Middle ear equalization
equalising of pressure in middle ears
Middle ear equalization, also known as ear clearing, is the process of balancing the pressure of gas in the middle ear with ambient pressure. Pressure regulation is principally achieved by passage of gas through the Eustachian tube, which connects the middle ear to the nasopharynx. The tube normally opens intermittently, including during swallowing and yawning, but deliberate equalization may be required when ambient pressure changes more rapidly than normal Eustachian tube function can compensate.
Equalization is particularly important during underwater diving, rapid changes in altitude and aviation, hyperbaric treatment, and work in compressed-air environments such as saturation diving. During an increase in ambient pressure, gas must enter the middle ear to prevent the middle-ear pressure from falling below that of the environment; during a decrease in ambient pressure, expanding middle-ear gas normally vents through the Eustachian tube.
Middle-ear pressure can be equalized naturally by swallowing or yawning, or deliberately using techniques such as the Valsalva, Frenzel and Toynbee manoeuvres and voluntary tubal opening. Failure to equalize can result in middle ear barotrauma. Inner-ear barotrauma may also occur during failed equalization or following forceful equalization manoeuvres, while asymmetric equalization between the ears can cause alternobaric vertigo.
Physiology
The middle ear is a gas-filled cavity separated from the external auditory canal by the tympanic membrane (or 'ear drum'). It communicates with the nasopharynx through the Eustachian tube.
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