Optimization of Shunt Placement for the Norwood Surgery Using Multi-Domain Modeling

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Mahdi Esmaily Moghadam ◽  
Francesco Migliavacca ◽  
Irene E. Vignon-Clementel ◽  
Tain-Yen Hsia ◽  
Alison L. Marsden ◽  
...  
Keyword(s):  
Oxygen Delivery ◽  
Closed Loop ◽  
Surgical Anatomy ◽  
Global Changes ◽  
Local Geometry ◽  
Domain Modeling ◽  
Lumped Parameter ◽  
Implicit Approach ◽  
Artery Flow ◽  
Norwood Surgery

An idealized systemic-to-pulmonary shunt anatomy is parameterized and coupled to a closed loop, lumped parameter network (LPN) in a multidomain model of the Norwood surgical anatomy. The LPN approach is essential for obtaining information on global changes in cardiac output and oxygen delivery resulting from changes in local geometry and physiology. The LPN is fully coupled to a custom 3D finite element solver using a semi-implicit approach to model the heart and downstream circulation. This closed loop multidomain model is then integrated with a fully automated derivative-free optimization algorithm to obtain optimal shunt geometries with variable parameters of shunt diameter, anastomosis location, and angles. Three objective functions: (1) systemic; (2) coronary; and (3) combined systemic and coronary oxygen deliveries are maximized. Results show that a smaller shunt diameter with a distal shunt-brachiocephalic anastomosis is optimal for systemic oxygen delivery, whereas a more proximal anastomosis is optimal for coronary oxygen delivery and a shunt between these two anatomies is optimal for both systemic and coronary oxygen deliveries. Results are used to quantify the origin of blood flow going through the shunt and its relationship with shunt geometry. Results show that coronary artery flow is directly related to shunt position.

An Efficient Preconditioner for Linear System Solution in Multi-Domain Modeling of the Circulatory System

2013 ◽  
Author(s):  
Mahdi Esmaily Moghadam ◽  
Yuri Bazilevs ◽  
Tain-Yen Hsia ◽  
Alison Marsden
Keyword(s):  
Strong Coupling ◽  
Large Scale ◽  
Computational Cost ◽  
Circulatory System ◽  
Flow Simulation ◽  
Global Dynamics ◽  
Domain Modeling ◽  
Computationally Efficient ◽  
Lumped Parameter ◽  
System Solution

A closed-loop lumped parameter network (LPN) coupled to a 3D domain is a powerful tool that can be used to model the global dynamics of the circulatory system. Coupling a 0D LPN to a 3D CFD domain is a numerically challenging problem, often associated with instabilities, extra computational cost, and loss of modularity. A computationally efficient finite element framework has been recently proposed that achieves numerical stability without sacrificing modularity [1]. This type of coupling introduces new challenges in the linear algebraic equation solver (LS), producing an strong coupling between flow and pressure that leads to an ill-conditioned tangent matrix. In this paper we exploit this strong coupling to obtain a novel and efficient algorithm for the linear solver (LS). We illustrate the efficiency of this method on several large-scale cardiovascular blood flow simulation problems.

Closed-Loop Lumped Parameter Cardiovascular Model of Infarct Border Zone Pacing

2010 ◽  
Author(s):  
James J. Pilla ◽  
Kevin Koomalsingh ◽  
Robert C. Gorman
Keyword(s):  
Closed Loop ◽  
Border Zone ◽  
Unique Form ◽  
Cardiovascular Hemodynamics ◽  
Strain Pattern ◽  
Cardiovascular Model ◽  
Lumped Parameter ◽  
And Function ◽  
Infarct Border Zone ◽  
Infarct Border

The border zone (BZ) region has been classified as a unique form of dysfunctional myocardium adjacent to an infarct that is normally perfused but has an abnormal systolic strain pattern (1). This abnormal strain has been theorized to result in a proliferation of the hypocontractility region to extend to involve progressively more normally functioning myocardium, resulting in ventricular dilatation and heart failure (2,3). It has been theorized that contracting the BZ prior to the remote myocardium can normalize strain distribution, which could improve cardiac function and mitigate remodeling. This study developed a closed-loop lumped parameter cardiovascular model to evaluate the effect of BZ pacing on cardiovascular hemodynamics and function.

scholarly journals Virtual surgeries in patients with congenital heart disease: a multi-scale modelling test case

2011 ◽  
Vol 369 (1954) ◽  
pp. 4316-4330 ◽  
Author(s):  
A. Baretta ◽  
C. Corsini ◽  
W. Yang ◽  
I. E. Vignon-Clementel ◽  
A. L. Marsden ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Congenital Heart ◽  
Closed Loop ◽  
Three Dimensional ◽  
Scale Model ◽  
Patient Specific ◽  
Loop Model ◽  
Multi Scale ◽  
Venae Cavae ◽  
Lumped Parameter

The objective of this work is to perform a virtual planning of surgical repairs in patients with congenital heart diseases—to test the predictive capability of a closed-loop multi-scale model. As a first step, we reproduced the pre-operative state of a specific patient with a univentricular circulation and a bidirectional cavopulmonary anastomosis (BCPA), starting from the patient's clinical data. Namely, by adopting a closed-loop multi-scale approach, the boundary conditions at the inlet and outlet sections of the three-dimensional model were automatically calculated by a lumped parameter network. Successively, we simulated three alternative surgical designs of the total cavopulmonary connection (TCPC). In particular, a T-junction of the venae cavae to the pulmonary arteries (T-TCPC), a design with an offset between the venae cavae (O-TCPC) and a Y-graft design (Y-TCPC) were compared. A multi-scale closed-loop model consisting of a lumped parameter network representing the whole circulation and a patient-specific three-dimensional finite volume model of the BCPA with detailed pulmonary anatomy was built. The three TCPC alternatives were investigated in terms of energetics and haemodynamics. Effects of exercise were also investigated. Results showed that the pre-operative caval flows should not be used as boundary conditions in post-operative simulations owing to changes in the flow waveforms post-operatively. The multi-scale approach is a possible solution to overcome this incongruence. Power losses of the Y-TCPC were lower than all other TCPC models both at rest and under exercise conditions and it distributed the inferior vena cava flow evenly to both lungs. Further work is needed to correlate results from these simulations with clinical outcomes.

Variable responses of regional renal oxygenation and perfusion to vasoactive agents in awake sheep

2015 ◽  
Vol 309 (10) ◽  
pp. R1226-R1233 ◽  
Author(s):  
Paolo Calzavacca ◽  
Roger G. Evans ◽  
Michael Bailey ◽  
Rinaldo Bellomo ◽  
Clive N. May
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Delivery ◽  
Tissue Perfusion ◽  
Renal Tissue ◽  
Laser Doppler ◽  
Vasoactive Agents ◽  
Doppler Probe ◽  
Renal Oxygen Consumption ◽  
Artery Flow ◽  
Renal Oxygen

Vasoactive agents are used in critical care to optimize circulatory function, but their effects on renal tissue oxygenation in the absence of anesthesia remain largely unknown. Therefore, we assessed the effects of multiple vasoactive agents on regional kidney oxygenation in awake sheep. Sheep were surgically instrumented with pulmonary and renal artery flow probes, and combination fiber-optic probes, in the renal cortex and medulla, comprising a fluorescence optode to measure tissue Po2 and a laser-Doppler probe to assess tissue perfusion. Carotid arterial and renal venous cannulas enabled measurement of arterial pressure and total renal oxygen delivery and consumption. Norepinephrine (0.1 or 0.8 μg·kg−1·min−1) dose-dependently reduced cortical and medullary laser Doppler flux (LDF) and Po2 without significantly altering renal blood flow (RBF), or renal oxygen delivery or consumption. Angiotensin II (9.8 ± 2.1 μg/h) reduced RBF by 21%, renal oxygen delivery by 28%, oxygen consumption by 18%, and medullary Po2 by 38%, but did not significantly alter cortical Po2 or cortical or medullary LDF. Arginine vasopressin (3.3 ± 0.5 μg/h) caused similar decreases in RBF and renal oxygen delivery, but did not significantly alter renal oxygen consumption or cortical or medullary LDF or Po2. Captopril had no observable effects on cortical or medullary LDF or Po2, at a dose that increased renal oxygen delivery by 24%, but did not significantly alter renal oxygen consumption. We conclude that vasoactive agents have diverse effects on regional kidney oxygenation in awake sheep that are not predictable from their effects on LDF, RBF, or total renal oxygen delivery and consumption.

Multilevel Hierarchical Estimation for Thermal Management Systems of Electrified Vehicles With Experimental Validation

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Pamela J. Tannous ◽  
Andrew G. Alleyne
Keyword(s):  
Thermal Management ◽  
Closed Loop ◽  
Order Reduction ◽  
Management Systems ◽  
Estimation Accuracy ◽  
Loop Control ◽  
Hierarchical Estimation ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
Electrified Vehicles

Abstract This paper presents a multilevel model-based hierarchical estimation framework for complex thermal management systems of electrified vehicles. System dynamics are represented by physics-based lumped parameter models derived from a graph-based modeling approach. The complexity of the hierarchical models is reduced by applying an aggregation-based model-order reduction technique that preserves the physical correspondence between a reduced-order model and the physical system. This paper also presents a case study in which a hierarchical observer is designed to estimate the dynamics of a candidate system. The hierarchical observer is connected to a previously developed hierarchical controller for closed-loop control, and the closed-loop performance is demonstrated through simulation and real-time experimental results. A comparison between the proposed hierarchical observer and a centralized observer shows the tradeoff between the estimation accuracy and the computational complexity of the two approaches.

scholarly journals THE TIME DELAY OF AIR/OXYGEN MIXTURE DELIVERY AFTER THE CHANGE OF SET FIO2: AN IMPROVEMENT OF A NEONATAL MATHEMATICAL MODEL

2020 ◽  
Vol 49 (3) ◽  
pp. 77-82
Author(s):  
Leoš Tejkl ◽  
Jakub Ráfl ◽  
Petr Kudrna
Keyword(s):  
Mathematical Model ◽  
Time Delay ◽  
Oxygen Transport ◽  
Oxygen Delivery ◽  
Closed Loop ◽  
Oxygen Mixture ◽  
Peripheral Oxygen Saturation ◽  
Loop Control ◽  
Closed Loop Systems ◽  
Ventilation Support

<p>Oxygen therapy is an essential treatment of premature infants suffering from hypoxemia. Normoxemia is maintained by an adjustment of the fraction of oxygen (FiO<sub>2</sub>) in the inhaled gas mixture that is set manually or automatically based on peripheral oxygen saturation (SpO<sub>2</sub>). Automatic closed-loop systems could be more successful in controlling SpO<sub>2</sub> than traditional manual approaches. Computer models of neonatal oxygen transport have been developed as a tool for design, validation, and comparison of the automatic control algorithms. The aim of this study was to investigate and implement the time delay of oxygen delivery after a change of set FiO<sub>2</sub> during noninvasive ventilation support to enhance an available mathematical model of neonatal oxygen transport. The time delay of oxygen delivery after the change of FiO<sub>2</sub> during the noninvasive nasal Continuous Positive Airway Pressure (nCPAP) ventilation support and during the High Flow High Humidity Nasal Cannula (HFHHNC) ventilation support was experimentally measured using an electromechanical gas blender and a physical model of neonatal lungs. Results show the overall time delay of the change in the oxygen fraction can be divided into the baseline of delay, with a typical time delay 5.5 s for nCPAP and 6.5 s for HFHHNC s, and an exponential rising phase with a time constant about 2–3 s. A delay subsystem was implemented into the mathematical model for a more realistic performance when simulating closed-loop control of oxygenation.</p>

Warship propulsion system control

2012 ◽  
Vol 226 (10) ◽  
pp. 2402-2421 ◽  
Author(s):  
Robert Whalley ◽  
Alaa Abdul-Ameer
Keyword(s):  
Closed Loop ◽  
Spatial Dispersion ◽  
Controller Design ◽  
Twist Angle ◽  
Propulsion System ◽  
System Control ◽  
Closed Loop System ◽  
Lumped Parameter ◽  
Parameter Approach ◽  
Reference Input

The modelling of a dual gas turbine, single-shaft transmission drive, for a naval propulsion system, is considered. Owing to the spatial dispersion of the arrangement, a distributed–lumped parameter approach to the dynamic analysis problem is necessary. This enables the relatively concentrated assemblies to be included as lumped, pointwise representations and the propulsion shaft to be incorporated as a dispersed inertia and stiffness element. A multivariable, least effort controller design strategy is employed to achieve the regulation required. The performance of the closed-loop system following reference input and load disturbances is evaluated and the drive shaft speed and twist angle response transients are computed.

Power Transmission System Modeling

2005 ◽  
Author(s):  
M. Ebrahimi ◽  
R. Whalley
Keyword(s):  
Closed Loop ◽  
Power Transmission ◽  
System Modeling ◽  
Analytical Models ◽  
Response Dynamics ◽  
Torsional Response ◽  
Lumped Parameter ◽  
Power Transmission Systems ◽  
Stiffness Characteristics ◽  
Computer Studies

The modeling of mechanical power transmission systems comprising rotors, shafts and bearing assemblies will be considered. Spatially dispersed elements, with significant distributed inertia and stiffness characteristics, will be included in the system descriptions. Relatively concentrated units will be modeled using conventional lumped parameter techniques. Compact, accurate analytical models in impedance and admittance form will be derived enabling the investigation of the combined distributed-lumped system’s, torsional response dynamics. The performance of the system under open and closed -loop conditions will be illustrated via computer studies. Typical mechanical drive application will be presented.

scholarly journals A Simulation Protocol for Exercise Physiology in Fontan Patients Using a Closed Loop Lumped-Parameter Model

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Ethan Kung ◽  
Giancarlo Pennati ◽  
Francesco Migliavacca ◽  
Tain-Yen Hsia ◽  
Richard Figliola ◽  
...  
Keyword(s):  
Clinical Data ◽  
Closed Loop ◽  
Exercise Physiology ◽  
Clinical Findings ◽  
Lumped Parameter Model ◽  
Patient Specific ◽  
Specific Reference ◽  
Fontan Patient ◽  
Lumped Parameter ◽  
Fontan Patients

Background: Reduced exercise capacity is nearly universal among Fontan patients, though its etiology is not yet fully understood. While previous computational studies have attempted to model Fontan exercise, they did not fully account for global physiologic mechanisms nor directly compare results against clinical and physiologic data. Methods: In this study, we developed a protocol to simulate Fontan lower-body exercise using a closed-loop lumped-parameter model describing the entire circulation. We analyzed clinical exercise data from a cohort of Fontan patients, incorporated previous clinical findings from literature, quantified a comprehensive list of physiological changes during exercise, translated them into a computational model of the Fontan circulation, and designed a general protocol to model Fontan exercise behavior. Using inputs of patient weight, height, and if available, patient-specific reference heart rate (HR) and oxygen consumption, this protocol enables the derivation of a full set of parameters necessary to model a typical Fontan patient of a given body-size over a range of physiologic exercise levels. Results: In light of previous literature data and clinical knowledge, the model successfully produced realistic trends in physiological parameters with exercise level. Applying this method retrospectively to a set of clinical Fontan exercise data, direct comparison between simulation results and clinical data demonstrated that the model successfully reproduced the average exercise response of a cohort of typical Fontan patients. Conclusion: This work is intended to offer a foundation for future advances in modeling Fontan exercise, highlight the needs in clinical data collection, and provide clinicians with quantitative reference exercise physiologies for Fontan patients.

Sign in / Sign up

Export Citation Format

Share Document