I would encourage everyone to be slow about using any single paper, especially one from this small a study, to change the way they feel about any scientific topic. Scientists routinely make errors in study design, study execution, and statistical analysis. Even when we manage to avoid all these pitfalls, we are still vulnerable to arriving at incorrect conclusions about the results. This study presumes (among many things) the connection between venous bubbles and DCS, and futher presumes the reduction of venous bubbles will produce an associated drop in the risk of DCS. These are not unreasonable presumptions, but they are also somewhat controversial, and by no means scientifically settled. Not to mention that there is no data in this particular paper that specifically supports or refutes these presumptions. The findings actually were:
1) They found that venous bubbles were less in the hydrated group (barely significant, not enough subjects to be very confident in this result).
2)They found that pre-dive hydration increased plasma volume and that diving decreased plasma volume. Pretty basic physiology, but reassuring to see it still works.
3) Surface tension did not change with hydration or diving. Also (though not super clear from the way they phrased it) for some reason, even with the crossover design, the subjects all tended to have lower ST scores at the beginning of the hydration trial (before the hydration and diving actually occurred). This is interesting, since this was the protocol that produced lower bubbling. If you believe that decreased surface tension leads to less bubbles, then protocol 1 was biased to a low bubble score before they even drank the fluid, or got in the water. If truly biased, it would be hard to figure out whether it came by chance (again, only 8 people) or if this was an unexpected and undetected consequence of their protcol design.
4) Finally, they reported some physiologic results that are fairly expected findings, given the physiology involved.
That's it. Straight from their results section. Now go through the discussion and see how many sentences are devoted to discussing these findings, and how many roam far afield trying to connect the dots to DCS. It could all be true, but not from this paper. Which is why you have to suspend judgement while you accumulate information from many sources before you can really be sure about anything. And sometimes you will still be wrong.
Robert W. Perkins, MD, MPH
LCDR, MC, USN (DMO)
Head, Biomedical Research
Navy Experimental Diving Unit
