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2008 Annual Meeting Abstracts

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Vibration-Induced Nerve Injury and Recovery in a Rat Tail Model
Michael A. Loffredo, MD, Dennis Kao, MD, Ji-Geng Yan, MD, PhD, Danny A. Riley, PhD, Lin-Ling Zhang, MD, Hani S. Matloub, MD.
Medical College of Wisconsin, Milwaukee, WI, USA.

Purpose
Hand-Arm Vibration Syndrome (HAVS), a condition consisting of neurological and vascular dysfunction, is caused by exposure to vibration tools. The present study investigates the effect of vibration exposure duration on the disruption of nerve conduction velocity, and the ability for recovery of nerve function in a rat tail model.
Methods
Forty eight male Sprague-Dawley rats were randomly assigned to one of six groups, with four of eight rats in each group serving as a non-vibrated control. The controls had their tails taped to a non-vibrating platform. The vibrated tails were exposed to linear vertical oscillations of 60 Hz and 5 g (49 m/s2) acceleration. The duration of vibration was constant at 4 hours/day, and the total exposure was either 7 or 14 days. Group A was exposed to 14 days of vibration followed by 60 days of recovery. Group B was exposed to 7 days of vibration followed by 60 days of recovery. Group C was exposed to 14 days of vibration followed by 30 days of recovery. Group D was exposed to 7 days of vibration followed by 30 days of recovery. Group E was exposed to 7 days of vibration followed by 0 days of recovery, and group F was exposed to 14 days of vibration followed by 0 days of recovery. Nerve conduction velocity (NCV) was then performed in the ventral lateral nerve trunk of the tail on the final day of recovery.
Results
We combined all 24 control rats into one group (total control), and the mean NCV of this group was 3.95 cm/ms +/- 0.21. The mean NCV of the vibrated rats were as follows: Group A = 2.99 +/- 0.47 cm/ms, Group B = 4.25 +/- 0.29 cm/ms, Group C = 2.82 +/- 0.40 cm/ms, Group D = 3.35 +/- 0.34 cm/ms, Group E = 2.62 +/- 0.46 cm/ms, and Group F = 2.47 +/- 0.43 cm/ms. When compared to the total control group, Groups A, C, D, E, and F all demonstrated a statistically significant difference with groups A,C,E, and F having a P value < 0.001 and Group D having a P value < 0.05. Group B was not statistically different.
Conclusions
The rat tail model is a valuable tool in studying vibration injury in HAVS because the tail has structural similarities to the human hand and digits. The present study demonstrates the effect on NCV after prolonged vibration and the ability of the rat tail nerve to recover from 7 day exposure but not 14 day exposure. Vibration for 14 days causes a decrease in NCV that does not return to normal after a recovery period of 60 days. Vibration for 7 days also causes a significant decrease in NCV, but the injury, although still significant, shows some recovery 30 days post vibration (Group D) and complete recovery 60 days following vibration. Our findings suggest that 14 day vibration may produce irreversible nerve damage or require more than 60 days recovery. Thus, recovery is a slower process than injury.


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