Study of Whole Blood Viscosity Using a Microfluidic Device

Cardiovascular diseases include a wide range of disorders that affect heart and blood vessels, and are the leading cause of death in the United States. Whole blood viscosity, a parameter to describe the rheologic properties of blood, is an important measure of various cardiovascular diseases. It is used clinically to assess the risks of heart attack, hypertension, thrombosis and strokes. Currently used viscometers measure whole blood viscosity by inducing Couette flow to drive the blood at a certain shear rate. The blood viscosity is derived from the resistance toque measured by the toque sensor integrated within the shaft. Although effective, this method is limited due to the expensive toque sensor and the relatively large amount of blood required. More important, the fluidic conditions within the viscometer are vastly different from those in natural blood vessels (Poiseuille flow), which makes this method inappropriate to predict actual blood viscosity and its effect under natural conditions. In this work, we demonstrate whole blood viscosity measurement from the electrical resistance of the blood sample using a microfluidic device. Since the predominant parameters of the blood viscosity also determine the electrical impedance of the blood sample, the microdevice can be used as a new route of measure for blood viscosity. Blood samples with different hematocrit levels were flowed through a microchannel at different velocities that correspond to different shear rates. The electrical resistance at 20 kHz AC stimulation was recorded and compared with the viscosities measured by a commercialized rheometer. The results showed that the representative rheologic parameters (hematocrit and shear rate) are measurable by the electrical impedance. The correlation between the blood viscosity and the electrical resistance was quantitatively determined by regression analysis with a high determination coefficient. This study provides a solution for low cost, quick measurement of blood viscosity with minimal blood consumption. It also enables the in-depth investigation of blood rheology under in vivo like conditions.