An action performed by forcefully exhaling against a closed airway that increases pressure in the middle ear and also increases intrathoracic pressure that dramatically affects venous return, cardiac output, arterial pressure, and heart rate.  This is usually done with the nostrils and mouth, or the glottis, closed.  This maneuver can be used as a diagnostic tool, treatment aid, or to clear the ears.  Often people perform this maneuver unintentionally when they cough, sneeze, gag, vomit, bend, engage in sexual intercourse, strain during urination or a bowel movement, lift heavy objects, or get off a bed using their arm and upper trunk muscles.