Can We Agree On How To Measure The Similarity Of Dive Profiles?

[kr2y5]

To address one possible source of confusion in this discussion: I don't think anyone has ever claimed here, or anywhere, that two different individuals, diving the same or a similar profile, will experience the same outcomes. What could conceivably be claimed is, at best, that similar profiles could lead to a similar statistical distribution of outcomes, over a greater population of divers, and it is in that context that I've been asking the question.

Over the decades, what research has been done has been done by using a lot of test subjects, with the assumption that all of those personal variables will even out. We have not even mentioned perhaps the most important of the personal factors--patent foramen ovale (PFO). In all of those tests, we must assume that the same percentage of test divers had undetected PFOs (or other issues) as are found in the general population. We can then as individuals make our own judgments.

When I dive, I dive knowing that in terms of whatever test populations have preceded me, I am older than that average, I am probably reasonably average in terms of fitness (even considering my age), and I know I do not have a PFO. I have a number of other health issues that I can throw into the mix as I make my decisions.

So when I am choosing decompression algorithms (and this is very much a key subject for me), I take all of this into consideration. That is why a word like "similar" has absolutely no meaning to me in comparing dive profiles. I will want to look at the specific details, and then I will decide--based on MY criteria--how similar they might be, and how important that similarity is for me.

I have a question, John: when you contemplate individual profiles, and exercise judgment, or make some individual adjustments, do you find that there is any sort of a systematic pattern to what you do? Could you say a few more words about that?

 

[NAM001]

Without reading all the posts I would say that the profile specifics may not be so much the key as is the degree of nitrogen saturation is. What I refer to is this for instance.... EAD. Equivilant air depth. no matter what the depths or times are there is the NDL that is the mark for alligning the profiles. NDL is the point of equality. Is that not the basis for say the rule of 120????? if yo use EAN xxx and your dive limit is say 70 ft and 70 minutes I wound think that it would be the same as 60 ft for 60 min on air They would become the same profile deco wise at those ndl times. perhaps likewise a 100 ft dive yeilding 5 min deco at 20 and 3 min at 10 ft would be the same as a 70 ft longer dive that yielded the same deco requirements. So for me it is not a depth time issue it is a physical result/impact of a depth time that is the factor to base the equality on. Just guessing here. This will be an interesting thread. especially as comments are posted for both the rec and tec side of things.

 

[boulderjohn]

I have a question, John: when you contemplate individual profiles, and exercise judgment, or make some individual adjustments, do you find that there is any sort of a systematic pattern to what you do? Could you say a few more words about that?

My personal factors put me somewhat in the middle of the diver physiology, so I do't do a whole lot special. My age is really the only important factor to me. Having read the recent threads as carefully as my abilities allow (and accepting that some of it is over my head), and having conferred with a real expert (being a decompression theory expert is part of his job), I have decided to use the Bühlmann ZHL 16-C with GF 40/70 for tech diving. I think that fits me and my physical characteristics. This past winter, when doing NDL dives, I started bringing an AL 40 filled with O2 along with me, and I switched to it while doing my stops. It should be unnecessary, but I had the bottle full, and I used very little O2 during the stops, so I decided to bring it along. It lasted quite a few dives.

 

[DiveNav]

In this thread, the question I was specifically interested in is, whether and how we can measure the similarity of dive profiles, in a way that may be practically useful......

So, I got it right. I am not yet completely demented

........One direction that was suggested earlier is that, if we pick some reference model M that expresses some value V of interest that we believe to be physiologically significant (in this case, it was tissue supersaturation, if memory serves me well) for each point in the dive profile, then we can measure profile similarity in terms of how much the values V differ throughout the dive (whether by maximum, integral, or whatever).......

IMHO, if you want to compare dive profiles, then stick to depth and time (and maybe ascent rates).
To do what you indicated above you will need to use a reference decompression algorithm that itself could be a variable too.
As an example, if you pick ZH-L16C I suspect that different computer manufacturers implemented it in slightly different ways. I know that we did it. See this link for more info.

 

[dmaziuk]

And each of these is of questionable value.

I didn't say they were valuable, I said they were [more or less] available. I do think the least useless primary measurement is pressure over time and if you want to come up with an objective -- as opposed to "I'm in good shape for may age but I'm feeling a bit under the weather from last night" -- representation of a dive profile, that what you have to base it on.

 

[boulderjohn]

I do think the least useless primary measurement is pressure over time

...because...?

 

[dmaziuk]

...because...?

... that is what's recorded by the dive computer. What do you mean because?

 

[boulderjohn]

... that is what's recorded by the dive computer. What do you mean because?

You said "I do think the least useless primary measurement is pressure over time," suggesting (as I understood your point) that this information would have some use for decompression planning. (Maybe I misunderstood the context of your point.) I was wondering why you thought that of all the things you mentioned (tank pressure, temperature, and heart rate), this would have the most value.

If your point was simply that it is useful to know how fast you are using gas for the purpose of gas planning, then I withdraw the question.

 

[dmaziuk]

You said "I do think the least useless primary measurement is pressure over time," suggesting (as I understood your point) that this information would have some use for decompression planning. (Maybe I misunderstood the context of your point.) I was wondering why you thought that of all the things you mentioned (tank pressure, temperature, and heart rate), this would have the most value.

No, I was speaking in the context of designing a normalized representation of a dive profile that would allow for meaningful comparison of dive profiles, as per the thread's topic.

 

[agilis]

No, I was speaking in the context of designing a normalized representation of a dive profile that would allow for meaningful comparison of dive profiles, as per the thread's topic.

Let me apologize for asking, but I've been trying to understand this topic.

What would be represented in the dive profile? The actual times at depth ascending and descending plus what?

What do you mean by normalized? Do you mean averaged, and if so based on what data?

What would actually be measured, and subsequently provided as adjunct information along with the physical/depth/time positions in the profile?

In other words, what are you trying to determine and what data would be gathered and subsequently added in the process of elaborating and expanding on the basic physical positioning involved in a current dive profile?