DCS in Cozumel
- Thread starter Butch Fries
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mediumone
Contributor
mcohen 1021 please feel free to weigh in again with your wise counsel.
mcohen 1021 please feel free to weigh in again with your wise counsel.
Doc said not to get your advise from the internet, so I stopped reading after that, was there some good advise I missed?
Unfortunately Dave those long dives that you are known for and your policy that everyone ascends as a group is exactly what the op does not need. And if he is the experienced diver his years diving and profile suggests, the beginner boat is probably not what he is looking for. A better choice would be a boat that will let him dive his computer.
tarponchik
Contributor
Looks like something is wrong with math here
Id say, the expected percentage would be 62.5%:100*{0.25/[0.25+(1-0.25)*0.2]} = 62.5%
Assuming, of course, that the percentage of PFO carriers among the divers is the same 25%.
Sorry, but those two pieces of data are apples and oranges, @tarponchik.
Five-fold increase in certain types of DCS if you have PFO, from 2/10,000 to 10/10,000.
Not all PFO get DCS, and only a small part of DCS is from R to L shunt, as opposed to local tissue bubbling.
What was left unsaid here, but is in the literature, is the distribution of PFO among DCS patients.
Since PFO'ers are 25% of the general population, if having a PFO made no difference you'd expect that of any group of DCS patients, 25% would have a PFO. In fact, as I recollect, in the 30-40% range of DCS patients have PFO's. But counting certain causes for DCS, PFO is very significant. Where? Where arterial bubbles traveling in the circulation cause impairment of critical circulation.
The big unknown here is where the threshold is for DCS when you bubble across to the left side of the circulation. Some bubbles get through in healthy patients without PFO via capillary channels in the lungs that bypass the alveoli. But not all those divers who have some transfer to the arterial side get bent. We just don't yet know how much and of what size bubble is required. And in some cases, even one tiny bubble to a critical area of the nervous system can have huge negative results.
All we currently measure is subjective outcome, objective venous bubbles by Doppler, and some inflammatory markers. We just don't know enough yet, and don't have sensitive enough methods of evaluating subclinical DCS in divers.
So we advise what tilts the odds: decrease your bubble mass, decrease the size of those bubbles, and when appropriate, close a PFO. But in which patients? And for what profiles? And with what gases?
Too complex an issue with too small a population to easily acquire statistically significant results. Just look at the history of how our dive tables were devised.
I didn't directly answer your numbers, but you see the problem.
Five-fold increase in certain types of DCS if you have PFO, from 2/10,000 to 10/10,000.
Not all PFO get DCS, and only a small part of DCS is from R to L shunt, as opposed to local tissue bubbling.
What was left unsaid here, but is in the literature, is the distribution of PFO among DCS patients.
Since PFO'ers are 25% of the general population, if having a PFO made no difference you'd expect that of any group of DCS patients, 25% would have a PFO. In fact, as I recollect, in the 30-40% range of DCS patients have PFO's. But counting certain causes for DCS, PFO is very significant. Where? Where arterial bubbles traveling in the circulation cause impairment of critical circulation.
The big unknown here is where the threshold is for DCS when you bubble across to the left side of the circulation. Some bubbles get through in healthy patients without PFO via capillary channels in the lungs that bypass the alveoli. But not all those divers who have some transfer to the arterial side get bent. We just don't yet know how much and of what size bubble is required. And in some cases, even one tiny bubble to a critical area of the nervous system can have huge negative results.
All we currently measure is subjective outcome, objective venous bubbles by Doppler, and some inflammatory markers. We just don't know enough yet, and don't have sensitive enough methods of evaluating subclinical DCS in divers.
So we advise what tilts the odds: decrease your bubble mass, decrease the size of those bubbles, and when appropriate, close a PFO. But in which patients? And for what profiles? And with what gases?
Too complex an issue with too small a population to easily acquire statistically significant results. Just look at the history of how our dive tables were devised.
I didn't directly answer your numbers, but you see the problem.
tarponchik
Contributor
But isn't it one of the two? Either the percentage of PFO carriers in DCS cases is statistically higher than in scuba divers in general, and then having PFO matters; or the difference is not statistically significant, and then having PFO does not matter.
Yes, it is the first. The percentage of PFO positive in DCS is statistically higher than in scuba divers in general, and having a PFO matters.
For example, (and I quote from the Consensus Workshop referenced above),
"The calculation of DCS risk in a diver with a PFO is done using the Baye's formula that incorporates the probability of a PFO in the general population.
In Bove, Undersea and Hyperbaric Medicine 25:175: 1998, the probability of DCS with PFO was 4.7 per 10,000 dives, while for those divers without PFO, the probability was only 1.9 per 10,000 dives, a 2.52-fold increase in risk, and statistically significant with p<0.001"
But since the absolute incidence is so low, this also shows that just having a PFO does not make DCS likely. It makes it 2.5-10x more probable but still is a one in a thousand thing. Thus, we need other markers to help divers decide whether or not to have a PFO closed.
An echo study of a PFO can grade the degree of shunting that occurs, for example. Torti, Billinger and Schwerzmann published "Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale", in European Heart Journal, 2004; 25:1014-1020. In that study, they confirmed the expected incidence of PFO in the general diving population (28%). They found a self-reported DCS incidence of 1.5 /10,000 dives in those with no PFO, but 9/10,000 in divers with a large PFO.
I commented above about subclinical DCI. Again drawing from the Consensus Workshop findings, Billinger studied a group of 104 divers with 18,000 dives in five years! When we think about scary DCS, it is neurologic incidents (stroke and paralysis). In this group, there were NO neuro events per 10,000 dives in the group with no PFO. There were 0.5 events/10,000 dives in a group with a PFO that had been closed. But there were 36 neuro events per 10,000 dives among the group of divers with an open PFO.
There were brain lesions found on MRI in many divers, of unknown significance. But the incidence of those lesions averaged one in the no-PFO group, and 3.3 in the PFO group. Lesions on the MRI were 104/10,000 dives with a PFO
Lesions on the MRI were 16/10,000 with a closed PFO
Lesions on the MRI were 6/10,000 dives with no PFO.
The last two groups were not statistically different, but PFO versus no or closed PFO certainly was.
But it's still a rare event, so not everyone with a PFO (25% of us) needs an echo study or closure of an asymptomatic PFO.
Our OP may be different. Two hits of unknown significance. Maybe he needs to consider being formally evaluated. But two hits in 25 years of diving is still pretty low, compared with some in our technical diving community. He needs to decide on his own, but probably doesn't need an air ambulance standing by his private boat.
For me, the TYPE of DCS that occurs with this lesion is what makes it scary. Although (for unknown reasons) skin bends is a lot more common in this group, so is neurologic catastrophe.
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So, why do we read and post on Scubaboard even though sometimes we get assailed, humiliated, downright bludgeoned? Because of posts like rsingler's, Christi's and others that really teach us something. Having a pal get multiple skins bends and choosing to have the PFO surgery resulting in no more skin bends is not dispositive nor does that make me an expert. So, I read Scubaboard to hear from those who know and experience more. As I age, I've changed my diving profile and that makes me comfortable. What the OP choses to do, hopefully, will be based on his/her(?) comfort level and using the best scientific information available. Thanks to those of you who hung with this sometimes maddening thread to give me good information to dive by. 8 days to a week in Cabo Pulmo, 4 dives a day and I will be pretty shallow for the afternoon dives. Makes me happy.
Rob
Rob
Dogbowl
Contributor
I really hope the OP (@Butch Fries) reads all this info. If I had this issue, I would really appreciate all this info to consider.
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