The representative from Respirtech who is a respiratory therapist visited us last week to train us on my son's vest. He described this technique. He said that air is trapped deep in the lungs. That is why the average person takes a deep breathe every few hours - they need to clear this air deep in their lungs. I think this technique that you all are describing clears the mucus in this area.
Sharon, mom of Sophia, 5 and Jack, 3 both with cf