Near-Newtonian Blood Behavior – Is It Good to Be a Camel?

Abstract

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.

Shear Thinning in the Prandtl Model and Its Relation to Generalized Newtonian Fluids

“…It appears obvious that stiff springs have to be used in the Prandtl model to account for the stiff red blood cells of camels. Increasing the (dimensionless) stiffness in the Prandtl model significantly reduces shear thinning, in agreement with the rheology of camel blood [33]. There might be even more details of the rheological response of blood that the Prandtl model is able to reproduce.…”

“…Assume next that the Prandtl model is parameterized to reproduce the rheological response of human blood cells, for which n = 0.5 appears to describe the shear thinning reasonably well [28]. Now, a camel comes along, which happens to belong to a species with extraordinarily stiff red blood cells [33]. It appears obvious that stiff springs have to be used in the Prandtl model to account for the stiff red blood cells of camels.…”

Thermographic ranges of dromedary camels during physical exercise: applications for physical health/welfare monitoring and phenotypic selection

“…Elementary analyses of the biomechanics of gait ( 7 – 9 ), the elastic extension of tendons ( 10 ), the morphology of some parts of the distal skeleton ( 7 , 11 – 13 ), and the pedal anatomy ( 14 ) in one-humped camels shed light on the normal movements, osteomuscular composition, and locomotor adaptations of these animals to sandy terrains in desert ecosystems. More specifically, the repercussions that different exercise conditions have at a biochemical and hormonal level are relatively widely studied ( 15 – 17 ), highlighting the near-Newtonian behavior of camel blood as a response to endurance activities ( 18 ). In regards to animal-dependent factors, Al-Shorepy ( 19 ) concludes that age and sex have a significant effect on racing performance.…”

Comparison of the human’s and camel’s erythrocyte deformability by optical tweezers and Raman spectroscopy

“…Camel RBCs were investigated with varying techniques and modalities such as Klett photometer, 21 microcinematography, 9 flame photometer, 22 sonic irradiation, 17 gel electrophoresis, 6,18,20 viscometric techniques, 5 scanning electron microscope, 6 scanning and transmission electron microscopy, 19 chromatography, 23 blood count, 12 proteomics, 15 and rheometry. 24 These studies focused on osmotic behaviors, susceptibility to direct hemolysin of cobra venom, protein composition, and organization of the membrane, the relationship between cell shape and membrane structure, homeostasis, and viscosity.…”