Shallow Water Blackout vs. Deep Water Blackout

[Tratish]

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]

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

[trux]

I touched exactly this topic already once in this thread: http://forums.deeperblue.net/safety/...ing-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/...ing-death.html is quite interesting and may be worth of reading if you are interested in the topic, or concerned about safety

[Adrian]

I'm moving this to the Safety forum to keep it together with all the other similar threads.

[Seacidal]

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]

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.

[trux]

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]

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.

[Erik]

^ agreed ^

[Mafnet]

Wikipedia yet again the purveyor of accurate information

[Erik]

Originally Posted by Mafnet

Wikipedia yet again the purveyor of accurate information

LOL, yeah, if it's on the intardnet, it must be right!