A discussion on the threshold limit for hemolysis related to Reynolds shear stress.

Turbulence-related damage to blood is a major problem with the use of prosthetic devices, such as mechanical heart valves. An often-cited paper by Sallam and Hwang (1984). Biorheology 21, 783-797) quantified the threshold for hemolysis to be about 400 N m(-2), a value that has hitherto contributed to the evaluation of the potential dangerousness of a medical implantable device. We propose a discussion of the mentioned experiment, based on the application of stress analysis concepts to the original measurements: this is necessary to assess the peak turbulence shear stress value that could have been found in Sallam and Hwangs experiment, with a suitable orientation of the measurement axes. The result of our theoretical discussion is that the threshold value of 400 N m(-2) could probably be considerably underestimated: following this point of view, a 3-D stress analysis shows that the peak turbulence shear stress at the inception of hemolysis should be at least 600 N m(-2). This result, obtained on the basis of the study of RBCs' response to a turbulent environment, indicates that blood particles are probably more resistant to short-time shear stresses than it was thought.