Patent ID: 8545427

Claim:
A blood treatment apparatus comprising: a blood treatment unit configured to receive untreated blood and fresh blood treatment fluid, and emit treated blood and used blood treatment fluid, a pair of fluid pumps configured to pass the blood treatment fluid through the blood treatment unit, a pair of blood pumps configured to extract the untreated blood from a blood source, pass the extracted untreated blood through the blood treatment unit and deliver the emitted treated blood to a target vessel, wherein each blood pump includes a pump chamber and a flexible member separating the pumping chamber into a blood accumulating container and a working fluid accumulating container, where the flexible member is configured to flex to vary a volume relationship between the blood and the working fluid accumulation containers; a control unit, and a measuring device configured to emit a feedback signal indicative of the amount of working fluid received into or discharged from at least one of the working fluid accumulation containers whereby a mass or volume of the working fluid is determined by the control unit at an arbitrary position of the flexible member.