Sera Toshihiro, Fujioka Hideki, Yokota Hideo, Makinouchi Akitake, Himeno Ryutaro, Schroter Robert C, Tanishita Kazuo
Center for Life Science and Technology, School of Fundamental Science and Technology, Keio University, Yokohama 223-8522, Japan.
J Appl Physiol (1985). 2004 May;96(5):1665-73. doi: 10.1152/japplphysiol.00624.2003. Epub 2004 Feb 6.
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 ( approximately 150 microm ID) and then evaluated the localized compliance as a function of airway generation (Z). For smaller (<300-microm-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 V(1/3) (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.
气道顺应性是理解肺力学的关键因素，并且被用作一项临床诊断指标。从生理和临床角度理解小气道的这种力学特性至关重要。我们已经确定了在“接近”生理条件下小气道的“形态计量学变化”和“局部顺应性”；也就是说，气道被包埋在实质组织中，未进行脱水和固定处理。此前，我们开发了一种两步法，通过用不透射线的溶液对肺组织进行染色，然后使用锥束微焦点X射线计算机断层扫描系统对组织进行成像，从而详细观察小气道（Sera等人，《生物力学杂志》36: 1587 - 1594，2003年）。在本研究中，我们使用该技术分析了同一小气道（内径约150微米）的直径和长度变化，然后评估了作为气道分级（Z）函数的局部顺应性。对于较小（直径<300微米）的气道，在呼气末吸气时直径增大36%，在肺总量时增大89%；长度在呼气末吸气时增大18%，在肺总量时比在功能残气量时增大43%。直径，尤其是较小气道的直径，与V(1/3)（其中V是体积）并非呈线性关系。随着肺内压升高，直径在特定压力下急剧变化，而长度在充气和放气过程中大致呈线性变化。较小气道的气道体积百分比与肺体积百分比并非呈线性关系。随着Z值增加，较小气道通常比较大气道更具顺应性，并且其直径变化表现出滞后现象。较高Z值的气道在较低压力下发生变形，而较低Z值的气道则不然。这些结果表明，较小气道的行为并非均匀一致。
