Hello All,

I'm not subscribed to your elists, so please forward this email as you 
please. I read George's forward.  I've sending the original post at the 
very bottom of this message, to improve the formatting.  Matthias commented 
that the ff comment appear more in-line, versus a 'DAN' position, I bring 
up this further comment extracted from this thread:

> > -- Unfortunately for those with PFO, a rise in pulmonary
> > -- arterial pressure,

While this is one mechanism for a bubble transit via a PFO without 
increased chest pressure, in many cases [ as human anatomy varies in 
strength, location and response] if significant acute pulmonary 
hypertension occured by bubbles embolizing the pulmonary artery, bubbles 
must be forming faster than its rate of clearance through the lungs, in 
such events even with chamber treatment, deaths from right heart, and 
circulatory failure is high.  AGE via a PFO would be the least of your 
problems if significant pulmonary hypertension developed via an offgassing 
event.  This is close to Chris Rouses' death described in the book, "The 
Last Dive."

Mikey's description of a TEE with bubble contrast is superbly researched 
and crafted.  I will add that about 0.5ml of air is mixed with 10-20ml of 
saline, shaken to view gross bubbles, and injected into the patient to see 
if these bubbles transit accross the PFO, hence to the arterial circulation 
and the brain.  If doing this test is problematic, you could opt for a new 
transcranial doppler to track bubbles within the cerebral circulation, in 
both tests no harm occurs from bubbles. Both test are superior to a TTE, 
with the TEE the gold standard.  Transcranial doppler is less invasive than 
TEE with similar results but its too new to tell. However, if you've got a 
positive transcranial or TTE result, why endure a TEE?  To the cost, the 
TEE requires a physician to perform the procedure, escalating the cost.  A 
TTE is ~$1000.

So how then can post-dive bubbles crossing a PFO be harmful?  There must be 
another factor besides the PFO for risk for AGE.  A very large quantity of 
bubbles? How large? If routinely individual tech divers stray far from 
surfacing M-value in very deep dives and dive profiles produce "more 
bubbles" without overt DCS than recreation divers, this maybe cause for 
concern.

However, as 'tech' information has been collected by DAN only since 1997, 
in the 2000 report info reveals DCS and AGE rates for tech dives no greater 
than recreational, but higher death during tech dives, all causes, most 
among the most experienced and instructor certification level.  If tech 
organizations recommending PFO screening have information DAN doesn't it 
would be good to share it, as to Do It Right, suggests use the Right 
information.

Repairing a PFO carrys 0.2-1% risk of death via a cardiac catetherization 
procedure.  NONFATAL AGE risk with an open PFO is roughly about 0.21% and 
if AGE is treated early and heals without residual symptoms, a recovered 
diver can dive again.  Thus, beyond cost/benefit, there is no risk/benefit 
to PFO screening unless one experiences neurologic symptoms first, and 
later find a PFO.

For those into statistics, a Bayesian analysis suggests that anyone pushing 
the envelope in decompression theory would opt to minimize any known risk 
factor, considering a very high a priori risk for injury.  Just as 
astronauts were superb physical specimens to deal with the unknowns of 
early space travel, so would pioneers in risky ventures, such as very deep 
dives.  The physical requirements for Earth orbit mission astronauts is not 
high these days, but those for Mars are.  This analogy maybe an optimal way 
for tech divers to approach the issue of PFO.

As apprentice tech diver myself, I put my life where my mouth is, as we all 
do in this sport.

My regards to George and Mikey [ I was Mr. Ear trouble that weekend on the 
Lowrance].  I regret I haven't the pleasure of meeting/diving with the 
others from the "Florida" group, but I hope to in the near future.  George 
showed me quite a great deal, and the tech community, equipment, dive 
conditions, and support logistics in George's neighborhood is an incredible 
phenomenon for nurturing superb technical diving skills.  Alas, all I can 
muster safely in Philadelphia is the Atlantic Ocean, or a 100 ft quarry.

Dive safe All!









At 04:25 PM 6/11/2001 +0200, Matthias Voss wrote:
>I think Mike's comment is much closer to the point than the DAN's
>insights.
>Matthias
>
>George Morris schrieb:
> >
> > Commentary from Marvin Gozum, DAN trained physician. Forwarded with
> > permission.
> >
> > >--
> > >--  >-- Yes, this is the mechanism that does it, and unfortunately
> > >--  >-- is what allows
> > >--  >-- for the dive industry's RJ Reynolds twist of the facts. Most
> > >--  >-- PFO's require
> > >--  >-- the bubbles to raise the pressure to open the flap, so many
> > >--  >-- people can do
> > >--  >-- hundreds or even thousands of dives without consequence, and
> > >--  >-- then end up in
> > >--  >-- a wheelchair . The morons at DAN call that an "unearned
> > >--  >-- hit". I call it
> > >--  >-- lying and denial. 30% of us have it. Do you feel lucky?
> > >-- Well do ya?
> > --
> > -- At 09:17 PM 6/7/2001 -0400, wrote:
> > --
> > -- >Sure, that's the point behind not exerting yourself for a
> > -- while after
> > -- >the in water part of your off gassing.  Until you stop bubbling,
> > -- >anything you do that causes a rise in chest cavity
> > -- pressure- bending and
> > -- >lifting, straining, etc- can open the PFO and shunt bubbles
> > -- into your
> > -- >brain.
> > --
> > -- Unfortunately for those with PFO, a rise in pulmonary
> > -- arterial pressure,
> > -- and retrograde rise in right atrial pressure secondary to
> > -- the pulmonary
> > -- embolization of nitrogen/helium bubbles at the alveolar-capillary
> > -- complex would also cause right-to-left shunting through the PFO - no
> > -- exertion required.
> > --
> > -- All the more reason to get tested if you're doing technical diving.




http://www.emedicine.com/ped/topic2494.htm


"
Comment in:
Undersea Hyperb Med. 1999 Spring;26(1):49-50

Risk of decompression sickness with patent foramen ovale.

Bove AA.

Cardiology Section, Temple University Medical School, Philadelphia, 
Pennsylvania, USA.

Several reports have described populations of divers with decompression 
sickness (DCS) who have a patent foramen ovale (PFO). The presence of a PFO 
is known to occur in about 30% of the normal population, hence 30% of 
divers are likely to have a PFO. Although observations have been made on 
the presence of a PFO in divers with and without DCS, the risk of 
developing DCS when a diver has a PFO has not been determined. In this 
study, Logistic Regression and Bayes' theorem were used to calculate the 
risk of DCS from data of three studies that reported on echocardiographic 
analysis of PFO in a diving population, some of whom developed DCS. Overall 
incidence of DCS was obtained from the sport diving population, from the 
U.S. Navy diving population, and from a commercial population. The analysis 
indicates that the presence of a PFO produces a 2.5 time increase in the 
odds ratio for developing serious (type II) DCS in all three types of 
divers. Since the incidence of type II DCS in these three populations 
averages 2.28/10,000 dives, the risk of developing DCS in the presence of a 
PFO remains small, and does not warrant routine screening by 
echocardiography of sport, military, or commercial divers.

""

That incidences of venous bubbling by doppler [ regardless of the Spencer 
Scale] occurs in a very large fraction of dives, the current Summer 2001 
issue of Immersed reports it exceeds 85% if one does >1 dive/day, and over 
67% of these are 'high grade' in size;  37% occurred in a single dive, as 
far as 90 minutes post-dive.

The above findings already reinforce that the relationship between having 
venous bubbles and DCS is poor, otherwise we'd all have been bent, 
paralyzed or stroked by now since bubbles occur nearly in all dives.

Further, despite the high incidence of venous bubbles in dives from either 
well executed deco dives or no-stop dives and the 30% incidence of PFOs in 
the population, the incidence of _all_ DCS in toto is still < .07% or 
7/10,000.  The status quo is not to ban diver with PFOs nor screen for PFOs 
in general yet the incidence of AGE among divers is not proportionate to 
the baseline population risk of PFO ~30%. Clearly some other factor is at 
work to make AGE occur in a setting of PFOs.

As Dr. Bove notes, there is a 2.5x increase in 'odds ratio' for DCS 2 with 
PFO, which we translate here loosely as 'risk'.

A Valsalva or coughing, after bubbles are intentionally injected into the 
venous system, is done routinely in a bubble contrast echocardiogram to 
view bubble transits in diagnosing PFO. Despite that, patient's don't 
stroke.  This test suggests large quanitities and size of the bubbles are 
vital to cause harm.

As for technical diving, anything increasing the decompression obligation 
increases the production of venous bubbles, and this means diving deep, 
and/or multiple dives per day.  Its is unknown if He with nitrox deco 
decreases the risk of venous bubbles versus air in deep dives, however its 
assumed logically that properly executed He, nitrox or 100% 02 dives 
significantly diminishes the nitrogen load, and logically allow these 
divers to dive deep and assume a risk akin to recreational divers for 
venous bubbling.

You can still have right-to-left shunting from within the lungs itself, 
either congenital OR acquired lung trauma [barotrauma, smoking damage, age 
related weaknesses.]  This allows bubbles to squeeze through the
lungs and removes its filtering effect, and there's no way to test for it 
to date.

Finally, assuming you do do the recommendation of determing your existence 
of a PFO before embarking on a technical dive.  What do you do if you find 
a PFO?  If divers have been diving with a PFO without incident, would you 
repair an asymptomatic PFO to lower a theoretical risk for AGE with diving 
or stop diving?  An echocardiogram is ~>$1000 and the cath will set you 
back $10,000 plus endure a 1.0->0.2% risk of death, a risk higher than the 
3 fold risk [~.21%] of _nonfatal_ AGE from PFO, assuming a baseline DCS 
risk of .07%.



Warm regards,


Marv


--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]