fat folks and diving

[DivingDoc]

detroit diver once bubbled...

BigT touched on the Nitrogen perfusing issue.

CO2- When your body uses the air that you inhale, you exhale carbon dioxide, or CO2 as a byproduct. Working (and breathing) harder produces higher levels of CO2. When you are out of shape, you must work harder to accomplish the same tasks as someone who is in good shape. This might occur during a strong current, or stressful situations. When you build up high levels of CO2, your risk of dizziness and passing out greatly increases. And that's not good while diving!

Actually, this is not quite right -- mostly right, but not all right. The body generates CO2 during the normal coarse of metabolism and also with exercise. More CO2 is generated with exercise. That is why we normally breathe faster when we exercise in order to "blow off" the extra CO2 that is generated. If we are generating CO2 faster than we can blow it off, the body retains CO2 and therefore the blood becomes more acidic. At some point we switch to anerobic metabolism as opposed to aerobic metabolism, which can also cause increased acidity due to the generation of lactic acid.

Increased CO2 levels do not cause dizzyness. It is the opposite. If you breathe faster than you need to for the amount of CO2 your body is generating, then you are said to be "hyperventilating." This can happen during a panic attack or if you are at the doctor's office and the doctor tells you to breathe in and out deeply while he/she is examining you. People get dizzy from this because they are "blowing off" more CO2 than their body is generating, therefore the pH of the blood rises (becomes more alkaline). Alkaline pH causes the blood vessels in the brain to constrict. Therfore there is less blood going to the brain and the subject becomes dizzy.

When diving, some people retain CO2 i.e. they under-ventilate. This (Dr. Deco please correct me) relates more to the increased resistance of having to move denser air in and out of your lungs than you did while on the surface. I am not sure if this phenomenon tracks with being overweight or not.

As I understand it (Dr. Deco, again, correct me if I am wrong), people who carry a higher body fat percentage absorb more nitrogen at depth because nitrogen dissolves very well in fatty tissue. Therefore, theoretically, people with a higher body fat percentage could be more prone to DCS because of the greater volume of nitrogen that would need to be eliminated during ascent. Not sure if this is only theory or if it has been borne out in emirical observations.

ET:doctor:

 

[John C. Ratliff]

I heard it mentioned, but not really as a big benifit above. Fatter divers stay warm and comfortable longer than thinner divers. There's a reason. Have you see a "thin" seal, sea lion or whale? They develop their blubber (a whaling term, I think) for thermal protection and because some of these animals migrate long distances where there isn't much food. So I would think that being what our society terms "fat" would not be too bad for diving. There are other physiological differences (mentioned aptly above), but that shouldn't worry someone in otherwise good health. Enjoy the diving, and if you dive often enough, not only will you see a lot of very interesting things, experience weightlessness and the joys of buoyance, but you probably will loose some of that weight too.

Enjoy!

SeaRat

PS--a good proportion of Navy Divers are what would now be considered "overweight" (Body Mass Index over 27).

 

[DivingDoc]

I have to agree that overall fat divers stay warmer than thin ones. I'm not a small woman -- wear size 16, and I usually stay pretty warm, although I won't part with my 3 mm Henderson hyperstretch wetsuit even when I'm diving in warm 82 degrees tropical water just because it fits like a glove, is so easy to get on and off, and is just plain comfortable. OTOH, my son-in-law, who is a bean pole -- 5' 11" and 135 lbs, gets really cold. He had to wear his 2/3 mm wetsuit we gave him for all the pool classes for his basic OW cert, even though the pool temp was 82 degrees.

 

[Big Blue One]

IMHO your ability to handle yourself in the water and perform on the surface tasks - swimming to the boat, getting ashore in surf, struggling onto a boat ladder in a swell with all your gear on - without getting overly tired is more important than what size your wetsuit is.

Most accidents occur on the surface.

They tend to involve situations of panic and incorrect response.

Panic is often caused by tiredness and inability to handle the situation.

In your early diving this is more likely to harm you than gas effects in fatty tissue. This other stuff you will learn as you go anyway.

Get a decent level of fitness - if you drop a few pounds on the way then good for you but this doesn't need to be the primary goal - there are many other good reasons for dropping weight but this is not a necessity for diving.

 

[BIGJC]

Physical fitness is the key here I think. I'm fat but I'm in good health otherwise. Deco is a little risky but you can plan it so that you have an acceptable safety margin. If your a recreational diver it most likley won't be a problem. Personally I ride a bike about 30 minutes 4 times a week and I am in better shape than almost all of my DIR tech buddies... it's funny actually, they preach fitness but I'm the only one doing it!!

Enjoy diving, it's a great pass time!

 

[Dr Deco]

Dear Readers:

Fitness :lifter:

We certainly can say the “Conservative is as conservative does.” This means that conservative diving is found within the diver and not something obtained that is a deus ex machina. The attachment is a graph adapted from the reference cited below.

Physical fitness in the laboratory is measured by determining the maximal oxygen uptake. The higher the uptake, the better the fitness level. The graph shows that good physical fitness (high oxygen uptake) tends to produce lower Doppler bubble grades. As is true with most things in diving, the correleation is only general.:mean:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

Abstract

Carturan D, Boussuges A, Vanuxem P, Bar-Hen A, Burnet H, Gardette B. Ascent rate, age, maximal oxygen uptake, adiposity, and circulating venous bubbles after diving. J Appl Physiol 2002 Oct;93(4):1349-56

Decompression sickness in diving is recognized as a multifactorial phenomenon, depending on several factors, such as decompression rate and individual susceptibility. The Doppler ultrasonic detection of circulating venous bubbles after diving is considered a useful index for the safety of decompression because of the relationship between bubbles and decompression sickness risk. The aim of this study was to assess the effects of ascent rate, age, maximal oxygen uptake (VO(2 max)), and percent body fat on the production of bubbles after diving. Fifty male recreational divers performed two dives at 35 m during 25 min and then ascended in one case at 9 m/min and in the other case at 17 m/min. They performed the same decompression stops in the two cases. Twenty-eight divers were Doppler monitored at 10-min intervals, until 60 min after surfacing. Twenty-two divers were monitored 60 min after surfacing. The effect on bubble production 60 min after surfacing of the four variables was studied in 47 divers. The analysis showed that the 17 m/min ascent produced more elevated grades of bubbles than the 9 m/min ascent , except at the 40-min interval, and showed relationships between grades of bubbles and ascent rate and age and interaction terms between VO(2 max) and age, as well as VO(2 max) and percent body fat. Younger, slimmer, or aerobically fitter divers produced fewer bubbles compared with older, fatter, or poorly physically fit divers. These findings and the conclusions of previous studies performed on animals and humans led us to support that ascent rate, age, aerobic fitness, and adiposity are factors of susceptibility to bubble formation after diving.