How to assess black out risk in DYN

[PhilippeB]

Hi - I am training regularly dynamic apnea with a monofin in a pool and I was wondering is there is a way to feel when I am close to a black out? Are there symptoms appearing like the vision field becoming smaller or other signs that would tell the diver to surface? I find it hard to know how far to push given that I can feel the lack of oxygen but don't receive any "alarm" that tells me my body desperately needs air at some point

Any advice would be greatly appreciated!

Thank you,
Philippe

 

[yunuschiro]

hey philippe, never train apnea alone. thats rule number one. and not two people are the same.

 

[Eran]

There is no reliable way to predict a B/O that is why ppl get them more than once.. If there were a way, you would get it only once and then know how to avoid it.
The only way to deal with them (if you do not want to avoid them by not diving...) is to dive with a buddy.
The problem is that when your brain is low on O2 and a B/O is close, your decision making process is impaired as you are low on O2, so you can not avoid it... you can learn to know the feeling of being on the last bits of lucidity, but its very tricky...

 

[cdavis]

Phillipe,

There are a fair number of experienced competition type divers who report being able to distinguish between the feeling of hi c02 and the feeling of low 02. Most of that experience came from having a fair number of BOs. I suspect you won't be able to reliably tell the difference yourself well enough to do something about it without that kind of experience.

Search everything posted by EricF, Mullins, Tony Babowicz. It will take a while, but you should find some of what you are looking for.

We are assuming you dive with a trained buddy, nuf said.

Connor

 

[PhilippeB]

Thank you for your comments, this is helpful

... and of course, I am not practicing alone :+)

 

[MikkoP]

I get quite clear symptoms from hypoxia. The most easily noticeable thing is the greyout, which is "transient loss of vision characterized by a perceived dimming of light and color, sometimes accompanied a loss of peripheral vision" (Wikipedia). Other signs are tingling in the fingers and just this strange hypoxic feeling that is hard to describe. For some reason I get the signs a bit more clearly and slower when doing dynamics than statics.

I've found that quite an easy way to get used to those feelings and learning to interpret them is to try to get yourself a packing blackout. The symptoms appear the same way in packing blackout and hypoxic blackout, except in a packing blackout it's possible to push the feeling a bit further without actually blacking out. Sometimes after packing you can actually completely lose your vision, yet still remain conscious. That's not possible with hypoxia. Sometimes I also get the greyout when I suddenly stand up after sitting or lying for a long time, especially if I'm dehydrated.

Of course, I don't recommend anyone to actually black out while doing those "exercises", so when you start to feel the symptoms, crouch or do some hook breaths. Or both. This way you can combine two exercises, learning to notice the signs before a blackout and teaching yourself to do hook breaths when you are close to the limit. Very useful.

One more important point is that no matter how well you know the warning signs, you will almost inevitably ignore them completely if you set yourself a spesific target before the dive. If you have already decided that you will try and go for distance X, you will go for it and while focusing on the meters and thinking how much more you still have to dive, you won't be able to recognize any of the signs. Or even if you recognize, you will just ignore them. That is just how your mind works. That's why I always try not to think about the meters at all during the dive or before it. I just try to decide that I will dive until I get the feeling I have to come up. And then I come up. That way I have done all my personal bests, because I don't have to stress and worry about the result, so the oxygen consumption is lower. I just dive and the result comes, well, as a result. In competitions this approach can be very difficult to execute, but it's what I always try to do.

 

[Tony Babowicz]

There is no reliable way to predict a B/O that is why ppl get them more than once.. If there were a way, you would get it only once and then know how to avoid it.
The only way to deal with them (if you do not want to avoid them by not diving...) is to dive with a buddy.
The problem is that when your brain is low on O2 and a B/O is close, your decision making process is impaired as you are low on O2, so you can not avoid it... you can learn to know the feeling of being on the last bits of lucidity, but its very tricky...

+1 for this post. Also good points in Mikko's post. Setting goals and target can easily lead to a blackout. When you learn to tolerate the discomfort of high CO2, you can easily misjudge your limits. I have bo'd on swims that I should have had no problem with. You can function under hypoxia for quite some time. If I came up with the first sign of hypoxia, I would be many meters short of my personal best.Ultimately, you want to train with someone who knows your "body language" and can alert you to when you need to come up. Subtle signs like deteriorating technique are a good sign to stop.
Here is video of a blackout. It should have been a routine swim, but as you can see, it didn't end well. When I go over this swim in my mind, I'm not sure if I would have pulled off a good surface protocol anywhere after 150m. Just one of those days I guess. Be sure to train with a competent safety....

 

[PhilippeB]

Thank you Tony and Mikko for your thoughtful posts. I am not at the point yet where I can tell the difference between high CO2 or hypoxia but I did experience a bit of greying out a couple of times and that was for me the sign to surface. I do also experience (rarely) greyout/restricted vision field when I am very tired and I stand up suddenly but they have been a lot more intense than when I am swimming. I found the analogy interesting. I also liked the point of goal vs. feeling. So far, I have been trying to listen to my feelings rather than get to a distance and I will keep it that way :+)

The video of the black out is very intriguing as the BO happens several seconds after restarting the breathing

 

[Tony Babowicz]

Thank you Tony and Mikko for your thoughtful posts. I am not at the point yet where I can tell the difference between high CO2 or hypoxia but I did experience a bit of greying out a couple of times and that was for me the sign to surface. I do also experience (rarely) greyout/restricted vision field when I am very tired and I stand up suddenly but they have been a lot more intense than when I am swimming. I found the analogy interesting. I also liked the point of goal vs. feeling. So far, I have been trying to listen to my feelings rather than get to a distance and I will keep it that way :+)

The video of the black out is very intriguing as the BO happens several seconds after restarting the breathing

Actually , I never did get a breath in. I exhaled and it was pretty much lights out after that. The video has a 3 second audio delay and you might hear breathing, it's just not mine.