Shallow Water Blackout Question

[Ghost95]

Good morning all.
I just read this article...

I watched my husband almost die in front of his family on vacation after playfully holding his breath underwater. We're lucky he survived a condition we'd never even heard of.

Erin Watson was frozen to the spot as she watched her father-in-law pull her husband's gray, lifeless body out of the pool at the hotel where they were staying.

www.yahoo.com

and was wondering, is this actually "shallow water blackout" or something else? I thought shallow water blackout had to do with decreasing pressure in addition to excessive hyperventilation not just holding your breath too long.

Just looking to understand.

Have a good day.

 

[Rollin Bonz]

nm...

 

[SpaceCat]

Those yahoo articles are never the most accurate. I am not sure at all about the shallow water blackout aspect of this article as it doesn't mention him hyperventilating prior to diving under, but I do find it a little odd that he went from "dead" to released from the hospital in under 6 hours. Unless he peaced out of the hospital AMA, that doesn't seem like the full/real story.

 

[Ken Kurtis]

I thought shallow water blackout had to do with decreasing pressure in addition to excessive hyperventilation not just holding your breath too long.

The explanation for SWB is actually contained in the article: You burn up all your O2 before you feel the need to breathe and pass you out while still underwater. The reason for this is (even though its not stated in the article) hyperventilation which doesn't "build up" oxygen but severely depresses your starting CO2 level, which then sets up the scenario I just mentioned. So in its simplest form, this article presents itself as a classic case of SWB. Ascending from a depth is not required.

 

[Ghost95]

Ok, thanks for the info.

For some reason I thought I read somewhere that SWB had to do with hyperventilation but also the partial pressures changing during an ascent from a decent depth. It sticks in my mind that most of the SWB seemed to happen at about 15'...but that would also be at the end of the dive.

 

[Eric Sedletzky]

Ok, thanks for the info.

For some reason I thought I read somewhere that SWB had to do with hyperventilation but also the partial pressures changing during an ascent from a decent depth. It sticks in my mind that most of the SWB seemed to happen at about 15'...but that would also be at the end of the dive.

SWB does have to do with ascent and decreasing pressure/and low O2 levels.
If you use up too much oxygen at depth, which can happen when you overstay your safety limit and then ascend, what happens as the pressure reduces as you come up, your lungs will will re-expand sucking up the remaining oxygen out of your muscles/tissues and rob it from your brain thus causing you to black out. 15’ is right in the middle of the depth that has the most change since 33’ is one full ATM, so this where all the bad stuff usually happens.
But it is possible to lose consciousness in shallow water too if you blow off your CO2 first then have the discipline to fight off any urge to breathe.

 

[Ghost95]

Thanks for the additional info.

So is SWB a separate phenomenon from just holding your breath too long or is is the same? It seems different even though the results are the same.

 

[KevinNM]

Blood can hold more oxygen at depth, or under pressure. At some depth, inside recreational depth iirc, your blood plasma can hold enough oxygen to sustain life without any red blood cells. SWB is why people shouldn’t free dive alone.

 

[Trace Malinowski]

Thanks for the additional info.

So is SWB a separate phenomenon from just holding your breath too long or is is the same? It seems different even though the results are the same.

The term "shallow water blackout" is often used by people outside the freediving world for all hypoxic losses of consciousness that happen to breath-hold divers. In the freediving world, it is a specific form of hypoxic loss of consciousness (HLOC).

Obviously, if you stop breathing, you will eventually pass out. How long that will take depends on many factors, but blood gas analysis of physically fit, female Japanese and Korean Ama freedivers who harvest food from the sea on a daily basis show significant levels of hypoxia in just one minute of breath-hold time. These women don't dive very deep (average of just 20 - 30 feet) and don't hold their breath longer than about 40 seconds max. I'm pulling up these numbers from memory. They may not be entirely accurate but you get the idea: shallow dives and short breath hold times. They have a reportedly good safety record over a 2,000 year history.

Western freedivers tend to push breath-hold times in three ways:
1. Static - holding one's breath without moving. This is often how kids and even Navy SEALs die competing to see who can hold their breath the longest. Compared to a car, they just idled until they ran out of gas.
2. Dynamic - swimming underwater while holding one's breath. This is like driving a car. The faster you swim, the more gas you burn because your muscles will demand oxygen.
3. Depth - with depth you also add the compression of one's air spaces due to Boyle's Law. If you have twice the pressure, you reduce the volume by half. 3 x pressure = 1/3 volume. 4 x pressure = 1/4 volume. When the pressure is reduced and these spaces return to normal volume, the tissues around these spaces like those in the lungs and sinuses will draw blood back into them causing a reduced concentration of oxygen in the blood and increasing the risk that you will run out of gas.

They may also employ hyperventilation which reduces the carbon dioxide level in the blood. CO2 stimulates our urge to breathe. It's like tampering with the gas gauge in the car so the needle shows more gas than is in the tank.

The most common freediving accident was in shallow water. If we look at what used to be the most popular freediving activity for decades, underwater hunting, we can see how all of these things come together in one dive.

A spearfisherman hyperventilates before a dive so he doesn't feel uncomfortable while hunting. He gracefully surface-dives and uses little energy to descend to a deep reef. He stays still, holding his breath longer than he should because he feels no urge to breathe, and locates a fish. He then moves slowly to stalk the fish burning a little more oxygen. He fires the spear and now must fight the fish. Struggling with the shot fish burns even more energy. At this point, he may have spent a couple of minutes underwater and now feels the urge to breathe. He begins to ascend more rapidly bringing a large fish with him. His muscles require more oxygen as his large leg muscles work to swim up with the additional drag and weight of a fish. It may even still be alive and he may be working to control it. As his lungs and sinuses return to their normal volume, what little oxygen he has left is further reduced. He passes out within a few feet of the surface in shallow water. This was the most common type of open water freediving blackout outside of depth competitions.

The most common in pools was people either trying to hold their breath for a long time or when swimming the length of a pool with an inefficient stroke that burned a lot of oxygen. Even professional freedivers blackout when performing static and dynamic apnea in competitions. There are videos on YouTube showing lots of blackouts.

All of these are just due to hypoxia but terms like deep water blackout and shallow water blackout are sometimes used to describe the point of the dive where a blackout occurred, and SWBO has just become a generic term for a freediving blackout in layman's terms.

 

[johndiver999]

It is very unusual for a freediver to black out when deep. If that happens they probably had some sort of problem that delayed their ascent or they just way, way over exerted themselves or way over estimated their abilities. So almost all BO occur at or very near the surface and occur during or immediately AFTER completing the ascent. The decreasing partial pressure of oxygen in the brain is the primary cause. At depth, the pressure is higher, so the partial pressure of oxygen is higher as well.
PP is directly related to: (total pressure) X (% of oxygen).

You can also black out while holding your head underwater or swimming horizontally at a shallow depth, but these incidents usually involve someone who is really pushing themselves hard into the uncomfortable zone of Carbon dioxide build up and often did hyperventilation a lot before hand.

If a breathhold black out victim is recovered quickly, it is extremely unlikely that their heart has stopped. They have just suspended breathing and the natural stimulus to resume breathing needs to be initiated right away.

This involves exposure of the face to air, blowing air across it, verbally commanding the diver to breath (often they are blind and paralyzed but can still hear) and tapping their face to "wake them up"... and if all that doesn't work in roughly 15 or 20 seconds, then rescue breaths are indicated while the diver is still in the water.

This video just popped up on youtube.