Mechanical hemolysis of cross-bonded red cells in the microcirculation

In favic crises the effective surface area of red cells is reduced by a mechanism called membrane cross bonding (Fischer et al., Brit. J. Haematol. 59, 159, 1985). In these crises massive intravascular hemolysis is observed the cause of which is unknown. One possibility is mechanical hemolysis of cross-bonded red cells that cannot negotiate the microcirculation due to their decreased effective surface area. To investigate this possibility critical phenomena of red cell behavior in the microcirculation were studied using Laplace's law. In model calculations an idealized vessel geometry was used: a funnel in which the angle of the conical part and the radius of the cylindrical part were varied. A map of these two parameters was established showing where red cells either enter the funnel or get stuck and where they would hemolyse under a pressure difference of 3 mm Hg. Adopting a teleological point of view it was assumed that red cell and vessel geometry are mutually adapted. Based on this assumption those combinations of the two parameters cone angle and radius were found that allow the passage of the complete population of normal red cells without hemolysis. Assuming a reduction in red cell surface area similar to that observed in favic crises it was found that only a small portion of the population would hemolyse. Therefore, mechanical hemolysis may not suffice to explain the observed intravascular hemolysis.