Optional “hypershear”-induced thrombus formation

In the GTT, blood flows under the influence of gravity at a shear rate of ≈12,000s-1 (corresponding shear stress 480 dyne/cm2). Although such a pathological high shear rate is above the threshold required for von Willebrand factor induced platelet activation (>10,000s-1), the rate of platelet activation in GTT is slow. This is evidenced by the relatively long time from the start of the measurement until measurable occlusion is detected. The likely reason is that at a shear rate of >10,000s-1, platelet activation-dependent aggregation takes time until the initial unstable aggregates stabilise, thrombin is generated, and fibrin-stabilized thrombi cause lasting occlusion. However, when shear rate exceeds >20,000s-1 (activation-independent platelet aggregation), stable aggregates are formed instantaneously without contribution from platelet activation and the timely release of ADP. At such high shear rate the antithrombotic effect of common antiplatelet drugs are greatly reduced or diminished. In “Hypershear Mode” (available in GTT-3 model), repetitive cycles of pressure are applied on blood to increase the flow and the shear rate to ≈22,000s-1 until occlusion is detected. Each cycle consists of 5 seconds of pressure-driven flow at a shear rate of ≈22,000 s- 1 followed by 15 seconds of flow under gravity at a shear rate of ≈12,000 s-1. This results in significant acceleration of the rate of occlusion resulting 30-50% reduced occlusion time (OT) as compared to flow under gravity.