PB1150 - Shear rates in hemorrhagic vascular injury

Background: A primary hemostatic clot may form through Shear Induced Platelet Aggregation (SIPA) under high shear rates >5000s-1 or through coagulation under low shear rates. The goal of this study was to estimate the shear rates during hemorrhage under arterial and venous pressures by injury size.

Aims: Quantify shear rates in hemorrhagic injuries for SIPA.

Methods: The shear rates for blood flow exiting an injury are estimated for two geometries: a side hole laceration or a transected vessel. Computational fluid dynamics (CFD) is used for a side hole injury where flow is not developed. CFD uses a flat entrance profile along with an ambient pressure outlet to model the shear rate through the vessel wall. A Poiseuille model was used for a transecting injury with developed inlet flow. A Torricelli approximation is used for bleeding flow rates.

Results: For laceration side hole injuries, shear rates quantified by CFD are pathologically elevated, being >100,000s-1 for arteries and >10,000s-1 for veins (Figure 1). The shear rate values are almost 10x greater for CFD than using Poiseuille assumptions. Shear rates for side holes are < 5,000s-1 for small holes < 0.5mm at < 1mmHg. For transecting end holes, shear rates exceed 5,000s-1 for all injuries with pressures greater than 10 mmHg and injuries less than 2mm (Fig 2A). Shear is < 5,000s-1 for holes >1 mm under venous pressures and low flow rates < 30 mL/min (Fig 2B). Thus, SIPA conditions are expected for all arterial injuries and smaller venous injuries.

Conclusion(s): Hemorrhagic trauma of major blood vessels typically leads to high shear conditions above than 5,000s-1 under both arterial and venous conditions. These pathologically elevated shear rates would drive primary platelet hemostasis through SIPA and are inconsistent with static coagulation to close the injury. Poiseuille assumptions vastly underestimate shear rates for side hole injuries.