Theory behind the half-life of CNS toxicity?

[Centrals]

I would be very grateful if anyone could provide any info on this question.
Much obliged.

 

[Michael Guerrero]

Have you checked for papers posted on Rubicon Foundation ?

 

[Pao]

This is how biologic enzyme system (and a lot of other things in nature) works. Enzyme systems in the body convert the generated free radicals to non-harmful substances such as oxygen and water. Since the substrate (free radicals) are continuously broken down but the enzymes are not consumed in the reaction, the reaction rate is not linear, hence the concept of half life. 1 half-life means that 1/2 of the substrate has reacted, or in this case-detoxified. Let's say you have 100 oxygen radicals to begin with. After 1 half-life you only have 50. After another half life you have 25, then after another half life you have 12.5 and so on. The key to understanding this is that a constant fraction and not a constant number/amount of the substrate reacts per half-life. I hope this helps.

---------- Post added November 22nd, 2015 at 11:47 AM ----------

A peculiarity of this concept is that the amount of the substrate approaches, but does not quite reach zero (1/2, 1/4, 1/8, 1/16, 1/32, 1/64 and so on....). However; for practical purposes the amount of the initial substance is assumed to be insignificant usually after 5 half-lives (1/32nd of the original amount), depending on the system.

 

[Centrals]

Have you checked for papers posted on Rubicon Foundation ?

Not quite there yet.
"A provisional method of O2 exposure management for a recreational dive computer" by Bohrer CR and Hamilton RW.
Quoted:....For recovery we used exponential decay, letting the Oxygen Limit Index decrease with a half life time of approximately 90mins when the PO2 is less than the established threshold of 0.5atm. This allows 50% recovery in 1.5hrs, 90% in 5, and full recovery in 9hrs. Precise data to support this recovery rate is lacking but it is......

---------- Post added November 22nd, 2015 at 04:27 PM ----------

This is how biologic enzyme system (and a lot of other things in nature) works. Enzyme systems in the body convert the generated free radicals to non-harmful substances such as oxygen and water. Since the substrate (free radicals) are continuously broken down but the enzymes are not consumed in the reaction, the reaction rate is not linear, hence the concept of half life. 1 half-life means that 1/2 of the substrate has reacted, or in this case-detoxified. Let's say you have 100 oxygen radicals to begin with. After 1 half-life you only have 50. After another half life you have 25, then after another half life you have 12.5 and so on. The key to understanding this is that a constant fraction and not a constant number/amount of the substrate reacts per half-life. I hope this helps.

---------- Post added November 22nd, 2015 at 11:47 AM ----------

A peculiarity of this concept is that the amount of the substrate approaches, but does not quite reach zero (1/2, 1/4, 1/8, 1/16, 1/32, 1/64 and so on....). However; for practical purposes the amount of the initial substance is assumed to be insignificant usually after 5 half-lives (1/32nd of the original amount), depending on the system.

We all know about the half-live of radioactive elements eg. Pu239(24100yrs).
But I am looking for the theory suggesting that the CNS toxicity has the half-live of 90mins.

 

[KenGordon]

This thread discusses the point.

Is the CNS loading 'half life' concept the result of a misunderstanding?

 

[tursiops]

This abstract may be the source of the 90-minute half-time.
[abstract] A PROVISIONAL METHOD OF OXYGEN EXPOSURE MANAGEMENT FOR A RECREATIONAL DIVE COMPUTER

 

[PfcAJ]

This abstract may be the source of the 90-minute half-time.
[abstract] A PROVISIONAL METHOD OF OXYGEN EXPOSURE MANAGEMENT FOR A RECREATIONAL DIVE COMPUTER

That reads to me "hey we programmed a computer to do this and it appears to work".

I I don't see anything to suggest that the 90min half life has been tested or validated by experiment.

 

[tursiops]

That reads to me "hey we programmed a computer to do this and it appears to work".

I I don't see anything to suggest that the 90min half life has been tested or validated by experiment.

I don't think you'll find anything. That is why Hamilton later called it BS science. ...who better to know than the guy who made it up? To be fair, however, there was some prior evidence that 2h actually had some effect (see his earlier Rubicon article), but this would imply 12h (6 halftimes) are needed for full O2 cleansing. Perhaps (my guess) Hamilton thought 9h were enough, which would then imply 9/6=1.5h=90min halftime.

 

[Lorenzoid]

This thread discusses the point.

Is the CNS loading 'half life' concept the result of a misunderstanding?

They didn't seem to be able to point to anything specific over in that thread, either.

This quote from Mark Powell over there is interesting: "There is very little scientific basis for the 90 minute half life but that doesn't mean there is no evidence for it. Just look how many divers are using it."

That divers have been using it and not toxing seems to be all the "evidence" there is to support it.

 

[Centrals]

They didn't seem to be able to point to anything specific over in that thread, either.

This quote from Mark Powell over there is interesting: "There is very little scientific basis for the 90 minute half life but that doesn't mean there is no evidence for it. Just look how many divers are using it."

That divers have been using it and not toxing seems to be all the "evidence" there is to support it.

Who started the practice in the beginning?
And most of us just followed it blindly!!
And some do get O2 tox even within the "safety limit"!
And how many computer manufacturers are corporating this unproven exponent into their algorithms in tracking O2 exposure?