Shear stresses in fluid flow through curved tubes and their applications in extracorporeal circuit design

ONE OF the possible reasons for haemolysis (blood cell damage) in extracorporeal systems is the high shear stresses caused by flow in curved tubes subjected to high pressure gradients. At shear stress levels of 9 N m-2 the haemolysis is 0-1 per cent (SHAPIRO and WILLIAMS, 1970) whereas at shear stress levels of 18 N m -2 the haemolysis is 0.6 per cent. For example, in the heart-lung machine, curved tubes and roller pumps are used to pump oxygenated blood to perfuse the body organs. The use of curved tubes in roller pumps for prescribed flow rates gives rise to high shear stresses and pressure gradients, thereby causing haer~lolysis in the extracorporeal system. Hence it is impot rant to choose the tube sizes and curvatures of extracorporeal conduits such that