Optional Additional Features

The GTT 3 can be customised by the user to measure additional features, if required.

  • Optional “Hypershear” mode
  • Repetitive cycles of pressure increase the shear rate from ≈12,000 s-1 to ≈22,000 s-1 until OT is reached. This can assess the effectiveness of antiplatelet medications at very high shear rates, such as those which occur in severely stenotic arteries or ventricular assist devices.

  • Using GTT-3 to work as GTT-2
  • A simple change in Settings to disable the pressure pumps allows GTT-3 to function in all channels as GTT-2, measuring OT and LT under gravity flow.

  • Parallel measurements to simultaneously assess flow under gravity and in hypershear
  • Using GTT-3 in hypershear mode, 2 samples of identical blood can be tested in parallel with one of the channels connected to pressure tubing (shear rate ≈22,000 s-1) while the other is not and assesses flow under gravity (shear rate ≈12,000 s-1).

    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 high shear rate is above the threshold required for von Willebrand factor induced platelet activation (>10,000s-1), the rate of platelet activation in the 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 for such a long “lag time” is that at a shear rate of >10,000s-1, platelet activation-dependent aggregation takes time until the initial unstable aggregates stabilized, 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), repetitive cycles of pressure are applied to flowing 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 greatly accelerates the rate of occlusion, reducing occlusion time by 30-50% compared to flow under gravity.

    Possible benefits of hypershear testing

  • Assessing the effectiveness of antiplatelet medication at very high shear rates, such as those which occur in severely stenotic arteries or ventricular assist devices. At such high shear rates the antithrombotic effects of common antiplatelet drugs may be greatly reduced or diminished.
  • Comparing the effectiveness of medications at very high shear, reflecting antithrombotic effect, with the effects at low shear, which reflect haemostasis and bleeding risk.
  • Typical GTT-3 recording in “Hypershear” mode.
    1= gravity flow; 2= pressure-driven flow.