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TECHNICAL PAPERS: Fluids/Heat/Transport

# Turbulent Flow Evaluation of the Venous Needle During Hemodialysis

[+] Author and Article Information
Sunil Unnikrishnan, Thanh N. Huynh

Department of Biomedical Engineering, University of Alabama, Birmingham, AL

B. C. Brott

Division of Interventional Cardiology, University of Alabama, Birmingham, AL

Y. Ito, C. H. Cheng, A. M. Shih

Department of Mechanical Engineering, University of Alabama at Birmingham, Birmingham, AL

M. Allon

Division of Nephrology, University of Alabama, Birmingham, AL

Andreas S. Anayiotos1

Department of Biomedical Engineering, University of Alabama, Birmingham, AL

1

Address for correspondence: Department of Biomedical Engineering, University of Alabama at Birmingham, 1075 13th Street South, Birmingham, Alabama, 35294-4440; e-mail: aanayiot@eng.uab.edu

J Biomech Eng 127(7), 1141-1146 (Jul 26, 2005) (6 pages) doi:10.1115/1.2112927 History: Received July 20, 2004; Revised July 26, 2005

## Abstract

Arteriovenous (AV) grafts and fistulas used for hemodialysis frequently develop intimal hyperplasia (IH) at the venous anastomosis of the graft, leading to flow-limiting stenosis, and ultimately to graft failure due to thrombosis. Although the high AV access blood flow has been implicated in the pathogenesis of graft stenosis, the potential role of needle turbulence during hemodialysis is relatively unexplored. High turbulent stresses from the needle jet that reach the venous anastomosis may contribute to endothelial denudation and vessel wall injury. This may trigger the molecular and cellular cascade involving platelet activation and IH, leading to eventual graft failure. In an in-vitro graft/needle model dye injection flow visualization was used for qualitative study of flow patterns, whereas laser Doppler velocimetry was used to compare the levels of turbulence at the venous anastomosis in the presence and absence of a venous needle jet. Considerably higher turbulence was observed downstream of the venous needle, in comparison to graft flow alone without the needle. While turbulent RMS remained around $0.1m∕s$ for the graft flow alone, turbulent RMS fluctuations downstream of the needle soared to $0.4–0.7m∕s$ at 2 cm from the tip of the needle and maintained values higher than $0.1m∕s$ up to 7–8 cm downstream. Turbulent intensities were 5–6 times greater in the presence of the needle, in comparison with graft flow alone. Since hemodialysis patients are exposed to needle turbulence for four hours three times a week, the role of post-venous needle turbulence may be important in the pathogenesis of AV graft complications. A better understanding of the role of needle turbulence in the mechanisms of AV graft failure may lead to improved design of AV grafts and venous needles associated with reduced turbulence, and to pharmacological interventions that attenuate IH and graft failure resulting from turbulence.

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## Figures

Figure 1

(a) A patient’s forearm with arteriovenous access PTFE conduit with arterial and venous needles during hemodialysis. (b) Arteriovenous access PTFE graft with the arterial and venous needles.

Figure 2

AV Graft/Needle flow system and model

Figure 3

(a) Lateral view of needle tip. (b) Top view of needle tip.

Figure 4

Dye injection flow visualization in the graft model for (a) 300ml∕min needle, 800ml∕min graft, (b) 300ml∕min needle, 1200ml∕min graft, and (c) 300ml∕min needle, 1600ml∕min graft flows. Annular recirculation occurs for case (a) where the graft to needle flow ratio is low.

Figure 5

(a) Mean velocity obtained in the axial direction along the axis of the graft and needle downstream the tip of the needle. The zone between the dotted straight lines is for the mean velocities of the equivalent access AV flow without needle flow. Velocities start at about 3.5m∕s and drop to about 1m∕s, 9 cm from the tip of the needle. The equivalent mean velocities in corresponding access flows without needle are much lower (between 0.5 and 1m∕s throughout the graft). (b) RMS of turbulent velocity fluctuations obtained in the axial direction along the axis of the graft and needle downstream the tip of the needle. The zone between the dotted straight lines represents the RMS of the fluctuations for equivalent graft AV flow without needle flow. Turbulent fluctuations downstream of the needle soar to 0.4m∕s–0.7m∕s from 0.5 cm–2 cm from the tip of the needle and subsequently maintain higher values compared to equivalent graft flow without needle flow until 7 cm–8 cm downstream. The RMS values for equivalent graft flow without the needle are much lower, between 0.05m∕s and 0.1m∕s throughout the graft. The RMS values between needle flow and no needle flow become comparable 7 cm past the tip of the needle. (c) Turbulent intensities (RMS/mean velocity) of the needle disturbances obtained in the axial direction along the axis of the graft and needle downstream the tip of the needle. The zone between the dotted straight lines represents turbulent intensities for equivalent graft AV flow without needle flow. Turbulent intensities downstream of the needle peak to around 30% of the mean velocity between 1 cm–3 cm from the tip of the needle and subsequently maintain higher values compared to equivalent graft flow without needle flow until 9 cm downstream. The turbulent intensities for equivalent graft flow without the needle are much lower, between 5% and 7% of the mean velocities throughout the graft.

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