WordNet records no synonym and no antonym for vital capacity. 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 maximum amount of air that can be exhaled after a maximum inhalation (usually tested with a spirometer); used to determine the condition of lung tissue
Synonyms, antonyms and the broader and narrower relations for vital capacity come from Princeton University’s WordNet. Full sources and licences.