Development of a predictne framework to forecast venous stenosis

The end stage renal disease (ESRD) patient population is growing at a troubling rate, calling for a focused attention to investigate the chronic kidney diseases, their characteristics and our lines of defense against them. One major medical treatment for ESRD patients is hemodialysis which is facilitated through vascular access (VA). The vascular access of particular interest in this investigation as well as the med- ical community is the brachiocephalic fistula (BCF), which is a form of arteriovenous fistula (AVF), created surgically by connecting the brachial artery and the cephalic vein. It is commonly used for elderly patients and for those with poor circulation systems, e.g. diabetics. The extreme hemodynamic environment that BCF creates triggers the onset of neointimal hyperplasia (NH) in most of these patients which leads to access failure and a high morbidity and mortality rate. This process happens in a matter of months, providing an excellent translational medicine experimental stage to observe as the vessel walls react and adapt to the new hemodynamically violent conditions. Through extensive analysis of the venous deformation and subsequent hemodynamics of a patient cohort of 160, a prognosticative framework to predict the vein deformation in these patients prior to the occurrence of the failure has been developed. The obtained results are the consequence of the integration of clinical practice and computational science. The proposed method was first based on our hypothesis which roots the NH in non-physiological wall shear stresses (WSS), and was then improved and modified using rigorous optimization and numerical approaches. This finding is essential to the modification of the current VA techniques to increase the patency of the AVFs, to prevent the diminishing functionality of the access, and to increase the life expectancy of ESRD patients. Moreover, this finding will further assist us in comprehension of the human vasculature growth and remodeling (G&R;) through bypassing the analysis of unknown biological phenomena, as it is achieved purely by juxtaposing well-defined mathematical, physical, and medical concepts

Electrostatic Self-Cleaning Gecko-like Adhesives

Using a two-phase square wave at 5Hz frequency to remove 100 μm glass beads on directional gecko-like adhesiv

Increased Inlet Blood Flow Velocity Predicts Low Wall Shear Stress in the Cephalic Arch of Patients with Brachiocephalic Fistula Access

Background: An autogenous arteriovenous fistula is the optimal vascular access for hemodialysis. In the case of brachiocephalic fistula, cephalic arch stenosis commonly develops leading to access failure. We have hypothesized that a contribution to fistula failure is low wall shear stress resulting from post-fistula creation hemodynamic changes that occur in the cephalic arch. Methods: Twenty-two subjects with advanced renal failure had brachiocephalic fistulae placed. The following procedures were performed at mapping (pre-operative) and at fistula maturation (8–32 weeks post-operative): venogram, Doppler to measure venous blood flow velocity, and whole blood viscosity. Geometric and computational modeling was performed to determine wall shear stress and other geometric parameters. The relationship between hemodynamic parameters and clinical findings was examined using univariate analysis and linear regression. Results: The percent low wall shear stress was linearly related to the increase in blood flow velocity (p Conclusions: The curvature and hemodynamic changes during fistula maturation increase the percentage of low wall shear stress regions within the cephalic arch. Low wall shear stress may contribute to subsequent neointimal hyperplasia and resultant cephalic arch stenosis. If this hypothesis remains tenable with further studies, ways of protecting the arch through control of blood flow velocity may need to be developed.</p

Increased Inlet Blood Flow Velocity Predicts Low Wall Shear Stress in the Cephalic Arch of Patients with Brachiocephalic Fistula Access

<div><p>Background</p><p>An autogenous arteriovenous fistula is the optimal vascular access for hemodialysis. In the case of brachiocephalic fistula, cephalic arch stenosis commonly develops leading to access failure. We have hypothesized that a contribution to fistula failure is low wall shear stress resulting from post-fistula creation hemodynamic changes that occur in the cephalic arch.</p><p>Methods</p><p>Twenty-two subjects with advanced renal failure had brachiocephalic fistulae placed. The following procedures were performed at mapping (pre-operative) and at fistula maturation (8–32 weeks post-operative): venogram, Doppler to measure venous blood flow velocity, and whole blood viscosity. Geometric and computational modeling was performed to determine wall shear stress and other geometric parameters. The relationship between hemodynamic parameters and clinical findings was examined using univariate analysis and linear regression.</p><p>Results</p><p>The percent low wall shear stress was linearly related to the increase in blood flow velocity (<i>p</i> < 0.01). This relationship was more significant in non-diabetic patients (<i>p</i> < 0.01) than diabetic patients. The change in global measures of arch curvature and asymmetry also evolve with time to maturation (<i>p</i> < 0.05).</p><p>Conclusions</p><p>The curvature and hemodynamic changes during fistula maturation increase the percentage of low wall shear stress regions within the cephalic arch. Low wall shear stress may contribute to subsequent neointimal hyperplasia and resultant cephalic arch stenosis. If this hypothesis remains tenable with further studies, ways of protecting the arch through control of blood flow velocity may need to be developed.</p></div

Scatterplots depicting the relationship between weeks since access placement and Global Curvature or Global Asymmetry.

<p>Time since access placement (weeks) is shown on the <i>x</i>-axis and change in Global Curvature and Global Asymmetry are shown on the <i>y</i>-axis. Changes in Global Curvature (left panel) and Global Asymmetry (right panel) increase with time since the fistula was placed (<i>p</i> < 0.05). The relationship did not differ significantly in patients with diabetes (closed circles) compared to those without diabetes (open circles) (<i>p</i> < 0.05).</p

Scatterplot depicting the relationship of blood flow velocity and WSS at maturation.

<p>Maximum blood flow velocity (cm/sec) is shown on the <i>x</i>-axis and percent low wall shear stress is shown on the <i>y</i>-axis. Blood flow velocity is correlated with changes in low wall shear stress (solid line) (<i>p</i> < 0.05). The patients with diabetes are represented by closed circles, the patients without diabetes by open circles with significant correlation in non-diabetics (<i>p</i> < 0.05).</p

Wall shear stress at mapping in 12 subjects.

<p>WSS (log <i>Pa</i>) at mapping for 12 subjects. Within-patient log-transformed wall shear stress values in the upper (dark grey) and lower wall (light grey). Red reference lines show the normal range on the original scale log scale [log(0.076)-log(0.76)].</p

Patient Measured Parameters.

<p>Patient Measured Parameters.</p

Computational flow plot of cephalic arch.

<p>Terminal cephalic arch with inflow from right to left. Critical wall shear regions (< 0.076 Pa) are denoted with bold, red lines and are superimposed on streamlines. Computational flow plot for subject 7 at baseline (Panel A) and 30 weeks (Panel B). Computational flow plot for subject 2 at baseline (Panel C) and 8 weeks (Panel D). Black arrow on Panel D shows tiny area of low wall shear stress.</p