Hypercapnic blackouts - warning signs?

[mystiach]

Hi,

Sorry if there's a thread on this already, but I couldn't find one.

Due to having no buddy, my pool training is all technique based, with some hypercapnic exercises thrown in. I'm friends with one of the lifeguards, and swim in the outer lane where he keeps an eye on me if I say I'm doing something that *may* be slightly risky, but generally I'm not doing anything that could be cause for concern.

I normally warm up with a CO2 pyramid, 1km, freestyle starting breathing 6 and going up to 14 and back to 4. 14 strokes would take me about 20 seconds, give or take. I'd just like to add here that when I used to seriously swim, I'd breathe unusually infrequently, 9-11 strokes, and this is when I was 11, so I have trained like this for years and years, without even a clue that this could cause blackout until I started freediving a few months ago! So this pyramid doesn't go near my limits. Anyway, today I was feeling good (despite having eaten right before getting in the pool - sigh) so went up to 16. I am really certain that I wasn't hypoxic, but I just had a feeling that something didn't feel quite right, and I didn't know if it was a signal I might be close to hypercapnic blackout. Or it might have been the sushi :head

Are there any specific signs of hypercapnia to the point of BO? I'm not sure if the type of training I was doing would allow for enough CO2 to create that situation. Deep (obviously not full) exhale and inhale every max 30 seconds, swimming at medium pace. Any advice is, as always, gratefully received

Cheers

EDIT: When I started these pyramids, I asked a physiologist/sport scientist about the risk of hypercapnic blackout in this situation and he said it would be really unlikely - if this is not true, I really want to know about it! Safety first!!!!! And, if anyone could outline a situation that they have had or seen hypercapnic blackout I'd be really interested.

 

[Rik]

I don't have any experience with hypercapnic black-outs. I haven't had one myself, nor have I seen one in my environment. I however do have some experience with high levels of CO2, and the danger of them. In my experience it works like a narcotic, and can cause misjudgment and erratic behavior.

Although I am likely to agree with the sports scientist, I would recommend to adapt your training if you would experience the narcotic effects. The narcotic state could cloud your judgement when starting with your next training routine after the pyramid exercise. Misjudgment is something to avoid, because you don't have a fully committed safety diver during your training.

 

[BennyB]

Hi Mystiach,

Where do you train in Australia (suburb and/or city)? I might be able to put you onto some freedive buddies so you don't have to train alone.

Cheers,
Ben

 

[trux]

Eric Fattah could write some info about hypercapnic blackout - I remember he already posted about it in the past, so you may be able to find it in the archive.

However, at the intensive hypercapnic exercises, despite the high level of CO2 (and hence higher tolerance against hypoxia), you are not safe from a hypoxic blackout at all. No only that during the short recoveries, the body does not have enough time to recharge oxygen stores, but because of the high hypercapnia, the Bohr saturation curve is shifted, and the affinity of hemoglobin to oxygen reduced. That's very good thing in deep hypoxia, since it protects you against blackout, by better discharging oxygen from blood where it is needed, but it is very bad for recoveries, because you are not able to bind oxygen on hemoglobin in blood, and hence leaving for the next dive already pretty hypoxic. Hence intensive hypercapnic training is not as safe as one often learns, and can lead to a plain hypoxic (not hypercapnic) blackout too. I am not aware of any such case, but felt personally already pretty close a few times.

Strong headaches are another sign of excessive hypercapnic training - so if you get some during an exercise, you better interrupt it and get some rest.

 

[mystiach]

Thanks Trux, I was concerned that something like this may be the case. I looked through trying to find some info that Eric had written, but maybe the posts are so old the search function isn't finding them or they are in relation to other things (eg packing BO). Do you know the specific thread/s?

Re. hypoxia - in this situation, did you feel the usual symptoms of a hypoxic blackout? One breath every 25 seconds (at the peak of the pyramid) doesn't seem like a long 'dive', and I am swimming at cruise speed, so not really expending much energy. Is my body really so unable to utilise the oxygen? I don't feel any of the hypoxic sensations I get when doing long DYN or DNF. I also think the way I breathe might help - I exhale over 2 or 3 strokes so I can take a full inhale. When most people swim, they exhale and inhale on the breath stroke, which means that they never really take a proper breath (I see it all the time!). Sorry for all the questions, but I'm still learning about this - if it's ridiculous, please correct me!

I might try with a buddy, keep upping the number of strokes, and see if I can reach BO, and then at least I will have some idea of what it feels like. I really think I'll have to bail due to discomfort long before I reach the point of hypercapnic BO or hypoxia. If I feel ultra-motivated and do it I'll keep a sensation log to keep y'all informed

 

[mystiach]

Strong headaches are another sign of excessive hypercapnic training - so if you get some during an exercise, you better interrupt it and get some rest.

I get occasional headaches from dehydration, but I have never had a headache appear during a hypercapnic exercise - if so I'll bail!

Cheers!