Impact of aortic repair based on flow field computer simulation within the thoracic aorta

Unusual Aneurysm of a Cervical Aortic Arch: Surgical Repair Improves Fluid Dynamics

The cervical aortic arch is a rare congenital vascular abnormality related to the anomalous development of the aortic arch. We present the case of a 6-year-old patient with a large aneurysmal cervical aortic arch who underwent surgical correction and arch reconstruction. Surgical repair was indicated based on the risk of progressive dilation and rupture, aiming to restore correct geometry and hemodynamics. We evaluated preoperative and postoperative hemodynamics using computational fluid dynamics simulations, and we also identified, within the repaired region, an area that remains affected by greater turbulent flow, requiring follow-up surveillance.

A mosaic structure multi-level vascular network design for skull tissue engineering

In human skull tissue engineering scaffolds, cell growth and osteogenesis are limited due to the lack of vascular structure. Therefore, a mosaic structure vascular parameterized design method is proposed according to the scanning characteristics of the diploic vein. Using micro-CT scans of skull samples, the features of the diploic vein were extracted, and a multi-level vascular network model was established based on a power diagram. Considering the characteristics of blood flow in the veins, finite element analysis (FEA) of the fluid-solid coupling was established to analyze the effect of blood on vessels with four-level mosaic structures. The results showed that the deformation and stress distribution of vessels were reasonable, and the blood pressure, velocity and shear stress in the designed vascular structure could meet the cell growth requirements. The mosaic structure was prepared by PDMS and cultured in vitro using HUVECs. It was found that most of the cells survived after 48 h, and some cells were attached to the surface mosaic structure. In this method, different levels of vessels nest together, with a curvature that matches the shape of the skull, forming a similar morphology to the native diploic vein, and the local structures can be adjusted flexibly. This mosaic structure vascular design method can be used for network vascular design and experimental studies in hard tissues.

Computational Fluid Dynamics and Aortic Dissections: Panacea or Panic?

This paper reviews the methodology, benefits and limitations associated with computational flow dynamics (CFD) in the field of vascular surgery. Combined with traditional imaging of the vasculature, CFD simulation enables accurate characterisation of real-time physiological and haemodynamic parameters such as wall shear stress. This enables vascular surgeons to understand haemodynamic changes in true and false lumens, and exit and re-entry tears. This crucial information may facilitate triaging decisions. Furthermore, CFD can be used to assess the impact of stent graft treatment, as it provides a haemodynamic account of what may cause procedure-related complications. Efforts to integrate conventional imaging, individual patient data and CFD are paramount to its success, given its potential to replace traditional registry-based, population-averaged data. Nonetheless, methodological limitations must be addressed before clinical implementation. This must be accompanied by further research with large sample sizes, to establish the association between haemodynamic patterns as observed by CFD and progression of aortic dissection.

Numerical simulation of patient-specific left ventricular model with both mitral and aortic valves by FSI approach

Intraventricular flow is important in understanding left ventricular function; however, relevant numerical simulations are limited, especially when heart valve function is taken into account. In this study, intraventricular flow in a patient-specific left ventricle has been modelled in two-dimension (2D) with both mitral and aortic valves integrated. The arbitrary Lagrangian-Eulerian (ALE) approach was employed to handle the large mesh deformation induced by the beating ventricular wall and moving leaflets. Ventricular wall deformation was predefined based on MRI data, while leaflet dynamics were predicted numerically by fluid-structure interaction (FSI). Comparisons of simulation results with in vitro and in vivo measurements reported in the literature demonstrated that numerical method in combination with MRI was able to predict qualitatively the patient-specific intraventricular flow. To the best of our knowledge, we are the first to simulate patient-specific ventricular flow taking into account both mitral and aortic valves.

Computational fluid dynamics investigation of chronic aortic dissection hemodynamics versus normal aorta

OBJECTIVES

To evaluate hemodynamic changes during aneurysmal dilatation in chronic type B aortic dissections compared to hemodynamic parameters in the healthy aorta with the use of computational fluid dynamics (CFD).

METHODS

True lumen (TL)/false lumen (FL) dimensional changes, changes in total pressure (TP), and wall shear stress (WSS) were evaluated at follow-up (FU) compared to initial examination (IE) with transient CFD simulation with geometries derived from clinical image data and inflow boundary conditions from magnetic resonance images. The TL/FL pressure gradient between ascending and descending aorta (DAo) and maximum WSS at the site of largest dilatation was compared to values for the healthy aorta.

RESULTS

Hemodynamic changes at site of largest FL dilatation included 77% WSS reduction and 69% TP reduction. Compared to the healthy aorta, pressure gradient between ascending and DAo was a factor of 1.4 higher in the TL and a factor of 1.5 in the FL and increased at FU (1.6 and 1.7, respectively). Maximum WSS at the site of largest dilatation was a factor of 3 lower than that for the healthy aorta at IE and decreased by more than a factor of 2 at FU.

CONCLUSIONS

The FL dilatation at FU favorably reduced TP. In contrast, unfavorable increase in pressure gradient between ascending and DAo was observed with higher values than in the healthy aorta. Maximum WSS was reduced at the site of largest dilation compared to healthy aorta.

Mapping cyclic stretch in the postpneumonectomy murine lung

In many mammalian species, the removal of one lung [pneumonectomy (PNX)] is associated with the compensatory growth of the remaining lung. To investigate the hypothesis that parenchymal deformation may trigger lung regeneration, we used respiratory-gated micro-computed tomography scanning to create three-dimensional finite-element geometric models of the murine cardiac lobe with cyclic breathing. Models were constructed of respiratory-gated micro-computed tomography scans pre-PNX and 24 h post-PNX. The computational models demonstrated that the maximum stretch ratio map was patchy and heterogeneous, particularly in subpleural, juxta-diaphragmatic, and cephalad regions of the lobe. In these parenchymal regions, the material line segments at peak inspiration were frequently two- to fourfold greater after PNX; some regions of the post-PNX cardiac lobe demonstrated parenchymal compression at peak inspiration. Similarly, analyses of parenchymal maximum shear strain demonstrated heterogeneous regions of mechanical stress with focal regions demonstrating a threefold increase in shear strain after PNX. Consistent with previously identified growth patterns, these subpleural regions of enhanced stretch and shear strain are compatible with a mechanical signal, likely involving cyclic parenchymal stretch, triggering lung growth.

Blood flow vectoring control in aortic arch using full and partial clamps

BACKGROUND

Early diagnosis and treatment of aneurysm plays an important role in reducing the mortality risk of rupture. The aneurysm is a complex phenomenon and caused by different reasons, such as arteriosclerosis and heredity. In addition, pressure and Wall Shear Stress are two known factors influencing the establishment of an aneurysm. The aim of this study is to investigate the effect of using a full or partial clamp to control the blood flow streamlines and hence the location of stress concentration in a clean configuration of aorta. The main question is how to control the stresses distribution in order to reduce the possibility of aneurysm growth with less negative effects on the other sides.

METHODS AND RESULTS

A simple form of aortic arch with three branches is considered to simulate the effect of changing blood flow streamlines directions. A parameter study has been performed on the main characteristics of clamp, i.e. size, location, and the percentage of coverage. The Shear Stress Transport model is employed to simulate steady-state Newtonian blood flow when the Reynolds number is about 6500. Simulations are conducted using the commercial CFD solver ANSYS Fluent. The obtained results show that the location of clamp is more effective than the size. It is also found that increasing the depth of clamp has a negative impact on mean velocity field and hence on stress concentration.

CONCLUSION

The present results demonstrate that the Blood Flow Vectoring Control (BFVC) can change the main form of flow streamlines and consequently the distributions of pressure and Wall Shear Stress. A partial clamp leads to better results.

Impact of endografting on the thoracic aortic anatomy: comparative analysis of the aortic geometry before and after the endograft implantation

PURPOSE

Although the widespread acceptance of thoracic endovascular aortic repair (TEVAR) as a first-line treatment option for a multitude of thoracic aortic diseases, little is known about the consequences of the device implantation on the native aortic anatomy. We propose a comparative analysis of the pre- and postoperative geometry on a clinical series of patients and discuss the potential clinical implications

METHODS

CT pre- and postoperative acquisitions of 30 consecutive patients treated by TEVAR for different pathologies (20 thoracic aortic aneurysms, 6 false aneurysms, 3 penetrating ulcers, 1 traumatic rupture) were used to model the vascular geometry. Pre- and postoperative geometries were compared for each patient by pairing and matching the 3D models. An implantation site was identified, and focal differences were detected and described.

RESULTS

Segmentation of the data sets was successfully performed for all 30 subjects. Geometry differences between the pre- and postoperative meshes were depicted in 23 patients (76 %). Modifications at the upper implantation site were detected in 14 patients (47 %), and among them, the implantation site involved the arch (Z0-3) in 11 (78 %).

CONCLUSION

Modeling the vascular geometry on the basis of imaging data offers an effective tool to perform patient-specific analysis of the vascular geometry before and after the treatment. Future studies will evaluate the consequences of these changes on the aortic function.

Longitudinal computational fluid dynamics study of aneurysmal dilatation in a chronic DeBakey type III aortic dissection

Computational fluid dynamics, which uses numeric methods and algorithms for the simulation of blood flow by solving the Navier-Stokes equations on computational meshes, is enhancing the understanding of disease progression in type III aortic dissections. To illustrate this, we examined the changes in patient-derived geometries of aortic dissections, which showed progressive false lumen aneurysmal dilatation (26% diameter increase) during follow-up. Total pressure was decreased by 29% during systole and by 34% during retrograde flow. At the site of the highest false lumen dilatation, the temporal average of total pressure decreased from 45 to 22 Pa, and maximal average wall shear stress decreased from 0.9 to 0.4 Pa. These first results in the study of disease progression of type III DeBakey aortic dissection with computational fluid dynamics are encouraging.