isobar /ī″səbär/ [Gk, isos + barrios, weight] , 1. a line connecting points of equal pressure on a graph, such as lines connecting points of equal carbon dioxide tension on a pH-bicarbonate diagram. 2. (in nuclear medicine) one of a group of nuclides having the same total number of neutrons and protons in the nucleus but so proportioned that their atomic numbers have different values.
