Then let a man meditate on the udgîtha (Om) as vyâna indeed. If we breathe up, that is prâna, the up-breathing. If we breathe down, that is apâna, the down-breathing. The combination of prâna and apâna is vyâna, back-breathing or holding in of the breath. This vyâna is speech. Therefore when we utter speech, we neither breathe up nor down.

In plain words: One should also meditate on Om as vyana, the held breath. Breathing out is prana and breathing in is apana; the pause between them is vyana. Speech happens in that pause, because when we talk we neither breathe in nor out.