Rochester Institute of Technology, Department of Mechanical Engineering, Kate Gleason College of Engineering, 76 Lomb Memorial Drive, Building 9, Rochester, NY 14623, USA.
J Biomech. 2010 Apr 19;43(6):1039-47. doi: 10.1016/j.jbiomech.2009.12.019. Epub 2010 Jan 29.
Inhaled particles reaching the alveolar walls have the potential to cross the blood-gas barrier and enter the blood stream. Experimental evidence of pulmonary dosimetry, however, cannot be explained by current whole lung dosimetry models. Numerical and experimental studies shed some light on the mechanisms of particle transport, but realistic geometries have not been investigated. In this study, a three dimensional expanding model including two generations of respiratory bronchioles and five terminal alveolar sacs was created from a replica human lung cast. Flow visualization techniques were employed to quantify the fluid flow while utilizing streamlines to evaluate recirculation. Pathlines were plotted to track the fluid motion and estimate penetration depth of inhaled air. This study provides evidence that the two generations immediately proximal to the terminal alveolar sacs do not have recirculating eddies, even for intense breathing. Results of Peclet number calculations indicate that substantial convective motion is present in vivo for the case of deep breathing, which significantly increases particle penetration into the alveoli. However, particle diffusion remains the dominant mechanism of particle transport over convection, even for intense breathing because inhaled particles do not reach the alveolar wall in a single breath by convection alone. Examination of the velocity fields revealed significant uneven ventilation of the alveoli during a single breath, likely due to variations in size and location. This flow field data, obtained from replica model geometry with realistic breathing conditions, provides information to better understand fluid and particle behavior in the acinus region of the lung.
吸入到肺泡壁的颗粒有穿过血-气屏障进入血流的潜力。然而，肺部整体剂量模型并不能解释实验性肺部剂量学的证据。数值和实验研究揭示了一些颗粒输运的机制，但还没有研究现实的几何形状。在这项研究中，从复制的人体肺铸型创建了一个包含两代呼吸细支气管和五个终末肺泡囊的三维扩展模型。采用流动可视化技术来量化流体流动，同时利用流线来评估再循环。绘制路径线来跟踪流体运动并估计吸入空气的穿透深度。这项研究表明，即使在剧烈呼吸的情况下，紧邻终末肺泡囊的两代呼吸细支气管也没有再循环涡流。佩克莱数计算结果表明，对于深吸气的情况，体内存在大量的对流运动，这显著增加了颗粒进入肺泡的穿透深度。然而，即使在剧烈呼吸的情况下，颗粒扩散仍然是颗粒输运的主要机制，超过对流，这是因为吸入的颗粒不能仅通过对流在单次呼吸中到达肺泡壁。对速度场的检查揭示了单次呼吸中肺泡的通气明显不均匀，这可能是由于大小和位置的变化所致。从具有现实呼吸条件的复制模型几何形状获得的这个流场数据，可以更好地了解肺部腺泡区域内的流体和颗粒行为。
