[Uwh-announce] Shallow water blackout.

[Simon Talbot]

Hi Guys – please don't just write this off as something that happens to other people!!!

>From a breath-hold diving perspective, more than three or four deep breaths in a row before a breath-hold dive is considered to be hyperventilation, and can lead to the outcome Mark has described.

I personally know (knew) 3 people who have drowned either in pools or the ocean – almost certainly because of doing this.
I am aware of a heck of a lot more shallow-water blackouts where the individual concerned didn't die – mainly because they were lucky. That includes myself, twice. OK – so I'm a bit slow (and probably a lot slower now than I would have been before the shallow water blackouts! :-)  ).

Cheers,

Simon

From: Mark LEWIS <Mark.Lewis at csiro.au<mailto:Mark.Lewis at csiro.au>>
Date: Wed, 14 Dec 2011 13:36:23 +1100
To: UWH Announce UWH Tasmania <uwh-announce at vm.hovo.id.au<mailto:uwh-announce at vm.hovo.id.au>>
Subject: [Uwh-announce] Shallow water blackout.

I am circulating this document to re-enforce the point that hyperventilating is highly discouraged during training or games of underwater hockey.
Sincerely
                Mark

Shallow Water Black out

Shallow water blackout (SWB) is the sudden loss of consciousness caused by oxygen starvation following a breath holding dive.
Once you lose consciousness you are likely to drown. The blackout occurs quickly, insidiously and without warning. The victims of this condition die without any idea of their impending death.

There are about 7000 drownings in the U.S. annually - many of whom are good swimmers. Craig, in 1976 reported interviews of survivors of near drowning. All had hyperventilated prior to the swim, had the urge to breathe, and had no warning of the impending unconsciousness.

Hyperventilation

Hyperventilation is the practice of excessive breathing with an increase in the rate of respiration or an increase in the depth of respiration, or both. This will not store extra oxygen. On the contrary, if practiced too vigorously, it will actually rob the body of oxygen. Rapid or deep breathing reduces carbon dioxide levels rapidly. It is high levels of carbon dioxide, not low levels of oxygen, that stimulate the need to breathe.

Normally metabolizing body tissues, producing carbon dioxide at a regular rate. Hyperventilation causes some central nervous system changes. Practiced to excess, hyperventilation causes decreased cerebral blood flow, dizziness and muscle cramping in the arms and legs. But moderate degrees of hyperventilation can cause a state of euphoria and well-being. This can lead to overconfidence and the dramatic consequence of a body performing too long without a breath: blackout.

With hyperventilation the body uses oxygen to an extent that they will black out while the carbon dioxide levels have not increased sufficiently to stimulate the urge to breathe. The blackout is instantaneous and without warning. It is the result of a critically low level of oxygen, which in effect, switches off the brain.

While playing underwater hockey we don’t tend to hyperventilate (blow off carbon dioxide) and we have sufficient levels of carbon dioxide from playing the game to trigger the urge to breathe. The problem has occurred during training sessions when people have tried to gain extra distance or time on a breath-hold by first hyperventilating. Two people have died in the last couple of years from this. So DON’T HYPERVENTILATE for breath-hold training.

Reference:

http://www.scuba-doc.com/latenthypoxia.html


Mark Lewis
President
Tasmanian Underwater Hockey
Mob: 0407 879 759


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