Giles Cokelet 1999 Recipient of the Jean-Leonard-Marie Poiseuille Award Outstanding Work in Furthering the Understanding of the Macro- and Microrheology of Blood

Giles Cokelet was awarded the Poiseuille Medal during the 10th International Congress of Biorheology. Dr.Cokelet brought to Biorheology a body of investigations into the mechanics of blood flow in the microcirculation distinguished by the thoughtfulness and the outstanding scientific accuracy with which they were carried out.

Among his more important works are manuscripts dealing with the question of a yield stress for mammalian blood, the Fåhraeus and Fåhraeus-Lindqvist Effects, and most recently, papers dealing with microvascular hydrodynamic resistance and cell distribution in microvascular networks. Dr. Cokelet pointed out that many of the claims of other investigators that there exists a small yield stress were unreliable because of artifacts in their measurements. In carefully thought-out and executed experiments, Dr. Cokelet explored the Fåhraeus Effect in small tubes and quantitated its dependence on tube diameter, hematocrit and flow rate. The work in vitro then led him to consider the application of the Fåhraeus and Fåhraeus-Lindqvist Effects to the living microcirculation. He determined from in vitro experiments how red cell distribution at bifurcations was affected by flow and vessel geometry. To do this, he pioneered methods for the construction of tiny bifurcations having diameters from 20 to 100 µm diameter. Then, he applied the knowledge of single vessel experiments to a microvascular network and was able to show quite conclusively that non-uniform distribution of flow at microvascular bifurcations tends to induce a difference in the overall velocity of the red cells traversing the microvessel network compared to that of the plasma. The mean discharge hematocrit of the network will be less than the hematocrit of the feeding and draining vessels, and mean vessel hematocrit will be lower than the inflow arterial hematocrit. This effect was termed the Network Fåhraeus Effect. Most recently there has been work on white cell hemodynamics, in particular studies of the interactions of leukocytes with the endothelium and their effect on flow resistance and drag forces in capillary and postcapillary vessels.