"of or pertaining to the lungs; affecting the lungs; done by means of the lungs," 1704, from French pulmonaire and directly from Latin pulmonarius "of the lungs," from pulmo (genitive pulmonis) "lung(s)," cognate with Greek pleumon "lung," Old Church Slavonic plusta, Lithuanian plaučiai "lungs," all from PIE -*pl(e)umon- "lung(s)," literally "floater," suffixed form of root *pleu- "to flow."
The explanation behind the proposed PIE etymology is the fact that, when thrown into a pot of water, lungs of a slaughtered animal float, while the heart, liver, etc., do not. Compare Middle English lights "the lungs," literally "the light (in weight) organs." Also see pneumo-.
<a href="https://www.etymonline.com/word/cardiopulmonary">Etymology of cardiopulmonary by etymonline</a>
Harper, D. (n.d.). Etymology of cardiopulmonary. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/cardiopulmonary