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TECHNICAL PAPERS: Fluids/Heat/Transport

Flow Limitation in Liquid-Filled Lungs: Effects of Liquid Properties

[+] Author and Article Information
Joseph L. Bull1

Department of Biomedical Engineering,  The University of Michigan, Ann Arbor, MI 48109

Craig A. Reickert, Stefano Tredici, Eisaku Komori, David O. Brant, Ronald B. Hirschl

Department of Surgery,  The University of Michigan, Ann Arbor, MI 48109

Elizabeth L. Frank, James B. Grotberg

Department of Biomedical Engineering,  The University of Michigan, Ann Arbor, MI 48109

1

Contact information: Joseph L. Bull, Ph.D., Assistant Professor, Department of Biomedical Engineering, The University of Michigan, 1107 Gerstacker Bldg., 2200 Bonisteel Blvd., Ann Arbor, MI 48109. Telephone: 734-647-5395; fax: 734-936-1905; electronic mail: joebull@umich.edu

J Biomech Eng 127(4), 630-636 (Feb 06, 2005) (7 pages) doi:10.1115/1.1934099 History: Received April 29, 2004; Revised February 06, 2005

Flow limitation in liquid-filled lungs is examined in intact rabbit experiments and a theoretical model. Flow limitation (“choked” flow) occurs when the expiratory flow reaches a maximum value and further increases in driving pressure do not increase the flow. In total liquid ventilation this is characterized by the sudden development of excessively negative airway pressures and airway collapse at the choke point. The occurrence of flow limitation limits the efficacy of total liquid ventilation by reducing the minute ventilation. In this paper we investigate the effects of liquid properties on flow limitation in liquid-filled lungs. It is found that the behavior of liquids with similar densities and viscosities can be quite different. The results of the theoretical model, which incorporates alveolar compliance and airway resistance, agrees qualitatively well with the experimental results. Lung compliance and airway resistance are shown to vary with the perfluorocarbon liquid used to fill the lungs. Surfactant is found to modify the interfacial tension between saline and perfluorocarbon, and surfactant activity at the interface of perfluorocarbon and the native aqueous lining of the lungs appears to induce hysteresis in pressure–volume curves for liquid-filled lungs. Ventilation with a liquid that results in low viscous resistance and high elastic recoil can reduce the amount of liquid remaining in the lungs when choke occurs, and, therefore, may be desirable for liquid ventilation.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of setup for flow limitation experiments. A computer-controlled piston pump provides constant flow expiration. Pressure and flow data is acquired via an A/D converter and data acquisition system.

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Figure 2

Sketch of model geometry. The alveoli are modeled by a compliant sphere and the airways by a rigid tube. The thoracic cavity is modeled as a rigid box containing the pleural fluid and lungs. Gravity acts normal to the trachea as in the experiments.

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Figure 3

Pressure–volume curves for PFC-filled lungs. The pressure was measured relative to the pressure at a lung volume of 15ml∕kg, and hence all curves pass through the point (0, 15). Hysteresis is apparent in the curves for each PFC.

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Figure 4

Flow versus time data for the calculation of airway resistance. A typical plot is shown for PFOB. The solid line indicates the experimental data and the dotted line indicates the fit to the data. The fit to the data provides RC for the experiment, and R could be determined since C was already measured. Airway resistance, R, was calculated for each experiment and was then averaged to provide an average resistance for each PFC. (a) Plot with a linear scale on both axes; (b) log-linear plot of the same data.

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Figure 5

The volume of PFC remaining at choke, Vch, versus expiratory flow rate, Q, a comparison of theory and experiments. Vch was lowest for PFOB and highest for PFDEC.

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