Effects of volume replacement fluids on blood flow in-vitro and in-vivo

从物理角度来看，红细胞（rbc）是高度可变形的物体，可以通过毛细血管和小于自身直径的收缩。它们由一个由聚合光谱网络支撑的脂质双层膜组成，它包裹着含有血红蛋白的内部液体。由于红细胞的高可变形性，它们与流动有强烈的相互作用，并且根据流动的类型，预测和观察到许多不同的形状，无论是在简单剪切流动还是在泊泽维尔流动中。从这个意义上说，红细胞是研究流体与软结构相互作用的一个很好的模型系统。在生理血管流动中，大多数压降发生在毛细血管上，一次只有一个细胞可以通过，但流场与壁面的相互作用引起了额外的复杂性。在这种强约束下，即使在稳定流动中，也观察到细胞形状从简单振荡到混沌的强烈时间动态。生理流动通常是不平稳的，要么是由于心脏的脉动，要么是由于毛细血管网络的复杂性导致的流动不规则，其中局部密度波动导致严重的压力和流速波动。细胞悬浮在含有大约8%大分子蛋白质的水介质——血浆中。它们引起红细胞之间的强烈吸引，导致聚集，这是导致血液明显剪切变薄的原因。至少在伸长流动中，等离子体也具有粘弹性。在临床上严重失血导致休克的情况下，采用不同的溶液替代血容量。这些包括晶体，基本上是离子缓冲液和胶体（所谓的等离子体膨胀剂），它们由大分子组成，因此表现出维持较高等离子体肿瘤压力的能力。我们将通过实验研究单个红细胞在体外微流体几何和体内仓鼠模型脉动流中的时间动力学。我们的目标是了解不同的复苏液体和粘弹性模型溶液对血液流体力学的影响。我们也对病理性红细胞对血流特性的影响感兴趣，这具有激励的临床意义。在许多血液疾病中，红细胞改变其形状和柔韧性，产生高度改变的流变学和流体动力学特性。同样，我们想研究聚合物替代液的应用是否会导致体内体积流速的改善，至少是暂时的。

Red blood cells (RBCs) are from a physical point of view highly deformable objects that can pass capillaries and constrictions smaller than their own diameter. They consist of a lipid bilayer membrane that is supported by a polymeric spectrin network, which encloses the inner fluid that contains hemoglobin. Due to their high deformability, RBCs interact strongly with the flow and depending on the type of flow many different shapes have been predicted and observed, both in simple shear and in Poiseuille flow. In this sense, RBCs serve as an excellent model system to study fluid with soft structure interaction. In physiological vascular flow most of the pressure drop occurs along capillaries, where only one single cell can pass at a time, but the interaction of the flow field with the wall induces an additional complexity. In such strong confinements a strong temporal dynamic of the cell shape ranging from simple oscillations up to chaos is observed, even in steady flow. Physiological flow is generally unstationary, either due to the pulsation of the heart or due to flow irregularities caused by the complexity of the capillary network, where local density fluctuations lead to severe pressure and flow rate fluctuations. The cells are suspended in an aqueous medium, the plasma, that contains about 8% of macromolecular proteins. They cause a strong attraction between RBCs leading to aggregates that are the cause of the pronounced shear thinning of blood. At least in elongational flow, the plasma has viscoelastic properties, as well. In the clinical situations of severe blood loss and the resulting shock, different solutions are used to substitute the blood volume. These include crystalloids that are basically ionic buffers and colloids (so-called plasma expanders), which consist of macromolecules and, thus, exhibit the capability to maintain a higher plasma oncotic pressure. We will experimentally study the temporal dynamics of single RBCs in pulsating flow in-vitro in a microfluidic geometry and in-vivo in a hamster model. Our goal is to understand the effect of different resuscitation fluids and viscoelastic model solutions on the fluid mechanics of blood. We are also interested in the effect of pathological RBCs on the flow properties, which has motivating clinical implication. In many blood diseases, RBCs change their shape and flexibility yielding highly altered rheological and fluid dynamical properties. Again, we want to study if the application of polymeric replacement fluids might lead to a, at least temporal, improvement of the volumetric flow rate in-vivo.