Blood pump

A blood pump system, the system comprising:

• a delivery tube;
• a receiving tube;
• and
• an extracorporeal positive displacement blood pump comprising:
• a first non-return valve;
• a second non-return valve;
• a flexible inner duct providing a blood flow region between the first non-return valve and the second non-return valve,
• an outer duct arranged to surround the flexible inner duct and arranged to accommodate a pumping liquid, the flexible inner duct having a blood inlet for receiving blood from the delivery tube through the first non-return value into the blood flow region, a blood outlet for passing blood out from the blood flow region through the second non-return valve to the receiving tube, the outer duct being a fixed volume and having a liquid port for the pumping liquid, and
• a pump device comprising a piston driven within a piston cylinder, the pump device configured to:
• cyclically deliver and withdraw a controlled volume of pumping liquid to the liquid port by the piston, to cyclically compress and expand the flexible inner duct to urge an equal controlled volume of blood through the blood flow region and to deliver a pulsating blood flow through the blood outlet, the pulsating blood flow having a controlled pulse profile;
• wherein to urge the volume of blood through the blood flow region, the piston is configured to withdraw the volume of pumping liquid from the liquid port when the first non-return valve is open and the second non-return valve is closed, and to deliver the volume of pumping liquid to the liquid port when the first non-return valve is closed and the second non-return valve is open, and
• wherein movement of the piston within the piston cylinder is further configured to control the volume of pumping liquid delivered to the liquid port to vary the volume of blood urged through the blood flow region and to control the pulse profile.