Etymology

ortho- +‎ -pnoea, from Ancient Greek ὀρθόπνοια ‎(orthópnoia, “breathing only in an upright posture”), from ὀρθός ‎(orthós, “straight”) + πνοή ‎(pnoḗ, “breath”).

Pronunciation

See full workup of the variants at Wikipedia > Shortness of breath > Collation of -pnea transcriptions.