EAN, Air and a propensity towards bubble formation

[Duke Dive Medicine]

Perhaps you folks have heard? There's no such thing as "No decompression Limits". There are NDL recommendations, by and for specific groups and allowing for specific numbers of hits even within those limits, but no absolute limits. Anyone have a copy of the old Navy tables? 60/60, NDL, right? Except, it is 60/50 now and has been for some years. The research is ongoing and the "acceptable" percentage of hits is no longer acceptable outside of combat.

There's also no reason that the OP should "suspect" a PFO for more than 30 days. That's how long it takes to find a cardiologist and do the tests that will say if he does or doesn't have a PFO. If he does...things have to be considered or changed. If he doesn't?

He still has to simply accept that, assuming his math for his dives has been right, HE is more susceptible than "average" and HE needs to bump his safety factors up two steps, or else accept the fact that he WILL get hit if he keeps using NDLs that work for *other* people.

Really, there shouldn't be any mystery here. He just needs to make the choices.

No-stop limits are the currently accepted safe bottom time parameters for no-stop diving. The fact that they have changed over time does not mean that they can't be used as a reference point for adding a safety factor to dives. Most industries and recreational pursuits have safety parameters that evolve with time, increasing knowledge, and research.

Also, with his present condition and his changing diving practices, an argument could be made to forego the PFO test. He seems to be doing everything that we would advise divers with PFO to do anyway.

Best regards,
DDM

 

[Duke Dive Medicine]

This is my understanding. I believe he drew this conclusion based on the nature of my symptoms, which were skin and cognitive. We both poured over the profile details in my computer and couldn’t really find anything that would have confirmed that.

As for diving Nitrox on an air profile- after much tinkering, I've discovered that a P2 factor with 32% Nitrox basically gives me an air profile. I'd love to get my hands on some 34%+ but it's not always available.

I've been milking my safety stops. Fortunately, I seldom surface with under 1000 PSIs so have the luxury of putting them to good use.

That's interesting. AGE does not present with skin symptoms but DCI does. It sounds like you're on the right track. I would recommend you continue to dive very conservatively. If you have another episode of DCS, you'll need further followup with a cardiologist and a physician with training and experience in examining divers.

Best regards,
DDM

 

[BubbleBubble7]

No-stop limits are the currently accepted safe bottom time parameters for no-stop diving. The fact that they have changed over time does not mean that they can't be used as a reference point for adding a safety factor to dives. Most industries and recreational pursuits have safety parameters that evolve with time, increasing knowledge, and research.

Also, with his present condition and his changing diving practices, an argument could be made to forego the PFO test. He seems to be doing everything that we would advise divers with PFO to do anyway.

Best regards,
DDM

Your feedback exactly mirrors the feedback that I received from the doctor who treated my DCS and the two doctors I spoke to upon follow up (one I saw in person and one I talked to on the phone via DAN). All suspected I probably had a PFO (I also get migraine with aura which is, apparently, another potential indicator) but none felt strongly that my circumstances warranted further evaluation of that unless I had another "hit". The consensus across all three was that, if the more conservative approach prevented the problem, medical procedures (which carry their own set of risks) were probably uncalled for.

 

[doctormike]

That's interesting. AGE does not present with skin symptoms but DCI does. It sounds like you're on the right track. I would recommend you continue to dive very conservatively. If you have another episode of DCS, you'll need further followup with a cardiologist and a physician with training and experience in examining divers.

Best regards,
DDM

I defer to you on these matters, but isn't DCI a broad term that is divided into DCS and AGE?

Yes, I have heard that AGE in decompression science is traditionally used to refer to arterialized bubbles that arise from pulmonary barotrauma, but there are a number of ways that bubbles can enter the arterial circulation: Lung injury (gas flow from the alveoli to the blood downstream of the capillaries), PFO, atrial septal defect (unlikely unrepaired in a diver), pulmonary shunts (like an arteriovenous malformation where the blood bypasses the alveolar "filter"), or severe DCS where the bubbles actually form on the arterial side or where venous bubbles overwhelm the lung's ability to filter them out.

I agree with your recommendation (not that I have any real professional experience in this field). But as far as I can tell, it's not even clear that repairing a PFO always changes the DCI risk. In some cases, it may be a marker for other risk factors.

 

[Duke Dive Medicine]

Mike, DCI can also refer to venous bubbles that paradoxically cross an A/V shunt and cause symptoms. There is some literature out there that suggests that PFO closure decreases incidence of DCS in divers who previously suffered shunt-related symptoms.

Best regards,
DDM

 

[doctormike]

Mike, DCI can also refer to venous bubbles that paradoxically cross an A/V shunt and cause symptoms. There is some literature out there that suggests that PFO closure decreases incidence of DCS in divers who previously suffered shunt-related symptoms.

Best regards,
DDM

Yeah, I had looked into that thing about the closure at one point for a friend. I did find a few articles supporting it but I didn't really find a consensus. The person in my institution who does most of the PFOs felt that it was still up in the air about benefit, but I might personally go for it if i was in that position!

My point about DCI was that it is a broad term, including DCS and AGE, and therefore would also include arterialized bubbles that form on the venous side in classic DCS (i.e. DCS + shunt -> AGE).

But thanks, as always, for your expertise and explanations! I just dig out earwax for a living, but I find this stuff fascinating...

 

[Duke Dive Medicine]

Mike, this is the article I was talking about:

Patent foramen ovale closure in recreational divers: effect on decompression illness and ischaemic brain lesions during long-term follow-up. - PubMed - NCBI

Whether this generalizes to all divers who undergo PFO closure is another question, and your point about causal relationship is certainly well taken.

For clarity, we typically do not advise closure for divers with PFO because historically the risk of closure has outweighed the risk of occurrence of DCS with PFO. More recent literature suggests that the scale may have tipped, so to speak, so that may change with time. We still advise conservative diving instead of closure but will refer a diver to an interventional cardiologist if he or she wants to consider it.

Best regards,
DDM

 

[doctormike]

Yup, interesting! From a physiological point of view, I can absolutely see how closing a shunt of any type would reduce the risk of arterial side injury (like strokes, TIA, etc..). We all bubble to some degree on ascent, the lungs clear the bubbles if we are doing it right. But if you have a shunt, you could get an AGE even without excessive bubbling (i.e. without DCS).

On the other hand, the question of PFO closure in divers usually comes up for a person who gets a couple of DCS hits, maybe "undeserved" (I hate that word!), and so they get checked for a PFO. 25% of humans have one, so there is a good chance that they will find one. And then the question is raised about closure. But in that case (DCS without AGE), I can't understand how closing a PFO would have any effect on the chance of future DCS (not DCI), which is - as I understand - the clinical manifestation of excessive venous side bubbling.

 

[Duke Dive Medicine]

Mike, that's a good point for clarification. Testing should only be considered for divers with unexplained (we use that instead of undeserved ) sudden-onset severe neurological DCS, inner ear DCS, and/or cutis marmorata ("type II" skin rash) since those are the symptoms and presentation that are associated with PFO. Testing a diver with multiple type I hits (hive-like skin rash, itching skin, joint pain, lymphatic DCS/swelling) would be inappropriate, and presence of PFO in cases like that would probably be a red herring.

Best regards,
DDM

 

[doctormike]

Mike, that's a good point for clarification. Testing should only be considered for divers with unexplained (we use that instead of undeserved ) sudden-onset severe neurological DCS, inner ear DCS, and/or cutis marmorata ("type II" skin rash) since those are the symptoms and presentation that are associated with PFO. Testing a diver with multiple type I hits (hive-like skin rash, itching skin, joint pain, lymphatic DCS/swelling) would be inappropriate, and presence of PFO in cases like that would be a red herring.

Best regards,
DDM

Right! Unless your PFO doc needs to get his numbers up...