Fluid-Flow Energetics for Curved or Angulated Pathways Associated with Staged Operations for the Modified Fontan Procedure

Martin Guillot, Nancy Ross-Ascuitto, Robert Ascuitto
For the operations comprising the modified Fontan procedure for single-ventricle complex, blood flow is required to negotiate sharply curved or abruptly angulated (!) passages to perfuse the lungs. We postulated such changes in flow direction would exacerbate pressure drop ("P), energy loss ("E) and shear stress, important determinates of viscous dissipation for a fluid in motion. Computational fluid dynamics (CFD) was used to model viscous fluid flowing through channels, designed to simulate
more » ... igned to simulate blood traversing aortopulmonary or cavopulmonary Fontan connections. Viscosity values [(3-8) x 10-3 kg/m-s] were chosen to reflect clinically-relevant blood hematocrits (30% to 60%). Numerical solutions to the Navier-Stokes equations (finite volume analysis) were used to construct fluid pressure distributions, flow-velocity fields and contour plots of wall shear stress, along fluid pathways. The quantities "P(#,!), "$(#,!) and wall shear stress were found to increase significantly with rising viscosity (#) and advancing angle (!) of flow deflection. These hemodynamic parameters were also studied for staged operations required to carry-out the modified Fontan procedure; namely, aorta-to-pulmonary artery shunt in a neonate, bidirectional Glenn shunt in a 5 month old and completed total cavopulmonary connection (TCPC) in a 36 month old. Cardiac output was assumed to be 3L/min/m. 2 Simplified analytical descriptions are introduced to provide insight into fluid shear stress development and flow-energy depleting processes associated with a viscous fluid undergoing changes in pathway orientation. These findings have important clinical implications for maintaining energy efficient cavopulmonary blood flow in modified Fontan patients.