Differences in Transient and Steady State Isobaric Counterdiffusion.

In order to develop an experimentally supportable and predictive theory of gas elimination and bubble formation which is needed both for avoiding and treating decompression sickness, we need further understanding of both the physical and physiological factors involved in bubble formation and growth. Recent studies in this laboratory have demonstrated not only the interpretive difficulty associated with decompression experiments - whether or not they use doppler bubble detection - but also the advantages associated with isobaric experiments involving either transient or steady-state counter-techniques (11); (5) a very pronounced periodicity in numbers of bubbles with time following a gas switch which is as yet unexplained but may be most easily accounted for on the basis of periodic blood flow changes linked with other natural cycles. Periods appear to range in time from 40-90 minutes, and may be due to simple factors such as bubbles building up and sticking in areas of sluggish venous flow and then being released over a period of several minutes. Finally, perspectives for future work in this area are very encouraging in that our results confirmed and extended our previous work and have suggested that combined experiments where a given area of skin is masked with an ability to pass helium over it) and combined with breathing a more soluble gas (such as nitrous oxide) to produce central venous bubbles, would then allow an approximate calculation of actual numbers of bubble sites in the skin! This has never before been possible; however, the advantage of this hypothesis is that it can be tested and is no longer subject to the uncertainties inherent in post-decompression studies. (Author)