Verse 11

तस्य स्पन्दवशादन्तः क्रियावैचित्र्यमीयुषः ।अपानादीनि नामानि कल्पितानि कृतात्मभिः

In plain words

By the power of its vibration, coming within the body to a variety of functions, names beginning with apāna have been given to it by the adepts.