Development of miniaturized mass-flow meter for an axial flow blood pump using a curved cannula.

To grasp conditions of patients and implantable artificial hearts, it is important to measure the pump flow rate continuously and noninvasively. In this study, a miniaturized mass-flow meter for discharged patients with an implantable axial flow blood pump was developed. The mass-flow meter makes use of centrifugal force generated by mass-flow rate around the curved cannula. Based on the computational fluid dynamics (CFD) analysis, the prototype miniaturized mass-flow meter was developed. Two strain gauges were adopted as the sensor elements. The first strain gauge, attached to the straight area, measured static pressure. The second strain gauge, attached to the curved area, measured static pressure and the centrifugal force. By subtracting the output of the first strain gauge from the output of the second strain gauge, the mass-flow rate was determined. In the evaluation tests using the mock-up circulation loop, the mass-flow meter was compared to a commercial flow meter. As a result, measurement error was less than 1.0 L/min, and time delay was less than 0.2 s. We confirmed that the miniaturized mass-flow meter could accurately measure the mass-flow rate continuously and noninvasively.