Evidence for frequency-dependent arterial damage in vibrated rat tails

Exposure to emissions generated by 3-dimensional printing with polycarbonate: effects on peripheral vascular function, cardiac vascular morphology and expression of markers of oxidative stress in male rat cardiac tissue

Three-dimensional (3D) printing with polycarbonate (PC) plastic occurs in manufacturing settings, homes, and schools. Emissions generated during printing with PC stock and bisphenol-A (BPA), an endocrine disrupter in PC, may induce adverse health effects. Inhalation of 3D printer emissions, and changes in endocrine function may lead to cardiovascular dysfunction. The goal of this study was to determine whether there were any changes in markers of peripheral or cardiovascular dysfunction in animals exposed to PC-emissions. Male Sprague Dawley rats were exposed to PC-emissions generated by 3D printing for 1, 4, 8, 15 or 30 d. Exposure induced a reduction in the expression of the antioxidant catalase (Cat) and endothelial nitric oxide synthase (eNos). Endothelin and hypoxia-induced factor 1α transcripts increased after 30 d. Alterations in transcription were associated with elevations in immunostaining for estrogen and androgen receptors, nitrotyrosine, and vascular endothelial growth factor in cardiac arteries of PC-emission exposed animals. There was also a reduction eNOS immunostaining in cardiac arteries from rats exposed to PC-emissions. Histological analyses of heart sections revealed that exposure to PC-emissions resulted in vasoconstriction of cardiac arteries and thickening of the vascular smooth muscle wall, suggesting there was a prolonged vasoconstriction. These findings are consistent with studies showing that inhalation 3D-printer emissions affect cardiovascular function. Although BPA levels in animals were relatively low, exposure-induced changes in immunostaining for estrogen and androgen receptors in cardiac arteries suggest that changes in the action of steroid hormones may have contributed to the alterations in morphology and markers of cardiac function.

The effects of local calf vibration on balance, blood flow, and nerve conductivity in patients with diabetic peripheral neuropathy: a pilot study

OBJECTIVES

This study aimed to evaluate the effects of local calf vibration on balance, blood flow, and nerve conductivity in patients with diabetic peripheral neuropathy (DPN).

METHODS

An open-label controlled trial was designed. Patients with confirmed diagnoses of type 2 diabetes and DPN were enrolled in the study and underwent ten sessions of local calf vibration therapy for the dominant leg. The other leg was considered the control. Balance evaluation, nerve conduction studies, and color Doppler ultrasound were performed before and after the treatment course. The Wilcoxon signed rank test and the Mann-Whitney test were used to evaluate the differences between the test results before and after the intervention and between the intervention and control legs.

RESULTS

Seventeen patients with a mean age of 60.3 ± 5.6 years (11 males) participated in the study. Mean Brief BESTest total scores were significantly improved (14.06 vs. 17.35; P = .01, Cohen's d = 0.743). There were no significant differences between the treated and control legs regarding the nerve conduction and color Doppler ultrasound parameters before and after the intervention (P ≥ .054). Changes in the parameters were also not significantly different between legs (P ≥ .078), except for common peroneal nerve conduction velocity, for which there was a higher increase in its value in the treated legs compared to the control legs (4.17 vs. 0.9, P = .002).

CONCLUSION

Local calf vibration may positively affect balance and lower extremities nerve conduction in patients with DPN, and the findings of this study can be a basis for studies evaluating the efficacy of local calf vibration for treating DPN.

Locked-in syndrome following elective cervical foraminotomy: a case report

INTRODUCTION

There are no previously reported cases of locked-in syndrome occurring following cervical spinal surgery. We describe a case of locked-in syndrome following an elective cervical foraminotomy and discuss potential etiologies and contributing factors to our patient's presentation.

CASE PRESENTATION

A 54-year-old male with a history of head and neck cancer and prior anterior cervical discectomy and fusion presented with neck pain following a motor vehicle accident. The patient underwent C4-C7 left-sided cervical posterior foraminotomy with no intraoperative complications. On postoperative day 1, the patient suddenly developed rapidly progressing weakness of the extremities and soon became non-verbal. CT angiography and near-infrared spectroscopy confirmed a basilar artery occlusion and left vertebral artery dissection. On MRI, infarcts involving the bilateral pons, left cerebral hemisphere, and left cerebellar infarct were identified.

CONCLUSION

The etiology of locked-in syndrome in our patient remains unclear, but it is likely multifactorial. It is possible that the patient was predisposed to vascular injury from prior radiation therapy to the head and neck. In addition, intraoperative vascular insult may have occurred from vibrational shear stress, in turn leading to a vertebral artery dissection, basilar artery occlusion, and pontine infarct, ultimately resulting in our patient's locked-in state.

Serum biomarkers in patients with hand-arm vibration injury and in controls

Hand-arm vibration injury is a well-known occupational disorder that affects many workers globally. The diagnosis is based mainly on quantitative psychophysical tests and medical history. Typical manifestations of hand-arm vibration injury entail episodes of finger blanching, Raynaud's phenomenon (RP) and sensorineural symptoms from affected nerve fibres and mechanoreceptors in the skin. Differences in serum levels of 17 different biomarkers between 92 patients with hand-arm vibration injury and 51 controls were analysed. Patients with hand-arm vibration injury entailing RP and sensorineural manifestations showed elevated levels of biomarkers associated with endothelial injury or dysfunction, inflammation, vaso- or neuroprotective compensatory, or apoptotic mechanisms: intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1 (MCP-1); thrombomodulin (TM), heat shock protein 27 (HSP27); von Willebrand factor, calcitonin gene-related peptide (CGRP) and caspase-3. This study adds important knowledge on pathophysiological mechanisms that can contribute to the implementation of a more objective method for diagnosis of hand-arm vibration injury.

Quantification of mechanical behavior of rat tail under compression

BACKGORUND

The development of vibration-induced finger disorders is likely associated with combined static and dynamic responses of the fingers to vibration exposure. To study the mechanism of the disorders, a new rat-tail model has been established to mimic the finger vibration and pressure exposures. However, the mechanical behavior of the tail during compression needs to be better understood to improve the model and its applications.

OBJECTIVE

To investigate the static and time-dependent force responses of the rat tail during compression.

METHODS

Compression tests were conducted on Sprague-Dawley cadaver rat tails using a micromechanical system at three deformation velocities and three deformation magnitudes. Contact-width and the time-histories of force and deformation were measured. Additionally, force-relaxation tests were conducted and a Prony series was used to model the force-relaxation behavior of the tail.

RESULTS

The rat tails' force-deformation and stiffness-deformation relationships were strongly nonlinear and time-dependent. Force/stiffness increased with an increase in deformation and deformation velocity. The time-dependent force-relaxation characteristics of the tails can be well described using a Prony series.

CONCULSIONS

We successfully quantified the static and time-dependent force responses of rat tails under compression. The identified mechanical behavior of the tail can help improve the rat-tail model and its applications.

Near-wall hemodynamic parameters of finger arteries altered by hand-transmitted vibration

BACKGROUND

Sustained exposure to high-level hand-transmitted vibrations may result in angioneurotic disorders, which partly originate from vibration-altered hemodynamics in the finger arteries when repeating these disturbances throughout working life. Hence, the aim of this study is to assess the most relevant hemodynamic descriptors in the digital arteries, determine the relationship between the latter and vibration features, and gain better understanding of the physiological mechanisms involved.

METHODS

An experimental setup, mainly comprised of an ultra-high frequency ultrasound scanner and a vibration shaker, was used to image the digital proper volar arteries of the forefinger. Raw ultrasound data were post-processed by custom-made numerical routines to supply a pulsatile fluid mechanics model for computing the hemodynamic descriptors. Twenty-four healthy volunteers participated in the measurement campaign. Classical statistical methods were then applied to the dataset and also the wavelet transform for calculating the signal power in the frequency bands matching cardiac, respiratory, myogenic and neurogenic activities.

RESULTS

The artery diameter, the wall shear stress - WSS - and the WSS temporal gradient - WSSTG - were found to be the most relevant descriptors. Vibration-induced WSS was divided by three compared to its basal value whatever the vibration frequency and it was proportional to log2 of the acceleration level. Marked increases in WSSTG when stopping vibration might also lead to adverse health effects. Vibration caused a drop in WSS power for the frequency band associated with the neurogenic activity of the sympathetic nervous system.

CONCLUSION

This study may pave the way for a new framework to prevent vibration-induced vascular risk.

A novel rat-tail model for studying human finger vibration health effects

It has been hypothesized that the biodynamic responses of the human finger tissues to vibration are among the major stimuli that cause vibration health effects. Furthermore, the finger contact pressure can alter these effects. It is difficult to test these hypotheses using human subjects or existing animal models. The objective of this study was to develop a new rat-tail vibration model to investigate the combined effects of vibration and contact pressure and to identify their relationships with the biodynamic responses. Physically, the new exposure system was developed by adding a loading device to an existing rat-tail model. An analytical model of the rat-tail exposure system was proposed and used to formulate the methods for quantifying the biodynamic responses. A series of tests with six tails dissected from rat cadavers were conducted to test and evaluate the new model. The experimental and modeling results demonstrate that the new model behaves as predicted. Unlike the previous model, the vibration strain and stress of the rat tail does not depend primarily on the vibration response of the tail itself but on that of the loading device. This makes it possible to quantify and control the biodynamic responses conveniently and reliably by measuring the loading device response. This study also identified the basic characteristics of the tail biodynamic responses in the exposure system, which can be used to help design the experiments for studying vibration biological effects.

A Multiscale Approach for Predicting Certain Effects of Hand-Transmitted Vibration on Finger Arteries

Prolonged exposure to strong hand-arm vibrations can lead to vascular disorders such as Vibration White Finger (VWF). We modeled the onset of this peripheral vascular disease in two steps. The first consists in assessing the reduction in shearing forces exerted by the blood on the walls of the arteries (Wall Shear Stress—WSS) during exposure to vibrations. An acute but repeated reduction in WSS can lead to arterial stenosis characteristic of VWF. The second step is devoted to using a numerical mechano-biological model to predict this stenosis as a function of WSS. WSS is reduced by a factor of 3 during exposure to vibration of 40 m·s−2. This reduction is independent of the frequency of excitation between 31 Hz and 400 Hz. WSS decreases logarithmically when the amplitude of the vibration increases. The mechano-biological model simulated arterial stenosis of 30% for an employee exposed for 4 h a day for 10 years. This model also highlighted the chronic accumulation of matrix metalloproteinase 2. By considering daily exposure and the vibratory level, we can calculate the degree of stenosis, thus that of the disease for chronic exposure to vibrations.

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 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.

Can Blood Flow be Used to Monitor Changes in Peripheral Vascular Function That Occur in Response to Segmental Vibration Exposure?

OBJECTIVES

Laser Doppler blood flow measurements have been used for diagnosis or detection of peripheral vascular dysfunction. This study used a rat tail model of vibration-induced vascular injury to determine how laser Doppler measurements were affected by acute and repeated exposures to vibration, and to identify changes in the Doppler signal that were associated with the exposure.

METHODS

Blood flow was measured immediately after a single exposure to vibration, or before vibration exposure on days 1, 5, 10, 15, and 20 of a 20 days exposure.

RESULTS

After a single exposure to vibration, average tail blood flow was reduced. With 20 days of exposure, there was a reduction in the amplitude of the arterial pulse on days 10 to 20 in vibrated rats and days 15 to 20 in control rats.

CONCLUSIONS

More detailed statistical analyses of laser Doppler data may be needed to identify early changes in peripheral circulation after exposure to vibration.

Sound and Vibration as Research Variables in Terrestrial Vertebrate Models

Sound and vibration have been shown to alter animal behavior and induce physiological changes as well as to cause effects at the cellular and molecular level. For these reasons, both environmental factors have a considerable potential to alter research outcomes when the outcome of the study is dependent on the animal existing in a normal or predictable biological state. Determining the specific levels of sound or vibration that will alter research is complex, as species will respond to different frequencies and have varying frequencies where they are most sensitive. In consideration of the potential of these factors to alter research, a thorough review of the literature and the conditions that likely exist in the research facility should occur specific to each research study. This review will summarize the fundamental physical properties of sound and vibration in relation to deriving maximal level standards, consider the sources of exposure, review the effects on animals, and discuss means by which the adverse effects of these factors can be mitigated.

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.

A three-dimensional visco-hyperelastic FE model for simulating the mechanical dynamic response of preloaded phalanges

This study lays the groundwork for a multi-scale strategy that will lead to a better understanding and prediction of the effects of vibration on the digital arterial network. This is accomplished by modelling the mechanical and biological factors that could disturb the basal vasoconstriction balance in the fingertip. The first stage of this novel approach involved building and validating an original dissipative constitutive law for the fingertip soft tissue for the purpose of finite element modelling of the mechanical response of preloaded phalanges in vibration. This visco-hyperelastic constitutive law was established by means of a two-stage procedure for combining a classical pure static nonlinear law with an original dissipative model. First, the parameters of an Ogden-Hill pure static nonlinear constitutive law were identified using a constrained optimisation algorithm. Second, an original viscous dissipation model was proposed in the spectral domain. This model is based on the linearization of the nonlinear quasi-linear viscoelasticity law and the use of a viscoelastic relaxation modulus, expressed as a continuous distribution of relaxation spectra suitable for living tissues. The experimental data used to fit this model were the static and dynamic stiffnesses of preloaded fingertips acquired from a group of 20 subjects. The relative errors between the measured and simulated stiffnesses were less than 5% in the static procedure and approximately 8% using dynamic analysis. The computed mechanical pressure and maximal tangential stress within the fingertip were high in the soft tissues close to the vibration excitation and also in the bones and interphalangeal cartilages far from the vibration source. Mechanical power was only dissipated significantly in the immediate vicinity of the contact area between the probe and the finger. The main contribution of this study was to implement and identify the parameters of a new spectral dissipative law for fingertip soft tissues. This work may apply in occupational health for modifying the vibration dose assessment or for the follow-up and screening of connective tissue diseases.

Snoring and carotid artery disease: A new risk factor emerges

OBJECTIVES/HYPOTHESIS

Previous studies have identified a relationship between snoring, carotid intima media thickening, and the presence of atherosclerosis. This study examines the correlation between snoring and carotid artery disease through use of duplex ultrasound identifying greater than 50% internal carotid artery stenosis.

STUDY DESIGN

Prospective cohort study.

METHODS

Patients presenting to three academic vascular laboratories for carotid duplex examination completed the following surveys: demographic information, assessment of risk factors for carotid stenosis, assessment of history of obstructive sleep apnea, or continuous positive airway pressure use and Snoring Outcomes Survey. Patients were categorized into 2 groups based on the presence or absence of carotid disease. Data were analyzed by univariate contingency tables and logistic regression analysis.

RESULTS

Five hundred one patients completed the survey, of whom 243/501 (49%) had evidence of carotid occlusive disease. On univariate analysis, smoking, hypertension, heart disease, hypercholesterolemia, diabetes, and stroke all correlated with greater than 50% carotid stenosis. Multivariate analysis indicated that snorers were significantly more likely to have carotid disease. Three hundred twenty-seven participants were thought to have primary snoring. On univariate analysis, snorers were found to be significantly more likely to have carotid disease. After adjustment for covariates, snoring was not significant for carotid disease. However, multivariate analysis showed snorers to be significantly more likely to have bilateral carotid disease.

CONCLUSIONS

This study shows a potential relationship between snoring and bilateral carotid artery stenosis greater than 50%; snorers have risk of carotid stenosis twice that of nonsnorers. Further investigation is warranted to better elucidate this relationship.

LEVEL OF EVIDENCE

2b Laryngoscope, 129:265-268, 2019.

Vibration in mice: A review of comparative effects and use in translational research

Sound pressure waves surround individuals in everyday life and are perceived by animals and humans primarily through sound or vibration. When sound pressure waves traverse through a solid medium, vibration will result. Vibration has long been considered an unwanted variable in animal research and may confound scientific endeavors using animals. Understanding the characteristics of vibration is required to determine whether effects in animals are likely to be therapeutic or result in adverse biological effects. The eighth edition of the "Guide for the Care and Use of Laboratory Animals" highlights the importance of considering vibration and its effects on animals in the research setting, but knowledge of the level of vibration for eliciting these effects was unknown. The literature provides information regarding therapeutic use of vibration in humans, but the range of conditions to be of therapeutic benefit is varied and without clarity. Understanding the characteristics of vibration (eg, frequency and magnitude) necessary to cause various effects will ultimately assist in the evaluation of this environmental factor and its role on a number of potential therapeutic regimens for use in humans. This paper will review the principles of vibration, sources within a research setting, comparative physiological effects in various species, and the relative potential use of vibration in the mouse as a translational research model.

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.

Association between Snoring and High-Risk Carotid Plaque Features

Objectives Previous studies have demonstrated an association between snoring and carotid disease independent of sleep apnea. The aim of this study was to quantify the association between self-reported snoring and high-risk carotid plaque features on magnetic resonance imaging (MRI) that predict stroke. Study Design Cross-sectional. Setting Tertiary care university hospital and affiliated county hospital. Methods We surveyed 133 subjects with asymptomatic carotid artery disease that had been previously evaluated with high-resolution MRI. The survey captured data on self-reported snoring (exposure) and covariates (age, sex, body mass index, and sleep apnea via the STOP-Bang questionnaire). A subset of patients underwent home sleep apnea testing. High-risk carotid plaque features were identified on the high-resolution MRI and included thin/ruptured fibrous cap and intraplaque hemorrhage (outcomes). We quantified the association between snoring and high-risk carotid plaque features with the chi-square test (unadjusted analysis) and multivariate logistic regression adjusting for the covariates. Results Of 133 subjects surveyed, 61 (46%) responded; 32 (52%) reported snoring. Significantly higher proportions of snorers than nonsnorers had a thin/ruptured fibrous cap (56% vs 25%, P = .01) and intraplaque hemorrhage (63% vs 29%, P < .01). In multivariate analysis, snoring was associated with thin/ruptured fibrous cap (odds ratio, 4.4; 95% CI, 1.1-16.6; P = .04) and intraplaque hemorrhage (odds ratio, 8.2; 95% CI, 2.1-31.6; P < .01) after adjusting for age, sex, body mass index, and sleep apnea. Conclusion This pilot study suggests a significant independent association between snoring and high-risk carotid plaque features on MRI. Further study is warranted to confirm these results in a larger cohort of subjects.

Vertebral artery dissection following a posterior cervical foraminotomy

Vertebral artery dissection following a posterior cervical foraminotomy with rhizolysis of the subaxial spine has not been described before. A 46-year-old lady underwent the procedure for a left C6 radiculopathy with a focal disc herniation with no intraoperative complications. Seven hours post-operatively, she developed a right homonymous hemianopia, thalamic dysphasia, gait and memory impairment. Imaging demonstrated an occlusion to the left vertebral artery from C7/T1 to C4 with a dissection flap noted at the inferior margin. This was further complicated with thrombosis of the dissected artery and subsequent emboli causing acute posterior circulation infarctions. Given that the dissection occurred at the level of the surgery, an indirect surgical cause is likely. We hypothesize that the vibration transmitted via bone from the high-speed drill led to arterial injury and dissection.

A two scale modeling and computational framework for vibration-induced Raynaud syndrome

Hand-Arm Vibration syndrome (HAVS), usually caused by long-term use of hand-held power tools, can in certain manifestations alter the peripheral blood circulation in the hand-arm region. HAVS typically occurs after exposure to cold, causing an abnormally strong vasoconstriction of blood vessels. A pathoanatomical mechanism suggests that a reduction of the lumen of the blood vessels in VWF (Vibration White Finger) subjects, due to either hypertrophy or thickening of the vessel wall, may be at the origin of the disease. However, the direct and indirect effects of the load of the hand-held tools on the structure of blood vessels remain controversial:.one hypothesis is the mechanical action of vibration on the local acral dysregulation and/or on the vessel histomorphological modifications. Another hypothesis is the participation of the sympathetic nervous system to this dysregulation. In this paper, we assume the modifications as mechanobiological growth and the load-effect relationship may be interpreted as directly or indirectly induced. This work is the first attempt to model the effect of vibration through soft tissues onto the distal capillaries, addressing the double paradigm of multi space-time scales, i.e. low period vibration versus high time constant of the growth phenomenon as well as vibrations propagating in the macroscopic tissue including the microscopic capillary structures subjected to a pathological microstructural evolution. The objective is to lay down the theoretical basis of growth modeling for the small distal artery, with the ability to predict the geometrical and structural changes of the arterial walls caused by vibration exposure. We adopt the key idea of splitting the problem into one global vibration problem at the macroscopic scale and one local growth problem at the micro level. The macroscopic hyperelastic viscous dynamic model of the fingertip cross-section is validated by fitting experimental data. It is then used in steady-state vibration conditions to predict the mechanical fields in the close vicinity of capillaries. The space scale transfer from macroscopic to microscopic levels is ensured by considering a representative volume element (RVE) embedding a single capillary in its center. The vibrations emitted by the hand held power tool are next linked to the capillary growth through the adopted biomechanical growth model at the capillary level. The obtained results show that vibrations induce an increase of the thickness of the capillary's wall, thereby confirming the scenario of vibrations induced reduction of the lumen of blood vessels.

Vibration inhibits deterioration in rat deep-tissue injury through HIF1-MMP axis

Deep-tissue injury (DTI) is a unique type of pressure ulcer (PU) in which deep-tissue damage expands outwards to the superficial skin. DTI progresses rapidly into a severe PU, despite initially appearing as only a bruise or darkened tissue in the superficial skin. Although some DTI detection methods are available, there is currently no strategy for treating deteriorating DTI. This study investigated the efficacy of vibration therapy for preventing DTI deterioration through down-regulation of the hypoxia-inducible factor-1 matrix metalloproteinase (MMP) axis in rats. We prepared a conventional PU rat model (PU group) and a DTI deterioration rat model (DTI group). The DTI group was further divided into two groups subjected to vibration and control treatments, respectively. Macroscopic and histological features, hypoxia, oxidative stress, apoptosis, and MMP2 and MMP9 activities in compressed skin were analyzed. Hypoxia, oxidative stress, and MMP activity were enhanced in the DTI group compared with the PU group. Vibration remarkably inhibited DTI deterioration, hypoxia, and the expression/activities of MMP2 and MMP9. These results suggest that vibration therapy can effectively attenuate deterioration of DTI. This report provides the first evidence for a therapeutic treatment for deteriorating DTI.

Low-Magnitude, High-Frequency Vibration Fails to Accelerate Ligament Healing but Stimulates Collagen Synthesis in the Achilles Tendon

Background:

Low-magnitude, high-frequency vibration accelerates fracture and wound healing and prevents disuse atrophy in musculoskeletal tissues.

Purpose:

To investigate the role of low-magnitude, high-frequency vibration as a treatment to accelerate healing of an acute ligament injury and to examine gene expression in the intact Achilles tendon of the injured limb after low-magnitude, high-frequency vibration.

Study Design:

Controlled laboratory study.

Methods:

Complete surgical transection of the medial collateral ligament (MCL) was performed in 32 Sprague-Dawley rats, divided into control and low-magnitude, high-frequency vibration groups. Low-magnitude, high-frequency vibration started on postoperative day 2, and rats received vibration for 30 minutes a day for 12 days. All rats were sacrificed 2 weeks after the operation, and their intact and injured MCLs were biomechanically tested or used for histological analysis. Intact Achilles tendons from the injured limb were evaluated for differences in gene expression.

Results:

Mechanical testing revealed no differences in the ultimate tensile load or the structural stiffness between the control and vibration groups for either the injured or intact MCL. Vibration exposure increased gene expression of collagen 1 alpha (3-fold), interleukin 6 (7-fold), cyclooxygenase 2 (5-fold), and bone morphogenetic protein 12 (4-fold) in the intact Achilles tendon when compared with control tendons (P < .05).

Conclusion:

While no differences were observed in the mechanical or histological properties of the fully transected MCL after low-magnitude, high-frequency vibration treatment, significant enhancements in gene expression were observed in the intact Achilles tendon. These included collagen, several inflammatory cytokines, and growth factors critical for tendons.

Clinical Relevance:

As low-magnitude, high-frequency vibration had no negative effects on ligament healing, vibration therapy may be a useful tool to accelerate healing of other tissues (bone) in multitrauma injuries without inhibiting ligament healing. Additionally, the enhanced gene expression in response to low-magnitude, high-frequency vibration in the intact Achilles tendon suggests the need to further study its potential to accelerate tendon healing in partial injury or repair models.

Vibration induced white-feet: overview and field study of vibration exposure and reported symptoms in workers

BACKGROUND

Workers who stand on platforms or equipment that vibrate are exposed to foot-transmitted vibration (FTV). Exposure to FTV can lead to vibration white feet/toes resulting in blanching of the toes, and tingling and numbness in the feet and toes.

OBJECTIVES

The objectives are 1) to review the current state of knowledge of the health risks associated with foot-transmitted vibration (FTV), and 2) to identify the characteristics of FTV and discuss the associated risk of vibration-induced injury.

PARTICIPANTS

Workers who operated locomotives (n=3), bolting platforms (n=10), jumbo drills (n=7), raise drilling platforms (n=4), and crushers (n=3), participated.

METHODS

A tri-axial accelerometer was used to measure FTV in accordance with ISO 2631-1 guidelines. Frequency-weighted root-mean-square acceleration and the dominant frequency are reported. Participants were also asked to report pain/ache/discomfort in the hands and/or feet.

RESULTS

Reports of pain/discomfort/ache were highest in raise platform workers and jumbo drill operators who were exposed to FTV in the 40 Hz and 28 Hz range respectively. Reports of discomfort/ache/pain were lowest in the locomotive and crusher operators who were exposed to FTV below 10 Hz. These findings are consistent with animal studies that have shown vascular and neural damage in exposed appendages occurs at frequencies above 40 Hz.

CONCLUSIONS

Operators exposed to FTV at 40 Hz appear to be at greater risk of experiencing vibration induced injury. Future research is required to document the characteristics of FTV and epidemiological evidence is required to link exposure with injury.

Effect of higher frequency components and duration of vibration on bone tissue alterations in the rat-tail model

To formulate more accurate guidelines for musculoskeletal disorders (MSD) linked to Hand-Arm Vibration Syndrome (HAVS), delineation of the response of bone tissue under different frequencies and duration of vibration needs elucidation. Rat-tails were vibrated at 125 Hz (9 rats) and 250 Hz (9 rats), at 49 m/s(2), for 1D (6 rats), 5D (6 rats) and 20D (6 rats); D=days (4 h/d). Rats in the control group (6 rats for the vibration groups; 2 each for 1D, 5D, and 20D) were left in their cages, without being subjected to any vibration. Structural and biochemical damages were quantified using empty lacunae count and nitrotyrosine signal-intensity, respectively. One-way repeated-measure mixed-model ANOVA at p<0.05 level of significance was used for analysis. In the cortical bone, structural damage quantified through empty lacunae count was significant (p<0.05) at 250 Hz (10.82 ± 0.66) in comparison to the control group (7.41 ± 0.76). The biochemical damage was significant (p<0.05) at both the 125 Hz and 250 Hz vibration frequencies. The structural damage was significant (p<0.05) at 5D for cortical bone while the trabecular bone showed significant (p<0.05) damage at 20D time point. Further, the biochemical damage increased with increase in the duration of vibration with a significant (p<0.05) damage observed at 20D time point and a near significant change (p=0.08) observed at 5D time point. Structural and biochemical changes in bone tissue are dependent upon higher vibration frequencies of 125 Hz, 250 Hz and the duration of vibration (5D, 20D).

Antivibration gloves: effects on vascular and sensorineural function, an animal model

Anti-vibration gloves have been used to block the transmission of vibration from powered hand tools to the user, and to protect users from the negative health consequences associated with exposure to vibration. However, there are conflicting reports as to the efficacy of gloves in protecting workers. The goal of this study was to use a characterized animal model of vibration-induced peripheral vascular and nerve injury to determine whether antivibration materials reduced or inhibited the effects of vibration on these physiological symptoms. Rats were exposed to 4 h of tail vibration at 125 Hz with an acceleration 49 m/s(2). The platform was either bare or covered with antivibrating glove material. Rats were tested for tactile sensitivity to applied pressure before and after vibration exposure. One day following the exposure, ventral tail arteries were assessed for sensitivity to vasodilating and vasoconstricting factors and nerves were examined histologically for early indicators of edema and inflammation. Ventral tail artery responses to an α2C-adrenoreceptor agonist were enhanced in arteries from vibration-exposed rats compared to controls, regardless of whether antivibration materials were used or not. Rats exposed to vibration were also less sensitive to pressure after exposure. These findings are consistent with experimental findings in humans suggesting that antivibration gloves may not provide protection against the adverse health consequences of vibration exposure in all conditions. Additional studies need to be done examining newer antivibration materials.

Recovery of vascular function after exposure to a single bout of segmental vibration

Work rotation schedules may be used to reduce the negative effects of vibration on vascular function. This study determined how long it takes vascular function to recover after a single exposure to vibration in rats (125 Hz, acceleration 5 g). The responsiveness of rat-tail arteries to the vasoconstricting factor UK14304, an α2C-adrenoreceptor agonist, and the vasodilating factor acetylcholine (ACh) were measured ex vivo 1, 2, 7, or 9 d after exposure to a single bout of vibration. Vasoconstriction induced by UK14304 returned to control levels after 1 d of recovery. However, re-dilation induced by ACh did not return to baseline until after 9 d of recovery. Exposure to vibration exerted prolonged effects on peripheral vascular function, and altered vascular responses to a subsequent exposure. To optimize the positive results of work rotation schedules, it is suggested that studies assessing recovery of vascular function after exposure to a single bout of vibration be performed in humans.

The effects of impact vibration on peripheral blood vessels and nerves

Research regarding the risk of developing hand-arm vibration syndrome after exposure to impact vibration has produced conflicting results. This study used an established animal model of vibration-induced dysfunction to determine how exposure to impact vibration affects peripheral blood vessels and nerves. The tails of male rats were exposed to a single bout of impact vibration (15 min exposure, at a dominant frequency of 30 Hz and an unweighted acceleration of approximately 345 m/s(2)) generated by a riveting hammer. Responsiveness of the ventral tail artery to adrenoreceptor-mediated vasoconstriction and acetylcholine-mediated re-dilation was measured ex vivo. Ventral tail nerves and nerve endings in the skin were assessed using morphological and immunohistochemical techniques. Impact vibration did not alter vascular responsiveness to any factors or affect trunk nerves. However, 4 days following exposure there was an increase in protein-gene product (PGP) 9.5 staining around hair follicles. A single exposure to impact vibration, with the exposure characteristics described above, affects peripheral nerves but not blood vessels.

Dependence of vascular damage on higher frequency components in the rat-tail model

Hand-Arm Vibration Syndrome (HAVS) is caused by hand-transmitted vibration in industrial workers. Current ISO guidelines (ISO 5349) might underestimate vascular injury associated with range of vibration frequencies near resonance. A rat-tail model was used to investigate the effects of higher frequencies >100 Hz on early vascular damage. 13 Male Sprague-Dawley rats (250 ± 15 gm) were used. Rat-tails were vibrated at 125 Hz and 250 Hz (49 m/s(2)) for 1D, 5D and 10D; D=days (4 h/day). Structural damage of the ventral artery was quantified by vacuole count using Toluidine blue staining whereas biochemical changes were assessed by nitrotyrosine (NT) staining. The results were analyzed using one-way repeated measures mixed-model ANOVA at p<0.05 level of significance. The structural damage increased at 125 Hz causing significant number of vacuoles (40.62 ± 9.8) compared to control group (8.36 ± 2.49) and reduced at 250 Hz (12.33 ± 2.98) compared to control group (8.36 ± 2.49). However, the biochemical alterations (NT-signal) increased significantly for 125 Hz (143.35 ± 5.8 gray scale value, GSV) and for 250 Hz (155.8 ± 7.35 GSV) compared to the control group (101.7 ± 4.18 GSV). Our results demonstrate that vascular damage in the form of structural and bio chemical disruption is significant at 125 Hz and 250 Hz. Hence the current ISO guidelines might underestimate vascular damage at frequencies>100 Hz.

Frequency-dependent effects of vibration on physiological systems: experiments with animals and other human surrogates

Occupational exposure to vibration through the use of power- and pneumatic hand-tools results in cold-induced vasospasms, finger blanching, and alterations in sensorineural function. Collectively, these symptoms are referred to as hand-arm vibration syndrome (HAVS). Currently the International Standards Organization (ISO) standard ISO 5349-1 contains a frequency-weighting curve to help workers and employers predict the risk of developing HAVS with exposure to vibration of different frequencies. However, recent epidemiological and experimental evidence suggests that this curve under-represents the risk of injuries to the hands and fingers induced by exposure to vibration at higher frequencies (>100 Hz). To improve the curve, better exposure-response data need to be collected. The goal of this review is to summarize the results of animal and computational modeling studies that have examined the frequency-dependent effects of vibration, and discuss where additional research would be beneficial to fill these research gaps.

Vibration from a riveting hammer causes severe nerve damage in the rat tail model

INTRODUCTION

Hand-arm vibration syndrome (HAVS) is an occupational neurodegenerative and vasospastic disorder in workers who use powered hand tools. Frequency weighting (ISO 5349) predicts little risk of injury for frequencies >500 HZ. Potentially damaging high frequencies abound in impact tool-generated shock waves.

METHODS

A rat tail impact vibration model was developed to deliver shock-wave vibration from a riveting hammer to simulate bucking bar exposure. Rat tails were vibrated continuously for 12 min. Tail flick withdrawal times were determined for noxious heat. Nerve trunks and skin were processed for light and electron microscopy.

RESULTS

Immediately after vibration, the tails were hyperalgesic and had disrupted myelinated axons, fragmented nerve endings, and mast-cell degranulation. By 4 days, the tails were hypoalgesic; nerve endings were lost in the skin.

CONCLUSIONS

Shock-wave vibration causes severe nerve damage. Frequency weighting seriously underestimates the risk of nerve injury with impact tools.

Tissue vibration induces carotid artery endothelial dysfunction: a mechanism linking snoring and carotid atherosclerosis?

STUDY OBJECTIVES

We have previously identified heavy snoring as an independent risk factor for carotid atherosclerosis. In order to explore the hypothesis that snoring-associated vibration of the carotid artery induces endothelial dysfunction (an established atherogenic precursor), we utilized an animal model to examine direct effects of peri-carotid tissue vibration on carotid artery endothelial function and structure.

DESIGN

In supine anesthetized, ventilated rabbits, the right carotid artery (RCA) was directly exposed to vibrations for 6 h (peak frequency 60 Hz, energy matched to that of induced snoring in rabbits). Similarly instrumented unvibrated rabbits served as controls. Features of OSA such as hypoxemia, large intra-pleural swings and blood pressure volatility were prevented. Carotid endothelial function was then examined: (1) biochemically by measurement of tissue cyclic guanosine monophosphate (cGMP) to acetylcholine (ACh) and sodium nitroprusside (SNP); and (2) functionally by monitoring vessel relaxation with acetylcholine in a myobath.

MEASUREMENT AND RESULTS

Vessel cGMP after stimulation with ACh was reduced in vibrated RCA compared with unvibrated (control) arteries in a vibration energy dose-dependent manner. Vibrated RCA also showed decreased vasorelaxation to ACh compared with control arteries. Notably, after addition of SNP (nitric oxide donor), cGMP levels did not differ between vibrated and control arteries, thereby isolating vibration-induced dysfunction to the endothelium alone. This dysfunction occurred in the presence of a morphologically intact endothelium without increased apoptosis.

CONCLUSIONS

Carotid arteries subjected to 6 h of continuous peri-carotid tissue vibration displayed endothelial dysfunction, suggesting a direct plausible mechanism linking heavy snoring to the development of carotid atherosclerosis.

The preventive effects of apolipoprotein mimetic D-4F from vibration injury-experiment in rats

Hand-arm vibration syndrome (HAVS) is a debilitating sequela of neurological and vascular injuries caused by prolonged occupational exposure to hand-transmitted vibration. Our previous study demonstrated that short-term exposure to vibration can induce vasoconstriction and endothelial cell damage in the ventral artery of the rat's tail. The present study investigated whether pretreatment with D-4F, an apolipoprotein A-1 mimetic with known anti-oxidant and vasodilatory properties, prevents vibration-induced vasoconstriction, endothelial cell injury, and protein nitration. Rats were injected intraperitoneally with 3 mg/kg D-4F at 1 h before vibration of the tails for 4 h/day at 60 Hz, 49 m/s(2) r.m.s. acceleration for either 1 or 3 days. Vibration-induced endothelial cell damage was examined by light microscopy and nitrotyrosine immunoreactivity (a marker for free radical production). One and 3-day vibration produced vasoconstriction and increased nitrotyrosine. Preemptive treatment with D-4F prevented these negative changes. These findings suggest that D-4F may be useful in the prevention of HAVS.

Vibration disrupts vascular function in a model of metabolic syndrome

Vibration-induced white finger (VWF) is a disorder seen in workers exposed to hand-transmitted vibration, and is characterized by cold-induced vasospasms and finger blanching. Because overweight people with metabolic syndrome are pre-disposed to developing peripheral vascular disorders, it has been suggested that they also may be at greater risk of developing VWF if exposed to occupational vibration. We used an animal model of metabolic syndrome, the obese Zucker rat, to determine if metabolic syndrome alters vascular responses to vibration. Tails of lean and obese Zucker rats were exposed to vibration (125 Hz, 49 m/s(2) r.m.s.) or control conditions for 4 h/d for 10 d. Ventral tail arteries were collected and assessed for changes in gene expression, levels of reactive oxygen species (ROS) and for responsiveness to vasomodulating factors. Vibration exposure generally reduced the sensitivity of arteries to acetylcholine (ACh)-induced vasodilation. This decrease in sensitivity was most apparent in obese rats. Vibration also induced reductions in vascular nitric oxide concentrations and increases in vascular concentrations of ROS in obese rats. These results indicate that vibration interferes with endothelial-mediated vasodilation, and that metabolic syndrome exacerbates these effects. These findings are consistent with idea that workers with metabolic syndrome have an increased risk of developing VWF.

Effects of whole body vibration on the skeleton and other organ systems in man and animal models: what we know and what we need to know

Previous investigations reported enhanced osseous parameters subsequent to administration of whole body vibration (WBV). While the efficacy of WBV continues to be explored, scientific inquiries should consider several key factors. Bone remodeling patterns differ according to age and hormonal status. Therefore, WBV protocols should be designed specifically for the subject population investigated. Further, administration of WBV to individuals at greatest risk for osteoporosis may elicit secondary physiological benefits (e.g., improved balance and mobility). Secondly, there is a paucity of data in the literature regarding the physiological modulation of WBV on other organ systems and tissues. Vibration-induced modulation of systemic hormones may provide a mechanism by which skeletal tissue is enhanced. Lastly, the most appropriate frequencies, durations, and amplitudes of vibration necessary for a beneficial response are unknown, and the type of vibratory signal (e.g., sinusoidal) is often not reported. This review summarizes the physiological responses of several organ systems in an attempt to link the global influence of WBV. Further, we report findings focused on subject populations that may benefit most from such a therapy (i.e., the elderly, postmenopausal women, etc.) in hopes of eliciting multidisciplinary scientific inquiries into this potentially therapeutic aid which presumably has global ramifications.

Vibration causes acute vascular injury in a two-step process: vasoconstriction and vacuole disruption

Hand-arm vibration syndrome is a vasospastic and neurodegenerative occupational disease. In the current study, the mechanism of vibration-induced vascular smooth muscle cell (SMC) injury was examined in a rat-tail vibration model. Tails of male Sprague Dawley rats were vibrated continuously for 4 hr at 60 Hz, 49 m/s(2) with or without general anesthesia. Ventral tail arteries were aldehyde fixed and embedded in epoxy resin to enable morphological analysis. Vibration without anesthesia caused vasoconstriction and vacuoles in the SMC. Anesthetizing rats during vibration prevented vasoconstriction and vacuole formation. Exposing tail arteries in situ to 1 mM norepinephrine (NE) for 15 min induced the greatest vasoconstriction and vacuolation. NE induced vacuoles were twice as large as those formed during vibration. When vibrated 4 hr under anesthesia after pretreatment with NE for 15 min, the SMC lacked vacuoles and exhibited a longitudinal banding pattern of dark and light staining. The extracellular matrix was filled with particulates, which were confirmed by electron microscopy to be cellular debris. The present findings demonstrate that vibration-induced vasoconstriction (SMC contraction) requires functioning central nervous system reflexes, and the physical stress of vibration damages the contracted SMC by dislodging and fragmenting SMC vacuoles.

Oscillatory pressure wave transmission from the upper airway to the carotid artery

Snoring-associated vibration energy transmission from the upper airway to the carotid artery has been hypothesized as a potential atherosclerotic plaque initiating/rupturing event that may provide a pathogenic mechanism linking snoring and embolic stroke. We examined transmission of oscillatory pressure waves from the pharyngeal lumen to the common carotid artery wall and lumen in seven male, anesthetized, spontaneously breathing New Zealand White rabbits. Airflow was monitored via a pneumotachograph inserted in series in the intact trachea. Fifteen 20-s runs of, separately, 40-, 60-, and 90-Hz oscillatory pressure waves [pressure amplitude in the trachea (Ptr(amp)), amplitude 2-20 cmH(2)O] were generated by a loudspeaker driven by a sine wave generator and amplifier and superimposed on tidal breathing via the cranial tracheal connector. Pressure transducer-tipped catheters measured pressure amplitudes in the tissues adjacent to the common carotid artery bifurcation (Pcti(amp)) and within the lumen (carotid sinus; Pcs(amp)). Data were analyzed using power spectrum analysis and linear mixed-effects statistical modeling. Both the frequency (f) and amplitude of the injected pressure wave influenced Pcti(amp) and Pcs(amp), in that ln Pcti(amp) = 1.2(Ptr(amp)) + 0.02(f) - 5.2, and ln Pcs(amp) = 0.6(Ptr(amp)) + 0.02(f) - 4.9 (both P < 0.05). Across all frequencies tested, transfer of oscillatory pressure across the carotid artery wall was associated with an amplitude gain, as expressed by a Pcs(amp)-to-Pcti(amp) ratio of 1.8 +/- 0.3 (n = 6). Our findings confirm transmission of oscillatory pressure waves from the upper airway lumen to the peripharyngeal tissues and across the carotid artery wall to the lumen. Further studies are required to establish the role of this incident energy in the pathogenesis of carotid artery vascular disease.

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

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.

Effects of temperature on vibration-induced damage in nerves and arteries

Vasospastic episodes in hand-arm vibration syndrome are more prevalent among power-tool workers in cold climates. To test whether cold enhances vibration-induced damage in arteries and nerves, tails of Sprague-Dawley rats were vibrated at room temperature (RT) or with tail cooling (<15 degrees C). Cold vibration resulted in a colder tail than either treatment alone. Vibration at both temperatures reduced arterial lumen size. RT vibration generated more vacuoles in arteries than cold vibration. Vibration and cold induced nitration of tyrosine residues in arteries, suggesting free-radical production. Vibration and cold generated similar percentages of myelinated axons with disrupted myelin. Cold with and without vibration caused intraneural edema and dilation of arterioles and venules with blood stasis, whereas vibration alone did not. The similarities, differences, and interactive effects of cold and vibration on nerve and artery damage indicate that temperature is involved mechanistically in the pathophysiology of hand-arm vibration syndrome.

Nifedipine pretreatment reduces vibration-induced vascular damage

A rat-tail vibration model of hand-arm vibration was employed to test whether preemptive administration of nifedipine (5 mg/kg) to block vasoconstriction prevents vibration-induced arterial damage. The tails of vibrated and nifedipine-pretreated vibrated Sprague-Dawley rats were exposed continuously to 4 h of 60-HZ vibration at 49 m/s(2) rms. In nonvibrated anesthetized rats, the ventral tail arteries were bathed for 15 min in situ in 1 mM epinephrine or 1 mM norepinephrine to induce structural changes indicative of intense vasoconstriction. Arteries were processed for light and electron microscopy 45 min after treatment. Compared to sham control, 4-h vibration significantly (P < 0.01) reduced lumen size, generated endothelial disruption (7.0 +/- 2.6%), elevated nuclear factor of activated T cells c3 (NFATc3) expression in endothelial and smooth muscle cells, and increased smooth muscle cell vacuolization. The findings demonstrate that blockage of vibration-induced vasoconstriction with nifedipine prevents acute vascular damage. Smooth muscle and endothelial cells structurally altered by vasoconstriction are rendered susceptible to damage by vibration.