NDL Times

[tech3324]

Dr Deco once bubbled...
Dear Readers:


To repeat it again, more likely than not, DCS is the result of something not considered in the tables. This might be vigorous, excessive activity at depth that loads the tissue compartments in ways not considered by the algorithm. Also, vigorous activity will generate tissue micronuclei that will radically change the off gassing and possibilities for DCS.

Dr Deco :doctor:

Dr. Deco, this is a great topic, and one I've wondered about many times. But I'm unsure of how to interpret your reply. If you are you saying that DCS is the result of something not considered in the tables, then does it follow that this factor is also not considered in our dive computers?

If so, then it seems like the only purpose of a computer is to set some extreme outer boundary beyond which we know we will likely get bent. If that's the case, then shouldn't we dive the most liberal computers possible, but take other steps to minimize the possibility of DCS, such as the deep safety stops suggested by Richard Pyle?

I'd appreciate hearing more of your thoughts and ideas on this. Thanks.

Don

 

[Dr Deco]

Dear Don and Readers:

What Else?

It certainly is correct that the meters and tables are at the very far edge of the DCS risk curve. It is for this reason that they will all work even if their NDLs etc are different. What is not considered in the algorithms is the concentration of micronuclei in the tissues. It is the nuclei, as proposed by EN Harvey in 1943, that forms the real basis of the Haldane system.

The controlling equation is that of Young and Laplace and relates pressure change, surface tension of the bubble, and initial bubble radius. For a given pressure change (in a gas-saturated fluid), unless the radius is of a given size or larger, the bubbles will not grow.

All real fluids contain these nuclei. You know they are in our bodies because a pressure reduction will cause them to enlarge. They are [probably] not present in the same amount in all divers, because people respond differently to depressurization. Surface tension is likewise not the same.

Where do you get the Nuclei?

Nuclei originate from physical activity. The simple fact of moving around in living creatures will create them. We cannot escape them. (“Resistance is useless,” as the Borg would say.)

We can minimize the effect by avoidance of strenuous activities before, during, and following dives. Long-time readers will note that this concept has been stressed in this FORUM for the last couple of years. The other way to minimize the effect is be means of safety stops (or deep stops, if you are decompression diving). This, along with slow ascents, is a way to prevent growth of bubbles based on physics. The “Pyle stops” are a type of deep stop.

Try It Yourself :mean:

Open a screw-capped bottle of soda pop. If do quickly, it will bubble. Performed slowly, the liquid will remain largely quiescent. You are not decompressing the liquid in the sense that the dissolved gas is gone. What you are doing is preventing the sudden Boyle’s Law expansion of nuclei with its concomitant reduction in the Laplace pressure (= surface tension pressure that contracts the bubbles). Slow depressurizations will keep bubbles small. None of this is built into tables or deco meters. You can do it yourself for no cost.

I know that this is not simple to visualize. It is simple in principle but not necessarily easy to see.

Dr Deco :doctor:

 

[leadweight]

After reading Dr. Deco's discussion I am drifting towards the conclusion that one might as well use the most liberal computer. After all, Aeris/Oceanic computers are used by a significant percentage of recreational divers, yet the incidence of DCS is not that great.

When using a more liberal computer the diver can back off or do additional safety stops. Lockouts are a pain. Some dive boats have a no mandatory deco stop policy. It just seems like the more conservative computers add inconvenience without an offsetting benefit, especially considering that strenuous physical activity is a major factor. Am I missing something?

(Does anyone know if there are any statistics on which brand of computer was in use by bent divers?)

 

[WreckWriter]

leadweight once bubbled...
(Does anyone know if there are any statistics on which brand of computer was in use by bent divers?)

I'm sure DAN has those statistics. There might be a problem getting them though since such things being known would surely cut into manufacturer's profits.

Tom

 

[Dr Deco]

Dear leadweight:

You really summed it up quite nicely

Dr Deco:doctor:

 

[Scuba]

Dive Tables or Deco Models give us the parameters or boundaries of the dive, with respect to time and place. I would include deco stops in this category. What we do within these boundaries, wether dictated by the model or not, can also have an impact on reducing or increasing the risk of DCS, such as rapid or slow ascent, overexertion or not underwater,and on surface between dives.

Are there any studies where at least some of the variables remain constant allowing a fair comparison of one system to another, wether they consider physiological differences in individuals or not?

This is one area in which computers with the ability to record key dive profile data could be very useful in studies to detect and analyze patterns.

 

[Dr Deco]

Dear Readers:

Testing

Over the years, numerous tests have been performed of such factors as exercise while on the bottom, mild exercise during depressurization, strenuous exercise during decompression, and general physical fitness.

Not all of these make their way into the literature generally available to recreational divers. One purpose of this FORUM is to disseminate some of that information along with commentary.

Below are some references which have be used over that past two years to answer questions on the site. While most readers will not care to look further into these, it is of interest to see that indeed work has been performed in laboratories around the world.

References

== Ascent Rate on Bubble Production

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.

Carturan D, Boussuges A, Molenat F, Burnet H, Fondarai J, Gardette B. Ascent rate and circulating venous bubbles in recreational diving. Int J Sports Med. 2000 Oct; 21(7): 459-62.

Reinertsen RE, Flook V, Koteng S, Brubakk AO. Effect of oxygen tension and rate of pressure reduction during decompression on central gas bubbles. J Appl Physiol. 1998 Jan; 84(1): 351-6.


== Physical Fitness and DCS Protection

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.

Wisloff U, Brubakk AO. Aerobic endurance training reduces bubble formation and increases survival in rats exposed to hyperbaric pressure. J Physiol. 2001 Dec 1; 537(Pt 2): 607-11.

Carturan D, Boussuges A, Burnet H, Fondarai J, Vanuxem P, Gardette B. Circulating venous bubbles in recreational diving: relationships with age, weight, maximal oxygen uptake and body fat percentage. Int J Sports Med. 1999 Aug; 20(6): 410-4.

Broome JR, Dutka AJ, McNamee GA. Exercise conditioning reduces the risk of neurologic decompression illness in swine. Undersea Hyperb Med. 1995 Mar; 22(1): 73-85.

Rattner BA, Gruenau SP, Altland PD. Cross-adaptive effects of cold, hypoxia, or physical training on decompression sickness in mice. J Appl Physiol. 1979 Aug; 47(2): 412-7.


== Exercise and Gas Washout

Jankowski LW, Nishi RY, Eaton DJ, Griffin AP. Exercise during decompression reduces the amount of venous gas emboli. Undersea Hyperb Med. 1997 Jun; 24(2): 59-65.

Loftin KC, Conkin J, Powell MR. Modeling the effects of exercise during 100% oxygen prebreathe on the risk of hypobaric decompression sickness. Aviat Space Environ Med. 1997 Mar; 68(3): 199-204.


== Exercise and DCS/Bubble Formation

Haske TL, Pilmanis AA. Decompression sickness latency as a function of altitude to 25,000 feet.
Aviat Space Environ Med. 2002 Nov; 73(11): 1059-62.

Dervay JP, Powell MR, Butler B, Fife CE. The effect of exercise and rest duration on the generation of venous gas bubbles at altitude. Aviat Space Environ Med. 2002 Jan; 73(1): 22-7.

Webb JT, Krause KM, Pilmanis AA, Fischer MD, Kannan N. The effect of exposure to 35,000 ft on incidence of altitude decompression sickness. Aviat Space Environ Med. 2001 Jun; 72(6): 509-12.

Conkin J, Powell MR. Lower body adynamia as a factor to reduce the risk of hypobaric decompression sickness. Aviat Space Environ Med. 2001 Mar; 72(3): 202-14.

Webb JT, Pilmanis AA, Kannan N, Olson RM. The effect of staged decompression while breathing 100% oxygen on altitude decompression sickness. Aviat Space Environ Med. 2000 Jul; 71(7): 692-8.

Pilmanis AA, Olson RM, Fischer MD, Wiegman JF, Webb JT. Exercise-induced altitude decompression sickness. Aviat Space Environ Med. 1999 Jan; 70(1): 22-9.

Jankowski LW, Nishi RY, Eaton DJ, Griffin AP. Exercise during decompression reduces the amount of venous gas emboli. Undersea Hyperb Med. 1997 Jun; 24(2): 59-65.

Webb JT, Fischer MD, Heaps CL, Pilmanis AA. Exercise-enhanced preoxygenation increases protection from decompression sickness. Aviat Space Environ Med. 1996 Jul; 67(7): 618-24.

Pollard GW, Marsh PL, Fife CE, Smith LR, Vann RD. Ascent rate, post-dive exercise, and decompression sickness in the rat. Undersea Hyperb Med. 1995 Dec; 22(4): 367-76.

Kumar KV. Decompression sickness and the role of exercise during decompression.
Aviat Space Environ Med. 1988 Nov; 59(11 Pt 1): 1080-2.

Krutz RW Jr, Dixon GA. The effects of exercise on bubble formation and bends susceptibility at 9,100 m (30,000 ft; 4.3 psia). Aviat Space Environ Med. 1987 Sep;58(9 Pt 2):A97-9.

Gooden BA, LeMessurier DH. Effect of exercise produced by partial immersion on the incidence of Dysbarism in rats after "free ascent" . Aerosp Med. 1970 Jun;41(6):597-601.

Dr Deco :doctor:

 

[wreckchick]

I'm bumping this thread because I find it facinating and think it's worth a read to anyone who missed it the first time like I did.

R

 

[RickM]

I am a police Underwater Search diver, and did my training with Strathclyde Police in Scotland.

One subject the instructors were constantly hammering home during our deep dive week was that we were not to go to the gym, or even have sex! They said that any strenuous exercise could result in a DCI.

All police diving is carried out under Health and Safety legislation, and as such is more than likely very conservative, however much of what these intructors said was backed up by scientific reports.

By the way, I have just bought a Sunnto Vyper. Have I bought the wrong one then from what you are all saying?

Happy Diving
:cop:

 

[Dr Deco]

Dear RickM:

Dive Computers

Your meter is fine and there has not been a correlation found between DCS and any particular brand (for recreational diving) of which I am aware. I am even a little surprised to find no real increase in DCS with the shift from tables to dive computers. This last statement is made because tables always add a little conservatism from the rounding off to deeper depth and longer time.

Physical Activity

This is difficult to add and never has been added to tables. This is in a large measure because the Haldane method does not consider the “tissues” to respond to changes in anything. Short tissues, in that model, are brain, intermediate are muscle, and long are, e.g., fat. In the Haldane view, you do not change fat tissue to muscle tissue. It is really possible that this model is incorrect, and I have discussed this many times on the board in the past.

Most researchers now consider these to be model “compartments” and represent a mixture of fat and aqueous tissue components, e.g., the Schreiner-Kelly model. Even this could not allow for a change in DCS incidence with activity level. These models simply do not work.

How Long Before Diving?

Physical activity before diving mostly comprises walking. Beyond that, whatever you do has little influence as far as physical activity is concerned. This was checked in a series of subjects who were weight lifters (study by Vann and Gerth). Walking predominates.

Walking also predominates following the dive when you are supersaturated. This is the most critical time for a diver. Climbing boat ladders with all of you gear, lugging gas bottles around on the boat, climbing ladders, etc are all a bad idea and will contribute to DCS risk if you have a big enough dose of nitrogen.:boom:

Dr Deco :doctor: