Depth Blackout

[Brian Allen]

I've just been reading Sheck Exley's Basic Cave Diving, a blueprint for survival and have come across something which I had always assumed was some kind of combined narcosis and passive panic.

Quote: (Originally Posted by Sheck Exley)

Accident Report:
Two Divers from Miami, Barry and Luke, drove up on Thursday night, met some other divers and entered the water at Eagle's Nest Sink at 12:40AM. Barry was an experienced cave and deep diver, but Luke, while experienced at open water diving, had only minimal experience at cave and deep diving. Despite the fact that Luke had never been below 200ft, and both divers were tired from the long drive, a dive was planned to 270ft depth. When Barry and Luke failed to surface, the other divers called the sheriff's dept. on 6/2/72.

We found Luke's body at a depth of 260ft, some 500ft from the cave entrance, and Barry's inert form about 100ft closer at a depth of 240ft. Both divers were completely out of air and the silt on the floor around the bodies did not show any signs of stuggling.

Analysis:
From the lack of signs of a struggle it would appear that both divers lost consciousness before running out of air, probably due in part to the effects of breathing compressed air at great depth.

The "Depth Balckout":
A victim of depth blackout appears to be asleep with his eyes open, and does not move other than continuing to breathe. It is not known why the victim retains his mouthpiece, but it's a fact that the victims of depth blackout will go on breathing lying inert on the bottom, until they run out of air. Further, the shallowest depth at which depth blackout - the most likely cause of Barry and Luke's deaths - has been observed to occur is 150ft

5 years ago before I started down the DIR route myself and 2 friends went for a 36m air dive on a site known as Devil's point. It is very dark there, and known to have fierce currents unless you plan an exact dive. We were entering the water 20 minutes before HW, to drift upriver for 20 mins and when the tide turned drift back to the start point. As we approached 36m, Paul, the least experienced diver (and this was his deepest dive so far) stopped moving. His eyes were open, and he was breathing but he just kinda went limp and was falling backwards down to the bottom (c.40m), I grabbed hold of him but despite waving my hand across his face their was no response, but he was breathing. I towed him in to the wall, grabbed hold of some rock, and established his buoyancy, he didn't come round. I began taking him up to the surface, and around 24m he woke up. It was one of the more bizzarre things I've had to deal with underwater and at the time we put it down to narcosis, and then forgot about it.

Has anyone had any similar experiences, or know anything more about this?

[finbar.taylor]

Quote: (Originally Posted by Brian A)

Has anyone had any similar experiences, or know anything more about this?

I pulled a diver up with exactly the same sympton but conciderably shallower.
She just went completely blank at about 12m.

the similarity is it was very dark and a large plankton bloom so vis was non existant. masks were toughing to see her eyes!

My instructor at the time called it "passive panik" -but he was a complete idiot so might be nothing like it.

Fin

[Brian Allen]

A few other things:

1. Paul was a postal worker and often worked odd shifts so could have been tired.
2. He had no memory of the event whatsoever.
3. His face was calm, there was just no one in.

Have googled this around and it seems to be atributed to nitrogen narcosis by many, but I think there may be more to it.

What happened with your girl at 12m? I often find that beginners having problems will often just go limp and let you do whatever you need to to fix the situation, but if you look in their face they'll normally register/focus on you.

[JohnKendall]

Quote: (Originally Posted by Brian A)

A few other things:

1. Paul was a postal worker and often worked odd shifts so could have been tired.
2. He had no memory of the event whatsoever.
3. His face was calm, there was just no one in.

Have googled this around and it seems to be atributed to nitrogen narcosis by many, but I think there may be more to it.

What happened with your girl at 12m? I often find that beginners having problems will often just go limp and let you do whatever you need to to fix the situation, but if you look in their face they'll normally register/focus on you.

I've had someone do much the same thing as Fin's girl. A student on their 1st openwater dive, completely still, no responses, no focus. However it was in 3m and was pretty cold. I put that down to "passive panic". I suspect that we are looking at 2 different things. The "deep blackout" I suspect is more to do with narcotic effect (remember that CO2 is a big contributing factor in air dives), whereas the "passive panic" is more about a new diver's inability to comprehend what is going on, so the brain just deals with trying to stay alive in an alien environment.

That said, It's just my thoughts, and I haven't got any kind of data.

Thanks
John

[LCF]

Somebody I met at the dive shop the other day told me a story about being dropped off a boat in the wrong place. There was a novice diver in the group. Instead of finding the bottom at about 50 feet as they'd been briefed, it turned out to be about 120. The novice diver lost buoyancy control on the way down and went all the way to the bottom. She was found unconscious but breathing, brought to the surface, and woke up, without any sequelae.

There's also a story of one of the deaths on the Doria, where the diver was found OOA with no signs of a struggle. It was put down to probably CO2 narcosis, as the diver in question was known to skip breathe and was proud of his low gas consumption.

[rjack]

Generically, "narcosis" is the depression of neural pathways/signaling. Lots of chemicals (other than nitrogen) can cause narcotic symptoms. The effects of narcosis tend to be a rather non-specific CNS depression and additive. There are some toxicological studies which have demonstrated that each chemical has a specific potency based on their structure and that the sum of their molar concentrations roughly equals the total narcotic effect.

I would not be the least but surprised if nitrogen (under pressure) is additively or antagonisticly narcotic with hundreds or thousands of other chemicals. Both exogenous (e.g. a cold medication containing condeine) and endogenous (e.g. CO2 or low serotonin levels - serotonin and dopamine are neurotransmitters).

The multitude of other chemical players (other than the extreme ENDs used by Exley) are probably key to the "shallow" blackout events.

Richard

[Kevrumbo]

Quote:

Undersea Biomedical Research, Vol 5, No. 4 December 1978 Hesser, Fagraeus, and Adolfson:

Studies on the narcotic action of various gases have shown that the ratio of narcotic or anesthetic potency of CO2 and N2O approximates 4:1 and that of N2O and N2 30:1. From these figures it can be calculated that CO2 has at least 120 times the narcotic potency of nitrogen. Our data would suggest that the narcotic potency of CO2 is even greater, i.e. several hundred times as great as that of nitrogen.

"Helium is our Friend. . ." GI3

[Clare Gledhill]

Substitute the word 'anesthetic' for 'narcotic' and it starts to make sense.

The Meyer Overton's index oft quoted in narcosis studies in diving was actually a study which sought to correlate lipid solubility of an anaesthetic agent. This suggests that onset of anaesthesia occurs when sufficient molecules of the anaesthetic agent have dissolved in the cell's lipid membranes, resulting at a certain level in an unresponsive subject.

[Brian Allen]

The body has such a small tolerance to elevated CO2 levels, do you not think other symptoms such as rapid breathing, panic would have occured first if it was just carbon dioxide and nitrogen narcosis?

RJack - i think you're right and it's probable there is an additive effect to narcotic agents with the chemicals causing narcosis to be almost too numerous to guess.

There also seems to be something else in play in that the 2 examples sited here (mine and LCFs) are also where the diver is doing there deepest dive to date, suggesting that there could also be a bodily reaction to stress or "first nacosis" perhaps?

It would be interesting if there were more examples of this relatively shallow blackout.

[Martin Burnard]

I had a chat with an aneasthetist, about 2 years ago, and he said that it (aneasthetics) was an area inwhich we new what happend, but not why and only approximately to what extent. Research was being carried out constantly.

Due to its similarity with narcosis, there is probably an opportunity for cross pollination of ideas, but that requires somebody with detailed knowledge of both areas to identify. This was the point where he said "and that dear friend is the problem", areas of research are narrow due to the constraints of funding, but without doubt very expensive research is unknowingly repeated in different formats.

Maybe one day one central research data bank will be created. What a resource that would be!