Research Papers

Validation of an Experimental Setup to Reliably Simulate Flow Through Nonvalved Glaucoma Drainage Devices

[+] Author and Article Information
Tabitha H. T. Teo

Department of Mechanical Engineering,
University of Kansas,
1530 W. 15th Street, 3138 Learned Hall,
Lawrence, KS 66045
e-mail: tabithateo55@gmail.com

Ajay Ramani

800 Tower Dr., Suite 700,
Troy, MI 48098
e-mail: logontoajay@gmail.com

Paul M. Munden

Oklahoma City VA Health Care System,
921 NE 13th Street,
Oklahoma City, OK 73104
e-mail: Paul.Munden@va.gov

Sara E. Wilson

ASME Fellow
Human Motion Control Laboratory,
Department of Mechanical Engineering,
University of Kansas,
1530 W. 15th Street, 3138 Learned Hall,
Lawrence, KS 66045
e-mail: sewilson@ku.edu

Sarah L. Kieweg

Department of Mechanical Engineering,
University of Kansas,
1530 W. 15th Street, 3138 Learned Hall,
Lawrence, KS 66045
e-mail: sarah.kieweg@gmail.com

Ronald L. Dougherty

ASME Fellow
Department of Mechanical Engineering,
University of Kansas,
1530 W. 15th Street, 3138 Learned Hall,
Lawrence, KS 66045
e-mail: doughrty@ku.edu

1Corresponding author.

Manuscript received February 12, 2018; final manuscript received June 4, 2018; published online July 3, 2018. Assoc. Editor: Xun Yu.

ASME J of Medical Diagnostics 1(4), 041001 (Jul 03, 2018) (8 pages) Paper No: JESMDT-18-1007; doi: 10.1115/1.4040498 History: Received February 12, 2018; Revised June 04, 2018

Treatment of vision-threating elevated intraocular pressure (IOP) for severe glaucoma may require implantation of a glaucoma drainage device (GDD) to shunt aqueous humor (AH) from the anterior chamber of the eye and lower IOP to acceptable levels between 8 and 21 mm Hg. Nonvalved GDDs (NVGDDs) cannot maintain IOP in that acceptable range during the early postoperative period and require intra-operative modifications for IOP control during the first 30 days after surgery. Other GDDs have valves to overcome this issue, but are less successful with maintaining long-term IOP. Our research goal is to improve NVGDD postoperative performance. Little rigorous research has been done to systematically analyze flow/pressure characteristics in NVGDDs. We describe an experimental system developed to assess the pressure drop for physiologic flow rates through NVGDD-like microtubes of various lengths/diameters, some with annular inserts. Experimental pressure measurements for flow through hollow microtubes are within predictive theory's limits. For instance, a 50.4 μm inner diameter microtube yields an average experimental pressure of 33.7 mm Hg, while theory predicts 31.0–64.2 mm Hg. An annular example, with 358.8 μm outside and 330.7 μm inside diameters, yields an experimental pressure of 9.6 mm Hg, within theoretical predictions of 4.2–19.2 mm Hg. These results are repeatable and consistent over 25 days, which fits the 20–35 day period needed for scar tissue formation to achieve long-term IOP control. This work introduces a novel method for controlling IOP and demonstrates an experiment to examine this over 25 days. Future efforts will study insert size and degradable inserts.

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Fig. 1

Configuration of proposed modification with a degradable insert placed inside of NVGDD tube: (a) photo of typical NVGDD and (b) schematic of NVGDD with insert

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Fig. 2

Theoretical pressure loss, velocity, and Reynolds number for flow through single tubes with different Do's (Q = 2.5 μl/min; properties at 25 °C)

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Fig. 3

Example of theoretical pressure drop, velocity, effective diameter, and Reynolds number as functions of varying insert outer diameter, Di, for a 24G tube having a fixed Do = 355.3 μm (Q = 2.5 μl/min, L = 8 mm; properties at 25 °C)

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Fig. 4

Schematic of microflow pressure and flow rate measurement test setup

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Fig. 5

Pressures from nominal 50 μm and 75 μm Do PEEKsil microtube trials (Q = 2.5 μl/min; 25 °C test conditions). Dashed lines are essentially constant from 3 h through the applicable 2-day or 10-day trial.

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Fig. 6

Example micro-CT images of the cross section of a nominal 75 μm Do PEEKsil microtube in the planes: (a) perpendicular to the flow direction and (b) parallel to the flow direction

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Fig. 7

Example micro-CT images of the cross section of a 24G SS hypodermic tube, with a 28G nichrome wire insert, in the planes: (a) perpendicular to the flow direction and (b) parallel to the flow direction

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Fig. 8

Experimental pressures for annular flow in 23G, 24G, and 30G SS hypodermic tubes having 26G, 28G, 30G, and 36G nichrome inserts (Q = 2.5 μl/min, L = 8 mm; 25 °C test conditions)

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Fig. 9

Comparison among long-term pressure results for 50 μm tubes without and with cleaning and sterilization protocol (Q = 2.5 μl/min, L = 25 mm; 25 °C test conditions)



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