Measurement of the Effect of Cartilaginous Rings on Particle Deposition in a Proximal Lung Bifurcation Model

Although cartilaginous rings are present in the trachea and main bronchi of actual human conducting airways, and despite previous authors' theoretical predictions that these effects are significant, little systematic experimental study has been conducted to quantify the effects of such localized morphological features on particle deposition. In the present study, the possible effects of cartilaginous rings upon particle deposition in an idealized airway model are investigated experimentally. The airway model includes the oral cavity, pharynx, larynx, trachea, and first three generations of bronchi. Gravimetry is used to determine the deposition of monodisperse aerosol particles with mass median diameters ranging between 2.9–6.3 µm for steady inhalation flow rates of 30 and 60 l/min. Particle deposition efficiency obtained from a model with cartilaginous rings present in the trachea is compared with that from a smooth-walled tracheo-bronchial model. Significantly enhanced deposition fraction in the trachea with cartilaginous rings present in the trachea is observed for all inhalation rates and particle sizes. The data also indicates that the disturbance of the airflow within the trachea by the presence of cartilaginous rings promotes deposition of particles through the entire trachea, but this influence does not propagate to bifurcations further downstream. The present work indicates that cartilaginous rings may be a critical element to be integrated into future modelling of airways due to their significant effect on inhaled aerosol deposition.

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