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Research Papers

Neonatal Aortic Arch Hemodynamics and Perfusion During Cardiopulmonary Bypass

[+] Author and Article Information
Kerem Pekkan

Department of Biomedical Engineering, Carnegie Mellon University, 2100 Doherty Hall, Pittsburgh, PA 15213-3890kpekkan@andrew.cmu.edu

Onur Dur

Department of Biomedical Engineering, Carnegie Mellon University, 2100 Doherty Hall, Pittsburgh, PA 15213-3890

Kartik Sundareswaran

Cardiovascular Fluid Mechanics Laboratory, Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332-0535

Kirk Kanter

Pediatric Cardiothoracic Surgery, Emory University School of Medicine, 1440 Clifton Road, Atlanta, GA 30322

Mark Fogel

 Children’s Hospital of Philadelphia, 34th Street, Civic Center Boulevard, Philadelphia, PA 19104

Ajit Yoganathan

Cardiovascular Fluid Mechanics Laboratory, Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 315 Ferst Drive, Atlanta, GA 30332-0535A

Akif Ündar

Department of Pediatrics, Surgery and Bioengineering, Penn State College of Medicine, Hershey, PA 17033

1

Corresponding author.

J Biomech Eng 130(6), 061012 (Oct 15, 2008) (13 pages) doi:10.1115/1.2978988 History: Received July 13, 2007; Revised April 21, 2008; Published October 15, 2008

The objective of this study is to quantify the detailed three-dimensional (3D) pulsatile hemodynamics, mechanical loading, and perfusion characteristics of a patient-specific neonatal aortic arch during cardiopulmonary bypass (CPB). The 3D cardiac magnetic resonance imaging (MRI) reconstruction of a pediatric patient with a normal aortic arch is modified based on clinical literature to represent the neonatal morphology and flow conditions. The anatomical dimensions are verified from several literature sources. The CPB is created virtually in the computer by clamping the ascending aorta and inserting the computer-aided design model of the 10 Fr tapered generic cannula. Pulsatile (130 bpm) 3D blood flow velocities and pressures are computed using the commercial computational fluid dynamics (CFD) software. Second order accurate CFD settings are validated against particle image velocimetry experiments in an earlier study with a complex cardiovascular unsteady benchmark. CFD results in this manuscript are further compared with the in vivo physiological CPB pressure waveforms and demonstrated excellent agreement. Cannula inlet flow waveforms are measured from in vivo PC-MRI and 3 kg piglet neonatal animal model physiological experiments, distributed equally between the head-neck vessels and the descending aorta. Neonatal 3D aortic hemodynamics is also compared with that of the pediatric and fetal aortic stages. Detailed 3D flow fields, blood damage, wall shear stress (WSS), pressure drop, perfusion, and hemodynamic parameters describing the pulsatile energetics are calculated for both the physiological neonatal aorta and for the CPB aorta assembly. The primary flow structure is the high-speed canulla jet flow (3.0m/s at peak flow), which eventually stagnates at the anterior aortic arch wall and low velocity flow in the cross-clamp pouch. These structures contributed to the reduced flow pulsatility (85%), increased WSS (50%), power loss (28%), and blood damage (288%), compared with normal neonatal aortic physiology. These drastic hemodynamic differences and associated intense biophysical loading of the pathological CPB configuration necessitate urgent bioengineering improvements—in hardware design, perfusion flow waveform, and configuration. This study serves to document the baseline condition, while the methodology presented can be utilized in preliminary CPB cannula design and in optimization studies reducing animal experiments. Coupled to a lumped-parameter model the 3D hemodynamic characteristics will aid the surgical decision making process of the perfusion strategies in complex congenital heart surgeries.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

A schematic of the cardiopulmonary bypass (CPB) circuit. CPB procedures are used extensively during cardiac surgery to withdraw venous blood from the right atrium and pump it through an oxygenator, and then return the oxygenated blood to the patient through the ascending thoracic aorta, bypassing the heart and the lungs. During CPB, the heart is usually arrested and the cardiac surgeon performs the operation on the motionless heart. A cannula is inserted into the patient’s right atrium to drain venous return. The venous blood is fed into the venous reservoir by gravity. The blood is pumped through the membrane oxygenator and an arterial filter removes any air bubbles and blood emboli. The blood is then returned into the aorta distal to a cross-clamp (LA: left atrium).

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Figure 2

(Left) Surgeon sketches of the CPB assembly, including the aortic cross-clamp location, are prepared by pediatric surgeon; top and bottom views. (Right) CPB cannulation (tapered 10 Fr) is created “virtually” on the computer based on the patient-specific “surgical planning” modeling protocols.

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Figure 3

Close-up view of the tetrahedral grids at the cannula tip region for the CPB Ao model. The grids are shown on an axial plane that goes through the aortic arch.

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Figure 4

Inlet flow waveforms specified in neonatal aorta, 10 year old pediatric aorta, and neonatal cardiopulmonary bypass cannula

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Figure 6

Comparisons of the calculated pressure waveforms with in vivo physiological measurements for three grid refinement levels. (Top) Precannula pressure. (Bottom) Postcannula pressure. The head-neck to descending aorta flow-split ratio is 40/60. Only one period of the experimental measurements is shown for clarity.

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Figure 7

(a) Anterior and cranial views of the particle pathlines for the neonatal CPB model during acceleration (t=0–0.2 s, left) and second deceleration (t=0.3–0.525 s, right) phases. (b) Typical particle pathlines for the neonatal Ao observed during three instances; mid-, late deceleration, and end-systole, Δt1, Δt2, and Δt3, respectively. The arrow indicates flow separation at the inferior wall of the arch. (c) Velocity magnitudes (m/s) during peak flow for normal neonatal Ao (left, t=0.05 s) and neonatal CPB assembly (right, t=0.2 s).

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Figure 8

Velocity magnitude (m/s) along the typical cross sections of the ascending and descending aortas during acceleration (left) and deceleration (right) phases for neonatal (a), pediatric (b), and cardiopulmonary bypass (c) models. The dashed line corresponds to the aortic arch centerline: (A) anterior, (P) posterior, (L) left, and (R) right directions.

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Figure 9

The distribution of dissipation function (mW/m3), Eq. 4, and the development of cannula jet shear layer for the CPB model at t=0.425 s. DAo: descending aorta, IA: innominate artery, LCC: left common carotid artery, and LSA: left subclavian artery.

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Figure 10

Wall shear stress (N/m2) and surface traction vectors plotted for normal and CPB aortas during peak flow. The arrows indicate the primary shear stress hot-spots for both models. For normal aorta high shear is observed at the head-neck vessels while squeezed stagnant CPB jet created high wall shear stress at the descending aorta entrance. DAo: descending aorta, IA: innominate artery, LCC: left common carotid artery, and LSA: left subclavian artery.

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Figure 5

Comparisons of flow profiles for grid verification study. Velocity magnitudes (m/s) and vectors are plotted along the midsection of the aortic arch. The top right corner shows the detailed comparison of velocity profiles along section a-a. CPB cannula model with 60/40 DAo/head-neck flow-split at t=0.475 s (see Fig. 3).

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