4 Decompression Research Takeaways
“Navy Study”
The NEDU study on deep stops is very interesting and has set the stage for a bit of controversy. The study is the most complete picture we have on doing deeper stops. It has been criticized for poor experimental design, probably rightfully so. The study does not “debunk” profiles with deeper stops but it does show that middle stops, after an initial deep stop, are not conducive for off gassing and that the profiles used in the study have a higher incidence of DCS.
Exercise is Most Important?
These might be the most important overlooked studies on decompression sickness. While conducted in rats, the impact on human DCS occurrence is probably the same. The 20 hour exercise study shows a very marked difference in DCS, a difference that isn’t matched by any other single decompression stress factor research I am aware of. There are a few notable studies pertaining to exercise. The first showed that exercise ~20 hours before a dive (mild cardiovascular exercise) reduced the chance of DCS. The second study inhibited nitric oxide production and showed an increase of bubbles. The third artificially introduced NO and reduced bubble formation. An important note, this isn’t new or citing edge research. It’s been around since the early 2000s. Anyone who wants to mitigate DCS in a serious way should take a look at the implication of these studies.
Bubbles Cause DCS
Bubbles cause DCS. Crush the bubble and DCS is no more. Well….not exactly. The original buhlmann model of “bubble=bad” isn’t correct. While the buhlmann derived algorithms that drive our dive computers typically provide good results, the theory behind them is clearly incorrect. The theories behind bubble models on the other hand, seem to be more correct however the algorithms don’t seem as effective as the buhlmann theories (that’s a contentious topic though).
Helium Penalty
When you put the proper amount of helium in your shearwater you get more decompression than if you have less helium. Clearly, something is wrong here. Slow to diffuse big diatomic Nitrogen gives you less decompression than tiny Helium? That’s correct. The “helium penalty” is bogus from a theoretical standpoint. However, diving with high helium mixtures usually means diving deeper. While the “helium penalty” is bogus in the sense that helium isn’t slower, it does seem to give a better decompression schedule (from the standpoint of less DCS incients) for deeper dives. This probably has to do with the higher critical supersaturation point at depth, but regardless, the takeaway is “right deco, wrong reasons”.