Quote:
Originally Posted by gundogger
Well, that may be so if you free dive to set personal records but I only dived, usually, in order to get my dinner. I have shot grouper in Turkey at 50 feet or so in 1956 when compressed air was not easily obtained and one needed to be active underwater for quite some time. No chance for me to relax and as for losing the breathing reflex, in never happened to me.
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That's exactly the opposite case. When you are trying to set a personal record, you usually have buddies and other security measures in place (unless you are a complete fool) and hence can take some risk of blacking out. At spearing, or any diving alone, hyperventilation simply greatly increases the risk of a blackout which is then usually fatal. And hundreds of dead spearos (including some of the best ones) prove it every year.
When I spoke about relaxation, I do not necessarily mean minutes long yoga-like meditations. I mean calming out from inside and forgetting about breath control - when you calm from inside (which you most likely do anyway between the dives, if you are an experienced diver), then the body mechanism starts to ventilate in the optimal way without the need to think about it. That's why I am telling beginners should better forgot about any breath-up and rather concentrate on the piece of mind and relaxation which will care of the breath up automatically, better, and safer.
Experienced divers do it in this way without even being aware of it. The problem is with beginners who either hyperventilate out of fear, or because they think they get more oxygen into the body, or because they know their dive is more comfortable after a hyperventilation. Unfortunately, what they usually do not realize or do not know is that with the hyperventilation they in fact increase their oxygen consumption, while greatly reducing the safety margin and exposing them so to a very serious risk of a fatal blackout.
And you are also not right about the diving reflex - it is well known, studied, and well proven that the diving response (bradycardia, vasoconstriction, blood shift, spleen contraction, etc) are depending on several factors and controlled by different receptors (Pa-O2, Pa-CO2, pH, pressure, temperature, light,...), but one of the most important factors is definitely the CO2. So what happens when you artificially reduce the CO2 level? Naturally, you delay the proper diving response. Of course, it comes anyway (thanks to the other signals), but it won't be as strong and as early as it would be with normal level of CO2.
Additionally, hyperventilation will initially also increase your heart rate and contract the carotids (that's the body reaction on low CO2), so in extreme case you can black out immediately at the beginning of the dive. In any way, the blood supply of the brain is lower than normal after hyperventilation and may lead to incorrect reactions.
Hence, believe me, although it feels easier to dive after hyperventilating, it is much much
much better and safer to avoid it.
