The eustachian tube is a selective valve that allows air to enter behind the sealed eardrum. The eustachian tube connects the back of the nose to the middle ear. The eustachian tube replaces the air the body absorbs from the middle ear. The eustachian tube also equalizes the pressure changes in the outside air. This is what causes the "popping" that people describe when going up or down in the mountains or an airplane. The ability to "pop" the ears is very beneficial.

Have you noticed that hearing is worse just before your ears pop? This is because of the property called compliance. If the air pressure is not equal on both sides of the eardrum, the ear drum will not move or vibrate efficiently (reduced compliance). The eustachian tube maintains the optimal compliance by keeping the air pressure outside the ear the same as air pressure inside the ear. The end result is that the eustachian tube preserves and maintains optimal hearing.

If the eustachian tube is not functioning properly, due to a cold, allergies or other illnesses that affect the throat, it will not open as often as it should. The result of this malfunction is a hollow sounding voice, a feeling of something blocking your ear canal and if it open for an extended period of time fluid may build up behind the eardrum.