any forced expiratory effort against a closed or blocked air passage, as blowing hard with nose and mouth closed during an ascent or descent in an aircraft to equalize pressure in the ears
See Valsalva maneuver in American Heritage Dictionary 4
(văl-sălˈvə)
noun
Expiratory effort when the mouth is closed and the nostrils are pinched shut, which forces air into the eustachian tubes and increases pressure on the inside of the eardrum.
Expiratory effort against a closed glottis, which increases pressure within the thoracic cavity and thereby impedes venous return of blood to the heart.