International Journal for Numerical Methods in Biomedical Engineering最新文献

Diastolic/systolic blood pressure ratio (D/S) ≥ 1.2 is the gold standard of enhanced external counterpulsation (EECP) treatment, but it does not show a clear clinical correspondence with the configuration of the EECP mode. As such, a single target results in different treatment effects in different individuals. The local haemodynamic effect (wall shear stress, WSS) of EECP on vascular endothelial cells is conducive to promote the growth of collateral circulation vessels and restore the blood supply distal to the stenosis lesion. Considering the haemodynamic effects of WSS on human arteries, this study developed a real-time patient-specific treatment strategy of EECP for patients with cardio-cerebrovascular diseases. Based on patient-specific haemodynamic data from 113 individuals, an optimization algorithm was developed to achieve the individualization of a 0D lumped-parameter model of the human circulatory system, thereby simulating the patient-specific global haemodynamic effects. 0D/3D coupled cardio-cerebrovascular models of two subjects were established to simulate the local WSS. We then established statistical models to evaluate clinically unmeasurable WSS based on measurable global haemodynamic indicators. With the aim of attaining appropriate area- and time-averaged WSS (ATAWSS, 4–7 Pa), as evaluated by global haemodynamic indicators, a closed-loop feedback tuning method was developed to provide patient-specific EECP treatment strategies. Results showed that for clinical data collected from 113 individuals, the individualized 0D model can accurately simulate patient-specific global haemodynamic effects (average error <5%). Based on two subjects, the statistical models can be used to evaluate local ATAWSS (error <6%) for coronary arteries and for cerebral arteries. An EECP mode planned by the patient-specific treatment strategy can promote an appropriate ATAWSS within a 16 s calculation time. The real-time patient-specific treatment strategy of EECP is expected to improve the long-term outcome for each patient and have potential clinical significance.

The deformability of blood vessels in one-dimensional blood flow models is typically described through a pressure-area relation, known as the tube law. The most used tube laws take into account the elastic and viscous components of the tension of the vessel wall. Accurately parametrizing the tube laws is vital for replicating pressure and flow wave propagation phenomena. Here, we present a novel mathematical-property-preserving approach for the estimation of the parameters of the elastic and viscoelastic tube laws. Our goal was to estimate the parameters by using ovine and human in vitro data, while constraining them to meet prescribed mathematical properties. Results show that both elastic and viscoelastic tube laws accurately describe experimental pressure-area data concerning both quantitative and qualitative aspects. Additionally, the viscoelastic tube law can provide a qualitative explanation for the observed hysteresis cycles. The two models were evaluated using two approaches: (i) allowing all parameters to freely vary within their respective ranges and (ii) fixing some of the parameters. The former approach was found to be the most suitable for reproducing pressure-area curves.

In this study, a moving boundary deformation model based on four-dimensional computed tomography angiography (4D-CTA) with high temporal resolution is constructed, and blood flow dynamics of cerebral aneurysms are investigated by numerical simulation. A realistic moving boundary deformation model of a cerebral aneurysm was constructed based on 4D-CTA in each phase. Four hemodynamic factors (wall shear stress [WSS], wall shear stress divergence [WSSD], oscillatory shear index [OSI], and residual residence time [RRT]) were obtained from numerical simulations, and these factors were evaluated in basilar artery aneurysms. Comparison of the rigid body condition and the moving boundary condition investigating the relationship between wall displacement and hemodynamic factors clarified that the spatial-averaged WSS and maximum WSSD considering only the aneurysmal dome has a large difference between conditions during the peak systole, and there were also significant differences in OSI and RRT.

Computational fluid dynamics (CFD) studies of left atrial flows have reached a sophisticated level, for example, revealing plausible relationships between hemodynamics and stresses with atrial fibrillation. However, little focus has been on fundamental fluid modeling of LA flows. The purpose of this study was to investigate the spatiotemporal convergence, along with the differences between high- (HR) versus normal-resolution/accuracy (NR) solution strategies, respectively. Rigid wall CFD simulations were conducted on 12 patient-specific left atrial geometries obtained from computed tomography scans, utilizing a second-order accurate and space/time-centered solver. The convergence studies showed an average variability of around 30% and 55% for time averaged wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT), and endothelial cell activation potential (ECAP), even between intermediate spatial and temporal resolutions, in the left atrium (LA) and left atrial appendage (LAA), respectively. The comparison between HR and NR simulations showed good correlation in the LA for WSS, RRT, and ECAP ($��R^2�>�.9�$), but not for OSI ($��R^2�=�.63�$). However, there were poor correlations in the LAA especially for OSI, RRT, and ECAP ($��R^2�=�$ .55, .63, and .61, respectively), except for WSS ($��R^2�=�.81�$). The errors are comparable to differences previously reported with disease correlations. To robustly predict atrial hemodynamics and stresses, numerical resolutions of 10 M elements (i.e., $��\Delta �x�=�\sim �$.5 mm) and 10 k time-steps per cycle seem necessary (i.e., one order of magnitude higher than normally used in both space and time). In conclusion, attention to fundamental numerical aspects is essential toward establishing a plausible, robust, and reliable model of LA flows.

Endovascular coiling is the predominant method for treating cerebral aneurysms. Extensive reports on selecting coil length, hardness, and material are available. However, the impact of coil diameter on postoperative outcomes remains unclear. This study enrolled six personalized geometric models of intracranial aneurysms: three bifurcation aneurysms and three sidewall aneurysms. Four coil models were constructed by changing the coil diameter. Coil embolization was simulated using the finite element method. Computational fluid dynamics was used to characterize hemodynamics in the aneurysms after embolization. Evaluation parameters included velocity reduction, wall shear stress (WSS), low WSS (LWSS), oscillatory shear index (OSI), relative residence time (RRT), and residual flow volume in the aneurysms. At the peak time (t = 0.17 s), the proportion of LWSS area in bifurcation aneurysms increase with the rise in coil diameter: 0.8D, 71.28 ± 12.62% versus 1D, 74.97 ± 19.17% versus 1.2D, 78.88 ± 18.56% versus 1.4D, 84.00 ± 11.53% (mean ± SD). The proportion of high OSI area decreases as the coil diameter increases: 0.8D, 4.41% ± 2.82% versus 1.0D, 3.78 ± 3.33% versus 1.2D, 2.28% ± 1.77% versus 1.4D, 1.58% ± 1.11% (mean ± SD). The proportion of high RRT area increases as the coil diameter rises: 0.8D, 3.40% ± 1.68% versus 1.0D, 7.67 ± 4.12% versus 1.2D, 9.84% ± 9.50% versus 1.4D, 22.29% ± 14.28% (mean ± SD). Side wall aneurysms do not exhibit the aforementioned trend. Bifurcation aneurysms plugged with a coil of 1.4 times the diameter have the largest RFVs (<10 mm/s) within the group. Aforementioned patterns are not found in sidewall aneurysms. In the treatment of aneurysms with coiling, varying coil diameters can result in different hemodynamic environments within the aneurysm. Larger coil diameters have improved hemodynamic performance for bifurcation aneurysms. However, coil diameter and embolization effectiveness have no significant relationship for sidewall aneurysms.

Clinical studies have extensively demonstrated that central aortic blood pressure (CABP) has greater clinical significance in comparison with peripheral blood pressure. Despite the existence of various techniques for noninvasively measuring CABP, the clinical applications of most techniques are hampered by the unsatisfactory accuracy or large variability in measurement errors. In this study, we proposed a new method for noninvasively estimating CABP with improved accuracy and reduced uncertain errors. The main idea was to optimize the estimation of the pulse wave transit time from the aorta to the occluded lumen of the brachial artery under a suprasystolic cuff by identifying and utilizing the characteristic information of the cuff oscillation wave, thereby improving the accuracy and stability of the CABP estimation algorithms under various physiological conditions. The method was firstly developed and verified based on large-scale virtual subject data (n = 800) generated by a computational model of the cardiovascular system coupled to a brachial cuff, and then validated with small-scale in vivo data (n = 34). The estimation errors for the aortic systolic pressure were −0.05 ± 0.63 mmHg in the test group of the virtual subjects and −1.09 ± 3.70 mmHg in the test group of the patients, both demonstrating a good performance. In particular, the estimation errors were found to be insensitive to variations in hemodynamic conditions and cardiovascular properties, manifesting the high robustness of the method. The method may have promising clinical applicability, although further validation studies with larger-scale clinical data remain necessary.

Endoprosthetic hip replacement is the conventional way to treat osteoarthritis or a fracture of a dysfunctional joint. Different manufacturing methods are employed to create reliable patient-specific devices with long-term performance and biocompatibility. Recently, additive manufacturing has become a promising technique for the fabrication of medical devices, because it allows to produce complex samples with various structures of pores. Moreover, the limitations of traditional fabrication methods can be avoided. It is known that a well-designed porous structure provides a better proliferation of cells, leading to improved bone remodeling. Additionally, porosity can be used to adjust the mechanical properties of designed structures. This makes the design and choice of the structure's basic cell a crucial task. This study focuses on a novel computational method, based on the basic-cell concept to design a hip endoprosthesis with an unregularly complex structure. A cube with spheroid pores was utilized as a basic cell, with each cell having its own porosity and mechanical properties. A novelty of the suggested method is in its combination of the topology optimization method and the structural design algorithm. Bending and compression cases were analyzed for a cylinder structure and two hip implants. The ability of basic-cell geometry to influence the structure's stress–strain state was shown. The relative change in the volume of the original structure and the designed cylinder structure was 6.8%. Computational assessments of a stress–strain state using the proposed method and direct modeling were carried out. The volumes of the two types of implants decreased by 9% and 11%, respectively. The maximum von Mises stress was 600 MPa in the initial design. After the algorithm application, it increased to 630 MPa for the first type of implant, while it is not changing in the second type of implant. At the same time, the load-bearing capacity of the hip endoprostheses was retained. The internal structure of the optimized implants was significantly different from the traditional designs, but better structural integrity is likely to be achieved with less material. Additionally, this method leads to time reduction both for the initial design and its variations. Moreover, it enables to produce medical implants with specific functional structures with an additive manufacturing method avoiding the constraints of traditional technologies.

Pulmonary hypertension is a cardiovascular disorder manifested by elevated mean arterial blood pressure (>20 mmHg) together with vessel wall stiffening and thickening due to alterations in collagen, elastin, and smooth muscle cells. Hypoxia-induced (type 3) pulmonary hypertension can be studied in animals exposed to a low oxygen environment for prolonged time periods leading to biomechanical alterations in vessel wall structure. This study introduces a novel approach to formulating a reduced order nonlinear elastic structural wall model for a large pulmonary artery. The model relating blood pressure and area is calibrated using ex vivo measurements of vessel diameter and wall thickness changes, under controlled pressure conditions, in left pulmonary arteries isolated from control and hypertensive mice. A two-layer, hyperelastic, and anisotropic model incorporating residual stresses is formulated using the Holzapfel–Gasser–Ogden model. Complex relations predicting vessel area and wall thickness with increasing blood pressure are derived and calibrated using the data. Sensitivity analysis, parameter estimation, subset selection, and physical plausibility arguments are used to systematically reduce the 16-parameter model to one in which a much smaller subset of identifiable parameters is estimated via solution of an inverse problem. Our final reduced one layer model includes a single set of three elastic moduli. Estimated ranges of these parameters demonstrate that nonlinear stiffening is dominated by elastin in the control animals and by collagen in the hypertensive animals. The pressure–area relation developed in this novel manner has potential impact on one-dimensional fluids network models of vessel wall remodeling in the presence of cardiovascular disease.

Peristalsis is a common motion in various biological systems, especially the upper urinary tract, where it plays a pivotal role in conveying urine from the kidneys to the bladder. Using computational fluid dynamics, this study aims to investigate the effect of various peristaltic parameters on the motion of an obstacle through a two-dimensional ureter. Methodologically, Incompressible Navier–Stokes equations were utilized as the fluid domain's governing equations, and the Dynamic Mesh method (DM) was employed to simulate the peristaltic and obstacle motion. The peristaltic motion was modeled by a sinusoidal contraction wave propagating alongside the ureter at the physiological speed, and the motion of the obstruction through the ureter, which is caused by the fluid forces applied on its surface, was explored using the equation of Newton's second law. Various test cases of different shapes and sizes were supposed as kidney stones to understand the influence of the peristalsis properties on the stone removal process. The results show that the motion of the kidney stone is highly influenced by the gradient pressure force applied to its surface in the fluid domain. Moreover, investigating the effects of the peristaltic physical properties on the obstacle's motion indicates that the stone's motion is dependent on these parameters. Furthermore, this analysis provides insight into the peristaltic motion effects, assisting physicians in developing new medicines to facilitate the kidney stone removal process based on its shape and size.

Many transtibial amputees rate the fit between their residual limb and prosthetic socket as the most critical factor in satisfaction with using their prosthesis. This study aims to address the issue of prosthetic socket fit by reconfiguring the socket shape at the interface of the residual limb and socket. The proposed reconfigurable socket shifts pressure from sensitive areas and compensates for residual limb volume fluctuations, the most important factors in determining a good socket fit. Computed tomography scan images are employed to create the phantom limb of an amputee and to manufacture the reconfigurable socket. The performance of the reconfigurable socket was evaluated both experimentally and numerically using finite element modelling. The study showed that the reconfigurable socket can reduce interface pressure at targeted areas by up to 61%.