Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada.
Am J Physiol Heart Circ Physiol. 2011 Dec;301(6):H2473-81. doi: 10.1152/ajpheart.00475.2011. Epub 2011 Sep 30.
Shear stress, a mechanical force created by blood flow, is known to affect the developing cardiovascular system. Shear stress is a function of both shear rate and viscosity. While established techniques for measuring shear rate in embryos have been developed, the viscosity of embryonic blood has never been known but always assumed to be like adult blood. Blood is a non-Newtonian fluid, where the relationship between shear rate and shear stress is nonlinear. In this work, we analyzed the non-Newtonian behavior of embryonic chicken blood using a microviscometer and present the apparent viscosity at different hematocrits, different shear rates, and at different stages during development from 4 days (Hamburger-Hamilton stage 22) to 8 days (about Hamburger-Hamilton stage 34) of incubation. We chose the chicken embryo since it has become a common animal model for studying hemodynamics in the developing cardiovascular system. We found that the hematocrit increases with the stage of development. The viscosity of embryonic avian blood in all developmental stages studied was shear rate dependent and behaved in a non-Newtonian manner similar to that of adult blood. The range of shear rates and hematocrits at which non-Newtonian behavior was observed is, however, outside the physiological range for the larger vessels of the embryo. Under low shear stress conditions, the spherical nucleated blood cells that make up embryonic blood formed into small aggregates of cells. We found that the apparent blood viscosity decreases at a given hematocrit during embryonic development, not due to changes in protein composition of the plasma but possibly due to the changes in cellular composition of embryonic blood. This decrease in apparent viscosity was only visible at high hematocrit. At physiological values of hematocrit, embryonic blood viscosity did not change significantly with the stage of development.
切应力是一种由血流产生的机械力，已知它会影响正在发育的心血管系统。切应力是剪切率和粘度的函数。虽然已经开发出了用于测量胚胎中剪切率的既定技术，但胚胎血液的粘度却一直未知，而只是假设与成人血液相同。血液是一种非牛顿流体，剪切率与切应力之间的关系是非线性的。在这项工作中，我们使用微粘度计分析了胚胎鸡血液的非牛顿行为，并在不同的红细胞压积、不同的剪切率以及在从孵化 4 天（汉堡-汉密尔顿 22 期）到 8 天（约汉堡-汉密尔顿 34 期）的不同发育阶段呈现出不同的表观粘度。我们选择鸡胚胎是因为它已成为研究发育中心血管系统血液动力学的常用动物模型。我们发现，红细胞压积随发育阶段而增加。在所研究的所有发育阶段中，胚胎禽类血液的粘度均依赖于剪切率并表现出类似于成人血液的非牛顿行为。然而，观察到非牛顿行为的剪切率和红细胞压积范围超出了胚胎较大血管的生理范围。在低切应力条件下，构成胚胎血液的有核球形血细胞会形成细胞小聚集体。我们发现，在胚胎发育过程中，给定红细胞压积下的表观血液粘度会降低，这不是由于血浆蛋白组成的变化，而是可能由于胚胎血液中细胞组成的变化。这种表观粘度的降低仅在高红细胞压积下可见。在生理红细胞压积下，胚胎血液粘度随发育阶段的变化不明显。
