A blood processing device includes a venous-access device, a blood component separation device, a return line, a draw line, a first pressure sensor, a second pressure sensor, and a first pump. The first pressure sensor is located on the return line between the blood component separation device and the venous-access device, and determines a first pressure. The second pressure sensor is located on the draw line between the blood component separation device and the venous-access device, and determines a second pressure. The first pump is connected to at least one of the return line and the draw line and controls a flow rate within the connected line based on a subject access pressure determined based upon the first and second pressures.
