What causes CNS convulsion?

[daddybear]

Hi all, i am a technical diver and obviously aware of cns oxygen toxicity. Also that if you exceed 1.4ppo2 on your working portion of a dive you risk have a convulsion. Ive never had it clearly explained however why the high ppo2 triggers a convulsion. I would be gratefull if you could enlighten me. Thanks.

 

[Gene_Hobbs]

From wikipedia's Oxygen toxicity: Mechanism section.

A high concentration of oxygen damages cells.[16] Higher than normal concentrations lead to increased levels of reactive oxygen species (ROS),[46] and while not all mechanisms of damage are understood, the process of lipid peroxidation is known to cause damage to cell membranes.[47] ROS form as a natural byproduct of the normal metabolism of oxygen and have important roles in cell signaling. However, during times of environmental stress ROS levels can increase dramatically, which can result in significant damage to cell structures. This cumulates into a situation known as oxidative stress.[16][48] One example is that oxygen has a propensity to react with certain metals to form the ROS superoxide, which attacks double bonds in many organic molecules, including the unsaturated fatty acid residues in cells.[49][50] High concentrations of oxygen are also known to increase the formation of free radicals which harm DNA and other structures (see nitric oxide, peroxynitrite, and trioxidane).[16][51] Normally the body has many defense systems against such injury, such as glutathione, catalase, and superoxide dismutase, but at higher concentrations of free oxygen, these systems are eventually overwhelmed, and the rate of damage to cell membranes exceeds the capacity of the systems which control or repair it.[52][53][54] Cell damage and cell death then result.[55]

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[TSandM]

The short answer is that a bunch of mechanisms have been postulated, but nobody really knows.

 

[meierdierck]

Go to the dan website and download the tec coference on o2 toxicity
it is excellent, and you will learn way more than you want to know about the current theory, and science

 

[cutlass]

Gene's Wiki excerpt cites a good, readable paper I found the section "Risk Factors" to be especially interesting because it highlights the variability of ox-tox.

I must also retract my comment in this recent post An earlier work by the Bittermans' : paper (free download of the full text) unexpectedly observed that the presence of additional arginine (L-arginine specifically), an amino acid, delayed onset of convulsions in rat models. This was unexpected because oxygen plus arginine produce nitric oxide (NO) which is a neuro-active molecule. Theoretically, more arginine and/or more O2 would be expected to produce earlier neurologic effects. But it was found to be the opposite and other research works indicate a dose dependency; there isn't a necessary straight correlation of increasing arginine to increasing NO efffects.

 

[bvanant]

From the hyperbaric literature, my take is that there is no single mechanism, but rather there are a whole bunch of mechanisms involving neuromodulators and neurotransmitters as well as changes in both active and passive membrane transport. Probably the multiplicity of mechanistic effects explains why CNS toxicity is so variable. In the lab, you only typically measure the things you look for so everyone who does an experiment has a theory.

 

[Dr Deco]

There is no single answer.

It appears to be oxygen-derived reactive intermediates (compounds) at react with something in the nervous system. CNS problems occur when the normal defense enzymes are overwhelmed by the increased oxygen concentration in the cells.