SUPERIMPOSED OSCILLATIONS ENHANCE THE CLEARANCE OF MUCUS SIMULANT AT LOW AIR FLOWS IN A RIGID TRACHEAL MODEL

摘要

Clearance of mucus by the beating action of cilia is the primary means of removing inhaled particulates and airway debris from airways in healthy people. However many pulmonary diseases are associated with impaired mucociliary clearance mechanisms. For these patients, cough is the default airway clearance mechanism. Unfortunately most pulmonary disease patients can only produce low expiratory flow rates and have difficulty coughing for this reason. Mucus is viscoelastic gel that shows a very rapid decrease in dynamic viscosity (shear thinning behavior) with increasing frequency and much less increase in elasticity Because of this change with oscillations, it is possible that airway oscillations may alter the properties of mucus such that it is more easily cleared by cough mechanics. Simulated airway mucus also has been shown to couple with airflow during cough at a more vertical angle This effect was attributed to a change in the aerodynamic shape of the aliquot of mucus due to gravity Airway oscillations (wheezes and rhonchi) have long been used as a physical diagnostic sign that indicates airway narrowing and/or hypersecretion of airway mucus. Our study demonstrates that thick more solid like mucus (SM) simulating the secretions of COPD patients moves upward against gravity at flows as low as 60 LPM when 5 Hz oscillations are superimposed. Not only does net upward movement occur but the SM moves as a coherent glob. More liquid like mucus simulant (LM) that may represent the mucus in healthy conditions backslid under similar conditions of bias flow, and required much higher cough transient flows (over 200 LPM) to move upwards against gravity; when LM moved it did not move as a coherent glob but rather, smeared along the tracheal model. These data support the conclusion that superimposition of airway oscillations facilitates cough clearance and that airway oscillations are not just a marker for disease but serve an important physiologic function.