>...Assuming that circulatory rate remains unchanged & gas is
>normoxic --->
>At any depth n, the extraction of O2 from blood (dissolved +
>HBO2), with HbO2 saturation remaining relatively constant with
>depth (nitpicking about a few 0.000m%) will be driven first by
>dissolved O2.  The more dissolved O2 available for given O2
>requirement, the more the Hb will remain as HbO2.
>Thus the lower the HbCO2 transport ability of RBC's
>The other problem is ventilatory.  Viscosity of gases increase
>with pressure - read depth.  This introduces a ventilatory CO2
>issue...

I'm in agreement. (I was trying to keep from turning tech.diver into a 
physiology journal, but se la vie. 

I wouldn't underestimate the increased "viscosity with depth" effect, 
effectively increasing the ventilatory end pressure. Partly because of 
the markedly increased solubility of CO2 vs O2 and partly because of 
mechanical retention, ppCO2 will go up with relatively small increases in 
ventilatory end pressures. This has been the problem with using positive 
end pressures with hospitalized ventilatory patients (say with 
respiratory distress syndrome where your attempting to use positive end 
pressures to keep the alveoli from collapsing. This becomes a real 
balancing act clinically. Depending on various individual factors, the 
sensitivity of increased ppCO2 with positive end pressures can be quit 
profound. (but do keep in mind that in this situation we're dealing with 
post-op or respiratory patients with compromised pulmonary function to 
begin with.

Now, apply that to a diver at depth with increasing gas density and 
increased exhalatory resistance...

You guys are really trying to talk me out of going to these depths aren't 
you? At my current working depth and current rate of breathing, I'm more 
in danger of blowing *off* CO2 and putting myself into respiratory 
alkalosis!

Robb W  

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