Platelet aggregation in poiseuille flow: II. Effect of shear rate.

Using a double infusion technique described in the previous paper, the effect of shear rate, G, on platelet aggregation was studied in citrated platelet-rich plasma in Poiseuille flow over a range of mean linear flow rates, u3 from 50 to 1500 microns-1 corresponding to G from 2 to 54 sec-1. At 1 micron ADP, aggregates were formed at all u3 and, except at the lowest flow rate, both the degree of aggregation (net fraction of cells in aggregates, A') and size of the aggregates increased with distance down the tube. The degree of aggregation was both time and shear rate-dependent. Over the first 10 sec, A' appeared to be independent of the mean transit time indicating that the collision capture efficiency decreased with increasing G. Thereafter, A' increased with increasing shear rate leading to the formation of an appreciable number of aggregates greater than 10 cells at G greater than 24 sec-1. Small aggregates initially formed near the tube wall and, as they grew in size, migrated toward the axis as their rotation was physically impeded by the wall. In addition, the values of A' in cPRP from five female donors were significantly greater than those from five male donors.