Douglas Harper's Etymology Dictionary
so called for Italian physician Bartolomeo Eustachio (d.1574), who discovered the passages from the ears to the throat. His name is from Latin Eustachius (see Eustace).
Wikipedia
The Eustachian tube , also known as the auditory tube or pharyngotympanic tube, is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately long and in diameter. It is named after the sixteenth-century anatomist Bartolomeo Eustachi.
In humans and other land animals the middle ear (like the ear canal) is normally filled with air. Unlike the open ear canal, however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The Eustachian tube connects from the chamber of the middle ear to the back of the nasopharynx.
Normally, the Eustachian tube is collapsed, but it gapes open both with swallowing and with positive pressure. When taking off in an airplane, the surrounding air pressure goes from higher (on the ground) to lower (in the sky). The air in the middle ear expands as the plane gains altitude, and pushes its way into the back of the nose and mouth. On the way down, the volume of air in the middle ear shrinks, and a slight vacuum is produced. Active opening of the Eustachian tube is required to equalize the pressure between the middle ear and the surrounding atmosphere as the plane descends. The diver also experiences this change in pressure, but with greater rates of pressure change; active opening of the Eustachian tube is required more frequently as the diver goes deeper into higher pressure.
Usage examples of "eustachian tube".
A connection called the eustachian tube, beginning on the nether side of the eardrum, is linked to a reservoir of air provided by the cavity located just above the roof of your mouth.
When you swallow, the eustachian tube opens and admits enough pressure to equalize the inside and outside pressures.
But during the rapid changes in air pressure that occur during an elevator ride or an airplane dive, the eustachian tube remains closed, and it takes some vigorous swallowing to even things out afterward.
In persons in whom from disease or a cold the eustachian tube is permanently or temporarily closed, the sense of hearing is injured.
He kept swallowing as the pressure increased, to allow his Eustachian tube to open and admit air under higher pressure.
My mouth was performing an automatic yawning and gasping, emptying the Eustachian tube to protect my ear drums and delicate inner ear.
Toytoo inhaled deeply, manipulating his eustachian tube so that smoke squirted in perfect rings from his ears.
A bullet had nicked his left ear, too, and though the wound was superficial, blood followed the folds of the ear, into the resonant depths, half deafening him but also oozing down his eustachian tube and into his throat, causing him to cough in fits.