Old Habits Die Hard: Why Hyperventilating Before A Free Dive Can Be Deadly
Recently, I was on a dive in my local waters. As we came out of the water, around sunset, a couple of speargun fishermen were in the water with us, a bit closer to shore than where we surfaced, floating in the surface spotting for fish below.
We passed them at a good distance to avoid startling any fish and ruining a potential catch, but even from the distance, I could hear one of them take several deep, rapid breaths before he dove down to give chase to a fish.
He came up seconds later with a nice catch, and shortly after, the two fishermen came to shore as well. When they did I asked him about the hyperventilation he had done in the water.
“Yeah,” he said, “it helps me hold my breath longer, because it saturates my blood with oxygen. I’m surprised you haven’t heard of that trick, I got it from a scuba diving textbook.”
A Dangerously Outmoded Idea
He reached into his bag and pulled out and old, dog-eared copy of a entry level scuba diving course textbook from a very well-known scuba diving certification agency.
He flipped to the page that dealt with the snorkeling and skin diving portion, and pointed to the paragraph where it did indeed mention the benefits of hyperventilating before a breath-hold dive.
Problem was, the book was published in 1998. Since then, that particular paragraph has been updated so that it now staunchly warns against hyperventilating before a breath-hold dive.
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What Happens During Hyperventilation
The problem with hyperventilation is that it doesn’t really supersaturate the blood and tissues with oxygen, as was once hypothesized, but rather depletes the bloodstream and tissues of carbon dioxide.
So rather than creating a state of hyperoxia, or excess of oxygen, it really creates more of a state of hypocapnia, or reduced CO2.
Considering that CO2 is only a byproduct of our metabolism, and something that needs to be dispelled when we exhale, that doesn’t sound so bad.
But there’s more to it than that.
Risk Of Hyperventilating Before A Free Dive
A state of elevated amounts of CO2, called hypercapnia, is one of the warning signs our body uses to tell our brain to breathe.
Generally, the urge to breathe that we experience when we hold our breaths, is triggered more by too much CO2, rather than not enough O2 in our bodies.
So by depleting our systems of CO2 by hyperventilating, we risk delaying this reaction, to the point where we have too little oxygen in our systems to remain conscious, before we feel the need to breathe, causing us to suddenly pass out, typically at the end of our dive, what is known as a shallow-water blackout among free divers.
The more aggressively we hyperventilate, the greater the risk.
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Preparing The Right Way
Rather than hyperventilate, a breath-hold diver should breathe normally, seeking to reduce his or her breathing rate and pulse to a slow, relaxed state before diving.
The advice in the textbook represented the best of the knowledge available at the time it was published. It just wasn’t relevant anymore.
And because free diving (whether in the form of actual free diving, snorkeling, or spearfishing) seems so intuitive – after all, we all know how to hold our breaths – people tend to just pick up a bit of knowledge here and there, without a chance to have it verified by a qualified instructor.
This is why it is important to make sure we have the most relevant and updated information possible.
And why I would always recommend taking an introductory course in free diving before attempting breath-hold diving.