Restoration of wall shear stress in the cephalic vein during extreme hemodynamics

Abstract

The surgical creation of an artery-vein connection via a Brachicephalic fistula (BCF) in patients with end stage renal disease (ESRD) provides a unique opportunity to study blood vessel response mechanisms to extreme hemodynamic conditions in relatively short timeframes. After BCF creation, the flow rate in the vein increases by an order of magnitude leading to separated flows and corresponding abnormally low, or negative, wall shear stress (WSS) in the curved arch segment of the cephalic vein. Locations of abnormally low WSS are shown to correlate with development of neointimal hyperplasia (NH) and subsequent stenosis. It is found that the stenosis, prior to a surgical intervention, restores the normal physiological WSS in the vein. As a result, this investigation provides evidence that the adaptation principle, known to apply in the arterial system, is also valid in the venous system. A novel graphical method is developed that combines clinical and computational data to assist in interpreting these physiological mechanisms including adaptation that lead to changes in vein geometry over time.

Keywords: Cephalic; brachiocephalic; fistula; vein adaptation; wall shear stress.

Figure 1.

(a) Example venograms illustrating the cephalic vein and arch. The blood flow is from right to left. Note a collateral vein is present in the arch but is observed to degrade over time.

Figure 2.

The zone scatter plot. Characterization of postulated vein response mechanisms by zones based on τ_w and ∆d*. NPR for the cephalic vein is the area inside the grey region, corresponding to 0.076 < τ_w < 0.76 Pa.

Figure 3.

Examples of patient-specific cephalic veins illustrating typical flow patterns, low wall shear stress regions, and postulated response mechanisms. Red colour indicates abnormally low wall shear stresses, i.e. τ_w < 0.076 Pa, and gray lines are streamlines. Note length scales are not identical due to different vein lengths.

Figure 4.

Wall shear stresses plotted on horizontal axis for cephalic vein prior to BCF creation in 12 patients based upon ESRD patient-specific geometries, and measured velocities and viscosities. NPR of 0.076 < τ_w < 0.76 Pa is area between red dashed lines. Here, the average WSS is 0.22 Pa and is denoted by red *. This is the same data as Figure 3 of Hammes et al. [27] plotted in the present format.

Figure 5.

Case 1: ψ-τ_w contour plots illustrating cephalic vein adaptation for patient 26. τ_w < 0.076 Pa denoted by red lines.

Figure 6.

Case 1: Adaptation in cephalic vein for patient 26, cf. Fig. 5.

Figure 7.

Case 2: Adaptation interrupted by surgical intervention for patient 14 (typical scenario).