Simulations of Congenital Septal Defect Closure and Reactivity Testing in Patient-Specific Models of the Pediatric Pulmonary Vasculature: A 3D Numerical Study With Fluid-Structure Interaction

Abstract

Clinical imaging methods are highly effective in the diagnosis of vascular pathologies, but they do not currently provide enough detail to shed light on the cause or progression of such diseases, and would be hard pressed to foresee the outcome of surgical interventions. Greater detail of and prediction capabilities for vascular hemodynamics and arterial mechanics are obtained here through the coupling of clinical imaging methods with computational techniques. Three-dimensional, patient-specific geometric reconstructions of the pediatric proximal pulmonary vasculature were obtained from x-ray angiogram images and meshed for use with commercial computational software. Two such models from hypertensive patients, one with multiple septal defects, the other who underwent vascular reactivity testing, were each completed with two sets of suitable fluid and structural initial and boundary conditions and used to obtain detailed transient simulations of artery wall motion and hemodynamics in both clinically measured and predicted configurations. The simulation of septal defect closure, in which input flow and proximal vascular stiffness were decreased, exhibited substantial decreases in proximal velocity, wall shear stress (WSS), and pressure in the post-op state. The simulation of vascular reactivity, in which distal vascular resistance and proximal vascular stiffness were decreased, displayed negligible changes in velocity and WSS but a significant drop in proximal pressure in the reactive state. This new patient-specific technique provides much greater detail regarding the function of the pulmonary circuit than can be obtained with current medical imaging methods alone, and holds promise for enabling surgical planning.

Pulmonary vascular input impedance is a combined measure of pulmonary vascular resistance and stiffness and predicts clinical outcomes better than pulmonary vascular resistance alone in pediatric patients with pulmonary hypertension

“…"top-hat" profile); this is not unreasonable since typical Womersley numbers found in the MPA are much greater than 1.0, indicating flat profiles [6]. Computational fluid dynamics studies from our group have confirmed that velocity profiles within the main PA are indeed flat over the pulsatile cycle [7]. The pressure and calculated velocity time-histories were then separated into individual cardiac cycles (n > 20) based on ECG gating.…”

Progress in the CFD Modeling of Flow Instabilities in Anatomical Total Cavopulmonary Connections

“…Meshes consisting of entirely tetrahedral elements are already being employed in complex anatomical domains with great success. 19,20,25 And for simpler anatomies, hexahedral unstructured grids can be readily implemented 14 as the boundary-layer mesh uniformity can be controlled with reasonable manual mesh generation effort. The algorithms for creating unstructured grids are also more amenable to automation.…”

Patient-specific surgical planning and hemodynamic computational fluid dynamics optimization through free-form haptic anatomy editing tool (SURGEM)

“…Steinman et al have attempted similar planning techniques towards the detection and removal of atherosclerotic plaques using unsteady pulsatile CFD simulations with geometries and boundary conditions prescribed using patient-specific MRI [64][65][66][67]. Similar methods were applied to other cardiovascular systems such as the abdominal aortic aneurism [16,31,32,54,80] endovascular grafts [16,20], pediatrics [19,30], coronary arteries [51,52], and congenital heart diseases [39,40]. However, all of these studies primarily utilize surgical planning methods towards analysis of a limited number of anatomical geometries, and no one to date has used such methods towards systematic geometric optimization by combining MRI and CFD.…”