WordNet records no synonym and no antonym for blood pressure. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the pressure of the circulating blood against the walls of the blood vessels; results from the systole of the left ventricle of the heart; sometimes measured for a quick evaluation of a person's health
“adult blood pressure is considered normal at 120/80 where the first number is the systolic pressure and the second is the diastolic pressure”
Synonyms, antonyms and the broader and narrower relations for blood pressure come from Princeton University’s WordNet. Full sources and licences.