A numerical study of blood flow in coronary artery bypass graft side-to-side anastomoses.

Purpose: When sequential grafts are used in multivessel coronary artery bypass grafting, the graft first supplies blood to one or more coronary arteries via a side-to-side anastomosis. We studied hemodynamics in idealized models of "parallel" and "diamond" side-to-side anastomoses, identifying features that might promote restenosis.

Methods: Blood flow was computed in three representative anastomosis configurations: parallel side-to-side, diamond side-to-side, and end-to-side.

Computational modeling of mass transfer and links to atherosclerosis.

In the context of atherogenesis, mass transport refers to the movement of atherogenic molecules from flowing blood into the artery wall, or vice versa. Although LDL transport clearly plays a role in atherosclerotic plaque development, it is much less clear whether abnormalities in mass transfer patterns are in themselves atherogenic. A powerful way of addressing this question is through computational modeling, which provides detailed descriptions of local mass transport features.

Computational analysis of coupled blood-wall arterial LDL transport.

The transport of macromolecules, such as low density lipoproteins (LDLs), across the artery wall and their accumulation in the wall is a key step in atherogenesis. Our objective was to model fluid flow within both the lumen and wall of a constricted, axisymmetric tube simulating a stenosed artery, and to then use this flow pattern to study LDL mass transport from the blood to the artery wall. Coupled analysis of lumenal blood flow and transmural fluid flow was achieved through the solution of Brinkman's model, which is an extension of the Navier-Stokes equations for porous media.

Cationic ferritin changes outflow facility in human eyes whereas anionic ferritin does not.

Purpose: To determine the effect of charged moieties within the outflow pathway on aqueous outflow facility in human eyes.

Methods: After baseline facility measurement in human eye bank eyes (n = 10 pairs), one eye of each pair received anterior chamber exchange and continued perfusion with medium containing 10 mg/ml cationic ferritin. Contralateral eyes were treated in a similar manner with anionic ferritin (10.

Role of EGF receptor tyrosine kinase activity in antiapoptotic effect of EGF on mouse hepatocytes.

The apoptotic Fas pathway is potentially involved in the pathogenesis of liver diseases. Growth factors, such as epidermal growth factor (EGF), can protect cells against apoptosis induced by a variety of stimuli, including Fas receptor stimulation. However, the underlying mechanisms of this protection have yet to be determined.

Requirements for mesh resolution in 3D computational hemodynamics.

Computational techniques are widely used for studying large artery hemodynamics. Current trends favor analyzing flow in more anatomically realistic arteries. A significant obstacle to such analyses is generation of computational meshes that accurately resolve both the complex geometry and the physiologically relevant flow features.

Mass transport in an anatomically realistic human right coronary artery.

The coronary arteries are a common site of atherosclerotic plaque formation, which has been putatively linked to hemodynamic and mass transport patterns. The purpose of this paper was to study mass transport patterns in a human right coronary artery (RCA) model, focusing on the effects of local geometric features on mass transfer from blood to artery walls. Using a previously developed characteristic/finite element scheme for solving advection-dominated transport problems, mass transfer calculations were performed in a rigid, anatomically realistic model of a human RCA.

Factors influencing blood flow patterns in the human right coronary artery.

Evidence suggests that atherogenesis is linked to local hemodynamic factors such as wall shear stress. We investigated the velocity and wall shear stress patterns within a human right coronary artery (RCA), an important site of atherosclerotic lesion development. Emphasis was placed on evaluating the effect of flow waveform and inlet flow velocity profile on the hemodynamics in the proximal, medial, and distal arterial regions.

Effect of Healon and Viscoat on outflow facility in human cadaver eyes.

Purpose: To compare the acute effects of Healon (sodium hyaluronate) and Viscoat (sodium chondroitin sulfate-sodium hyaluronate) on outflow facility in human cadaver eyes and determine which viscoelastic agent is least likely to cause an intraocular pressure (IOP) spike after cataract surgery.

Setting: The Glaucoma Research Lab, University of Toronto, Ontario, Canada.

Methods: In this prospective paired study, 15 pairs of human cadaver eyes were used.

Hepatic artery buffer response following left portal vein ligation: its role in liver tissue homeostasis.

Occlusion of a lobar portal vein is known to induce atrophy of downstream liver lobes and hypertrophy of contralateral lobes. Changes in portal flow are known to be compensated by changes in hepatic arterial flow, thus defining the hepatic artery buffer response (HABR). To understand the role of liver flow in liver atrophy, we measured portal flow and hepatic artery flow after different degrees of left portal vein stenosis (LPVS).

Computational blood flow modeling based on in vivo measurements.

Study of the relationship between hemodynamics and atherogenesis requires accurate three-dimensional descriptions of in vivo arterial geometries. Common methods for obtaining such geometries include in vivo medical imaging and postmortem preparations (vessel casts, pressure-fixed vessels). We sought to determine the relative accuracy of these methods.

Measurement of Gd-DTPA diffusion through PVA hydrogel using a novel magnetic resonance imaging method.

Polyvinyl alcohol-cryogel (PVA-C) is a hydrogel that is an excellent tissue mimic. In order to characterize mass transfer in this material, as well as to demonstrate in principle the ability to noninvasively measure solute diffusion in tissue, we measured the diffusion coefficient of the magnetic resonance (MR) contrast agent gadolinium diethylene triaminopentaacetic acid (Gd-DTPA) through PVA-C using a clinical MR imager. The method involved filling thick-walled rectangular PVA-C "cups" with known concentrations of Gd-DTPA solutions.

A numerical study of blood flow patterns in anatomically realistic and simplified end-to-side anastomoses.

Purpose: Recently, some numerical and experimental studies of blood flow in large arteries have attempted to accurately replicate in vivo arterial geometries, while others have utilized simplified models. The objective of this study was to determine how much an anatomically realistic geometry can be simplified without the loss of significant hemodynamic information.

Method: A human femoral-popliteal bypass graft was used to reconstruct an anatomically faithful finite element model of an end-to-side anastomosis.

Effects of ethacrynic acid on Schlemm's canal inner wall and outflow facility in human eyes.

Purpose: The role of the inner wall of Schlemm's canal in determining aqueous outflow facility is poorly understood. To quantify the relationship between inner wall pore characteristics and aqueous outflow facility in human eyes, both control eyes and eyes in which facility had been pharmacologically increased by ethacrynic acid (ECA) infusion were studied.

Methods: Outflow facility was measured in enucleated human eyes before and after delivery of 0.

Enthacrynic and acid effects on inner wall pores in living monkeys.

Purpose: The influence of the inner wall of Schlemm's canal on aqueous outflow facility remains poorly understood. We examined the relationship between inner wall pore characteristics and outflow facility in living primate eyes in which facility had been pharmacologically increased by ethacrynic acid (ECA) infusion and in contralateral control eyes.

Methods: Outflow facility (two-level constant pressure perfusion) was measured in eight pairs of living monkey eyes before and after administration of a bolus dose of either 0.

Evaluation of hepatocyte injury following partial ligation of the left portal vein.

Background/aims: Total ligation of the left portal vein is thought to induce both hepatocyte apoptosis and necrosis. The pathological impact of partial ligation of a branch of the portal vein has not yet been evaluated.

Methods: We studied the degree of hepatocyte injury following 0, 43, 48, 59, 68, 72, 78 and 100% left portal vein stenosis in 200-g Sprague-Dawley male rats.

Accuracy of computational hemodynamics in complex arterial geometries reconstructed from magnetic resonance imaging.

Purpose: Combining computational blood flow modeling with three-dimensional medical imaging provides a new approach for studying links between hemodynamic factors and arterial disease. Although this provides patient-specific hemodynamic information, it is subject to several potential errors. This study quantifies some of these errors and identifies optimal reconstruction methodologies.

Flow waveform effects on end-to-side anastomotic flow patterns.

Purpose: Restenosis due to distal anastomotic intimal hyperplasia, a leading cause of arterial bypass graft failure, is thought to be promoted by hemodynamic effects, specifically 'abnormal' wall shear stress patterns. The purpose of this study was to quantify the effects of flow waveform on peri-anastomotic flow and wall shear stress patterns.

Methods: Blood flow and wall shear stress patterns were numerically computed in a representative three-dimensional anastomosis using femoral, iliac and coronary flow waveforms suitable for humans at rest.

Two pore types in the inner-wall endothelium of Schlemm's canal.

Purpose: It has been reported that fixation conditions significantly influence the apparent pore density in the inner-wall endothelium of Schlemm's canal. In the present study, the manner in which fixation conditions affect the two subtypes of inner-wall pores, intracellular pores and intercellular (or border) pores, was investigated.

Methods: Outflow facility was measured in enucleated human eyes.

Study of regional deformation of the optic nerve head using scanning laser tomography.

Purpose: Previous studies have suggested that IOP-induced deformation of the optic nerve head (ONH) at the level of the lamina cribrosa may contribute to axonal damage in glaucomatous optic neuropathy. Our purpose was to introduce a novel enucleated eye model for characterizing acute IOP-induced changes in ONH topography, and to develop improved analytical methods for detection of regional topographic change in the ONH.

Methods: Using a specially designed experimental apparatus, enucleated human eyes were progressively pressurized to 5, 15, 30, and 50 mmHg.

Metabolic and hormonal responses to exercise in partially hepatectomised rats.

To characterise how the liver affects metabolic and hormonal exercise responses, hepatectomised (70%; HX) rats were submitted to a 30- or 50-min treadmill exercise (26 m/min, 0% slope) 48 hr or 7 days after surgery (reduced or normal liver mass, respectively). To determine whether metabolic effects of liver mass reduction during exercise were caused by reduced capacity of the liver to produce glucose, metabolic and hormonal responses to the same exercise protocol were measured in 48-hr HX rats. Euglycemia, maintained by exogenous glucose infusion, produced attenuated lactate, insulin, and glucagon values in 48-hr HX rats but did not affect FFA, glycerol, and plasma catecholamine responses.

Computational blood flow modelling: errors associated with reconstructing finite element models from magnetic resonance images.

Construction of computational blood flow models from magnetic resonance (MR) scans of real arteries is a powerful tool for studying arterial hemodynamics. In this report we experimentally determine a lower bound for errors associated with such an approach, and present techniques for minimizing such errors. A known, simple three-dimensional geometry (cylindrical tube) was imaged using a commercial MR scanner, and the resulting images were used to construct finite element flow models.

Hypocalcemia modifies the intracellular calcium response to the alpha 1-adrenergic agent phenylephrine in rat hepatocytes.

In vivo, extracellular calcium ([Ca2+]e) homeostasis is maintained within a very narrow range by the calcium regulating hormones. At the cellular level, the response to many agents is transduced by changes in cytosolic Ca2+ ([Ca2+]i) which involves both mobilization of cellular pools and entry of [Ca2+]e through plasma membrane channels. To investigate the cellular effects of chronic hypocalcemia (Ca-) on [Ca2+]i homeostasis, hepatocytes, a cell type well characterized for its [Ca2+]i response, were used.