ZV₅₀ describes the activation state of adhered platelets in flowing human blood. Fibrillar collagen, monomeric collagen, or combinations of GFOGER, VWF-III, and one of a panel of CRP-like peptides containing increasing numbers of GPO triplets were used to coat slides. These were perfused with DiOC₆-labeled whole human blood for 5 minutes at a shear rate of 1000s⁻¹ with or without preincubation with 20 μg/mL of the anti-GpVI 10B12 or 10μM of the α_IIbβ₃ inhibitory compound, GR144053. (A) Schematic diagram showing the derivation of ZV₅₀ and mean thrombus height. Consecutive volumes of each slice were accumulated sequentially until a value of 50% of the total volume was reached. This value corresponds to ZV₅₀. Mean thrombus height is the thrombus volume per unit area of coverslip imaged (supplemental Figure 1). (B-C) Thrombus formation onto peptide mixtures of GFOGER and VWF-III with one of a panel of CRP-like peptides after treatment with 10B12. (D-E) Thrombus formation onto peptide combinations after treatment with GR144053. (B,D) Surface coverage (%). (C,E) ZV₅₀ (μm). (F) ZV₅₀ values obtained for combinations of CRP, GFOGER, and VWF-III peptides after blood flow at different shear rates. Data are mean ± SEM. Shear rates: indicates 100s⁻¹; , 300s⁻¹; , 1000s⁻¹; and ▭, 3000s⁻¹.