Development of a Compact-Sized Falling Needle Rheometer for Measurement of Flow Properties of Fresh Human Blood

A compact-sized falling needle rheometer with rapid operation and automatic flow analysis has been developed for viscometry of fresh human blood without anticoagulant. The volume of a fresh blood sample only needs to be 3 mL, and the measuring time is within 2 min after taking a blood sample from the human body. Measured flow properties of human blood are evaluated as a flow curve, that is, the relationship between the shear stress (τ) and shear rate (γ). Observed flow curves of fresh human blood show three typical fluid regions, that is, the Casson fluid region for a low shear rate range of 0 < γ > 140 s^?1, the transition region for a shear rate near 140 s^?1 < γ < 160 s^?1, and the Newtonian fluid region for a high shear rate range of 160 s^?1 < γ > 400 s^?1. Flow properties of human blood such as the yield stress (τ _y) in the Casson fluid region and the apparent viscosity (μ) in the Newtonian fluid region are measured, and they are compared between male and female blood. It is found that the range of human blood viscosity for males is (5.5 to 6.4) mPa · s, and for females is (4.5 to 5.3) mPa · s. The viscosities of male blood without anticoagulant show higher values than those of female blood. Human blood viscosities with anticoagulant show a lower value than that without anticoagulant. A linear relationship between the hematocrit value, that is, the volume percentage of red corpuscles in the human blood, and the apparent viscosity are observed for both male and female blood. This article is concerned with the flow analysis of fresh human blood viscosity without anticoagulant using a newly developed compact-sized falling needle rheometer.