Outflow boundary conditions for arterial networks with multiple outlets.

Simulation of blood flow in three-dimensional geometrically complex arterial networks involves many inlets and outlets and requires large-scale parallel computing. It should be based on physiologically correct boundary conditions, which are accurate, robust, and simple to implement in the parallel framework. While a secondary closure problem can be solved to provide approximate outflow conditions, it is preferable, when possible, to impose the clinically measured flow rates. We have developed a new method to incorporate such measurements at multiple outlets, based on a time-dependent resistance boundary condition for the pressure in conjunction with a Neumann boundary condition for the velocity. Convergence of the numerical solution for the specified outlet flow rates is achieved very fast at a computational complexity comparable to the widely used Resistance or Windkessel boundary conditions. The method is verified using a patient-specific cranial vascular network involving 20 arteries and 10 outlets.