Contact area affects frequency-dependent responses to vibration in the peripheral vascular and sensorineural systems

Abstract

Repetitive exposure to hand-transmitted vibration is associated with development of peripheral vascular and sensorineural dysfunctions. These disorders and symptoms associated with it are referred to as hand-arm vibration syndrome (HAVS). Although the symptoms of the disorder have been well characterized, the etiology and contribution of various exposure factors to development of the dysfunctions are not well understood. Previous studies performed using a rat-tail model of vibration demonstrated that vascular and peripheral nervous system adverse effects of vibration are frequency-dependent, with vibration frequencies at or near the resonant frequency producing the most severe injury. However, in these investigations, the amplitude of the exposed tissue was greater than amplitude typically noted in human fingers. To determine how contact with vibrating source and amplitude of the biodynamic response of the tissue affects the risk of injury occurring, this study compared the influence of frequency using different levels of restraint to assess how maintaining contact of the tail with vibrating source affects the transmission of vibration. Data demonstrated that for the most part, increasing the contact of the tail with the platform by restraining it with additional straps resulted in an enhancement in transmission of vibration signal and elevation in factors associated with vascular and peripheral nerve injury. In addition, there were also frequency-dependent effects, with exposure at 250 Hz generating greater effects than vibration at 62.5 Hz. These observations are consistent with studies in humans demonstrating that greater contact and exposure to frequencies near the resonant frequency pose the highest risk for generating peripheral vascular and sensorineural dysfunction.

A Review of Hand–Arm Vibration Studies Conducted by US NIOSH since 2000

“…Exposure to vibration also resulted in a significant increase in concentrations of the anti-oxidant enzyme, SOD2 in the DRG, but only with exposure to vibration at 250 Hz and using 7 straps for restraint. These findings are consistent with the hypothesis that increasing the coupling between the tissue and the vibrating source will exacerbate the effects of the vibration exposure, and that in most cases, the effects are more prominent when the exposure is at the resonant frequency [ 217 ].…”

“…The effects of increased coupling on sensorineural function were also assessed by comparing the effects of tail restraint with 4 vs. 7 straps as described above [ 217 ]. The effects of vibration on sensory physiology were not measured in this study.…”

“…Exposure to vibration at 250 Hz resulted in a significant increase in transcript levels for GTP-cyclohydrolase-1, a gene that has been associated with an increased risk for developing chronic pain, and hypoxia-induced factor-1a, regardless of the number of straps used or restraint. However, the increase in the transcription of these genes was greater when the tail was restrained with 7 than with 4 straps [ 217 ]. Myelin-associated glycoprotein ( mag) , a marker of myelin regeneration, was only increased in tail nerves with exposure to vibration at 62.5 Hz and only when 4 straps were used for restraint.…”

“…Exposure to vibration at 250 Hz resulted in an increased expression of the neurotrophic tyrosine kinase receptor and a reduction in the transient-vanilloid receptor protein-1 ( trpv-1 ), an ion channel that is located in nervous system cells that transmit information about peripheral and visceral pain, itch and temperature to the nervous system [ 219 , 220 ]. Restraining the tail with 7 straps significantly increased the expression of these genes in the DRG as compared to restraint with 4 straps in animals exposed to vibration at 250 Hz [ 217 ]. Exposure to vibration also resulted in a significant increase in concentrations of the anti-oxidant enzyme, SOD2 in the DRG, but only with exposure to vibration at 250 Hz and using 7 straps for restraint.…”

“…Tests of touch or applied pressure have also been used to detect changes in sensorineural function after exposure to occupational HTV in humans diagnosed with HAVS [ 280 , 281 ] and in animals exposed to vibration [ 201 , 217 , 238 , 310 ]. In humans, sensitivity to tactile stimulation or applied pressure is usually measured with von Frey or Semmes Weinstein monofilaments [ 223 , 280 , 281 ].…”