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1Center for Life Science and Technology, School of Fundamental Science and Technology, and 7Department of System Design Engineering, Keio University, Yokohama 223-8522; 4Advanced Computing Center and 5Integrated V-CAD System Research Program, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198; and 2Life and Environmental Science Division, Japan Synchrotron Radiation Institute (SPring-8), Hyogo 679-5198, Japan; 3Biomedical Engineering Department, The University of Michigan, Ann Arbor, Michigan 48109-2099; and 6Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
Submitted 17 June 2003 ; accepted in final form 18 December 2003
Airway compliance is a key factor in understanding lung mechanics and is used as a clinical diagnostic index. Understanding such mechanics in small airways physiologically and clinically is critical. We have determined the "morphometric change" and "localized compliance" of small airways under "near"-physiological conditions; namely, the airways were embedded in parenchyma without dehydration and fixation. Previously, we developed a two-step method to visualize small airways in detail by staining the lung tissue with a radiopaque solution and then visualizing the tissue with a cone-beam microfocal X-ray computed tomography system (Sera et al. J Biomech 36: 1587-1594, 2003). In this study, we used this technique to analyze changes in diameter and length of the same small airways (
150 µm ID) and then evaluated the localized compliance as a function of airway generation (Z). For smaller (<300-µm-diameter) airways, diameter was 36% larger at end-tidal inspiration and 89% larger at total lung capacity; length was 18% larger at end-tidal inspiration and 43% larger at total lung capacity than at functional residual capacity. Diameter, especially at smaller airways, did not behave linearly with V1/3 (where V is volume). With increasing lung pressure, diameter changed dramatically at a particular pressure and length changed approximately linearly during inflation and deflation. Percentage of airway volume for smaller airways did not behave linearly with that of lung volume. Smaller airways were generally more compliant than larger airways with increasing Z and exhibited hysteresis in their diameter behavior. Airways at higher Z deformed at a lower pressure than those at lower Z. These results indicated that smaller airways did not behave homogeneously.
soft tissue; morphometry change; tissue elasticity; surface tension
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