Numerical analysis of Venous External Scaffolding Technology for Saphenous Vein Grafts.

This paper presents a method for analyzing and comparing numerically Saphenous Vein Grafts (SVGs) following Coronary Artery Bypass Graft surgery (CABG). The method analyses the flow dynamics inside vein grafts with and without supporting using Venous External Scaffolding Technology (VEST). The numerical method uses patients׳ specific computational fluid dynamics (CFD) methods to characterize the relevant hemodynamic parameters of patients׳ SVGs. The method was used to compare the hemodynamics of six patient׳s specific model and flow conditions of stented and non-stented SVGs, 12 months post-transplantation. The flow parameters used to characterize the grafts׳ hemodynamics include Time Averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI) and Relative Residence Time (RRT). The effect of stenting was clearly demonstrated by the chosen parameters. SVGs under constriction of VEST were associated with similar spatial average of TAWSS (10.73 vs 10.29 dyn/cm(2)), yet had fewer lesions with low TAWSS, lower OSI (0.041 vs 0.08) and RRT (0.12 vs 0.24), and more uniform flow with less flow discrepancies. In conclusion, the suggested method and parameters well demonstrated the advantage of VEST support. Stenting vein grafts with VEST improved hemodynamic factors which are correlated to graft failure following CABG procedure.

Human melanoma cells expressing the alphavbeta3 integrin are partially protected from necrotic cell death induced by dynamic matrix detachment.

Anchorage-independence is a hallmark of metastatic cancer cells. In previous studies we characterized a novel model for anchorage-independence employing dynamic matrix detachment (DMD) using rotation in low shear stress conditions. We observed that in contrast to the classical apoptosis-inducing static matrix detachment (SMD) model, the venous circulation-mimicking DMD model induced necrosis in transformed cells. In the current study we revisited the mechanism of DMD-induced cell death and evaluated the contribution of alphavbeta3 integrin overexpression in human melanoma cells to anchorage-independence in DMD. DMD cell culture induced primarily necrosis in the melanoma cells studied. alphavbeta3, but not the control related alphaIIbbeta3 integrin, could confer survival advantage in DMD. While apoptosis was unaffected, constitutive, unligated alphavbeta3 overexpression was associated with attenuation of necrosis in DMD. alphavbeta3 overexpressing melanoma cells manifested AKT activation that was independent of DMD conditions. Furthermore, while a small molecular inhibitor of AKT phosphorylation induced apoptosis in adherent cells, in DMD conditions it had no effect on cell outcome. Thus, alphavbeta3-overexpressing melanoma cells are partially protected from DMD-induced cell death in an apoptosis-independent mechanism. This finding may be one of the factors accounting for anchorage-independence in circulating metastatic melanoma cells.

Enigma of primary aortoduodenal fistula.

A diagnosis of primary aortoenteric fistula is difficult to make despite a high level of clinical suspicion. It should be considered in any elderly patient who presents with upper gastrointestinal bleeding in the context of a known abdominal aortic aneurysm. We present the case of young man with no history of abdominal aortic aneurysm who presented with massive upper gastrointestinal bleeding. Initial misdiagnosis led to a delay in treatment and the patient succumbing to the illness. This case is unique in that the fistula formed as a result of complex atherosclerotic disease of the abdominal aorta, and not from an aneurysm.

Hemobilia due to hepatic artery aneurysm as the presenting sign of fibro-muscular dysplasia.

Fibro-muscular dysplasia (FMD) is a rare but well documented disease with multiple arterial aneurysms. The patients, usually women, present with various clinical manifestations according to the specific arteries that are affected. Typical findings are aneurysmatic dilatations of medium-sized arteries. The renal and the internal carotid arteries are most frequently affected, but other anatomical sites might be affected too. The typical angiographic picture is that of a "string of beads". Common histological features are additionally described. Here we present a case of a 47-year-old woman, who was hospitalized due to intractable abdominal pain. A routine work-up revealed a liver mass near the portal vein. Before a definite diagnosis was reached, the patient developed massive upper gastrointestinal bleeding. In order to control the hemorrhage, celiac angiography was performed revealing features of FMD in several arteries, including large aneurysms of the hepatic artery. Active bleeding from one of these aneurysms into the biliary tree indicated selective embolization of the hepatic artery. The immediate results were satisfactory, and the 5 years follow-up revealed absence of any clinical symptoms.

Can vortices in the flow across mechanical heart valves contribute to cavitation?

Cavitation in mechanical heart valves is traditionally attributed to the hammer effect and to squeeze and clearance flow occurring at the moment of valve closure. In the present study, an additional factor is considered--the contribution of vortex flow. Using a computational fluid dynamics analysis of a 2D model of a tilting disk mitral valve, we demonstrate that vortices may form in the vicinity of the inflow side of the valve. These vortices roll up from shear layers emanating from the valve tips during regurgitation. A significant decrease in the pressure at the centre of the vortices is found. The contribution of the vortex to the total pressure drop at the instant of closure is of the order of 70 mmHg. Adding this figure to the other pressure drop sources that reach 670 mmHg, it might be that this is the deciding factor that causes the drop in blood pressure below vapour pressure. The total pressure drop near the upper tip (750 mmHg) is larger than near the lower tip (670 mmHg), indicating a preferential location for cavitation inception, in agreement with existing experimental findings.