Mechanical Cavopulmonary Assistance of a Patient-Specific Fontan Physiology: Numerical Simulations, Lumped Parameter Modeling, and Suction Experiments

Abstract

This study investigated the performance of a magnetically levitated, intravascular axial flow blood pump for mechanical circulatory support of the thousands of Fontan patients in desperate need of a therapeutic alternative. Four models of the extracardiac, total cavopulmonary connection (TCPC) Fontan configuration were evaluated to formulate numerical predictions: an idealized TCPC, a patient-specific TCPC per magnetic resonance imaging data, and each of these two models having a blood pump in the inferior vena cava (IVC). A lumped parameter model of the Fontan physiology was used to specify boundary conditions. Pressure-flow characteristics, energy gain calculations, scalar stress levels, and blood damage estimations were executed for each model. Suction limitation experiments using the Sylgard elastomer tubing were also conducted. The pump produced pressures of 1-16 mm Hg for 2000-6000 rpm and flow rates of 0.5-4.5 L/min. The pump inlet or IVC pressure was found to decrease at higher rotational speeds. Maximum scalar stress estimations were 3 Pa for the nonpump models and 290 Pa for the pump-supported cases. The blood residence times for the pump-supported cases were shorter (0.9 s) as compared with the nonsupported configurations (2.5 s). However, the blood damage indices were higher (1.5%) for the anatomic model with pump support. The pump successfully augmented pressure in the TCPC junction and increased the hydraulic energy of the TCPC as a function of flow rate and rotational speed. The suction experiments revealed minimal deformation (<3%) at 9000 rpm. The findings of this study support the continued design and development of this blood pump.

Experimental Measurements of Energy Augmentation for Mechanical Circulatory Assistance in a Patient-Specific Fontan Model

“…The Thoratec HeartMate II blood pump, however, was designed to support a normal biventricular circulation having left ventricular failure and was not developed for the unique anatomic configuration of the TCPC. Previous in vitro research has investigated the probability of vessel suction and vein collapse on the inlet side of our pump . In the case of the impeller by itself without a supportive protective cage, venous collapse did not occur at rotational speeds below 9000 rpm, and only minimal deformation occurred over the entire range of rotational speeds .…”

Design of Axial Blood Pumps for Patients With Dysfunctional Fontan Physiology: Computational Studies and Performance Testing

“…The performance achievements met the desired pressure-flow requirements to support a Fontan patient (3,(5)(6)(7)(8). All of the pump designs produced a pressure rise over the flow range evaluated and rotational speeds of 4000-7000 RPM.…”

“…ANSYS CFX 12.1 software (ANSYS, Inc., Canonsburg, PA, USA) was used to simulate the pump performance (8)(9)(10). ANSYS CFX 12.1 software (ANSYS, Inc., Canonsburg, PA, USA) was used to simulate the pump performance (8)(9)(10).…”

“…Prior work (5)(6)(7)(8) has focused on axial impeller designs and protective stent geometries around the device. Each pump may be percutaneously inserted into the femoral vein, subsequently advanced into the inferior vena cava (IVC), and located distal to the entrance of the TCPC junction.…”

Invited commentary: Personalized surgical planning by computational and visual methods in 21st‐century medical engineering

“…In combination with computational studies, we are able to leverage 2D MRI to create patient‐specific 3D anatomic geometries for analysis. We transform the MRI data slices by importing the data sets, generating a 3D point cloud mesh, and then performing a surface knitting technique using computer‐aided design (CAD) software to build a 3D anatomic model 7 . Having the 3D anatomic model constructed in a CAD program allows for 3D rapid prototyping and printing via a range of materials, which allows for visualization and assessment of treatment strategies 8 .…”