The Eustachian Tube: Keeping Air Pressure Equal
The eustachian tube helps maintain equal air pressure on both sides of the eardrum by allowing outside air to enter the middle ear. If the eustachian tube is blocked, air cannot reach the middle ear, so the pressure there decreases. When air pressure is lower in the middle ear than in the ear canal, the eardrum bulges inward. The pressure difference can cause pain and can bruise or rupture the eardrum.