Re-descending after a dive during which bubbling has occurred ... introduces the potential for those bubbles to be compressed and passed from the venous side over to the arterial side in just enough time to re-ascend, turning a benign bubble into a potential type II neurological hit.
Let me stipulate that I agree with Blackwood's warning that we don't really know whether re-descending is helpful or harmful. Just because people get away with it may only prove that some people are lucky. But ALL of this stuff is only theory combined with experience -- not hard science.
So I am not disputing the claim about "bubble pumping." I am asking: Can this really happen? If so, how does it happen in the absence of a shunt, such as a patent foramen ovale?
With respect to re-descending: Re-descending has been called "a poor man's recompression chamber." Well, like the rest of life, you may get what you pay for. While the theory is fine, in practice you are more likely to run out of air or run out of time long before those bubbles go back into solution. And the conditions are a whole lot less controlled than in a chamber. If the worry is that strong, why risk it?
"Well," one might reply, "we aren't talking about treating DCS, but preventing it." Okay, so re-descending is not to try to reverse what has already happened, but to try to lower the risk by decreasing the nitrogen gradient, thereby slowing the dissolution of nitrogen from the tissues, and hopefully keeping an asymptomatic condition from turning into a symptomatic one.
But now we have raised the question: If you re-descend, do you now trade one risk for another? What happens to those bubbles which have already formed? Do they compress? Do they break up into smaller bubbles? Can they really cross the pulmonary circulation to enter the left side of the heart? Can they really cause a stroke?
I don't know the answer, but Gene Hobbs might.
In the meantime, if a dive profile seriously leaves one at the surface worrying whether s/he is going to get bent, why not just get on some oxygen and call it a day?