Yo, doc, subscribe!
Wendell Grogan


Gozum_NT at OIT wrote:
> 
> 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]