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Effect of ventilation rate on instilled surfactant distribution in the pulmonary airways of rats

¹Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109, ²Marquette University and Medical College of Wisconsin, Milwaukee 53201; ³Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin 53295; and ⁴Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208

Submitted 12 June 2003 ; accepted in final form 10 February 2004

Liquid can be instilled into the pulmonary airways during medical procedures such as surfactant replacement therapy, partial liquid ventilation, and pulmonary drug delivery. For all cases, understanding the dynamics of liquid distribution in the lung will increase the efficacy of treatment. A recently developed imaging technique for the study of real-time liquid transport dynamics in the pulmonary airways was used to investigate the effect of respiratory rate on the distribution of an instilled liquid, surfactant, in a rat lung. Twelve excised rat lungs were suspended vertically, and a single bolus (0.05 ml) of exogenous surfactant (Survanta, Ross Laboratories, Columbus, OH) mixed with radiopaque tracer was instilled as a plug into the trachea. The lungs were ventilated with a 4-ml tidal volume for 20 breaths at one of two respiratory rates: 20 or 60 breaths/min. The motion of radiodense surfactant was imaged at 30 frames/s with a microfocal X-ray source and an image intensifier. Dynamics of surfactant distribution were quantified for each image by use of distribution statistics and a homogeneity index. We found that the liquid distribution depended on the time to liquid plug rupture, which depends on ventilation rate. At 20 breaths/min, liquid was localized in the gravity-dependent region of the lung. At 60 breaths/min, the liquid coated the airways, providing a more vertically uniform liquid distribution.

surfactant replacement therapy; respiratory distress syndrome; drug delivery; exogenous lung surfactant; liquid bolus instillation

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