By Fred Bove, M.D., Ph.D.
One of the most discussed problems with diving is that of ear injuries. This has been a topic of numerous Skin Diver articles, but it needs to be reviewed periodically because of the number of ear injuries, and the fact that most divers will eventually have an ear injury of some sort that interferes with diving. The ears are most susceptible to injuries related to changes in pressure because they are organs that depend on pressure for their function.
Because the eardrum is sensitive to minute pressure waves, the large changes in pressure that we impose on the eardrum during diving can exceed the range of normal pressures sensed by the eardrum, and injury can result.
The eardrum is protected from large changes in pressure by having a passage from the throat to the middle ear (the Eustachian tube) that allows the pressure on both sides of the drum to equalize (see figure). When the pressures are equal, no disturbance of the drum occurs, and all is well. If the pressure across the eardrum is increased to about two pounds per square inch (PSI), at about five feet of depth, the eardrum will be displaced more than normal, and a sensation of fullness or pain will result. When the pressure difference across the eardrum reaches about five PSI, at a depth of about 11 feet, the drum is in danger of being torn or ruptured. These facts are translated into real experience in what we call ear squeeze. The official name is barotitis, or ear injury due to pressure. Ear squeeze usually occurs during descent through the first 10 to 15 feet from the surface, where volume of gas is changing rapidly with depth. Examination of Boyle's law shows that air volume changes occur to the greatest degree near the surface, so injury resulting from gas volume changes will be most evident there.
Ear squeeze is most common on descent when air in the middle
ear cannot be equalized with the ambient air because of obstruction of the Eustachian tube. If the pressure continues to increase, the drum will rupture.
Ear squeeze is well enough known to physicians that it has been categorized into various levels of severity. One grading classification proposed by Teed provides five grades of severity, ranging from mild redness of the eardrum to hemorrhage and rupture. Examining the eardrum with an otoscope allows the physician to determine the grade of injury and provide treatment accordingly. Severity levels beyond Teed 2 usually are severe enough that the accompanying inflammation causes swelling and closure of the Eustachian tube. Equalization becomes impossible, and diving cannot be done until the injury resolves. Many diving vacations have turned into land tours because of ear squeezes occurring on the first dives.
Besides the injury that develops from descent, it is also possible to sustain an ear squeeze during ascent. This is called a reverse squeeze, is much less common and is due to the inability to open the Eustachian tube during ascent. Since the Eustachian tube is easy to force open by a small rise in middle ear pressure during ascent, reverse squeeze is uncommon. Reverse squeeze can also occur if the external ear canal is blocked during descent. A tight fitting wetsuit hood or earplugs will cause this problem.
Round Window Rupture
A more serious form of ear barotrauma occurs when the round window to the inner ear ruptures due to pressure and volume changes on descent. The event is caused by forceful Valsalva maneuvers while descending with a blocked Eustachian tube. The pressure in the middle ear is below ambient pressure because of the blocked Eustachian tube. The forceful Valsalva maneuver causes a sharp rise above ambient in the pressure of the inner ear fluid (endolymph). The pressure difference between the increased endolymph pressure and the low inner ear pressure is often adequate to rupture the round window (see figure). This is a sudden event that may cause dizziness, vertigo, loss of hearing and buzzing in the ear (tinnitus). Rupture of the eardrum may or may not occur. The rapid onset of symptoms often causes disorientation of the diver. Some divers do not notice the symptoms until ascent at the end of the dive.
Ear squeeze is best prevented by avoiding diving when the nose and throat are inflamed. This will occur with upper respiratory infections and allergies. Mild decongestants are helpful. Clearing your ears using a gentle Valsalva maneuver on the surface is a good test of your ability to clear. Descending feet first and equalizing continuously during descent will prevent ear squeeze. Don't continue to descend if your ears hurt. At depth, you can open the Eustachian tube only with a forceful Valsalva maneuver, and you risk a round window rupture. If an ear begins hurting, ascend about two feet, or until the pain disappears, try again to equalize, then descent slowly with frequent efforts to equalize before pain occurs.
An experienced diver should not get an ear squeeze. If clearing cannot be done on the surface, it surely cannot be done at depth, and diving should not be done that day. Clearing continuously from the surface to the bottom should become a habit that will prevent serious ear injuries. You can find more on ear injury at our web site www.scubamed.com.