2 DCS hits and a PFO closure

[Anny Art]

And do you know why?

 

[uncfnp]

We had a chamber operator who was like this. He got skin bends practically every time he dove.

Best regards,
DDM

Oy vey!

 

[Duke Dive Medicine]

Nope. Some people just bubble more than others, for reasons yet unknown.

Best regards,
DDM

 

[Kevrumbo]

Nope. Some people just bubble more than others, for reasons yet unknown.

Best regards,
DDM

Actually as reasonable speculation, an inflammatory/immune system response to micro inert gas bubbles could be a compounding factor to it all as well. . .

We're not discussing the diagnosis of illness, so the quote above has no bearing here. It's also only true for tests that are near-perfect; risk stratification (probabilistic calculations) can tremendously improve your diagnostic yield for tests that do not have excellent sensitivity AND specificity (i.e. most of them), and understanding of the epidemiology is necessary for correct interpretation.

You're advocating testing for a fairly poorly characterised risk factor for DCS in asymptomatic, healthy individuals. The question here is purely one of risk assessment; you have a 1:4 chance of having a PFO, and if you do, this may mean nothing (most small PFO likely entail no additional risk, although again, the evidence is slim), or may mean you have a 1:1000 chance (based on population evidence) of developing a condition. This changes if you place yourself in a higher risk category by actually having developed unexplained DCS. And even in this group, the value of finding a small PFO remains a little unclear, but that's just medical practice as we know it.

Ditto @mattia_v re: your quote. It's irrelevant in this situation because it's talking about the "cause of illness". PFO does not cause DCS. It is associated with DCS, and there is a large difference. It makes logical sense that venous gas emboli can be arterialized through it and cause symptoms, but for all we really know (and I've heard this debated by people with far better minds than mine), there's another as-yet-undiscovered factor that increases the risk of DCS in divers with PFO that has nothing to do with the PFO. This may change as researchers like Drs. Ebersole and Denoble accumulate data on divers who've had PFO closure.

Again, (merging your other post here) you are assuming that TCD is diagnostic for PFO and you've just had an interventional cardiologist/tech diver/rebreather diver who does PFO research tell you that it isn't. I don't speak for North Florida cave divers, but I don't imagine too many would give up tech diving if they found out through a TCD screening that they had a right-to-left shunt.

I will at this point tip my hat to you and wish you a happy and safe New Year, and let the future readers of this thread do what they will with the information contained here.

Best regards,
DDM

The point to be aware of is- there's a dilemma in considering the low statistical incidence of DCI in the general diver population versus the high morbid consequences of suffering a type II DCS/AGE in specialized technical decompression diving, with a PFO as a possible contributing -or "associated" condition. So you have a low probability event vs a severe health & welfare outcome if you unluckily suffered such an occurrence.

It may seem like a fallacy apples & oranges comparison, but it actually turns out to be a continuum of personal risk management: In other words, the chances are low of contracting DCI in regular NDL recreational diving, but on the other hand, would you do 3hr runtime, saw-tooth profile, decompression cave dives in hypothermic stress if you knew you had an underlying PFO condition to begin with?

. . .Again, (merging your other post here) you are assuming that TCD is diagnostic for PFO and you've just had an interventional cardiologist/tech diver/rebreather diver who does PFO research tell you that it isn't. . .

Some second opinions:

Transcranial doppler ultrasonography should it be the first choice for persistent foramen ovale screening?

Journal of the American College of Cardiology -Cardiovascular Imaging: Accuracy of TCD in the Diagnosis of Right to Left Shunt

A Comparison of Transthroracic Echocardiograpy and Transcranial Doppler With Contrast Agent for Detection of Patent Foramen Ovale With or Without the Valsalva Maneuver

Contrast Transcranial Doppler Ultrasound in the Detection of Right-to-Left Shunts | Stroke

Aetna Policy on Trans Cranial Doppler Ultrasonography

 

[Duke Dive Medicine]

Actually as reasonable speculation, an inflammatory/immune system response to micro inert gas bubbles could be a compounding factor to it all as well. . .



The point to be aware of is- there's a dilemma in considering the low statistical incidence of DCI in the general diver population versus the high morbid consequences of suffering a type II DCS/AGE in specialized technical decompression diving, with a PFO as a possible contributing -or "associated" condition. So you have a low probability event vs a severe health & welfare outcome if you unluckily suffered such an occurrence.

It may seem like a fallacy apples & oranges comparison, but it actually turns out to be a continuum of personal risk management: In other words, the chances are low of contracting DCI in regular NDL recreational diving, but on the other hand, would you do 3hr runtime, saw-tooth profile, decompression cave dives in hypothermic stress if you knew you had an underlying PFO condition to begin with?
Some second opinions:

Transcranial doppler ultrasonography should it be the first choice for persistent foramen ovale screening?

Journal of the American College of Cardiology -Cardiovascular Imaging: Accuracy of TCD in the Diagnosis of Right to Left Shunt

A Comparison of Transthroracic Echocardiograpy and Transcranial Doppler With Contrast Agent for Detection of Patent Foramen Ovale With or Without the Valsalva Maneuver

Contrast Transcranial Doppler Ultrasound in the Detection of Right-to-Left Shunts | Stroke

Aetna Policy on Trans Cranial Doppler Ultrasonography

Ok, I'll bite but I'll probably regret it.

These are not second opinions, they actually back up what both Dr. Ebersole and I have been saying. Each one refers to the use of TCD as a screening tool in individuals with conditions that raise the index of suspicion for right-to-left shunt. Most of them are careful to say that PFO is not the only right-to-left shunt that can exist in an human.

Nobody is saying that a diver can't go out and get himself or herself screened if he/she wants the peace of mind of knowing that he/she does not have a PFO or other right-to-left shunt. However, it is not recommended by the diving medical community and it won't be covered under insurance, for reasons that have previously been described in detail.

Best regards,
DDM

 

[Kevrumbo]

Ok, I'll bite but I'll probably regret it.

These are not second opinions, they actually back up what both Dr. Ebersole and I have been saying. Each one refers to the use of TCD as a screening tool in individuals with conditions that raise the index of suspicion for right-to-left shunt. Most of them are careful to say that PFO is not the only right-to-left shunt that can exist in an human.

Nobody is saying that a diver can't go out and get himself or herself screened if he/she wants the peace of mind of knowing that he/she does not have a PFO or other right-to-left shunt. However, it is not recommended by the diving medical community and it won't be covered under insurance, for reasons that have previously been described in detail.

Best regards,
DDM

Fair enough. . .

@Duke Dive Medicine, this is the actual article from 1998 that you, @debersole and @mattia_v base your opinion on:

http://archive.rubicon-foundation.o...e/123456789/5949/SPUMS_V28N3_9.pdf?sequence=1

From your own Dr. Richard Moon, Dept of Anesthesiology, Duke University Medical Center (1998):

". . .For recreational divers I believe there is no need for a screening examination to look for a Patent Foramen Ovale (PFO). The only relationship we have found between PFO and DCI is for serious neurological bends, a rare disorder, and largely attributable to risk factors which are associated with the dive itself, such as depth, bottom time and rate of ascent. On the other hand, for a person who plans to perform dives that have a high risk of venous gas embolism for long periods of time, for example saturation diving [and especially with regard to modern day long runtime open circuit or CCR decompression dives now becoming common to sport recreational advanced technical diving -italics mine @Kevrumbo ], then I would recommend a PFO Study. . ."

 

[Duke Dive Medicine]

Fair enough. . .

@Duke Dive Medicine, this is the actual article from 1998 that you, @debersole and @mattia_v base your opinion on:

http://archive.rubicon-foundation.o...e/123456789/5949/SPUMS_V28N3_9.pdf?sequence=1

From your own Dr. Richard Moon, Dept of Anesthesiology, Duke University Medical Center (1998):

". . .For recreational divers I believe there is no need for a screening examination to look for a Patent Foramen Ovale (PFO). The only relationship we have found between PFO and DCI is for serious neurological bends, a rare disorder, and largely attributable to risk factors which are associated with the dive itself, such as depth, bottom time and rate of ascent. On the other hand, for a person who plans to perform dives that have a high risk of venous gas embolism for long periods of time, for example saturation diving [and especially with regard to modern day long runtime open circuit or CCR decompression dives now becoming common to sport recreational advanced technical diving -italics mine @Kevrumbo ], then I would recommend a PFO Study. . ."

Hi Kevin,

That's an old reference and the position has evolved. A more recent position statement consistent with current recommendations is here:

Joint position statement on persistent foramen ovale (PFO) and diving. South Pacific Underwater Medicine Society (SPUMS) and the United Kingdom Spor... - PubMed - NCBI

An interesting paper from Dr. Germonpre:

Persistent (patent) foramen ovale (PFO): implications for safe diving. - PubMed - NCBI

Perhaps most relevant to the conversation are the joint UHMS/DAN PFO and fitness to dive workshop proceedings published in June of last year, linked below. Dr. Moon's current position is reflected on page 156 (I called him to double check), and Duke Dive Medicine's position follows his.

https://www.diversalertnetwork.org/...Proceedings/2015-pfo-workshop-proceedings.pdf

These are the current recommendations, and I am quite frankly the wrong person/entity to debate them with. I believe them myself because they were written by the leading physician/scientists in the field and they make sense to me. Feel free to contact the authors of the position statement and try to convince them to change their viewpoints.

Meanwhile, I'll say again, aside from financial constraints there's nothing to prevent divers from getting themselves screened if they still want to after reviewing these recommendations. Dr. Ebersole's elegant posts from above are good reading for those considering it. A negative test may be reassuring but should be interpreted with caution depending on the testing method and the diver's age (PFO can increase in size with age) and considering case reports, some outlined here, of positive PFO tests in individuals with previously negative test results. Positive results should be interpreted with even more caution and acted upon under the guidance of a physician trained and experienced in examination of divers.

Best regards,
DDM

 

[Kevrumbo]

DDM,

In my opinion, the latest position & recommendation above is more of an equivocation than an evolution of Dr. Moon's original 1998 statement. . . Again, finding out you have a pre-existing PFO through suffering a type II DCS episode is neither preferable nor ethical if you could have screened for it beforehand with at least a contrast TCD.

It's not about changing or debating viewpoints of leading hyperbaric scientists/physicians, but for us laypeople to insist and argue in making an informed decision regarding our own personal risk management threshold.

 

[Duke Dive Medicine]

It's not about changing or debating viewpoints of leading hyperbaric scientists/physicians, but for us laypeople to insist and argue in making an informed decision regarding our own personal risk management threshold.

Of course. Hopefully enough information has been provided here that readers can begin to formulate that informed decision.

Best regards,
DDM

 

[Johnoly]

...There has got to be some as yet undefined factor or factors that make some individuals more prone to bubble then others under identical dive conditions,....

After 100's of years, Dr. Neal Pollock has a very simple chart to explain Identical Dives but why different outcomes.

{Source: Alert Diver Magazine, Fall 2016 Pages 86 thru 89, Dr. Neal Pollock PH.D}
It's an excellent article and covers almost every question asked in this thread