Acute type A aortic dissection (ATAAD) is a life-threatening aortic emergency with high mortality. Currently, hemiarch replacement (HAR) and total arch replacement (TAR) are the primary surgeries for ATAAD, but their long-term outcomes remain debated, possibly due to the influence of clinical factors in multicenter studies. This study aims to evaluate the long-term outcomes of HAR and TAR by in silico analysis, mitigating the impact of clinical factors. A personalized model was reconstructed to simulate HAR and TAR by altering the material properties at the replacement regions, obtaining hemodynamic and wall response parameters through two-way fluid–structure interaction analysis. HAR exhibits a higher increase in von Mises stress at the anastomosis compared to pre-operation levels (HAR: 4.39 times normal, TAR: 2.42 times normal), increasing the risk of pseudoaneurysm formation. TAR induced more severe streamline absence in the arch branches, potentially resulting in intermittent blood flow to the upper limbs and brain. HAR poses a higher risk of pseudoaneurysm formation at the anastomosis, while TAR carries increased risks of upper limb and cerebral ischemia. Enhanced monitoring of the anastomosis in HAR patients and vigilance for upper limb fatigue and cerebral ischemic events in TAR patients are recommended. This study offers effective guidance for managing postoperative HAR and TAR patients, contributing to the prevention of complications and enhancing their postoperative quality of life.
Hybrid repair is a valuable alternative treatment for aortic arch disease in Marfan syndrome patients after proximal aorta replacement. This study aimed to investigate the long-term durability of this technique with the use of parallel stent-grafts and evaluate strategies to prevent abdominal aortic dilation. One Marfan syndrome patient who underwent hybrid aortic repair with parallel stent-grafts for arch dissection after the Bentall procedure was admitted. Five patient-specific three-dimensional models were reconstructed based on preoperative and follow-up computed tomography angiography scans. Three hypothetical models addressing the closure of an endoleak or reentry tears were created. Hemodynamic parameters were assessed using computational fluid dynamics. Postoperatively, increased blood flow into the descending aorta and rising abdominal aortic pressure were observed. During the 5-year follow-up, no new thoracic aorta-related adverse events occurred. One early type III endoleak persisted, and three reentry tears were identified in the descending aorta. The abdominal aorta dilated from 31 to 49 mm. Simultaneously addressing both the endoleak and reentry tears was more effective in reducing false lumen pressure and flow velocity in the abdominal aorta and expanding the high-value relative residence time region. Longitudinal follow-up imaging demonstrated the long-term durability of hybrid aortic arch repair with parallel stent-grafts in a Marfan syndrome patient after ascending aorta replacement. The increased pressure resulting from blood flow redistribution was associated with downstream aortic dilation. Furthermore, computational fluid dynamics simulations can offer predictive analyses for optimizing intervention strategies in the treatment of distal aneurysmal degeneration.
Many pathologies are related to hemodynamic changes occurring at the microvascular level, where small vessels pierce the tissue, perfusing it with blood. Since there is a large number of vessels of small caliber, it is impractical to model the fluid flow through each one of them separately, as it is done in the case of large arteries using, for example, the Navier–Stokes equations. As an alternative, tissue perfusion is modeled here via three-dimensional (3D) partial differential equations (PDEs) for fluid flow through deformable porous media, where blood vessels are modeled as pores within a deformable solid representing the tissue. Since it is known that the local perfusion is related to the systemic features of surrounding blood circulation, we couple the PDE system with a zero-dimensional (0D) lumped circuit model, obtained by the analogy between fluid flows in hydraulic networks and current flowing in electrical circuits. An important feature in this multiscale 3D–0D coupling is the specification of interface conditions between the 3D and the 0D parts of the system. In this article, we focus on two types of interface conditions driven by physical considerations, and compare the behavior of the solutions for the two different scenarios.
One of the primary challenges encountered during the extrusion bioprinting process involves managing mechanical stresses within the printer nozzle. These stresses ultimately have an impact on the health and functionality of the cells within the printed structure. Statistical models in bioprinting predict cell damage but are empirical, disregard key interactions, and lack single-cell prediction. Our ultimate objective is to develop an efficient validated computational model simulating human dermal fibroblast deformability in extrusion bioprinting, considering all important interactions. The spring-network model shows promise in simulating cellular deformation. However, its widespread adoption and efficiency rely on a significant challenge of accurately calibrating model coefficients. This calibration process is complex due to the lack of a manual method tailored for eukaryotic cells suspended in hydrodynamic flow. In this study, we described a new method to calibrate the model coefficients manually for human dermal fibroblasts. To achieve this calibration, experimental data of human dermal fibroblasts passing through narrow microfluidics constriction was used. The calibration process was initiated by using coefficients associated with red blood cells and subsequently adjusted by comparing the model's behavior with experimental data. The elastic coefficients were calibrated to closely replicate the entry time observed in the experiments with a 5% error margin. However, notable differences persisted in the cell deformation behavior between simulation and experiment. Moreover, adding membrane viscosity minimally reduced transient cell deformation by less than 10% without affecting steady-state deformation.
Signaling networks can be used to describe the dynamic interplay of hormonal and mechanical factors that regulate heart growth. However, a qualitative analysis of signaling networks is often difficult due to their complexity and nonlinear behavior. In this work, a global sensitivity analysis of signaling networks is conducted to determine the most influential factors for heart growth over a range of model inputs. Furthermore, the local production of the hormone insulin-like growth factor 1 (IGF1) in response to high mechanical stretches as recently described by Zaman et al.(Immunity, 54, 2057) and Wong et al.(Immunity, 54, 2072) is incorporated. The computational results show that this increases the influence of mechanical stretch on heart growth significantly. Further key influential factors are the hormones norepinephrine (NE), angiotensin II (AngII), and globally produced IGF1 (g-IGF1). Our sensitivity analysis indicates that the novel consideration of local IGF1 (l-IGF1) production has to be considered in signaling networks for heart growth.
Although axillary artery venoarterial extracorporeal membrane oxygenation (VA-ECMO) has been utilized as a mechanical circulatory support for patients with end-stage heart failure (HF), there is currently insufficient evidence to support its effectiveness and safety. The objective of this study was to analyze the hemodynamic effects of axillary artery VA-ECMO. To this end, we obtained CT angiographic imaging data of the aorta from a carefully selected heart failure patient with a cardiac output of 2.1 L/min. These data were used to construct a detailed fluid–structure interaction model of the aorta. Axillary artery VA-ECMO was then simulated within this model, maintaining a constant flow rate of 3 L/min. The intra-aortic balloon counterpulsation (IABP) balloon was simulated to inflate and deflate in synchrony with the diastolic and systolic phases of the cardiac cycle. Hemodynamic effects, including left ventricular (LV) pressure afterload, vessel wall stress, perfusion of vital organs, blood flow pulsatility, and the watershed region, were calculated using fluid–structure interaction analysis. We found that axillary artery VA-ECMO delivers well-distributed, oxygen-rich blood flow but may increase left ventricular (LV) afterload and reduce cerebral blood flow. However, when combined with IABP, it unloads LV pressure and increases cerebral blood flow. Integrating axillary artery VA-ECMO with IABP can promote cardiac function recovery and improve oxygen-rich blood perfusion to the vital organs of heart failure patients.
Bone scaffolds are increasingly regarded as viable alternatives to autografts and allografts in clinical settings. However, their effectiveness can vary based on certain anatomical characteristics, highlighting the importance of image-based structural analysis. High-resolution imaging is crucial to accurately assess the performance of bone scaffolds. Despite this, the resolution of current clinical medical images is constrained by concerns regarding radiation exposure. The efficacy of these analyses can be improved by quantitatively evaluating the similarities and differences between low- and high-resolution images. This study quantitatively compared the structural behavior of bone scaffolds using both high- and low-resolution images. This study downscaled a high-resolution image, implanted a bone scaffold, and conducted finite element analysis. The findings suggest that the resolution needed for accurate structural analysis of skeletal images varies based on the implantation site of the scaffold. Additionally, it was found that the less influence the loading conditions have, the higher the resolution required to accurately assess the structural behavior.
There is a five-decade recorded history indicating that persons with transfemoral amputation experience bone loss in their amputated femur at levels seen in bedridden and post-menopausal individuals, irrespective of age or mobility levels. We used computer simulation to recreate the mechanical environment created by the mechanical design of a prosthetic device in the surviving femur of individuals with transfemoral amputations. Finite element models of gait instances were developed from the hip joint computerized tomography scan of a subject along with a coupled ischial containment prosthetic socket fitted as per standard clinical guidelines. Accompanying mirror models, assembled similarly but without the prosthetic socket were used for stimulus comparison. Simulation showed that more than 90% of the trabecular bone volume in the amputated femur with an ischial containment socket registered compressive strain magnitudes below 300με. These strain magnitudes are below the threshold for bone maintenance as per mechanotransduction theory (i.e., they lie within the disuse window). Only 50% of the bone was in the disuse window for the mirror model for the gait instances considered. These results are consistent with reported in vivo evidence which shows that transfemoral prosthesis users may lose bone mass irrespective of age or mobility levels when using traditional socket designs. Clinically, this study shows that prosthetic sockets that support load through the ischium alter the kinetic chain and preclude application of mechanical stimulus that sustains healthy levels of bone mass in the proximal femur. The study also shows that femur length, prosthetic alignment and tissue tone influence this stimulus.
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