Scuba Nitrox Incident for Analysis

[Wibble]

PFO (Patent Foramen Ovale) -- AKA hole in the heart.

Stopped many a diver from diving and causes various DCI.

 

[tursiops]

PFO (Patent Foramen Ovale) -- AKA hole in the heart.

Stopped many a diver from diving and causes various DCI.

Wibble strikes again with a nonsense post!
Jeez, man, do a little research before posting!

 

[Wibble]

Wibble strikes again with a nonsense post!
Jeez, man, do a little research before posting!

Awww.

So it wouldn't give the feeling of being out of breath? One of the features of a PFO is inefficient gas transfer to and from the blood, hence all the DCI grief associated with it.

This hypothetical 'problem' is deliberately worded in a vague way to promote discussion, and there's many causes that could fit the symptoms.

Which way is the (unlikely) suggestion of a PFO not going to fit the symptom of being out of breath after stress?

 

[kammel78]

"it seems to correlate with lipid solubility" is a far cry from "we fully understand this mechanism and there are no mysteries at play". If I'm mistaken on the current state of research (being just a dumb diver not a doctor) I'd really appreciate a proper explanation of the biochemistry involved.

I apologize, I realize I combined 2 thoughts into one here. My statement regarding no mysteries was referring to this specific incident, not our, granted, incomplete understanding of narcosis. However, there is some great research being done to understand the fundamental mechanisms at play. Predicting and modeling those, on the other hand, is still fully theoretical.

Awww.

So it wouldn't give the feeling of being out of breath? One of the features of a PFO is inefficient gas transfer to and from the blood, hence all the DCI grief associated with it.

This hypothetical 'problem' is deliberately worded in a vague way to promote discussion, and there's many causes that could fit the symptoms.

Which way is the (unlikely) suggestion of a PFO not going to fit the symptom of being out of breath after stress?

DCI? Underwater during the dive? Then got better during the dive?

I mean, technically, one of his lungs spontaneously combusting underwater could cause shortness of breath...

 

[Celt]

Okay, Jim, I’ll bite. I’m a diver for decades, and have been in the safety profession for over 30 years. So here goes.

A couple of things from the video:
—he was using (supposedly) 36% nitrox. That means the gas was 36% oxygen, the rest (baring contaminants) being nitrogen. That would be 64% nitrogen.
—depth where symptoms happened, 75 feet (23 meters); he felt that even though he was receiving the required gas from the regulator, he wasn’t getting enough oxygen.
—he had a spaced-out buddy, who couldn’t or would not help.
—upon heading for the surface, he felt better at 30 feet (9 meters)
—Once he returned to the bottom, things were fine, and he resumed the dive without surfacing or needing the buddy’s safe second (octopus), assuming that the buddy had one (not sure, equipment configurations were not detailed).
—He asked about stratification of the gases within the cylinder (separation, he said).

I’d like to point out that the gas wasn’t tested for composition. So we don’t know the actual mix. Also, there was some panic in this description, as he said he felt the need to surface even with the risk of lung over-expansion or the bends (no mention of how long they had been at depth.

Because the dive resumed without incident at the 75 foot level (23 meters), I’d place this to his lack of experience, and probable hyperventilation. He got anxious, and then started breathing with quick, short, shallow breaths, which really did not pass oxygen to the circulation from the lungs, as the lungs did not receive “new” air from the regulator. Then, as he began ascending, his breathing stabilized, and he got more oxygen into his lungs from the deeper breathing he was using on the ascent. Relaxing more, with his breathing under control, he felt more at ease and resumed the dive by swimming back down to his buddy at 75 feet (23 meters).

Concerning the air “separating,” to my knowledge that simply doesn’t happen. Yes, they are slightly different densities, but the Brownian Motion would cause these molecules to evenly distribute throughout the cylinder.

There was no regulator malfunction, as the dive resumed and it breathed normally.

So the lessons learned are that breathing is important, and a diver needs to breath more deeply and slowly than people on the surface, especially when exercising. We used to call this the “hyperpnia-exhaustion syndrome,” but that has been discontinued from what I can see.
Hyperventilation syndrome - Wikipedia

This, by the way, can also happen on the surface. Here’s an incident which happened to my buddy on a dive last summer here in Oregon.


SeaRat

After watching 40 seconds of the video it was clear the man was in no shape to dive. He couldn’t get his breath putting his fin on while on the pontoon.

 

[Wibble]

DCI? Underwater during the dive? Then got better during the dive?

I mean, technically, one of his lungs spontaneously combusting underwater could cause shortness of breath...

Once more; a PFO causes circulation problems which would mean low oxygen levels, being out of breath?

PFOs can spontaneously happen. Lots of experienced divers suffer, typically a bend (which is caused through inefficient off-gassing), and discover they've a PFO and can't dive until it's fixed.

In the case of this hypothetical, the diver is out of breath underwater when they've been stressed and working hard. It's an NDL dive, with a rich mix, so no ceilings breached. After calming down and relaxing, the oxygen levels rise.

All I'm saying is that a PFO could fit these symptoms, but it's unlikely to be "the answer".

 

[Celt]

Scuba Nitrox Incident for Analysis
This apparent true incident was taken from Scuba Board almost 20 years ago. I use it in my nitrox course before the final exam as a discussion exercise for students in small groups. Here, I describe the incident, please post your analysis in the comments, and I'll post my video analysis next week.

A great deal can be learned from the incident analysis. We get to learn from the mistakes and bad luck of others, without having to experience the "pain" of the actual incident. In this spirit, I am grateful for all incidents that are posted, and the generosity and humility of the posters. We analyze these events not to mock the inexperience, poor decisions, or bad fortune of others, but to make ourselves better divers.

Who knows, an account of a dive 20 years ago. Most likely panic brought on by the depth combined with what he believed to be poor vis.

 

[tursiops]

PFOs can spontaneously happen.

Right. Got a source for this info?

 

[OTF]

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.

 

[wetb4igetinthewater]

PFOs can spontaneously happen.

Kind of like spontaneous human combustion?