Henry F S, Haber S, Haberthür D, Filipovic N, Milasinovic D, Schittny J C, Tsuda A
Molecular and Integrative Physiological Sciences, Department of Environmental Health, Harvard School of Public Health, Boston, MA 02115, USA.
J Biomech Eng. 2012 Dec;134(12):121001. doi: 10.1115/1.4007949.
In an effort to understand the fate of inhaled submicron particles in the small sacs, or alveoli, comprising the gas-exchange region of the lung, we calculated the flow in three-dimensional (3D) rhythmically expanding models of alveolated ducts. Since convection toward the alveolar walls is a precursor to particle deposition, it was the goal of this paper to investigate the streamline maps' dependence upon alveoli location along the acinar tree. On the alveolar midplane, the recirculating flow pattern exhibited closed streamlines with a stagnation saddle point. Off the midplane we found no closed streamlines but nested, funnel-like, spiral, structures (reminiscent of Russian nesting dolls) that were directed towards the expanding walls in inspiration, and away from the contracting walls in expiration. These nested, funnel-like, structures were surrounded by air that flowed into the cavity from the central channel over inspiration and flowed from the cavity to the central channel over expiration. We also found that fluid particle tracks exhibited similar nested funnel-like spiral structures. We conclude that these unique alveolar flow structures may be of importance in enhancing deposition. In addition, due to inertia, the nested, funnel-like, structures change shape and position slightly during a breathing cycle, resulting in flow mixing. Also, each inspiration feeds a fresh supply of particle-laden air from the central channel to the region surrounding the mixing region. Thus, this combination of flow mixer and flow feeder makes each individual alveolus an effective mixing unit, which is likely to play an important role in determining the overall efficiency of convective mixing in the acinus.
为了了解吸入的亚微米颗粒在构成肺气体交换区域的小囊（即肺泡）中的命运，我们计算了肺泡管三维（3D）节律性扩张模型中的气流。由于朝向肺泡壁的对流是颗粒沉积的先兆，本文的目的是研究流线图对沿腺泡树的肺泡位置的依赖性。在肺泡中平面上，再循环流型呈现出带有停滞鞍点的封闭流线。在中平面之外，我们没有发现封闭流线，而是发现了嵌套的、漏斗状的螺旋结构（让人联想到俄罗斯套娃），这些结构在吸气时指向扩张的壁，在呼气时背离收缩的壁。这些嵌套的、漏斗状的结构被空气包围，空气在吸气时从中央通道流入腔室，在呼气时从腔室流向中央通道。我们还发现流体颗粒轨迹呈现出类似的嵌套漏斗状螺旋结构。我们得出结论，这些独特的肺泡流动结构可能对增强沉积具有重要意义。此外，由于惯性，嵌套的、漏斗状的结构在呼吸周期中会稍微改变形状和位置，从而导致气流混合。而且，每次吸气都会从中央通道向混合区域周围的区域输送新鲜的含颗粒空气。因此，这种气流混合器和气流输送器的组合使每个肺泡成为一个有效的混合单元，这可能在决定腺泡中对流混合的整体效率方面发挥重要作用。
