INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING Int. J. Numer. Meth. Biomed. Engng. 2014; 30:603–604 Published online 27 November 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cnm.2617
EDITORIAL - PAPER PRESENTED AT WCCM 2012 - 10TH WORLD CONGRESS ON COMPUTATIONAL MECHANICS
Computational mechanics and electro-mechanics in cardiovascular physiology and disease GUEST EDITOR: Thomas Franz 1,2,3, * ,† 1 Cardiovascular
Research Unit, Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Observatory, South Africa 2 Research Office, University of Cape Town, Mowbray, South Africa 3 Centre for Research in Computational and Applied Mechanics, University of Cape Town, Rondebosch, South Africa
This special issue provides a collection of invited papers from the Symposium on Computational Mechanics and Functional Imaging in Cardiovascular Diseases that was part of the 10th World Congress on Computational Mechanics held in São Paulo, Brazil during 8–13 July 2012. Cardiovascular diseases are, along with cancer, the leading cause of death worldwide with a steady increase in mortalities predicted between 2002 and 2030 by the World Health Organisation [1]. The advancement of understanding, prevention and treatment of cardiovascular pathologies can greatly benefit from interdisciplinary approaches that include computational modelling in preclinical and clinical research. Furthermore, computational methods can provide access to data that are difficult, if not impossible, to obtain with experimental approaches. The collection of papers presented here is concerned with investigation of diseases of the coronary circulation, resulting pathologies and therapies for these pathologies. Many patients that undergo balloon angioplasty and endovascular stenting to treat coronary artery disease require repeated intervention due to restenosis, that is, the re-narrowing of the artery. The mechanical effects of endovascular interventions on the arterial tissue including vascular injury have been postulated to contribute considerably to restenosis. Employing a method based on the simulation of tube hydroforming, Araújo et al. [2] propose an explicit computational approach to assess the mechanical stent-artery interactions and the structural integrity of the stent during and after deployment. It was demonstrated that structural integrity of a commercial 316L stainless steel stent was preserved. However, the deployed device caused substantial strains and stresses in the arterial wall and plaque that, although not critical in terms of rupture risk, may lead to intimal hyperplasia and restenosis. A treatment option for coronary artery disease typically required once endovascular interventions become insufficient, namely, coronary artery bypass grafting, was the focus of a study presented by Vimmr et al. [3]. The long-term patency of coronary bypass grafts is known to be significantly affected by local haemodynamics. Vimmr et al. investigated pulsatile blood flow in three different patient-specific aorto-coronary bypasses varying in the number of distal side-to-side and end-to-side anastomoses. For the cases studied, results obtained for the blood flow and wall shear stress in the grafts did not significantly differ between non-Newtonian and Newtonian treatment of blood. It was observed that the diameter of the bypass grafts, that is, the patient-specific geometric variations, was a much more pronounced determinant of the flow fields, wall shear stress and oscillatory shear index – in particular in sequential bypass grafts. *Correspondence to: Thomas Franz, Cardiovascular Research Unit, Faculty of Health Sciences, University of Cape Town, Private Bag X3, Observatory 7935, South Africa. † E-mail: [email protected] Papers are collected together in a virtual issue at http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2040-7947/ homepage/custom_copy.htm Copyright © 2013 John Wiley & Sons, Ltd.
604
G. E. T. FRANZ
Cardiac physiology and pathologies are topic of three papers of this special issue. de Oliveira et al. [4] explored cardiac electro-mechanics by studying the effect of myocardial deformation on the transmural dispersion of repolarization and surface electrograms. An electrophysiology model of the human left ventricle was coupled with an active contraction model re-parameterized for human cells and embedded in a system of bidomain equations and nonlinear solid mechanics at the tissue level. Results of this study suggest that a considerable percentage of the T-wave amplitude (up to 15%) of surface electrograms may be related to myocardial deformation on the basis of changes to the coupling between neighbouring cardiomyocytes, also known as electrotonic effect. Miller et al. [5] in a study on intra-myocardial hydrogel injections as a therapy for myocardial infarction (i.e. heart attack) found that the efficacy depends on the in situ distribution of the biomaterial in the injured myocardium. Injectate distributions – striated, layered versus bulk like – were observed to depend on the time point of delivery after the infarct event. In a finite element model of a patient-specific left ventricle, these distinct distributions were studied with regard to functional improvement and wall mechanics in an early-stage ischemic and late-stage scarred infarct. For a similar study on treatment on myocardial infarction, Legner et al. [6] developed a numerical framework based on an element-free Galerkin method to simulate ventricular mechanics and function. A strain invariant-based stored energy function, allowing frame-invariant and more compact expressions for the stress and material tensors, was proposed to account for the passive myocardial behaviour, which also makes provision for active contraction. Biomaterial injections in the infarcted myocardium were represented using an additive homogenization approach that allows discriminating between stresses in the myocardium and the biomaterial. Patients with heart failure, for example, caused by adverse remodelling of the heart after an infarction, may require a heart transplant. While waiting for a suitable donor organ, patients often receive temporary support from ventricular assist devices and artificial hearts. One of the issues with such devices is haemolysis, that is, the destruction of red blood cells for example due to non-physiologically high shear stresses. To improve the estimation of haemolysis, Nakamura et al. [7] examined the deformation of a red blood cell in various flow fields and investigated whether the extent of deformation of the cell is correlated with the shear stress used as a haemolysis index. The results suggest that the accuracy of estimating the mechanical damage of red blood cells is limited when based on macroscopic flow fields only. It is proposed that considering the dynamic deformation of red blood cells provides an improved prediction of haemolysis. REFERENCES 1. WHO. World Health Statistics 2007. World Health Organization: Geneva, 2007. 2. Araújo R, Guimarães TA, Oliveira SAG. An analysis of the contact between the stent and the artery using tube hydroforming simulation. International Journal for Numerical Methods in Biomedical Engineering 2013; 29(11):1214–1222. 3. Vimmr J, Jonášová A, Bublík O. Numerical analysis of non-newtonian blood flow and wall shear stress in realistic single, double and triple aorto-coronary bypasses. International Journal for Numerical Methods in Biomedical Engineering 2013; 29:1057–1081. 4. de Oliveira BL, Rocha BM, Barra LPS, Toledo EM, Sundnes J, Weber dos Santos R. Effects of deformation on transmural dispersion of repolarization using in silico models of human left ventricular wedge. International Journal for Numerical Methods in Biomedical Engineering 2013; 29(12):1323–1337. 5. Miller R, Davies NH, Kortsmit J, Zilla P, Franz T. Outcomes of myocardial infarction hydrogel injection therapy in the human left ventricle dependent on injectate distribution. International Journal for Numerical Methods in Biomedical Engineering 2013; 29:870–884. 6. Legner D, Skatulla S, MBewu J, Rama R, Reddy B, Sansour C, Davies N, Franz T. Studying the influence of hydrogel injections into the infarcted left ventricle using the element-free galerkin method. International Journal for Numerical Methods in Biomedical Engineering 2014; 30(3):416–429. 7. Nakamura M, Bessho S, Wada S. Analysis of red blood cell deformation under fast shear flow for better estimation of hemolysis. International Journal for Numerical Methods in Biomedical Engineering 2014; 30(1):42–54.
Copyright © 2013 John Wiley & Sons, Ltd.
Int. J. Numer. Meth. Biomed. Engng. 2014; 30:603–604 DOI: 10.1002/cnm
EDITORIAL - PAPER PRESENTED AT WCCM 2012 - 10TH WORLD CONGRESS ON COMPUTATIONAL MECHANICS
Computational mechanics and electro-mechanics in cardiovascular physiology and disease GUEST EDITOR: Thomas Franz 1,2,3, * ,† 1 Cardiovascular
Research Unit, Chris Barnard Division of Cardiothoracic Surgery, University of Cape Town, Observatory, South Africa 2 Research Office, University of Cape Town, Mowbray, South Africa 3 Centre for Research in Computational and Applied Mechanics, University of Cape Town, Rondebosch, South Africa
This special issue provides a collection of invited papers from the Symposium on Computational Mechanics and Functional Imaging in Cardiovascular Diseases that was part of the 10th World Congress on Computational Mechanics held in São Paulo, Brazil during 8–13 July 2012. Cardiovascular diseases are, along with cancer, the leading cause of death worldwide with a steady increase in mortalities predicted between 2002 and 2030 by the World Health Organisation [1]. The advancement of understanding, prevention and treatment of cardiovascular pathologies can greatly benefit from interdisciplinary approaches that include computational modelling in preclinical and clinical research. Furthermore, computational methods can provide access to data that are difficult, if not impossible, to obtain with experimental approaches. The collection of papers presented here is concerned with investigation of diseases of the coronary circulation, resulting pathologies and therapies for these pathologies. Many patients that undergo balloon angioplasty and endovascular stenting to treat coronary artery disease require repeated intervention due to restenosis, that is, the re-narrowing of the artery. The mechanical effects of endovascular interventions on the arterial tissue including vascular injury have been postulated to contribute considerably to restenosis. Employing a method based on the simulation of tube hydroforming, Araújo et al. [2] propose an explicit computational approach to assess the mechanical stent-artery interactions and the structural integrity of the stent during and after deployment. It was demonstrated that structural integrity of a commercial 316L stainless steel stent was preserved. However, the deployed device caused substantial strains and stresses in the arterial wall and plaque that, although not critical in terms of rupture risk, may lead to intimal hyperplasia and restenosis. A treatment option for coronary artery disease typically required once endovascular interventions become insufficient, namely, coronary artery bypass grafting, was the focus of a study presented by Vimmr et al. [3]. The long-term patency of coronary bypass grafts is known to be significantly affected by local haemodynamics. Vimmr et al. investigated pulsatile blood flow in three different patient-specific aorto-coronary bypasses varying in the number of distal side-to-side and end-to-side anastomoses. For the cases studied, results obtained for the blood flow and wall shear stress in the grafts did not significantly differ between non-Newtonian and Newtonian treatment of blood. It was observed that the diameter of the bypass grafts, that is, the patient-specific geometric variations, was a much more pronounced determinant of the flow fields, wall shear stress and oscillatory shear index – in particular in sequential bypass grafts. *Correspondence to: Thomas Franz, Cardiovascular Research Unit, Faculty of Health Sciences, University of Cape Town, Private Bag X3, Observatory 7935, South Africa. † E-mail: [email protected] Papers are collected together in a virtual issue at http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2040-7947/ homepage/custom_copy.htm Copyright © 2013 John Wiley & Sons, Ltd.
604
G. E. T. FRANZ
Cardiac physiology and pathologies are topic of three papers of this special issue. de Oliveira et al. [4] explored cardiac electro-mechanics by studying the effect of myocardial deformation on the transmural dispersion of repolarization and surface electrograms. An electrophysiology model of the human left ventricle was coupled with an active contraction model re-parameterized for human cells and embedded in a system of bidomain equations and nonlinear solid mechanics at the tissue level. Results of this study suggest that a considerable percentage of the T-wave amplitude (up to 15%) of surface electrograms may be related to myocardial deformation on the basis of changes to the coupling between neighbouring cardiomyocytes, also known as electrotonic effect. Miller et al. [5] in a study on intra-myocardial hydrogel injections as a therapy for myocardial infarction (i.e. heart attack) found that the efficacy depends on the in situ distribution of the biomaterial in the injured myocardium. Injectate distributions – striated, layered versus bulk like – were observed to depend on the time point of delivery after the infarct event. In a finite element model of a patient-specific left ventricle, these distinct distributions were studied with regard to functional improvement and wall mechanics in an early-stage ischemic and late-stage scarred infarct. For a similar study on treatment on myocardial infarction, Legner et al. [6] developed a numerical framework based on an element-free Galerkin method to simulate ventricular mechanics and function. A strain invariant-based stored energy function, allowing frame-invariant and more compact expressions for the stress and material tensors, was proposed to account for the passive myocardial behaviour, which also makes provision for active contraction. Biomaterial injections in the infarcted myocardium were represented using an additive homogenization approach that allows discriminating between stresses in the myocardium and the biomaterial. Patients with heart failure, for example, caused by adverse remodelling of the heart after an infarction, may require a heart transplant. While waiting for a suitable donor organ, patients often receive temporary support from ventricular assist devices and artificial hearts. One of the issues with such devices is haemolysis, that is, the destruction of red blood cells for example due to non-physiologically high shear stresses. To improve the estimation of haemolysis, Nakamura et al. [7] examined the deformation of a red blood cell in various flow fields and investigated whether the extent of deformation of the cell is correlated with the shear stress used as a haemolysis index. The results suggest that the accuracy of estimating the mechanical damage of red blood cells is limited when based on macroscopic flow fields only. It is proposed that considering the dynamic deformation of red blood cells provides an improved prediction of haemolysis. REFERENCES 1. WHO. World Health Statistics 2007. World Health Organization: Geneva, 2007. 2. Araújo R, Guimarães TA, Oliveira SAG. An analysis of the contact between the stent and the artery using tube hydroforming simulation. International Journal for Numerical Methods in Biomedical Engineering 2013; 29(11):1214–1222. 3. Vimmr J, Jonášová A, Bublík O. Numerical analysis of non-newtonian blood flow and wall shear stress in realistic single, double and triple aorto-coronary bypasses. International Journal for Numerical Methods in Biomedical Engineering 2013; 29:1057–1081. 4. de Oliveira BL, Rocha BM, Barra LPS, Toledo EM, Sundnes J, Weber dos Santos R. Effects of deformation on transmural dispersion of repolarization using in silico models of human left ventricular wedge. International Journal for Numerical Methods in Biomedical Engineering 2013; 29(12):1323–1337. 5. Miller R, Davies NH, Kortsmit J, Zilla P, Franz T. Outcomes of myocardial infarction hydrogel injection therapy in the human left ventricle dependent on injectate distribution. International Journal for Numerical Methods in Biomedical Engineering 2013; 29:870–884. 6. Legner D, Skatulla S, MBewu J, Rama R, Reddy B, Sansour C, Davies N, Franz T. Studying the influence of hydrogel injections into the infarcted left ventricle using the element-free galerkin method. International Journal for Numerical Methods in Biomedical Engineering 2014; 30(3):416–429. 7. Nakamura M, Bessho S, Wada S. Analysis of red blood cell deformation under fast shear flow for better estimation of hemolysis. International Journal for Numerical Methods in Biomedical Engineering 2014; 30(1):42–54.
Copyright © 2013 John Wiley & Sons, Ltd.
Int. J. Numer. Meth. Biomed. Engng. 2014; 30:603–604 DOI: 10.1002/cnm
