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Experiments show importance of flow-induced pressure on endothelial cell shape and alignment

While the importance of haemodynamic forces on vascular disease is well recognized, the biologic response to these forces is not well understood. Indeed, as will be discussed, even the nature of the forces themselves is not understood; wall shear stress acting on arterial walls is commonly understood to be the primary, if not the sole, source of haemodynamic loading. The ultimate goal of this research is to experimentally quantify the complete force distribution acting on endothelial cells (ECs) and to directly examine the biochemical response of ECs to variations in haemodynamic loading. This report contains a description of the first spatially resolved microscopic particle image velocimetry (μPIV) flow measurements over individual human ECs. Using velocity data from multiple two-dimensional planes, it was possible to reconstruct the three-dimensional shear stress and pressure distributions over the cells. Data indicate that flow-induced pressure is of the same magnitude as shear with maximum magnitudes at the ‘toe’ and ‘heel’ of the ECs. Arguments are then made that EC response to pressure includes (i) reshaping to minimize drag, (ii) realigning to minimize shear-induced torque, and (iii) minimizing attachment forces required to maintain adhesion.