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?
> >--
> >--
> >-- http://www.emedicine.com/ped/topic2494.htm
> >--
> >--
> >-- In 1991, the PFO Issue was put on the map by a DAN physician, Fred
> >-- Bove.  The current standing recommendation is:
> >--
> >-- "
> >-- 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.
> >--
> >-- ""
> >--
> >-- We know:
> >--
> >-- That venous bubbling by doppler [ regardless of the Spencer
> >-- Scale] occurs
> >-- in a very large fraction of dives, the current Summer 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.
> >--
> >-- Despite the high incidence of venous bubbles in dives,
> >-- either well executed
> >-- deco or a no-stop, and the 30% incidence of PFOs in the
> >-- population, the
> >-- incidence of DCS in toto is still < .07% or 7/10,000 as
> >-- note, _the status
> >-- quo is NOT to screen for PFOs_ among divers in general.
> >-- Therefore, if PFO
> >-- is a risk factor in diving, the number of cases of emboli should be
> >-- proportionate to the proportion of divers similar to the baseline
> >-- population risk of PFO ~30%. This is not seen in reality.
> >--
> >-- As for technical diving, anything increasing the
> >-- decompression obligation
> >-- increases the production of venous bubbles, and this means
> >-- diving deep, and
> >-- multiple per day.  Its is unknown if He with nitrox deco
> >-- decreases the risk
> >-- of venous bubbles versus air, however its assumed logically
> >-- that He, nitrox
> >-- or 100% 02 significantly diminishes the nitrogen load, and
> >-- logically allow
> >-- these divers to dive deep and assume a risk akin to
> >-- recreational divers for
> >-- venous bubbling.
> >--
> >--  >-- >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.
> >--
> >--
> >-- While many mechanisms are possible, to cause pulmonary
> >-- artery hypertension
> >-- from bubbles alone suggests a massive plethora of bubbles.
> >-- By the time
> >-- this happens, the patient would probably be dead from
> >-- cardiac failure, less
> >-- likely from embolization from a bubble transit through a
> >-- PFO, induced by
> >-- the resistance the bubbles produce to the flow of blood in
> >-- general ... as
> >-- was described in the book, "Last Dive" for the death of Chris Rouse.
> >--
> >-- 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 suspected PFO. Despite that, patient's don't
> >-- stroke.  This test suggests the large quanitity and size of
> >-- the bubbles is
> >-- vital to cause harm.
> >--
> >-- You can still have 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.
> >--
> >-- Finally, to repeat, there hasn't been a correlation between
> >-- venous bubbling
> >-- and DCS.
> >--
> >-- Assuming you do do the WKPP/DIR 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 0.5% risk of death, a risk
> >-- higher than the 3
> >-- fold likelihood [~.21%] of AGE from PFO from a baseline DCS
> >-- risk of .07%.
> >--
> >-- The standing recommendation for PFO repair is if it
> >-- demonstrates harm IN
> >-- INDIVIDUAL PATIENTS.  If a diver developed a DCS3 hit under
> >-- a NSL dive or
> >-- proper dive with a deco procedure, was treated in the
> >-- chamber and recovered
> >-- to dive again, a PFO can be screened for and may then be
> >-- considered for
> >-- repair should a patient wish to pursue diving.
> >--
> -- -----Original Message-----
> -- From: Trey [mailto:trey@ne*.co*]
> -- Sent: Friday, June 08, 2001 5:51 AM
> -- To: Rodriguez; Wendell Grogan
> -- Cc: Bruce Sherman; Quest@Gu*. Com; Techdiver List
> -- Subject: RE: Not opening PFO's, waqs RE: Repairing PFO's
> --
> --
> --
> -- 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?
> --
> -- -----Original Message-----
> -- From: Rodriguez [mailto:mikey@ma*.co*]
> -- Sent: Friday, June 08, 2001 1:09 AM
> -- To: Wendell Grogan
> -- Cc: Trey; Bruce Sherman; Quest@Gu*. Com; Techdiver List
> -- Subject: Re: Not opening PFO's, waqs RE: Repairing PFO's
> --
> --
> -- At 09:17 PM 6/7/2001 -0400, Wendell Grogan 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.
> --
> -- -Mike Rodriguez
> -- <mikey@mi*.ne*>
> -- http://www.mikey.net/scuba
> -- Pn(x) = (1/(2^n)n!)[d/dx]^n(x^2 - 1)^n
> --
> 
> --
> Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
> Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
--
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]