Measurement of human blood viscosity a using Falling Needle Rheometer and the correlation to the Modified Herschel-Bulkley model equation.

We measured the blood viscosity of 25 male and 25 female healthy people (total 50) using a compact-sized falling needle viscometer (Falling Needle Rheometer) capable of highly accurate measurements. Based on the analysis of the flow characteristics, most of the blood specific non-Newtonian fluid (Casson fluid) behavior was confirmed. Additionally, the blood from males has a higher apparent viscosity and Casson yield value than that from women. Furthermore, a new Herschel-Bulkley type model equation representing the relationship between the shear rate and apparent viscosity of human blood was proposed based on the measured blood flow characteristics. The proposed model improved the exponential term on the shear rate and added the constant term on the yield stress so that the measured value can be correlated with a high accuracy. Using the proposed model equation, the correlation accuracy of all of the measured human blood viscosities was better than in the Herschel-Bulkley model equation and Casson model in a wide range of shear rate regions. By incorporating numerical flow analysis (computational fluid dynamics), this model equation may contribute to analyses considering the non-Newtonian fluidity of human blood.