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causes and cases of deep water blackout

chschoenb

New Member
Oct 4, 2018
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Brunnen
Dear all,
I'm currently researching the subject of deep water blackout. Blackouts that can occur during a deep dive (deeper than 20 meters, although they are very rare). I'm particularly interested in the following questions:
- what causes can deep water blackouts have, besides the known causes of blackouts in general like a fast decrease of oxygen partial pressure and hypocapnia? Are there any scientific studies on this?
- is there an overview of blackouts at the last five AIDA or CMAS World Cups including the approximate depth of the blackouts? If not, do you know prominent examples (e.g. this year at the cmas worldcup)?

Thank you very much for all the pertinent hints, Chris
 

Fitz-Clarke

Well-Known Member
Dec 9, 2004
63
26
98
Halifax, Canada
I am not aware of any mechanism that would differ from blackout in shallow water. You could certainly blackout at greater depth if you dive deeper, stay longer, or consume oxygen faster. The physiology should be the same, with arterial PO2 supplying the brain dropping below a critical level due to drop in alveolar pressure on ascent.

The only different case to my knowledge was Herbert Nitsche blacking out around 100 m on ascent from 253 m but regaining consciousness later in the ascent. That would argue against hypoxia being the cause. Most likely it was due to severe narcosis with delayed onset due to the lag in nitrogen kinetics in the brain relative to ambient pressure, such that peak nitrogen concentration occured during the ascent rather than at maximum depth.

In a theoretical paper in 2009 entitled “Lung compression effects on gas exchange in human breath-hold diving”, I proposed that deep water hypoxic blackout could occur at the depth of complete lung collapse, where all the compressed lung gas is pushed into the rigid airways, depriving the alveoli of oxygen, followed by depletion of remaining blood oxygen down to the critical level. This has not been known to occur, as it would happen beyond present record depths.
 

_Seb

Member
Jan 14, 2015
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Hong Kong
i remember the case of a female diver blacking out quite deep (not sure about the depth..) because her mask skirt had flipped (she said she didn t equalize it properly) and the pressure on the eye from the skirt made her black out on ascent. can t remember her name. will post it here if i find it.
 

Nathan Vinski

Well-Known Member
Apr 19, 2015
198
117
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Canada
i remember the case of a female diver blacking out quite deep (not sure about the depth..) because her mask skirt had flipped (she said she didn t equalize it properly) and the pressure on the eye from the skirt made her black out on ascent. can t remember her name. will post it here if i find it.
Anna Von boetticher.

The pressure on her eye cases an increase in blood pressure. Once her mask expanded on the ascent and the eye pressure was relieved her BP dropped so much she feinted ( not exactly a bo.. more like standing up too fast).

You can get the same effect pressing on your eyelids with your fingers
 

_Seb

Member
Jan 14, 2015
4
0
11
35
Hong Kong
Anna Von boetticher.

The pressure on her eye cases an increase in blood pressure. Once her mask expanded on the ascent and the eye pressure was relieved her BP dropped so much she feinted ( not exactly a bo.. more like standing up too fast).

You can get the same effect pressing on your eyelids with your fingers
yes i think that s her !! thanks Nathan
indeed no a hypoxic BO but she lost consciousness, so it s still a BO in my understanding. thought it was interesting to mention this as a possible cause.
 

Fitz-Clarke

Well-Known Member
Dec 9, 2004
63
26
98
Halifax, Canada
This is an interesting case. It sounds like activation of the oculocardiac reflex (OCR) which involves a brainstem connection between the sensory trigeminal nerve from the eye and the vagus nerve that induces a reflex drop in heart rate, and subsequent drop in blood pressure and brain perfusion. OCR activation is commonly seen during eye surgery, particularly in children undergoing stabismus correction. It causes bradycardia, but there have also been reported cases of brief asystole from heart block where the heart stops for a few seconds. There were three OCR-related fatalities reported in the 1950s. To have this activated by diving mask dislodgement would be extremely rare. Peripheral vasoconstriction from the diving response should compensate for any drop in blood pressure, and being immersed in water also enhances return of blood to the heart (preload), so actually fainting from the OCR during a dive would be extremely unusual. Maybe this diver experienced such an intense vagal response that there was a long enough period of complete heart block to cause loss of consciousness.
 

Bill McIntyre

San Clemente, CA
Staff member
Forum Mentor
Jan 27, 2005
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San Clemente, CA
I'm not sure if this will be helpful, but I can tell you about a spearfishing friend who blacked out and died at 30 meters. He was found kneeling on the bottom with his head and shoulders under a ledge, gripping his shaft with both hands and with a wrap of cable shooting line wrapped around one hand as if to help pull a fish out of the hole. There was no fish on the shaft, but earlier in the day he had shot some big pargo. Pargo are very strong and notorious for holing up. We guessed that he had shot another one, but it had torn off.

This doesn't seem to fit any of the theories mentioned here and it certainly wasn't swb since he didn't ascend. He doesn't seem to have been restrained since the diver who recovered him had no difficulty pulling the shaft out of the hole.
 

hteas

Well-Known Member
Mar 9, 2005
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Anchorage, AK
What about Audre Maestre? The lead safety diver for the attempt, Matt Briseno, in discussions we had after her death, thought that the extreme depth at which she blacked out (about 120m) suggested that the initial blackout was hypercapnia. From there, it turned into a very sad circus of mistakes.
 

Fitz-Clarke

Well-Known Member
Dec 9, 2004
63
26
98
Halifax, Canada
I analyzed Audrey’s dive back in 2011 using a computer simulation of lung mechanics and alveolar collapse (reference 1) and pulmonary gas exchange (reference 2). The depth profile was obtained from Kim McCoy’s data recorder that Audrey wore. I didn’t comment on this analysis at the time out of sensitivity to the tragedy. But results of the simulation provide insight into what happened.

What is unique about her dive is not just the record depth, but the long time spent at or near the maximum depth while she struggled and waited for assistance. It was 2 min and 8 sec from sled contact at 170 m to blackout at 120 m. If we assume her lung volume TLC plus packing was 8 litres at the start, collapse depth predicted by the simulation would be somewhere around 180 m. We can assume her lungs were not completely collapsed at her maximum depth of 170 m, but the excessive time spent there resulted in additional gas absorption and further decrease of lung volume. This is because O2 is still taken up from the lungs, but CO2 does not flow into the lungs at depth because its high solubility retains it in the blood until near the surface when alveolar CO2 drops enough to reverse the gradient and allow CO2 back into the alveoli. So it is conceivable that her lungs collapsed while she was stuck near bottom depth, and this ultimately caused blackout from hypoxia. This is what I called the “hypoxia wall”, which is predicted to occur after total lung collapse. I discussed this idea a little more in a recent review paper (reference 3).

When I ran her dive profile through the simulation, I found that at the time of blackout her lungs would have collapsed completely, at which point arterial PaO2 drops to 25.4 mmHg, which is exactly when the blackout threshold should occur. Blackout typically occurs around 20 to 30 mmHg, depending on various factors. You might think that the high ambient pressure would keep PaO2 high at depth, but arterial oxygen drops to the level of venous oxygen PvO2 due to full shunting of blood past the collapsed alveoli, which shuts off pulmonary gas exchange. Predicted arterial PaCO2 was 57.3 mmHg at blackout - not an extreme level, but similar to that seen when terminating static apnea.

Hypoxia is therefore the primary cause of blackout, not high CO2. Once there is loss of consciousness, the negative airway pressure at that depth due to outward rib cage recoil and relaxation of the closed glottis would cause water to be forced into the lungs.

1. Fitz-Clarke JR. Lung compression effects on gas exchange in human breath-hold diving. Respir Physiol Neurobiol 165: 221-228, 2009.

2. Fitz-Clarke JR. Mechanics of airway and alveolar collapse in human breath-hold diving. Respir Physiol Neurobiol 159: 202-210, 2007.

3. Fitz-Clarke JR. Breath-hold diving. Compr Physiol 8: 585-630, 2018.