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Reima -
Interesting that you should raise the subject of dive-computer-related DCI
in this group. Earlier this spring, I posted a message to rec.scuba about
apparent cases of DCI that I had contracted from repetitive diving that
were within the limits of a computer. I received a series of informative
replies from various people, including Bill Mayne and Dr. Guy Dear--the
assistant medical director for DAN. The general consensus seemed to be that
basing multi-day dive profiles on computers could be hazardous to one's health.
At the risk of boring other more knowledgeable divers, I'm tacking my summary
of their replies onto the end of this note. The summary also contains material
on DCI that's not directly relevant to the original request, but interesting.
People who have already seen this message should simply ignore the balance.
Thanks for being patient with my use of bandwidth.
-- Phil
P.S.: Disclaimer: I have done no technical diving whatsoever, and am not
qualified to do anything other than to report my experiences, or other's
people's good advice.
------------------------------------------------------------------------
------------------------------------------------------------------------
This is a longish summary of the key comments in the notes that I received
in response to my queries on DCI, in chronological order.
******************************************************************************
*** ***
*** Comments by the Assistant Medical Director of Dan, Dr. Guy Dear ***
*** [MB FRCA (NOAA trained)] who responded last, appear after helpful ***
*** comments by the three others who responded. ***
*** ***
******************************************************************************
Dr. Dear originally meant to post directly to the net, but the postings
miscarried, and ended up in my e-mailbox. I have edited (rearranged) the
contents of his two notes to me to make them flow better, but I have not,
I believe, changed the substance of his remarks. By the way, let me publicly
thank Dr. Dear for taking time to compose a gracious and considered reply
to to my earlier, unhappy posting.
------
from Knut Hunstad (Norway):
[Knut, in an earlier posting, observed that Norwegian training agencies
recommended limiting one's diving to 2 dives per day. I then responded
that I hadn't heard this before.]
In response to a comment that my certification courses predated the
era of heavy repetitive diving, and warnings about making >2 dives/day:
"I have been diving since 1981 and didn't learn this myself until 3 years
ago.... Our tables actually go even further than mentioned before, as
they state that after several (3-4) days of diving 2 times a day you
should take one day off (no diving at all below 9')! ... A typical dive
here includes a lot more strain than in warmer places, cold weather
(and water), more wind, more gear etc. I don't know if this affects the
dive tables in any way, it just came to my mind... "
Knut said the information on repetitive was mentioned in a somewhat
obscure place in the Norwegian book of dive tables.
<Some good advice from Knut about risks inherent in stretching the
tables omitted.>
------
On the subject of the risks of diving with a PFO
(i.e.: a hole between the two large chambers of the heart, a condition
that I have):
"My personal literature reviews on the subject, as well as having
witnessed the flow of microemboli across the atrial septum in a clinical
setting, leads me to believe that diving should be discouraged in
patients with PFO. There are several articles on the subject in a
recent set of abstracts from an Undersea and Hyperbaric Medicine
symposium."
------
from <individual who did not give permission to quote>, (USA):
I mentioned that I let the Oceanic DataMax get into the Yellow on
one of my dives ....
"I dive with a DataMax, and I won't surface until I get the meter at
LEAST two pixels into the green. In general, I treat it as if there
were at LEAST two or three more pixels lit than actually are .... BTW,
the ability to define your own safety margins in terms of saturation
rather than time is one of the DataMax's advantages."
On a remark about using nitrox for an extra margin of safety:
"Phil Sammet, the captain of the Cypress Sea out of Monterey, dives
with a pony bottle of Nitrox and switches to it at about 50 feet on
ascent. He still dives a conservative air table. I'm considering
the same thing."
>>>
>>> Also received stronger comments in support of nitrox and oxygen
>>> from a person with a great dea of expertise in technical diving.
>>>
On PFO: ".... there is certainly a body of evidence that those with it
are more susceptible to DCS. There was a great description of how it
could affect DCS in either Alert Diver or Rodale's in the last couple of
months. Based on that description, I suspect a small PFO could be even
worse than a large one (PERSONAL OPINION) because of the higher fluid
velocities through the hole."
>> This person could not find the article in question in Rodale's
>> after rechecking.
>Finally, from Dr. Guy Dear, DAN:
"To briefly answer your points and also to indicate that we do monitor
Rec.Scuba please peruse!!"
*. About DAN phone protocols:
DAN always asks for names because this allows them to call back in
case of a disconnect. DAN gets calls from all over the world with
differing phone systems, including ship to shore radios, etc.
DAN asks for the profiles and the numbers of dives because these
are "important clues as to the amount of nitrogen load as well as
the probability of DCI in your case."
DAN does not make formal diagnoses by phone. Furthermore, DAN will
give advice about profiles over the phone. "The EMTs that in general
answer the phone to more than 12000 people per year cannot give much
information about symptomatology. This is not to say that anyone
who does have current specific symptoms will be ignored for those are
just the divers we want to refer on to an MD."
In short:
"We can and do refer interested divers to knowledgeable physicians."
*. Reasons for DAN's concerns about discussing profiles and making
diagnoses by phone:
"No one yet has hard data on the risks of DCI for sport divers....
Really, DAN is not able to answer in great detail specific questions
about the likelihood of DCI in certain situations."
"No diving physician or EMT can make a formal diagnosis over the
phone.... It is important not to attempt self diagnosis, though
an index of suspicion should be raised. Many divers are not aware
of subtle neurological deficits which may be found on careful
examination."
*. General comments on diving-related risks, and particularly on PFO:
"Nearly 50% or more of divers bubble after diving if carefully
examined (Dunfrd et al UBR 1991 18(s) p62) and the % increases
with deeper dives. These are mostly asymptomatic of course.
We don't know of the long term sequel to all these bubbles but
it seems from examination of various organs notably spinal cord
and long bones that there may be unnoticed continual damage which
is a worrying thought."
"Inference[s] [regarding the safety of deep, repetitive diving]
can be made from examination of data from the development of the
PADI Wheel, from the UK and Norway. DAN's own data recorded in
the annual Report on Diving Accidents & Fatalities (Similar data
available from BSAC HQ) in dicates that repetitive dives (>2 day)
deeper than 80 ft were associated with an increased risk."
"PFO (Patent Foramen Ovale interATRIAL hole in the heart) though
apparently asymptomatic increased the risk by 4-5 times."
"As regards tables or computers, all artificial aids have to assume
that all divers are the same. [This is] not likely!! There can
then be an implied acceptance of risk of DCI. New tables are being
created using the Maximum Likelihood techniques used by Vann and
Weathersby etc. To do this data is needed on [safe] as well as
Bending dives.... At present noone knows the incidence of DCI as
no one knows how many divers make how many dives a year and
especially how many cases of MILD DCI never get reported!!!"
*. Comments about DCI and mild DCI:
"Any of the general texts such as Diving Medicine (Bove), Physiology
& Medicine of Diving (Bennett & Elliott), Diving & Subaquatic
Medicine (Edmonds) give good info on the signs and symptoms of DCI."
"Mild DCI may resolve and like the posted message about the diver
[i.e., yours truly] with skin bends (sounded like Cutis Marmorata)
often will go away by themselves. This does not mean that the
problem has resolved however. Whatever the lesion in the body that
gives the symptoms of DCI may have just recovered enough to allow
for resolution of the symptoms but is just waiting for the next last
straw to cause a catastrophe. Repetitive dives in this situation
are not a good idea. Subtle symptoms may develop into more serious
ones later and mild symptoms should NOT be ignored. The files at
DAN are full of divers who had minor problems initially. Research
is now going on to try to link onset with outcome."
"I think that anyone who had what sounded like an episode of DCI (of
whatever nature) should talk to a knowledgeable MD before diving
again. An examiination at this stage [when this was written, two
weeks after the incident reported on USENET] would be unlikely
to reveal anything unless you have residual neurological symptoms.
Detailed studies of the brain and spinal cord may show damage but
this is a little controversial. Ask about CT, MRI and SPECT imaging
if you want to know more."
"I doubt that anyone would give recommended profiles bearing in mind
liability problems. However I recommend to any divers that have
suffered a previous DCI that they dive much more conservatively
in future. Conservative I believe means shallow, short and few!!!"
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