Published ahead of print on July 12, 2007, doi:10.1164/rccm.200701-088OC
© 2007 American Thoracic Society doi: 10.1164/rccm.200701-088OC
Airway Strain during Mechanical Ventilation in an Intact Animal Model 1 Department of Medicine and 2 Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee; and 3 Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin Correspondence and requests for reprints should be addressed to Christopher M. Waters, Ph.D., Department of Physiology, University of Tennessee Health Science Center, 894 Union Avenue, Nash 426, Memphis, TN 38163. E-mail: cwaters2{at}utmem.edu Rationale: Mechanical ventilation with large tidal volumes causes ventilator-induced lung injury in animal models. Little direct evidence exists regarding the deformation of airways in vivo during mechanical ventilation, or in the presence of positive end-expiratory pressure (PEEP). Objectives: To measure airway strain and to estimate airway wall tension during mechanical ventilation in an intact animal model. Methods: Sprague-Dawley rats were anesthetized and mechanically ventilated with tidal volumes of 6, 12, and 25 cm3/kg with and without 10–cm H2O PEEP. Real-time tantalum bronchograms were obtained for each condition, using microfocal X-ray imaging. Images were used to calculate circumferential and longitudinal airway strains, and on the basis of a simplified mathematical model we estimated airway wall tensions. Measurements and Main Results: Circumferential and longitudinal airway strains increased with increasing tidal volume. Levels of mechanical strain were heterogeneous throughout the bronchial tree. Circumferential strains were higher in smaller airways (less than 800 µm). Airway size did not influence longitudinal strain. When PEEP was applied, wall tensions increased more rapidly than did strain levels, suggesting that a "strain limit" had been reached. Airway collapse was not observed under any experimental condition. Conclusions: Mechanical ventilation results in significant airway mechanical strain that is heterogeneously distributed in the uninjured lung. The magnitude of circumferential but not axial strain varies with airway diameter. Airways exhibit a "strain limit" above which an abrupt dramatic rise in wall tension is observed.
Key Words: airway strain • wall tension • ventilator-induced lung injury • mechanical ventilation • airway mechanics
This article has been cited by other articles:
|
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
