Comparison of continuous and intermittent vibration effects on rat‐tail artery and nerve

Abstract

Hand-transmitted vibration from powered-tools can cause peripheral vasospasm and neuropathy. A rat-tail model was used to investigate whether the pattern of vibration influenced the type and severity of tissue damage. The tails of awake rats were vibrated continuously or intermittently for a total of 4 hours at 60 HZ, 49 m/s(2). Nerves and arteries were harvested immediately or 24 hours after treatment. Tails subjected to intermittent vibration showed transiently increased sensitivity to thermal stimuli. Intermittent vibration caused the most nerve injury immediately and 24 hours after vibration. Continuous vibration invoked a persistent reduction in vascular lumen size. Compared to epinephrine-induced transient vacuolation in vascular smooth muscle cells, both continuous and intermittent vibration caused greater persistence of vacuoles, indicating a vibration-induced pathological process. All vibration groups exhibited elevated nitrotyrosine immunoreactivity indicative of free-radical damage. Pattern of vibration exposure may exert a major influence on the type of vibration injury.

Vibration Causes Acute Vascular Injury in a Two‐Step Process: Vasoconstriction and Vacuole Disruption

“…We have previously reported that nearly half the number of SMC vacuoles induced by 4-hr vibration persist 24 hr later (Govindaraju et al, 2006a). Repeated mechanical displacement in vibrated arteries may shear connections of vacuoles and dislodge them from the parent cell.…”

“…Structurally similar vacuoles have been observed in SMC of arteries induced to undergo intense vasoconstriction by topical norepinephrine (NE) or epinephrine (Joris and Majno, 1977;Curry et al, 2005b;Govindaraju et al, 2006a). Joris et al, in an elegant series of electron microscopic studies, called the vacuoles herniations because the majority were continuous with the parent cell by slender necks (Joris and Majno, 1977).…”

Nerve damage occurs at a wide range of vibration frequencies

“…Rats in the vibration apparatus were observed for signs of discomfort like porphyrin (reddish-black secretions from the eye), excessive vocalization, grinding of teeth and loose stools as described earlier (Govindaraju et al, 2006a).…”

Vibration Disrupts Vascular Function in a Model of Metabolic Syndrome

“…However, vibration also consistently induces an increase in oxidative stress and reduction in endothelial-mediated vasodilation 14,16,37) , and these effects were more pronounced in obese than in lean rats. Because obese rats display many of the symptoms seen in humans with metabolic syndrome 11) , we believe that these results suggest that pre-existing vascular dysfunction caused by metabolic syndrome may make workers more susceptible to vibration-induced vascular injury, and put them at greater risk of developing VWF.…”