Mobilization of mucus by airway oscillations.

The effects of high frequency asymmetric airway oscillations on mucus clearance were evaluated in excised tracheas of sheep, in an animal model of excessive mucus production, and in patients with bronchiectasis. Asymmetric high frequency ventilation (15 Hz) with expiratory biased flow profiles (expiratory peak-flow greater than inspiratory peak-flow) could move mucus droplets towards the pharynx in rigid and flexible tracheas by gas-liquid interaction. In rigid tracheas the mucus was transported towards the periphery of the model lung if the oscillations were inspiratory biased. In very collapsible tracheas, however, even inspiratory biased oscillations moved the mucus cephalad. Parameters influencing direction and speed of mucus are airflow profile, peak-flow, airway compliance and lung resistance. Gamma-camera studies showed that in anesthetized dogs radiolabeled artificial mucus followed the direction of the bias during high frequency ventilation. In five human volunteers with bronchiectasis and excessive secretions the asymmetric airway oscillations were superimposed during spontaneous breathing using a mouthpiece. Airway wall vibrations following the pressure swings of the oscillator could be observed. During forced expiration inward bulging of the posterior membranes of trachea and bronchi occurred at the negative pressure phase of the oscillations. This event was associated with increased appearance of sputum in the central airways. We conclude that high frequency ventilation with asymmetric flow profiles applied via tube or mouthpiece might be an effective future treatment of mucostasis.