THE EAR AND PRESSURE
There are 3 main parts to the human ear. The outer ear is the part you see including the hole that goes into the head to the ear drum (tympanic membrane). The middle ear starts on the other side of the ear drum and is a hollow space that is about 1/2" in diameter. The inner ear consists of fluids and solids. Since the outer ear is open to the water there is little concern for pressure-related injuries in it. There is no gas in the inner ear usually so the same is true for that. The middle ear is a gas space and is subject to compression and expansion in accord with Boyle's law.
The Outer Ear is labeled. The Middle Ear is the space to the right of the Ear Drum. The Inner Ear is above the Middle Ear.
On one side of the middle ear is the ear drum. It is a flexible membrane. On the other side is a small tube, the eustachian tube, which connects to the throat above where the back of the mouth is. So, there you have it: Go down in the water and the middle ear tries to contract. The ear drum is pushed inward by the high pressure of the water in the outer ear. The discomfort turns to pain as the ear is being damaged. It takes only a difference in pressure between the water and the middle ear of about 60mm to start feeling pain. That is equivalent to about 2 1/2' of water! As the pain increases more damage is done. If the situation does not change the ear drum could rupture allowing cool water to enter the middle ear. That will cool down the inner ear's semicircular canals (Vestibule). They provide you with orientation. The diver may get dizzy and lose the ability to distinguish between going up and down. This is not a pleasant experience underwater!
It is important to keep the pressure inside the middle ear the same as the ambient water pressure! This will prevent ear barotrauma (baro=pressure-related; trauma= injury). It is also known as, "Middle Ear Squeeze." The eustachian tube is the key. Before the diver descends air should be forced up the eustachian tube to open it up and add pressure to the middle ear. It is best to descend feet first (head up). As the diver descends more air should be forced up the eustachian tube and into the middle ear. This may not always be easy because the eustachian is not totally open in the throat. Air has to be gently forced up the tube. That is best done with a valsalva maneuver: Block the nose, lift the head slightly, and GENTLY blow into the nose. With a round bottom mask the nose may be blocked using both thumbs at the bottom. If there is a nose piece, just pinch the nostrils. After the valsalva maneuver is done the ears should feel normal. If they don't stop descending! Go up a little and try the valsalva maneuver again. Do not descend unless the ears clear and they feel normal. When you feel pain, damage is being done! If you feel pain you have gone too deep and should ascend immediately.
The eustachian tube is almost closed where it joins the throat. That is why it is difficult to get air to go into it and then up into the middle ear. If the pressure in the throat gets too great, and the pressure in the middle ear has not been increased the eustachian tube may close completely and not allow any air to enter it. All it takes is a pressure differential of about 90 mm. That is equivalent to 4' of water! That is why it is important to push air into the middle ear before going down even a few feet. But this has to be gentle. Trying too hard to force air into the middle ear may have the same affect as going too deep before trying to "clear the ears." Some divers are so persistent in trying to force air into the middle ear they actually shut down the entrance of the eustachian tube, just as if they went too deep before trying to clear the ears. The valsalva MUST BE GENTLE! If you hear a crackling sound that indicates the eustachian tube has opened but does not allow the passage of air easily. Take your time on the descent.
A Case in Point: A diver did a back roll off a boat in the Caribbean. He had too much weight on his belt and no air in his BC. His descent was rapid and he could not clear his ears. There was a lot of pain in both ears. Finally at about 25' he did a forceful valsalva. Notice in the diagram below the small stirrup bone (center of diagram) is resting against the inner ear's oval window. When the stirrup pushes against the oval window it moves it inward against the fluid of the inner ear. Since we learned fluid is incompressible, the round window bends outward to prevent damage to the inner ear. If a diver descends without equalizing pressure the stirrup will push quite hard against the oval window and the round window will bulge outward. If a Valsalva is attempted the extra pressure could cause the round window to burst outward. In the above diver's case, the greater pressure in the inner ear caused the round window to rupture. Inner ear fluid (perilymph) flowed into the middle ear. The diver was dizzy for years and his orientation was hampered. An inner ear operation was necessary.
The Oval Window is under the Stirrup Bone (D). The Round Window is the dark oval above the E arrow.
Many divers resort to decongestants prior to diving to reduce any mucus covering the eustachian tube, and to shrink the membranes around the tube to open it up. It usually works. However, if the decongestant wears off during the dive it is possible for mucus to build up again. This could lead to a reverse block, which is explained below. It is also not wise to use nasal decongestants day after day.
There are other methods in getting air to go up the eustachian tube. Yawning and swallowing, not so easy to do underwater, and not as successful with most divers as the valsalva is, can stretch the muscles in the throat which will open the end of the eustachian tube allowing high pressure air to enter the middle ear. Chewing gum on an airplane accomplishes the same thing. Holding the nostrils and making the sound of the letter "K" sometimes works.
The Divers Alert Network (1-919-684-9111) has offered the following methods for clearing the ears:
Reverse blocks occur when air gets into a space on the descent but cannot get out on the ascent. The diver suffering from a reverse block after surfacing usually is grimacing, moving their jaw from side to side, and indicating they are experiencing pain in one or both ears. It can happen in the ear, lung, tooth, sinus, and stomach. In the ear it might happen if mucus is in (or forced into) the middle ear. The air might pass freely by the mucus as the diver descends, but when the ascent is underway the mucus could act as a plug. If the diver continues to ascend the ear drum could rupture outward. In this case, prevention would be to not to do a forceful valsalva maneuver on the descent that could send mucus up the eustachian tube. Treatment would be to descend if pain is felt on the way up, and then ascend very slowly to allow the air to escape without pain. Some divers have found that if a valsalva after going back down it sometimes pushes the mucus block aside. All of this is good reason to avoid running low on air in your scuba tank!
The dark circle represents the area where a Reverse Block could occur.
It has been thought an ear plug, similar to those worn by swimmers, could be inserted in the outer ear in order to prevent pressure on the ear drum. This is foolish. As a diver descends with an ear plug it would be forced into the ear by the water pressure. That would be a serious problem! Since the plug would move into the ear the pressure would still increase so the middle ear squeeze would not have been avoided.
On occasion divers experience a lightheaded, dizzy feeling while ascending. It is caused by the ears not decompressing equally. One ear may clear easily as the diver goes up and the other may be partially blocked. This ascent vertigo usually goes away in less than 1 minute after the diver stops ascending or reaches the surface.
In the unlikely event the diver has serious barotrauma to one or both ears it is imperative professional medical advice is obtained in order to prevent possible permanent damage resulting in hearing loss!
Ear infections are one further consideration in diving. For that matter, whenever you get water in your ears there is a chance an infection may occur. The water can be as clean as distilled or from a filthy sewer pipe. It's the water that causes the problem, not the quality of the water.
Water causes the wax in the outer ear to be removed. The more wax, the more water it will take to remove it. If you keep your ears very clean then it does not take too much water to cause an infection. When the wax is removed the pH of the skin will be changed by water contact and it will support bacteria that are just waiting to make you miserable. If the pH becomes too high (alkaline) bacteria will multiply and create the infection known as "Swimmer's Ear." Once this happens it's time to visit the doctor, go on antibiotics, and stay out of diving for at least 2 weeks!
Divers and swimmers MUST prevent Swimmer's Ear. Religiously, it is important to keep the bacteria from gaining hold. There are at least 2 methods to do that. After each day of swimming, diving, showering, etc. either alcohol or acid must be put in the outer ear. Rubbing (Isopropyl) alcohol will do 2 things: Dry out the ear and kill bacteria. Boric acid, or dilute acetic acid (dilute vinegar), will keep the skin acidic and that will prevent the ear from becoming infected. THIS MUST BE DONE AFTER EVERY DAY OF WATER ACTIVITIES! If you do not have either the alcohol or the acetic acid use white wine. It contains both. If an infection begins neither the alcohol or the acids will do anything to stop it unless you follow a regimen that I cannot publish in this on-line book (call me).