International Journal for Numerical Methods in Biomedical Engineering

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.3106

No abstract is available for this article.

Florio, C.S.

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2976pmid: 29508548

A computational model was used to compare the local bone strengthening effectiveness of various isometric exercises that may reduce the likelihood of distal tibial stress fractures. The developed model predicts local endosteal and periosteal cortical accretion and resorption based on relative local and global measures of the tibial stress state and its surface variation. Using a multisegment 3‐dimensional leg model, tibia shape adaptations due to 33 combinations of hip, knee, and ankle joint angles and the direction of a single or sequential series of generated isometric resultant forces were predicted. The maximum stress at a common fracture‐prone region in each optimized geometry was compared under likely stress fracture‐inducing midstance jogging conditions. No direct correlations were found between stress reductions over an initially uniform circular hollow cylindrical geometry under these critical design conditions and the exercise‐based sets of active muscles, joint angles, or individual muscle force and local stress magnitudes. Additionally, typically favorable increases in cross‐sectional geometric measures did not guarantee stress decreases at these locations. Instead, tibial stress distributions under the exercise conditions best predicted strengthening ability. Exercises producing larger anterior distal stresses created optimized tibia shapes that better resisted the high midstance jogging bending stresses. Bent leg configurations generating anteriorly directed or inferiorly directed resultant forces created favorable adaptations. None of the studied loads produced by a straight leg was significantly advantageous. These predictions and the insight gained can provide preliminary guidance in the screening and development of targeted bone strengthening techniques for those susceptible to distal tibial stress fractures.

Canuto, Daniel; Chong, Kwitae; Bowles, Cayley; Dutson, Erik P.; Eldredge, Jeff D.; Benharash, Peyman

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2975pmid: 29500858

A computational tool is developed for simulating the dynamic response of the human cardiovascular system to various stressors and injuries. The tool couples 0‐dimensional models of the heart, pulmonary vasculature, and peripheral vasculature to 1‐dimensional models of the major systemic arteries. To simulate autonomic response, this multiscale circulatory model is integrated with a feedback model of the baroreflex, allowing control of heart rate, cardiac contractility, and peripheral impedance. The performance of the tool is demonstrated in 2 scenarios: neurogenic hypertension by sustained stimulation of the sympathetic nervous system and an acute 10% hemorrhage from the left femoral artery.

Ren, Shuai; Shi, Yan; Cai, Maolin; Zhao, Hongmei; Zhang, Zhaozhi; Zhang, Xiaohua Douglas

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2978pmid: 29504248

Coughing is an irritable reaction that protects the respiratory system from infection and improves mucus clearance. However, for the patients who cannot cough autonomously, an assisted cough device is essential for mucus clearance. Considering the low efficiency of current assisted cough devices, a new simulated cough device based on the pneumatic system is proposed in this paper. Given the uncertainty of airflow rates necessary to clear mucus from airways, the computational fluid dynamics Eulerian wall film model and cough efficiency (CE) were used in this study to simulate the cough process and evaluate cough effectiveness. The Ansys‐Matlab co‐simulation model was set up and verified through experimental studies using Newtonian fluids. Next, model simulations were performed using non‐Newtonian fluids, and peak cough flow (PCF) and PCF duration time were analyzed to determine their influence on mucus clearance. CE growth rate (λ) was calculated to reflect the CE variation trend. From the numerical simulation results, we find that CE rises as PCF increases while the growth rate trends to slow as PCF increases; when PCF changes from 60 to 360 L/min, CE changes from 3.2% to 51.5% which is approximately 16 times the initial value. Meanwhile, keeping a long PCF duration time could greatly improve CE under the same cough expired volume and PCF. The results indicated that increasing the PCF and PCF duration time can improve the efficiency of mucus clearance. This paper provides a new approach and a research direction for control strategy in simulated cough devices for airway mucus clearance.

Lee, Tae‐Rin; Hong, Ji‐Ah; Yoo, Sung Sic; Kim, Do Wan

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2981pmid: 29521012

Microvascular transport is complex due to its heterogeneity. Many researchers have been developing mathematical and computational models in predicting microvascular geometries and blood transport. However, previous works were focused on developing simulation models, not on validating suggested models with microvascular geometry and blood flow in the real microvasculature. In this paper, we suggest a computational model for microvascular transport with experimental validation in its geometry and blood flow. The geometry is generated by controlling asymmetric conditions of microvascular network. Also, the blood flow in microvascular networks is predicted by considering in vivo viscosity, Poiseuille flow model, and hematocrit redistribution by plasma skimming. The suggested model is validated by the measured data in rat mesentery. Also, the microvascular transport in a case of mouse cortex is predicted and compared against experimental data to check applicability of the suggested model.

Vy, Phuoc; Auffret, Vincent; Castro, Miguel; Badel, Pierre; Rochette, Michel; Haigron, Pascal; Avril, Stéphane

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2974pmid: 29486528

Transcatheter aortic valve implantation is a recent mini‐invasive procedure to implant an aortic valve prosthesis. Prosthesis positioning in transcatheter aortic valve implantation appears as an important aspect for the success of the intervention. Accordingly, we developed a patient‐specific finite element framework to predict the insertion of the stiff guidewire, used to position the aortic valve. We simulated the guidewire insertion for 2 patients based on their pre‐operative CT scans. The model was designed to primarily predict the position and the angle of the guidewires in the aortic valve, and the results were successfully compared with intraoperative images.

Luo, Yuanming; Fan, Zhiwei; Baek, Stephen; Lu, Jia

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2977pmid: 29504264

Machine learning was applied to classify tension‐strain curves harvested from inflation tests on ascending thoracic aneurysm samples. The curves were classified into rupture and nonrupture groups using prerupture response features. Two groups of features were used as the basis for classification. The first was the constitutive parameters fitted from the tension‐strain data, and the second was geometric parameters extracted from the tension‐strain curve. Based on the importance scores provided by the machine learning, implications of some features were interrogated. It was found that (1) the value of a constitutive parameter is nearly the same for all members in the rupture group and (2) the strength correlates strongly with a tension in the early phase of response as well as with the end stiffness. The study suggests that the strength, which is not available without rupturing the tissue, may be indirectly inferred from prerupture response features.

Miller, Renee; Kolipaka, Arunark; Nash, Martyn P.; Young, Alistair A.

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2979pmid: 29528568

Magnetic resonance elastography (MRE) has been used to estimate isotropic myocardial stiffness. However, anisotropic stiffness estimates may give insight into structural changes that occur in the myocardium as a result of pathologies such as diastolic heart failure. The virtual fields method (VFM) has been proposed for estimating material stiffness from image data. This study applied the optimised VFM to identify transversely isotropic material properties from both simulated harmonic displacements in a left ventricular (LV) model with a fibre field measured from histology as well as isotropic phantom MRE data. Two material model formulations were implemented, estimating either 3 or 5 material properties. The 3‐parameter formulation writes the transversely isotropic constitutive relation in a way that dissociates the bulk modulus from other parameters. Accurate identification of transversely isotropic material properties in the LV model was shown to be dependent on the loading condition applied, amount of Gaussian noise in the signal, and frequency of excitation. Parameter sensitivity values showed that shear moduli are less sensitive to noise than the other parameters. This preliminary investigation showed the feasibility and limitations of using the VFM to identify transversely isotropic material properties from MRE images of a phantom as well as simulated harmonic displacements in an LV geometry.

Pinto, S.I.S.; Campos, J.B.L.M.; Azevedo, E.; Castro, C.F.; Sousa, L.C.

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2972pmid: 29470857

The definition of a suitable mesh to simulate blood flow in the human carotid bifurcation has been investigated. In this research, a novel mesh generation method is proposed: hexahedral cells at the center of the vessel and a fine grid of tetrahedral cells near the artery wall, in order to correctly simulate the large blood velocity gradients associated with specific locations. The selected numerical examples to show the pertinence of the novel generation method are supported by carotid ultrasound image data of a patient‐specific case. Doppler systolic blood velocities measured during ultrasound examination are compared with simulated velocities using 4 different combinations of hexahedral and tetrahedral meshes and different fluid dynamic simulators. The Lin's test was applied to show the concordance of the results. Wall shear stress–based descriptors and localized normalized helicity descriptor emphasize the performance of the new method. Another feature is the reduced computation time required by the developed methodology. With the accurate combined mesh, different flow rate partitions, between the internal carotid artery and external carotid artery, were studied. The overall effect of the partitions is mainly in the blood flow patterns and in the hot‐spot modulation of atherosclerosis‐susceptible regions, rather than in their distribution along the bifurcation.

Yuniarti, Ana Rahma; Setianto, Febrian; Marcellinus, Aroli; Hwang, Han Jeong; Choi, Seong Wook; Trayanova, Natalia; Lim, Ki Moo

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2970pmid: 29488358

There is growing interest in genetic arrhythmia since mutations in gene which encodes the ion channel underlie numerous arrhythmias. Hasegawa et al reported that G229D mutation in KCNQ1 underlies atrial fibrillation due to significant shortening of action potential duration (APD) in atrial cells. Here, we predicted whether KCNQ1 G229D mutation affects ventricular fibrillation generation, although it shortens APD slightly compared with the atrial cell. We analyzed the effects of G229D mutation on electrical and mechanical ventricle behaviors (not considered in previous studies). We compared action potential shapes under wild‐type and mutant conditions. Electrical wave propagations through ventricles were analyzed during sinus rhythm and reentrant conditions. IKs enhancement due to G229D mutation shortened the APD in the ventricular cells (6%, 0.3%, and 8% for endo, M, and epi‐cells, respectively). The shortened APD contributed to 7% shortening of QT intervals, 29% shortening of wavelengths, 20% decrease in intraventricular pressure, and increase in end‐systolic volume 17%, end‐diastolic volume 7%, and end‐diastolic pressure 11%, which further resulted in reduction in stroke volume as well as cardiac output (28%), ejection fraction 33% stroke work 44%, and ATP consumption 28%. In short, using computational model of the ventricle, we predicted that G229D mutation decreased cardiac pumping efficacy and increased the vulnerability of ventricular fibrillation.

Ni, Xiao‐Yu; Zhang, Yan‐Hong; Zhao, Hai‐Xia; Pan, Chang‐Wang

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.2971pmid: 29461690

Quasi‐static and dynamic numerical analyses are carried out by referring to computational models of commercial self‐expandable braided stents with 3 commonly used end shapes, to evaluate the influence of different end shapes of stent on the biomechanical interaction between stent and oesophagus. The end shape has no influence on the equivalent stress, but has a great influence on the contact stress in the narrowest zone of the oesophagus‐neoplasm system. However, the end shapes have significant effect on the equivalent stress and the contact stress in the healthy area of the oesophagus in contact with the stent ends. The results show that the maximum equivalent stress of the oesophagus occurs in the zone contact with the cup‐shaped end and the maximum contact stress occurs in the zone contact with the edge of the trumpet‐shaped stent end. Moreover, the stent apposition is almost not affected by the end shapes. Although small zones with an incomplete stent apposition appear in the transition zones of spherical‐cup‐shaped stent, such occurrence might not contribute to stent malapposition or stent migration. Therefore, these stents with 3 types of end shapes all have good stent apposition. Finally, the numerical simulation results can be used to assess the mechanical performance of stents with different end shapes, the effectiveness of stent expansion therapy, and the possibility of complications after stent implantation.

Pinto, S.I.S.; Campos, J.B.L.M.; Azevedo, E.; Castro, C.F.; Sousa, L.C.

2018 International Journal for Numerical Methods in Biomedical Engineering

doi: 10.1002/cnm.3113