Changes in platelet thrombi generated under low shear rate conditions by stepwise increase of shear rate during perfusion in BSS or type 3 vWD. Blood from control (•), BSS (patient No. 1) (○), or type 3 vWD (▿) was perfused over a collagen surface under 340 s⁻¹ for 7 minutes. The shear rate applied was then increased stepwise to 1,500 s⁻¹ for 2 minutes and subsequently to 4,500 s⁻¹ for 1 minute and to 9,000 s⁻¹ for 1 minute. Based on the amount of platelets adhering to the surface, the time-dependent thrombus growth in BSS or type 3 vWD was arrested when the applied shear rate was raised to 1,500 s⁻¹, although thrombus growth in control blood was greatly accelerated in a shear-dependent manner.