CFD Simulations
CFD (Computational Fluids Dynamics) simulations have been at the core of Cardiost’s work with the University of Denver’s Cardiovascular Biomechanics Lab (DUCBL) - mainly as a tool for hemodynamic analysis and decision-making from clinical as well as surgical point of view.
During our latest set of simulations using SIMVascular and ANSYS, CFD simulations were conducted under pulsatile flow conditions in an aortic root with a LAUD that was modeled virtually by assigning a constant flow rate at the inlet of a conduit connecting the left atrium to the aorta. To create the aortic model, computed tomography (CT) scans of a 23-year-old male (Model #94) were obtained from an open-source database called Vascular Model Repository (VMR). SimVascular was then used for image segmentation, geometry reconstruction, mesh generation, and patient-specific flow simulation and analysis. Venturi devices were placed in the descending aorta in some of the computational models. The idea behind a venturi device is based on the Paradoxical Flow Valve of the Heart (PFVH), described in the United States Patent 7384389, and on the Parallel Narrow Section (PNS), described in United States Provisional Patent P291354US01. Figure 1 shows the three different models that were created in this study, namely:
Control - based on Model #94 of the VMR
LAUD no venturi
LAUD with venturi
The control model was based on Model #94 of the VMR. In Model 0, a LAUD was considered in the simulations, and a 12-mm conduit connected the left atrium to descending aorta. The conduit size was selected based on the smallest available size of Medtronic Contegra. The LAUD’s pumping function was modeled by considering a constant flow rate at the inlet of the conduit. In Models 1, 2, and 3, venturi devices were placed in the descending aorta. Venturi throat to descending aorta area ratio in Models 1, 2, and 3 was 35%, 50%, and 75%, respectively. In all three venturi devices, the length of the convergent and divergent sections was 3.43 cm and 6.87 cm, respectively. A 20 mm straight section was considered between the convergent and divergent segments to facilitate the connection of the conduit to the venturi. Consequently, the total length of the venturi devices was 12.29 cm. In Models 1, 2, and 3, the shape of the conduit was modified, and a conical nozzle (diameter changing from 12 mm to 7.5 mm) was created on the venturi end of the conduit to allow easy connection of the conduit to the throat of the venturi devices. An identical conduit geometry was considered in Models 1, 2, and 3.
The Navier-Stokes equations mathematically govern the dynamics of blood flow in the model. To numerically solve the Navier–Stokes equations, the models were meshed using SimVascular. Following the generation of an unstructured mesh in each model, svPre was called to create prerequisite data files for the flow solver. A blood density of 1,060 kg/m3 and viscosity of 4 centipoises was considered in the simulations. No-slip boundary conditions were applied to the walls. A pulsatile flow was considered in the inlet (i.e., ascending aorta). The flow curves shown below in Figure 2 were used for different cardiac outputs (COs).
Control Model
Pressure distribution
CO = 5.0 L/min, no LAUD
Velocity vectors
CO = 5.0 L/min, no LAUD
Model 0 - LAUD, no Venturi stent
Pressure distribution
CO = 4.5 L/min, LAUD = 0.5 L/min
Velocity vectors
CO = 4.5 L/min, LAUD = 0.5 L/min
Velocity streamlines
CO = 4.5 L/min, LAUD = 0.5 L/min
Model 3 - LAUD with Venturi stent (75%)
Pressure distribution
CO = 3.5 L/min, LAUD = 1.5 L/min
Velocity vectors
CO = 3.5 L/min, LAUD = 1.5 L/min
Velocity streamlines
CO = 3.5 L/min, LAUD = 1.5 L/min