do you to the HTS in conjunction with your airway clearance? i find that if i just do the saline (i do 7%) that it does work but not as well as when i do it while i'm doing my vest. this is just for me personally and probably isn't true across the board but you could see if that helps....obviously if you use the acapella or something like that for airway clearance you couldn't do them at the same time so try what amy said and do it before the acapella/flutter/pep etc.