UWSojourner
Contributor
Hey Daniel,
I would say the following about ISS:
I would say the following about ISS:
- It is clearly NOT the only variable on which DCS depends. Nobody ever stated that. So picking one quote from Dr. Mitchell (from among the literally thousands of posts on this deep stop topic spread across multiple forums) might not be a reliable indicator of the nuances of the topic.
- ISS is clearly an important variable. Supersaturation is a condition of bubble formation so more supersaturation implies more bubble formation (all other things equal). So if you have profiles that are EXACTLY the same except for their distribution of stop time and one profile has 30+% more supersaturation exposure (as measured by ISS), I think it's fair to ask "what is this profile giving me that justifies the additional exposure"? In my opinion the only likely answer is "higher P(DCS)".
- A fairer reading of what has been said is this: For similar profiles (same runtimes, same depths, same gases) that only vary by how they distribute the same stop time, ISS is a pretty good index of the relative decompression stresses between the profiles. Yes, you can come up with profiles where ascending to 1 fsw and spending all your time there will generate a lower ISS. But we have other reasons to believe that the "Ascend to 1-fsw and stop there" Deco Method is likely sub-optimal in most decompression settings so we're really not too interested in that method.
- ISS is a principal "ingredient" in many decompression models, VPM included. So clearly it's not irrelevant. The US Navy believes the difference in supersaturation exposure is the most plausible explanation of the NEDU study results.
- The simple ISS measure was predictive (i.e. gives the right signal) in both the NEDU study and the Spisni study. Blind luck? I doubt it.