EXPERIMENTAL INVESTIGATION OF UNSTEADY-FLOW BEHAVIOR WITHIN A SAC-TYPE VENTRICULAR ASSIST DEVICE (VAD)

The flow behaviour of human blood in a pneumatically driven sac-type v entricular assist device (VAD) has been simulated by a non-Newtonian p olymer (Separan) solution, and investigated by both a one-component la ser Doppler anemometer (LDA) in back-scattering mode and flow visualis ation. The device was driven by a pneumatic driver with a squarewave o utput pressure, and was operated at a pumping rate of 70 bpm, and a sy stolic duration of 35% of the pumping cycle. The preload and the avera ge afterload to the device were set at 10 mmHg and 100 mmHg respective ly. The output flow rate was 4.05 1 min-1. The wall of the peripheral and the central parts of the blood chamber of the VAD were well 'washe d' by a main vortex developed during filling and the flow components p erpendicular to the base of the VAD produced by the diaphragm motions, respectively, Flow recirculation regions were found at several locati ons. Around the junction between the tube sections and the blood chamb er, the recirculation with an associated fluid particle deposition ind icates an underlying fisk of thrombus formation. This risk will be red uced by modifying the device design. The maximum turbulent shear stres s estimated from the maximum turbulent normal stress (74 Nm-2), is unl ikely to cause significant damage to blood for the exposure times foun d. The maximum particle residence time was found to be closely related to the heart rate and the degree of completion of ejection/filling. A t a given flow rate, the operating conditions which produce the highes t stroke volume give the shortest residence times.