Body Fat and BP in models...

[cmalinowski]

OK, so I'm still trying to learn as much as possible to help limit my exposure to a DCS problem. First off, I am 6'1" and 250lbs. That, in case you don't have a picture in your head, is not gigantic but I am fairly overweight. Some BMI say obese.

So, knowing that body fat impacts off-gassing and holds nitrogen longer, wouldn't it make sense to figure out, to some degree, the impact of BMI or body fat percentage on models? I mean, lets say that I am 25% body fat. Are there any studies that would say "the models were done on people with an average BF of x%. As BF increases the off-gassing ability of your body generally goes down by n%." ???

I would wonder that, since blood flow impacts off-gassing as well, wouldn't something like blood pressure or some other indicator of blood flow help provide another variable that could help individualize the formulas?

I mean, wouldn't it be great to feel a little more secure knowing that, hey, my general resting BP is 120/75 and my body fat is 23%. Let me put those variables in a see what effect it has on the tables which were based on healthy, male, navy divers...

I understand that it wouldn't be exact, but it would be more exact than what we have now. And saying to "be more conservative" is not very objective either. So, I'm just trying to figure out how to figure out more about the impacts of extra variables on dive profiles.

Thanks.

 

[Stirling]

"the models were done on people with an average BF of x%. As BF increases the off-gassing ability of your body generally goes down by n%. ..."

Would it be nice to have that kind of information available? I suppose, if it were reliable and actually useful. But I don't know if all of the data built up over the years and incorporated into models used for dive tables and computers include information about body fat percentage. Or whether body fat percentage (or any other single factor) is the most important variable.

Would it be misleading to say that changes in body fat % affect off-gassing by a certain amount, without also explaining that [some other variable or combination of variables, such as exertion, poor circulation, effects of warmth or cold, age, or whatever] affects off-gassing by a similar amount - and maybe even in the opposite direction?

Does anybody know whether it is even possible to say that, "as body fat % increases the off-gassing ability of your body generally goes down by n%" and give a value for n that is sufficiently accurate to be reliable? What if the value of n is actually highly variable and the values for most divers are distributed over a range that is not trivial? Should we use an average value? The median?

Finally, would it actually be useful if most people don't know their actual body fat %? (I suspect that most people estimate their own body fat % and IQ, so that everybody is below average on the first and above average on the second.) I had my body fat % tested accurately, but that was a long time ago. Whatever it is today - and I think I would rather not know, because it might make me depressed - it's higher than it used to be. How often and how accurately do most people track that kind of information?

 

[cmalinowski]

"the models were done on people with an average BF of x%. As BF increases the off-gassing ability of your body generally goes down by n%. ..."

Would it be nice to have that kind of information available? I suppose, if it were reliable and actually useful. But I don't know if all of the data built up over the years and incorporated into models used for dive tables and computers include information about body fat percentage. Or whether body fat percentage (or any other single factor) is the most important variable.

I guess my question is "would that info be available and would it be useful?"

Would it be misleading to say that changes in body fat % affect off-gassing by a certain amount, without also explaining that [some other variable or combination of variables, such as exertion, poor circulation, effects of warmth or cold, age, or whatever] affects off-gassing by a similar amount - and maybe even in the opposite direction?

Rigth, but if you could base it on a number (like BMI or BF%), then it makes more sense then say "poor circlation."

Does anybody know whether it is even possible to say that, "as body fat % increases the off-gassing ability of your body generally goes down by n%" and give a value for n that is sufficiently accurate to be reliable? What if the value of n is actually highly variable and the values for most divers are distributed over a range that is not trivial? Should we use an average value? The median?

It would have been nice to know the BF or BMI that the models were originally based on. I thought all of the models were based on research of navy divers. If that is the case, I am not close to a navy diver. If the average navy diver has a BMI 24.5 because they average 73"/185lbs while I am BMI of 33 because... well... I'm fat.

Finally, would it actually be useful if most people don't know their actual body fat %? (I suspect that most people estimate their own body fat % and IQ, so that everybody is below average on the first and above average on the second.) I had my body fat % tested accurately, but that was a long time ago. Whatever it is today - and I think I would rather not know, because it might make me depressed - it's higher than it used to be. How often and how accurately do most people track that kind of information?

Yea, but if they did know it accurately, or even came close, it's probably better than basing your calcs on a navy diver... unless you are built like one.

I'm not suggesting that we give up being conservative if you know you are out of shape, overweight, know you have poor circulation, or any other miriad of factors that impact your ability to off-gas. Or, even more-so, just being conservative for conservative's sake. But if you are being conserative based on a navy diver, you may be pushing your NDL's. If you knew better what "your" NDL's might be (it will never be exact), I think it would help.

 

[Stirling]

Originally Posted by Stirling: Would it be misleading to say that changes in body fat % affect off-gassing by a certain amount, without also explaining that [some other variable or combination of variables, such as exertion, poor circulation, effects of warmth or cold, age, or whatever] affects off-gassing by a similar amount - and maybe even in the opposite direction?

Response from cmalinowski: "Rigth, but if you could base it on a number (like BMI or BF%), then it makes more sense then say "poor circlation."

I have two problems with this response:

First, if you *could* base it on a number, I would agree. But if poor circulation is a variable factor, and BMI or body fat % are not proxies for circulation (people with high body fat % may have excellent circulation, and people with low body fat % poor circulation, and there may be no reliable way to predict one from knowing the other), you can't substitute one for the other, or use one to represent or predict the other.

Second, I think you always have to watch out for the danger of attaching importance to the things you can measure. We do that a lot. If I can't measure and calculate the effects of dehydration on DCS, then I don't measure it. But if I can measure body fat, then I will take that measurement and incorporate it into my models and calculations - which has the effect of attaching more importance to the thing I am measuring than to the thing I cannot measure, even if the thing I cannot measure is actually a more important variable.

I'm certainly not opposed to better technology, incorporating the knowledge gained from better science. I think I agree with you that - properly handled, anyway - more complete, more accurate, and more specific (to the individual) information is better. In this case, I think "properly handled" would almost certainly mean with a computer for *most* divers. There are going to be an awful lot of opportunities to screw up your calculations when you start using models with a whole bunch of moving parts.

I *suspect* the technology is already available to do much more sophisticated and individual specific monitoring, but what is lacking is sufficient empirical evidence to develop individually variable models.

 

[Dr Deco]

Readers:

Body fat is more of a problem in missed decompression. Here, many gas bubbles are released from adipose [fat] tissue into the venous return and carried to the heart. There they can arterialize through the lung circulation, a PFO, or cause an "air lock" that hinders the heart's pumping action [no output of blood].

Excessive body fat is usually (but not always) indicative of poor physical fitness [and a low maximum oxygen uptake.] It is fitness that is a big determinate in DCS risk. :bomb:

In general, tables are built with enough "wiggle room" that you are far from the DCS limits.

Dr Deco

On vacation this week [Anchorage, AK - - really]. :06: