Blood viscometer using capillary blood flow under disposable compliance pump

Blood viscosity is considered a promising indicator of cardiovascular disease and helps predict disease risks. However, conventional methods require two highly precise pumps to maintain consistent flow rates in co-flowing streams. In this study, a low-cost and disposable compliance pump was fabricated by inserting three components (a syringe needle, a blood-loaded syringe, and an air compliance unit [ACU]) into a three-way valve. Since the pump induces transient blood flow, accurately obtaining the transient flow rate is necessary. A correction factor was employed to improve the blood velocity obtained by microparticle image velocimetry. Air pressure inside the ACU was estimated using the ideal gas law. A discrete fluid circuit model was constructed to estimate the flow rate and pressure in a microfluidic channel. Four types of fluid physical properties (fluid resistance, fluid viscosity, time constant, and compliance coefficient) were obtained by analysing flow rate and pressure. The proposed method was employed to detect several types of suspended blood (variations in haematocrit, thermal-shocked RBCs, and RBC aggregation-enhanced blood). From the quantitative comparison, the proposed method provides better results than the previous method. Therefore, the proposed method is a promising tool for detecting biophysical variations in suspended blood.