Viscosity control for a mock circulation thus plays an important role for assessing the required motor current of ventricular assist devices. The influence of different viscosities on the measured head pressure is negligible. At a flow rate of 5 L/min, both show a deviation of roughly 15 and 10% in motor current for high rotor speeds.
Two rotary blood pumps that are in clinical use are tested at different viscosities. The control response has no overshoot and the settling time is 8.4 min for a viscosity step of 0.3 cP, equivalent to a hematocrit step of 3.6%. With a mixture ratio of 49 mass percent of aqueous-glycerol solution, the controller can mimic a viscosity range corresponding to a hematocrit between 29 and 42% in a temperature range of 30-42☌. The results obtained with different fluid viscosities show that a viscosity controller is vital for repeatable experimental conditions on mock circulations. To that end, an existing mock circulation was extended with an industrial viscometer, temperature probes, and a heating nozzle band. This method makes use of the relationship between temperature and viscosity of aqueous-glycerol solutions and employs the automatic control of the viscosity of the fluid. This article presents a method to control the viscosity in a mock circulation. Additionally, the solution needs to be exchanged to account for changing viscosities when mimicking different hematocrits.
Due to evaporation and temperature changes, the viscosity of the solution drifts from its initial value and therefore, deviates substantially from the targeted viscosity of blood. An aqueous-glycerol solution is commonly used to mimic the viscosity of blood.
A mock circulation allows the in vitro investigation, development, and testing of ventricular assist devices.
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