Long-term daily vibration exposure alters current perception threshold (CPT) sensitivity and myelinated axons in a rat-tail model of vibration-induced injury

Applied Force Alters Sensorineural and Peripheral Vascular Function in a Rat Model of Hand-Arm Vibration Syndrome

OBJECTIVE

This study described the effects of applied force (grip) on vascular and sensorineural function in an animal model of hand-arm vibration syndrome (HAVS).

METHODS

Rat tails were exposed to 0, 2, or 4 N of applied force 4 hr/d for 10 days. Blood flow and sensitivity to transcutaneous electrical stimulation and pressure were measured.

RESULTS

Applied force increased blood flow but reduced measures of arterial plasticity. Animals exposed to force tended to be more sensitive to 250-Hz electrical stimulation and pressure applied to the tail.

CONCLUSIONS

Effects of applied force on blood flow and sensation are different than those of vibration. Studies examining co-exposures to force and vibration will provide data that can be used to determine how these factors affect risk of workers developing vascular and sensorineural dysfunction (ie, HAVS).

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

Studies on hand-transmitted vibration exposure, biodynamic responses, and biological effects were conducted by researchers at the Health Effects Laboratory Division (HELD) of the National Institute for Occupational Safety and Health (NIOSH) during the last 20 years. These studies are systematically reviewed in this report, along with the identification of areas where additional research is needed. The majority of the studies cover the following aspects: (i) the methods and techniques for measuring hand-transmitted vibration exposure; (ii) vibration biodynamics of the hand-arm system and the quantification of vibration exposure; (iii) biological effects of hand-transmitted vibration exposure; (iv) measurements of vibration-induced health effects; (iv) quantification of influencing biomechanical effects; and (v) intervention methods and technologies for controlling hand-transmitted vibration exposure. The major findings of the studies are summarized and discussed.

Vibration Exposure Safety Guidelines for Surgeons Using Power-Assisted Liposuction (PAL)

BACKGROUND

As power-assisted liposuction (PAL) gains in popularity, plastic surgeons operating these devices experience occupational exposure to hand-transmitted vibration, which can result in hand-arm vibration syndrome, a debilitating neurovasculopathy.

OBJECTIVES

The objective of the study was to determine vibration exposure from the utilization of a PAL device during surgery to generate recommendations for safe use.

METHODS

Vibration emission of a commonly utilized PAL system (MicroAire-650, Surgical Instruments, Charlottesville, VA) was examined employing a vibration data logger under both controlled laboratory conditions and during 13 typical liposuction cases. Data were analyzed and compared with established safety limits of vibration exposure.

RESULTS

The experiments demonstrated a mean vibration magnitude of typical liposuction surgeries to be 5.69 ± 0.77 m/s2 (range, 4.59-6.27 m/s2), which is significantly higher than the manufacturer declared value of 3.77 m/s2. Cannula size was shown to be the most significant contributor to vibration magnitude, with larger cannulas causing more vibration transmission.

CONCLUSIONS

These results indicate that recommendations must be made to prevent undue occupational exposure to vibration from PAL. The MicroAire-650 can generally be safely utilized for less than 1.5 h/d. At exposure levels >1.5 h/d, there is increased risk of developing vibration-related injuries, and vibration-reducing strategies should be implemented. At exposure levels >6 h/d, the safety limit is exceeded and there is significantly increased risk of developing hand-arm vibration syndrome and vibration exposure should be halted.

LEVEL OF EVIDENCE: 4

Vibrotactile sensitivity testing for occupational and disease-induce peripheral neuropathies

The International Standard Organization (ISO) standard 13091-1 describes methods and procedures for performing the vibrotactile perception threshold (VPT) testing to diagnose changes in tactile sensory function associated with occupational exposures. However, the VPT test also has been used in the diagnosis of peripheral neuropathies associated with a number of disorders. This review examines the VPT test, variations in procedures that have been used, as well as disorders and diseases in which this test has been reliable for the detection of sensory changes. Mechanisms potentially underlying the changes in VPTs are also discussed along with procedural and subject/patient factors that may affect the interpretation of test results. Based upon the review of the literature, there are also suggestions for where additional research might improve the administration of this test, depending upon the subject/patient population and interpretation of data.

Vibration Suppression of a Composite Prosthetic Foot Using Piezoelectric Shunt Damping: Implications to Vibration-Induced Cumulative Trauma

OBJECTIVE

Energy-storage-and-return (ESAR) prosthetic feet have improved amputee mobility due to their efficient conversion of strain energy to mechanical work. However, this efficiency is typically achieved using light-weight, high-stiffness materials, which generate high-frequency vibrations that are potentially injurious if transmitted to biological tissues. To reduce the vibration which may cause cumulative tissue trauma, high-frequency vibration suppression by piezoelectric shunt damping patches on a commercial ESAR foot was evaluated.

METHODS

Two patches with either passive or active shunt circuits were placed on the foot to investigate vibration suppression during experimental tests where a plastic hammer was used to hit a clamped ESAR foot on the free end. Prosthesis bending moments at each modal frequency were obtained by finite element methods to identify piezoelectric patch placement.

RESULTS

Both shunt circuits decreased vibration amplitudes at specific modes better than the no shunt case, but also increased the amplitude at specific frequencies. The vibration suppression performance of the active shunt circuit deteriorated at the second mode, while the vibration suppression performance of the passive shunt circuit deteriorated at all frequencies above the third mode.

CONCLUSIONS

These results indicate piezoelectric shunt patches may be a viable strategy for decreasing vibrations of an ESAR foot, with active methods more efficient at suppressing high-frequency vibrations. Additional research is necessary to fine-tune the method for maximal vibration suppression.

SIGNIFICANCE

Overall, this study indicates that high-frequency vibration suppression is possible using piezoelectric patches, possibly decreasing the cumulative tissue damage that may occur with repetitive exposure to vibration.

Riveting hammer vibration damages mechanosensory nerve endings

Hand-arm vibration syndrome (HAVS) is an irreversible neurodegenerative, vasospastic, and musculoskeletal occupational disease of workers who use powered hand tools. The etiology is poorly understood. Neurological symptoms include numbness, tingling, and pain. This study examines impact hammer vibration-induced injury and recoverability of hair mechanosensory innervation. Rat tails were vibrated 12 min/d for 5 weeks followed by 5 week recovery with synchronous non-vibrated controls. Nerve fibers were PGP9.5 immunostained. Lanceolate complex innervation was compared quantitatively in vibrated vs sham. Vibration peak acceleration magnitudes were characterized by frequency power spectral analysis. Average magnitude (2515 m/s² , root mean squared) in kHz frequencies was 109 times that (23 m/s² ) in low Hz. Percentage of hairs innervated by lanceolate complexes was 69.1% in 5-week sham and 53.4% in 5-week vibration generating a denervation difference of 15.7% higher in vibration. Hair innervation was 76.9% in 5-weeks recovery sham and 62.0% in 5-week recovery vibration producing a denervation difference 14.9% higher in recovery vibration. Lanceolate number per complex (18.4 ± 0.2) after vibration remained near sham (19.3 ± 0.3), but 44.9% of lanceolate complexes were abnormal in 5 weeks vibrated compared to 18.8% in sham. The largest vibration energies are peak kHz accelerations (approximately 100 000 m/s² ) from shock waves. The existing ISO 5349-1 standard excludes kHz vibrations, seriously underestimating vibration injury risk. The present study validates the rat tail, impact hammer vibration as a model for investigating irreversible nerve damage. Persistence of higher denervation difference after 5-week recovery suggests repeated vibration injury destroys the capability of lanceolate nerve endings to regenerate.

Frequency-dependent changes in mitochondrial number and generation of reactive oxygen species in a rat model of vibration-induced injury

Regular use of vibrating hand tools results in cold-induced vasoconstriction, finger blanching, and a reduction in tactile sensitivity and manual dexterity. Depending upon the length and frequency, vibration induces regeneration, or dysfunction and apoptosis, inflammation and an increase in reactive oxygen species (ROS) levels. These changes may be associated with mitochondria, this study examined the effects of vibration on total and functional mitochondria number. Male rats were exposed to restraint or tail vibration at 62.5, 125, or 250 Hz. The frequency-dependent effects of vibration on mitochondrial number and generation of oxidative stress were examined. After 10 days of exposure at 125 Hz, ventral tail arteries (VTA) were constricted and there was an increase in mitochondrial number and intensity of ROS staining. In the skin, the influence of vibration on arterioles displayed a similar but insignificant response in VTA. There was also a reduction in the number of small nerves with exposure to vibration at 250 Hz, and a reduction in mitochondrial number in nerves in restrained and all vibrated conditions. There was a significant rise in the size of the sensory receptors with vibration at 125 Hz, and an elevation in ROS levels. Based upon these results, mitochondria number and activity are affected by vibration, especially at frequencies at or near resonance. The influence of vibration on the vascular system may either be adaptive or maladaptive. However, the effects on cutaneous nerves might be a precursor to loss of innervation and sensory function noted in workers exposed to vibration.

Quantitative Evaluation of the Function of the Sensory Nerve Fibers of the Palate in Patients With Obstructive Sleep Apnea

STUDY OBJECTIVES

To quantitatively evaluate the functional integrity of sensory nerve fibers of the palate in patients with obstructive sleep apnea (OSA) using the Neurometer system.

METHODS

A total of 32 patients with OSA and 18 healthy control patients were included in the study. All participants were selected based on medical history, physical examination, and nocturnal polysomnography (PSG) and divided into two groups. The palatal sensory status of participants was examined with a Neurometer current perception threshold (CPT) system. The system was used to deliver an electrical stimulus at three different frequencies (2,000 Hz, 250 Hz, and 5 Hz) by an investigator blinded to the PSG results.

RESULTS

There were no significant differences in the CPT values of the hard palate between the patients with OSA and control patients at any of the three stimulation frequencies. The differences in the CPT values of the soft palate between these groups failed to show any statistical significance at 250 Hz and 5 Hz. However, the patients with OSA showed significantly higher CPT values of the soft palate at 2,000 Hz than the age-matched healthy control patients (256.56 ± 129.34 versus 372.13 ± 152.06; P = .009).

CONCLUSIONS

Our study revealed an impairment of 2,000 Hz-related sensory nerve function of the soft palate among patients with OSA. The CPT test could be a useful tool for the quantitative and selective assessment of the sensory nerve function in patients with OSA. Additional research is required to evaluate the different types of sensory nerve dysfunctions among such patients.

CLINICAL TRIAL REGISTRATION

Registry: ClinicalTrials.gov; Title: The Effects of Nasal Airflow on Upper Airway Dilator Muscles During Sleep; Identifier: NCT03506178; URL: https://clinicaltrials.gov/ct2/show/NCT03506178.

CITATION

An Y, Li Y, Chang W, Gao F, Ding X, Xu W, Han D. Quantitative evaluation of the function of the sensory nerve fibers of the palate in patients with obstructive sleep apnea. J Clin Sleep Med. 2019;15(9):1347-1353.

Acute Vibration Induces Peripheral Nerve Sensitization in a Rat Tail Model: Possible Role of Oxidative Stress and Inflammation

Prolonged occupational exposure to hand-held vibrating tools leads to pain and reductions in tactile sensitivity, grip strength and manual dexterity. The goal of the current study was to use a rat-tail vibration model to determine how vibration frequency influences factors related to nerve injury and dysfunction. Rats were exposed to restraint, or restraint plus tail vibration at 62.5 Hz or 250 Hz. Nerve function was assessed using the current perception threshold (CPT) test. Exposure to vibration at 62.5 and 250 Hz, resulted in a reduction in the CPT at 2000 and 250-Hz electrical stimulation (i.e. increased Aβ and Aδ, nerve fiber sensitivity). Vibration exposure at 250 Hz also resulted in an increased sensitivity of C-fibers to electrical stimulation and thermal nociception. These changes in nerve fiber sensitivity were associated with increased expression of interleukin (IL)-1β and tumor necrosis factor (TNF)-α in ventral tail nerves, and increases in circulating concentrations of IL-1 β in rats exposed to 250-Hz vibration. There was an increase in glutathione, but no changes in other measures of oxidative activity in the peripheral nerve. However, measures of oxidative stress were increased in the dorsal root ganglia (DRG). These changes in pro-inflammatory factors and markers of oxidative stress in the peripheral nerve and DRG were associated with inflammation, and reductions in myelin basic protein and post-synaptic density protein (PSD)-95 gene expression, suggesting that vibration-induced changes in sensory function may be the result of changes at the exposed nerve, the DRG and/or the spinal cord.

Systemic Effects of Segmental Vibration in an Animal Model of Hand-Arm Vibration Syndrome

OBJECTIVE

Epidemiology suggests that occupational exposure to hand-transmitted (segmental) vibration has local and systemic effects. This study used an animal model of segmental vibration to characterize the systemic effects of vibration.

METHODS

Male Sprague Dawley rats were exposed to tail vibration for 10 days. Genes indicative of inflammation, oxidative stress, and cell cycle, along were measured in the heart, kidney, prostate, and liver.

RESULTS

Vibration increased oxidative stress and pro-inflammatory gene expression, and decreased anti-oxidant enzymes in heart tissue. In the prostate and liver, vibration resulted in changes in the expression of pro-inflammatory factors and genes involved in cell cycle regulation.

CONCLUSIONS

These changes are consistent with epidemiological studies suggesting that segmental vibration has systemic effects. These effects may be mediated by changes in autonomic nervous system function, and/or inflammation and oxidative stress.

Health effects associated with occupational exposure to hand-arm or whole body vibration

Workers in a number of different occupational sectors are exposed to workplace vibration on a daily basis. This exposure may arise through the use of powered-hand tools or hand-transmitted vibration (HTV). Workers might also be exposed to whole body vibration (WBV) by driving delivery vehicles, earth moving equipment, or through use of tools that generate vibration at low dominant frequencies and high amplitudes, such as jackhammers. Occupational exposure to vibration has been associated with an increased risk of musculoskeletal pain in the back, neck, hands, shoulders, and hips. Occupational exposure may also contribute to the development of peripheral and cardiovascular disorders and gastrointestinal problems. In addition, there are more recent data suggesting that occupational exposure to vibration may enhance the risk of developing certain cancers. The aim of this review is to provide an assessment of the occupations where exposure to vibration is most prevalent, and a description of the adverse health effects associated with occupational exposure to vibration. This review will examine (1) various experimental methods used to measure and describe the characteristics of vibration generated by various tools and vehicles, (2) the etiology of vibration-induced disorders, and (3) how these data were employed to assess and improve intervention strategies and equipment that reduces the transmission of vibration to the body. Finally, there is a discussion of the research gaps that need to be investigated to further reduction in the incidence of vibration-induced illnesses and injuries.

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

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.