The process of breathing out while holding the nostrils closed and keeping the mouth shut, used in order to test the functioning of the Eustachian tubes or to adjust the pressure in the middle ear.
This is carried out by closing the mouth, holding the nose and attempting to blow hard. The manoeuvre raises pressure in the chest and, indirectly, the abdomen and forces air from the back of the nose down the eustachian tube to the middle ear. This latter effect can be used to clear the tube during descent in an aircraft, when it sometimes becomes blocked or partially blocked, producing differential pressures on the two sides of the eardrum, usually accompanied by temporary pain and deafness.
An intentional effort to exhale while the air passage is blocked is known as this maneuver. It occurs naturally, for instance, at the onset of a sneeze, when you try to exhale while keeping the vocal cords tightly closed. When consciously executed by clamping the nose shut and keeping the mouth closed, this technique can help avoid pressure-induced damage to the eardrums.