A blood flow meter includes a rotor configured to be placed within a flow of blood and to be driven to rotate by the flow of blood； a magnetic encoder configured to sense the rotation of the rotor and to generate a rotation signal based on the sensed rotation of the rotor； a first pressure sensor configured to measure an upstream pressure； a second pressure sensor configured to measure a downstream pressure； and a control unit. The control unit is configured to determine a differential pressure, the differential pressure including a difference between the downstream pressure and the upstream pressure； and cause an alteration to the rotation of the rotor based on the differential pressure.
