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> Mike Wallace writes:
> Sotiris Tzanlis <[log in to unmask]> writes:
>
[snip]
> >
>> As our 'experimental diver' stops it's dive and starts the ascent, the
>> partial pressure of these gases is decreasing. As a result, the dissolved
>> gasses start to decreased (escaping from the lungs during breathing
>>cycles).
>
>Yep.....
 
Agreed: offgassing begins upon the start of the 1st dive's ascent.
 
 
> >> 2) In the second dive our diver uses a mixture of 64% Nitrogen and 36%
>> Oxygen.
>>  In the depth of 20m the TOTAL PRESSURE is 3 ATM which is the sum of 1,92
>> ATM of Nitrogen, 1,08 ATM of Oxygen AND 0 ATM OF HELIUM (Because there
>> is NO HELIUM in the mixture).
>>
>>  Now according to Henry's law, since the partial pressure of Helium is
>> ZERO IN ANY DEPTH, the dissolved helium is still escape from the lungs,
>>until it reaches the Helium's partial pressure witch is ZERO. In other
words our
>> diver will continue to release Helium from his body, nomater what the
>> pressure of the Nitrogen is.
>
> But what about the He that has not yet escaped the tissues and gone back
> into solution from the first dive assuming that some of the tissues became
> supersaturated during the first dive?
 
If a gas isn't in solution, you're bending.   As such, its not that the He
has to "go back into" solution - - its already there.    Its merely a
question of how its going to come out and if it is going to interfere with
anything else while its doing so.
 
 
> ...If the diver is not completely clear of this remaing He then what
remains is
> at an increased partial pressure during the second dive.
 
The question is where the He really goes during the 2nd dive.
 
Our concept of compartments to represent "fast" and "slow" tissues is an
admission that the He is never homogeneously distributed throughout the
diver's body:  at the beginning of the 2nd dive, the slow He compartments
are empty because the first dive wasn't long enough to put anything here,
the medium He compartments are partially filled and the fast He compartments
are empty because of they offgassed during the SI.
 
Per solubility laws, the He will diffuse to lower concentration areas - -
that which goes into the blood ("fast tissue") goes to the lungs and is
offgassed.  However, it will also diffuse out into the slow compartments,
too.
 
If this offgassing occurs during a dive, per Henry's Law, the increased
pressure during a 2nd dive increases solubility, which means that He that
wasn't really necessarily prone to dissipate into a slower compartments
while on the surface will probably be more prone to do so during the 2nd
dive.  Once pushed into this slower compartment by the 2nd dive, it will
take longer for this He to eventually work its way out.   Net effect?  Good
question.
 
The other issue seems to be that Dalton's & Henry's generally assume ideal
gas conditions of independance and superposition, but we're dealing with a
complex biological system where these simplifications may not apply.   The
question appears to be if the on/off-gassing solubility rates (per Henry's
Law) is an independant function, or if it can be influenced by other
factors, such as the prescence of other gasses in or out of solution.
 
 
 
-hh