Nurullah Arslan

Transitional Flow at the Venous Anastomosis of an Arteriovenous Graft: Potential Activation of the ERK1/2 Mechanotransduction Pathway

We present experimental and computational results that describe the level, distribution, and importance of velocity fluctuations within the venous anastomosis of an arteriovenous graft. The motivation of this work is to understand better the importance of biomechanical forces in the development of intimal hyperplasia within these grafts. Steady-flow in vitro studies (Re = 1060 and 1820) were conducted within a graft model that represents the venous anastomosis to measure velocity by means of laser Doppler anemometry. Numerical simulations with the same geometry and flow conditions were conducted by employing the spectral element technique. As flow enters the vein from the graft, the velocity field exhibits flow separation and coherent structures (weak turbulence) that originate from the separation shear layer. We also report results of a porcine animal study in which the distribution and magnitude of vein-wall vibration on the venous anastomosis were measured at the time of graft construction. Preliminary molecular biology studies indicate elevated activity levels of the extracellular regulatory kinase ERK1/2, a mitogen-activated protein kinase involved in mechanotransduction, at regions of increased vein-wall vibration. These findings suggest a potential relationship between the associated turbulence-induced vein-wall vibration and the development of intimal hyperplasia in arteriovenous grafts. Further research is necessary, however, in order to determine if a correlation exists and to differentiate the vibration effect from that of flow related effects.

Obesity in adults in Turkey: age and regional effects

BACKGROUND In this study, the body mass index (BMI) of Turkish population is calculated using a sample of 4205 persons consisting of 2263 male and 1942 female individuals in 2007. The study contains data from all seven geographical regions (Aegean, Black Sea, Central Anatolia, Eastern Anatolia, Marmara, Mediterranean and Southeast Anatolia) of Turkey and from all age groups from 20 to 85 years. METHOD In this study, height and weight data were measured and used for calculating the BMI of Turkish population accounting for age and regional effects. RESULTS This studys analysis found that age, region and gender are significant determinants on obesity of Turkish population. Also, Turkish population has higher obesity prevalence than most of the European countries. Overall, it was found that 56% of Turkish Population is overweight while 41% is in the normal range. CONCLUSIONS This is the first study related to obesity in Turkey covering all seven regions and all age groups. Analyzing the differences of obesity prevalence between genders, geographical regions and age groups will be beneficial for better understanding the reasons behind obesity in Turkey.

On the numerical solution of the diffusion equation with variable space operator

In present paper numerical schemes are developed for obtaining approximate solutions to the mixed problem for one-dimensional diffusion equation with variable space operator.The method of lines semidiscretization approach is used to transform the model partial differential equation into a system of first-order linear ordinary differential equations. The partial derivative with respect to the space variable is approximated by the first and second-order finite-difference approximation. For the solution of the resulting system of first-order ordinary differential equations we apply the first and second order of accuracy difference schemes. Stability estimates for the solution of these difference schemes are established. Numerical techniques are developed by applying a procedure of the solution of first order linear difference equation with matrix coefficients. The algorithms are tested on a model problem in biofluid mechanics. Two regions are considered close to the endothelial cells (EC) which can be modeled taking the mixed problem for one-dimensional diffusion equation with variable space operator.

In vitro pulsatile flow waveform simulation and comparison using AC pump and proportional pneumatic valve

Patients, with renal failure, can be taken to the hemodialysis after fistula or graft surgery. In hemodialysis, blood is pumped with the help of the artificial kidney machine and the waste product from the blood is filtered and blood is returned to the patients after cleaning process. AV graft implantation is the creation of a polytetrafluoroethylene (PTFE) bridge a bridge between the arteries and veins. In this study simulation of the pulsatile flow signal in the AV graft and vein connection is aimed experimentally. Suitable for this purpose AC centrifugal pump, pump driver card, pneumatic valve, data acquisition card, flow meters and other equipments are used for close loop control mechanism in laboratory. Pulsatile waveforms obtained by AC centrifugal pump and pneumatic valve performance are compared to each other in close loop control. The results showed that AV graft signal can be modeled by AC centrifugal pump and pneumatic valve successfully. Current study could be a guide and motivation to the establishment of the different experimental systems in future.

FLOW CHARACTERIZATION INSIDE A COMPLEX AV GRAFT TO VEIN CONNECTION

Flow field characterization inside a complex arteriovenous (AV) graft to vein connection using laser Doppler anemometry (LDA) under steady flow conditions is done in this study. The objective of the current study is to find the critical flow regions and to understand the importance of biomechanical forces in the development of intimal hyperplasia (IH) within these grafts. In vivo studies were done by [Fillinger, 1990]. They correlated Reynolds number characterizing the flow with the fluctuations inside anastomosis. Loth, 2003 analyzed the flow field inside AV graft to vein connection and found the turbulence level inside the connection region

Femoral artery's Blood Volume Pulse signal modelling

Cardiovascular diseases are important disease to affecting our world recently. Numerical and experimental simulations are rapidly increasing in this research area. Blood Volume Pulse uses frequently to diagnose and treatment of this kind of disease. Data was obtained from modeling of blood vessel and blood flow in vitro experimental system, supports for instruct to direction diagnose and treatment of disease. Because of that femoral artery blood volume signal modeling was chosen as goal, has important place in cardiovascular area. Suitable for this purpose centrifugal pump, pump driver card, data acquisition card, flow meter and other equipments were established for close loop control mechanism in our universitys laboratory. Results of obtained indicate that is available model of the femoral artery blood flow taken data from the real patients. There is the motivation result to improve new approach diagnosed and treatment ways of different blood vein and blood volume pulse signals modeling.

Modeling of Blood Flow inside Human Left Coronary Artery Bifurcation with Aneurysms: Kawasaki Disease

Coronary artery aneurysms primarily seen in younger children is thought to be caused due to Kawasaki disease (KD). The flow phenomena inside the left coronary artery (LCA) and its branches with aneurysms located at various locations were studied computationally under steady flow conditions. Reynolds numbers representing the steady flow were 110, and 200 for average, and diastolic peak flow that are represented by pulsatile flow waveform, respectively. Local arterial flow dynamics were analyzed inside the aneurysms with two different sizes (four and eight millimeters) located at LCA and at the left anterior descending (LAD) artery. The critical flow regions such as flow separation, flow recirculation that can cause the low wall shear stresses (WSS) inside the LCA and its branches were observed with changing magnitudes. Simulation of the flow patterns may provide us important information regarding the possible long-term implications of Kawasaki disease in children, which may help us in taking appropriate early actions in order to prevent some of the adverse outcomes. Further in vivo and experimental modeling studies will help to understand the flow field inside the coronary bifurcation with aneurysm in detail.