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Hey Heart, Slow Down !!!

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New Member
Sep 11, 2003

I want to know if this happened to you. When I take a really (really) deep breath (or packing), my heart starts to go fast and sometime, what I see is...nothing...everything is black for a couple of seconds...no lost of conscience but I think I'm not very far of it. It doesn't happen often and, most interesting, never happened while I was underwater. It only happens during dry static session...Btw, no hyperventilation...:confused:

This is pretty common...packing causes a drop in blood pressure...off the top of my head I believe that it is called hypocapnia. The reduction of CO2 in the body results in vasoconstriction in the cerebral blood vessels...effectively decreasing the blood flow to your brain and resulting in blackout.
I am far from an expert on the subject so hopefully someone a bit more knowledgable on freedive physiology will add their info.

hope this helps-

Also-Be careful packing and diving....just slowly increase your number of packs over time, I have heard of people passing out in the first few meters of their dive due to this. Hyperventilation results in hypocapnia as well, so be really careful combining the two.

Dive safe!
Common experience, especially if you have been sitting for a long time. Sitting, without movement, causes your adrenal glands to shut off. Once you inhale, the pressure on your heart causes the adrenals to excrete various adrenalin compounds to increase the BP in your head; however since your adrenals have shut off from long sitting, the process is delayed, and the BP compensation is delayed; combined with the slight hypocapnia from the deep breath, the result can be fading vision and eventually a blackout. I actually blacked out from a deep breath while I was driving once! Scary.

Eric Fattah
BC, Canada
In addition I will said the high pressure in the thoracic cavity after packing can be the cause of the symptoms.
Usually you pack after a full inhalation. At full inhalation the alveolus are fully distended and the capillars get compressed, so the blood that goes from lung to left ventricle is less, and the Cardiac Output (the volume of blood ejected after contraction) is less. After you pack, the pressure in the thorax is higher than usual and it affects the venous blood that comes to the rigth ventricle, the Cardiac Ouput of it is less, so less blood goes to the pulmonary circulation, and less bood will reach the left ventricle.
Finally your left cardiac output is so low that you faint (BO)
I used to have the same problem with packing, and just two packs would bring me close to BO, but after plenty of practise I can now do five or six packs with no problems, and I always do this for long statics.

When this happened I did not let go of any air, and always went on to do a good static!!!

Thanks a lot guys,

Eric, your explanation is very interesting. This is probably why I never BO underwater and happens only while I'm sitting/laid on bed. Thanks to all of you.

Oh yeah, Eric, don't dive and drive !!! :naughty ;)
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