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Research Papers

A Novel Device to Evaluate the Vibrotactile Threshold

[+] Author and Article Information
Minu Shikha Gandhi

Department of Mechanical Engineering,  University of Utah, Salt Lake City, UT, 84112minugandhi@gmail.comDepartment of Physiology,  University of Utah, Salt Lake City, UT, 84112minugandhi@gmail.comIndustrial and Systems Engineering Department,  Auburn University, Auburn, AL, 36849minugandhi@gmail.com

Christian B. Redd

Department of Mechanical Engineering,  University of Utah, Salt Lake City, UT, 84112christian.redd@gmail.comDepartment of Physiology,  University of Utah, Salt Lake City, UT, 84112christian.redd@gmail.comIndustrial and Systems Engineering Department,  Auburn University, Auburn, AL, 36849christian.redd@gmail.com

Robert P. Tuckett

Department of Mechanical Engineering,  University of Utah, Salt Lake City, UT, 84112robert.p.tuckett@hsc.utah.eduDepartment of Physiology,  University of Utah, Salt Lake City, UT, 84112robert.p.tuckett@hsc.utah.eduIndustrial and Systems Engineering Department,  Auburn University, Auburn, AL, 36849robert.p.tuckett@hsc.utah.edu

Richard F. Sesek

Department of Mechanical Engineering,  University of Utah, Salt Lake City, UT, 84112sesek@auburn.eduDepartment of Physiology,  University of Utah, Salt Lake City, UT, 84112sesek@auburn.eduIndustrial and Systems Engineering Department,  Auburn University, Auburn, AL, 36849sesek@auburn.edu

Stacy J. M. Bamberg1

Deptartment of Mechanical Engineering,  University of Utah, Salt Lake City, UT, 84112sjm.bamberg@utah.edu

1

Corresponding author.

J. Med. Devices 6(3), 031001 (Jul 30, 2012) (9 pages) doi:10.1115/1.4006901 History: Received March 30, 2011; Revised April 30, 2012; Published July 30, 2012; Online July 30, 2012

This paper presents the initial prototype design of a vibrotactile threshold evaluator for the workplace (VTEW), which is portable and configurable in terms of the probe diameter (2–10 mm), applied frequency (1–500 Hz), angle of probe (0–120 deg), and displacement of probe (1–1500 μm), and is operated with a customizable LABVIEW interface. The vibrotactile threshold is the minimum amplitude of vibration that is perceived at a particular frequency by a subject and is analogous to a hearing test. It can be used to evaluate neuropathy, for instance due to carpal tunnel syndrome or peripheral neuropathy secondary to diabetes. The vibrotactile threshold (VT) at 50 Hz was evaluated using VTEW and an established device, the Vibrotactile Tester (VTT). These results were compared for validation of VTEW. Each subject underwent Phalen’s and Tinel’s test, and the results of these clinical evaluations for carpal tunnel syndrome were used to classify subjects as symptomatic and asymptomatic. The results of the VTEW and the VTT were statistically similar and the age correction developed for both devices from this study were similar to the previously conducted studies. The mean VT values from the VTEW showed an increased VT for symptomatic subjects. The low frequency range of the VTEW was used to evaluate the VT at 4 Hz, and a comparison of VT at 4 Hz and 50 Hz showed a higher sensitivity of subjects to 50 Hz as compared to 4 Hz. The gender effect on VT was also studied and discussed, along with recommendation for further investigation. A novel and highly customizable device for testing the vibrotactile threshold is presented, with results demonstrating identification of symptomatic subjects. This device could be used to regularly test workers at risk for developing carpal tunnel syndrome (e.g. assembly line workers) to monitor for elevations in VT. Other applications include using the low frequency to evaluate peripheral neuropathy.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 3

Two interval forced choice testing protocol with vibration stimulus duration of 1 s. The dashed lines represent the two intervals and the solid lines represent the two pauses. The upper schematic shows the scenario with vibration stimulus in interval 2. The subject was presented with no vibration for the first 1 s, followed by a pause of 0.5 s, 1 s of vibration stimulus, and another 0.5 s pause, whereas the lower schematic shows the scenario for vibration stimulus in interval 1 with similar timing. In both cases, the last pause was followed by a variable response time during which the subject was instructed to choose interval 1 or 2 as their response. The next cycle began only after the subject had responded.

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Figure 4

Set up for VT testing and response. The top row of boxes represents the labels for LED lights to indicate current interval or pause in progress. The second row represents LEDs with different colors to differentiate intervals and pauses. The LEDs are activated according to the interval or pause in progress. The third row shows the response buttons in gray color. If the subject decided that the first interval contained the vibration stimulus, button 1 was pushed. If the subject decided that the second interval contained the vibration stimulus, button 2 was pushed.

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Figure 5

A demonstration of changing step size used for this study. A correct response resulted in decrease in amplitude by a step size and an incorrect response resulted in an increase in amplitude by a step size. The current amplitude of vibrations stimulus determined the step size. Step size 1 corresponded to amplitudes above 25 μm, step size 2 corresponded to amplitude in the range between 20–25 μm, and step size 3 corresponded to amplitudes less than 20 μm.

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Figure 6

Screenshot of LABVIEW interface. Top left box (‘Automation Control’) shows the reset button for starting a test from 0.5 mm amplitude. The plot data button provides an instant plot of the amplitudes tested versus the test cycles. The bottom left box (‘Additional Controls’) allows the user to change the properties of the signal and assign the output channels on the data acquisition device used. The initial amplitude can be modified in the top right box (‘Test Control’) along with frequency used in the test. During a test, the middle row of buttons in the top right box shows the current interval while the bottom row (‘Input Answer’) indicates when the program is waiting for the subject’s response. The user can update which interval will have the stimulus in the bottom right box (‘Interval Control’) by randomly assigning the vibration stimulus to Interval 1 or Interval 2. The first row indicates the interval with stimulus in the current test cycle. The second row shows the step size (‘x’), used for adjusting the amplitude and the bottom row provides information about the total number of test cycles at the current amplitude as well as the overall number of cycles performed for the entire test. The user can also select appropriate path for saving test results using the bottom row of this box.

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Figure 7

Position sensor for measurement of probe position with of active region shaded and denoted by L. Two anodes output voltages V1 and V2 . The distance to the light source (indicated by the white dot) is x, and is measured from the midpoint of the position sensor.

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Figure 8

Boxplot of VT distribution data obtained from VTT and VTEW at 50 Hz. The boxplot shows observations that are unusually high or low as outliers (indicated by *). The top and bottom whiskers (vertical lines above and below the boxes) extend to the highest and lowest data points. The lower and upper lines of the box represent the first and third quartile of the data points. The middle line shows the median of the distribution. The p-value was 0.15 (α = 0.05, 95% CI). Sample size was n = 56.

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Figure 9

VT as a function of age for all subjects evaluated by VTT and VTEW at 50 Hz. The trend lines are shown for VT obtained by both devices. For VTT, the age regression slope was 0.12 and Y-intercept was 3.38. For VTEW, the age regression slope was 0.12 and the Y-intercept was 2.22. The sample size was n = 56.

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Figure 10

Boxplot of VT distribution data obtained at 4 Hz and 50 Hz using VTEW. The top and bottom whiskers (vertical lines above and below the boxes) extend to the highest and lowest data points. The lower and upper lines of the box represent the first and third quartile of the data points. Unusually high observations are marked as outliers by *. No overlap was observed between the data obtained at 4 Hz and 50 Hz showing statistically significant difference. The p-value was 0.00 (α = 0.05, 95% CI). Sample size was n = 56.

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Figure 11

VT mean value trends for symptomatic and asymptomatic subjects, (a) at 4 Hz and (b) at 50 Hz on the VTEW. The main effect plot shows that presence or absence of symptoms affects the mean VT obtained at both 4 Hz and 50 Hz. The symptomatic subjects show elevated mean VT as compared to the asymptomatic subjects at both frequencies. The horizontal line shows the mean VT (41.37 μm at 4 Hz and 6. 94 μm at 50 Hz) for total population as a reference. Mean VT of symptomatic subjects lie above the mean VT of entire subject population. The sample size for asymptomatic (n = 37) and symptomatic (n = 19) subjects is same at both frequencies.

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Figure 12

VT mean value trends for all subjects (n = 56) using (a) VTT at 50 Hz, (b) VTEW at 50 Hz, and (c) VTEW at 4 Hz. Main effects plot shows that gender affects the VT. Females tend to have higher mean VT as compared to males at both 4 Hz and 50 Hz using VTEW. The horizontal line shows the mean VT for total population as a reference. The sample size for asymptomatic females (n = 14) and males (n = 23), symptomatic females (n = 11) and males (n = 8) was same at both frequencies and for both devices.

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Figure 1

The VTEW implementation. (a) CAD model of VTEW demonstrating the pivoting mechanism by an arrow. The range of motion achieved by this pivoting was 120 deg. (b) VTEW prototype with angle measurement and adjustment string for supporting and pivoting voice coil assembly.

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Figure 2

CAD model of voice coil housed in the carriage supported by a shaft at either end. (a) Assembled view of all components and (b) exploded view of all components. A probe connector was secured at the top of the voice coil. The probe was attached to the probe connector and suspended on the translating voice coil by a flexure. The top cover acted as the surround encircling the probe and housed the position sensor.

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