2 DCS hits and a PFO closure

[Pullnglide]

I have to say I am confused about PFOs. Here we see testimonials, andmy student is an absolute beleiver that closing her PFO has changed her life for the better in all aspects, not jsut diving.

Yet the literature for this is not at all convincing. If you call DAN about PFOs, they will be more than a little dismissive--no big deal for diving. (That was my student's experience--don't bother getting it fixed--it won't make any difference.

A lot of it is theory and there are active studies to increase or decrease the credibility of there being an advantage to having it closed. I was told by a prominent source and I'm assuming it is in accordance with research (maybe unpublished, I'm not sure) it reduces my risk by 5 times. I will continue to do the dives I've been doing for several years when I return in May. I'll admit I'm a bit skeptical but enough of a believer to go through the entire process of having the procedure done. All I can say is after 24 months, if I don't encounter any "unexplained" DCS then it'll make me even more of a believer.

 

[boulderjohn]

A lot of it is theory and there are active studies to increase or decrease the credibility of there being an advantage to having it closed. I was told by a prominent source and I'm assuming it is in accordance with research (maybe unpublished, I'm not sure) it reduces my risk by 5 times. I will continue to do the dives I've been doing for several years when I return in May. I'll admit I'm a bit skeptical but enough of a believer to go through the entire process of having the procedure done. All I can say is after 24 months, if I don't encounter any "unexplained" DCS then it'll make me even more of a believer.

Just as further explanation, when my student was considering the procedure, she consulted a lot of sources, including Doug Ebersole. She finally decided to do it, and she is very much a believer that it has helped her, not only in diving but in life in general. She no longer has dizzy spells or migraines, both of which she used to have frequently.

But she met with a lot of opposition when she was still considering it. In particular, the person with whom she spoke at DAN was quite dismissive, essentially telling her it would probably do her no good whatsoever.

 

[Duke Dive Medicine]

I think it's a vital issue to be aware of for all divers, and especially for those going into tech diving should consider mandatory PFO diagnostic screening:

I'm sure I'm going to open a can of worms here, but Kevin, this is contrary to best practice. Routine screening for PFO in divers is not recommended. It is not even a requirement for US military or commercial diver candidates, many of whom go well beyond what most people consider tech diving.

Best regards,
DDM

 

[Duke Dive Medicine]

If 25% of divers are potentially at risk to DCS from PFO, are there pre-condition checks that we as divers can ask for in the form of a fairly unobtrusive test from our GP to order up? 25% seems like high odds, and using an already "bent" condition as an indicator that we have this seems like we have already forayed past the casual diving point that many of us take with this sport.

That's not what this means. PFO is associated with severe neurological DCS, inner ear DCS and cutis marmorata, but the correlation is nowhere close to 1:1. About 25% of the population has a PFO. By extension about 25% of the diving population has one. The overall rate of occurrence of DCS, however, is between about 0.01% and 0.019% in recreational divers (reference: Decompression illness. - PubMed - NCBI).

If one narrows the field down to divers with PFO, the DCS rate varies depending on which study you look at. The Torti study linked below looked at 230 divers, 63 of whom had a PFO. They showed a five-fold risk increase in divers with PFO, but the mean number of dives in divers with PFO was significantly higher than those without (650 vs 400) and the divers with PFO were less likely to use compressed air as a breathing medium, both of which are confounding factors. They also showed an overall DCS occurrence rate of 2.5 incidents per 10,000 dives (0.025%) which is slightly higher than Vann et al found in the reference in the preceding paragraph.

Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale. - PubMed - NCBI

Liou et al looked at 75 divers: 39 with PFO, 36 without. They showed an occurrence rate of serious DCS of 1.8% in divers with PFO. However, the DCS rates in both populations were quite high (the overall DCS rate in all 75 divers was 5.4%), which makes it difficult to generalize their data to the rest of the recreational diving population. The authors themselves say that their study should be used primarily as hypothesis-generating.

Patent foramen ovale influences the presentation of decompression illness in SCUBA divers. - PubMed - NCBI

In a nutshell, the overall risk of DCS is extremely low. The risk for serious DCS seems to be higher in divers with PFO than without. At present, routine screening for PFO is not recommended for divers. In practice, if we see a diver with a history of multiple unexpected serious DCS hits, it raises our index of suspicion for PFO and we will probably recommend testing.

Best regards,
DDM

 

[Kevrumbo]

I'm sure I'm going to open a can of worms here, but Kevin, this is contrary to best practice. Routine screening for PFO in divers is not recommended. It is not even a requirement for US military or commercial diver candidates, many of whom go well beyond what most people consider tech diving.

Best regards,
DDM

Then I would seek a second opinion from a diving cardiologist, especially for something as simple & quick as a non-invasive contrast Trans Cranial Doppler Study. An ounce of prevention is always better than a pound of cure. . .

Commercial and Military Divers also have immediate access recompression chambers on site or standing-by during deep diving operations.

 

[Duke Dive Medicine]

Then I would seek a second opinion from a diving cardiologist, especially for something as simple & quick as a non-invasive contrast Trans Cranial Doppler Study. An ounce of prevention is always better than a pound of cure. . .

Commercial and Military Divers also have immediate access recompression chambers on site or standing-by during deep diving operations.

A diving cardiologist will tell you that transcranial doppler is not diagnostic for PFO.

Best regards,
DDM

 

[Kevrumbo]

A diving cardiologist will tell you that transcranial doppler is not diagnostic for PFO.

Best regards,
DDM

But it's a better initial diagnostic tool than nothing -or worse by confirmation post-autopsy. . .

 

[Duke Dive Medicine]

But it's a better initial diagnostic tool than nothing -or worse by confirmation post-autopsy. . .

No, Kevin, it isn't, and you are engaging in hyperbole. Transcranial doppler can detect shunted bubbles but it can't determine where the bubbles came from. Dreamdive and I are discussing intrapulmonary shunts in another thread.

<edit> TCD may be able to differentiate an intrapulmonary shunt by the timing of the bubbles.

Best regards,
DDM

 

[Kevrumbo]

No, Kevin, it isn't, and you are engaging in hyperbole. Transcranial doppler can detect shunted bubbles but it can't determine where the bubbles came from. Dreamdive and I are discussing intrapulmonary shunts in another thread.

Best regards,
DDM

Then you order more definitive imaging echocardiographic techniques, including transthoracic, transesophageal, and/or intracardiac echocardiography. Transesophageal echocardiography (TEE) with bubble tests is currently considered the gold standard for the diagnosis of right-to-left shunt due to PFO, as well as for morphological characterization of the inter-atrial septum.

That's not what this means. PFO is associated with severe neurological DCS, inner ear DCS and cutis marmorata, but the correlation is nowhere close to 1:1. About 25% of the population has a PFO. By extension about 25% of the diving population has one. The overall rate of occurrence of DCS, however, is between about 0.01% and 0.019% in recreational divers (reference: Decompression illness. - PubMed - NCBI).

If one narrows the field down to divers with PFO, the DCS rate varies depending on which study you look at. The Torti study linked below looked at 230 divers, 63 of whom had a PFO. They showed a five-fold risk increase in divers with PFO, but the mean number of dives in divers with PFO was significantly higher than those without (650 vs 400) and the divers with PFO were less likely to use compressed air as a breathing medium, both of which are confounding factors. They also showed an overall DCS occurrence rate of 2.5 incidents per 10,000 dives (0.025%) which is slightly higher than Vann et al found in the reference in the preceding paragraph.

Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale. - PubMed - NCBI

Liou et al looked at 75 divers: 39 with PFO, 36 without. They showed an occurrence rate of serious DCS of 1.8% in divers with PFO. However, the DCS rates in both populations were quite high (the overall DCS rate in all 75 divers was 5.4%), which makes it difficult to generalize their data to the rest of the recreational diving population. The authors themselves say that their study should be used primarily as hypothesis-generating.

Patent foramen ovale influences the presentation of decompression illness in SCUBA divers. - PubMed - NCBI

In a nutshell, the overall risk of DCS is extremely low. The risk for serious DCS seems to be higher in divers with PFO than without. At present, routine screening for PFO is not recommended for divers. In practice, if we see a diver with a history of multiple unexpected serious DCS hits, it raises our index of suspicion for PFO and we will probably recommend testing.

Best regards,
DDM

With regards to the OP @Pullnglide :

In making the diagnosis of the cause of illness in an individual case, calculations of probability have no meaning. The pertinent question is whether the disease is present or not. Whether it is rare or common does not change the odds in a single patient. ... If the diagnosis can be made on the basis of specific criteria, then these criteria are either fulfilled or not fulfilled. — A. McGehee Harvey, James Bordley II, Jeremiah Barondess

 

[Duke Dive Medicine]

Then you order more definitive imaging echocardiographic techniques, including transthoracic, transesophageal, and/or intracardiac echocardiography. Transesophageal echocardiography (TEE) with bubble tests is currently considered the gold standard for the diagnosis of right-to-left shunt due to PFO, as well as for morphological characterisation of the inter-atrial septum.

With regards to the OP:

In making the diagnosis of the cause of illness in an individual case, calculations of probability have no meaning. The pertinent question is whether the disease is present or not. Whether it is rare or common does not change the odds in a single patient. ... If the diagnosis can be made on the basis of specific criteria, then these criteria are either fulfilled or not fulfilled. — A. McGehee Harvey, James Bordley II, Jeremiah Barondess

Once again, routine screening of divers for PFO is not recommended, especially not with a highly invasive procedure like intracardiac echo.

Best regards,
DDM