Physiology of Freediving

Pages in this article 1  2   January 1, 2005 5:22 PM

Our bodies are designed to adapt to Freediving. We evolved from an aquatic species into what we are today. This section looks at the effects of increased water pressure and breath holding on our bodies.

Ear pressure
As a Freediver (or a Scuba diver) makes his descent into the sea, the pressure on the outside of the eardrum increases and as a result the eardrum is pushed toward the inside with pain as a result. The diver uses what is known as an "ear pressure equalization" technique, to let air into the middle ear in order to "equalize" the pressure at both sides of the eardrum. A couple of techniques are available but the most common one involves closing the nose while trying to blow air through it. This "artificial" air pressure forces air to the middle ear through the "Eustachian tube".
A piece of history: In the older years, the Greek sponge divers used to "break" their ear drums when they were young by diving in deep waters without using ear pressure equalization (although they knew the technique). By doing so, they wouldn't need to equalize the pressure in their ears anymore. I know it sounds unbelievable, but it's just the truth.

Body Pressure
Imagine the following experiment. A CLOSED plastic container filled with air is slowly submerged in water. As water pressure increases around it, the container is soon or later forced to crush into itself (if the container was not closed, water would go in it and the pressures in and out of the container would be equal). Now think of our lungs as being the plastic container mentioned above. If you are a Scuba diver, you know (or you SHOULD know :) ) that our lungs are not crushed because the air we breathe is equalizing those two pressures (the one on our lungs from the outside and the one inside our lungs). But what happens when you Freedive? Clearly there is no extra air going into our lungs to equalize the pressures. Indeed the lungs get a good squeeze. For years, Doctors used to believe that if Freedivers go deeper than a certain depth, their lungs would "crush" and death would occur. But the Freediving champions proved them wrong. In fact those divers went well deeper than the calculations of Doctors would permit. After further experiments and observations, it was found that a "blood shift" mechanism is present in the human body. As we go deeper in water, blood starts to "shift" from other parts of our bodies and begins to flood our lungs to equalize the outside water pressure. Our heart rate slows down and blood pressure increases. This is why our lungs won't "crush" into themselves as Doctors used to believe.

Interesting note: The same "blood shift" mechanism is present at all sea mammals.

Breath Holding
Holding our breath alone (even without the water pressure) makes our heart rate slow down.

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