Hello Readers:
Sorry about the lateness of this reply. I was ill for several days.
Deep Stops Theory
The theory of the deep stop is that it prevents micronuclei from expanding during an ascent, in accordance with Boyle's Law.
When the nuclei are small, the internal, Laplace pressure generated by surface tension remains high. This, in turn, maintains a high pressure inside the nuclei and the driving gradient is for the free-gas phase to move from the microbubble into the liquid portion of the tissue. Migration by diffusion then allows the dissolved nitrogen to be carried away by the circulation.
That is the theory, anyway.
Putting deep stops into practice requires knowledge of the size of the microbubbles. Since these come in a variety of diameters, it also requires a knowledge of the size-number distribution. None of this is really known and it probably varies quite a bit from diver to diver.
Dive Studies
Only one study to date has been clear about that concept [reference below]. This was a crossover study that increased the statistical power of the study. It is not a particularly deep dive as recreational diving goes. It did show a clear reduction in Doppler-detectable gas bubbles with the deep stop.
In the recent class on Deep Stops at the Annual UHMS meeting, there was a lot of "evidence" along the lines of "well, it works." Things can work though not for the reason given. I suspect that this will be a difficult issue to sort out.
Dr Deco :doctor:
References :read:
Marroni A, Bennett PB, Cronje FJ, Cali-Corleo R, Germonpre P, Pieri M, Bonuccelli C, Balestra C. A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. Undersea Hyperb Med 2004; 31(2):233-243.