The Iceni
Medical Moderator
Hi Netdoc,NetDoc once bubbled...
. . .It is hard for me to conceptualize bubbles that are not homogenous. While bubbles might be incredibly tiny, I would venture that molecules are tinier still and the Van Der Wall forces that they possess would show little discrimination over which other molecule they would form bubbles with. Hence it would follow that we would not have discrete bubbles of nitrogen and oxygen but bubbles that would be comprised of both in similar proportions as their PP in the plasma.
You appear to be making the same mistake Haldane made when he invented the first decompression tables. The body is not the lump of homogenous jelly he thought it to be, it is a dynamic system right down to the microcellular level. As you know we now conceptualise the body as having several "compartments" which ongas and offgas in relation to their blood supply (perfusion) and their ability to dissolve the gas of interest, in this case nitrogen and helium.
As you know, Henry's law tells us that the amount of gas dissolved is proportional to its partial pressure, as is the rate of diffusion. Thus bacteria and protozoans can survive without lungs and a circulation because they are small enough for sufficient gas for metabolism to be transported by diffusion alone. This is the situation at the microscopic level of the capillaries of the body. You are therefore right in that the bubbles will contain the same gasses in proportion to those found in the immediately surrounding blood and tissues (not the average seen in the great veins).
I am sure it does but this also is where Henry's law applies. The tissues are removing the oxygen all the time by metaobolism reducing its local partial pressure which therefore increases the pressure differential between the oxygen in the bubble and that in the hypoxic tissue. Hence the oxygen will move out of the bubble and into solution while nitognen will not as it is not being removed by metabolism.It would also make sense to me that Oxygen, once out of solution, would probably exhibit the same resistance to re-enter solution as nitrogen.
In the lungs, maybe, but remember DCI does not appear in the lungs.Since lung tissues (surfactant et al) are optimized to increase the transfer of Oxygen into the blood, they might keep plasma blood oxygen saturation high enough to inhibit a quick re-adsorption of oxygen in bubble form.
Physiologists learn about the Haldane effect, which by the way, has nothing to do with DCI. It is the ability of venous blood to carry more carbon dioxide than arterial blood. We now know this is because in venous blood less of the Hb receptors are occupied by oxygen and are therefore able to carry carbon dioxide molecules in (inactive) chemical combination as carbaminohaemoglobin. This again is not an all-or-nothing, single tissue phenomenon. It is a dynamic system wher the gas molecules follow the concentration gradients. However, you must remember CO2 is very soluble (and dissolved gas does not generate a partial pressure) and it is rapidly excreted by the body, so once an oxygen molecule has been used for metabolism it disappears to be replaced by molecules of CO2 and H2O.This brings yet another question to mind... IF oxygen displaces CO2 in the red blood cell. Would this happen continually throughout the bloodstream? Is this a function of perfusion that occurs only in the alveoli? Would this cause an increase of CO2 levels dissolved in plasma? Do red blood cells transport CO2 at all? If they don't then this starts to make a lot more sense. Once free of it's oxygen load (taken by a cell) would the cell then absorb another free roaming oxygen molecule with the resultant being released in to the blood stream as a free molecule???
I hope this helps. :doctor: