Shear rate versus shear stress.
(A) Shear-induced platelet activation in undiluted citrated whole blood (●) was compared with citrated PRP with platelets at 10 × 106 cells/mL (▪). Platelet activation levels assayed using Annexin V–FITC are reported at 180 seconds for whole blood runs and at 30 seconds for citrated PRP. Lower shear rates of 2200/s (shear stress, approximately 83 dyn/cm2) were required for platelet activation in whole blood compared with 6800/s (shear stress, approximately 75 dyn/cm2) for platelets in PRP. The threshold shear stress requirement was comparable for both treatments. (B) Media viscosity was doubled by the addition of 1.5% wt/vol dextran, and the effect of increasing media viscosity on isolated platelets at 10 × 106 cells/mL was examined at 9600/s after 30 seconds of shear. GpIb blocking antibody AN-51 reduced platelet activation levels to baseline values in the presence and in the absence of dextran. Data are mean ± SEM for n = 3-4. *P < .05 with respect to run, without the addition of dextran.
