PARTICLE VOLUMETRIC RESIDENCE TIME CALCULATIONS IN ARTERIAL GEOMETRIES

The quantification of particle (platelet) residence times in arterial geometries is relevant to the pathogenesis of several arterial disease s. In this manuscript, the concept of ''volumetric residence time'' (V RT) is introduced The VRT takes into account where particles accumulat e and how long they remain there, and is well-suited to characterizing particle distributions in the complex geometries typical of the cardi ovascular system. A technique for the calculation of volumetric reside nce time is described, which assumes that platelets are neutrally buoy ant passive tracer particles, and which tracks small Lagrangian fluid elements containing a uniform concentration of platelets. This approac h is used to quantify particle (platelet) residence times in the regio n of a modeled stenosis with a 45 percent area reduction. Residence ti me distributions are computed for a representative population of plate lets, and for a subpopulation assumed to be ''activated'' by exposure to shear stresses above a threshold value. For activated platelets, hi gh particle residence times were observed just distal to the apex of t he stenosis throat, which can be explained by the presence of high she ar stresses and low velocities in the throat immediately adjacent to t he vessel wall. Interestingly, the separation zone distal to the steno sis showed only modestly elevated residence times, due to its highly m obile and transient nature. This calculation demonstrates the utility of the VRT concept for cardiovascular studies, particularly if a subpo pulation of all particles is to be tracked. We conclude that the volum etric residence time is a useful tool.