DAN Medical Frequently Asked Questions
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>Middle-ear equalization is a basic, required diver skill that enables the equalization of the pressure in the sinuses and middle-ear spaces with ambient pressure.
>As divers descend in the column of water, environmental pressure increases in a linear fashion at a rate of one-half pound per square inch (PSI) for each foot (0.1 kg/cm2 for each meter) and transmits across the body tissues and fluids. Boyle's law describes how the volume of the gas decreases when pressure increases, if the amount (mass) of gas and the temperature remain the same. The middle ear is a rigid cavity with the exception of the eardrum. So when pressure increases, the only way for the volume to decrease is the bowing of the eardrum toward the middle-ear cavity (unless gas is added to the space). After the eardrum stretches to its limits, further reduction of middle-ear cavity volume is not possible; if descent continues, the pressure in the middle-ear cavity remains lower than its surroundings. Modest pressure difference will cause leakage of fluid and bleeding from the eardrum and mucosa lining the middle-ear cavity (ear barotrauma O'Neil grade 1). When the pressure difference reaches 5 PSI (0.35 bar), the eardrum may rupture in some divers; at a pressure difference greater than 10 PSI (0.75 bar), rupture will occur in most divers (ear barotrauma O'Neil grade 2). In addition, sudden and large pressure changes may cause inner-ear injury.
>So now you understand why during descent you must let more gas into your middle ear to keep the volume of the gas constant and equalize the pressure. A normal middle ear has only one physical communication with the source of additional gas, and that is the Eustachian tube that connects to the nasal cavity (rhinopharynx). Under normal circumstances, the Eustachian tubes are closed, but every time we swallow or yawn, the muscles in our throat allow for a small transient opening that is enough to ventilate our middle ear and compensate pressure.
>Nothing challenges our ears and Eustachian tubes more than scuba and breath-hold diving. To become a safe scuba diver and avoid middle-ear injuries, it is essential that you understand the effects of Boyle's law and learn how to actively let air into your middle ears via the Eustachian tubes. In the following sections, you will find different equalization techniques for you to try.
>On ascent, the surrounding pressure decreases and the pressure in the middle remains higher if the gas has no way to leave the middle-ear cavity. When the pressure in the middle ear exceeds surrounding pressure by 15-80 centimeters of water (cm H2O) which corresponds to an ascent in water of 0.5-2.5 feet, the Eustachian tubes open, and surplus gas escapes. If your ears do not equalize at the same rate and the pressure difference reaches about 66 cm H2O (2 feet), vertigo due to unequal pressure stimulus (alternobaric vertigo) may occur.
>Upper respiratory tract infections, hay fever, allergies, snorting drugs, cigarette smoking or a deviated nasal septum may compromise equalization. When properly employed, the following techniques are effective in middle-ear and sinus squeeze in healthy subjects. Passive: Requires no effort. Occurs during ascent.
>Voluntary tubal opening: Try yawning or wiggling your jaw. Up to 30 percent of divers can successfully master this technique.
>Valsalva maneuver: Pinch your nostrils, and gently blow through your nose.
>Toynbee maneuver: Pinch your nostrils and swallow (good technique if equalization is needed during ascent).
>Frenzel maneuver: Pinch your nostrils while contracting your throat muscles, and make the sound of the letter "k."
>Lowry technique: Pinch your nostrils, and gently try to blow air out of your nose while swallowing (think Valsalva maneuver meets the Toynbee maneuver).
>Edmonds technique: Push your jaw forward, and employ the Valsalva maneuver or the Frenzel maneuver.
# Prior to descent, while you are neutrally buoyant with no air in your buoyancy control device (BCD), gently inflate your ears with one of the listed techniques. This gives you a little extra air in the middle ear and sinuses as you descend.
- Descend feet first, if possible. This allows air to travel upward into the Eustachian tube and middle ear, a more natural direction. Use a descent line or the anchor line to control the speed of descent.
- Inflate your ears gently every few feet for the first 10 to 15 feet.
- Pain is not acceptable. If there is pain, you have descended without adequately equalizing. Ascend a few feet until the pain stops.
- If you do not feel your ears opening, stop and try again; you may need to ascend a few feet to diminish the pressure around you. Do not bounce up and down.
- It may be helpful to tilt the blocked ear toward the surface.
- If you are unable to equalize, abort the dive. The consequences of descending without equalizing could ruin an entire dive trip or cause permanent damage and hearing loss.
- Decongestants and nasal sprays may be used prior to diving to reduce swelling in the nasal and ear passages. If your doctor agrees with your decision to use decongestants, take them one to two hours before descent. They should last from eight to 12 hours, so you don't need to take a second dose before a repetitive dive. Nasal sprays should be used approximately 30 minutes before descent and usually last 12 hours. Take caution when using over-the-counter nasal sprays; repeated use can cause a rebound reaction resulting in increased congestion and possible reverse block on ascent. Decongestants may have side effects. Do not use them before dive if you do not have previous experience.
- If at any time during the dive you feel pain, experience vertigo or note sudden hearing loss, abort the dive. If these symptoms persist, do not dive again and consult your physician.