Johan Pretorius

My diving colleagues and myself had an interresting debate over the weekend, and I promised to put the subject on the forum for other input.

It is generally accepted (according to training materials available) that you need a low body fat percentage for optimum decompression and that "obese" divers stand metter chance of incurring DCS. Medically, obese means a body fat percentage is + 25%.

Reasons being (amongst other things) is that Nitrogen is more soluble in lipids, but harder to release from than muscle tissue as there is a goop perfusion of blood etc etc
Therefore a navy seal body type person (5-10% body fat) should have a better offgassing and more complete decompression than a person carrying 40% body fat, thus the chances of incurring decompression sickness is much less.

Does any research prove or disprove the theory?

How does this equate in whales and seals, that regularily do very deep and long dives, contain very high body fat percentages and do not seem to "bend"
OK, they do it on one breath may be the argument, thus they do not absorb as much nitrogen as a human diver would

A person I know, was an national spearfishing competitor, with International colours. This means they are cardiovascular very fit, although not the typical long distance marathion athelete body type. This person has the "record" for being one of the few freedivers that have bent on breath hold diving.

Impossible some would say....

This person, on the day he bent, was part of a national spearfishing competition.
The competitions generally last for 6 hours, and the competitors dive for every second that they can.
He made uncounted dives between 30-40m (100-130 Ft) with approximately 4min bottom time for the duration of the day.
After 6 hours of strenous diving, back on and he felt unwell, with classic symptoms of DCS.
He went for a chamber ride that respolved all issues....
Diagnoised with DCS.....

Back to body fat percentage.

What does medical research say?
Has any research been done?

voets

I think I read that Whales and seals exhale before they dive. So they dive with little air in their lungs. And they do have the capability to store a lot of oxygen in their blood and tissues. Also the hearbeat slows down to a few beats per minute.

dreamdive

You can check out this link: Obesity and DCS. , http://www.faa.gov/pilots/safety/pil.../media/dcs.pdf

Also, most fat is white vs dark (which is more vascular). In decompression theory, fast tissues are perfusion controlled and slow tissues are diffusion controlled. The decompression stop is determined usually by the first tissue reaching M-value. White fat is a slow tissue. The problem is with Nitrogen solubility. Something that goes quickly into solution is also coming out of solution more quickly. Also, if the fraction of body fat to other tissue types is high, you will see increased overall nitrogen loading. Given the current algorithms in deco programs, I am not sure they account for high adipose tissues. Interestingly, although women typically have a higher body fat content than males (in fit people that is), women don't appear more prone to DCS.

dreamdive

Gender differences in circulating... [Clin Physiol Funct Imaging. 2009] - PubMed - NCBI, jap.physiology.org/content/93/4/1349.full,

Dug a little deeper and found these for you. Mind you those studies are done within recreational limits!!

Hope this helps.

Dive safe!

jkaterenchuk

To answer your question is there any research then I would say yes. I was recently on a deep diving liveaboard trip to the Oriskany (max depth 220fsw). invited along was Dr Neal Pollack from DAN/Duke and his research intern Jenna. They are conducting a long term Technical Diver DCS study.

Part of the study includes taking of body fat composition using skin fold calipers. They also have the participants complete some general fitness and flexibility tests. During the study period the divers conduct there dives and then post dive they are monitored every 20 minutes thru the use of a portable sonogram machine on the chest wall to provide a view of the chambers of the heart. Video and grading of bubble traveling thru the heart are done at rest, with movement of the arm and with movement of the leg. The bubbles are then graded on a scale (non-linear I believe) the reflect the quantity of bubbles, and the number of cardiac cycles in which they are evident. The test continues every 20 minutes for a minimum of 2 hours post dive.

Additionally, the divers have some blood samples drawn at intervals during the study and diving period and the dive profiles are also taken from both a Sensa monitor and the divers PO2 computer.

Now regarding body fat versus DCS risk. Before I participated in this study I would clearly be in the opinion that it has a major effect. Now I believe that the major risk with DCS is dive profile. Hydration, Fat %, age etc are all smaller contributing factors.

The reason I now feel that way is because of how I performed during the tests of bubbles post dive. A little background information might help with understanding how I was "blown away" when I looked at the screen after the first dive and the blood flowing thru my heart looked like it belonged to Mr. Bubble when I moved my right leg three times.

I am almost 54 years old, 5ft 11in and about 185lbs. I run 30-40 miles per week at sub 8 min mile pace. I do some light weight lifting type exercise only to maintain muscle tone. Comparing myself to most of the other participants in the study during this trip IMHO I was one of the oldest, on the lower end of body fat % and in better physical fitness shape. However, it would seem that I was the person on the study that seemed to bubble the most post dive. I cannot be sure because the results are not shared with everyone but it seemed I routinely spent in excess of 2 hours post testing and after the first dive it was more like 5 hours post dive testing until the bubbles were graded low on the scale.

So if body fat was a major risk factor with DCS then I would have expected those with much higher levels of body fat to mine to have had more bubbles then I did. From what I could observe during the study that was not the case but I cannot be sure since results are confidential.

However I did decide during the study to change my GF and hence move to a more conservative profile and the results were immediately visible during post dive bubble grading. On the first dive I did a dive at GF 20/85 (quite a normal setting for a trimix dive) to roughly 220fsw for a total run time of 90 minutes. During monitoring bubbles post dive I had grade 5+ bubbles going thru my heart when I moved my right leg. I think the max grade is 6 but visually it looked like a bottle of champagne that had just been uncorked. The bubbles peaked at about 90 minutes post dive and continued at high level until about 4 hours post dive then decayed to grade 2 at about 5 hours post dive.

I decided to change the GF to 30/75 and I conducted another dive with similar depth and times and during post dive monitoring I was mostly a grade 2 with the occasion grade 3. To give you an idea of the difference visually at grade 3 I would need to have the bubble pointed out to me on the screen to be able to see them. At grade 5+ it was a "holy shit look at that" moment.

So when I compare my body, age and fitness level to the other participants and the results I showed it seemed obvious to me that selection of the GF (hence dive profile) has a much greater effect on DCS risk (as shown via bubble present in the heart post dive) then the other factors.

John

Johan Pretorius

Thank you very much for the info...
This is interresting reading

danijeladir

Mostly I agree with you. But you can also look at it in an another way. Are YOU going to decompress better if you have less bodyfat. Less fat means better fitness, quality food etc. These are all things that can contribute. I think it is wrong to compere person to person according to their fat content and bring out conclusions about their decompression quality. It is individual. If you look at the caison workers in the 19th century there are a lot of evidence that bigger and fatter persons had more DCS trouble. From my personal experience being and staying fit and with a body fat below 10% make me feel better after most dives and sometimes encourage me to do very "fast" profiles without any serious incidents so far.

Best regards
Mirko

jkaterenchuk

In general terms it would always be better to have all the known/suspected factors aligned in your favour for the best decompression results. The problem comes when you try to do that in reality and want to make a decision like should I reduce from 15% body fat to 10% body fat. And if I go thru that long term reduction and effort how much of payout do I get with decompression efficiency. And how does that improvement in efficiency compare to a simpler more immediate result like changing my VPM or GF to be more conservative.

Last time I had a body fat analysis I was around 16% so I know it would take several months and alot of time/effort to get down to 10%. But I know immediately I can get a significant improvement by changing from 20/85 to 30/75 and it only adds a little additional time to my decompression time in the water.

John

aainslie

John,

Why did you increase the deep gf from 20 to 30?

__________________
Andrew Ainslie

"I damajed my perfials wunce" - nailer99

jnroy

is there a good reference/articleetc.. on the choice of gf actually ?