Research Papers

Hemodialysis Graft Resistance Adjustment Device

[+] Author and Article Information
Brandon J. Hopkins1

School of Engineering and Applied Sciences,  Harvard University, Cambridge, MA, 02138bhopkins@mit.edu

Huayin Wu1

School of Engineering and Applied Sciences,  Harvard University, Cambridge, MA, 02138hwu@seas.harvard.edu

William H. Marks1

School of Engineering and Applied Sciences,  Harvard University, Cambridge, MA, 02138whmarks@seas.harvard.edu

Qimin Quan1

School of Engineering and Applied Sciences,  Harvard University, Cambridge, MA, 02138quan@fas.harvard.edu

Samuel Kesner

School of Engineering and Applied Sciences,  Harvard University, Cambridge, MA, 02138skesner@seas.harvard.edu

C. Keith Ozaki

Department of Vascular and Endovascular Surgery,  Brigham and Women’s Hospital, Boston, MA, 02115cozaki1@partners.org

Conor Walsh

School of Engineering and Applied Sciences,  Harvard University, Cambridge, MA, 02138walsh@seas.harvard.edu


B. Hopkins, H. Wu, W. H. Marks, and Q. Quan contributed equally to this work.

J. Med. Devices 6(2), 021011 (May 07, 2012) (6 pages) doi:10.1115/1.4006545 History: Received November 04, 2011; Accepted February 20, 2012; Published May 07, 2012; Online May 07, 2012

Up to eight percent of patients develop steal syndrome after prosthetic dialysis access graft placement, which is characterized by low blood flow to the hand. Steal syndrome results in a cold hand, pain, and in extreme cases, loss of function and tissue damage. A practical and easy way of adjusting the fluidic resistance in a graft to attenuate the risk of steal physiology would greatly benefit both surgeons and patients. This paper describes the design and development of a device that can be attached to a dialysis access graft at the time of surgical implantation to enable providers to externally adjust the resistance of the graft postoperatively. Bench level flow experiments and magnetic setups were used to establish design requirements and test prototypes. The Graft Resistance Adjustment Mechanism (GRAM) can be applied to a standard graft before or after it is implanted and a non-contact magnetic coupling enables actuation through the skin for graft compression. The device features a winch-driven system to provide translational movement for a graft compression unit. We expect such a device to enable noninvasive management of steal syndrome in a manner that does not change the existing graft and support technologies, thus reducing patient complications and reducing costs to hospitals.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

(a) Schematic of the concept to use magnetic force to actuate a device that is implanted inside the body. (b) Schematic of the inside structure of the device.

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Figure 2

Schematic cross section of a compressed graft modeled as a cylinder with uniformly decreased radius

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Figure 3

Contour plot of the flow rate change |Δv/v| (value marked on the plot) as a function of Δr/r0 and ΔL/L0 , the normalized change in radius and compressed length, respectively, as predicted by the model

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Figure 4

(a) Compressing the graft by varying degrees using a clamp. (b) Plot of the flow rate as a function of various amounts of compression.

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Figure 5

(a) Standard weight compressing the tube used to determine the force requirement for the actuator. (b) Plot of the percentage of the resistance change (change in flow) as a function of weight applied to the graft.

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Figure 6

(a) Experimental setup used to measure the shear force between two components of a noncontact magnetic coupling. Magnets attached to two freely-rotating plates were used to lift various weights. (b) Plot of the weight lifted by the two magnets at different spacing levels.

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Figure 7

The four concepts for the drive mechanism for transmitting motion from the magnets in the wand to compression of the graft: (a) slider crank, (b) worm gear, (c) helical gear, and (d) winch designs. Components common to all designs are labeled with numbers: magnets (1), slot for graft insertion (2), plate that compresses the graft (3). The winch design (circled) was ultimately selected for its simplicity and functionality.

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Figure 8

(a) Isometric view of device as it is intended to be used. The device and graft will be implanted while the wand controls the device externally. (b) Exploded view of the device to show the various components.

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Figure 9

Section (a) and isometric (b) views of the wand

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Figure 10

Flow rate in the graft as the wand is turned



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