Indiana University-Purdue University Indianapolis (IUPUI) / The endothelium is a single layer of cells lining the arteries and is involved in many physiological reactions which are responsible for vascular tone. Free radicals are important participants in these chemical reactions in the endothelium. Here we quantify free radicals, ex vivo, in biological tissue with continuous wave electron paramagnetic resonance (EPR). In all of the experiments in this thesis, we use a novel EPR spin trapping technique that has been developed for tissue segments. EPR spin trapping is often considered the ‘gold standard’ in reactive oxygen species (ROS) detection because of its sensitivity and non-invasive nature. In all experiments, tissue was placed in physiological saline solution with 190-mM PBN (N-tert-butyl-α-phenylnitrone), 10% by volume dimethyl-sulphoxide (DMSO) for cryopreservation, and incubated in the dark for between 30 minutes up to 2 hours at 37°C while gently being stirred. Tissue and supernatant were then loaded into a syringe and frozen at -80°C until EPR analysis. In our experiments, the EPR spectra were normalized with respect to tissue volume. Conducting experiments at liquid nitrogen temperature leads to some experimental advantages. The freezing of the spin adducts renders them stable over a longer period, which allows ample time to analyze tissue samples for ROS. The dielectric constant of ice is greatly reduced over its liquid counterpart; this property of water enables larger sample volumes to be inserted into the EPR cavity without overloading it and leads to enhanced signal detection. Due to Maxwell-Boltzmann statistics, the population difference goes up as the temperature goes down, so this phenomenon enhances the signal intensity as well. With the ‘gold standard’ assertion in mind, we investigated whether slicing tissue to assay ROS that is commonly used in fluorescence experiments will show more free radical generation than tissue of a similar volume that remains unsliced. Sliced tissue exhibited a 76% increase in ROS generation; this implies that higher ROS concentrations in sliced tissue indicate extraneous ROS generation not associated with the ROS stimulus of interest. We also investigated the role of ROS in chronic flow overload (CFO). Elevation of shear stress that increases production of vascular ROS has not been well investigated. We hypothesize that CFO increases ROS production mediated in part by NADPH oxidase, which leads to endothelial dysfunction. ROS production increased threefold in response to CFO. The endothelium dependent vasorelaxation was compromised in the CFO group. Treatment with apocynin significantly reduced ROS production in the vessel wall, preserved endothelial function, and inhibited expressions of p22/p47phox and NOX2/NOX4. The present data implicate NADPH oxidase produced ROS and eNOS uncoupling in endothelial dysfunction at 1 wk of CFO. In further work, a swine right ventricular hypertrophy (RVH) model induced by pulmonary artery (PA) banding was used to study right coronary artery (RCA) endothelial function and ROS level. Endothelial function was compromised in RCA of RVH as attributed to insufficient endothelial nitric oxide synthase cofactor tetrahydrobiopterin. In conclusion, stretch due to outward remodeling of RCA during RVH (at constant wall shear stress), similar to vessel stretch in hypertension, appears to induce ROS elevation, endothelial dysfunction, and an increase in basal tone. Finally, although hypertension-induced vascular stiffness and dysfunction are well established in patients and animal models, we hypothesize that stretch or distension due to hypertension and outward expansion is the cause of endothelial dysfunction mediated by angiotensin II type 1 (AT1) receptor in coronary arteries. The expression and activation of AT1 receptor and the production of ROS were up regulated and endothelial function deteriorated in the RCA. The acute inhibition of AT1 receptor and NADPH oxidase partially restored the endothelial function. Stretch or distension activates the AT1 receptor which mediates ROS production; this collectively leads to endothelial dysfunction in coronary arteries.

Indiana University-Purdue University Indianapolis (IUPUI) / Atherosclerotic lesions of human beings are common diagnosed in regions of arte- rial branching and curvature. The prevalence of atherosclerosis is usually associated with hardening and ballooning of aortic wall surfaces because of narrowing of flow path by the deposition of fatty materials, platelets and influx of plasma through in- timal wall of Aorta. High Wall Shear Stress (WSS) is proved to be the main cause behind all these aortic diseases by physicians and researchers. Due to the fact that the atherosclerotic regions are associated with complex blood flow patterns, it has believed that hemodynamics and fluid-structure interaction play important roles in regulating atherogenesis. As one of the most complex flow situations found in cardio- vascular system due to the strong curvature effects, irregular geometry, tapering and branching, and twisting, theoretical prediction and in vivo quantitative experimental data regarding to the complex blood flow dynamics are substantial paucity. In recent years, computational fluid dynamics (CFD) has emerged as a popular research tool to study the characteristics of aortic flow and aim to enhance the understanding of the underlying physics behind arteriosclerosis. In this research, we study the hemo- dynamics and flow-vessel interaction in patient specific normal (healthy) and dilated (diseased) aortas using Ansys-Fluent and Ansys-Workbench. The computation con- sists of three parts: segmentation of arterial geometry for the CFD simulation from computed tomography (CT) scanning data using MIMICS; finite volume simulation of hemodynamics of steady and pulsatile flow using Ansys-Fluent; an attempt to perform the Fluid Structure Simulation of the normal aorta using Ansys-Workbench. Instead of neglecting the branching or smoothing out the wall for simplification as a lot of similar computation in literature, we use the exact aortic geometry. Segmen- tation from real time CT images from two patients, one young and another old to represent healthy and diseased aorta respectively, is on MIMICS. The MIMICS seg- mentation operation includes: first cropping the required part of aorta from CT dicom data of the whole chest, masking of the aorta from coronal, axial and saggital views of the same to extract the exact 3D geometry of the aorta. Next step was to perform surface improvement using MIMICS 3-matic module to repair for holes, noise shells and overlapping triangles to create a good quality surface of the geometry. A hexahe- dral volume mesh was created in T-Grid. Since T-grid cannot recognize the geometry format created by MIMICS 3-matic; the required step geometry file was created in Pro-Engineer. After the meshing operation is performed, the mesh is exported to Ansys Fluent to perform the required fluid simulation imposing adequate boundary conditions accordingly. Two types of study are performed for hemodynamics. First is a steady flow driven by specified parabolic velocity at inlet. We captured the flow feature such as skewness of velocity around the aortic arch regions and vortices pairs, which are in good agreement with open data in literature. Second is a pulsatile flow. Two pulsatile velocity profiles are imposed at the inlet of healthy and diseased aorta respectively. The pulsatile analysis was accomplished for peak systolic, mid systolic and diastolic phase of the entire cardiac cycle. During peak systole and mid-systole, high WSS was found at the aortic branch roots and arch regions and diastole resulted in flow reversals and low WSS values due to small aortic inflow. In brief, areas of sudden geometry change, i.e. the branch roots and irregular surfaces of the geom- etry experience more WSS. Also it was found that dilated aorta has more sporadic nature of WSS in different regions than normal aorta which displays a more uniform WSS distribution all over the aorta surface. Fluid-Structure Interaction simulation is performed on Ansys-WorkBench through the coupling of fluid dynamics and solid mechanics. Focus is on the maximum displacement and equivalent stress to find out the future failure regions for the peak velocity of the cardiac cycle.