Abstract
During cardiac surgery with cardiopulmonary bypass(CPB), blood viscosity changes as blood temperature and hematocrit values change. Because blood viscosity has a high influence on hemodynamics in surgical patients, it can be a useful parameter during CPB. To measure blood viscosity, a rotational viscometer is commonly used. When using rotational viscometer, blood sampling is required and measuring blood viscosity during CPB in real time is difficult. Thus, blood viscosity is not routinely monitored. In this study, we proposed a system for measuring blood viscosity during CPB in real time and evaluated its performance.We constructed the system by utilizing an extracorporeal ultrafiltration circuit, in which a hemoconcentrator was incorporated. We applied the Hagen-Poiseuille equation to a fluid flowing through the circuit and programmed it to calculate the viscosity of the fluid using the flow rate and the pressure difference between the two sides of the hemoconcentrator.We measured the viscosities of Newtonian glycerin solution, non-Newtonian xanthan gum solution, and bovine blood using this system and a commercially available rotational viscometer. In both measurement systems, we found that the viscosity was approximately constant in the glycerin solution, whereas it decreased with increasing shear rate in the xanthan gum solution and bovine blood. Error rates in both systems were≤±10%. The flow in the hemoconcentrator is laminar and obeys the Hagen-Poiseuille law at a flow rate of 100-500mL/min; therefore, we could efficiently calculate the viscosity using flow rate and pressure difference.The change in blood viscosity during CPB has an influence on systemic vascular resistance and CPB circuit internal pressure. This method will enable us to not only measure blood viscosity during CPB in real time but also accurately assess systemic perfusion, by considering peripheral circulation in patients and blood viscosity in a CPB circuit.
