Impact of Fluid versus Solid Stresses on Air-Blood Integrity

描述(由申请人提供)：机械通气是治疗急性呼吸窘迫综合征(ARDS)患者的关键疗法；然而，已有证据表明，不适当的通风会促进进一步的细胞水平的损伤，导致ARDS样症状的恶化，称为呼吸机诱导的肺损伤(VILI)。在VILI中发现的细胞水平的损伤被认为是循环和流体机械应力的组合导致的，这些机械应力是由于肺泡不张、塌陷和重新开放而产生的。当上皮细胞在过度扩张和收缩过程中暴露在肺泡的周期性拉伸和松弛中时，就会产生固体机械应力(创伤)。液体机械应力在气体-血液屏障完整性的破坏中的作用已被认为是基于液体机械通气治疗过程中的观察结果。在液体通风中，肺泡完全充满了全氟碳化合物，有效地消除了负责大多数流体机械应力的气液界面。这些活体研究表明，仅靠气囊创伤不足以造成VILI所见的空气-血液屏障破坏程度的损害，但缺乏能够复制流体机械应力的体外模型，限制了对ARDS-病理学中流体应力的研究。微流控技术的最新进展使得体外研究流体机械应力在气道损伤发展中的作用成为可能。类似地，当流体在水肿性肺泡内重新分布时，我们假设在所产生的气液界面上将产生高的流体机械应力。在机械通风过程中，当肺泡压力梯度产生时，这种气-液界面以循环方式移动。肺泡囊和导管的小尺寸使气液界面的剪切条件导致细胞损伤和死亡。体内研究表明，这些流体机械应力单独或与循环拉伸(固体机械)相结合的影响，但尚未得到证实。需要的是系统地研究流体机械应力单独以及与固体机械应力(拉伸)联合作用对肺泡上皮细胞的影响。目前的系统缺乏同时研究拉伸和剪切影响的能力。该项目将通过创造具有细胞空气-血液界面的微组织工程化肺泡来填补这一空白，其中生理流体机械事件可以在体外以高度受控的形式在肺泡上皮细胞上重现。作为这种微工程牙槽骨的初步应用，我将单独和联合研究流体流动和循环拉伸的影响。这项提议将专门测试流体机械应力通过一种独立于机械细胞拉伸的机制损害空气-血液屏障完整性的假设。

DESCRIPTION (provided by applicant): Mechanical ventilation is a crucial therapy for patients with acute respiratory distress syndrome (ARDS); however, improper ventilation has been shown to promote further cellular-level injury, leading to an exacerbation of ARDS-like symptoms, termed ventilator-induced lung injury (VILI). Cellular-level damage found in VILI is hypothesized to result from a combination of cyclic and fluidic mechanical stresses generated as atelectactic alveoli collapse and re-open. Solid mechanical stress (volutrauma) occurs as epithelial cells are exposed to the cyclic stretching and relaxation of the alveolus during over-expansion and contraction. The role of fluid mechanical stress in the breakdown of air-blood barrier integrity has been suggested based upon observations during liquid ventilation treatment. In liquid ventilation the alveolus is completely filled with perfluorocarbons, effectively eliminating the air-liquid interface responsible for most fluid mechanical stresses. These in vivo studies suggest that volutrauma alone is not sufficient to cause damage to the degree of air-blood barrier damage seen in VILI, but the lack of in vitro models capable of replicating fluid mechanical stress has limited research on fluid stress in ARDS-pathology. Recent advances in microfluidic fabrication have allowed in vitro study on the role fluid mechanical stress in the development of airway injuries. Similarly, as fluid is redistributed within an edematous alveolus, we hypothesize that high fluid mechanical stresses will be generated at the resulting air-liquid interface. This air-liquid interface moves in a cyclic fashion as alveolar pressure gradients are generated during mechanical ventilation. The small size of alveolar sacs and ducts enables shearing conditions at the air-liquid interface to cause cellular damage and death. The impact of these fluid mechanical stresses independently and in combination with cyclic stretching (solid mechanical) has been suggested by in vivo studies but has not been confirmed. What is required is a systematic study of the effect on alveolar epithelial cells of fluid mechanical stresses individually and in combination with solid mechanical stresses (stretch). Current systems lack the ability to simultaneously study the effects of both stretch and shear. This project will fill this gap by creating a micro- tissue engineered alveoli with a cellular air-blood interface where physiological fluid mechanical events can be recreated over the alveolar epithelial cells in a highly controlled in vitro format. As an initial application of this micro-engineered alveoli, I will study the effects of fluid flow and cyclic stretch independently and in combination. This proposal will specifically test the hypothesis that fluid mechanical stress damages the integrity of the air-blood barrier through a mechanism independent of mechanical cell stretching.