicted DAN.
Technology and knowledge moves ahead constantly, so why not in diving per se? Thus, its unlikely there is but one way, but a standard way helps coordinate and identify like minded individuals. After all, in diving the real opponents are not each other, but nature, the oceans and its depths.