>But let us look at the fit & fat diver. Inert gas uptake is dependent upon
>three things
>
>1. Time The amount of time a diver spends at depth under pressure. This
factor
>would be equal for both divers
>
>2. The pressure differential between the Partial Pressure (PP) of that
inert
>gas in the blood, &  PP of that gas in the lung. Again this would be the
same
>for both divers ( at least at the start of the dive)
>
>3. the soluability of the particular inert gas. He is absorbed at a
diffrent
>rate than N2. But again this would be the same for both divers.
>
>The fact that the fat guy is breathing heavier and circulating blood
faster,
>would not garuntee a greater uptake of inert gas. the fat guy would
certainly
>be producing more CO2 which can lead to trouble. The uptake up of inert gas
is
>driven by the pressure differential  not the amount of blood circulated.
>Unless of course the fit guys blood moved so slow that the whole blood
supply
>never made one full circut of the Pulmanary circulatory sytem. and that
small
>portion of blood that did, became too saturated with the inert gas to take
up
>gas as fast as "fresh unsaturated blood.  While this is possible. it is NOT
>applicable in an actual diving situation because Bottom times are long
enough
>for all the blood to go through the pulmanary sytem Many , Many times.
>
>VO2 max applies to 02 because that is CONSUMED not stored. That is the key
>difference here. The inert gases are stored. There is a much lower pressure
>gradient (at the surface where the tour De France takes place) driving the
>intake of 02 than of an inert gas at depth, so fitness at the surface much
>more greatly effects 02 uptake at the surface, than inert gas uptake at
depth.
>As bottom times approched complete saturation times (approx) 12 hours the
fit
>guys system may start absorbing at a slower rate than the fat guy because
the
>pressure differential which drives the inert gas uptake is much lower at
the
>end of saturation. But this length of bottom time is rare.
>
>If this senario is accepted, a fat guy  absorbs about the same amount of
inert
>gas as the fit guy. The fat guy would store more of his inert gas in fatty
>tissues which can lead to slower off gassing True. But how much slower  ??
can
>not the Fat man hang longer ??
>
>Captain Zero
>(a fat man)


Captain Zero :) ,

There are two main problems with your model. The greater issue in Helium and
Nitrogen exchange will be offgassing. You seem to think that inert gas will
be absorbed at a set rate, regardless how much gradient is applied to a
given volume of blood. I'm saying(  and the need to use the extremes in tech
and caving are necessary to illustrate the point) someone like George with a
VO2 max value in the high 70 ml/kg of body weight, will be able to circulate
his entire volume of blood, perhaps 4 times through his body, in the same
time unit the extremely fat and sedentary diver ( say with 10ml/kg VO2max)
will pump his entire volume of blood one time. As you are well aware, the
gradient each is exposed to is the same, but the duration of the gradient
being exposed to exchange potential at the alveoli, is 4 times larger for
someone like George , in this example. Neither will use a max heart rate
durring off-gassing, but easy comfortable exertion for George will create 4
times the exposure of his blood to offgassing gradient, as it will for the
obese diver. The issue of surface pressure and the "Tour"  needs to be
looked at as the ability of your body to send every blood cell all the way
around the body, in order for the blood cells to facillitate gas
exchange---clearly the faster they can do this, the more "fit" the
indivdiual. The difference at depth is that the blood cells are not the
primary "movers" of inert gas. It is the liquid of the blood that now
transports the helium and nitrogen, but its exchange rate will still be
based on how quickly the fluid can make a full circuit around the body, and
how much gradient will be acting on it as it returns to the alveoli.

The CO2 issue "DOES" involve the redblood cells and the more customary use
of VO2 max as a gas exchange rate unit, is an even better "fit".  This is
one issue we will be able to totally prove out in simulated chamber runs,
with each subject pedalling a bike ergometer to incapacitation, at a
simulated depth of 250 or 300 feet. I am very confident we will see huge
differences in the amount of unit work ( expressed in Watts) which the high
VO2 max divers will perform prior to onset of "system shutdown" , compared
to the low VO2 max divers, who are typically obese and sedentary.  We can
then equate the wattage levels each can produce in the simulations, with the
energy expenditures necessary to do simple tasks such as: to lift an anchor;
to swim and pull yourself briefly upcurrent;, etc.

Regards,
Dan


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