title: Activation status of platelet aggregates and platelet microparticles shed in sheared whole blood.
abstract: The role of temperature and shear rate in the activation status of aggregating platelets and platelet microparticles (MPs) was investigated in a modified concentric-cylinder rotational viscometer. Whole blood anticoagulated with citrate was exposed to a range of shear rates typical of cardiopulmonary bypass circuits (0, 1000, 2000 and 4000 s(-1)) over four temperatures spanning hypothermic to mildly hyperthermic conditions (24, 30, 37 and 42 degrees C) for short durations (100 s). Aliquots of blood were double-stained for CD41 (platelet GPIIb/IIIa) and CD62 (P-selectin). Platelets, platelet aggregates, MPs and red blood cell-platelet and -MP aggregates were identified by flow cytometry by acquiring only CD41-positive particles and differentiating on a plot of CD41 versus forward light scatter. The activation status of each particle was quantified by measuring CD62 expression (alpha-granule release). A degree of correlation between the shedding of MPs and the formation of platelet-platelet aggregates was observed for the data as a whole (r=0.85 for p<0.01), although this trend was not observed for a shear rate of 4000 s(-1). The mean expression of CD62 on both platelets and MPs was maintained at a very low level for all temperature and shear rate combinations. There was, however, a number of very highly activated MPs associated with red blood cells at high shear rates.
authors.affiliation: Department of Clinical Engineering, Liverpool University, UK.
authors.forename: N P
authors.initials: NP
authors.lastname: Rhodes
authors.forename: A P
authors.initials: AP
authors.lastname: Shortland
authors.forename: A
authors.initials: A
authors.lastname: Rattray
authors.forename: R A
authors.initials: RA
authors.lastname: Black
authors.forename: D F
authors.initials: DF
authors.lastname: Williams