When a liquid is instilled in the pulmonary airways during medical therapy, for example surfactant replacement, the method of instillation plays an important role in the distribution of the liquid throughout the lung. The resultant distribution depends on the flow dynamics of the instilled liquid, which are complex and not well understood. To investigate the fluid transport dynamics, a mixture of an exogenous surfactant (Survanta, Ross Labs) and a radio-opaque tracer (meglumine diatrizoate, 0.6g/ml) was instilled into the tracheas of vertical, excised rat lungs. The lungs were ventilated at 40 breaths/min with a 4ml tidal volume. Two instillation methods are compared: For Case A, the instilled liquid initially drains by gravity into the upper airways followed by inspiration; for Case B, the liquid initially forms a plug in the trachea, followed by inspiration. The instillation process was continuously recorded using a micro-focal, x-ray source and an image-intensifier, CCD image train. Recorded video images were digitized and analyzed. The dose transport dynamics of the first breath are quantified through statistical measures, and compared to a simple theoretical model of liquid plug propagation. A homogeneity index of liquid distribution is measured at the end of each breath, and Case A and Case B results are compared. The initial formation of a liquid plug in the trachea, prior to inspiration, is important in creating a more uniform distribution of the instilled liquid throughout the lungs. Support: NIH-HL41126, NSF-9412523, Ross Laboratories, Dept. of Vet. Affairs, and W.M. Keck Foundation.
Cassidy, K. J., J. L. Bull, M. R. Glucksberg, C. A. Dawson, S. T. Haworth, R. Hirschl, and J. B. Grotberg. A rat lung model of instilled liquid transport in the pulmonary airways. J. Applied Physiol., Submitted.
Video of liquid transport in rat pulmonary airways: Case A (7.8 Mb, Quicktime)
Video of liquid transport in rat pulmonary airways: Case B (7.6 Mb, Quicktime)