CNS calculation headaches

[Willem Ferguson]

On 2019/08/10 17:04, Robert Helling wrote:
> Willem,
>
>> On 10. Aug 2019, at 16:10, Willem Ferguson 
>> <willemferguson at zoology.up.ac.za 
>> <mailto:willemferguson at zoology.up.ac.za>> wrote:
>>
>> An interesting alternative, Robert. I am not happy with the deviation 
>> at 1.5 and 1.6. One would have to check what the effect of these two 
>> points are on the power curve. What is the effect on the overall fit 
>> of the power curve if one omits those two points? What of a 3rd order 
>> polynomial that could in principle accommodate the inflection at 1.4? 
>> I am not averse to a mathematical solution because the linear 
>> interpolation also causes some inaccuracy.
>>
>>
>
> here is the same on a log scale:
>
>
>
> I would not be happy to fit this with a line for all points including 
> the last two. Rather, I would use a new line for the last three points 
> (and extrapolate that) for values above pO2=1.5bar.
>
>
> Robert

Robert, I think we are making good progress here. The only real 
remaining question is what to do with pO2 values outside of the 
domain(s) of the function(s) used. My feeling is that the approach with 
the least error is to at least use a fixed value, e.g 1.65 for pO2 
values outside the domain. The CNS toxicity above 1.65 is highly 
unlikely to be less than that for 1.65. It is in fact expected to be 
more. I am not sure that omitting it is appropriate. I am worried about 
decompression at 6m which is right on that limit and which (at least in 
my case) often varies between 1.45 and 1.7, especially in the sea.

I am quite please the way this discussion has gone.

Kind regards,

willem



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