A rat lung model of instilled liquid transport in the pulmonary airways

When a liquid is instilled in the pulmonary airways during medical therapy, the method of instillation affects the liquid distribution throughout the lung. To investigate the fluid transport dynamics, exogenous surfactant (Su rvanta) mixed with a radiopaque tracer is instilled into tracheae of vertic al, excised rat lungs (ventilation 40 breaths/min, 4 ml tidal volume). Two methods are compared: For case A, the liquid drains by gravity into the upp er airways followed by inspiration; for case B, the liquid initially forms a plug in the trachea, followed by inspiration. Experiments are continuousl y recorded using a microfocal X-ray source and an image-intensifier, charge -coupled device image train. Video images recorded at 30 images/s are digit ized and analyzed. Transport dynamics during the first few breaths are quan tified statistically and follow trends for liquid plug propagation theory. A plug of liquid driven by forced air can reach alveolar regions within the first few breaths. Homogeneity of distribution measured at end inspiration for several breaths demonstrates that case B is twice as homogeneous as ca se A. The formation of a liquid plug in the trachea, before inspiration, is important in creating a more uniform liquid distribution throughout the lu ngs.