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Peter, Thanks for the response and references. Much appreciated although I think you committed a scuba net transgression by providing references to your statements. Furthermore, those references even include journals that contain multisyllabic words. Shame on you! I must confess a fair amount of ignorance on the many subtleties of DCS, but not quite to the extent of not knowing what post-dive doppler studies involve and its relationship (or lack thereof) to PFO. ;-) My post was less than precise or over-simplified a potential relationship between PFO, DCS, and what a post-dive doppler study can or cannot contribute to the former two. >The fact that the Navy and others use a given test, should >NOT be considered an endorsement of the test's validity. With all due >respect to the Navy, not everything it does, even as part of medical >evals, is based on sound medical logic. No argument. > Would I dive if I knew I had a PFO? Depends on how much I had >invested in my gear ;-) Probably not, if you believe that gas/foam can >cross through a PFO and create an embolus to your brain. But suppose that >the gas/foam is created largely where it causes the damage. It actually >forms around tiny nuclei that have no problem passing through your lungs >and so are present (under the right/wrong circumstances) in *both* the >arterial and the venous circulation? Then it doesn't really matter if you >have a PFO, except for those very unusual cases where a bubble or foam can >actually pass from the arterial to the venous side. > I believe it to be *possible* for a PFO to be a contributory factor in the severity of a DCS case. Can't support this with hard data, it's a somewhat religious thing. ;-) >So let's examine the data to see if that does happen: > Of the 15 deaths reported by DAN for 1994 that were autopsied and >listed arterial gas embolus or air embolus as either as a major or >the significant cause of death, *none* listed PFO as a contributing or >incidental finding. I would have expected PFO to turn up as an incidental >finding in at least 5 of the deaths, just by coincidence. > Didn't mention if they looked for a PFO, or is that std procedure during an autopsy? > >As Francis and Gorman summarize in Bennett & Elliots' book, "However, >further studies will be necessary before the association between atrial >septal defects (PFO) and decompression illness can be considered causal." > Same can be said about many other factors relating to incidences of DCS (% body fat, conditioning, smoking, exact mechanisms of inert gas solubility in tissues, etc.). Some factors do have more accurate data based on studies, but I am not convinced that many specific conclusions have been drawn or recommendations enacted (other than decompression algorithms and sometimes a statistical relationship to DCS of those algorithms), i.e. the study on fit pigs getting bent less often than non-fit pigs has not led to any significant emphasis on appropriate conditioning through the recreational agencies. Some of the issues I feel are more self evident, i.e. I don't need to slam my hand in the door jam five times in a row to know that it will indeed hurt 100% of the time -- when I stopped smoking my chances of not getting DCS (and possibly one or two other simple illnesses) improved significantly regardless of regular conditioning. Yet I'm sure we all have anecdotal evidence that points to the contrary. I witnessed a jelly donut couple do a 15 minute honest 140' dive w/o any stops (including safety) and immediately preceeding and concluding the dive had a smoke. I mean they finished their smoke literally seconds before getting wet and immediately after getting out of their gear. What I'm getting at is that I *feel* that it would be a good thing to test myself for a PFO using one of the means available if I'm serious about developing a career based on the imagery of the marine environments regardless of knowing precisely the sensitivity of the test. (Lucky for me I still have a decent day job!) And regardless of the improvement in sensitivity I don't think I would have preferred the administration of the saline in my groin (femoral). >So after all this, if you've decided that whatever, you won't dive if you >have a PFO, doesn't it make sense to *know* if you actually have a PFO? >(Yes George, if you've read this far, I know you're saying "Right! >Right!") BUT, I don't think the current tests do that reliably. A bad test >may be worse than no test because it may give you a false sense of >security. Much better to do all those things you can to reduce your chance >of getting DCS. > I apologize in advance for the pontificating, but I can rarely stop it in time. Your prior argument is a very good point IMO. No, its not a perfect test and it would be wrong to base assumptions of risk soley on this single test. Two incidents close to home involving my 70+ year old pop, who has frankly led a very clean lifestyle including daily workouts, remind me of the fallibilities of medical science. (1) A week after a thorough physical at a well known facility in Greenbrier WV, he developed a nose bleed which had to be cataurized (sp). During this simple procedure a cancerous tumor bigger than a golf ball was discovered in his throat. (He has been cancer free 8 years now :-)). (2) A couple of years ago towards the end of his daily work outs he noticed a certain tightness in his chest. Several tests at a couple of different cardiologists revealed nothing and they actually told him to tone down his workouts. Finally one cardiologist simply increased the stress level during the test and presto the symptoms were recreated which led to the discovery of 2 partially blocked arteries out of 4 (most folks have only 3). A successul angioplasty has now allowed him to continue at the pace he was accustomed to. Bottom line for me Peter, is as tremendous as medical knowledge and procedures have developed over the last several decades, I realize its not all infallible even though you folks are often held to what can be some impossible standards. Variations between individuals I think is tremendous. I also know that at least I don't have a gaping PFO even if have methane release at +1atm or cursing at anyone underwater, and that to me along with a 20min colorful SVHS tape of my beating heart was worth $680. After all, I might have spent that money on some fancy dive computer that would keep me in the water so long that the aforementioned couple would have had the time for two smokes. ;-) You have also forced me to finally order Bennett & Elliot's tome on diving physiology to complement my small but growing library on the subject. Long overdue, I know. Regards, John
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