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Chapter 4- Diving Physiology Diving Physiology 125 Ear Drum tubes to transfer air into your middle ear from your mouth. During ascent, you reverse the process, allowing middle ear air to exit through your Eustachian tubes. If you do not allow equalization, unequal pressure created across your ear drum (tympanic membrane) can cause it to bulge painfully, even break. If you delay ear clearing during descent, ambient pressure can seal your Eustachian tube closed, preventing equalization. This condition is termed the trapdoor effect. Some divers attempt to overcome a trapdoor effect by a forceful Valsalva equalization maneuver. The increased pressure in your throat seals the opening even more tightly. During ascent, you can get a painful reverse block or reverse ear squeeze if air cannot escape through your Eustachian tube. Reverse blocks usually occur when you dive with a sinus infection or a cold. In what we currently (though incorrectly) call the Valsalva equalization maneuver, you breathe out against a closed mouth and nose. Pressure builds up, transferring Auditory Nerves Cochlea (Hearing Organ) air through your Eustachian tubes, but occasionally enough to create barotrauma. On an interesting note, the technique originally described by Italian anatomist Antonio Maria Valsalva, was to forcibly exhale against a closed glottis, which would not equalize your ears. The technique we call the Valsalva for diving may have been developed by English physician Joseph Toynbee, who also developed another maneuver that we call the Toynbee, described below in “Prevention.” Effects: Pain and a feeling of fullness in your ear. If your ear drum ruptures, it will not only hurt, but cold water rushing into your middle ear can produce vertigo (a whirling sensation) by stimulating the semicircular canals in your inner ear, which control your equilibrium. You may have hearing loss, ear ringing, and may wind up spitting blood that drains into your throat through your Eustachian tube. FIGURE 4-13. ANATOMY OF THE EAR. Oval Window Round Window Eustachian Tube to Throat Semicircular canals


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