THE EFFECT OF TEMPERATURE AND SHEAR RATE ON PLATELET-AGGREGATION

Samples of whole blood were obtained from male volunteers and exposed to combinations of shear rates and temperatures representative of card iopulmonary bypass (CPB) in a modified computer-controlled concentric cylinder rotational viscometer for a period of 100 s. Blood sampled fr om the chamber was fixed in paraformaldehyde, stained with CD41 and an alysed by flow cytometry. Only platelet-positive particles were acquir ed, each individual cell, or aggregate of cells, identified by analysi s of its fluorescence and forward light scatter characteristics. Littl e platelet aggregation was observed at shear rates of less than 4000 s (-1) for temperatures of greater than 24 degrees C, but large numbers of aggregates were formed at all temperatures at 4000 s(-1) (p < 0.05) , with more aggregates forming at 24 and 30 degrees C than at 37 and 4 2 degrees C (p < 0.05). We conclude that the process of aggregation is dependent on both temperature and shear rate. We note that a large nu mber of platelets become involved in aggregates under conditions of te mperature and shear-rate typical of CPB.