Diving with gradient factors for a new recreational diver

[ginti]

I suppose I'm asking if PFOs can spontaneously happen, or are they congenital -- with you since birth?

Atrial septal defect - Wikipedia

en.wikipedia.org

Everyone has it at birth, but then it should close completely, the septa should fuse:

Foramen ovale (heart) - Wikipedia

en.wikipedia.org

But it doesn't always happen.

Just be aware that having a PFO itself is not necessarily a problem for diving. It depends on the degree of severity of the opening. For example, I have a PFO, but doctors say that I can go deep (hypoxic trimix depths) without any needs to close it.

 

[boulderjohn]

Question about PFOs: are there many cases of "late onset" PFOs in divers? Meaning that a diver who was doing decompression diving for some time before there was an 'incident' where the PFO was discovered.

PFOs are congenital. Everyone has one in utero, and they are supposed to heal after birth. They occur in about 25% of the population, and no one knows they have one until tested for it. The test is expensive and often not covered by insurance, so even divers who suspect they might have one often go without the test and just dive conservatively.

We can therefore assume that 25% of divers have PFOs, and since the incidence of DCS in all divers is so very small, we can assume that 99% of the people with PFOs dive without DCS. That means that almost all divers who have been discovered to have PFOs will have only discovered it after the fact. It is also why there is a serious debate as to whether a diver who is discovered to have a PFO should have the surgery to close it, since that surgery is not without risk.

In my small world, I know two divers who have gotten bent, learned they had PFOs, and had them closed. One was quite recent, so I have no follow-up. In the other case, the diver has continued to dive without incident, and she is also living without the chronic migraine headaches that plagued her all her life.

 

[doctormike]

Yup, was about to write what @boulderjohn said. The only way I can think of for someone to have an acquired PFO would be trauma, in which case DCS would be the least of your concerns!

Think of a PFO as one risk factor out of many. There are obviously (statistically) thousands of technical divers doing big dives who have PFOs and aren't getting bent. Just like there are obese, deconditioned smokers who don't get bent. A lot of things can contribute to every roll of the dice. Inert gas loading (mix, depth and time), sawtooth profiles, rapid ascents, environmental factors, genetic factors, etc...

I have a buddy who recently got a PFO closed after an inner ear hit, and I do have a good referral for this if anyone is interested and if they are in the NYC area...

 

[HomeBarista]

Maybe I'm biased, but it seems that a remarkable number of "undeserved hits" have been associated with PFOs detected after the fact.

I didn't realize the incidence of PFO in the general population was 25%. Seems like a major factor to control for in DCS research, but borderline impossible to get reliable data on the general population of recreational divers.

At the risk of skewing hypochondriacal, I'll look into whether I could convince my doctor to get me tested (would appreciate advise on how to do the convincing from fellow US residents!). I'm curious if the navy and professional organizations tests their tech divers in advance of getting them in the field.

 

[doctormike]

I didn't realize the incidence of PFO in the general population was 25%. Seems like a major factor to control for in DCS research, but borderline impossible to get reliable data on the general population of recreational divers.

At the risk of skewing hypochondriacal, I'll look into whether I could convince my doctor to get me tested (would appreciate advise on how to do the convincing from fellow US residents!). I'm curious if the navy and professional organizations tests their tech divers in advance of getting them in the field.

I wouldn't bother. You might not want a TEE. I know a lot of people doing very big technical dives, and I never heard of one getting tested before a hit.

Seriously, I think that you are WAY overthinking this. Learn to dive safely, don't push your N2 loading, use conservative gradient factors and/or stay away from NDL=0, ascend slowly, and you will be fine.

I have been bent and I have taken a chamber ride. I'm scared of a lot of things in diving, but DCS isn't at the top of the list...

 

[Wibble]

Talking of chamber rides... It really is an extremely educational experience to take a chamber ride. It's amazing how much the narcosis affects you and how "off your face" you are; the equivalent of several pints of decent beer.

Anyway, we've definitely been discussing some quite advanced stuff here. None of this should worry you as you start your diving career and work through the grades as it were. Many people are exceedingly happy with shallow warm water dives; others need deep cold wreck dives.

Whichever type you are, you need to start at the very beginning, it's a very good place to start... Sort out those core skills, get comfortable in the water, do some diving, talk crap with other divers on the dive boats, find some shiny stuff and just prepare to be amazed.

A great place to start is a dive club. Really important in the early stages; less so once you get some experience.

 

[scubadada]

Who were the study set?...

The subjects in the validation of the DSAT/PADI recreational dive planner are reasonably well described. They were recruited from the recreational dive community in the Pacific NW in 1987 and 1988.

In the phase IIb study of 4 dives per day for 6 days, there were 12 men and 8 women. In men, the mean age was 39 (21-61), mean weight 87 kg (59-111), and mean body fat 20.5% (15.5-36). In women, the mean age was 36 (24-45), mean weight 62 kg (50-75), and mean body fat 26.7% (21.6-35.3).

Of course, there is no mention of patent foramen ovale in this group. The association between PFO and stroke was only becoming more widely appreciated around this time.

 

[ginti]

I didn't realize the incidence of PFO in the general population was 25%. Seems like a major factor to control for in DCS research, but borderline impossible to get reliable data on the general population of recreational divers.

At the risk of skewing hypochondriacal, I'll look into whether I could convince my doctor to get me tested (would appreciate advise on how to do the convincing from fellow US residents!). I'm curious if the navy and professional organizations tests their tech divers in advance of getting them in the field.

I got tested for the PFO only when I started tech diving (in this case, I believe it makes sense). And I often have migraines with aura (a symptom of PFO). In other words, there is absolutely no reason at all to worry if you only do rec. @doctormike , I don't know in the US, but no TEE is required in Italy.

To be clear: DCS is not among the major risks in (recreational) diving. Since you mentioned some scientific reports saying that DCS happens within NDL, well -> read how many people suffer severe and permanent damages from DCS within recreational limits. You'll discover that the main things you need to worry about are far from decompression. The essential factors are:
- never hold your breaht
- never panic (how to avoid panic? take good training, and never dive outside your experience)
- if you are not young anymore, be physically fit and do not have heart issues

Forget the deco; it is by far your last concern.

 

[JonG1]

Not read the whole thread, but I had a PFO which I found by getting bent.

Potentially relevant though is that I dived on and off for years (5-37) with no clinical DCS, a few times I was tired, but this was '75-97 so a lot of air and not much nitrox until post 94.

I trained and qualified as a DM in the UK, and used an Oceanic computer for what we now call recreational diving. It was very conservative if you followed it's traffic light system.

Around 95 though I got involved in tech and started doing longer, deeper, planned deco, lots of deep air and some trimix.

Mostly I was fine, but I did pick up skin bends and finally some neuros (visual disturbance).

However on reflection I am fairly sure that the bends correlated with post dive exertion, either a spine ladder in twins and stage, ladder from boat to dock carrying gear, or hauling tech rigs up hills at quarries.

Ergo it's the physical exertion that pushed the crap through the hole.

At my PFO diagnosis, even a Valsalva would shove the champagne into the wrong place.

So, my point is that it's possibly less the wet profile and more the post dive profile that finds the holes.

 

[Akimbo]

What triggered me to start this thread was effectively looking for safe/conservative ascend / safety stop stop protocol

Expanding on comments above:​

In VERY simple terms, the problem is faster tissues will be off-gassing diluent while slower tissues can still be in-gassing during a delayed ascent. Avoiding getting bent is a balance between these conflicting factors.

This is one of the main arguments favoring decompressing on pure Oxygen. It significantly increases the rate of diluent removal and reduces absorption to zero since there is no diluent to absorb. Unfortunately, decompressing on pure O2 is not without risk or complication.

Info - Oxygen Toxicity Limits & Symptoms

Oxygen Toxicity Limits & Symptoms Oxygen toxicity limits can be very confusing, especially for PPO2 (Partial Pressure of Oxygen) levels above 1.6 ATA used in chamber-based hyperbaric treatment (recompression) and decompression tables. For example, here is a chart of one of the most common DCS...

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A simple strategy to decrease DCS risk is to set your computer for air while using Nitrox. This works fine as long as you stay above the MOD for the mix you are using. Your diluent absorption rate will be lower than your computer is calculating and removal will be faster on ascent. Nitrox certification is required and advanced Nitrox training will further expand your understanding, and allow using pure Oxygen.

Info - Decompression & Treatment Simplified

1: Introduction Everything should be made as simple as possible, but not simpler — Albert Einstein (paraphrased) I probably violated the "But Not Simpler" part, but I tried to include enough Hyperlinks to make amends. Clicking on them should allow any interested diver to "drill-down" as far...

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