Elsewhere I ask whether it's sufficient to pray in a whisper. See there, please, for a description of whispering and how it differs from speaking quietly.
Answers to that question indicate that whispering prayers is sufficient. Those answers are IMO not completely convincing; nonetheless, let's suppose whispering prayers is, indeed, a fine way to pray.
My question now is about whispering while inhaling. It is possible — try it! — to whisper while inhaling: the same, or very nearly the same, sound issues as when whispering while exhaling. Would whispering while inhaling be a sufficient way to pray?
Any source or argument is most welcome.