This "passive system" is not dependent on the effort of the patient. It uses a compressor to inflate and deflate the vest rhythmically at timed intervals and thus imposes high frequency chest wall oscillations that are transferred to the lungs. These oscillations thin thixotropic airway mucus, facilitating its removal by coughing.
A ThAIRapy Vest can cost up to $16,000. You control the frequency of the air manually.