Aortic arch aneurysm repair - Unsteady hemodynamics and perfusion at different heart rates.

The aortic arch aneurysm is a complex disease that requires branching of one or more aortic arch vessels and can be fatal if left untreated. In this in vitro study, we examine the effect of the treatment approach on the unsteady hemodynamics and blood perfusion to the upper vessel's in models of an aortic arch aneurysm, and of the three common repair approaches: open-chest surgical repair, chimney, and hybrid approach. A particle image velocimetry method was used to quantify the unsteady hemodynamics in the four models simulated in a mock circulatory loop, to evaluate unsteady hemodynamic parameters and measure perfusion to the brain and the upper body. According to the findings, in terms of perfusion to the brain and upper body, the surgery model has the highest flow rate comparing to the other models in most heart-rate conditions. It also shows oscillatory parameters in the upper vessels which in normal arteries are correlated with a better arterial function. Between the two endovascular procedures, the hybrid model exhibits slightly better hemodynamic characteristics than the chimney model, with lower shear stresses and more oscillatory flow and WSS in the upper vessels. The hybrid model had lower perfusion flow rates to upper vessels during rest conditions (90BPM). However, unlike the other models, perfusion in the hybrid model increased with heart rate, thus at 135 BPM, it results in flow rate to upper vessels similar to that of the chimney model. The results of this study may shed light on future endograft' design and placement techniques.

Biomechanical Aspects of Closing Approaches in Postcarotid Endarterectomy.

The carotid bifurcation tends to develop atherosclerotic stenoses which might interfere with cerebral blood supply. In cases of arterial blockage, the common clinical solution is to remove the plaque via carotid endarterectomy (CEA) surgery. Artery closure after surgery using primary closures along the cutting edge might lead to artery narrowing and restrict blood flow. An alternative approach is patch angioplasty which takes longer time and leads to more during-surgery complications. The present study uses numerical methods with fluid-structure interaction (FSI) to explore and compare the two solutions in terms of hemodynamics and stress and strain fields developed in the artery wall.

Approaches for treatment of aortic arch aneurysm, a numerical study.

Aortic arch aneurysm is a complex pathology which requires coverage of one or more aortic arch vessels. In this study we explore the hemodynamic behavior of the aortic arch in aneurysmatic and treated cases with three currently available treatment approaches: Surgery Graft, hybrid Stent-Graft and chimney Stent Graft. The analysis included four models of the time-dependent fluid domains of aneurysmatic arch and of the surgery, hybrid and chimney endovascular techniques. Dimensions of the models are based on typical anatomy, and boundary conditions are based on typical physiological flow. The simulations used computational fluid dynamics (CFD) methods to delineate the time-dependent flow dynamics in the four geometric models. Results of velocity vectors, flow patterns, blood pressure and wall shear stress distributions are presented. The results delineate disturbed and recirculating flow in the aortic arch aneurysm accompanied with low wall shear stress and velocities, compared to a uniformly directed flow and nominal wall shear stress (WSS) in the model of Surgery graft. Out of the two endograft procedures, the hybrid procedure clearly exhibits better hemodynamic performances over the chimney model, with lower WSS, lower pressure drop and less disturbed and vortical flow regions. Although the chimney procedure requires less manufacturing time and cost, it is associated with higher risk rates, and therefore, it is recommended only for emergency cases. This study may shed light on the hemodynamic factors for these complications and provide insight into ways to improve the procedure.

A novel emboli protection cannula during cardiac surgery: in vitro results.

OBJECTIVE: Intraoperative cerebral events are mainly caused by emboli generated by operative manipulation of the aorta. This study aimed to delineate the distribution profiles of emboli with 2 widely used cannulae and a third novel research cannula that simultaneously produces forward flow and backward suction to extract emboli from the distal aorta during cardiac surgery. METHODS: The current in vitro study used a silicone model of the aortic arch and branches. The main outcome measure was the distribution profile of embolic particles of different sizes to the aortic branches; 2 commercial cannulae and a third novel cannula with and without suction were used. The research cannula was examined at different suction levels and the amount of particles retrieved was measured. RESULTS: For the research curved-tip cannula, most of the small emboli were released into the brachiocephalic trunk in the model (P < .05). For the straight-tip cannula, most of the small emboli were released into the descending aorta (P < .05). Regarding the commercial curved-tipped cannula, most of the small emboli were released into the brachiocephalic trunk (47.14% ± 4.78%; P < .05) and the medium and large emboli were predominantly released into the descending aorta. Using suction, the research cannula retrieved most of the emboli released into the aorta for all particle sizes (50%-83%; P < .05). CONCLUSIONS: A straight-tip cannula may be safer in terms of cerebral embolic consequences during cardiac surgery. Furthermore, the use of the research aortic cannula may be beneficial in the cardiac surgery setting by reducing the postoperative risk for stroke.

Investigation of risks for cerebral embolism associated with the hemodynamics of cardiopulmonary bypass cannula: a numerical model.

Cerebral emboli originating in the ascending aorta are a major cause of noncardiac complications following cardiac surgery. The hemodynamics of the aortic cannula has been proven to play a significant role in emboli generation and distribution. The aim of the current study was to perform a thorough numerical investigation in order to examine the effect of the design and orientation of the cannula used during cardiopulmonary bypass on the risk to develop cerebral embolism. Hemodynamic analyses compared numerical models of 27 cases consisting of six different cannula orientations, four aortic anatomies, and three cannula designs. The cannula designs included a straight-tip (ST) cannula, a moderately curved tip cannula (TIP1 ), and a sharp-angle curved cannula (TIP2 ). Outcome measures included hemodynamic parameters such as emanating jet velocity, jet velocity drop, maximal shear stress, aortic wall reaction, emboli pathlines and distribution between upper and lower vessels, and stagnation regions. Based on these parameters, the risks for hemolysis, atheroembolism, and cerebral embolism were evaluated and compared. On one hand, the jet emerging from the ST cannula generated large wall-shear stress at the aortic wall; this may have triggered the erosion and distribution of embolic atheromatous debris from the aortic arch. On the other hand, it diverted more emboli from the clamp region to the descending aorta and thus reduced the risk for cerebral embolism. The TIP1 cannula demonstrated less shear stress on the aortic wall and diverted more emboli from the clamp region toward the upper vessels. The TIP2 cannula exhibited a stronger emanating jet, higher shear stress inside the cannula, and highly disturbed flow, which was more stagnant near the clamp region. Current findings support the significant impact of the cannula design and orientation on emboli generation and distribution. Specifically, the straight tip cannula demonstrated a reduced risk of cerebral embolism, which may be pivotal in the clinical setting.

Numerical investigation of a novel aortic cannula aimed at reducing cerebral embolism during cardiovascular bypass surgery.

The generation of emboli during cardiopulmonary bypass (CPB) is profoundly affected by the hemodynamic properties of the aortic cannula used in the current study. The aim of the current work was to numerically investigate the hemodynamic efficiency and feasibility of a novel, backward suction cannula (BSC), designed to drastically reduce the potential risk for cerebral emboli (CEP). In line with the standard cannulae, the BSC provides oxygenated blood from the CPB machine through its primary lumen. However, the unique feature of the BSC lies in its secondary lumen, which is used to suck blood and embolic matter back from the surgical field to the CPB machine for filtration. Analysis included a numerical investigation of the hemodynamic characteristics of 44 different models, encompassing various anatomic orientations, cannula types, cannula orientations and flow conditions. Hemodynamic efficacy and CEP were assessed via trajectories of particle released from the surgical region, while the cannula feasibility was evaluated through potential for atheroembolism (AP) and index for hemolysis (IH). Differences between the investigated cannulae in terms of these measures were tested using analyses of variance tests (ANOVAs). Results indicate that the BSC exhibited a significant improvement of the cannula performance in terms of CEP with no significant change in the risk for other hemodynamic complications, such as hemolysis or atheroembolism (AP and IH). These findings suggest the advantageous use of the BSC in the clinical setting for its potential to diminish the risk for cerebral emboli, which presents the most pertinent cause of noncardiac complications following open heart surgery.

A novel dynamic matrix detachment model reveals a shift from apoptosis to necrosis in melanoma cells.

Anchorage-independence is a hallmark of invasive cancer. The setback of the classical poly-HEMA static matrix detachment (SMD) anoikis model is the absence of dynamic fluid circulation, resulting in cell aggregates. We addressed this problem by developing a novel 3D cell culture dynamic matrix detachment (DMD) model with a turbulent-free laminar flow, yielding a very low shear stress. In this study, we focused on melanoma cells where apoptosis was evaluated both via annexin V flow cytometry and caspase cleavage. The DMD model was superior to SMD in the induction of melanoma cell death and in revealing a shift from apoptosis to necrotic cell death, as evident by failure to activate caspase 9 and a decrease in annexin V stain. Combination of DMD with cisplatin could further accentuate necrotic cell death in cisplatin-resistant melanoma cells. Thus, the DMD model may be a useful matrix deprivation model to identify necrotic vs. apoptotic cell death pathways.

A 3D rotary renal and mesenchymal stem cell culture model unveils cell death mechanisms induced by matrix deficiency and low shear stress.

BACKGROUND: In epithelial and endothelial cells, detachment from the matrix results in anoikis, a form of apoptosis, whereas stromal and cancer cells are often anchorage independent. The classical anoikis model is based on static 3D epithelial cell culture conditions (STCK). METHODS: We characterized a new model of renal, stromal and mesenchymal stem cell (MSC) matrix deprivation, based on slow rotation cell culture conditions (ROCK). This model induces anoikis using a low shear stress, laminar flow. The mechanism of cell death was determined via FACS (fluorescence-activated cell sorting) analysis for annexin V and propidium iodide uptake and via DNA laddering. RESULTS: While only renal epithelial cells progressively died in STCK, the ROCK model could induce apoptosis in stromal and transformed cells; cell survival decreased in ROCK versus STCK to 40%, 52%, 62% and 7% in human fibroblast, rat MSC, renal cell carcinoma (RCC) and human melanoma cell lines, respectively. Furthermore, while ROCK induced primarily apoptosis in renal epithelial cells, necrosis was more prevalent in transformed and cancer cells [necrosis/apoptosis ratio of 72.7% in CaKi-1 RCC cells versus 4.3% in MDCK (Madin-Darby canine kidney) cells]. The ROCK-mediated shift to necrosis in RCC cells was further accentuated 3.4-fold by H(2)O(2)-mediated oxidative stress while in adherent HK-2 renal epithelial cells, oxidative stress enhanced apoptosis. ROCK conditions could also unveil a similar pattern in the LZ100 rat MSC line where in ROCK 44% less apoptosis was observed versus STCK and 45% less apoptosis versus monolayer conditions. Apoptosis in response to oxidative stress was also attenuated in the rat MSC line in ROCK, thereby highlighting rat MSC transformation. CONCLUSIONS: The ROCK matrix-deficiency cell culture model may provide a valuable insight into the mechanism of renal and MSC cell death in response to matrix deprivation.

Influence of microcalcifications on vulnerable plaque mechanics using FSI modeling.

Sudden heart attacks remain one of the primary causes of premature death in the developed world. Asymptomatic vulnerable plaques that rupture are believed to prompt such fatal heart attacks and strokes. The role of microcalcifications in the vulnerable plaque rupture mechanics is still debated. Recent studies suggest the microcalcifications increase the plaque vulnerability. In this manuscript we present a numerical study of the role of microcalcifications in plaque vulnerability in an eccentric stenosis model using a transient fluid-structure interaction (FSI) analysis. Two cases are being compared (i) in the absence of a microcalcification (ii) with a microcalcification spot fully embedded in the fibrous cap. Critical plaque stress/strain conditions were affected considerably by the presence of a calcified spot, and were dependent on the timing (phase) during the flow cycle. The vulnerable plaque with the embedded calcification spot presented higher wall stress concentration region in the fibrous cap a bit upstream to the calcified spot, with stress propagating to the deformable parts of the structure around the calcified spot. Following previous studies, this finding supports the hypothesis that microcalcifications increase the plaque vulnerability. Further studies in which the effect of additional microcalcifications and parametric studies of critical plaque cap thickness based on plaque properties and thickness, will help to establish the mechanism by which microcalcifications weaken the plaque and may lead to its rupture.