Flow Separation, an Important Mechanism in the Formation of Mean Pulmonary Pressure During High-Frequency Oscillation

[+] Author and Article Information
E. H. Bush, P. F. Niederer

Institute of Biomedical Engineering and Medical Informatics, University of Zürich and Swiss Federal Institute of Technology, 8092 Zürich, Switzerland

D. R. Spahn, E. R. Schmid

Institute of Anesthesiology, University Hospital, 8091 Zürich, Switzerland

J Biomech Eng 111(1), 17-23 (Feb 01, 1989) (7 pages) doi:10.1115/1.3168333 History: Received May 17, 1988; Revised November 01, 1988; Online June 12, 2009


Mean pressures within the lungs and lung volume, respectively, are clinically important parameters. During ventilation by way of high-frequency oscillation (HFO), these parameters have been shown to be strongly frequency dependent. To identify mechanisms leading to mean pressure formation during HFO, findings of the theory of stationary flow were extended to oscillatory flow by a quasi-stationary approach. To confirm the theoretical findings, in-vitro experiments on HFO-models were performed. Flow separation was found to be an important mechanism in the formation of mean pressure. Flow separation causes a significant flow resistance, which may be distinctly different for in- and outflow. During oscillatory flow, a mean pressure difference thus results. This mechanism is of particular importance in bifurcations, which are present in the HFO-circuit as well as in the airways. With the direction-dependent flow separation, a general mechanism was found, which accounts for differing mean pressure values within the lungs with different HFO-circuits. This mechanism also contributes to interregionally different mean pressure values within the lungs.

Copyright © 1989 by ASME
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