Control system for driving fluids through an extracorporeal blood circuit

1. A photopheresis method comprising:

providing a disposable kit and a non-disposable tower;

withdrawing whole blood from a patient;

adding anticoagulant to form a mixture;

pumping the whole blood-anticoagulant mixture through the cassette to the centrifuge separation bowl;

operating the separation bowl until air in the bowl is displaced into the plasma bag;

collecting separated plasma in the plasma bag while continuing to pump the mixture into the bowl;

mixing plasma with priming fluid;

when a selected amount of plasma is collected, returning plasma to the patient at the same rate as incoming whole blood until red blood cells are detected at a bowl sensor;

withdrawing red cells and pumping at a speed controlled so as to maintain the red cell line at the sensor interface level;

mixing the withdrawn red blood cells with plasma from the plasma collection bag and returning the red blood cells-plasma mixture to the patient;

at a selected time, continuing to pump whole blood into the bowl while discontinuing withdrawing and pumping red blood cells, thereby causing the red blood cells to push buffy coat out of the bowl past the sensor into the buffy coat collection bag until a selected amount is collected;

discontinuing collection of buffy coat when red blood cells have been detected;

injecting photoactivation chemical into the buffy coat in the buffy coat collection bag;

recirculating buffy coat between the collection bag and the irradiation chamber;

irradiating the buffy coat in the irradiation chamber while recirculating;

pumping the irradiated buffy coat from the irradiation chamber;

pumping irradiated buffy coat from the collection bag through a filter in the cassette and then back to the patient; wherein said disposable kit comprises a cassette;

a saline bag inlet tube;

a treatment bag;

a plasma collection bag having an inlet tube for flowing plasma from the cassette and an outlet tube for flowing plasma to the cassette;

an anticoagulant inlet tube for flowing anticoagulant to the cassette;

an irradiation chamber having an inlet tube for flowing buffy coat from the cassette and an outlet tube for flowing irradiated buffy coat to the cassette;

a separation bowl having one tube for flowing blood to the separation chamber and at least two tubes for flowing separate blood fragments from the separation chamber;

means to withdraw blood from a patient comprising a tube for flowing blood to the cassette and means for connecting a needle; and

means to return blood fractions to the patient comprising a tube from the cassette and;

wherein said cassette comprises a rigid plastic housing;

flexible tube loops extending out of the housing;

flexible tubing other than loops extending into, within, and out from of the housing;

at least one section of flexible tube within the housing exposed on one side of the housing so that fluid flow through the exposed section can be prevented when pressure is exerted on the exposed section from the exposed side.