A blood pump system includes a pump housing and an impeller for rotating in a pump chamber within the housing. The impeller has a first side and a second side opposite the first side. The system includes a stator having drive coils for applying a torque to the impeller and at least one bearing mechanism for suspending the impeller within the pump chamber. The system includes a position control mechanism for moving the impeller in an axial direction within the pump chamber to adjust a size of a first gap and a size of a second gap, thereby controlling a washout rate at each of the first gap and the second gap. The first gap is defined by a distance between the first side and the housing and the second gap is defined by a distance between the second side and the pump housing.
