DAN DCS Study And Stats

[BRW]

Folks,

Thought you might like some non-religious facts
about DAN PDE, stats, and FAD incidence:

This comes off the DAN CD "DCS Case Series". Plus
return email from Dick Vann at my office (can FWD).

Dick gave a talk at DEMA on same -- maybe some
of you caught it:

1) -- only 46 cases of DCS are recorded across 70,000+
dive profile histories in PDE files;

2) -- 28 cases collected in the US, and 8 in Europe, and
most occured in cold water (Scapa Flow);

3) -- only 1 case was related to FAD.

Interesting and roughly agrees with stats reported by NAUI
at the Reverse Profiles Wkshp (with Proceedings available
from DAN) from accident reports.

BTW, NAUI does NOT follow the 24 hr FAD rule, as somebody
proclaimed. New NAUI Tables have protocol, based on 18 hr
repet cycle time, and for air:

1) -- single no-deco dive, wait 12 hrs FAD;

2) -- second repet no-deco, dive wait 15 hrs FAD;

3) -- third repet no-deco dive, wait 18 hrs FAD.

These new Tables also REQUIRE a 1/2 depth deep stop
for 1 minute, and 2 minutes in the 15 fsw zone.

IMMERSED Magazine is coming out with an article about
these Tables, and what's behind them. Plus other goodies.

Regards,

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr

 

[flw]

BRW once bubbled...
Folks,

Thought you might like some non-religious facts
about DAN PDE, stats, and FAD incidence:

This comes off the DAN CD "DCS Case Series". Plus
return email from Dick Vann at my office (can FWD).

Dick gave a talk at DEMA on same -- maybe some
of you caught it:

1) -- only 46 cases of DCS are recorded across 70,000+
dive profile histories in PDE files;

2) -- 28 cases collected in the US, and 8 in Europe, and
most occured in cold water (Scapa Flow);


I've been thinking about this - why is there such a variation in reported numbers - last November I went to a lecture by one of the consultant anaesthetists ( John ?) who run Aberdeen hyperbaric unit, one of the figures he quoted for Scapa Flow was an incident rate involving recompression ( as opposed to an actual confirmed dcs) of 1:200 dives for recreational divers - which is a bit higher than the more often quoted numbers.
Scapa is unusual as the dive boats are organised and report their total dives, so the figures are reasonably accurate, and certainly the chamber is regularly used on Thursdays ( Sundays for uncontrolled ascents)
Does the cold have such a significant effect on dcs or are there other factors at play - although in summer it is much the same in temperature as California, and the Flow is not particularly deep

F

 

[Dr Deco]

Hello flw:

Cold and DCS :cold:

It has been disputed for decades as to the effect of cold temperatures on DCS. Most seem to believe that there is a negative effect if the water is not too cold. The argument goes like this. When a diver is in cold water and the extremities are cold, blood is shunted to the arms and legs to maintain body temperature.

To this is added the effect of increased movement made by the divers, since we are all aware that bodily movement generates heat. To generate this, oxygen is needed and the blood carries that – along with additional dissolved inert gas.

Additionally, some areas have currents in addition to cold water. This will increase diver movement underwater.

Very Cold Water :cold:

If the individual in the water is very cold, blood will be shunted away from the extremities in an attempt by the body’s homeostatic mechanisms to maintain core (and brain) temperature. This extreme cold probably does not occur under normal dive conditions for a recreational diver.

DCS Incidence

It is known from a few laboratory studies, and considerable field experience that DCS is influenced by water temperature. Naturally, if the divers are moving more in the water, this might influence the tissue micronuclei number.

Dr Deco :doctor:

 

[flw]

Hi Dr Deco,

I appreciate that cold will influence bubble formation, however dan are quoting 1:70,000 as opposed to 1:200 - a 350 fold increase - and some of their figures are covering cold water areas - assuming both are correct, why the huge discrepancy
Most of the incidents in Scapa are in summer when the water starts aroun 7-8deg at Easter and goes up to around 14 deg by the end, almost 100% are drysuits/snuggly undersuits and probably not feeling particularly cold.
There are a couple of boats doing deep gas dives nearby, but they seem to have less problems for some reason.
Is it more to do with divers attitutudes to reporting dcs incidents rather than an actual big difference - I'll admit that on the one occasion I got 'niggled', although a dan member at the time it was never reported anywhere, although I don't think that was particularly sensible in hindsight.
Fi

 

[Dr Deco]

I would have no idea as to why the actual statistics are so different.

Dr D

 

[flw]

Oh well, I've noticed the disparity before, just hoping someone would come up with some reason for it - 'spose I'd better get back to the drug profiles I'm failing to find very interesting...

 

[BRW]

Guys,

If data from cold Scapa was downloaded into PDE (US
or Europe), it's there. The higher incidence rate in Scapa
(as you mentionl), is obviously a special subset. Thus, incidence
rate drops in overall PDE if Scapa is a special case (and not
included).

The 70,000+ plus is ALL profiles. When I get back,
I will pulse Vann on Scapa stats. And 1/200, if true
as somebody mentioned, is a study in itself.

DCS incidence rates in rec diving from all quarters
(meter manufacturers, training agencies, accident reports,
insurance folks) converge on 1/10,000 as the high side,
probably nearer 1/50,000). FAD is further down in that
noise.

But Scapa stats (as above) deserve very special
consideration. And will. So does the bigger question
of hot and cold water diving. And are under review
here at LANL. And the USN.

Cold and hot water diving, especially switches hot-to-cold
and cold-to-hot, are known to induce minispikes in DCS
incidence rates for divers. The USN sees higher DCS
rates in SEALs operating in warm waters. Such is a concern
being studied operationally is all I can say.

Only limited other studies have been conducted.
I have a ref list and can send post.

The question of hot and cold switches directly impacts
micronuclei formation, bubble skin response, and material
properties that affect gas diffusion and and Boyle response
for growth and elimination. Dr D mentioned this, plus other
temperature impacts on gas transfer. These mechanisms
have been quantified and await some "data" for folding
and implementation into RGBM. The rudiments of these
mechanisms can be seen in Basic Deco And Apps.

When I get some time, maybe I can try to post macroscopic
details. That is, temperature effects. For tissue and blood,
temperature changes enter into inspired breathing mix,
skin exposure, plus coupled physiological reactions to
these changes. This is NOT an easy problem, and is just
as difficult as folding a full phase model like RGBM over profiles.

Here at C & C, we get really environmentally protected, and
have not noted any minispikes in DCS incidence. Of course,
we are not an average diving test group. We are looking
into the prob though.

More on this later.

Best to all, and heading out again.

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr