Anomalous Shear Transience for Low Shear Rate Confined Blood Flows

The rheological properties of blood are linked to cardiovascular diseases and are potential diagnostic tools. One measurement challenge identified by current guidelines for hemorheology is anomalous, nonmonotonic transience in low-shear rate step-down viscosity measurements. This thixotropic behavior complicates the determination of steady shear viscosity and is considered a consequence of rouleaux formation. This study hypothesizes that transience is a direct consequence of rouleaux kinetics and examines the shear rheology of equine red blood cell suspensions with and without rouleaux formation. Further investigations into sedimentation and radial migration are conducted to test alternative hypotheses. A two-fluid model suggests that shear migration amplified by rouleaux formation is responsible for this transience, which is further confirmed by microfluidic measurements. This result supports conventional methods to extract steady shear viscosity from hemorheology protocols, thus enabling the development of future correlations between low-shear rheology and disease states.