Looks like I may have opened up some good discussion on outer ear blood vessel rupture, but I don’t think we should totally lose track of the main point post. It’s my fault though for stating too many points in the same post. Now granted Eric and Guss have probably killed my prediction about freedivers wearing rigid sealing ear cups, because I didn’t envision outer ear blood vessel rupture.
Middle-Ear Barotrauma, (aka Reverse Squeeze) is defined as an outward bulge of the eardrum. That’s why it’s called Middle-Ear Barotrauma. My theory was that this is not a problem in freediving because the breathing cavities of the diver are not at a high enough pressure to cause it. Outer ear blood vessel rupture actually supports this argument. The problem freedivers are having from reverse squeeze is blood vessel rupture in the outer ear, not the ear drum flexing outward. Once the blood vessel ruptures as Eric stated it filled the outer ear creating ambient pressure and with the low pressure in the middle ear, almost burst the drum by flexing it inward (not outward), until he was able to add air to middle ear by equalizing.
What is amazing to me is the complexity of Eustachian tube function and how much stuff has been written that really didn’t recognize it. The Eustachian tube is actually a combination of a one-way valve, and automatic regulating release valve. It’s a one-way valve in that you are able to add air through it on descent to increase the pressure in the middle ear and then it closes to hold the air pressure in. It’s an automatic regulating release valve in that it allows just the right amount of air to escape to equalize the middle ear to the ambient pressure on the outside of the ear drum. Now that’s quite a feat since the ambient pressure is constantly changing with depth.
In freediving this function ability is crucial, because the breathing cavities (pharynx, lungs, etc.) are at a lower then ambient pressure. Apparently the release is set for slightly higher pressure than ambient. When we equalize and stop, the middle ear pressure is just slightly higher than ambient so that there is a slight outward bulge in the eardrum. This is just enough for us to continue to descend a little further before we have to equalize again, but not enough that it is uncomfortable. This is also what is called over pressuring the ears at the surface. The ear can only be slightly over pressured unless we continue to pressure them through breathing cavity contraction.
Now imagine what it would be like if the E. tubes that stayed open all the time while freediving. Not only would it require constant air pressure from constant muscle contractions of the tongue or lungs (that would waste valuable energy), but it would be almost impossible to regulate it to the constantly changing ambient pressure. So one truth from this is that proper closure of the E. tubes is a crucial in freediving as them opening at the right time.
How this can be applied is to do short quick equalizations and then let the E. tubes do their thing. The military, where the Frenzel technique became popular, recommends that equalization should last no longer than 1½ seconds.
Don
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