Hemodynamic effects of hemodialyzer pump speed on arteriovenous fistulas
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AIM: Arteriovenous fistulas (AVF) are the optimal vascular access for hemodialysis although many fistulas fail. The impetus to increase hemodialyzer blood flow (QB) in order to maximize solute clearances may be counterbalanced if AVF suffer adverse hemodynamic effects from accelerated pump flows. The optimal QB to maintain adequate hemodialysis without potentially contributing to AVF dysfunction is unknown. The aim of this study was to measure the hemodynamic effects of increased QB on AVF. MATERIALS AND METHODS: A prospective cohort of 14 patients with primary brachiocephalic AVF underwent venous Doppler measurements prior to cannulation (QB0) and during hemodialysis with QB of 350 mL/min at a standardized anatomical location over 3 - 16 consecutive months. Measurements included vein diameter, blood flow velocity, and volumetric flow. RESULTS: 163 paired Doppler measurements (QB0 and QB350) were made in 14 subjects. There were no significant differences in venous diameter, but significant increases in blood flow velocity and volumetric flow (p < 0.001). Mean blood flow velocity increased from 86.6 ± 35.0 cm/s at QB0 to 105.7 ± 35.0 cm/s at QB350. Mean volumetric flow increased from 849 mL/min at QB0 to 1,059 mL/min at QB350. Vein diameters increased linearly over time, with no significant changes in blood velocity or volumetric flow, suggesting AVF maturation may improve tolerance of pumped blood flow. CONCLUSION: Blood flow velocity and volumetric flow increased when hemodialyzer blood pump was applied to an AVF, creating a situation in which increased turbulence and shear stress might be plausible. Further study is needed to determine if increased QB affects clinical outcomes of AVF.
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Characterization of the cephalic arch and location of stenosis.

PURPOSE: The purpose of this study is to accurately characterize the cephalic arch segments into four domains and to enable more specific evaluation of cephalic arch stenosis (CAS) and determine the frequency of stenosis in each domain. METHODS: After Institutional Review Board (IRB) approval, a retrospective chart review was done to define a population of patients receiving hemodialysis who developed CAS as apparent on clinically indicated radiologic imaging. A standardized approach was devised to categorize four domains of the cephalic arch. Domain I was defined as the peripheral portion of the arch and Domain IV was the distal portion of the cephalic vein near termination with the axillary vein. The magnitude of stenosis as measured by percentage was determined and compared in the four domains. RESULTS: The most frequent location for stenosis was found in domain IV when compared with domains II or I (p<0.01). The magnitude of stenosis differed across all domains (p<0.001) with the least common place for CAS in domain I. Treatment of CAS included angioplasty in all, thrombectomy in eight, and stent placement in five. CONCLUSIONS: CAS occurs most commonly in the terminal portion of the arch. Four standardized domains have been defined; future work will validate these findings and determine the best intervention for each domain.