Hyperoxic Seizures/Oxtox

[zaberman1]

I recently had a student ask me why psuedophederine increases the risk of CNS Oxtox and not other CNS exciters or stimulants such as caffeine. This was a very interesting question that I had to do a little research on to give him a more technical answer, he is PhD candidate in Exercise Physiology. After a few hours of searching and reading, I came up with a very interesting article I thought the community would gain from...

Current Thoughts on Mechanisms of Hyperoxic Seizures

http://www.gap-software.com/staticfiles/MechanismsofHyperoxicSeizures.pdf

 

[TSandM]

Very interesting article. Do you know its date? Looking through the bibliography, I didn't see any references past 1996.

 

[zaberman1]

2001, in the C on the last page of the bibliography

 

[firstdive2005]

Thanks for the link read, very interesting. I am not medically trained. And when I also read the bib I noticed that he had old references, 96 and older. This leads me to wonder about the relevence to todays findings, if there are any. Or does that mean that the older references are good enough to use in todays medical findings related to a study like this? None the less he did say what has been taught by many. Water up, rest, relax, watch ppo's, be more vigilent in cold dives, dont take antihistamines before diving, etc.. thanks again kev

 

[UCFKnightDiver]

I believe that DAN and the Rubicon Foundations stance on using sudafed for diving is that its fine in regards to oxtox.

 

[Bubbletrubble]

Interesting paper. Well written. As far as I know, not published in any peer-reviewed journal. The info on catecholamines and MAO makes a sound argument against taking pseudoephedrine while diving.

There's no mention of nitric oxide (NO) mechanisms in the article, and I think this "dates" the review. In recent years, much has been learned about how NO functions inside and outside the central nervous system. NO is known to be involved in neuronal death (via excitotoxicity) as well as intracellular signaling cascades (transcriptional activation, protein breakdown, neurogenesis, etc.). This is the focus of some pretty cutting edge stuff in the NO field. In case anyone's interested, a Pubmed search for "hyperoxic seizure" reveals several NO papers. Searching directly for "nitric oxide" on Pubmed will give you an avalanche of hits.

Oxygen can serve as a powerful cerebral vasoconstrictor. Exposure to hyperbaric oxygen stimulates an NO-mediated increase of cerebral blood flow. Several studies in rats show a correlation between increased cerebral blood flow and O2 convulsions.
(As a side note, this might bear relevance to divers using phosphodiesterase-5 blockers, a class of drugs including Viagra and Cialis. PDE-5 blockers work by amplifying the NO effect in blood vessels and they do cross the blood-brain barrier -- at least in rats. Here's a link to a study that looked specifically at PDE-5 inhibitors in the context of hyperoxic seizures.)