Flow observation and model experiments on blood damage in the area of the balloon used for intra-aortic balloon pumping

With a mock circulation, developed at the Aerodynamisches Institut, haemolysis and pressures were measured and the flow patterns near the balloon were made visible. Aortic diameter, length and diameter of the balloon, elasticity modulus of the tube and the pressure to fill and to empty the balloon were varied in the experiments. The pressure measurements indicate that the filling phase can be divided into unsteady and approximately steady parts. Flow visualisation, by means of the hydrogen-bubble technique, shows nearly rectangular velocity profiles. Wall shear stresses, evaluated from these profiles, allow one to determine a critical ratio of balloon to aortic diameter, beyond which damage to the aortic intima due to excessive frictional forces are to be expected. The concentration of plasmahaemoglobin of fresh ACD stabilised pig blood was measured to determine the rate of haemolysis. Scattering can be shown to be less than 10% if the data are properly reduced. One of the major results of this analysis is that the rate of haemolysis increases linearly with the magnitude of the balloon surface.