1/2 CNS % after 90 min. SI?

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90 min half life is prescribed by NOAA CNS exposure tables. I don't have a copy of TDI Advanced Nitrox manual at hand to give you a page number but it certainly is taught by TDI

Was taught to me in TDI basic nitrox and advanced several years ago (by different instructors).

 

[Jax]

Okay, we agree it is being taught, but from where does it come?

Empirical data? Studies? How do "they" (assuming NOAA) "know" there is a 50% reduction in O2 toxicity after 90 minutes? And if that is true, why do they extend the SI to two hours if two or more dives are to 1.6 ppo?

 

[lowviz]

I emailed Hyperbarics International, Inc., still awaiting any reply. Maybe if JAX tried emailing them we could get an answer. Nobody is refuting this procedure, CNS toxicity is way too variable even for the same subject. There is a historical nugget (aka really good inside story) out there. Somebody in the know, would you please share...

 

[Jax]

I emailed Hyperbarics International, Inc., still awaiting any reply. Maybe if JAX tried emailing them we could get an answer. Nobody is refuting this procedure, CNS toxicity is way too variable even for the same subject. There is a historical nugget (aka really good inside story) out there. Somebody in the know, would you please share...

Moi? I'm just curious . . . darned engineers!

 

[lowviz]

Moi? I'm just curious . . . darned engineers!

Exactly! We are all just curious. That's what this thread is all about.

 

[Jax]

It seems to me that dive computers are computing this "off-gassing" of O2 just like N2. Somewhere, somehow, that algoritm was developed, based on something. Darned funning how that 'something' cannot be discovered while there is so much on the Nitrogen.

 

[wedivebc]

This is a very interesting thread. I was taught this through ANDI, and TDI as a former ANDI and current TDI instructor I teach this to my students and have never really questioned the origin of this information. Perhaps I should start looking into some of the other "common knowledge " teachings

 

[Jax]

Good Article http://www.shearwater.com/tools/sof...perty=FileName&toolscontext.stepinput.id=3540

According to this document,

Along with the tolerance curves, Dr. Christian J. Lambertsen and colleagues at the Institute for Environmental Medicine, University of Pennsylvania, developed the current “tracking” method for pulmonary oxygen toxicity in the form of the unit pulmonary toxic dose (UPTD) and the cumulative pulmonary toxic dose (CPTD). The UPTD is more commonly referred to in the diving community as the oxygen toxicity unit (OTU). One UPTD (or OTU) is the degree of pulmonary oxygen toxicity produced by breathing 100% O2 continuously at a pressure of 1 atmosphere absolute (ATA) for 1 minute. The CPTD calculation (see Equation 1 below) converts any continuous oxygen exposure (PO2 above 0.5) and time combination to be expressed as UPTD’s (or OTU’s). The CPTD calculation is carried out for each segment of the dive profile and the results (expressed as OTU’s) are summed up to produce the total number of OTU’s for the dive. This number can then be compared against the daily and multi-day limits established by Dr. Bill Hamilton and colleagues in the NOAA Repetitive Excursions (REPEX) Procedures Report. These published limits have been widely adopted by the technical diving community.

Bolded emphasis is mine. Perhaps the referenced "NOAA Repetitive Excursions (REPEX) Procedures Report" is the source?

 

[Mr Carcharodon]

I do not know where GUE came up with their values. But exponential recovery seems to be the prevalent view in the literature.

This reference by Arieli seems to be what you are looking for: Eur J Appl Physiol Occup Physiol. 1997;75(2):182-7, “Recovery time constant in central nervous system O2 toxicity in the rat”, Arieli R, Gutterman A.

 

[Guy Alcala]

According to this document,

Quote:
Along with the tolerance curves, Dr. Christian J. Lambertsen and colleagues at the Institute for Environmental Medicine, University of Pennsylvania, developed the current “tracking” method for pulmonary oxygen toxicity in the form of the unit pulmonary toxic dose (UPTD) and the cumulative pulmonary toxic dose (CPTD). The UPTD is more commonly referred to in the diving community as the oxygen toxicity unit (OTU). One UPTD (or OTU) is the degree of pulmonary oxygen toxicity produced by breathing 100% O2 continuously at a pressure of 1 atmosphere absolute (ATA) for 1 minute. The CPTD calculation (see Equation 1 below) converts any continuous oxygen exposure (PO2 above 0.5) and time combination to be expressed as UPTD’s (or OTU’s). The CPTD calculation is carried out for each segment of the dive profile and the results (expressed as OTU’s) are summed up to produce the total number of OTU’s for the dive. This number can then be compared against the daily and multi-day limits established by Dr. Bill Hamilton and colleagues in the NOAA Repetitive Excursions (REPEX) Procedures Report. These published limits have been widely adopted by the technical diving community.

Bolded emphasis is mine. Perhaps the referenced "NOAA Repetitive Excursions (REPEX) Procedures Report" is the source?

I believe that just explains that you add the values together for multi-level dives. The formula for calculating the multiplier for OTUs is given in the NOAA Diving Manual:

[(PO2-0.5)/.5]^0.83. According to the manual, the exponent was determined to give the best fit curve for the data. The "-0.5" is because PO2s at or below that don't cause any toxicity problems. If you run the formula for typical PO2s, you'll see that the results are the same as those given in the NOAA charts for OTU multipliers, i.e. at 1.3 ata PO2 the formula will give you 1.48 as the multiplier.

Guy