Eustachian tube patency refers to how much the Eustachian tube is open. The Eustachian tube runs between the middle ear and the throat. It controls the pressure behind the eardrum and middle ear space, and helps keep the middle ear free of fluid.
The Eustachian tube is normally open, or patent. However, ear infections or altitude changes can increase pressure in the ear, causing the eustachian tube to become blocked.