Suitability of Bronchoscopic Spraying for Fluid Deposition in Lower Airway Regions: Fluorescence Analysis on a Transparent <i>In Vitro</i> Airway Model.

<b><i>Introduction:</i></b> Bronchoscopic spraying has potential for the application of therapeutic drugs in distal regions of the lung by bypassing the upper airways. However, there is a lack of understanding about the underlying fluid transport phenomena that are responsible for the intrapulmonary propagation of applied liquid. <b><i>Methods:</i></b> By using a transparent airway model, this study provides first experimental insights into relevant transport phenomena of bronchoscopic spraying. Furthermore, the penetration depth of the application is quantitatively evaluated. Laser-induced fluorescence is used to analyze fluid propagation in the transparent channels. Potential influencing factors such as the positioning in different airways, application number, breathing pattern, and lung obstructions are varied within this study to determine their influence on liquid deposition. <b><i>Findings:</i></b> This study shows that the method of bronchoscopic spraying allows the application of liquid in distal regions of the airway model. The position of the bronchoscope is a key influencing factor in increasing the penetration depth. We found that fluid transport along the distal airways essentially occurs by the film and plug flow phenomenon during application, which is similar to the transport mechanisms during instillation. Liquid plugs in lower airways are responsible for the reorganization of liquid during proximal movements and thereby influence the penetration depth in subsequent applications.