Should body fat % be a factor in NDL's?

[jtivat]

I am taking my DM and we are learning how different body tissues take on Nitrogen and off it at different levels. One example given is that fat tissue holds more nitrogen than muscle, and that because of less blood circulation it will off the nitrogen slower. So should the tables be different based on body fat %?

 

[jonnythan]

I think that the NDL numbers are so fudged to begin with, that such a fine level of detail would be meaningless. Various agency tables don't even agree with each other completely, and it seems every computer uses a different decompression model.

Further confusing the issue by adding a *third* dimension to the tables would give a false impression that the NDL is a definite line between "DCS" and "no DCS" and would probably not be based on any real research anyway.

 

[simbrooks]

Fat/muscle might be one thing, but there are other complicating factors as well. I agree with the fudging idea of how the tables were put together from statistics and empirical data from a broad spectrum of folks (or was it all from Navy divers and just made a bit more conservative for rec divers?) - at least a large sample group.

 

[jbd]

I am taking my DM and we are learning how different body tissues take on Nitrogen and off it at different levels. One example given is that fat tissue holds more nitrogen than muscle, and that because of less blood circulation it will off the nitrogen slower. So should the tables be different based on body fat %?

Would not the loading of nitrogen also be slower in fat tissue due to less blood circulation?

Some of the things that have been done with Navy based tables and procedures already address this issue somewhat.

Things like backing off one pressure group designator from the Navy max NDL, slowing ascent rate by adding safety stop(s), slowing the actual ascent rate from 60 feet per min to 30 feet per minute. There are some other things IIRC but I don't have Weinke's book in front of me at the moment.

 

[PRL]

From what I remember obese people have a higher risk of an "undeserved hit" (a topic in its own right) and they would do well to stay away from NDL.

I hold to a belief that the worse the shape the diver is in (dehydration, obesity, diet, etc)
the more the "undeserved hit" becomes deserved.

NDL tables are just a one size fits all model and in no way guarantee real time data.

 

[simbrooks]

Another thread on the subject is current in the Dr Deco forum body fat in models - see where that one goes.

 

[jonnythan]

I hold to a belief that the worse the shape the diver is in (dehydration, obesity, diet, etc)
the more the "undeserved hit" becomes deserved.

Dang, you're tough.. thinking the divers with weight issues should be punished!!

 

[cmalinowski]

I asked this question yesterday as well in the Dr Deco section. I guess my point, or question of relavence really, is whether numerical, objective data can be used to help refine the NDL models? If the models are based on navy divers, I'm not close to one. We can say we are being conservative but we may actually be pushing the limits of "our individual" NDL's.

I understand the argument that people may feel that since they've refined the NDL's to closer match their physical makeup and my then feel like it is more of an absolute number rather than a guess based on models. But those people are kidding themselves much like they would now by using the tables as absolutes.

I just think that the algorithms are based on numbers and addding more variables to narrow that down would be helpful. And I'm talking about objective actually measurements like maybe BMI or body fat %. These are measurable numbers that do not shift with "subjectivity" like saying that someone was "severely dehydrated". These are also numbers that don't change drastically like dehydration, etc.

Don't you think that if there was a way to calculate NDL impact based on blood sugar levels that everyone would be purchasing a meter and taking their readings just before their dive????

What is the average physical makeup of the individuals that they models were based on??? Since we've found that hydration has a great impact on DCS, we can probably find other measurable factors too.

When people say that obese people are more likely to get an undeserved hit, I guess the question should be posed "by how much"????

 

[Wijbrandus]

I'm a big fat diver. I stay away from the NDL. Well, most of the time. I do also make liberal use of my safety stops. Usually a 3-5 minute minimum, and sometimes more if I've got the air and the patience.

 

[cmalinowski]

I'm a big fat diver. I stay away from the NDL. Well, most of the time. I do also make liberal use of my safety stops. Usually a 3-5 minute minimum, and sometimes more if I've got the air and the patience.

But how do you know that you are being conservative? Your staying away from navy diver NDL's. You may be dancing dangerously close to "your" NDL's. Not knowing what impact my belly (and it's a well-formed belly at that) has on NDL's, means that I really don't know what the NDL's are to stay away from.