The Term "SAMBA"

[Cacia]

So, one of the freedivers blacked out Wednesday. I assume it was classic shallow water blackout where the partial pressure of O2 drops precipitously and cannot meet the cellular demands of the brain.

I learned what it looks like ( a slow motion seizure ). His buddy saw it begin around 15ft and grabbed him by the armpit, bringing his airway to the surface. He did not bother dropping the few pounds on his belt but concentrated on using his strength and hold to position his airway high out of the water. His head then fell backwards. I was thinking a rescue breath was in order "any time now" when he came to and started jibberish. About 20 seconds, we decided. It took about an hour for his color to return to normal. He has no memory of the event.

They claim not to feel anything too different before they black out, just narrowed vision. He had asked to borrow my camera and I kept saying "don't drop my camera, bud". He had a little too much drag on the way up.

It's important not to push.

I wonder what the critical (average) depth is when shallow water black out most frequently happens? Does it depend at all on the speed of the ascent, or just the depth where the pressure drops the fastest?

Any precautions you can take?

 

[NJMike]

Can this also occur in a diver who takes a deep breath of air at depth, then does a free ascent to the surface?

 

[dumpsterDiver]

There is no rule of thumb with regard to depth or dive time or even exertion level. Divers need to try not to push their personal limits too hard. However, a diver's personal limit can apparently vary greatly from day to day. Most black outs occur at the surface and very often after the diver has completely surfaced and has already taken a breath or two at the surface. This is counter-intuitive, but just because the diver got some gas exchange at the lungs, doesn't mean that the brain has. It takes a little while for the oxygen level to increase in the brain where it is need to keep someone awake. It is critical that a freediver is closely watched after the ascent for a good 20-30 seconds. Divers have ascended, taken a breath, exhaled and sunk to their death. There are also some more complicated issues associated with blood pressure and blood shift which is also related to why the black-out can occur after the surface is reached (but I don't understand them).

The surface rest interval can be as important as the depth/time, especally for the spearfisherman. Rules of thumb for the surface rest may be like 2 times the dive time or something along that order. The speed of the ascent is probably not related to SWB. Excessive hyper-ventilation is related to it. I can imagine that dragging a camera up from depth could be a major factor, also. A freediver is very streamlimed and efficient and even dragging a 3 lb fish up from depth can make a large increase in exertion level.


From what I understand the first aid for a black out is to support the diver above the water, remove the mask and blow on the face. Supposedly recue breaths are rarely needed because if the diver was retreived immediately after the black out, the air on the face will stimuate breathing.

 

[Dive Right In Scuba]

Can this also occur in a diver who takes a deep breath of air at depth, then does a free ascent to the surface?

I hope that divers exhaling on the way up or bye bye lungs :light:

 

[steve70638]

I hope that divers exhaling on the way up or bye bye lungs

This is about freediving. No lung expansion issues because no breaths are taken under pressure.

 

[H2Andy]

no, NJMike specifically asked about a diver inhaling at depth

only way to do that is scuba ... well... within reason

He has no memory of the event.

that is one lucky sob

I wonder what the critical (average) depth is when shallow water black out most frequently happens? Does it depend at all on the speed of the ascent, or just the depth where the pressure drops the fastest?

Any precautions you can take?

if you dont' skip breathe before free diving, you probably have nothing to worry about,
unless you are trained and can overcome the "urge to breathe" and thus stay down longer while your o2 is depleted.

what happens is that the o2 left in your system on ascent is not sufficient to meet the needs of your brain and it shuts down

this is normally not a problem because the "urge to breathe" (which is controlled by how much CO2 is in your system) will kick in long before there's an issue (unless, like i said, you're skip bretahing or highly trained)

 

[drbill]

Any precautions you can take?

I take the most important one I can think of... I don't do any breathhold free diving, just SCUBA. These blackouts scare me... one of Catalina's dive sites is a pinnacle named after Deputy Bill Kroll who passed away while freediving.

 

[Cacia]

I am trying to get better at freediving. It makes me a little nervous after witnessing that. I am a "fainter" and have fainted about ten times in my life. Standing at the flag pole in camp...boom. Shopping on the north shore...boom. I don't know if it would predispose me to this though, probably a different mechanism.

I was impressed with the rapid response of his buddy. Somebody wearing weights like that would sink right to the bottom pretty fast. AND it is amazing that their laryngospasm keeps the water out. These boys heart rates get down in the 40's.

I am playing with a HR monitor and breathing exercises. I can drop myself into the mid 60's from the 80's but need to learn more about the biofeedback methods. I ordered a book today and I am hoping it will have some techniques.
Those guys say they will teach me... I have my doubts cause they are very athletic. he says you dont have to be in top aerobic shape to get good. And sometimes I see people who don't look like they are, dive pretty deep for a couple minutes.

 

[dumpsterDiver]

Make sure they teach you about the recovery breathing which is done for maybe 10-20 seconds after every dive, I think that it helps to keep the blood pressure up after surfacing and reduces the likelihood of blacking out.