Physical and computer modelling of blood flow in a systemic-to-pulmonary shunt

The aim of this work was the application of computer and physical in vitro simulation methods for estimating surgery procedure hemodynamics. The modified Blalock-Taussig (mB-T) palliative surgical procedure is performed to increase the pulmonary blood flow in children with congenital heart defects. Such a systemic-to-pulmonary shunt yields substantial modification in the blood flow within the large blood vessels. The objective of the present study was to investigate basic characteristics of the flow, flow pattern and pressure-flow efficiency, before and after opening of the mB-T graft.

The model was based on the vessel geometry obtained from the Visible Human Project and included the arch of aorta, the three arteries branching from the arch, the pulmonary trunck, and the left and right pulmonary arteries. The graft was added between the left subclavian artery and the left pulmonary artery. The glass model of the vessels was produced and investigated in a physical model of the cardiovascular system with an artificial ventricular device as the blood pump. Flow rate and hydrostatic pressure were measured at the inlet to and outlets from the glass model and in a few points within the system. Laser flow visualization was also performed. Computer simulations were done using the boundary conditions from the physical model.

The opening of the mB-T graft changed flow distribution in all branches (including inflow). A complex flow pattern with large eddies and channelling of the flow in the vicinity of the graft and within it was observed in flow visualization and in computer simulations. Because of that complexity the local measurements of hydrostatic pressure at the vessel wall could not predict the average flow rate. The reversed flow in the graft was observed during the systole.

The complex flow pattern developed in the physical model of the mB-T graft. The channelling of the flow and the formation of large eddies may yield high shear stress and modify blood properties. The rigid wall model can describe only some flow characteristics observed in vivo. Computer simulation is a very fast and accurate method which permits earlier qualification of cardiac surgeons on how to change cardiac vascular blood flow after operations.