Windberger Ursula, Auer Roland, Seltenhammer Monika, Mach Georg, Skidmore Julian A
Center for Biomedical Research, Medical University of Vienna, Vienna, Austria.
Center for Forensic Medicine, Medical University of Vienna, Vienna, Austria.
Front Physiol. 2019 Jul 17;10:906. doi: 10.3389/fphys.2019.00906. eCollection 2019.
From a certain level of exercise-intensity onward, hematocrit increases in horses, which brings more oxygen carriers into the bloodstream. Camels, however, when used in competitive racing could be even in need of iron supplementation and blood transfusions due to a severe reduction of their available hematocrit compared to their resting hematocrit. Since the extrinsic and intrinsic mechanical properties of camel erythrocytes (RBC) are so different compared to RBCs of other mammals, the question arises whether this observation might be a response to endurance exercise aiming at keeping the RBC count low. Rheometry indicated dromedary camel blood to behave almost Newtonian, which is unique amongst mammals. Shear thinning did increase with the hematocrit, but remained marginal compared to horses. As a result, camel whole blood viscosity (WBV) exceeded horse WBV at high shear rates, an effect, which was significantly augmented when the packed cell volume (PCV) was increased. Therefore, in camels any infusion of RBCs into the bloodstream can increase the cardiac work and the energy input into the endothelium more effectively, which should generate vascular remodeling in the long term. Yielding, however, was completely absent in camel blood, confirming low cohesion between its components at quasi-static flow. Camel blood remained a viscous liquid without a threshold even at unphysiologically high PCVs. This can help to washout lactate when camels start to dehydrate and might contribute to the sustained working ability of these animals. The subtle pseudoplastic behavior and the high viscosity contrast across the RBC membrane point to weak coupling between blood flow and red cell behavior. We predict that RBCs flow as separate entities and can show various types of motion, which can lead to friction instead of being collectively aligned to the flow direction. In comparison to horses, this behavior will become relevant at higher RBC counts in front of flow obstacles and possibly cause vascular remodeling if the PCV rises during strenuous exercise, a matter that should be avoided.
从一定运动强度开始，马的血细胞比容会增加，这会使更多的氧气载体进入血液。然而，骆驼在参加竞技比赛时，由于其可用血细胞比容相较于静息时严重降低，甚至可能需要补充铁剂和输血。由于骆驼红细胞（RBC）的外在和内在力学特性与其他哺乳动物的红细胞有很大不同，因此产生了一个问题，即这种现象是否是对耐力运动的一种反应，目的是保持红细胞计数较低。流变学表明单峰驼血液几乎表现为牛顿流体，这在哺乳动物中是独一无二的。剪切变稀确实随着血细胞比容的增加而增加，但与马相比仍然很微小。结果，在高剪切速率下，骆驼全血粘度（WBV）超过了马的全血粘度，当血细胞压积（PCV）增加时，这种影响会显著增强。因此，在骆驼中，任何向血液中输注红细胞的操作都能更有效地增加心脏工作和内皮细胞的能量输入，并从长期来看会导致血管重塑。然而，骆驼血液中完全没有屈服现象，这证实了其成分在准静态流动下的低内聚力。即使在非生理性的高血细胞压积情况下，骆驼血液仍然是一种没有阈值的粘性液体。这有助于在骆驼开始脱水时清除乳酸，并可能有助于这些动物的持续工作能力。微妙的假塑性行为以及红细胞膜两侧的高粘度差异表明血流与红细胞行为之间的耦合较弱。我们预测红细胞会作为独立的个体流动，并且可以表现出各种类型的运动，这会导致摩擦而不是集体排列成流动方向。与马相比，这种行为在流动障碍物前红细胞计数较高时会变得明显，如果在剧烈运动期间血细胞压积升高，可能会导致血管重塑，这是应该避免的。
