size, vascular resistances, and heart rate Modeling of the Norwood circulation: effects of shunt
Gonzalo UrcelayEdward L. BoveTain‐Yen HsiaMarc R. de LevalFrancesco MigliavaccaGiancarlo PennatiGabriele DubiniRoberto FumeroRiccardo
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Norwood procedure
Circulation (fluid dynamics)
Systemic circulation
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The Fontan palliation was introduced as surgical repair method for tricuspid atresia, creating a univentricular serial circulation. However, it is used as treatment for other life threatening complex congenital heart diseases as well. The variation of underlying pathologies treated with this palliation makes optimization difficult. To assist the optimization process, we adjusted a lumped parameter computational model of the biventricular circulation (CircAdapt) and evaluated the univentricular circulation. The model simulates beat-to-beat dynamics of the two cardiac chambers, the valves, and the systemic and pulmonary circulations. The univentricular circulation in rest and exercise was simulated. Exercise resulted in increased stroke volume, heart rate, pulse pressure, and stressed blood volume. Central venous pressure rose as a result of the constant pulmonary resistance, reducing systemic pressure drop. Reduced systemic pressure drop implies either reduction of systemic flow or further decrease of systemic resistance. Based on our simulation results, we conclude that exercise capacity in Fontan patients is limited due to increase of central venous pressure and the impossibility to reduce systemic resistance further, restricting systemic flow.
Fontan Procedure
Tricuspid atresia
Venous return curve
Systemic circulation
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The growing population of failing single-ventricle (SV) patients might benefit from ventricular assist device (VAD) support as a bridge to heart transplantation. However, the documented experience is limited to isolated case reports. Considering the complex and different physiopathology of Norwood, Glenn, and Fontan patients and the lack of established experience, the aim of this work is to realize and test a lumped parameter model of the cardiovascular system able to simulate SV hemodynamics and VAD implantation effects to support clinical decision. Hemodynamic and echocardiographic data of 30 SV patients (10 Norwood, 10 Glenn, and 10 Fontan) were retrospectively collected and used to simulate patients' baseline. Then, the effects of VAD implantation were simulated. Simulation results suggest that the implantation of VAD: (i) increases the cardiac output and the mean arterial systemic pressure in all the three palliation conditions (Norwood 77.2 and 19.7%, Glenn 38.6 and 32.2%, and Fontan 17.2 and 14.2%); (ii) decreases the SV external work (Norwood 55%, Glenn 35.6%, and Fontan 41%); (iii) decreases the pressure pulsatility index (Norwood 65.2%, Glenn 81.3%, and Fontan 64.8%); (iv) increases the pulmonary arterial pressure in particular in the Norwood circulation (Norwood 39.7%, Glenn 12.1% and Fontan 3%); and (v) decreases the atrial pressure (Norwood 2%, Glenn 10.6%, and Fontan 8.6%). Finally, the VAD work is lower in the Norwood circulation (30.4 mL·mm Hg) in comparison with Fontan (40.3 mL·mm Hg) and to Glenn (64.5 mL·mm Hg) circulations. The use of VAD in SV physiology could be helpful to bridge patients to heart transplantations by increasing the CO and unloading the SV with a decrement of the atrial pressure and the SV external work. The regulation of the pulmonary flow is challenging because the Pap is increased by the presence of VAD. The hemodynamic changes are different in the different SV palliation step. The use of numerical models could be helpful to support patient and VAD selection to optimize the clinical outcome.
Norwood procedure
Fontan Procedure
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Introduction: Newborns with transposition of the great arteries (TGA) have systemic and pulmonary circulation in parallel; thus, mixing of both circulations is essential to maintain appropriate oxygen saturation level. However, shunt flow through a patent ductus arteriosus (PDA), ventricular septal defect (VSD), and atrial septal defect (ASD) may result in hemodynamic instability against a decrease in pulmonary arterial resistance. This tradeoff between oxygen saturation and hemodynamic stability should be fully understood for better management of patients with this unique circulation, but has never been elucidated. Methods: We developed a lumped parameter model for TGA circulation based on the 3-element Windkessel model coupled with the time-varying elastance model of the ventricles. We examined the impacts of the shunt sizes and locations on oxygen saturation and cardiac index (CI) by combining various sizes of ASD, VSD and PDA. Contribution of each shunt to the mixing between systemic and pulmonary cir...
Ductus arteriosus
Transposition (logic)
Systemic circulation
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Hypoplastic left heart syndrome (HLHS) is a congenital heart defect (CHD) in which left side of the heart is severely underdeveloped. To better understand this unique physiology, a computational model of the hypoplastic heart was constructed on the basis of compartmental analysis. Lumped parameter model of HLHS is developed based on the electrical circuit analogy. Model is made up of three parts: hypoplastic heart, pulmonary circulation and systemic circulation. Plots of blood pressure and flow for various parts of body show great match between predicted values and what we expected for the case of HLHS babies. Influence of patent ductus arteriosus (PDA) and ASD resistances on cardiac output and pulmonary to systemic flow was also studied. Results show that by increasing the PDA resistance causes more flow to pulmonary compartments and so the ratio increases. Blood flow increases by decreasing of pulmonary artery resistant. Increasing the PDA resistance causes decrease the cardiac output because of more resistance against blood occurs. Saturation increases by decreasing of pulmonary artery resistant.
Ductus arteriosus
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Norwood procedure
Coronary circulation
Pulmonary shunt
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Children with hypoplastic left heart syndrome (HLHS) must undergo multiple surgical stages to reconstruct the anatomy to a sustainable single ventricle system. Stage I palliation, or the Norwood procedure, provides circulation to both pulmonary and systemic vasculature. The aorta is reconstructed and attached to the right ventricle and a fraction of systemic flow is redirected to the pulmonary arteries (PAs) through a systemic-to-PA shunt. Despite abundant hemodynamic data available 4-5 months after Norwood palliation, data is very scarce immediately following stage I. This data is critical in determining post-operative success. In this work, we combined population data and computational fluid dynamics (CFD) to characterize hemodynamics immediately following stage I (post-stage I) and prior to stage II palliation (pre-stage II). A patient-specific model was constructed as a baseline geometry, which was then scaled to reflect population-based morphological data at both time-points. Population-based hemodynamic data was then used to calibrate each model to reproduce blood flow representative of HLHS patients. The post-stage I simulation produced a PA pressure of 22 mmHg and high-frequency oscillations within the flow field indicating highly disturbed hemodynamics. Despite PA mean pressure dropping to 14 mmHg, the pre-stage II model also produced high-frequency flow components and PA wall shear stress increases. These suboptimal conditions may be necessary to ensure adequate PA flow throughout the pre-stage II period, as the shunt becomes relatively smaller compared to the patient's somatic growth. In the future, CFD can be used to optimize shunt design and minimize these suboptimal conditions.
Norwood procedure
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The physiological limitations of the Fontan circulation have been extensively addressed in the literature. Many studies emphasized the importance of pulmonary vascular resistance in determining cardiac output (CO) but gave little attention to other cardiovascular properties that may play considerable roles as well. The present study was aimed to systemically investigate the effects of various cardiovascular properties on clinically relevant hemodynamic variables (e.g., CO and central venous pressure). To this aim, a computational modeling method was employed. The constructed models provided a useful tool for quantifying the hemodynamic effects of any cardiovascular property of interest by varying the corresponding model parameters in model-based simulations. Herein, the Fontan circulation was studied compared with a normal biventricular circulation so as to highlight the unique characteristics of the Fontan circulation. Based on a series of numerical experiments, it was found that 1) pulmonary vascular resistance, ventricular diastolic function, and systemic vascular compliance play a major role, while heart rate, ventricular contractility, and systemic vascular resistance play a secondary role in the regulation of CO in the Fontan circulation; 2) CO is nonlinearly related to any single cardiovascular property, with their relationship being simultaneously influenced by other cardiovascular properties; and 3) the stability of central venous pressure is significantly reduced in the Fontan circulation. The findings suggest that the hemodynamic performance of the Fontan circulation is codetermined by various cardiovascular properties and hence a full understanding of patient-specific cardiovascular conditions is necessary to optimize the treatment of Fontan patients.
Fontan Procedure
Contractility
Circulation (fluid dynamics)
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Both pulmonary and systemic circulation must be maintained by a single pump in Fontan circulation. This unique property of Fontan circulation may be related to decreased exercise tolerance or increased instantaneous postoperative mortality rate, often observed in patients with this circulation. To better understand Fontan physiology, the present study theoretically investigated cardiac performance of Fontan circulation by using ventricular-vascular coupling framework analysis.End-systolic volume elastance (Ees), as a chamber contractile property, and effective arterial elastance (Ea), a lumped measure of ventricular afterload, were estimated both in normal left ventricular systemic circulation and in Fontan circulation.End-systolic volume elastance was decreased and Ea was increased in Fontan circulation. Both ventricular external stroke work (SW) and mechanical efficiency (EFF) under Fontan circulation were lower compared with those under normal circulation. Furthermore, the Ees-Ea relationship in Fontan circulation predicted limited cardiac reserve in terms of SW and EFF. Such cardiac performance in Fontan circulation stemmed from increased impedance due to the additional connection of the pulmonary vascular bed to the systemic vasculature and from the lack of a compensatory increase in contractility for increased afterload.Thus, it was inferred that Fontan circulation had intrinsic disadvantages and this may explain, in part, abnormal functional status and decline in survival following this procedure.
Afterload
Fontan Procedure
Contractility
Circulation (fluid dynamics)
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