Scuba Nitrox Incident for Analysis

[Angelo Farina]

The no bc broke the camels back John C. Ratliff, and even the dumb snorkel that he thankfully didn't use
See there it is a guy starting to drown in still flat water, doesn't dump weights, no need to wonder what happens to divers in a moving ocean
I used to dive no bc before the bc didn't like it, still don't like it can do it to show off but it's too much work, dangerous.
Thank you.

When I was diving without BCD (in the seventies) we did not use so much weight. We were buoyant at the beginning and there was a special manouvre ("capovolta in squadra" in Italian, I cannot translate it properly) for being able to go underwater.
Apart being without BCD, and in bad shape, your friend was also evidently over-weighted. So staying afloat was requiring a lot of effort, and the CO2 build up was worsening...

 

[JohnN]

When I was diving without BCD (in the seventies) we did not use so much weight. We were buoyant at the beginning and there was a special manouvre ("capovolta in squadra" in Italian, I cannot translate it properly) for being able to go underwater.
Apart being without BCD, and in bad shape, your friend was also evidently over-weighted. So staying afloat was requiring a lot of effort, and the CO2 build up was worsening...

This?

 

[Wibble]

Again not a doctor and I'm sure one of the real medical people will chime in here, but it's my understanding that a PFO would not cause these symptoms. Intuitively it makes sense, but except from some rare massive cases that would be caught very early in life, PFOs are asymptomatic even during strenuous exercise. You wouldn't feel a lack of oxygen from it. That's why something like a quarter of all people are walking around with them and don't know it until they get bent. PFOs are generally small and only shunt tiny amounts of blood relative to what the heart is pumping. They're a specific risk in diving because while small, they can let bubbles through.

Did a simple 32m/100' dive on CCR with a friend. Nice dive, nice wreck. Hour on the bottom and 30 mins at deco. Slow ascent from 6m, deco fully cleared. No issues whatsoever.

Friend is young, fit, active, exercises and regularly dives on CCR. On the boat back he felt a bit tired and drove home straight after. He developed a rash on the drive which grew after a shower. Called the dive doc and had to do 5 days of decompression treatments in a chamber. Prime suspect is a PFO.

PFOs can spontaneously occur.

 

[Angelo Farina]

PFOs can spontaneously occur.

In most cases PFO is a remaining of childhood. Inside the uterus, the heart of everyone has a PFO. This is a bypass which allows blood circulation for the foetus when the blood comes form the umbilical chord.
Usually the PFO closes during childhood, but in many people it never closes completely (approximately 1 of 5 adults has a PFO of some entity).
So it is wrong to say that a PFO con "occur" spontaneously. It is a pre-existing condition, affecting billions of people worldwide... And most of them stay unaware of it for their life.

 

[Wibble]

In most cases PFO is a remaining of childhood. Inside the uterus, the heart of everyone has a PFO. This is a bypass which allows blood circulation for the foetus when the blood comes form the umbilical chord.
Usually the PFO closes during childhood, but in many people it never closes completely (approximately 1 of 5 adults has a PFO of some entity).
So it is wrong to say that a PFO con "occur" spontaneously. It is a pre-existing condition, affecting billions of people worldwide... And most of them stay unaware of it for their life.

How can someone who's fit and healthy suddenly succumb to a PFO in a gentle dive where they've made far more aggressive dives in the past?

 

[Angelo Farina]

How can someone who's fit and healthy suddenly succumb to a PFO in a gentle dive where they've made far more aggressive dives in the past?

This is exactly how people having a PFO suddenly discover they have it...
It was there since their birth, but it is entirely asymptomatic, until it is not anymore...

 

[Angelo Farina]

This?
View attachment 645524

Exactly! Where did you find that picture?
And what is its English name?
Or is this another of those Italian-only diving techniques which never landed in other countries?

 

[kammel78]

How can someone who's fit and healthy suddenly succumb to a PFO in a gentle dive where they've made far more aggressive dives in the past?

Because it's not the PFO directly that caused the DCI, it's the bubbles the PFO allowed to be shunted instead of exhaled. And bubble models are highly theoretical and highly debated because of their unpredictability. Angelo is exactly right, they're usually there since birth and I've heard 30% (maybe misremembering) of people have them and never notice. You can have plenty of dives where not enough bubbles get shunted for you to notice and then one dive, they randomly do shunt enough to notice.

Remember, DCI is not a line in the sand. Post dive fatigue, "brain fatigue", aches, et cetera are probably all very mild symptoms of DCI that we commonly attribute to other things. It's only when they get really noticeable (rashes, joint pain, et cetera) that we attribute them to being "bent".

 

[kammel78]

I wonder if it is CO2 contamination. It takes a while to build up, would go away in large part if you get shallower.

Did you mean CO and not CO2?

 

[kammel78]

Fraction of Gas, as opposed to partial pressure.

The fraction of the gas is what we commonly refer to as the percent, i.e. the mix is 32% oxygen. That tells you the ratio of gases but doesn't account for the actual pressure at depth. .21 O2 + .79N = 1 atm x 1 atm (surface) = 1 ata of total system pressure at the surface. Go down to 4 ATA and the pressures end up being 4x the FG.