Stress distribution in a three dimensional, geometric alveolar sac under normal and emphysematous conditions

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Authors: Jessica de Ryk, Jacqueline Thiesse, Eman Namati, Geoffrey McLennan

Published Date May 2007 Volume 2007:2(1) Pages 81 - 91

DOI: http://dx.doi.org/10.2147/COPD.S

Jessica de Ryk^1,2, Jacqueline Thiesse^1,2, Eman Namati¹, Geoffrey McLennan^1,2

¹Department of Internal Medicine, University of Iowa Hospitals and Clinics, Iowa City, Iowa; ²Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA

Abstract: Pulmonary emphysema is usually the result of chronic exposure to cigarette smoke in at risk individuals. To investigate the hypothesis that lung damage in emphysema results from coincident weakening in the structural properties of the tissue and increased mechanical forces—as one explanation of the continued development of pulmonary emphysema after smoking cessation—we developed a three dimensional, geometric dodecahedron-based acinar model. Using the model numerical analysis of the stress distribution in normal conditions could be compared with those resulting in emphysematous conditions. Finite element analysis was used to evaluate the model at a number of lung inflation levels, using quasi-static loading of the alveolar pressure. When internal alveolar pressure was increased along with the adjustment of the material properties to represent a weakening of one wall in the acinus, increased stress resulted at the perimeters of the weakened area. In particular this increased stress was localized at the junction points of the internal alveolar septa. It was also found that under the proposed simulated emphysematous conditions, a significant disruption in the stress distribution within the acinus model occurred at low, rather than high, lung volumes. This is supportive of the physiological observation that destruction of the diseased tissue can occur under less stress than those existing in the normal state.

Keywords: alveolar sac, emphysema, finite element analysis, stress distribution, mechanics