Seizure threshold & Rebreather diving deaths

nigelh

Is there any milage in considering the UK wartime system for selecting oxygen rebreather divers? AIUI They put you into the suit and took you to 45 feet (about 2.5bar) and waited. If nothing happened you proceded with training. If you woke up back on the dock you were assigned to other duties. The one exposure test was deemed sufficient although 'war time' admittedly does change the rules a bit.

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nigelh

saturation

To clarify, terminology tends to be troublesome and the manifestations of seizures, varied.

http://medlib.med.utah.edu/neuronet/epi/filloux1.html

Convulsions is a term commonly used in diving medicine to reflect findings in CNS studies and to emphasize a lack of a CNS abnormality associated with hyperoxic seizures.

Alas, in general medical usage the term seizures is synonymous with convulsions, which is troublesome as the term seizures is also used to classify true CNS related diseases.

Normal folks can be induced to seize with hypoxia, hypoglycemia, hyperoxia, ECT or head trauma etc., and you can clearly get a specific EEG finding at the time of the convulsion ... just as you can read EEG findings characteristic of sleep, mental activity or under CNS altering drugs. However in a true CNS focus, as example epilelpsy, an abnormality can detected consistently in seizure free periods.

That said, Bennett & Elliott do not conclude, but give the facts as they existed at time of publication.

In the next page, p378, based on human studies, a linked included here ends that section:

http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_DocSum

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Safe Diving and Best Wishes,

I.G. Saturation, MD

{ Comments are informational only and not meant to be medical advice applicable to a particular case. Consult your physician when considering information posted here }

saturation

A nice summary, although I am not very fond of biochemical mechanisms as they often conflict with clinical findings, while taking the reader on convoluted and not entirely practical path.

While alluded in association with sleep states, the biochemical focus obviates a key item: that is the effects of sedation in reducing cathecholamine release in reducing the risk for hyperoxic seizures. In practical terms, this means increasing the PN2 of a mix, as narcosis produces a calming effect that is removed by having too rich helium in mixes [ thus the recommendation of a lower P02 threshold in helium mixed gases].

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Safe Diving and Best Wishes,

I.G. Saturation, MD

{ Comments are informational only and not meant to be medical advice applicable to a particular case. Consult your physician when considering information posted here }

apitkin

The US Navy did this for years with their divers. Put them in a chamber at 3 bar and if anyone got symptoms (as if they would admit it!) they were out. They gave up for the simple reason that it proved to be a poor screening test, with low sensitivity and a very low positive predictive value.

One thing Donald (whose work you allude to) clearly demonstrated during the war was that an individual's susceptibility varied considerably from day to day. He concluded that the only useful preventive strategy was to limit exposure in everyone.

For anyone who hasn't read his book 'Oxygen and the Diver', I suggest they do. It has more directly obtained experimental evidence about oxygen toxicity in diving than any other work, and his work is unlikely to be repeated due to modern ethical constraints.

Andy

jhaaja

Don`t know eaxtly what you meant by being consciouss. I lost its just before i got the OC reg in ny mouth and came back aroun on the boat deck maybe 30mins after the hit.

JH

saturation

Hi JH, sorry my mistake .. faulty memory on my part.

Per the link, as you wrote, you lost consciousness at the time of the 02 convulsion. My mistake again.

__________________
Safe Diving and Best Wishes,

I.G. Saturation, MD

{ Comments are informational only and not meant to be medical advice applicable to a particular case. Consult your physician when considering information posted here }