(408e) Interspecies Variations in Hemorheology and Hemodynamics

Despite significant changes across species in body mass, lifestyle, and anatomy, the composition of blood generally remains constant. Red blood cells (RBCs), the main constituent in addition to plasma, are a common feature to blood for almost all vertebrates and the characteristic biconcave disc shape is present for almost all mammals. When compared to order of magnitude changes in body mass, the changes in RBC size and volume fraction across species are small and do not show any trend with species. Human blood has been widely studied and is known to exhibit complex flow effects under Poiseuille conditions such as the Fahraeus and Fahraeus-Lindqvist effects, a decrease in the local hematocrit and a decrease in the apparent viscosity, respectively. Rheologically, human blood also demonstrates complex behavior including pseudoplasticity, viscoelasticity, and thixotropy. These effects arise primarily because of the ability of human RBCs to aggregate, at low shear rates and in the presence of plasma proteins, into coin stack structures called rouleaux. Across species, the aggregation of RBCs is not a universal feature, and as a result, the flow properties of blood from different species can vary significantly.

In this work, we investigate blood from several species using bulk rheology and microfluidics. We present original measurements on blood viscosity from seven different species under both transient and steady conditions. Using the results, we fit a previously developed model for transient human blood rheology [1] to demonstrate the universality of the model in fitting blood rheology across species and to quantify the changes across species through the physically meaningful parameters. Using a microfluidic flow channel, we also track the RBC free layer that develops for blood flow under Poiseuille conditions as a function of hematocrit, flow rate, and aggregation tendency. The results are combined with computational fluid dynamics simulations to infer the pressure drop and the apparent viscosity. This work aims to bring awareness to the changes in the material properties of blood across species and investigate the evolutionary origin for these changes. By doing so, we can learn about the health implications of changes to blood material properties in an effort to establish guidelines for optimal hemodynamic conditions. Additionally, this work is relevant for clinical drug scaleup as various drugs are first tested on animals and often fail when transitioning across species.

[1] Horner J. S., M. J. Armstrong, N. J. Wagner, and A. N. Beris, J. Rheol., 62(2), (2018).