To assist the clearance of any retained bronchopulmonary secretions. A high expiratory flow rate (simulating a cough) is achieved by applying a positive pressure to the airway, and then rapidly shifting to a negative pressure. Any patient with retained secretions, that is unable to clear secretions due to reduced peak cough expiratory flow (weak or ineffective cough). E.g. Muscular Dystrophy, Spinal Muscular Atrophy, other neuromuscular conditions with some paralysis of the respiratory muscles e.g. spinal cord injury, end stage respiratory disease with fatigue. It can be used effectively with patients with a tracheostomy or non invasively.