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Clark AR, Burrowes KS, Tawhai MH. Integrative Computational Models of Lung Structure-Function Interactions. Compr Physiol 2021; 11:1501-1530. [PMID: 33577123 DOI: 10.1002/cphy.c200011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Anatomically based integrative models of the lung and their interaction with other key components of the respiratory system provide unique capabilities for investigating both normal and abnormal lung function. There is substantial regional variability in both structure and function within the normal lung, yet it remains capable of relatively efficient gas exchange by providing close matching of air delivery (ventilation) and blood delivery (perfusion) to regions of gas exchange tissue from the scale of the whole organ to the smallest continuous gas exchange units. This is despite remarkably different mechanisms of air and blood delivery, different fluid properties, and unique scale-dependent anatomical structures through which the blood and air are transported. This inherent heterogeneity can be exacerbated in the presence of disease or when the body is under stress. Current computational power and data availability allow for the construction of sophisticated data-driven integrative models that can mimic respiratory system structure, function, and response to intervention. Computational models do not have the same technical and ethical issues that can limit experimental studies and biomedical imaging, and if they are solidly grounded in physiology and physics they facilitate investigation of the underlying interaction between mechanisms that determine respiratory function and dysfunction, and to estimate otherwise difficult-to-access measures. © 2021 American Physiological Society. Compr Physiol 11:1501-1530, 2021.
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Affiliation(s)
- Alys R Clark
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Kelly S Burrowes
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
| | - Merryn H Tawhai
- Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand
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2
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Karthika CL, Ahalya S, Radhakrishnan N, Kartha CC, Sumi S. Hemodynamics mediated epigenetic regulators in the pathogenesis of vascular diseases. Mol Cell Biochem 2020; 476:125-143. [PMID: 32844345 DOI: 10.1007/s11010-020-03890-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 08/14/2020] [Indexed: 12/19/2022]
Abstract
Endothelium of blood vessels is continuously exposed to various hemodynamic forces. Flow-mediated epigenetic plasticity regulates vascular endothelial function. Recent studies have highlighted the significant role of mechanosensing-related epigenetics in localized endothelial dysfunction and the regional susceptibility for lesions in vascular diseases. In this article, we review the epigenetic mechanisms such as DNA de/methylation, histone modifications, as well as non-coding RNAs in promoting endothelial dysfunction in major arterial and venous diseases, consequent to hemodynamic alterations. We also discuss the current challenges and future prospects for the use of mechanoepigenetic mediators as biomarkers of early stages of vascular diseases and dysregulated mechanosensing-related epigenetic regulators as therapeutic targets in various vascular diseases.
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Affiliation(s)
- C L Karthika
- Cardiovascular Diseases and Diabetes Biology, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala, 695014, India
| | - S Ahalya
- Cardiovascular Diseases and Diabetes Biology, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala, 695014, India
| | - N Radhakrishnan
- St.Thomas Institute of Research on Venous Diseases, Changanassery, Kerala, India
| | - C C Kartha
- Society for Continuing Medical Education & Research (SOCOMER), Kerala Institute of Medical Sciences, Thiruvananthapuram, Kerala, India
| | - S Sumi
- Cardiovascular Diseases and Diabetes Biology, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala, 695014, India.
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3
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Hebbar UU, Banerjee RK. Influence of coupled hemodynamics-arterial wall interaction on compliance in a realistic pulmonary artery with variable intravascular wall properties. Med Image Anal 2019; 57:56-71. [PMID: 31279216 DOI: 10.1016/j.media.2019.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 05/01/2019] [Accepted: 06/19/2019] [Indexed: 11/15/2022]
Abstract
Pulmonary hypertension is characterized by elevation of pulmonary artery (PA) pressure (p) and structural remodeling of the PA wall, leading to reduction in arterial compliance (c). As a step towards improving diagnosis of pulmonary disease, we use the PA branch geometry (main pulmonary artery (MPA) branching into left (LPA) and right (RPA) pulmonary arteries) obtained from MRI in conjunction with an inverse algorithm to obtain the pre-stress level in the artery walls. Next, a coupled blood-wall interaction (BWI) calculation provides hemodynamic information as well as compliance of the PA walls. We show that the computed load-free geometry from the inverse algorithm exhibits a 27.8% lower inner diameter (d) and 18.5% lower outer d compared to the in vivo geometry from MRI. Further, the mean p computed from the BWI computation in the main PA (pMPA-n) is within 4% of the mean pMPA-e (n-numerical; e-experimental). Also, the mean Q computed in the left PA (QLPA-n) is within 10% of the mean QLPA-e. Finally, the compliance cMPA-n is computed to be 27% lower than cMPA-e, while the cLPA-n is computed to be 20.4% lower than cLPA-e. Importantly, the PA shows significant intra-vascular variation in compliance, with the MPA showing higher overall compliance compared to the LPA (3.5-4 times).
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Affiliation(s)
- Ullhas U Hebbar
- 593 Rhodes Hall, Department of Mechanical Engineering, University of Cincinnati, OH, 45221, United States
| | - Rupak K Banerjee
- 593 Rhodes Hall, Department of Mechanical Engineering, University of Cincinnati, OH, 45221, United States.
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4
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Kong F, Kheyfets V, Finol E, Cai XC. Simulation of unsteady blood flows in a patient-specific compliant pulmonary artery with a highly parallel monolithically coupled fluid-structure interaction algorithm. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2019; 35:e3208. [PMID: 30989794 DOI: 10.1002/cnm.3208] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Revised: 02/20/2019] [Accepted: 04/07/2019] [Indexed: 06/09/2023]
Abstract
Computational fluid dynamics (CFD) is increasingly used to study blood flows in patient-specific arteries for understanding certain cardiovascular diseases. The techniques work quite well for relatively simple problems but need improvements when the problems become harder when (a) the geometry becomes complex (eg, a few branches to a full pulmonary artery), (b) the model becomes more complex (eg, fluid-only to coupled fluid-structure interaction), (c) both the fluid and wall models become highly nonlinear, and (d) the computer on which we run the simulation is a supercomputer with tens of thousands of processor cores. To push the limit of CFD in all four fronts, in this paper, we develop and study a highly parallel algorithm for solving a monolithically coupled fluid-structure system for the modeling of the interaction of the blood flow and the arterial wall. As a case study, we consider a patient-specific, full size pulmonary artery obtained from computed tomography (CT) images, with an artificially added layer of wall with a fixed thickness. The fluid is modeled with a system of incompressible Navier-Stokes equations, and the wall is modeled by a geometrically nonlinear elasticity equation. As far as we know, this is the first time the unsteady blood flow in a full pulmonary artery is simulated without assuming a rigid wall. The proposed numerical algorithm and software scale well beyond 10 000 processor cores on a supercomputer for solving the fluid-structure interaction problem discretized with a stabilized finite element method in space and an implicit scheme in time involving hundreds of millions of unknowns.
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Affiliation(s)
- Fande Kong
- Modeling and Simulation, Idaho National Laboratory, Idaho Falls, Idaho
| | - Vitaly Kheyfets
- School of Medicine, University of Colorado Denver, Aurora, Colorado
| | - Ender Finol
- Department of Mechanical Engineering, University of Texas at San Antonio, San Antonio, Texas
| | - Xiao-Chuan Cai
- Department of Computer Science, University of Colorado Boulder, Boulder, Colorado
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5
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Evolution of hemodynamic forces in the pulmonary tree with progressively worsening pulmonary arterial hypertension in pediatric patients. Biomech Model Mechanobiol 2019; 18:779-796. [DOI: 10.1007/s10237-018-01114-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Accepted: 12/24/2018] [Indexed: 01/26/2023]
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6
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Kong F, Kheyfets V, Finol E, Cai XC. An efficient parallel simulation of unsteady blood flows in patient-specific pulmonary artery. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2018; 34:e2952. [PMID: 29245182 DOI: 10.1002/cnm.2952] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 10/26/2017] [Accepted: 12/02/2017] [Indexed: 06/07/2023]
Abstract
Simulation of blood flows in the pulmonary artery provides some insight into certain diseases by examining the relationship between some continuum metrics, eg, the wall shear stress acting on the vascular endothelium, which responds to flow-induced mechanical forces by releasing vasodilators/constrictors. V. Kheyfets, in his previous work, studies numerically a patient-specific pulmonary circulation to show that decreasing wall shear stress is correlated with increasing pulmonary vascular impedance. In this paper, we develop a scalable parallel algorithm based on domain decomposition methods to investigate an unsteady model with patient-specific pulsatile waveforms as the inlet boundary condition. The unsteady model offers tremendously more information about the dynamic behavior of the flow field, but computationally speaking, the simulation is a lot more expensive since a problem which is similar to the steady-state problem has to be solved many times, and therefore, the traditional sequential approach is not suitable anymore. We show computationally that simulations using the proposed parallel approach with up to 10 000 processor cores can be obtained with much reduced compute time. This makes the technology potentially usable for the routine study of the dynamic behavior of blood flows in the pulmonary artery, in particular, the changes of the blood flows and the wall shear stress in the spatial and temporal dimensions.
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Affiliation(s)
- Fande Kong
- Modeling and Simulation, Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-3840, USA
| | - Vitaly Kheyfets
- School of Medicine, University of Colorado Denver, Aurora, CO 80045-7109, USA
| | - Ender Finol
- Department of Mechanical Engineering, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Xiao-Chuan Cai
- Department of Computer Science, University of Colorado Boulder, Boulder, CO 80309-0430, USA
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Image-based computational assessment of vascular wall mechanics and hemodynamics in pulmonary arterial hypertension patients. J Biomech 2017; 68:84-92. [PMID: 29310945 DOI: 10.1016/j.jbiomech.2017.12.022] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 11/30/2017] [Accepted: 12/17/2017] [Indexed: 11/20/2022]
Abstract
Pulmonary arterial hypertension (PAH) is a disease characterized by an elevated pulmonary arterial (PA) pressure. While several computational hemodynamic models of the pulmonary vasculature have been developed to understand PAH, they are lacking in some aspects, such as the vessel wall deformation and its lack of calibration against measurements in humans. Here, we describe a computational modeling framework that addresses these limitations. Specifically, computational models describing the coupling of hemodynamics and vessel wall mechanics in the pulmonary vasculature of a PAH patient and a normal subject were developed. Model parameters, consisting of linearized stiffness E of the large vessels and Windkessel parameters for each outflow branch, were calibrated against in vivo measurements of pressure, flow and vessel wall deformation obtained, respectively, from right-heart catheterization, phase-contrast and cine magnetic resonance images. Calibrated stiffness E of the proximal PA was 2.0 and 0.5 MPa for the PAH and normal models, respectively. Calibrated total compliance CT and resistance RT of the distal vessels were, respectively, 0.32 ml/mmHg and 11.3 mmHg∗min/l for the PAH model, and 2.93 ml/mmHg and 2.6 mmHg∗min/l for the normal model. These results were consistent with previous findings that the pulmonary vasculature is stiffer with more constricted distal vessels in PAH patients. Individual effects on PA pressure due to remodeling of the distal and proximal compartments of the pulmonary vasculature were also investigated in a sensitivity analysis. The analysis suggests that the remodeling of distal vasculature contributes more to the increase in PA pressure than the remodeling of proximal vasculature.
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Abstract
Respiratory disease is a significant problem worldwide, and it is a problem with increasing prevalence. Pathology in the upper airways and lung is very difficult to diagnose and treat, as response to disease is often heterogeneous across patients. Computational models have long been used to help understand respiratory function, and these models have evolved alongside increases in the resolution of medical imaging and increased capability of functional imaging, advances in biological knowledge, mathematical techniques and computational power. The benefits of increasingly complex and realistic geometric and biophysical models of the respiratory system are that they are able to capture heterogeneity in patient response to disease and predict emergent function across spatial scales from the delicate alveolar structures to the whole organ level. However, with increasing complexity, models become harder to solve and in some cases harder to validate, which can reduce their impact clinically. Here, we review the evolution of complexity in computational models of the respiratory system, including successes in translation of models into the clinical arena. We also highlight major challenges in modelling the respiratory system, while making use of the evolving functional data that are available for model parameterisation and testing.
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Affiliation(s)
- Alys R Clark
- 1 Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| | - Haribalan Kumar
- 1 Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| | - Kelly Burrowes
- 2 Department of Chemical and Materials Engineering, The University of Auckland, Auckland, New Zealand
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Kheyfets VO, Rios L, Smith T, Schroeder T, Mueller J, Murali S, Lasorda D, Zikos A, Spotti J, Reilly JJ, Finol EA. Patient-specific computational modeling of blood flow in the pulmonary arterial circulation. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2015; 120:88-101. [PMID: 25975872 PMCID: PMC4441565 DOI: 10.1016/j.cmpb.2015.04.005] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Revised: 03/15/2015] [Accepted: 04/14/2015] [Indexed: 06/04/2023]
Abstract
Computational fluid dynamics (CFD) modeling of the pulmonary vasculature has the potential to reveal continuum metrics associated with the hemodynamic stress acting on the vascular endothelium. It is widely accepted that the endothelium responds to flow-induced stress by releasing vasoactive substances that can dilate and constrict blood vessels locally. The objectives of this study are to examine the extent of patient specificity required to obtain a significant association of CFD output metrics and clinical measures in models of the pulmonary arterial circulation, and to evaluate the potential correlation of wall shear stress (WSS) with established metrics indicative of right ventricular (RV) afterload in pulmonary hypertension (PH). Right Heart Catheterization (RHC) hemodynamic data and contrast-enhanced computed tomography (CT) imaging were retrospectively acquired for 10 PH patients and processed to simulate blood flow in the pulmonary arteries. While conducting CFD modeling of the reconstructed patient-specific vasculatures, we experimented with three different outflow boundary conditions to investigate the potential for using computationally derived spatially averaged wall shear stress (SAWSS) as a metric of RV afterload. SAWSS was correlated with both pulmonary vascular resistance (PVR) (R(2)=0.77, P<0.05) and arterial compliance (C) (R(2)=0.63, P<0.05), but the extent of the correlation was affected by the degree of patient specificity incorporated in the fluid flow boundary conditions. We found that decreasing the distal PVR alters the flow distribution and changes the local velocity profile in the distal vessels, thereby increasing the local WSS. Nevertheless, implementing generic outflow boundary conditions still resulted in statistically significant SAWSS correlations with respect to both metrics of RV afterload, suggesting that the CFD model could be executed without the need for complex outflow boundary conditions that require invasively obtained patient-specific data. A preliminary study investigating the relationship between outlet diameter and flow distribution in the pulmonary tree offers a potential computationally inexpensive alternative to pressure based outflow boundary conditions.
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Affiliation(s)
- Vitaly O Kheyfets
- Department of Bioengineering, UC Denver - Anschutz Medical Campus, Children's Hospital Colorado, 13123 E. 16th Ave B100, Aurora, CO 80045, United States.
| | - Lourdes Rios
- The University of Texas at San Antonio, Department of Biomedical Engineering, San Antonio, TX 78249, United States; The University of Texas at San Antonio, Department of Biological Sciences, San Antonio, TX 78249, United States.
| | - Triston Smith
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - Theodore Schroeder
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - Jeffrey Mueller
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - Srinivas Murali
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - David Lasorda
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - Anthony Zikos
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - Jennifer Spotti
- Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Radiology, Pittsburgh, PA 15212, United States; Western Pennsylvania Allegheny Health System, Allegheny General Hospital, McGinnis Cardiovascular Institute, Department of Cardiology, Pittsburgh, PA 15212, United States.
| | - John J Reilly
- University of Pittsburgh, Department of Medicine, Pittsburgh, PA 15261, United States.
| | - Ender A Finol
- The University of Texas at San Antonio, Department of Biomedical Engineering, San Antonio, TX 78249, United States.
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Lee N, Taylor MD, Banerjee RK. Right ventricle-pulmonary circulation dysfunction: a review of energy-based approach. Biomed Eng Online 2015; 14 Suppl 1:S8. [PMID: 25602641 PMCID: PMC4306123 DOI: 10.1186/1475-925x-14-s1-s8] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Patients with repaired or palliated right heart congenital heart disease (CHD) are often left with residual lesions that progress and can result in significant morbidity. However, right ventricular-pulmonary arterial evaluation and the timing of reintvervention is still subjective. Currently, it relies on symptomology, or RV imaging-based metrics from echocardiography or MR derived parameters including right ventricular (RV) ejection fraction (EF), end-systolic pressure (ESP), and end-diastolic volume (EDV). However, the RV is coupled to the pulmonary vasculature, and they are not typically evaluated together. For example, the dysfunctional right ventricular-pulmonary circulation (RV-PC) adversely affects the RV myocardial performance resulting in decreased efficiency. Therefore, comprehensive hemodynamic assessment should incorporate changes in RV-PC and energy efficiency for CHD patients. The ventricular pressure-volume relationship (PVR) and other energy-based endpoints derived from PVR, such as stroke work (SW) and ventricular elastance (Ees), can provide a measure of RV performance. However, a detailed explanation of the relationship between RV performance and pulmonary arterial hemodynamics is lacking. More importantly, PVR is impractical for routine longitudinal evaluation in a clinical setting, because it requires invasive catheterization. As an alternative, analytical methods and computational fluid dynamics (CFD) have been used to compute energy endpoints, such as power loss or energy dissipation, in abnormal physiologies. In this review, we review the causes of RV-PA failure and the limitation of current clinical parameters to quantify RV-PC dysfunction. Then, we describe the advantage of currently available energy-based endpoints and emerging energy endpoints, such as energy loss in the Pas or kinetic energy, obtained from a new non-invasive imaging technique, i.e. 4D phase contrast MRI.
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Fata B, Zhang W, Amini R, Sacks MS. Insights into regional adaptations in the growing pulmonary artery using a meso-scale structural model: effects of ascending aorta impingement. J Biomech Eng 2014; 136:021009. [PMID: 24402562 DOI: 10.1115/1.4026457] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 01/10/2014] [Indexed: 11/08/2022]
Abstract
As the next step in our investigations into the structural adaptations of the main pulmonary artery (PA) during postnatal growth, we utilized the extensive experimental measurements of the growing ovine PA from our previous study (Fata et al., 2013, "Estimated in vivo Postnatal Surface Growth Patterns of the Ovine Main Pulmonary Artery and Ascending Aorta," J. Biomech. Eng., 135(7), pp. 71010-71012). to develop a structural constitutive model for the PA wall tissue. Novel to the present approach was the treatment of the elastin network as a distributed fiber network rather than a continuum phase. We then utilized this model to delineate structure-function differences in the PA wall at the juvenile and adult stages. Overall, the predicted elastin moduli exhibited minor differences remained largely unchanged with age and region (in the range of 150 to 200 kPa). Similarly, the predicted collagen moduli ranged from ∼1,600 to 2700 kPa in the four regions studied in the juvenile state. Interestingly, we found for the medial region that the elastin and collagen fiber splay underwent opposite changes (collagen standard deviation juvenile = 17 deg to adult = 28 deg, elastin standard deviation juvenile = 35 deg to adult = 27 deg), along with a trend towards more rapid collagen fiber strain recruitment with age, along with a drop in collagen fiber moduli, which went from 2700 kPa for the juvenile stage to 746 kPa in the adult. These changes were likely due to the previously observed impingement of the relatively stiff ascending aorta on the growing PA medial region. Intuitively, the effects of the local impingement would be to lower the local wall stress, consistent with the observed parallel decrease in collagen modulus. These results suggest that during the postnatal somatic growth period local stresses can substantially modulate regional tissue microstructure and mechanical behaviors in the PA. We further underscore that our previous studies indicated an increase in effective PA wall stress with postnatal maturation. When taken together with the fact that the observed changes in mechanical behavior and structure in the growing PA wall were modest in the other three regions studied, our collective results suggest that the majority of the growing PA wall is subjected to increasing stress levels with age without undergoing major structural adaptations. This observation is contrary to the accepted theory of maintenance of homeostatic stress levels in the regulation of vascular function, and suggests alternative mechanisms might regulate postnatal somatic growth. Understanding the underlying mechanisms will help to improve our understanding of congenital defects of the PA and lay the basis for functional duplication in their repair and replacement.
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Influence of distal resistance and proximal stiffness on hemodynamics and RV afterload in progression and treatments of pulmonary hypertension: a computational study with validation using animal models. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2013; 2013:618326. [PMID: 24367392 PMCID: PMC3842075 DOI: 10.1155/2013/618326] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Revised: 09/09/2013] [Accepted: 09/25/2013] [Indexed: 01/17/2023]
Abstract
We develop a simple computational model based on measurements from a hypoxic neonatal calf model of pulmonary hypertension (PH) to investigate the interplay between vascular and ventricular measures in the setting of progressive PH. Model parameters were obtained directly from in vivo and ex vivo measurements of neonatal calves. Seventeen sets of model-predicted impedance and mean pulmonary arterial pressure (mPAP) show good agreement with the animal measurements, thereby validating the model. Next, we considered a predictive model in which three parameters, PVR, elastic modulus (EM), and arterial thickness, were varied singly from one simulation to the next to study their individual roles in PH progression. Finally, we used the model to predict the individual impacts of clinical (vasodilatory) and theoretical (compliance increasing) PH treatments on improving pulmonary hemodynamics. Our model (1) displayed excellent patient-specific agreement with measured global pulmonary parameters; (2) quantified relationships between PVR and mean pressure and PVS and pulse pressure, as well as studiying the right ventricular (RV) afterload, which could be measured as a hydraulic load calculated from spectral analysis of pulmonary artery pressure and flow waves; (3) qualitatively confirmed the derangement of vascular wall shear stress in progressive PH; and (4) established that decreasing proximal vascular stiffness through a theoretical treatment of reversing proximal vascular remodeling could decrease RV afterload.
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Kheyfets VO, O'Dell W, Smith T, Reilly JJ, Finol EA. Considerations for numerical modeling of the pulmonary circulation--a review with a focus on pulmonary hypertension. J Biomech Eng 2013; 135:61011-15. [PMID: 23699723 PMCID: PMC3705788 DOI: 10.1115/1.4024141] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Revised: 03/25/2013] [Accepted: 04/04/2013] [Indexed: 12/12/2022]
Abstract
Both in academic research and in clinical settings, virtual simulation of the cardiovascular system can be used to rapidly assess complex multivariable interactions between blood vessels, blood flow, and the heart. Moreover, metrics that can only be predicted with computational simulations (e.g., mechanical wall stress, oscillatory shear index, etc.) can be used to assess disease progression, for presurgical planning, and for interventional outcomes. Because the pulmonary vasculature is susceptible to a wide range of pathologies that directly impact and are affected by the hemodynamics (e.g., pulmonary hypertension), the ability to develop numerical models of pulmonary blood flow can be invaluable to the clinical scientist. Pulmonary hypertension is a devastating disease that can directly benefit from computational hemodynamics when used for diagnosis and basic research. In the present work, we provide a clinical overview of pulmonary hypertension with a focus on the hemodynamics, current treatments, and their limitations. Even with a rich history in computational modeling of the human circulation, hemodynamics in the pulmonary vasculature remains largely unexplored. Thus, we review the tasks involved in developing a computational model of pulmonary blood flow, namely vasculature reconstruction, meshing, and boundary conditions. We also address how inconsistencies between models can result in drastically different flow solutions and suggest avenues for future research opportunities. In its current state, the interpretation of this modeling technology can be subjective in a research environment and impractical for clinical practice. Therefore, considerations must be taken into account to make modeling reliable and reproducible in a laboratory setting and amenable to the vascular clinic. Finally, we discuss relevant existing models and how they have been used to gain insight into cardiopulmonary physiology and pathology.
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Affiliation(s)
- V. O. Kheyfets
- Department of Biomedical Engineering,The University of Texas at San Antonio,AET 1.360, One UTSA Circle,San Antonio, TX 78249
| | - W. O'Dell
- Department of Radiation Oncology,University of Florida,Shands Cancer Center,P.O. Box 100385,2033 Mowry Road,Gainesville, FL 32610
| | - T. Smith
- Western Allegheny Health System,Allegheny General Hospital,Gerald McGinnis Cardiovascular Institute,320 East North Avenue,Pittsburgh, PA 15212
| | - J. J. Reilly
- Department of Medicine,The University of Pittsburgh,1218 Scaife Hall,3550 Terrace Street,Pittsburgh, PA 15261
| | - E. A. Finol
- Department of Biomedical Engineering,The University of Texas at San Antonio,AET 1.360, One UTSA Circle,San Antonio, TX 78249e-mail:
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14
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Kamenskiy AV, Mactaggart JN, Pipinos II, Gupta PK, Dzenis YA. Hemodynamically motivated choice of patch angioplasty for the performance of carotid endarterectomy. Ann Biomed Eng 2013; 41:263-78. [PMID: 22923061 DOI: 10.1007/s10439-012-0640-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 08/10/2012] [Indexed: 01/10/2023]
Abstract
Patch angioplasty is the most common technique used for the performance of carotid endarterectomy. A large number of materials are available, but little is known to aid the surgeon in choosing a patch while caring for a patient with carotid disease. The objective of this study was to investigate biomechanics of the carotid artery (CA) repaired with patch angioplasty, study the influence of patch width and location of closure on hemodynamics, and to select the optimal patch material from those commonly used. For this purpose, a mathematical model was built that accounts for fluid-structure interaction, three-dimensional arterial geometry, non-linear anisotropic mechanical properties, non-Newtonian flow and in vivo boundary conditions. This model was used to study disease-related mechanical factors in the arterial wall and blood flow for different types of patch angioplasty. Analysis indicated that patch closures performed with autologous vein and bovine pericardium were hemodynamically superior to carotid endarterectomy with synthetic patch angioplasty (polytetrafluoroethylene, Dacron) in terms of restenosis potential. Width of the patch and location of arteriotomy were found to be of paramount importance, with narrow patches being superior to wide patches, and anterior arteriotomy being superior to the lateral arteriotomy. These data can aid vascular surgeons in their selection of patch angioplasty technique and material for the care of patients undergoing open CA repair.
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Affiliation(s)
- Alexey V Kamenskiy
- Department of Surgery, University of Nebraska-Medical Center, 985182 Nebraska-Medical Center, Omaha, NE 68198-5182, USA.
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Su Z, Hunter KS, Shandas R. Impact of pulmonary vascular stiffness and vasodilator treatment in pediatric pulmonary hypertension: 21 patient-specific fluid-structure interaction studies. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2012; 108:617-628. [PMID: 21975085 PMCID: PMC3272113 DOI: 10.1016/j.cmpb.2011.09.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2010] [Revised: 07/21/2011] [Accepted: 09/09/2011] [Indexed: 05/31/2023]
Abstract
Recent clinical studies of pulmonary arterial hypertension (PAH) have found correlations between increased pulmonary vascular stiffness (PVS) and poorer disease outcomes. However, mechanistic questions remain about the relationships amongst PVS, RV power, and vascular hemodynamics in the setting of progressive PAH that are difficult or impossible to answer using direct measurements. Clinically validated patient-specific computational modeling may allow exploration of these issues through perturbation-based predictive testing. Here we use a simple patient-specific model to answer four questions: how do hemodynamics change as PAH worsens? How does increasing PVS impact hemodynamics and RV power? For a patient with moderate PAH, what are the consequences if the pressures increase modestly yet sufficiently to engage collagen in those vessels? What impact does pressure-reducing vasodilator treatment have on hemodynamics? Twenty-one sets of model-predicted impedance and mean PA pressure (mPAP) show good agreement with clinical measurements, thereby validating the model. Worsening was modeled using data from three PAH outcomes groups; these show not only the expected increase in mPAP, but also an increase in pressure pulsatility. Interestingly, chronically increasing mPAP decreased WSS, suggesting that increased PA cross-sectional area affected WSS greater than increased PVS. For a patient with moderately high PVR (12.7 WU) with elastin-based upstream vascular remodeling, moving from elastin-dominant vessel behavior to collagen-dominant behavior caused substantial increases in mPAP, pressure and WSS pulsatility. For the same patient, reducing PVR through a simulated vasodilator to a value equivalent to mild PAH did not decrease pressure pulsatility and dramatically increased WSS pulsatility. Overall, these results suggest a close association between PVS and hemodynamics and that hemodynamics may play an important role in progressing PAH. These support the hypothesis that treatments should target decreasing or reversing upstream vascular remodeling in addition to decreasing mean pressures.
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Affiliation(s)
- Zhenbi Su
- Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309, USA.
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Lara M, Chen CY, Mannor P, Dur O, Menon PG, Yoganathan AP, Pekkan K. Hemodynamics of the Hepatic Venous Three-Vessel Confluences Using Particle Image Velocimetry. Ann Biomed Eng 2011; 39:2398-416. [DOI: 10.1007/s10439-011-0326-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2010] [Accepted: 05/10/2011] [Indexed: 11/27/2022]
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17
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Flow interactions with cells and tissues: cardiovascular flows and fluid-structure interactions. Sixth International Bio-Fluid Mechanics Symposium and Workshop, March 28-30, 2008, Pasadena, California. Ann Biomed Eng 2010; 38:1178-87. [PMID: 20336826 DOI: 10.1007/s10439-010-9900-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Interactions between flow and biological cells and tissues are intrinsic to the circulatory, respiratory, digestive and genitourinary systems. In the circulatory system, an understanding of the complex interaction between the arterial wall (a living multi-component organ with anisotropic, nonlinear material properties) and blood (a shear-thinning fluid with 45% by volume consisting of red blood cells, platelets, and white blood cells) is vital to our understanding of the physiology of the human circulation and the etiology and development of arterial diseases, and to the design and development of prosthetic implants and tissue-engineered substitutes. Similarly, an understanding of the complex dynamics of flow past native human heart valves and the effect of that flow on the valvular tissue is necessary to elucidate the etiology of valvular diseases and in the design and development of valve replacements. In this paper we address the influence of biomechanical factors on the arterial circulation. The first part presents our current understanding of the impact of blood flow on the arterial wall at the cellular level and the relationship between flow-induced stresses and the etiology of atherosclerosis. The second part describes recent advances in the application of fluid-structure interaction analysis to arterial flows and the dynamics of heart valves.
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18
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Li M, Stenmark KR, Shandas R, Tan W. Effects of pathological flow on pulmonary artery endothelial production of vasoactive mediators and growth factors. J Vasc Res 2009; 46:561-71. [PMID: 19571576 DOI: 10.1159/000226224] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Accepted: 11/03/2008] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Alterations in pulmonary blood flow are often associated with the initiation and progression of pulmonary vascular disease. However, the cellular mechanisms involved in mediating flow effects in the pulmonary circulation remain unclear. Depending on the disease condition, flow may be extremely low or high. We therefore examined effects of pathologically low and high flow on endothelial production of factors capable of affecting pulmonary vascular tone and structure as well as on potential underlying mechanisms. METHODS Flow effects on pulmonary endothelial release of NO, PGF(1a), ET-1 and TxB(2), on expression of total and phosphorylated eNOS as well as Akt, and on VEGF were examined. Additionally, in a coculture system, effects of flow-exposed endothelial cells on smooth muscle (SM) proliferation and contractile protein were studied. RESULTS Compared to physiological flow, pathologically high and low flow attenuated endothelial release of NO and PGF(1a), and enhanced release of ET-1. Physiological flow activated the Akt/eNOS pathway, while pathological flow depressed it. Pathologically high flow altered VE-cadherin expression. Pathologically high flow on the endothelium upregulated alpha-SM-actin and SM-MHC without affecting SM proliferation. CONCLUSION Physiological flow leads to production of mediators which favor vasodilation. Pathological flow alters the balance of mediator production which favors vasoconstriction.
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Affiliation(s)
- Min Li
- Department of Pediatrics and CVP Research, University of Colorado at Denver and Health Sciences Center, Denver, CO 80262, USA
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19
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Giannakoulas G, Dimopoulos K, Xu XY. Modelling in congenital heart disease. Art or science? Int J Cardiol 2009; 133:141-4. [PMID: 19046780 DOI: 10.1016/j.ijcard.2008.10.039] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Accepted: 10/25/2008] [Indexed: 11/15/2022]
Abstract
Despite the advances in imaging modalities and surgical techniques, the management of adults with congenital heart disease (ACHD) over the years has remained largely empirical rather than evidence-based. Animal models have been difficult to develop and very costly, while clinical trials are difficult to design and perform in ACHD, leaving gaps in our understanding of the pathophysiology and treatment of congenital heart disease. Disease modelling, both hypothetical and patient-specific, provides an alternative solution to many of these problems. Advances in cardiovascular imaging and diagnostics have led to the easy acquisition of large quantities of structural and functional information, which cannot be handled "intuitively". Computational modelling introduces mathematical rigour in the analysis and utilisation of these data by quantitative simulation and testing of clinically relevant hypotheses through experimentally validated models. Close multidisciplinary collaboration between bioengineers and clinicians is essential for transforming data and images derived from models of disease into clinically useful information.
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Abstract
Advances in computer power, novel diagnostic and therapeutic medical technologies, and an increasing knowledge of pathophysiology from gene to organ systems make it increasingly feasible to apply multiscale patient-specific modeling based on proven disease mechanisms. Such models may guide and predict the response to therapy in many areas of medicine. This is an exciting and relatively new approach, for which efficient methods and computational tools are of the utmost importance. Investigators have designed patient-specific models in almost all areas of human physiology. Not only will these models be useful in clinical settings to predict and optimize the outcome from surgery and non-interventional therapy, but they will also provide pathophysiologic insights from the cellular level to the organ system level. Models, therefore, will provide insight as to why specific interventions succeed or fail.
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21
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Pekkan K, Whited B, Kanter K, Sharma S, de Zelicourt D, Sundareswaran K, Frakes D, Rossignac J, Yoganathan AP. Patient-specific surgical planning and hemodynamic computational fluid dynamics optimization through free-form haptic anatomy editing tool (SURGEM). Med Biol Eng Comput 2008; 46:1139-52. [DOI: 10.1007/s11517-008-0377-0] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2007] [Accepted: 07/13/2008] [Indexed: 11/30/2022]
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Hunter KS, Gross JK, Lanning CJ, Kirby KS, Dyer KL, Ivy DD, Shandas R. Noninvasive methods for determining pulmonary vascular function in children with pulmonary arterial hypertension: application of a mechanical oscillator model. CONGENIT HEART DIS 2008; 3:106-16. [PMID: 18380759 DOI: 10.1111/j.1747-0803.2008.00172.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OBJECTIVE Noninvasive diagnostics for pulmonary arterial hypertension (PAH) have traditionally sought to predict main pulmonary artery pressure from qualitative or direct quantitative measures of the flow velocity pattern obtained from spectral Doppler ultrasound examination of the main pulmonary artery. A more detailed quantification of flow velocity patterns in the systemic circuit has been obtained by parameterizing the flow trace with a simple dynamic system model. Here, we investigate such a model's utility as a noninvasive predictor of total right heart afterload and right heart function. DESIGN Flow velocity and pressure was measured within the main pulmonary artery during right heart catheterization of patients with normal hemodynamics (19 subjects, 20 conditions) and those with PAH undergoing reactivity evaluation (34 patients, 69 conditions). Our model parameters were obtained by least-squares fitting the model velocity to the measured flow velocity. RESULTS Five parameter means displayed significant (P < .05) differences between normotensive and hypertensive groups. The model stiffness parameter correlated to actual pulmonary vascular resistance (r = 0.4924), pulmonary vascular stiffness (r = 0.6811), pulmonary flow (r = 0.6963), and stroke work (r = 0.7017), while the model initial displacement parameter had good correlation to stiffness (r = 0.6943) and flow (r = 0.6958). CONCLUSIONS As predictors of total right heart afterload (resistance and stiffness) and right ventricle work, the model parameters of stiffness and initial displacement offer more comprehensive measures of the disease state than previous noninvasive methods and may be useful in routine diagnostic monitoring of patients with PAH.
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Affiliation(s)
- Kendall S Hunter
- Center for Bioengineering, University of Colorado Health Science Center, Denver, CO 80045, USA.
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23
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Pekkan K, Dasi LP, Nourparvar P, Yerneni S, Tobita K, Fogel MA, Keller B, Yoganathan A. In vitro hemodynamic investigation of the embryonic aortic arch at late gestation. J Biomech 2008; 41:1697-706. [PMID: 18466908 PMCID: PMC3805112 DOI: 10.1016/j.jbiomech.2008.03.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Revised: 03/10/2008] [Accepted: 03/11/2008] [Indexed: 10/22/2022]
Abstract
This study focuses on the dynamic flow through the fetal aortic arch driven by the concurrent action of right and left ventricles. We created a parametric pulsatile computational fluid dynamics (CFD) model of the fetal aortic junction with physiologic vessel geometries. To gain a better biophysical understanding, an in vitro experimental fetal flow loop for flow visualization was constructed for identical CFD conditions. CFD and in vitro experimental results were comparable. Swirling flow during the acceleration phase of the cardiac cycle and unidirectional flow following mid-deceleration phase were observed in pulmonary arteries (PA), head-neck vessels, and descending aorta. Right-to-left (oxygenated) blood flowed through the ductus arteriosus (DA) posterior relative to the antegrade left ventricular outflow tract (LVOT) stream and resembled jet flow. LVOT and right ventricular outflow tract flow mixing had not completed until approximately 3.5 descending aorta diameters downstream of the DA insertion into the aortic arch. Normal arch model flow patterns were then compared to flow patterns of four common congenital heart malformations that include aortic arch anomalies. Weak oscillatory reversing flow through the DA junction was observed only for the Tetralogy of Fallot configuration. PA and hypoplastic left heart syndrome configurations demonstrated complex, abnormal flow patterns in the PAs and head-neck vessels. Aortic coarctation resulted in large-scale recirculating flow in the aortic arch proximal to the DA. Intravascular flow patterns spatially correlated with abnormal vascular structures consistent with the paradigm that abnormal intravascular flow patterns associated with congenital heart disease influence vascular growth and function.
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Affiliation(s)
- Kerem Pekkan
- Department of Biomedical and Mechanical Engineering, Carnegie Mellon University, PA, USA.
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Hunter KS, Lee PF, Lanning CJ, Ivy DD, Kirby KS, Claussen LR, Chan KC, Shandas R. 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. Am Heart J 2008; 155:166-74. [PMID: 18082509 PMCID: PMC3139982 DOI: 10.1016/j.ahj.2007.08.014] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Accepted: 08/12/2007] [Indexed: 10/22/2022]
Abstract
BACKGROUND Pulmonary vascular resistance (PVR) is the current standard for evaluating reactivity in children with pulmonary arterial hypertension (PAH). However, PVR measures only the mean component of right ventricular afterload and neglects pulsatile effects. We recently developed and validated a method to measure pulmonary vascular input impedance, which revealed excellent correlation between the zero harmonic impedance value and PVR and suggested a correlation between higher-harmonic impedance values and pulmonary vascular stiffness. Here we show that input impedance can be measured routinely and easily in the catheterization laboratory, that impedance provides PVR and pulmonary vascular stiffness from a single measurement, and that impedance is a better predictor of disease outcomes compared with PVR. METHODS Pressure and velocity waveforms within the main pulmonary artery were measured during right heart catheterization of patients with normal pulmonary artery hemodynamics (n = 14) and those with PAH undergoing reactivity evaluation (49 subjects, 95 conditions). A correction factor needed to transform velocity into flow was obtained by calibrating against cardiac output. Input impedance was obtained off-line by dividing Fourier-transformed pressure and flow waveforms. RESULTS Exceptional correlation was found between the indexed zero harmonic of impedance and indexed PVR (y = 1.095x + 1.381, R2 = 0.9620). In addition, the modulus sum of the first 2 harmonics of impedance was found to best correlate with indexed pulse pressure over stroke volume (y = 13.39x - 0.8058, R2 = 0.7962). Among a subset of patients with PAH (n = 25), cumulative logistic regression between outcomes to total indexed impedance was better (R(L)2 = 0.4012) than between outcomes and indexed PVR (R(L)2 = 0.3131). CONCLUSIONS Input impedance can be consistently and easily obtained from pulse-wave Doppler and a single catheter pressure measurement, provides comprehensive characterization of the main components of RV afterload, and better predicts patient outcomes compared with PVR alone.
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Affiliation(s)
- Kendall S. Hunter
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
| | - Po-Feng Lee
- Department of Bioengineering, Texas A&M University, College Station, TX 77843
| | - Craig J. Lanning
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
| | - D. Dunbar Ivy
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
| | - K. Scott Kirby
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
| | - Lori R. Claussen
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
| | - K. Chen Chan
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
| | - Robin Shandas
- Department of Pediatric Cardiology, University of Colorado Health Sciences Center, 1056 E. 19 Ave, Denver, CO 80218
- Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, CO 80309-0427
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Liu Y, Zhang W, Kassab GS. Effects of myocardial constraint on the passive mechanical behaviors of the coronary vessel wall. Am J Physiol Heart Circ Physiol 2007; 294:H514-23. [PMID: 17993601 DOI: 10.1152/ajpheart.00670.2007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The large epicardial coronary arteries and veins span the surface of the heart and gradually penetrate into the myocardium. It has recently been shown that remodeling of the epicardial veins in response to pressure overload strongly depends on the degree of myocardial support. The nontethered regions of the vessel wall show significant intimal hyperplasia compared with the tethered regions. Our hypothesis is that such circumferentially nonuniform structural adaptation in the vessel wall is due to nonuniform wall stress and strain. Transmural stress and strain are significantly influenced by the support of the surrounding myocardial tissue, which significantly limits distension of the vessel. In this finite-element study, we modeled the nonuniform support by embedding the left anterior descending artery into the myocardium to different depths and analyzed deformation and strain in the vessel wall. Circumferential wall strain was much higher in the untethered than tethered region at physiological pressure. On the basis of the hypothesis that elevated wall strain is the stimulus for remodeling, the simulation results suggest that large epicardial coronary vessels have a greater tendency to become thicker in the absence of myocardial constraint. This study provides a mechanical basis for understanding the local growth and remodeling of vessels subjected to various degrees of surrounding tissue.
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Affiliation(s)
- Yi Liu
- Department of Biomedical Engineering, Indiana University/Purdue University Indianapolis, 723 West Michigan Street, Indianapolis, IN 46202,USA
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Zhang W, Liu Y, Kassab GS. Flow-induced shear strain in intima of porcine coronary arteries. J Appl Physiol (1985) 2007; 103:587-93. [PMID: 17525296 DOI: 10.1152/japplphysiol.00199.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The in vivo circumferential strain has a small variation throughout the vascular system (aorta to arterioles). The axial strain has also been shown to be nearly the same as the circumferential strain under physiological loading. Since the endothelium is mechanically much softer than the media-adventitia in healthy arteries, the porcine intima was considered as a mechanically distinct layer from the media-adventitia in a two-layer computational model. Based on the simulation result, we hypothesize that the flow-induced shear strain in intima can be of similar value as the pressure-induced circumferential strain in healthy coronary arteries, even though the shear stress is orders of magnitude smaller than the circumferential stress. The nearly isotropic deformation (circumferential, axial, and shear strains) may have important implications for mechanical homeostasis of endothelial cells, mechanotransduction, growth, and remodeling of blood vessels.
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Affiliation(s)
- Wei Zhang
- Dept. of Biomedical Engineering, Indiana University Purdue University Indianapolis, Indianapolis, Indianapolis 46202, USA
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27
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Wang C, Pekkan K, de Zélicourt D, Horner M, Parihar A, Kulkarni A, Yoganathan AP. Progress in the CFD modeling of flow instabilities in anatomical total cavopulmonary connections. Ann Biomed Eng 2007; 35:1840-56. [PMID: 17641974 DOI: 10.1007/s10439-007-9356-0] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2006] [Accepted: 07/06/2007] [Indexed: 11/29/2022]
Abstract
Intrinsic flow instability has recently been reported in the blood flow pathways of the surgically created total-cavopulmonary connection. Besides its contribution to the hydrodynamic power loss and hepatic blood mixing, this flow unsteadiness causes enormous challenges in its computational fluid dynamics (CFD) modeling. This paper investigates the applicability of hybrid unstructured meshing and solver options of a commercially available CFD package (FLUENT, ANSYS Inc., NH) to model such complex flows. Two patient-specific anatomies with radically different transient flow dynamics are studied both numerically and experimentally (via unsteady particle image velocimetry and flow visualization). A new unstructured hybrid mesh layout consisting of an internal core of hexahedral elements surrounded by transition layers of tetrahedral elements is employed to mesh the flow domain. The numerical simulations are carried out using the parallelized second-order accurate upwind scheme of FLUENT. The numerical validation is conducted in two stages: first, by comparing the overall flow structures and velocity magnitudes of the numerical and experimental flow fields, and then by comparing the spectral content at different points in the connection. The numerical approach showed good quantitative agreement with experiment, and total simulation time was well within a clinically relevant time-scale of our surgical planning application. It also further establishes the ability to conduct accurate numerical simulations using hybrid unstructured meshes, a format that is attractive if one ever wants to pursue automated flow analysis in a large number of complex (patient-specific) geometries.
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Affiliation(s)
- Chang Wang
- Wallace H. Coulter School of Biomedical Engineering, Georgia Institute of Technology, Room 2119 U. A. Whitaker Building, 313 Ferst Dr, Atlanta, GA 30332-0535, USA
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Wang R, Lacour-Gayet FG, Lanning CJ, Rech BA, Kilfoil PJ, Hertzberg J, Shandas R. Initial Experience With the Development and Numerical and In Vitro Studies of A Novel Low-Pressure Artificial Right Ventricle for Pediatric Fontan Patients. ASAIO J 2006; 52:682-92. [PMID: 17117059 DOI: 10.1097/01.mat.0000249038.69048.3c] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
The Fontan operation, an efficient palliative surgery, is performed for patients with single-ventricle pathologies. The total cavopulmonary connection is a preferred Fontan procedure in which the superior and inferior vena cava are connected to the left and right pulmonary artery. The overall goal of this work is to develop an artificial right ventricle that can be introduced into the inferior vena cava, which would act to reverse the deleterious hemodynamics in post-Fontan patients. We present the initial design and computational analysis of a micro-axial pump, designed with the particular hemodynamics of Fontan physiology in mind. Preliminary in vitro data on a prototype pump are also presented. Computational studies showed that the new design can deliver a variety of advantageous operating conditions, including decreased venous pressure through proximal suction, increased pressure rise across the pump, increased pulmonary flows, and minimal changes in superior vena cava pressures. In vitro studies on a scaled prototype showed trends similar to those seen computationally. We conclude that a micro-axial flow pump can be designed to operate efficiently within the low-pressure, low-flow environment of cavopulmonary flows. The results provide encouragement to pursue this design to for in vitro studies and animal studies.
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Affiliation(s)
- Rui Wang
- Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, USA
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