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Shallow Water Blackout vs. Deep Water Blackout

Tratish

New Member
Nov 20, 2007
1
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#1
Hello Everyone,

In the Wikipedia Article about Shallow Water Blackout, the author asserts that Shallow Water Blackout is caused mainly by hyperventilation in shallow depth. He mentions something called "Deep water Blackout" which is a condition that takes into account deeper freedives in which pressure changes as one is going up are the main cause of the blackout. In some online references, though, and in my physiology class, the pressure changes are lumped into Shallow Water Blackout. I was wondering if there really is a distinction between these two forms of blackout and if anyone knows of any literature that outlines this difference.

This is what the Wikipedia article says about the two:

Deep water blackout occurs as the surface is approached following a breathe-hold dive of over ten metres and typically involves deep, free-divers practicing dynamic apnoea depth diving usually at sea. The immediate cause of deep water blackout is the rapid drop in the partial pressure of oxygen in the lungs on ascent.
Shallow water blackout only occurs where all phases of the dive have taken place in shallow water where depressurisation is not a factor and typically involves dynamic apnoea distance swimmers, usually in a swimming pool. The primary mechanism for shallow water blackout is hypocapnia brought about by hyperventilation prior to the dive.

Thank you,

Tratish

P.S. I missed a couple of points on a physiology exam about this because of not putting pressure as a common factor and I am curious to see if I missed these points rightly or wrongly :)
 

efattah

Well-Known Member
Mar 2, 2001
3,294
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173
BC, Canada
www.fluidgoggles.com
#2
Sorry, but the wikipedia article is totally incorrect -- any search on this forum will show that.

The correct distinction is:

1. Static apnea blackout -- blackout in shallow water simply caused by holding the breath too long (no pressure changes)

2. Shallow water blackout -- blackout during the ascent from a deeper dive, due to both holding the breath too long and a drop in pressure

3. Deep water blackout -- blackout that occurs on the bottom (i.e. near the deepest point of the dive), usually due to excessively high CO2 levels
 
Dec 9, 2005
6,522
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F:Lyon / CZ:Prague
apnea.cz
#3
I touched exactly this topic already once in this thread: http://forums.deeperblue.net/safety/68233-freediving-death.html (post #115), but Erik is right that Wikipedia is probably the only source defining SWB in this unusual way (well, there is certainly another one where Wiki took it from), but it is true that by SWB, is generally meant the depressurizing BO. Apart from Wiki, I yet have to see another place using their definition. At freedivers and spearos definitely SWB = ascent BO.

And from historical point of view this definition (SWB = ascent or depressurizing BO; DWB = BO in depth because of narcosis or gas toxicity) is much more justifiable, because the exact term "Shallow Water Blackout" was first used by S. Miles in early times of closed circuit rebreathers for inexplicable blackouts of rebreather divers in shallow depths. S. Miles discovered the depressurizing effect at the ascent and bedsides the term SWB used also the name "latent hypoxia" (source: Shallow Water Blackout)

I think it would be proper to try editing the Wiki entry accordingly.

Personally, since I am aware of the potential controversy, I usually refer to this type of blackout as "depressurizing" or "ascent BO", which is less misleading than the term SWB.

PS: the above mentioned thread http://forums.deeperblue.net/safety/68233-freediving-death.html is quite interesting and may be worth of reading if you are interested in the topic, or concerned about safety
 
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Seacidal

Seacidal Tendencies
Sep 27, 2005
116
8
0
Ventura, CA USA
#5
I also heard mention of a fourth type of blackout, or perhaps it's just a variant of SWB. That is the "surface blackout", in which the diver regains the surface, exhales or perhaps takes a brief breath, and loses consciousness.

In discussions with other experts, I've noticed the use of "underwater loss of consciousness" used as opposed to other terms. I understood this was done to avoid inferring one particular physiological cause over another, as Eric pointed out previously.

Does anybody have any comments or experience with either "surface blackout" or ULOC?

Thanks,
Chip
 

naiad

Apnea Carp
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Oct 11, 2003
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#6
Surface blackout is probably a variant of SWB, the diver becomes hypoxic due to the reasons mentioned above, and reaches the critical level for blackout after surfacing.
 
Dec 9, 2005
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F:Lyon / CZ:Prague
apnea.cz
#7
Well, there are always several factors leading to the hypoxic blackout - at an ascent it is the depressurizing effect, and on the surface it is the sudden exhale, forgetting to breath up properly, laryngospasm due to inhaling water from a snorkel, or samba. You may get lightly hypoxic on the ascent, get a light LMC which then can cause the loss of control of respiratory muscles, and you black out in consequence of it.
 

chrismar

Well-Known Member
Aug 15, 2007
740
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#8
Its possible that the blood pressure drop that happens after the exhale could contribute to surface blackout. I don't believe this has much to do with SWB as I've seen it happen in the pool.
 
Likes: Erik

Cornholio

Well-Known Member
Jan 14, 2003
98
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98
UK
www.scubanauts.co.uk
#12
Sorry, but the wikipedia article is totally incorrect -- any search on this forum will show that.

The correct distinction is:

1. Static apnea blackout -- blackout in shallow water simply caused by holding the breath too long (no pressure changes)

2. Shallow water blackout -- blackout during the ascent from a deeper dive, due to both holding the breath too long and a drop in pressure

3. Deep water blackout -- blackout that occurs on the bottom (i.e. near the deepest point of the dive), usually due to excessively high CO2 levels
Sorry to resurrect an old thread. I've just been reading through some current BSAC course notes. They claim that shallow water blackout is that which occurs during a breath hold in shallow water, e.g. static apnea.

Of course, the BSAC are not that big on freediving, so I was going to write and point out the error to them. However, I notice that the Wikipedia entry still agrees with their definition.

I always understood Eric's definition above to be correct. Is there an authoritative document on this?

:confused:
 
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haughki

New Member
Mar 9, 2005
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#14
DAN is likely a rather authoritative subject in any matters related to diving medicine, and they do use the SWB term for the depressurizing blackout. It is used in diverse documents, and on the website it is used in that context for example here:

DAN Divers Alert Network
Agree with Trux on this. At least within the freediving community, SWB has very much to do with ascent and depressurization, esp. in the final 5m of the dive. People often talk about a possible "vaccuum effect", where a rapidly decreasing partial pressure of oxygen in the lungs (because of the relatively rapid change and decrease in pressure as the diver nears the surface) "sucks" oxygen from the bloodstream (note: I don't know of any specific science out there which supports this notion). Pretty sure Terry Maas and David Sipperly's book "Freedive" discusses this.

Like Trux, I prefer the term "Ascent Blackout" for disambiguation from SWB (whatever various people think that means) and other types of blackouts.

Hawkeye Parker
San Francisco, CA
 
Likes: Cornholio

seanavent

Active Member
Sep 30, 2010
3
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36
San Francisco
#15
Although the diving community, including DAN, SCUBA divers, and freedivers, may define SWB one way, those who manage aquatic facilities and those who insure them define SWB differently.

These two communities rarely interact.

As an underwater hockey player I've been recently dealing with a lot of both communities lately fro a couple reasons:

1) A few swimming pools have banned underwater hockey because of it's risk for SWB (as defined by the aquatics industry). I've had to try to convince them that the danger of SWB by wither definition is not a high risk (we've never had a blackout reported in the over 1 million person hours of hockey since the early 1970's). so far we've gotten a couple reinstated but the insurance people are hiring 'experts' to see that no one ever holds his/her breath in a swimming pool for 'extended period' (i.e., 20 seconds).......

2) In trying to prove to some extent that the risk is low, I'm contacting those who study hypoxia. So far, I've not been able to come across enough literature to establish physiologically why underwater hockey players don't black out..... it's definitely not from the diver-defined pressure-related SWB......

I guess my overall point is that anyone can say anything is SWB - there is no one single overall authority for everyone. The divers can use their definition, but that's not going to convince aquatic managers who have other authorities to look to.

Sean
 
Dec 9, 2005
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F:Lyon / CZ:Prague
apnea.cz
#16
Well, aquatic managers do not care about the terminology. They only need to avoid any risk of liability in case of an accident. Still, it is not wise introducing or using confusing terminology, because then nobody knows what you are speaking about.

So as to your specific problem - UW rugby or hockey players do not suffer from the depressurizing type of BO, besides others because the depth is small.

And the chance they blackout is relatively small, because they stay with very high level of CO2 in the blood. It has two important effects - first of all it increases the urge to breathe, hence it become extremely difficult to hold the breath for prolonged time, and the players simply surface for a sip of air long time before they are really hypoxic.

And the second reason is that CO2 shifts the Bohr saturation curve, which means that blood oxygen gets easier discharged to the tissue, which in turn means that it significantly increases their hypoxic tolerance (they can go into much deeper hypoxia without risking loss of conscience). You do not really need to search any experts for confirming it - you will find it in any basic book about the physiology of breath hold diving.
 

seanavent

Active Member
Sep 30, 2010
3
0
36
San Francisco
#17
Trux -

Thanks much for your response. I appreciate it. And I do agree that they have misused the SWB term, but it is very well entrenched in the aquatics culture now:

What is Shallow Water Blackout
http://spot.pcc.edu/~lkidoguc/LGT/Blackout.pdf
Drowning, Dry Drowning, and Shallow Water Blackout
Underwater Swimming Dangers - Shallow Water Blackout
and anything from Aquatic Safety Research Group, LLC - We take water safety seriously

And it's something we have to deal with if we get in a pool. In talking to researchers working with DAN, they are using another term instead of SWB: hypoxia of ascent (HOA). I think they realize that SWB is a confusing term.

With regards to rugby or hockey, I've heard of people saying they almost blackout, but who knows. Many other articles say that an increase in exercise increases the risk of blackout because the O2 levels drop quicker than CO2 is built up. In addition, like freedivers, UWH players have been shown to have a higher CO2 level tolerance. I would love to find a study that analyzes CO2 and O2 levels during play to see exactly where the levels reside.

We did small study of how long UWH players stayed underwater and it was generally less than 20 seconds and on average less than 7 seconds. But recovery times were also short (average 15 seconds).

I'm really going to have to see how the Bohr saturation curve plays into our sport. If I could easily argue that to risk management, I''d be ahead of the game.

Cheers -

Sean
 
Dec 9, 2005
6,522
751
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F:Lyon / CZ:Prague
apnea.cz
#18
Many other articles say that an increase in exercise increases the risk of blackout because the O2 levels drop quicker than CO2 is built up.
This is pure nonsense. If you ever played UW rugby (and you surely did), you know you are charged with CO2 and acid lactic all the time. So there is no chance the CO2 built-up would be too slow - it is high above normal already when you start the breath-hold.

We did small study of how long UWH players stayed underwater and it was generally less than 20 seconds and on average less than 7 seconds. But recovery times were also short (average 15 seconds).
Do the authorities try to ban synchronized swimming too? The girls stay underwater in average for ~6 seconds too.

I'm really going to have to see how the Bohr saturation curve plays into our sport. If I could easily argue that to risk management, I''d be ahead of the game.
Try these ones:
http://www.dsls.usra.edu/meetings/bio2001/pdf/128.pdf
http://diss.kib.ki.se/2002/91-7349-314-7/thesis.pdf

Also contact John Fitz-Clarke, he is one of the world's top experts on freediving physiology, and I believe he is located in California, so he perhaps can help you better
 

seanavent

Active Member
Sep 30, 2010
3
0
36
San Francisco
#19
Trux -

I agree on all accounts, but try to get a person who in insurance and has never read a biology text to agree. What I need is simple proof, not theory, to convince them. The 'expert' on their side has a PhD in education and is basically broadening the risk to ANYONE who holds their breath:
Water safety expert Dr. Tom Griffiths of Aquatic Safety Research Group

And yes, pools who were influenced by the Redwoods Group did ban synchronized swimming too. Here's their link:
Breath Holding vs Breathing Control - Aquatics Blog

I'll definitely get a hold of those articles and then speak with John. Again, thanks!

Sean